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Background: By measuring the prevalence of neuronal traffic between two brain structures based on the notion that diffusion of water molecules along the axon in parallel bundles will create prominent anisotropy in the direction of the passage of action potentials, diffusion tensor imaging (DTI) may be taken as an effective tool for functional investigations. Demonstration of complementary results obtained from synchronized DTI of the baroreflex neural circuit and physiological or pathophysiological evaluation of baroreflex functionality should validate this notion. Methods: We implemented concurrent changes in neuronal traffic within the neural circuit of the baroreflex-mediated sympathetic vasomotor tone in the brain stem and alterations of its experimental surrogate under physiological and pathophysiological conditions. We further evaluated the functional and clinical implications of results obtained from this experimental paradigm in conjunction with baroreflex induction and a mevinphos intoxication model of brain stem death. Results: We found that robust connectivity existed between the nucleus tractus solitarii and rostral ventrolateral medulla, the afferent and efferent nuclei of the baroreflex-mediated sympathetic vasomotor. Intriguingly, this connectivity was either reversibly disrupted or irreversibly severed to reflect alterations in baroreflex responses to physiological or pathophysiological challenges. Conclusions: The capability to observe simultaneous and complementary changes in neuronal traffic within the neural circuit of the baroreflex-mediated sympathetic vasomotor tone and alterations of its experimental surrogate that bears technical, scientific and clinical implications sustains the notion that coupled with relevant physiological phenotypes, DTI can be an effective investigative tool for functional evaluations of brain stem activities. Keywords: Baroreflex functionality, Diffusion tensor imaging, Brain stem, Neural circuit

Based on work-done in the rostral ventrolateral medulla (RVLM), this review presents four lessons learnt from studying the differential impacts of oxidative stress and nitrosative stress on sympathetic vasomotor tone and their clinical and therapeutic implications. The first lesson is that an increase in sympathetic vasomotor tone because of augmented oxidative stress in the RVLM is responsible for the generation of neurogenic hypertension. On the other hand, a shift from oxidative stress to nitrosative stress in the RVLM underpins the succession of increase to decrease in sympathetic vasomotor tone during the progression towards brain stem death. The second lesson is that, by having different cellular sources, regulatory mechanisms on synthesis and degradation, kinetics of chemical reactions, and downstream signaling pathways, reactive oxygen species and reactive nitrogen species should not be regarded as a singular moiety. The third lesson is that well-defined differential roles of oxidative stress and nitrosative stress with distinct regulatory mechanisms in the RVLM during neurogenic hypertension and brain stem death clearly denote that they are not interchangeable phenomena with unified cellular actions. Special attention must be paid to their beneficial or detrimental roles under a specific disease or a particular time-window of that disease. The fourth lesson is that, to be successful, future antioxidant therapies against neurogenic hypertension must take into consideration the much more complicated picture than that presented in this review on the generation, maintenance, regulation or modulation of the sympathetic vasomotor tone. The identification that the progression towards brain stem death entails a shift from oxidative stress to nitrosative stress in the RVLM may open a new vista for therapeutic intervention to slow down this transition.

Arginine vasopressin (AVP) is critical for maintaining vasomotor tone and low levels have been associated with the development of irreversible shock. We investigated the clinical relationship between AVP, copeptin (the C-terminal fragment of the AVP precursor), and the development of relative AVP deficiency following hemorrhagic shock.A prospective, observational study of 21 hypotensive (SBP90 mmHg X 2) or presumptively bleeding trauma patients was conducted. Demographics, mechanism of injury, vital signs, laboratory values, transfusions, crystalloid volume, and blood samples were collected on arrival and serially for 48 h. AVP and copeptin were measured post hoc.AVP and copeptin levels were markedly elevated on admission, but decreased rapidly over time (p 0.001). AVP and copeptin levels were positively correlated on admission (r = 0.769, p 0.001), in the ICU (r = 0.768, p 0.001), and at 48 h (r = 0.537, p = 0.02). Initial AVP and copeptin levels predicted the need for ≥10 unit blood product transfusion (AUC = 81% and 87%, respectively). The development of a relative AVP deficiency occurred frequently and was associated with an increased need for blood product transfusion.Copeptin correlates well with AVP and initial values predict the need for massive transfusion in trauma patients. Copeptin demonstrates promise as a clinical biomarker in hemorrhagic shock.

Background Many behavioral and physiological studies of laboratory mice employ invasive methods such as radio telemetry to measure key aspects of behavior and physiology. Radio telemetry requires surgical implants, which may impact mouse health and behavior, and thus reduce the reliability of the data collected. New method We developed a method to measure key aspects of thermoregulatory behavior without compromising animal welfare. We examined the thermoregulatory response to heat stress in a custom-built arena that permitted the use of simultaneous and continuous infrared thermography (IRT) and video capture. This allowed us to measure changes in surface body temperature and determine total distance traveled using EthoVision XT animal tracking software. Results Locomotor activity and surface body temperature differed between heat-stressed mice and mice kept within their thermal comfort zone. The former had an increase in surface body temperature and a decline in locomotor activity, whereas the latter had a stable surface body temperature and showed greater activity levels. Methods Surface body temperature and locomotor activity are conventionally quantified by measurements taken at regular intervals, which limit the use and accuracy of the data. We obtained data of high resolution (i.e., recorded continuously) and accuracy that allowed for the examination of key physiological measurements such as energy expenditure and peripheral vasomotor tone. Conclusions This novel experimental method for studying thermoregulatory behavior in mice using non-invasive tools has advantages over radio-telemetry and represents an improvement in laboratory animal welfare.

Coronary artery vasospasm (CVS) is a relatively rare, under-recognized phenomenon in the setting of orthotopic heart transplantation (OHT). It is hypothesized that the transplanted heart undergoes heterogeneous re-innervation and has altered vasomotor tone in response to cholinergic and

During the last forty years tremendous progress has been made in our understanding of coronary atherosclerosis and in the development of methods to characterize atherosclerotic disease burden and risk. Stress testing is designed to elucidate abnormalities in myocardial perfusion during stress due to abnormal coronary vasomotor response. We summarize the underlying determinants of normal coronary vasomotor tone as well as its responsiveness to both exercise and pharmacologic stressors. We introduce the various methods of assessing the presence of myocardial ischemia. A detailed discussion of the most commonly used stress agents as well as their clinical advantages and limitations follows.

Various techniques have demonstrated that NREM sleep is associated with reduced sympathovagal tone (vagal dominance). The effect is characterized by lowered sympathetic vasomotor tone, downward resetting of the baroreflex, marginally increased BRS, and elevated parasympathetic activity. Because it has not been possible to isolate sympathetic effects on the heart during sleep, the central role of the SNS remains uncertain. It remains unclear whether the change in sympathovagal balance reflects an influence of sleep mechanisms over the ANS, or the reverse; the most likely scenario is that there are reciprocal influences. Sleep deprivation appears to have only minor effects on sympathovagal balance. However, the effects of OSA are substantial and are likely to mediate many pathophysiological processes associated with the disorder.

This article provides a synthesis of physiology and pathophysiology of the cardiovascular system and briefly presents the principles of regulation at the level of the whole organism and regional circulations. Decision algorithms, based on knowledge of physiology and pathophysiology are proposed. Their goal is to contribute to the improvement of cardiopulmonary bypass practice.

The availability of genetically manipulated mice offers a golden opportunity for the study of the contribution of the genome to diseases. Because of the technical difficulty in performing spinal subarachnoid catheterization in mice, this opportunity has hitherto been less harnessed in investigations on the role of the spinal cord in the physiological or pathological processes. Even less explored are spinal mechanisms that underlie cardiovascular regulation since subarachnoid catheterization of the mouse thoracic spinal cord, where preganglionic sympathetic neurons governing vasomotor tone are located posts the highest challenge because of the restricted operating area. We report a procedure for subarachnoid catheterization of the thoracic spinal cord in mice that did not require laminectomy or drilling of the lamina proper, and compared the suitability of two candidate catheters, polyethylene PE-5 catheter (0.51 mm, OD) and polyurethane PU-10 catheter (0.25 mm, OD). Whereas all implanted mice resumed normal feeding one day after surgery and were devoid of bladder dysfunction or self-mutilation, the smaller and softer PU-10 catheter compared favorably because of lower post-operative mortality rate and no unilateral lower limb paresis.

In anaesthetised rabbits, we analysed the cross-correlations of resting discharges in pairs of simultaneously recorded renal neurons. The study of 428 significant cross-correlations showed three pure types of neuronal co-ordination and two combined effects. Pure shared input was observed in 202 pairs of neurons (47.2%). The width of cross-correlogram peak was 222.9 +/- 7.2 ms. The peak height of shared input was 4.8 +/- 0.2 spikes s(-1) and was significantly related with correlogram width. Pure excitatory connection was found in 24 neuronal pairs (5.6%). Its peak width was 7.9 +/- 1.9 ms and it was shifted from time zero by 13.3 +/- 3.4 ms. The amplitude of the peak was 19.6 +/- 4.6 spikes s(-1). In 165 pairs of neurons (38.6%), excitatory connection was combined with shared input component. Pure reciprocal activation was seen in only 5 pairs of neurons (1.1%) while in 32 pairs (7.5%) it was accompanied by shared input co-ordination. The distance between narrow peaks measured in the combined type of co-ordination was 32.5 +/- 3.5 ms and the mean peak height was 4.1 +/- 0.7 spikes s(-1). Shared input in pure form and that accompanying both excitatory connection and reciprocal activation were significantly related to the frequency of discharge of neurons contributing to the cross-correlogram. The incidence and basic properties of the encountered types of neural coordination may indicate a pattern of interconnections between cells generating vasomotor tone in renal sympathetic neurons.

The physiologic role of nitric oxide (NO) in the maintenance of vasomotor tone is firmly established in both humans and animals. Evidence that excessive NO production plays a key role in the cardiovascular manifestations of septic shock also exists. Nitric oxide synthase (NOS) inhibitors have been used in both experimental and human sepsis as a means of raising blood pressure and restoring vasomotor tone. The use of NOS inhibitors in the treatment of septic shock is based on the following: the cardiovascular manifestations seen in septic shock are caused by an overproduction of NO, the increase in NO contributes to mortality, and NOS inhibitors are safe. This article discusses the evidence to support the use of NOS inhibitors in septic shock. Copyright © 2001 by W.B. Saunders Company

Infrared thermographic imaging (ITI) is the most sensitive objective imaging currently available for the detection of back disease in horses. It is, however, only a physiological study primarily of vasomotor tone overlying other superficial tissue factors. Interpretation requires extreme care in imaging protocol and in understanding the significance of altered sympathetic nervous tone and the sympathetic distribution. Most discussions on back pain have centered on nociception and inflammatory events. ITI provides information and localization for more significant than diagnosing areas of hot spots. Chronic back pain usually involves vasoconstriction at the affected sites and from ITI studies in man, we have an opportunity to appreciate chronic pain phenomena that involves non-inflammatory events. These occur commonly in horses, but are still seldom recognized and treated.

Maximal, reproducible and thus “standardized” dilation of epicardial coronary arteries can be easily achieved with intracoronary bolus administration of 0.1 mg nitroglycerin without considerable decrease in blood pressure. Addition of other nitrocompounds or calcium antagonists cannot increase coronary dilation after nitroglycerin, but may be hampered by adverse effects. Angiographic investigation may start 2 to 3 minutes after nitroglycerin injection, which should be repeated approximately every 10 minutes.

The purpose of this study was to examine vasomotor responses mediated by platelets from patients with diabetes mellitus.Diabetes mellitus is associated with increased cardiovascular morbidity and mortality, which in part may be due to a variety of abnormalities reported in diabetic platelets. However, the effects of diabetic platelets on vasomotor tone have not been characterized.We compared platelet-mediated vasodilation elicited by platelets isolated from 30 healthy volunteers and 29 patients with diabetes mellitus as they were perfused through a preconstricted normal rabbit carotid artery.Platelets from the diabetic patients mediated an impaired dilatory response in comparison with normal platelets: 2.7 +/- 2% versus 15.8 +/- 3.4% (p0.001) and 4.1 +/- 2.7% versus 32.7 +/- 3.3% (p0.001) (mean +/- SEM) increase in vessel diameter, for 5 X 10(7) and 1 X 10(8) platelets per milliliter perfused, respectively. The degree of impairment was similar for type I (insulin-dependent) and type II (non-insulin-dependent) diabetes mellitus. Normal platelets incubated in high D-glucose concentrations lost their ability to mediate dilation in a concentration-dependent and time-dependent manner. This was not true for incubation of normal platelets in high concentrations of L-glucose or insulin. However, there was not a significant correlation between glucose control in the diabetic patients and the ability of their platelets to mediate vasodilation.Platelets from patients with diabetes mellitus have an impaired ability to mediate vasodilation. This impairment appears to be mediated by high glucose concentration. Further work is needed to elucidate the mechanisms for this abnormality in diabetic platelets.

To analyse the vasomotion of a coronary segment in relationship to its intravascular ultrasound–virtual histology (IVUS–VH) composition. Coronary segments, transiently scaffolded by a fully absorbable sirolimus eluting Mg scaffold (DREAMS 2G), may in the long-term recover a normal vasomotor tone

During percutaneous transluminal coronary angioplasty (PTCA), part of the constraints developed by the inflated balloon beyond the value needed for splitting or fracturing the atherosclerotic plaque are absorbed by the elastic components of the arterial wall to be restored after balloon deflation. The return of these elastic components to their unstrained dimensions (elastic recoil) results in the loss of a significant part of the theoretical maximal gain in lumen diameter achieved during balloon inflation. Although the contribution of elastic recoil to the residual stenosis of coronary segments immediately after PTCA appears well established,1–3 controversy remains regarding the possible contribution of some progressive or delayed recoil to the restenosis observed in 17 to 47% of patients several weeks or months after PTCA.4 Morphologic studies of restenosis sites after PTCA have suggested that chronic recoil could be a mechanism of late luminal narrowing, independent of intimai fibrous proliferation.4–5 However, quantitative angiographic studies in small populations did not show a further reduction in minimal lumen diameter of dilated coronary segments during the first 24 hours after successful PTCA.1,2 The present study was designed to evaluate in a large group of patients whether gradual or delayed elastic recoil could result in a further luminal narrowing during the first 24 hours after successful PTCA. Alt angiographic data were obtained under standardized conditions, including local infusion of nitrates, to minimize the influence of vasomotor tone.

It is a great pleasure for me to participate in honoring my mentor, Dr. Donald W. Seldin. When I began my fellowship in Dailas in 1967, the field of renal physiology was booming. Laboratories all over the world were beginning to unravel the puzzle of sodium handling by the nephron and Seldin was one of the main catalysts. From this intellectual experience in Dallas, I spent the next decade or so studying the renal circulation, its effect on sodium transport, and various humoral factors that play a role in the regulation of renal resistance. It's incredible how much our knowledge has changed in these 23 years. I first heard of prostaglandins in 1968 at one of the weekly sessions in Dallas from a visiting professor. Renal autoregulation was poorly understood and few incisive experimental studies had been done. The kinin system was just beginning to emerge and obviously no one had heard of atrial natriuretic peptide or endothelin. In this brief article, I'd like to review two facets of the renal circulation: autoregulation and various humoral agents which regulate renal vasomotor tone. Because of space constraints, this will be quite brief and I would refer interested readers to a more extensive review of the subject by Dr. Claudia Hura and myself [1].

Cocaine increases myocardial oxygen demand and paradoxically decreases oxygen supply by reducing coronary blood flow. Such "inappropriate" vasoconstriction also occurs with exercise, which causes intense vasoconstriction of coronary artery segments narrowed by atherosclerosis. This study was done to assess the cocaine-induced change in vasomotor tone of diseased and nondiseased coronary artery segments. In 18 patients (15 men, 3 women, aged 35 to 67 years), coronary artery areas in diseased and nondiseased segments were quantitated before and 15 min after administration of intranasal saline solution (6 patients) or cocaine (2 mg/kg body weight) (12 patients). No variables changed after intake of the saline solution. In response to cocaine, the luminal areas of diseased and nondiseased segments decreased, but the magnitude of vasoconstriction was greater in the diseased segments (mean +/- SD 29 +/- 23% versus 13 +/- 8%, p less than 0.05). Thus, cocaine causes vasoconstriction of diseased and nondiseased coronary artery segments, but its effect is particularly marked in the former.

The purpose of this paper is to thoroughly review the literature and present a data base of the basic thermoregulatory parameters of the laboratory rat. This review surveys the pertinent papers dealing with various aspects of the thermal biology of the laboratory rat, including: metabolism, thermoneutrality, core and brain temperature, thermal tolerance, thermal conductance and insulation, thermoregulatory effectors (i.e., thermogenesis, peripheral vasomotor tone, evaporation, and behavior), thermal acclimation, growth and reproduction, ontogeny, aging, motor activity and exercise, circadian rhythm and sleep, gender differences, and other parameters. It is shown that many facets of the thermoregulatory system of the laboratory rat are typical to that of most homeothermic species. However, is several instances the rat exhibits unique thermoregulatory responses which are not comparable to other species.

T HE purpose of the circulation is perfusion of tissues, and the major role of blood vessels in determining tissue perfusion must be appreciated. Knowledge of cardiovascular reflexes and neurohumoral control of the peripheral circulation has exploded in recent years. Despite the complexity of the control mechanisms, a greater understanding of their influence on the circulation in physiologic and in some pathologic states has been achieved. Reflex control of the peripheral circulation encompasses the neurohumoral regulation of every segment of the vascular tree. Its understanding requires knowledge of central nervous system (CNS) autonomic functions, of the coupling of the CNS with the various components and segments of the peripheral circulation, and of the modification of neurohumoral control of the circulation by local metabolic factors in the tissues. Central nervous system control is achieved through the autonomic system with its sympathetic and parasympathetic branches. The neural discharge from autonomic CNS neurons on the circulation is defined by three factors: (1) The continuous influx of afferent neural impulses that originate in the cardiovascular system as well as in other tissues and other parts of the CNS. The integration of these multiple inputs and their impact on the autonomic neurons are complex but important in the moment-to-moment regulation of vasomotor tone and the peripheral circulation. (2) The selectivity and nonuniformity of activation of the different efferent nerves of the autonomic system. Contrary to the old belief, efferent impulses

The tail vasomotor tone in rats is reduced by the intraventricular injection of 5,7-dihydroxytryptamine but not by 6-hydroxydopamine. Central serotonergic but not noradrenergic neurons participate in vasoconstriction of the tail.

Plasma cholesterol levels are markedly reduced when doxazosin, a selective alpha 1-adrenoceptor inhibitor, is administered for several days to C57BR/cdJ mice that have been fed a high cholesterol diet. This system affords a useful model for investigating the mechanism by which selective alpha 1-adrenoceptor inhibitors decrease circulating lipid levels. The results indirectly suggest that hypercholesterolemia induced by dietary cholesterol may involve activation of the sympathetic nervous system. The basis for linkage between circulating cholesterol levels and sympathetic nervous activity, while not yet understood, may involve changes in the balance among cholesterol pathways in the liver, alteration of vasomotor tone and control of the activity of vascular endothelial lipases. An additive effect is described for cholestyramine and doxazosin, in which low density lipoprotein cholesterol is decreased by 76% by a combination of maximal doses of the 2 agents.

Ethanol ingestion has been implicated in accidental hypothermia of the elderly, but there is no prior data on the relative sensitivity to alcohol of aged homeotherms that might account for disproportionate dysthermia in this age group. To assess their sensitivity, ethanol (0.5-2.0 g/kg) or H20 was given by gavage to squirrel monkeys less than 4 yrs old, 4-9 yrs of age and over 9 yrs old. Dose-related decreases in body temperature occurred in all three groups in a 25.5 degrees C environment, with the greatest decreases in the oldest animals. In an 18.5 degrees C environment the hypothermias caused by 0.5 and 1.0 g/kg ethanol were greatly augmented in old monkeys and in some cases their temperatures fell to potentially life-threatening levels. In a 30.5 degrees C environment, 1.0 g/kg ethanol given to monkeys caused approximately equal temperature reductions in the three groups. When determined after 1.0 g/kg ethanol, peripheral vasomotor tone increased significantly in animals of each age group in all three environments. Decreases in rectal temperature were associated with parallel decreases in oxygen consumption. These results indicate that: 1) aging is associated with an increased sensitivity to the hypothermic action of ethanol in thermoneutral and cold environments, 2) ethanol in the doses tested inhibits heat production mechanisms without suppressing compensatory vasoconstriction in response to decreased body temperature.

The effects of altering preoptic and anterior hypothalamic temperature on behavioral thermoregulation, vasomotor tone, and core temperature were investigated in cold-exposed (5°C) squirrel monkeys. Cooling this region over a range of 32–38°C was associated with increases in behavioral responses for radiant heat reinforcement and increased peripheral vasomotor tone and core temperature. Conversely, warming the preoptic and anterior hypothalamus over a range of 39.5–43°C was associated with reduced responses for radiant heat reinforcement and decreased vasomotor tone and core temperature. The changes in behavioral response rates and core temperature were proportional to the displacement of preoptic and anterior hypothalamic temperature above or below specific thresholds. Elevations of temperature had a greater effect on behavioral response rates and core temperature than did reductions in temperature. It is concluded that the hypothalamic regulator of behavioral thermoregulatory responses has operating characteristics similar to the hypothalamic regulator of autonomic responses.

Lesions of the ventromedial portion of the nucleus reticularis lateralis (NRL) of the medulla oblongata in the rabbit significantly and markedly reduced the pressor component of the cerebral ischemic response (CIR) without altering vasomotor tone. Use of horseradish peroxidase as an anterograde and retrograde tracer indicated that the ventromedial NRL projects to the intermediolateral cell column (IML) of the upper thoracic spinal cord. Injections of glutamate into ventromedial NRL elevated blood pressure (BP), indicating that neuronal cell bodies in this area are capable of eliciting BP elevations when stimulated. These findings suggest that cell bodies in the ventromedial NRL are capable of eliciting pressor responses during the CIR via direct projections to sympathetic preganglionic cell bodies.

1. Rats and squirrels, placed in an operant chamber that was heated and cooled by convection, regulated air temperature (Ts) between 4–50°C by pushing a lever. 2. Abdominal temperatures (Tb) of rats increased to relatively high levels (higher than 38·8°C) following placement in the chamber and were maintained relatively stable (changing less than 0·2°C/hr) for at least 1 hr. 3. Tb's of the squirrels rapidly peaked, usually to values greater than 40°C, then declined linearly with time at a rate of 0·4–1·2°C/hr, but transiently varying 1°C or more in a 10 min period accompanying behavioral manipulation of the heaters. 4. Tb's during operant thermoregulation were higher during the night than during the day in the rats. 5. Heart rates varied during themoregulatory behavior in ways which suggest a metabolic component to the thermoregulation in the rats and changes of peripheral vasomotor tone in the squirrels.

Male broilers (3.0 to 3.4 kg) chronically implanted with an electromagnetic blood flow probe on the celiac artery were used to study the effect of feeding and heat exposure on celiac mean blood flow (MBF). Postprandial celiac MBF and a cyclic pattern of MBF, produced in response to feeding, were reduced (P less than .05) by a 60-min exposure to 37 C but returned during a thermoneutral (25 C) recovery period. The exact nature of this cyclic MBF phenomenon is unknown but may be related to intestinal smooth muscle activity alterations and sympathetic vasomotor tone.

1. 1.|An earlier study of the thermoregulatory effects of intracerebroventricularly injected (ICV) noradrenaline (NA) in the sheep indicated a general inhibitory influence. 2. 2.|This reinvestigation of the effect of ICV NA on peripheral vasomotor tone (PVMT) of the ears within the range of thermoneutrality for the unshorn sheep shows that whereas ICV NA inhibits panting at high ambient temperatures, and inhibits shivering at low ambient temperatures, its effect on PVMT is an excitatory one.

Monitoring of the central venous pressure is a simple, relatively inexpensive method of assessing a patient's cardiac status, circulating blood volume, and vasomotor tone. Although it is a measure of considerable value in patients with cardiac, vascular pulmonary, renal, or other acute problems, for regulation of fluid or blood administration, it is essential that the physicians and nurses be fully aware and take into consideration some of the inherent fallacies and inadequacies of the information derived. Inaccurate measurements are often obtained by the aberrant lodgment of the venous pressure catheter tip, in addition to the other well-known complications. Radiographic identification of the catheter tip is essential to eliminate these problems.

Eight normal male Ss were tested for vasomotor responses of four skin areas to the presentation of novel auditory stimuli. The reciprocal vasomotor responses of the finger (vasoconstriction) and head (vasodilatation) reported by Vinogradova and Sokolov (1957) were confirmed. These responses are consistent with the known dominant vasomotor tone of these areas. Measurement of the activity of the ear with a dominant constrictive tone and of the skin of the neck with a dominant dilatative tone indicate that the vasomotor component of the orienting reflex is an enhancement of the normal dominant vasomotor control.

The vasodilatation test, the measurement of blood flow when vasomotor tone is abolished, can be a determining factor in deciding whether or not arterial surgery should be attempted. The purpose of this work is to show the advantages in time, and usually in accuracy, of placing patients in a state of vasodilatation when performing the test. An advantage gained by allowing the feet to be in a slightly dependent position is also demonstrated.

1. 1. Hypoathalamic and nasal mucosal temperature and respiratory frequency were recorded in four unrestrained rabbits, exposed to ambient temperatures of 5–40°C, before and after ear amputation. 2. 2. The cerebral temperature regulation was unimpaired by ear amputation because mild vasodilatation of nasal vessels in cool ambient and panting during heat exposure substituted for the role of peripheral vasomotor tone of the ears. Panting was generated at ambient temperature significantly lower than in intact rabbits. 3. 3. The ears seem to be of great importance in water economy in warm environments, but are unnecessary for thermoregulation itself.