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Microneurographic recordings of human muscle sympathetic nerve activity responses to sudden sensory stimuli (ie, arousal) have revealed 2 intraindividually reproducible response profiles in healthy young males that predict different neural and blood pressure responses to more sustained stress. Approximately 50% of subjects inhibit muscle sympathetic nerve activity during arousal, whereas the remaining 50% do not, and the latter group displays a markedly greater blood pressure increase in response to arousal, as well as during and after 3 minutes of mental arithmetic. Studying a group of monozygotic twins (10 pairs, 2 excluded from analysis), the aim of the present study was to evaluate the degree of genetic determination of these sympathetic response profiles. Muscle sympathetic burst incidence at rest was similar in twins, with a within-pair burst incidence ratio of 0.87±0.02 (SEM) compared with 0.73±0.07 found in unrelated pairs ( P =0.002), confirming a previous study from our laboratory. In contrast, the sympathetic responses to arousal showed large twin within-pair variance (arousal inhibition ratio 0.56±0.11), which did not significantly differ ( P =0.939) from the variance in pairs of unrelated subjects (0.46±0.11). The finding that human muscle sympathetic nerve responses to arousal are less determined by genotype than the resting level of corresponding sympathetic nerve activity suggests that the arousal response pattern is more prone to be altered by environmental factors. This raises the possibility that these intraindividually reproducible sympathetic neural response profiles can be modified in a positive direction from a cardiovascular risk perspective.

Purpose The blood pressure ‘error signal’ represents the difference between an individual’s mean diastolic blood pressure and the diastolic blood pressure at which 50% of cardiac cycles are associated with a muscle sympathetic nerve activity burst (the ‘‘T50’’). In this study we evaluated whether T50 and the error signal related to the extent of change in blood pressure during autonomic blockade in young and older women, to study potential differences in sympathetic neural mechanisms regulating blood pressure before and after menopause. Methods We measured muscle sympathetic nerve activity and blood pressure in 12 premenopausal (25 ± 1 years) and 12 postmenopausal women (61 ± 2 years) before and during complete autonomic blockade with trimethaphan camsylate. Results At baseline, young women had a negative error signal (-8 ± 1 versus 2 ± 1 mmHg, p\0.001; respectively) and lower muscle sympathetic nerve activity (15 ± 1 versus 33 ± 3 bursts/min, p\0.001; respectively) than older women. The change in diastolic blood pressure after autonomic blockade was associated with baseline T50 in older women (r = -0.725, p = 0.008) but not in young women (r = -0.337, p = 0.29). Women with the most negative error signal had the lowest muscle sympathetic nerve activity in both groups (young: r = 0.886, p\0.001; older: r = 0.870, p\0.001). Conclusions Our results suggest that there are differences in baroreflex control of muscle sympathetic nerve activity between young and older women, using the T50 and error signal analysis. This approach provides further information on autonomic control of blood pressure in women.

Delayed labour progress is common in nulliparous women, often leading to caesarean section despite augmentation of labour with synthetic oxytocin.High- or low-dose oxytocin can be used for augmentation of delayed labour, but evidence for promoting high-dose is weak. Aim To ascertain the effect on caesarean section rate of high-dose versus low-dose oxytocin for augmentation of delayed labour in nulliparous women. Methods Multicentre parallel double-blind randomised controlled trial (ClinicalTrials.gov: NCT01587625) in six labour wards in Sweden. Healthy nulliparous women at term with singleton cephalic fetal presentation, spontaneous labour onset, confirmed delay in labour and ruptured membranes (n=1351) were randomised to labour augmentation with either high-dose (6.6 mU/minute) or low-dose (3.3 mU/minute) oxytocin infusion.1295 women were included in intention-to-treat analysis (high-dose n=647; low-dose n=648). Caesarean section rates did not differ between groups (12.4% and 12.3%, 95% Confidence Interval -3.7 to 3.8). Women with high-dose oxytocin had: shorter labours (-23.4min); more uterine tachysystole (43.2% versus 33.5%); similar rates of instrumental vaginal births, with more due to fetal distress (43.8% versus 22.7%) and fewer due to failure to progress (39.6% versus 58.8%). There were no differences in neonatal outcomes.Our study could not confirm results of two systematic reviews indicating, with weak evidence, that use of high-dose oxytocin was associated with lower frequency of caesarean section.We found no advantages for routine use of high-dose oxytocin in the management of delay in labour. Low-dose oxytocin regimen is recommended to avoid unnecessary events of tachysystole and fetal distress.

New Findings What is the topic of this review? Over the past decade, our team has investigated interindividual variability in human blood pressure regulation. What advances does it highlight? In men, we have found a tight relationship between indices of sympathetic activity and vascular resistance across the age span. This relationship is absent in young women but seen in postmenopausal women. These sex and age differences in vascular resistance are largely a result of changes in the balance of vasodilating and vasoconstricting adrenergic receptor tone. When these changes are considered along with cardiac output, a coherent picture is beginning to emerge of why blood pressure rises more with age in women than men. Arterial pressure is a key regulated variable in the cardiovascular system with important health implications. Over the last 12 years, we have used physiological measurements, including muscle sympathetic nerve activity (MSNA), to explore the balance among mean arterial blood pressure, cardiac output and total peripheral resistance (TPR) in normotensive humans. We have shown that these determinants of blood pressure can vary widely in different subjects and how they vary depends on sex and age. In young men, there is a direct relationship between MSNA and TPR but no relationship with blood pressure. This is because cardiac output is proportionally lower in those with high MSNA and TPR. In contrast, in young women there is no relationship between MSNA and TPR (or cardiac output); this is because β-adrenergic vasodilator mechanisms offset α-adrenergic vasoconstriction. Thus, blood pressure is unrelated to MSNA in young women. In older women, β-adrenergic vasodilator mechanisms are diminished, and a direct relationship between MSNA and TPR is seen. In older men, the relationships among these variables are less clear cut, perhaps owing to age-related alterations in endothelial function. With ageing, the relationship between MSNA and blood pressure becomes positive, more so in women than in men. The finding that the physiological control of blood pressure is so different in men and women and that it varies with age suggests that future studies of mechanisms of hypertension will reveal corresponding differences among groups.

It has long been known from microneurographic recordings in human subjects that the activity of postganglionic sympathetic axons occurs as spontaneous bursts, with muscle sympathetic nerve activity (MSNA) exhibiting strong cardiac rhythmicity via the baroreflex and skin sympathetic nerve activity showing much weaker cardiac modulation. Here we review the firing properties of single sympathetic neurons, obtained using highly selective microelectrodes. Individual vasoconstrictor neurons supplying muscle or skin, or sudomotor neurons supplying sweat glands, always discharge with a low firing probability (~30%) and at very low frequencies (~0.5 Hz). Moreover, they usually fire only once per cardiac interval but can fire greater than four times within a burst. Modeling has shown that this pattern can best be explained by individual neurons being driven by, on average, two preganglionic inputs. Unitary recordings of muscle vasoconstrictor neurons have been made in several pathophysiological states, including heart failure, hypertension, obstructive sleep apnea, bronchiectasis, chronic obstructive pulmonary disease, depression, and panic disorder. The augmented MSNA in each of these diseases features an increase in firing probability and discharge frequency of individual muscle vasoconstrictor neurons above that seen in healthy subjects, yet firing rates rarely exceed 1 Hz. However, unlike patients with heart failure, all patients with respiratory disease or panic disorder, and patients with hyperhidrosis, exhibited an increase in multiple within-burst firing, which emphasizes the different modes by which the sympathetic nervous system grades its output in pathophysiological states of high sympathetic nerve activity.

Interindividual variability in sympathetic nerve activity (SNA) has provided insight into integrative mechanisms contributing to blood pressure (BP) regulation in humans. In young people, the influence of high SNA on BP is balanced by lower cardiac output and less adrenergic vasoconstrictor responsiveness. Older people have higher SNA and higher BP. We hypothesized that SNA has a restraining effect on peripheral vasodilator responsiveness in young and older men, such that individuals with higher tonic SNA would show less forearm vasodilatation to exogenous vasodilators. We measured muscle SNA (MSNA; microneurography) and forearm vasodilator responses to intra-arterial infusions of acetylcholine (ACh; endothelium dependent) and sodium nitroprusside (SNP; endothelium independent) in 13 young (age; 27 ± 1 yr) and 16 older (61 ± 2 yr) men. Forearm vascular conductance (FVC) responses to ACh were lower in the older men at the two highest doses (2 and 4 μg·100 ml−1·min−1; Δ395 ± 81 vs. 592 ± 87% and 412 ± 87 vs. 616 ± 132%, P < 0.05), and MSNA was higher (64 ± 4 vs. 41 ± 2 bursts/100 hb; P < 0.05). There was no difference in the FVC response to SNP between young and older men ( P > 0.05). In young men, there was an inverse relationship between resting MSNA and FVC responses (%change) to both ACh and SNP ( r = −0.83 and r = −0.83, respectively; P < 0.05). In older men, however, this relationship was not observed. Tonic SNA may act to restrain vasodilator responses in young men, whereas in older men a lack of such restraint may be protective against the pressor effects of higher SNA.

Autonomic dysreflexia, a dangerous and sustained increase in blood pressure brought about by widespread, reflexly generated vasoconstriction, can be induced by visceral or somatic sensory inputs originating below the lesion following spinal cord injury (SCI). We assessed whether cutaneous vasoconstriction below the lesion could serve as a proxy marker of incipient autonomic dysreflexia during bladder distension. Skin blood flow (pulse plethysmography), sweat release, blood pressure, heart rate, bladder and rectal pressures were recorded during routine cystometry (urodynamics) in 16 patients with SCI. Eight urological patients without SCI served as control subjects. In all SCI patients, who had sustained injuries 2 months to 44 years previously at levels C3-T3, bladder filling (mean ± SD, 339 ± 132 ml) induced increases in detrusor (bladder-rectal) pressure (52 ± 25 cmH(2)O) and cutaneous vasoconstriction in the fingers, but no consistent increases in sweat release. This occurred irrespective of whether the spinal lesions were complete [American Spinal Injury Association (ASIA) grade A, n = 6] or incomplete (ASIA B-D; n = 10). Group mean blood pressure for the SCI patients increased by 17 ± 15 mmHg, but in four patients the pressure decreased or did not change. Despite similar bladder volumes (423 ± 126 ml) in the control patients, the increases in detrusor pressure (14 ± 8 cmH(2)O) and blood pressure (9 ± 12 mmHg) were significantly smaller than in the SCI patients; moreover, there were no consistent changes in skin blood flow in the control subjects. In all SCI patients, changes in finger pulse amplitudes were inversely correlated to changes in detrusor pressure (mean r = -0.62 ± 0.17). Changes in finger pulse amplitudes correlated inversely to changes in blood pressure in nine of 15 patients. It is concluded that cystometry in SCI patients is associated with detrusor and cardiovascular reflex effects that are exaggerated compared with those in intact subjects and that measurement of skin blood flow from the fingers in patients with a high spinal lesion provides a supplementary, clinically useful, non-invasive and continuous marker of spinally mediated viscerosympathetic reflex activity below the lesion in such patients.

Over the past several decades, studies of the sympathetic nervous system in humans, sheep, rabbits, rats, and mice have substantially increased mechanistic understanding of cardiovascular function and dysfunction. Recently, interest in sympathetic neural mechanisms contributing to blood pressure control has grown, in part because of the development of devices or surgical procedures that treat hypertension by manipulating sympathetic outflow. Studies in animal models have provided important insights into physiological and pathophysiological mechanisms that are not accessible in human studies. Across species and among laboratories, various approaches have been developed to record, quantify, analyze, and interpret sympathetic nerve activity (SNA). In general, SNA demonstrates “bursting” behavior, where groups of action potentials are synchronized and linked to the cardiac cycle via the arterial baroreflex. In humans, it is common to quantify SNA as bursts per minute or bursts per 100 heart beats. This type of quantification can be done in other species but is only commonly reported in sheep, which have heart rates similar to humans. In rabbits, rats, and mice, SNA is often recorded relative to a maximal level elicited in the laboratory to control for differences in electrode position among animals or on different study days. SNA in humans can also be presented as total activity, where normalization to the largest burst is a common approach. The goal of the present paper is to put together a summary of “best practices” in several of the most common experimental models and to discuss opportunities and challenges relative to the optimal measurement of SNA across species. Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/guidelines-for-measuring-sympathetic-nerve-activity/

Human muscle sympathetic activity (MSA) is modulated by arterial baroreflex mechanisms: the sympathetic impulses are grouped in pulse synchronous bursts occurring preferentially during transient reductions of blood pressure (Delius et al. 1972), and changes in arterial baroreceptor firing induce reciprocal changes in the strength of the MSA (Wallin et al. 1975; Wallin & Eckberg, 1982). In each subject an approximately constant baroreflex latency can be defined, i.e. a given sympathetic burst can always be related to a given cardiac cycle (Delius et al. 1972). This basic relationship is similar in all subjects despite the fact that some subjects have few, and others many, sympathetic bursts. Such interindividual differences in the amount of activity are highly reproducible over several years (Sundlof & Wallin, 1977; Fagius & Wallin, 1993). Different methods have been used to quantify the arterial baroreflex influence on MSA. In an early study, Sundlof & Wallin (1978) described the relationship between spontaneous variations of blood pressure and nerve traffic in terms of (1) threshold (i.e. whether or not a sympathetic burst is generated) and (2) baroreflex sensitivity (i.e. the slope of the relationship between the strength of a burst and the diastolic pressure in the corresponding heart beat). The same approach has been used to study baroreflex sensitivity during sleep (Nakazato et al. 1998) and to compare groups of normotensive and hypertensive subjects (Wallin & Sundlof, 1979). More commonly, baroreflex effects on MSA have been quantified by measuring the relationship between changes in MSA and blood pressure induced by injections of vasoactive drugs. This approach has been used to study baroreflex sensitivity in healthy subjects at different ages (e.g. Ebert et al. 1992; Matsukawa et al. 1996), in association with manoeuvres (e.g. Halliwill et al. 1996), in cardiovascular diseases (e.g. Ferguson et al. 1992; Grassi et al. 1995; Carlson et al. 1996; Meyrelles et al. 1997) or after administration of anaesthetic drugs (e.g. Sellgren et al. 1994; Muzi & Ebert, 1995). Surprisingly, neither method has been used to quantify arterial baroreflex characteristics in individual subjects. Thus, it is not known whether significant arterial baroreflex thresholds and sensitivites in MSA can be defined for all subjects, and whether, in a given subject, such measures of arterial baroreflex function are reproducible. It is also unknown whether baroreflex characteristics in MSA differ between subjects with few and many MSA bursts at rest. The aim of the present study was to answer these questions. Baroreflex threshold and sensitivity were determined from spontaneous variations of blood pressure/cardiac interval and sympathetic nerve traffic (Sundlof & Wallin, 1978). To minimize random variations in the results, a study of the method of analysis was also included.

Young women tend to have lower blood pressure, and less risk of hypertension, compared to young men. As people age, both blood pressure and the risk of hypertension increase in both sexes; this occurs most strikingly in women after menopause. However, the mechanisms for these influences of sex and age remain incompletely understood. In this review we are specifically interested in the interaction between neural (sympathetic nerve activity; SNA) and haemodynamic factors (cardiac output, blood pressure and vascular resistance) and how these change with sex and age. While peripheral vascular SNA can vary 7- to 10–fold among normotensive young men and women, it is reproducible in a given individual. Surprisingly, higher levels of SNA are not associated with higher blood pressures in these groups. In young men, high SNA is associated with higher total peripheral vascular resistance (TPR), and appears to be balanced by lower cardiac output and less peripheral vascular responsiveness to adrenergic stimulation. Young women do not exhibit the SNA–TPR relationship. Recent evidence suggests that β–adrenergic vasodilatation offsets the vasoconstrictor effects of α–adrenergic vasoconstriction in young women, which may contribute to the generally lower blood pressures in this group. Sympathetic nerve activity increases with age, and in groups over 40, levels of SNA are more tightly linked to levels of blood pressure. The potentially protective β–adrenergic effect seen in young women appears to be lost after menopause and probably contributes to the increased blood pressure and increased risk of hypertension seen in older women.

In men, muscle sympathetic nerve activity (MSNA) is positively related to total peripheral resistance (TPR) and inversely related to cardiac output (CO). However, this relationship was not observed in young women. We aimed to investigate whether simultaneous β-adrenergic stimulation offsets this balance in young women. Furthermore, we aimed to examine whether the ability of the β-adrenergic receptors to offset the transduction of MSNA into vasoconstrictor tone was lost in postmenopausal women. We measured MSNA (peroneal microneurography), arterial pressure (brachial line), CO (Modelflow), TPR and changes in forearm vascular conductance (FVC) to increasing doses of noradrenaline (NA; 2, 4 and 8 ng (100 ml)(-1) min(-1)) before and after systemic β-blockade with propranolol in 17 young men, 17 young women and 15 postmenopausal (PM) women. The percentage and absolute change in FVC to the last two doses of NA were greater during β-blockade in young women (P 0.05). Before β-blockade there was no relationship of MSNA to TPR or mean arterial pressure (MAP) in young women. Following β-blockade, MSNA became positively related to TPR (r = 0.59, P < 0.05) and MAP (r = 0.58, P < 0.05). In the PM women and young men, MSNA was positively associated with TPR. β-Blockade had no effect on this relationship. Our data suggest that the β-adrenergic receptors offset α-adrenergic vasoconstriction in young women but not young men or PM women. These findings may explain in part the tendency for blood pressure to rise after menopause in women.

Sympathetic baroreflex sensitivity (BRS) is greater during decreasing compared to increasing diastolic blood pressure (DBP) in young men and women. In older men and women there is no difference in sympathetic BRS to increasing and decreasing DBP. We investigated whether the sensitivity of the central nervous system to increasing and decreasing DBP is dependent upon baseline muscle sympathetic nerve activity (MSNA). We hypothesised that the difference in sympathetic BRS between falling and rising segments of DBP would be positively related to baseline MSNA in 30 young men, 21 young women, 14 older men and 14 postmenopausal women. MSNA was measured using peroneal microneurography and BRS was measured using the spontaneous baroreflex threshold technique. On average, sympathetic BRS was greater during decreasing compared to increasing DBP in young men (P 0.05). In summary, baseline MSNA plays a role in determining sympathetic BRS to falling and rising DBP in young and older men and postmenopausal women, but not in young women. This relationship is consistent with a decreased potential for sympathoexcitation in people with higher resting MSNA. Furthermore, the lack of relationship in young women suggests important contributions of sex hormones to differential responses of MSNA to falling and rising pressures.

The purpose of this study was to evaluate the relationship between the cardiac and sympathetic baroreflex sensitivities within healthy, young humans. The sensitivities of the cardiac and sympathetic baroreflexes were compared in 53 normotensive individuals (28 men and 25 women; age: 24.0±0.9 years; body mass index: 24.0±0.3 cm/kg 2 , mean±SEM). Heart rate, arterial blood pressure, and peroneal muscle sympathetic nerve activity were recorded under resting conditions (heart rate: 58±1 bpm; systolic blood pressure: 126±2 mm Hg; diastolic blood pressure: 72±1 mm Hg; mean arterial blood pressure: 89±1 mm Hg; muscle sympathetic nerve activity: 18±1 bursts per min) and during rapid changes in blood pressure induced by sequential boluses of nitroprusside and phenylephrine. Cardiac and sympathetic baroreflex sensitivities were analyzed using the slopes of the linear portions of the muscle sympathetic nerve activity-diastolic blood pressure and R-R interval-systolic blood pressure relationships, respectively. When individual cardiac baroreflex sensitivity was compared with sympathetic baroreflex sensitivity, no correlation (R-R interval: r =−0.13; heart rate: r =0.21) was observed when studied as a group. Analysis by sex unveiled a correlation in women between the cardiac and sympathetic baroreflex sensitivities (R-R interval: r =−0.54; P =0.01; no correlation with hazard ratio: r =0.29). No relationship was found in men (R-R interval: r =0.17; heart rate: r =0.12). These results indicate that, although both cardiac and sympathetic efferents function in baroreflex control of arterial pressure, there is no correlation in their sensitivities within healthy normotensive humans. However, sex-stratified data indicate that sex-based differential correlations might exist.

In chronic diffuse upper limb pain physical abnormalities are usually absent. The aims of our study were to investigate: (1) the function of somatosensory pathways and (2) the influence of mood on vibration perception. Measurements were made of: (i) vibrotactile perception thresholds (VPTs) and nerve conduction in working women with (n = 35) and without (n = 65) chronic diffuse upper limb pain, and (ii) perceived stress and energy using a two-dimensional mood adjective checklist. The groups did not differ in any nerve conduction measurements. Women with chronic pain had raised VPTs in the radial and ulnar nerve areas, but not in the median nerve area. Neither perceived stress nor energy appeared to influence the VPT. Increases of VPTs in chronic diffuse upper limb pain may be due to peripheral nerve affliction, but our findings support the idea that they may also be secondary to pain and may be related to a central nervous mechanism. Muscle Nerve, 2010

Among young normotensive men, a reciprocal balance between cardiac output and sympathetic nerve activity is important in the regulation of arterial pressure. In young women, the balance among cardiac output, peripheral resistance, and sympathetic nerve activity is unknown. Consequently, the aim of this study was to examine the relationship of cardiac output and total peripheral resistance to muscle sympathetic nerve activity in young women. Multiunit peroneal recordings of muscle sympathetic nerve activity were obtained in 17 women (mean±SEM: age 24±3 years) and 21 men (mean±SEM: age 25±5 years). Mean resting muscle sympathetic nerve activity was lower in women compared with men (19±3 versus 25±1 bursts minute −1 ; P P P =0.80) or women ( P =0.62). There was a positive relationship between total peripheral resistance and muscle sympathetic nerve activity ( r =0.62; P r =−0.69; P r =−0.27; P >0.05) or cardiac output ( r =0.23; P >0.05) in women. Our results demonstrate that men and women rely on different integrated physiological mechanisms to maintain a normal arterial pressure despite widely varying sympathetic nerve activity among individuals. These findings may have important implications for understanding how hypertension and other disorders of blood pressure regulation occur in men and women.

While sudden (startling) sensory stimuli are generally thought of as inducing sympathetic excitation, in humans there is a short-lasting inhibition of limb muscle sympathetic nerve activity (MSNA). This study is the first to examine and contrast the effects of acoustic startle and the prepulse inhibition of startle (PPI) on MSNA, blood pressure, heart rate, and eye blinks. Startle elicited a two-component withdrawal of MSNA: an early inhibition of one sympathetic burst followed by a second inhibition. PPI abolished the early, but not the late MSNA inhibition. Prepulse stimuli alone had no early inhibitory effects on MSNA. Early MSNA inhibition, which may occur at latencies of approximately 100 ms, appears to be part of a CNS-generated startle reflex which subserves automatic defensive responses to potential threats. The late MSNA inhibition coincided with the stimulus-induced blood pressure increase and is probably an inhibitory reflex response.

A total of 21 microelectrode recordings from the human thalamus were made during stereotactic operations on patients with Parkinson's disease, intention tremor and dystonia. The electrode consisted of a 0.5 mm laquered tungsten wire having an electrolytically sharpened tip of about 5 μ. The electrode was inserted into the thalamus coaxially in a guiding probe the distal uninsulated ring of which served as the indifferent electrode. The probe was fitted to the standard Riechert stereotactic crown. All but one of the patients were fully conscious during the study. Activity of both single and multiunit type was obtained from the ventrolateral (VL) nucleus. Spontaneous irregular and spontaneous rhytmic activities with different frequencies were recorded. Of special interest were the rhythms within the same range as the Parkinsonian tremor. The results of previous investigations were largely confirmed. The earlier reported phenomena connected with the initiation of voluntary motor acts were recorded but the results did not show the previously indicated close correlation between activated thalamic units and certain muscle groups. Muscle vibration causing local tonic vibration reflexes and a potentiation of the Parkinsonian tremor had no obvious effect upon the firing patterns of units in the VL nucleus. Marked changes in the activity of the VL neurons were often observed in response to arousal stimuli of different types. Anything happening suddenly to the subject could produce either intense bursts of single and multiunit activity, or interruption of spontaneous activity or changes in regularity of firing. Responses of this sort, which were characterized by rapid habituation, were seen most frequently in patients with intention tremor and dystonia. The findings suggest that in patients of this type the midbrain reticular activating system exerts an abnormal influence on the synaptic events in the ventrolateral nucleus.

Some women have severe low-back pain during childbirth. It has been shown that sterile water injections reduce this pain. This method, which is easy to learn and very cheap can be a good pain relief alternative primarily in countries with limited available pain relief options.The aim of this article was to describe published research concerning sterile water injections for treatment of low-back pain during labour.Three databases were searched from their inception until February 2008. The inclusion criteria were trials elucidating the pain relief effect of sterile water injections during childbirth. The search terms were labour, birth, obstetrics, parturient, pregnancy, pain relief, analgesia, injection, papules, blocks and sterile water. The computerised literature searches yielded 64 trials, 55 of which failed to meet our inclusion criteria. We used the Jadad Score Instrument to assess the quality of the remaining nine articles, of which six were of adequate quality.All studies in this review had similar aims, designs and measurement instruments and they reported good pain relief particularly for low-back pain during childbirth. In all studies the pain score reduction is approximately 60% and the effect remains up to two hours.Sterile water injections seem to be a good alternative for low-back pain during childbirth.

New ideas about the relative importance of the autonomic nervous system (and especially its sympathetic arm) in long-term blood pressure regulation are emerging. It is well known that mean arterial blood pressure is normally regulated in a fairly narrow range at rest and that blood pressure is also able to rise and fall ‘appropriately’ to meet the demands of various forms of mental, emotional and physical stress. By contrast, blood pressure varies widely when the autonomic nervous system is absent or when key mechanisms that govern it are destroyed. However, 24 h mean arterial pressure is still surprisingly normal under these conditions. Thus, the dominant idea has been that the kidney is the main long-term regulator of blood pressure and the autonomic nervous system is important in short-term regulation. However, this ‘renocentric’ scheme can be challenged by observations in humans showing that there is a high degree of individual variability in elements of the autonomic nervous system. Along these lines, the level of sympathetic outflow, the adrenergic responsiveness of blood vessels and individual haemodynamic patterns appear to exist in a complex, but appropriate, balance in normotension. Furthermore, evidence from animals and humans has now clearly shown that the sympathetic nervous system can play an important role in longer term blood pressure regulation in both normotension and hypertension. Finally, humans with high baseline sympathetic traffic might be at increased risk for hypertension if the ‘balance’ among factors deteriorates or is lost. In this context, the goal of this review is to encourage a comprehensive rethinking of the complexities related to long-term blood pressure regulation in humans and promote finer appreciation of physiological relationships among the autonomic nervous system, vascular function, ageing, metabolism and blood pressure.

In addition to A-beta fibres the human hairy skin has unmyelinated (C) fibres responsive to light touch. Previous functional magnetic resonance imaging (fMRI) studies in a subject with a neuronopathy who specifically lacks A-beta afferents indicated that tactile C afferents (CT) activate insular cortex, whereas no response was seen in somatosensory areas 1 and 2. Psychophysical tests suggested that CT afferents give rise to an inconsistent perception of weak and pleasant touch. By examining two neuronopathy subjects as well as control subjects we have now demonstrated that CT stimulation can elicit a sympathetic skin response. Further, the neuronopathy subjects' ability to localize stimuli which activate CT afferents was very poor but above chance level. The findings support the interpretation that the CT system is well suited to underpin affective rather than discriminative functions of tactile sensations.

The paper reviews findings in humans regarding interindividual differences in sympathetic nerve activity. Data come predominantly from microneurographic multi- or single fibre recordings of sympathetic nerve activity in healthy subjects. Findings relate to interindividual differences in muscle sympathetic nerve activity (MSNA) during resting conditions and in response to surprising sensory stimuli. At rest there are marked interindividual differences in the number of multiunit MSNA bursts. At the single fibre level the differences are because of more vasoconstrictor fibres being active in subjects with high than in subjects with low number of bursts. There are inverse relationships between (i) sympathetic burst incidence and cardiac output (CO) and (ii) between sympathetic burst incidence and vascular responsiveness to noradrenaline. Both findings contribute to explaining the absence of correlation between resting levels of MSNA and blood pressure. Surprising visual, somatosensory or auditory stimuli of sufficient strength cause a short lasting inhibition of MSNA in approx. 50-60% of healthy subjects. In subjects who display significant inhibition, the stimulus-induced blood pressure increase is smaller than in subjects without inhibition. The underlying mechanism may be related to fear of blood/injury. It is concluded that analysis of interindividual differences in sympathetic activity improves the understanding of central nervous control of the circulation.

Study design Measurement of cutaneous sympathetic reflexes and hemodynamic responses to brief electrical stimuli applied above (forehead) and below (abdominal wall) a spinal lesion. Objective To assess the validity of using cutaneous vasoconstriction as a sensitive indicator of increases in sympathetic activity in spinal cord injury. Setting Prince of Wales Medical Research Institute, Australia. Subjects Twenty spinal cord injured subjects with injuries ranging from C3–T11 and nine able-bodied controls. Method Cutaneous electrical stimulation was applied to the forehead and abdominal wall to subjects at unexpected times. Sudomotor and vasomotor responses, as well as continuous arterial pressure, heart rate and respiration were monitored. Results Sudomotor (electrodermal) responses to forehead stimulation were scarce in spinal cord injured subjects, whereas cutaneous vasoconstrictor responses (photoelectric pulse plethysmography) provided a sensitive indicator of any remaining central control of sympathetic function below the lesion. Electrical stimulation applied to the abdominal wall evoked vasoconstrictor reflexes below the lesion in the majority of spinal cord injured subjects, whereas only a limited number of electrodermal responses were observed. That these cutaneous vasoconstrictor responses could reflect parallel increases in muscle and splanchnic vasoconstrictor activity was indicated by the increases in blood pressure; patients lacking vasoconstrictor responses rarely showed stimulus-induced blood pressure increases. Conclusion Our findings show that skin vasomotor responses to somatosensory stimulation provide a more sensitive tool than electrodermal responses for evaluation of sympathetic function below a spinal cord lesion. Statement of ethics We certify that all applicable institutional and governmental regulations concerning the ethical use of human volunteers were followed during the course of this research, and all experiments were conducted with the understanding and consent of each subject.

Background. This study describes maternal and neonatal characteristics and delivery outcome in women with gestational diabetes mellitus [GDM], compared to a control group. Methods. A retrospective observational study of 719 women with GDM was undertaken in a Swedish urban district. All other parturients at the same hospital served as the control group. GDM was diagnosed using random capillary glucose levels at fixed intervals, beginning early in pregnancy. An oral glucose tolerance test was performed at glucose levels ≥7.0 mmol/l (127.8 mg/dl). Data was analysed according to glucose levels at diagnosis, ie, mild or severe GDM. Results. GDM was diagnosed in 2.28% of the women who were older and had higher Body Mass Index [BMI]. A high proportion was of non-Nordic origin (44.5%); they had severe GDM more often (49.1%) than the Nordic group (33.1%). The GDM-mild group had less complications and abnormalities, compared to the GDM-severe group, although both groups differed from the control group in this respect. Delivery was spontaneous in 70.2% of GDM-mild, 65.7% of GDM-severe and 81.0% of the control group. LGA (+2 SD) was found in 4.8, 10.5 and 3.2%, respectively. Conclusion. Early non-fasting random universal screening and multidisciplinary antenatal teamwork intervention seems to be favourable, with low rates of excessive fetal growth, instrumental vaginal delivery and caesarean section.

An overview is given of microneurographic studies of resting vasoconstrictor traffic in human muscle nerves (muscle sympathetic nerve activity = MSNA). In multiunit recordings, the activity consists of synchronized bursts of vasoconstrictor impulses, the outflow of which is under potent arterial baroreflex control. In agreement with this, the bursts always display cardiac rhythmicity and occur during temporary reductions of blood pressure. Burst occurrence shows a close inverse correlation to variations of diastolic blood pressure whereas the correlation to the strength of the bursts is weak or absent, suggesting that the mechanisms controlling the two parameters are not identical. These dynamic characteristics are similar in all subjects despite large, reproducible, interindividual differences in number of bursts. Such interindividual differences probably have a genetic origin, and since discharge frequencies in single vasoconstrictor fibers are similar in subjects with few and many bursts, the differences in multiunit activity are likely to be due to a higher number of active fibers in subjects with many bursts. The interindividual differences in multiunit activity are not associated with differences in resting blood pressure levels. Recent studies have revealed (a) an inverse relationship between resting levels of cardiac output and MSNA and (b) evidence of reduced vascular responsiveness to noradrenaline in subject with many sympathetic bursts at rest. These findings suggest that the vasoconstriction induced by the sympathetic impulses is balanced or reduced by these factors, which thereby contribute to the poor relationship between the mean number of sympathetic bursts and the blood pressure level.

Objectives: A literature report described significantly raised vibration threshold within the territory of the median nerve in a group of office workers and concluded that the results indicated a change in the function of large sensory fibres. The aim of the present cross-sectional study was to compare vibrotactile perception thresholds and nerve conduction measurements in the upper extremity between female computer users (secretaries) and female non-users (nurses). Methods: Eighty-two secretaries, aged 25–65 (median 44) years and 35 nurses, aged 24–57 (median 46) years went through nerve conduction measurements on the dominant hand and also a vibration threshold test with readings over the hand at five sites which tested cutaneous innervation of the median, ulnar, and radial nerves. Results: There was no significant difference in any parameter of the nerve conduction testing and there was no significant difference in any parameter of the vibration threshold test between secretaries and nurses. The numerical differences between groups were small and in both directions and thus do not indicate a power problem. Conclusions: We saw no signs of early neural deficits of large sensory fibres in subjects who intensively use computer keyboard equipment.

Swedish bureaucracy combines some structural peculiarities founded on constitutional traits from the 17th century with a clear formal division of labor between the national and local levels from the late 19th century. These structures have mainly remained unchanged during periods of strong expansion in the first post-WWII decades and preconditions for shrinking during the 1980s and 1990s. In this article, we highlight how these changes have put stress on the bureaucracy and the public sector in general, and how demands for reform and adapting have been managed and viewed by the administrative and political camps, respectively. Social, educational, and political changes among Swedish bureaucrats and their roles are presented and analyzed. The national bureaucracy has “muddled through” and has not been subjected to radical reforms. Its working is still approved—though by no means regarded as sacred—by its administrative agents and its political principals.

Aim: Congestive heart failure (CHF) and obstructive sleep apnoea syndrome (OSAS) are both associated with an intense sympathoexcitation, including an increased muscle sympathetic nerve activity (MSNA). We have studied the firing characteristics of single vasoconstrictor fibres to the muscle vascular bed in CHF and OSAS patients, at rest and during transient sympathoexcitatory stimuli, to elucidate the mechanisms by which vasoconstrictor output is augmented in these conditions. Results: The main alternatives for augmenting sympathetic output are an increased firing frequency of individual nerve fibres and an increased recruitment of nerve fibres. Starting with the frequency alternative, the inherent bursting character of MSNA provides two possibilities to increase the firing of individual fibres: (1) by increasing the proportion of neural bursts in which the fibre is active (increased firing probability) and (2) by increasing the number of spikes a fibre generates per burst (increased multiple within-burst firing). At rest and in cardiac sinus rhythm, an increased firing probability is seen in both CHF and OSAS patients, whereas increased multiple within-burst firing is found in OSAS but not in CHF. In response to transient sympathoexcitatory stimuli (such as pre-mature heart beats), both patient groups show marked shifts towards multiple within-burst firing. Thus, both mechanisms for augmenting discharge frequency are operating in these two pathological conditions, but the firing characteristics at rest differ significantly. During recording sessions in sympathoexcited patients, we have encountered vasoconstrictor fibres that are active almost exclusively during periods of transient sympathoexcitation, while being virtually silent at rest. This suggests that recruitment of previously inactive vasoconstrictor fibres, the second main alternative for increasing vasoconstrictor output, contributes to transient sympathoexcitatory responses in these patients. Although it seems reasonable to assume that recruitment may also contribute to the resting level of MSNA in CHF and OSAS, this issue is difficult to resolve in microneurographic studies. Conclusion: In conclusion, pathological sympathoexcitation appears to depend on both recruitment and increased firing frequency. A shift towards multiple within-burst firing, at rest or in response to transient stimuli, may constitute a risk factor per se as it entails neural volleys with high instantaneous firing frequencies and consequently higher release of neurotransmitters.

Aim: Surprising sensory stimuli causing arousal are known to evoke shortlasting activation of human sympathetic activity in skin but not in muscle nerves. In fact, anecdotal observations suggest that muscle sympathetic activity may be inhibited. To test this hypothesis, the effects of surprising somatosensory (electrical skin pulses) or visual (flash) stimuli on multiunit muscle sympathetic activity were studied in 36 healthy subjects, aged 19-71 years. Methods: The stimuli were given either 200 or 400 ms after the R-wave of the electrocardiogram. Dummy stimuli, consisting of trigger pulses without sensory stimuli, served as controls. Results: On a group basis, a single sensory stimulus of either type attenuated the amplitude of one or two sympathetic bursts, while no such effects occurred after dummy stimuli. Individually, the inhibition was evoked by at least one stimulus modality or delay in 16 subjects, whereas in three subjects no significant inhibition occurred. Electrodermal signs of skin sympathetic activation were present in all subjects. Compared with one, five repeated electrical skin pulses induced only minor additional inhibition of muscle sympathetic activity, indicating marked habituation of the neural response. In nine subjects, the experiments were repeated once and in three subjects twice (with intervals of 2-3 months); in 11 of thel2 subjects, the sympathetic effects were reproducible. In the group of subjects without significant sympathetic inhibition the stimuli induced a small, transient increase of mean blood pressure, which was not present in the group with sympathetic inhibition. Conclusion: The finding that different sensory stimuli induce similar effects that habituate markedly on repetition suggests that the inhibition of muscle sympathetic activity is because of arousal. The interindividual differences in sympathetic and blood pressure effects may be part of interindividual differences in behavioural responses to stress.

Surprising sensory stimuli causing arousal are known to evoke short-lasting activation of human sympathetic activity in skin but not in muscle nerves; anecdotal observations suggest that there may even be an inhibition of muscle sympathetic nerve activity (MSNA). To test this hypothesis we recorded multiunit MSNA in the peroneal nerve in 19 subjects aged 19-71 years, while sensory stimuli, consisting of either an electrical skin stimulus to a finger or a visual flash, were delivered repeatedly with intervals of approximately 20 s. The stimuli were given either 200 or 400 ms after the R wave of the electrocardiogram. Dummy stimuli, consisting of trigger pulses without sensory stimulation served as controls. Electrical skin resistance reductions were monitored from the palm of a hand as electrodermal signs of arousal-induced cutaneous sympathetic activity. On a group basis both types of sensory stimuli attenuated the amplitude of one or two bursts of MSNA, while no such effects occurred after dummy stimuli. Individually, the inhibition was evoked by at least one stimulus modality or delay in 16 subjects whereas in three subjects no significant inhibition occurred. Skin resistance responses were evoked in all subjects. Some subjects responded to one, others to both stimulus modalities, and electrical stimuli were more effective than visual stimuli in causing MSNA inhibition as well as skin resistance reduction. On the other hand, electrodermal signs of arousal were equally common in subjects with and without inhibitory responses. We suggest that the MSNA inhibition evoked by sensory stimuli is an arousal effect which varies markedly between individuals.

For over three decades, the technique of microneurography has allowed us to record sympathetic neural outflow directly from postganglionic axons in awake human subjects. But because sympathetic axons are clustered within a nerve fascicle, such recordings have been limited to the analysis of multi-unit neural activity. To improve the information content of intraneural recordings, we developed the single-unit approach, in which focal recordings can be made from a single C-fibre via a high-impedance tungsten microelectrode. In this review, we describe our methodology for analyzing unitary sympathetic activity and discuss the similarities in the firing properties of individual muscle vasoconstrictor, cutaneous vasoconstrictor and sudomotor neurones.

Five different procedures used to diagnose neuropathy were compared in a “blind” study with diabetic patients. The aim was to evaluate tests of tactile directional sensibility. Three matched groups were examined, two groups with type I diabetes, either with or without suspected neuropathy, and one of healthy controls. Testing consisted of: (1) examination by a specialist in neurology, (2) electrophysiologic measurement of nerve conduction velocity and determination of cool sensitivity, and (3) determination of directional sensibility in two stages, with categorical and quantitative techniques. Abnormal test results were obtained for both groups of diabetic patients. Quantitatively measured directional sensibility had the highest sensitivity (89%) and specificity (85%) when calculated for patients who had received a diagnosis of neuropathy from the neurologist, despite one case of abnormal directional sensibility among the healthy controls. Conduction velocity testing was almost comparably sensitive (80%) and cool sensitivity, comparably specific (85%) when calculated in the same manner. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 1496–1502, 2001

To evaluate the relief of pain in labour with subcutaneous and intracutaneous injections of sterile water, compared with placebo.Randomised controlled trial.Labour ward with approximately 3000 deliveries annually in a suburban area near Gothenburg, Sweden.Ninety-nine pregnant women at term, requiring pain relief for severe lower back pain during the first stage of labour. The women were randomised to receive four injections of 0.1 mL sterile water (without salt) intracutaneously (n = 33), four injections of 0.5 mL sterile water subcutaneously (n = 33) or placebo treatment (n = 33).Reduction of labour pain measured by visual analogue scale.The median visual analogue scale pain score for labour pain was significantly lower compared with initial values in the two study groups and compared with placebo at 10 and 45 minutes after treatment. The median reductions in visual analogue scores after 10 minutes were 5.0 cm and 4.5 cm in the intracutaneous and subcutaneous injection groups, respectively; women in the placebo group scored a median reduction of 1.7 cm. After 45 minutes the median reductions in the visual analogue scores were 4.9 cm and 4.0 cm in the intracutaneous and subcutaneous injection groups, respectively, compared with 1.0 cm for women in the placebo group. No significant differences in analgesic effect or pain experienced during administration were found between the two study groups.The new subcutaneous method of administering sterile water, as well as the earlier described intracutaneous injection method, were effective for the relief of pain in labour.

Partial coherence analysis was used to evaluate the extent to which coherence between resting muscle sympathetic activity (MSA) in different pairs of limbs in humans is explained by the common baroreceptor input and by other noncardiac-related factors. Multiunit MSA in two or three nerves, arterial blood pressure, and electrocardiogram were recorded simultaneously. Correlated MSA consisted of a sharp periodic component at the heart rate and a wideband component of relatively low power distributed between 0 and 2–2.5 Hz. Quantitative analysis revealed stronger coupling between MSAs in close limbs than in distant limbs (peak coherence leg-leg, 0.94 ± 0.03; arm-leg, 0.76 ± 0.11). Furthermore, the wideband component, unaffected by partialization with circulatory signals, was significantly stronger between leg-leg (0.67 ± 0.10) than between arm-leg pairs (0.29 ± 0.10), i.e., noncardiac-related components explained 71% of leg-leg and 38% of arm-leg coherences at the frequency of the heart. Our results indicate that nonuniform relationship exists between resting sympathetic outflow to muscles in close and distant extremities which is, however, partially masked by the effect of the common rhythmic baroreceptor input.

Respiratory modulation in the firing of postganglionic sympathetic neurones has been studied extensively in the anaesthetized cat and rat. In the cat, single muscle vasoconstrictor neurones fire during inspiration, whereas most cutaneous vasoconstrictor neurones show no modulation and sudomotor neurones discharge primarily in expiration (Boczek-Funcke et al. 1992a, b). In the rat, on the other hand, muscle and cutaneous vasoconstrictor neurones fire only during expiration (Habler et al. 1993, 1994, 1996; Johnson & Gilbey, 1996). However, Johnson & Gilbey (1996) recently showed that while the firing of some cutaneous vasoconstrictor neurones displayed respiratory rhythmicity, the discharge of others was independent of the central or peripheral respiratory rhythm. No evidence of cardiac rhythmicity was reported. In humans, single postganglionic muscle vasoconstrictor neurones fire with a respiratory rhythm, in addition to the dominant cardiac rhythm (Macefield et al. 1994). Furthermore, the respiratory periodicity is independent of the associated changes in blood pressure, so it cannot be explained by baroreceptor influences (Macefield & Wallin, 1995). A subpopulation of single human sudomotor neurones also express a cardiac rhythmicity, albeit weak, but it is unknown whether they are modulated by respiration (Macefield & Wallin, 1996). In the present study we continued our assessment of the firing properties of single sympathetic neurones in awake humans, by recording from single vasoconstrictor fibres innervating blood vessels in the skin on the dorsum of the foot. While multi-unit bursts of sympathetic activity in human cutaneous nerve fascicles often contain both vasoconstrictor and sudomotor (and in some instances vasodilator or pilomotor) impulses, it is known that exposing subjects to a cold or a warm environment can bias the sympathetic outflow towards essentially ‘pure’ vasoconstrictor or sudomotor neural traffic, respectively (Bini et al. 1980a, b). In the present study, vasoconstrictor activity was induced by whole-body cooling and external arousal stimuli that could lead to coactivation of sudomotor neurones were minimized. While multi-unit skin sympathetic activity may display a respiratory rhythm (Delius et al. 1972b; Hagbarth et al. 1972; Bini et al. 1980B), it is unknown whether each class of cutaneous sympathetic neurones expresses respiratory modulation. The primary purpose of the present investigation was to determine whether single cutaneous vasoconstrictor neurones exhibit respiratory and/or cardiac rhythmicity. Furthermore, we have reanalysed our recordings from single sudomotor neurones to assess whether these neurones fire with a respiratory periodicity.

In humans, a deep breath is known to induce cutaneous vasoconstriction in the warm state, and vasodilatation in the cold state. To investigate whether vasodilatation in the cold state is related to reduction of sympathetic vasoconstrictor nerve traffic, we studied the effect of a deep breath on vascular resistance in a skin area on the dorsum of the hand, in which release of noradrenaline from sympathetic nerves was blocked by iontophoretic pretreatment with bretylium tosylate. Simultaneous measurements were made in two control areas. In eight healthy subjects, data were obtained from deep breaths taken before bretylium in the warm state, after general cooling to a finger skin temperature below 25 °C and after rewarming to above 32 °C. In the warm state before bretylium pretreatment, the deep breath evoked short-lasting vasoconstrictions at all sites. In the cold state there was no change of vascular resistance in the bretylium-pretreated area, whereas in the control areas an initial tendency towards vasoconstriction was followed by a significant transient vasodilatation. After rewarming, transient vasoconstrictions reappeared at the control sites, whereas only a transient vasodilatation occurred at the bretylium-pretreated site. In six healthy subjects we also monitored the effects of a deep breath on skin sympathetic nerve activity (recorded by microneurography in the peroneal nerve), and skin vascular resistance within the innervation zone of the impaled nerve fascicle in the foot. Data from thirty deep breaths per subject were averaged. In the cold state, the deep breath induced a strong increase in neural discharge, followed by a transient reduction of nerve traffic lasting approximately 15 s and associated with a subsequent reduction of vascular resistance. We conclude that the deep breath-induced vasodilatation in the cold state is due to reduction of sympathetic vasoconstrictor nerve traffic. The vasodilatation after bretylium treatment in the warm state raises the possibility that a deep breath induces two simultaneous neural reactions, a vasoconstrictor and an active vasodilator component, the latter being weaker and normally masked by the strong vasoconstrictor component.

1. Resting human sympathetic vasoconstrictor traffic displays large reproducible inter-individual differences which are similar in nerves to muscle, heart and kidney. In spite of this there is no correlation between levels of blood pressure and sympathetic traffic. To test the hypothesis that the pressor effect of the vasoconstrictor activity is counteracted by a circulating dilating factor we measured muscle nerve sympathetic activity (MSA) and an indicator of nitric oxide release (plasma nitrate) in healthy young males. 2. Sympathetic activity was recorded with the microneurographic technique in the peroneal nerve and a forearm venous plasma sample was obtained in twenty-one normotensive males aged 21-28 years. Plasma nitrate was analysed by gas chromatography and mass spectrometry. 3. There was a positive linear correlation between the plasma nitrate concentration and the strength of MSA both when the nerve activity was expressed as bursts per minute and bursts per 100 heart beats (r = 0.51, P = 0.02 and r = 0.46, P = 0.04, respectively). 4. The data suggest that the stronger the sympathetic activity the higher the release of the dilating substance, nitric oxide. This would be expected to counteract vasoconstrictor effects of the nerve traffic and thereby contribute to the lack of relationship between resting levels of MSA and blood pressure. We speculate that altered coupling between sympathetic traffic and nitric oxide release may cause abnormal peripheral resistance, e.g. in hypertension.

Objective To achieve optimal diagnostic accuracy, measurements of nerve conduction velocity require standardised tissue temperatures. To warm an extremity to a desired temperature that remains constant during the measurement may be difficult, especially in subjects with low finger temperatures. The aim of this study was to investigate if a submaximal bicycle ergometer test before the examination would be a useful method of obtaining high and stable finger temperatures during nerve conduction studies in the hand. Methods 114 women aged 25–65 (median 44) performed a bicycle ergometer test on an electrically braked bicycle ergometer (Siemens-Elema) before they underwent a nerve conduction test. Results Before cycling, the mean finger temperature was 28.1 °C (range 20.5–35.4 °C) and 15 min after the test 35.1 °C (range 30.3–36.9 °C). The levels remained almost constant throughout the nerve conduction examination, which had a duration of approximately 25 min. Conclusions A bicycle ergometer test proved to be a simple and effective method of raising hand temperature.

The autonomic nervous system plays a central role in both acute and chronic blood pressure regulation in humans. The activity of the sympathetic branch of the autonomic nervous system is positively associated with peripheral resistance, an important determinant of mean arterial pressure in men. In contrast, there is no association between sympathetic nerve activity and peripheral resistance in women before menopause, yet a positive association after menopause. We hypothesized that autonomic support of blood pressure is higher after menopause in women. We examined the effect of ganglionic blockade on arterial blood pressure and how this relates to baseline muscle sympathetic nerve activity in 12 young (25±1 years) and 12 older postmenopausal (61±2 years) women. The women were studied before and during autonomic blockade using trimethaphan camsylate. At baseline, muscle sympathetic nerve activity burst frequency and burst incidence were higher in the older women (33±3 versus 15±1 bursts/min; 57±5 versus 25±2 bursts/100 heartbeats, respectively; P P P r =−0.74; P

Firing properties of single sudomotor axons were studied via tungsten microelectrodes inserted percutaneously into cutaneous fascicles of the peroneal nerve in awake subjects. Sweating was induced by radiant heat and measured by changes in skin electrical resistance within the innervation territory on the dorsum of the foot. Eight units were classified as sudomotor neurones because spike-triggered averaging revealed a time-locked relationship between the unitary discharge and the subsequent decrease in skin resistance (1.12 +/- 0.05 s), but no relationship to skin blood flow (measured by a laser-doppler probe). Sudomotor units usually fired only one (maximum six) spike(s) in a sympathetic burst. The mean firing rate was 0.62 Hz, but instantaneous frequencies above 50 Hz could be generated. R-wave triggered histograms and coherence analysis revealed significant coupling between the firing of three sudomotor neurones and the ECG. Moreover, the firing of four sudomotor neurones showed a weak but significant correlation with the spontaneous fluctuations in cardiac interval, diastolic pressure, or the rate of fall in arterial pressure. We conclude that the discharge of human sudomotor neurones is modulated by baroreceptor input.

Unilateral paresis remaining after poliomyelitis may affect the expression of inflammatory diseases by lateralization of the disease manifestations. The purpose of this study was to assess the impact of the unilateral paresis after poliomyelitis on lateralization of neurogenic inflammation and immune responsiveness. The delayed-type hypersensitivity (DTH) reaction to tuberculin was used as an in vivo measure of antigen-specific T lymphocyte reactivity. Assessment of axon reflex vasodilatation was simultaneously employed to test for neurogenic inflammation. Fourteen of the 16 polio patients displayed a positive DTH reaction to tuberculin. All but two showed weaker DTH reaction on the paretic- compared to the contralateral-side (P = 0.001). Magnitude of electrically evoked axon reflexes significantly correlated to asymmetries of DTH responses. We conclude that damage of lower motor neuron leads to ipsilateral down-regulation of T cell-mediated cutaneous inflammation. This lateralization of DTH responses is related to deficiencies in motor and sympathetic innervation of the paretic extremity.