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A wireless and wearable system was recently developed for mobile monitoring of respiratory rate (RR). The present study was designed to compare RR mobile measurements with reference capnographic measurements on a medical-surgical ward. The wearable sensor measures impedance variations of the chest from two thoracic and one abdominal electrode. Simultaneous measurements of RR from the wearable sensor and from the capnographic sensor (1 measure/minute) were compared in 36 ward patients. Patients were monitored for a period of 182 ± 56 min (range 68–331). Artifact-free RR measurements were available 81% of the monitoring time for capnography and 92% for the wearable monitoring system (p 20 (tachypnea) with a sensitivity of 81% and a specificity of 93%. In ward patients, the wearable sensor enabled accurate and precise measurements of RR within a relatively broad range (6–36 b/min) and the detection of tachypnea with high sensitivity and specificity.

PURPOSE: To evaluate the ability of a novel ultrasound (US) device, DiaMon, to monitor diaphragm movement via its proxy liver movement, and compare it with the respired flow measured with a flowmeter, in awake and healthy volunteers. We wanted to (1) establish the optimal anatomical position for attaching the DiaMon device to the abdominal wall, and (2) evaluate the accuracy of continuous monitoring of respiratory frequency. METHODS: Thirty healthy subjects were recruited. The DiaMon probe was applied subcostally in four different positions with the subjects in five different postures. The subjects breathed tidal volumes into a spirometer for 30–60 s with the DiaMon recording simultaneously. RESULTS: The device detected a readable signal in 83–100% of the position/posture-combinations. The technical correlation between the two signals was highest in the anterior axillary-supine position (mean ± SD: 0.95 ± 0.03), followed by paramidline-supine (0.90 ± 0.09) and midclavicular-supine (0.89 ± 0.12). The frequency measurements yielded a mean difference of 0.03 (95% limits of agreement − 0.11, 0.16) breaths per minute in the anterior axillary-supine position. CONCLUSION: The DiaMon device is able to detect liver movement in most subjects, and it measures breathing frequency accurately. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s40477-019-00412-2) contains supplementary material, which is available to authorized users.

Recently, many researchers have proposed a number of respiratory monitoring methods to monitor the respiratory amplitude and respiratory rate of athletes under different conditions. However, the problem with such methods is that their accuracy is not high. Therefore, this paper proposes a respiratory monitoring method based on a BP neural network combined with multisensor fusion technology. First, we fix multiple sensors on the chest and back of the human body so that we can accurately measure the acceleration and angular velocity changes caused by the contraction and expansion of the chest contour when athletes breathe under different motion conditions. After a coordinate measurement is performed on the data measured by the back measurement unit, the BP network algorithm is used to obtain the acceleration curve under the simple respiratory motion state. Finally, the respiratory frequency and respiratory depth parameters, which are important indicators for evaluating athletes’ physical fitness, can be obtained for the athletes under different motion states. Verification was carried out in an experimental platform, and the experimental results for different postures of the human body were compared with the standard respiratory mask measurement results. The accuracy rate was over 90%, thus realizing the networking, portability, and wearability of the breathing state sensors, which provide real-time accurate measurements.

The mediators of the perception of effort during exercise are still unclear. The aim of the present study was to examine physiological responses during runs using a rating of perceived exertion (RPE)-clamp model at the RPE corresponding to the gas exchange threshold (RPEGET) and 15% above GET (RPEGET+15%) to identify potential mediators and performance applications for RPE during treadmill running. Twenty-one runners ( $${\dot{V}\mathrm{O}}_{2}$$ max = 51.7 ± 8.3 ml kg−1 min−1) performed a graded exercise test to determine maximal oxygen consumption and the RPE associated with GET and GET + 15% followed by randomized 60 min RPE-clamp runs at RPEGET and RPEGET+15%. Mean differences for $${\dot{V}\mathrm{O}}_{2}$$ , heart rate (HR), minute ventilation ( $${\dot{V}}_{E}$$ ), respiratory frequency ( $${\mathcal{F}}_{R})$$ , respiratory exchange ratio (RER), and velocity were compared across each run. After minute 14, $${\dot{V}\mathrm{O}}_{2}$$ , RER and velocity did not differ across conditions, but decreased across time (p

During exercise, tidal volume initially contributes to ventilatory responses more than respiratory frequency, and respiratory frequency then increases rapidly while tidal volume stabilizes. Dyspnea intensity is also known to increase in a threshold-like manner. We tested the possibility that the threshold of tachypneic breathing is equal to that of dyspnea perception during cycle ergometer exercise (n = 27). Dyspnea intensity was scored by a visual analog scale. Thresholds were expressed as values of pulmonary O2 uptake at each breakpoint. Dyspnea intensity and respiratory frequency started increasing rapidly once the intensity of stimuli exceeded a threshold level. The thresholds for dyspnea intensity and for occurrence of tachypnea were significantly correlated. An intraclass correlation coefficient of 0.71 and narrow limits of agreement on the Bland–Altman plot indicated a good agreement between these thresholds. These results suggest that the start of tachypneic breathing coincides with the threshold for dyspnea intensity during cycle ergometer exercise.

Passive stretching, by inducing mechanical and chemical stimuli that activate receptors on the terminal end of group III and IV nerve fibres located within joints and muscle, may increase ventilation \((\dot VE)\)) during exercise. The aim of the study was to assess the effects of an acute bout of passive stretching on the ventilatory pattern. Maximum oxygen uptake was determined in nine participants who then performed a sustained cycle exercise of high intensity (constant workload of 85% of the minimum power to elicit maximum oxygen uptake, \(\dot W_{85} \)) with and without previous stretching. During the tests metabolic and respiratory parameters were recorded breath-by-breath. Time to exhaustion in the \(\dot W_{85} \) test was significantly shorter (−29%) with stretching. During the first 12 min of exercise the following parameters were significantly higher with stretching than without: oxygen uptake (+4%), ventilation (+9%), respiratory muscle power (+16%) and respiratory muscle oxygen uptake (+13%; P < 0.05). The increase in ventilation was accompanied mainly by an increase in respiratory frequency rather than in tidal volume. However, after stretching the metabolic rate also increased. Thus, the higher ventilation might have been a consequence of both higher muscle afferent activation and higher metabolic rate. Stretching alters the respiratory and metabolic response to exercise, but its effects on ventilation need further investigation.

The present study investigated whether ‘break-points’ in breathing pattern correspond to the first ( $$ G_{{{\text{EX}}_{1} }} $$ ) and second gas-exchange thresholds ( $$ G_{{{\text{EX}}_{ 2} }} $$ ) during incremental cycling. We used polynomial spline smoothing to detect accelerations and decelerations in pulmonary gas-exchange data, which provided an objective means of ‘break-point’ detection without assumption of the number and shape of said ‘break-points’. Twenty-eight recreational cyclists completed the study, with five individuals excluded from analyses due to low signal-to-noise ratios and/or high risk of ‘pseudo-threshold’ detection. In the remaining participants (n = 23), two separate and distinct accelerations in respiratory frequency (f R) during incremental work were observed, both of which demonstrated trivial biases and reasonably small ±95% limits of agreement (LOA) for the $$ G_{{{\text{EX}}_{1} }} $$ (0.2 ± 3.0 ml O2 kg−1 min−1) and $$ G_{{{\text{EX}}_{ 2} }} $$ (0.0 ± 2.4 ml O2 kg−1 min−1), respectively. A plateau in tidal volume (V T) data near the $$ G_{{{\text{EX}}_{1} }} $$ was identified in only 14 individuals, and yielded the most unsatisfactory mean bias ±LOA of all comparisons made (−0.4 ± 5.3 ml O2 kg−1 min−1). Conversely, 18 individuals displayed V T-plateau in close proximity to the $$ G_{{{\text{EX}}_{ 2} }} $$ evidenced by a mean bias ± LOA of 0.1 ± 3.1 ml O2 kg−1 min−1. Our findings suggest that both accelerations in f R correspond to the gas-exchange thresholds, and a plateau (or decline) in V T at the $$ G_{{{\text{EX}}_{ 2} }} $$ is a common (but not universal) feature of the breathing pattern response to incremental cycling.

Abstrqact The single intratracheal instillation (ITI) of bleomycin (BLM) is a widely used method for inducing experimental pulmonary fibrosis in rat model. In the present study, pulmonary function tests (PFTs) of tidal volume (VT), minute volume (VM), and respiratory frequency (FR) have been applied to study their possibility as a tool to monitor the progress of BLM-induced lung injury in rat model. Rats were treated with a single ITI of BLM (2.5 mg/kg) or saline (control). Animals were euthanized at 3, 7, 14, 21, and 28 days post-ITI. Lung toxicity effects were evaluated by inflammatory cell count, lactate dehydrogenase (LDH) activity in the bronchoalveolar lavage fluid (BALF), and light microscopic examination of lung injury. The PFT parameters were measured immediately before the animals were sacrificed. BLM treatment induced significant cellular changes in BALF-increase in number of total cells, neutrophils, and lymphocytes along with sustained increase in number of macrophages compared to the controls at days 3, 7, and 14. BALF LDH level was significantly increased compared to that in the controls up to day 14. On day 3, infiltration of neutrophils was observed in the alveolar spaces. These changes developed into marked peribronchiolar and interstitial infiltration by inflammatory cells, and extensive thickening of the interalveolar septa on day 7. At 14, 21, and 28 days, mild peribronchiolar fibrosis was observed along with inflammatory cell infiltration. The results of PFT show significant consistencies compared to the results of other toxicity tests. These data demonstrate that the most suitable time point for assessing lung fibrosis in this model is 14 days post-ITI of BLM based on the observation of fibrosis at 14, 21, and 28 days. Further, the progress of lung injury can be traced by monitoring the PFT parameters of FR, VT, and VM.

To evaluate the acute effect of hyperoxemia on the comfort and the respiratory variables in patients undergoing pressure support ventilation (PSV) for acute respiratory failure (ARF).Prospective, observational study performed in the intensive care unit of a university hospital.Thirteen semirecumbent patients were ventilated in PSV mode, the setting of which was established by the treating physician who was blinded to the study.The variables measured at different levels (21-80%) of FiO(2) randomly applied were: minute volume (V (E)), respiratory frequency (f) and the pressure develing during the first 100 ms of an occluded breath (P(0.1)). These variables were firstly measured at the level of FiO(2) chosen by the treating physician. Severity of dyspnea was rated using the visual analogue scale 15' after each FiO(2) variation.Modulation of FiO(2) was able to vary significantly the respiratory variables, since a FiO(2) increase was associated with a decrease in dyspnea, P(0.1), f, and V (E). While valuable variations were detected at both lower and higher values of FiO(2) than those established by the treating physician, a significant improvement in the respiratory variables was detected at FiO(2) 60%. The reduction in respiratory drive was statistically related to an amelioration of dyspnea (R(2)=0.89) even at values of FiO(2) higher than 60%.During PSV the respiratory drive can be heavily modulated by varying the FiO(2) since even at FiO(2) greater than 0.6 dyspnea and respiratory variables continued to improve.

The hypothesis that the initial responses to cold water immersion could be attenuated by repeated cold showers was tested. Eighteen (13 men, 5 women) non-habituated subjects undertook two 3-min head-out seated immersions into stirred water at 10 degrees C wearing swim wear. The immersions were separated by 4 days during which time they took six cold showers. The subjects were randomly split into three groups with different showering regimes: 3 min at 10 degrees C on the back (10B); 3 min at 15 degrees C on the back (15B); and 30 s at 10 degrees C on the back followed by 30 s on the front (10BF). Over the first 30 s of immersion respiratory frequency ( f (R)) was reduced by 21% in groups 10B and 10BF from 54 (14) to 44 (16) breaths.min(-1) ( P0.05), and 33 (8) to 26 (10) breaths.min(-1) ( P0.05) respectively, following repeated showers. Group 15B showed no change in f (R). The tachycardia induced on immersion in water at 10 degrees C was not reduced by repeated showers except in group 15B during the last 150 s [from 119 (23) to 105 (25) beats.min(-1), P0.05]. Repeated showering in water at 10 degrees C reduced the respiratory drive (as measured by f (R)) during head-out immersion in water at the same temperature. No such habituation was observed with repeated showers in warmer water (15 degrees C). It is concluded that when the body surface area cooled is the same, the rate of change of skin temperature is an important factor in determining the degree of habituation produced.

Objective. The aim of this study was to compare clinically relevant performance of: 1) a prototype respiratory sensor based on capnometry with two alternative signal receptor fixations, 2) a fibero ...

Objectives. To present further development of a fibre-optical respiratory rate monitor and evaluate the function in the final version. Methods. Respiration was recorded in 18 healthy volunteers of ages 9–83 years by three different methods simultaneously: fibre-optical monitoring, capnography and manually. The recordings were made breath by breath in four 3-minute periods in each subject. In total there were 54 observations, corresponding to 648 minutes. The recordings were fed simultaneously into a computer. Two subjects were excluded because of pronounced differences between all three methods. One person was later diagnosed as having a nasal septum deviation. Recordings with any kind of technical problem were also excluded. Results. In total 516 minutes were analysed. Students' paired t-test showed a mean of 0.5 and 0.3 more breaths were recorded by fibre-optical monitor compared with the manual method and capnography respectively. The 95% confidence interval of the differences between the fibre-optical monitor and the other two methods was –0.5 to +1.5 when the mean respiratory frequency was 14 breaths per minute. Analysis of variance revealed that the fibre-optical monitor tended to overestimate the mean respiratory rate (p < 0.001). Conclusion. The fibre-optical monitor has sufficient accuracy for clinical monitoring. It is easy to use and inexpensive. Combinations with pulse oximetry seem attractive, to use especially for application outside “high tech areas,” for example when respiratory depressant drugs are used or in ambulances.

Background Several scoring system have been developed with the aim to identify clinical deterioration among hospitalized patients and allocate resources in accordance with the degree of deterioration - most without validation. The aim of the present study was to describe to which degree the system “Tidlig Opsporing af Kritisk Sygdom” (TOKS) is able to identify patients who either have or develop severe sepsis or septic shock within 24 after arrival to hospital. Methods A retrospective descriptive study of patients hospitalized with community acquired severe sepsis or septic shock. Patients were identified based at discharge diagnosis ((IDC10 code A40.0-A41.9). Based at a manual evaluation of all patient records patients were included if they within the first 24 hours after arrival to the hospital fulfilled predefined criteria for severe sepsis or septic shock. Vital values registered at arrival to the hospital were identified and used for the present analysis. TOKS score is based at scores for respiratory frequency, saturation, systolic blood pressure, pulse rate, consciousness and temperature. The score range from 0 to 21 with an indication of need for a doctoral evaluation if the score is 3 or higher. Results

We assessed the central-chemoreflex ventilatory responses to carbon dioxide in six male volunteers using a hyperoxic rebreathing technique. Hyperventilation prior to rebreathing allowed both the threshold and the sensitivity of the response to be measured. We used immersion in water to control the body temperature (tympanic). The water temperature was adjusted to be either thermo-neutral or hot so that body temperature either remained normal [+0.2 (0.04) degrees C, mean (SEM)] or was elevated by 1.5 (0.08) degrees C. The sensitivities of the central-chemoreflex ventilatory responses to carbon dioxide were increased at elevated body temperatures, changing from a mean of 1.8 (0.2) 1.min-1. Torr-1 to 2.7 (0.1) 1.min-1. Torr-1. However, the thresholds did not change with temperature, and the mean threshold was 48(1) Torr at both normal and elevated temperatures. For all of the volunteers, ventilation was increased at elevated body temperatures for all levels of carbon dioxide, mainly by changes in respiratory frequency due to reductions in expiratory times. At subthreshold levels of carbon dioxide, mean ventilation changed significantly from 6.3(1.1) 1.min-1 at normal temperatures to 10.8 (1.9) 1.min-1 at elevated temperatures. Heart rates also increased significantly with temperature, changing from a mean of 66 (4) beats.min-1 to 102 (3) beats.min-1 at threshold levels of carbon dioxide. The mean rates of rise of carbon dioxide partial pressure during rebreathing were significantly increased with temperature as well, changing from 0.075 (0.008) Torr.min-1 to 0.089 (0.004) Torr.min-1. We concluded that elevating the body temperatures of our subjects not only increased their ventilation, heart rates and metabolic rates at all levels of carbon dioxide, but it also increased the sensitivity of their central chemoreflex ventilatory responses to carbon dioxide. Despite these increases, the thresholds of the central-chemoreflex ventilatory responses to carbon dioxide remained unchanged.

In conscious adult rabbits, "classical" respiratory sinus arrhythmia does not occur because the respiratory frequency (RF) always exceeds half the heart rate (HR). However, slow HR fluctuations, not synchronous with the respiratory rhythm but affected by it, occur systematically. We have shown that these can be calculated by using aliasing rules. During general anaesthesia, when the RF decreases so that respiratory frequency is less than half the heart rate, classical respiratory sinus arrhythmia occurs and can be greatly reduced by vagal blockade. The slow HR fluctuations which are not synchronous with the respiratory rhythms, but are affected by it are mainly vagally mediated, because vagal blockade virtually eliminates them.

The aim of this study was to specify whether exercise hyperpnoea was related to the CO2 sensitivity of the respiratory centres measured during steady-state exercise of mild intensity. Thus, ventilation % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Jf9qqqrpepC0xf9qiW7rqqrFfpeea0xe9LqFf0x% c9q8qqaqFn0dXdir-xcvk9pIe9q8qqaq-xir-f0-yqaqVeLsFr0-vr% 0-vr0xc8meaabaqaciGacaGaaeqabaWaaeaaeaaakeaacaGGOaGabm% OvayaacaWaaSbaaSqaaGqaaiaa-veaaeqaaOGaaiykaaaa!3D23! $$(\dot V_E )$$ , breathing pattern [tidal volume (V T), respiratory frequency (f), inspiratory time (T I), total time of the respiratory cycle (T TOT),V T/T I,T I/T TOT] and CO2 sensitivity of the respiratory centres determined by the rebreathing method were measured at rest (SCO2 re) and during steady-state exercise (SCO2 ex) of mild intensity [CO2 output % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Jf9qqqrpepC0xf9qiW7rqqrFfpeea0xe9LqFf0x% c9q8qqaqFn0dXdir-xcvk9pIe9q8qqaq-xir-f0-yqaqVeLsFr0-vr% 0-vr0xc8meaabaqaciGacaGaaeqabaWaaeaaeaaakeaacaGGOaGabm% OvayaacaWaaSbaaSqaaGqaaiaa-neacaWFpbWaaSbaaWqaaiaa-jda% aeqaaaWcbeaakiaacMcaaaa!3EDC! $$(\dot V_{CO_2 } )$$ =20 ml·kg−1·min−1] in 11 sedentary male subjects (aged 20–34 years). The results showed that SCO2 re and SCO2 ex were not significantly different. During exercise, there was no correlation between % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Jf9qqqrpepC0xf9qiW7rqqrFfpeea0xe9LqFf0x% c9q8qqaqFn0dXdir-xcvk9pIe9q8qqaq-xir-f0-yqaqVeLsFr0-vr% 0-vr0xc8meaabaqaciGacaGaaeqabaWaaeaaeaaakeaaceWGwbGbai% aadaWgaaWcbaacbaGaa8xraaqabaaaaa!3BC0! $$\dot V_E $$ and SCO2 ex and, for the same % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Jf9qqqrpepC0xf9qiW7rqqrFfpeea0xe9LqFf0x% c9q8qqaqFn0dXdir-xcvk9pIe9q8qqaq-xir-f0-yqaqVeLsFr0-vr% 0-vr0xc8meaabaqaciGacaGaaeqabaWaaeaaeaaakeaaceWGwbGbai% aadaWgaaWcbaacbaGaa83qaiaa-9eadaWgaaadbaGaa8Nmaaqabaaa% leqaaaaa!3D79! $$\dot V_{CO_2 } $$ , all subjects had very close % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Jf9qqqrpepC0xf9qiW7rqqrFfpeea0xe9LqFf0x% c9q8qqaqFn0dXdir-xcvk9pIe9q8qqaq-xir-f0-yqaqVeLsFr0-vr% 0-vr0xc8meaabaqaciGacaGaaeqabaWaaeaaeaaakeaaceWGwbGbai% aadaWgaaWcbaacbaGaa8xraaqabaaaaa!3BC0! $$\dot V_E $$ values normalized for body mass (bm), regardless of their SCO2 ex ( % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Jf9qqqrpepC0xf9qiW7rqqrFfpeea0xe9LqFf0x% c9q8qqaqFn0dXdir-xcvk9pIe9q8qqaq-xir-f0-yqaqVeLsFr0-vr% 0-vr0xc8meaabaqaciGacaGaaeqabaWaaeaaeaaakeaaceWGwbGbai% aadaWgaaWcbaacbaGaa8xraiaa-jgacaWFTbWaaWbaaWqabeaacaWF% WaGaa8Nlaiaa-DdacaWF1aaaaaWcbeaaaaa!4098! $$\dot V_{Ebm^{0.75} } $$ =1.44 l·min−1·kg−1 SD 0.10). A highly significant positive correlation between SCO2 ex andV T (normalised for bm) (r=0.80,P

Effects of Variations in Carbohydrate (CHO) Intake on Postprandial Gas Exchange, and Respiratory Frequency of Low Birth Weight (LBW) Infants

Twenty-four Large White weaners-twelve males and twelve females, were randomly divided into three groups of eight (four males and four females per two separate pens) and were assigned to three groups of two pens each for the males and the females weaners. One group of two pens was without wallow facility (control), one other group was provided with wallows (wet) and the third group was in air-conditioned room (cold). Twice a day, the respiratory rate and the rectal temperatures were measured early in the mornings at 8.00–9.00 hrs (A.M.) and late in the early evenings at 16.00–18.00 hrs. The mean respiratory frequency (A.M) ranged from 7 to 9; 6–12 and 8–13 breaths per minute for the cold, wet and control respectively while the mean respiratory frequency (P.M.) ranged from 6 to 9, 10 to 17 and 13 to 19 breaths per minute for the cold, wet and control respectively. The mean rectal temperatures (A.M.) ranged very slightly from 38.54° to 39.12°C; 38.50° to 39.05°C and 38.61°C to 39°C for the cold, wet as control respectively while the mean rectal temperatures (P.M.) ranged from 39.00° to 39.22°C; 38.97° to 39.29°C and 39.28° to 39.55°C for the cold, wet and control respectively. The animals were maintained for another seven to ten weeks and were slaughtered. The slaughter characteristics did not indicate an appreciable thermal stress except for the reproductive organs which showed weight increase indicating reduced efficiency of the thermally stressed animals as is the case in the tropical environment.

1. Metabolic rate (MR), deep body temperature (Tb) and respiratory frequency (f) were measured in rufous rat-kangaroos in a controlled environment at ambient temperatures (Ta) between 5 and 37 °C. Diurnal variations inTb, total motoric activity and activity pattern were recorded in the same animals in open outdoor enclosures. 2. The lowest MR of 2.74 W kg−0.75 occurred betweenTa=25 to 35 °C. Considerable changes in thermal conductance (C) resulted in a nonlinear increase in MR below the lower critical temperature of 25 °C. Changes inC were attributed to postural changes leading to a reduction in the effective surface area. Panting and saliva spreading were the main mechanisms of heat dissipation atTa above 30 °C. 3. A. rufescens showed a reproducible motoric activity pattern during the night. Total locomotor activity and activity patterns and circadian variations inTb were not affected byTa even below 0 °C. 4. The nest had an important insulative function during the day, the resting period of the animals, but was only seldomly used at night. 5. It is concluded that the locomotor activity may contribute to the regulation ofTb mainly by minor changes in hopping speed and in the duration of resting periods, but not by changes in total activity and activity patterns.

We have tested the hypothesis that autonomic instability, reflected in increased variability of heart rate and respiratory frequency, characterized high risk babies who died of sudden infant death syndrome. Using computer-based methods, we compared the power spectra of instantaneous heart rate and respiration on coded tape recordings from seven asymptomatic siblings and 10 babies with symptomatic apnea who died of sudden infant death syndrome to 34 age- and sex-matched controls. We confirmed our previous observation of increased respiratory bandwidth, an index of variability in respiratory frequency (p = 0.009) but failed to confirm our finding of increased low frequency fluctuations in heart rate (p = 0.18). In addition, we found an increase in mean respiratory frequency during quiet breathing (p = 0.001) and a significant relationship between respiratory bandwidth and mean respiratory frequency (r = 0.604, p = 0.0002). These variables along with those from a previous analysis of the same data base yield a discriminant function with 82% sensitivity and 100% specificity. These results confirm previous suggestions that high risk babies who die of sudden infant death syndrome exhibit autonomic instability.

1. Oxygen consumption\(\dot M_{O_2 } \), ventilation,\(\dot Vw\), and circulatory flow-rate,\(\dot Vb\), were studied in settled crayfishAstacus leptodactylus at different O2 partial pressures in the inspired water,\(PI_{O_2 } \), ranging from 250 to 8 Torr. From\(PI_{O_2 } \)=250 to 25 Torr,\(\dot M_{O_2 } \) was maintained constant while\(\dot Vw\) increased 16 times the hyperoxic value. Since\(P_{O_2 } \) of both arterialized hemolymph and expired water remained in a narrow range independent of\(PI_{O_2 } \), we propose that\(\dot Vw\) is adjusted in order to maintain the level of oxygenation at the gas exchanger. Down to\(PI_{O_2 } \)=40 Torr, the observed arterio-venous concentration difference and\(\dot Vb\) both remained constant. At\(PI_{O_2 } \)=25 Torr, however, a further increase in\(\dot Vw\) could not maintain the (a-v)O2 concentration difference. As\(\dot M_{O_2 } \) did not fall, it is concluded that\(\dot Vb\) increased. 2. The role of the peripheral O2 chemoreceptors in these ventilatory and circulatory adjustments was analysed by a study of responses to short periods of exposure to\(PI_{O_2 } \)≃600 Torr (one-minute ‘O2 test’). Giving O2 tests to animals at\(PI_{O_2 } \) plateaux situated between 150 and 15 Torr induced a rapid change in the respiratory frequency which started before the hyperoxic bolus could have reached the central nervous system (CNS). Response latencies were shorter the higher the reference\(\dot Vw\); they were independent of the time required for the hemolymph to reach the heart and hence the CNS. It is concluded that the responses were initiated by O2 chemoreceptors located in the branchial cavities. The branchial location of O2 reception is consistent with the above proposition of a\(P_{O_2 } \) regulation at the gas exchanger. The importance of a central O2 chemosensitivity is questioned.

The observation that dynamic compliance (Cdyn) tended to rise with respiratory frequency (f) in adult cattle led us to reassess the importance of inertial pressures in measuring Cdyn in large animals. Five healthy Friesian cows were selected for their ability to show an increase of f without significant change in tidal volume (VT). Dynamic compliance was measured three times, both at the resting f (21 +/- 1 cpm), and at higher f (49 +/- 3 cpm), obtained by an artificial increase in the dead space of the breathing mask. Frequency-response characteristics of the measuring instruments were matched up to 12 Hz. The inertia of the lungs and gas stream (In) was calculated as the ratio of the accelerative pressure change to the simultaneous change in volume acceleration. Inertance was also estimated from the dimensions of the bovine airways and from the relative linear flow velocities reported by Rohrer (1915). Dynamic compliance measured during rapid breathing was significantly higher (p less than or equal to 0.01) than base-line values. Dynamic compliance was strongly correlated with f (r = +0.96). Measured and estimated In were 0.002 and 0.003 kPa.sec2.L-1 respectively. Dynamic compliance did not differ significantly from base-line values when it was corrected for the estimated inertance effect.

The time course of the transient ventilatory response to a sudden change in inspired gas from room air to 4% CO2 in air was examined in 11 healthy preterm neonates. Changes in minute ventilation (VI), tidal volume (VT), and respiratory frequency (f) were determined over 4 to 5 min of CO2 inhalation during both quiet (QS) and active sleep (AS) in each infant. In both states there was a brisk increase of mean VI in response to 4% CO2, while mean VT increased more slowly and mean f only increased transiently at 1 to 2 min. Exponential curve fitting to the change in VI and VT for each infant accounted for 64 +/- 20% of the variance in VI during QS as compared to 30 +/- 18% during AS (p less than 0.003). In only six infants did exponential curves fitted to the changes in VI and VT during QS reach 90% of their steady state values within 4 to 5 min of CO2 exposure. Their time to reach 90% of steady state was always shorter for VI than VT (p less than 0.01). Frequency showed a biphasic response with a transient rise at 1 to 2 min (p less than 0.05) and return to control levels at steady state. These data indicate that not all preterm infants reach a new level of steady state ventilation within 4 to 5 min of 4% CO2 inhalation. Furthermore, many infants exhibit a biphasic response of f over time which causes VI to reach steady state prior to VT.

1. Pigeons with chronically implanted injection cannula in the hypothalamus were injected with noradrenaline (NA, 10 micrograms/microliter) and 5-hydroxytryptamine (5-HT, 10 micrograms/microliter) at the ambient temperature (Ta) of 38 degrees or 42 degrees C. 2. Initial tests at cold (6 degrees C) indicated that birds responded hypothermically to NA and in most instances also to 5-HT. 3. Intrahypothalamic injection of NA (10 micrograms/microliter) had no appreciable effect on oxygen consumption (VO2), body temperature (Tb), foot temperature (Tf), or heart and respiratory rates at Ta 38 degrees C. The increase of VO2, Tb and Tf noted after similar injection at 42 degrees C was in all probability due to observed excitement and bursts of struggling rather than effects on thermoregulatory mechanisms. 4. 5-HT (10 micrograms/microliter) injected at Ta 38 degrees C depressed respiratory frequency from panting (600 breaths.min-1) to normal rate (ca. 50.min-1) within 2--4 min. The absence of panting lasted about 10 min, but only a slight increase of VO2, Tb and Tf followed. At Ta 42 degrees C, no notable changes of VO2, Tb and Tf were recorded after 5-HT injection. 5. It is concluded that 5-HT has an inhibitory action on neuronal pathway controlling panting activity in the pigeon, but NA seems to be ineffective.

Ventilation (V) and respiratory water loss\(\left( {\dot M_{R,H_2 O} } \right)\) were measured in domestic fowlGallus gallus subjected to raised environmental temperatures (33±2°C) and breathing air, 8% O2 in N2, 3% CO2 in air or 5% CO2 in air. Birds breathing air underwent an 18.6-fold increase in respiratory frequency and a 5-fold reduction in tidal volume and panting was accompanied by vigorous gular flutter. Hypoxic and hypercapnic birds breathed more slowly and deeply and gular flutter was strongly inhibited. The\({{\dot M_{R,H_2 O} } \mathord{\left/ {\vphantom {{\dot M_{R,H_2 O} } {\dot V}}} \right. \kern-\nulldelimiterspace} {\dot V}}\) ratio was similar to that predicted on the basis of the measured ventilation assuming saturation of expired gas at measured gular mucosal temperature in hypoxic and hypercapnic birds but 54% greater than the predicted value in birds panting in air. It is concluded that the excess water loss during normal panting results from tidal airflow generated independently by the buccopharyngeal pump and that buccopharyngeal ventilation is equivalent to 54% of the respiratory ventilation.

We have studied the pattern of breathing before, during and after augmented breaths in spontaneously breathing, anesthetized cats with the larynx both in and out of the breathing circuit. Following augmented breaths we consistently observed increases in end-expiratory lung volume (EEV), end-expiratory transpulmonary pressure, dynamic lung compliance and respiratory frequency. These changes were of similar magnitude whether the larynx was in or out of circiut and were uninfluenced by section of the superior laryngeal nerves. Laryngeal resistance, measured under constant flow conditions with the larynx removed from the breathing circuit, showed an exaggerated inspiratory decrease during augmented breaths. Passive lung inflations, performed so as to mimic the pattern of augmented breaths, increased dynamic lung compliance but did not elicit changes in EEV or respiratory frequency. The results indicate that the increase in EEV cannot be attributed to increased lung compliance but results from a change in end-expiratory respiratory muscle tone. This change, and the change in respiratory frequency appear to be part of a reflexly evoked central response that includes the augmented breath itself. The larynx participates in the augmented breath, but its mechanical importance is small.

Subjects were instructed to synchronize finger tapping with visual signals of various frequencies. It was found that breathing rate became entrained to tapping rate if the latter fell within a range of two breaths per minute of the subject’s previous breathing rate. Entrainment did not occur when the subject merely monitored the visual stimuli but only during performance of tapping. The effect occurred without subjects’ awareness and was observed only in the absence of deliberate adjustments in respiratory frequency on the part of the subject. Temporal restrictions on the neural events responsible for motor output appear to be responsible for the phenomenon.

The respiratory frequency and gular flutter frequency of 12 domestic pigeons and one barn owl were determined during exposure to air temperatures of 35–50 ° C. In both species respiratory and gular flutter frequencies increased with increasing body temperature (Tb) until maximum rates were obtained (Figs. 1, 4). In pigeons, the increase in respiratory frequency was preceded by a 0.5–1.4 ° C rise inTb. Gular flutter and panting occurred synchronously (Fig. 2), and mean maximum and minimum flutter rates were significantly different in the pigeon. These results demonstrate that under moderate thermal loads pigeons, and perhaps barn owls, do not pant at the resonant frequency of the respiratory system.

Die Hochstwerte des Atemgrenzwertes werden bei Gesunden und auch bei Lungenkranken bei einer Atemfrequenz von 100/min erreicht. Von dann ab ist eine Zunahme nicht mehr statistisch sicher. Der Atemgrenzwert bleibt praktisch unverandert hoch. Auch bei einer Atemfrequenz von 200/min ist die geatmete Luftmenge nie kleiner als die des physiologischen Totraumes.

L-glutamic acid injected in doses of 200--1000 n moles . kg-1 into the cerebral ventricles of sheep had dose-dependent thermoregulatory effects: an increase in heat production and/or a decrease in respiratory frequency, and a rise in rectal temperature. A dose of 800 nmoles . kg-1 had effects comparable with those of a similar injection of 3 nmoles . kg-1 carbamylcholine.

There are two components to respiratory frequency in the premature infant: a phasic component related to the Hering Breuer reflex and a tonic component set by the bulbo-pontine centres. We have previously shown that the phasic component is related to gestational age.* We have now attempted to quantitate the bulbo-pontine output by measuring the inspiratory duration and pressure developed during airway occlusion at FRC. We have studied 10 infants under 1400g., all with periodic breathing, and correlated the results with the blood gases. There is a significant (p>0.01) correlation between inspiratory duration (1/Tiocc) and the rate of change of pressure (dP/dt) with pCO2 (1/Tiocc = 0.09 pCO2 - 1.66). There is no correlation with the pO2. These results suggest that the bulbo-pontine output is primarily determined by pCO2. However, because inspiratory duration becomes so short, the maximum pressure developed falls with rising pCO2. This makes the respiratory system very vulnerable to respiratory loads. This vulnerability is lost in older premature infants as they develop large pressures when breathing against an obstruction. * Pediat. Res. 7, 291, 1973.

This study was designed to determine cardiopulmonary responses to nasal obstruction in different sleep states. 8 healthy preterm infants (wt 1.8±.1Kg) were studied at a corrected G.A. of 35±2 wks by multiple 10 sec occlusions during active (AS) and quiet (QS) sleep, via nasal prongs fitted with a thermistor to measure airflow. Heart rate (HR), mouth airflow, transcutaneous PO2 (Tc PO2), chest wall movements, respiratory frequency (f) and sleep state were continuously monitored. Nasal occlusion was invariably accompanied by a fall in TcPO2, which was greater during AS than QS (8±2 vs 5±3 mmHg, p

The presence of unequal time constants in the lung should lead to a progressive inequality of ventilation distribution and gas exchange failure at high breathing frequencies. However, in a group of 8 adolescent asthmatics we have not been able to demonstrate such a relationship between breathing frequency and gas exchange. These subjects were trained to alter respiratory rate (f) over a wide range while maintaining their arterial carbon dioxide tension (PaCO2) within 3 mmHg of their resting values. At rest (f = 14.7 ± 4.8) the alveolar arterial oxygen gradient (AaDo2) was 37.0 ± 9.9. At an intermediate rate (f = 30.0 ± 3.77) the AaDo2 rose significantly to 39.4 ± 8.5. At high rates (f = 104.5 ± 18.9) the AaDo2 fell significantly to 34.1 ± 9.4. The validity of alveolar arterial gradients at high rates is doubtful, but a similar effect although not significantly different, was seen in the arterial oxygen tension: rest 72.3 ± 9.00, intermediate 70.4 ± 7.3, fast 73.3 ± 9.5. There was no significant difference in alveolar ventilation (rest 4.95 L/min ± 1.38, intermediate 5.31 ± 1.51, fast 5.76 ± 1.55). To explain this conservative behaviour, we have postulated that the regional resistances and compliances must be non-linear acting in a direction to equalize the ventilation distribution as frequency increases. In non-laminar flow, resistance is flow dependent and over-distention of regional units will reduce their compliance. Both these factors will tend to stabilize distribution.