bluuebunny/crossref_metadata_2025 huggingface dataset:
Responses of conscious rabbits to CO2 at ambient temperatures of 5, 20, and 35 degrees C
Authors: Maskrey M. , Nicol S. C.
Published: December 2017

Conscious rabbits were exposed to atmospheric air or to 6% CO2 in air at ambient temperatures (Ta) of 5, 20 and 35 degrees C. Measurements were made of rectal temperature (Tre), metabolic rate (MR), respiratory frequency (f), tidal volume (VT), and minute volume (VE). CO2 exposure did not affect Tre at any Ta and only affected MR at 35 degrees C when it caused an increase. At each Ta hypercapnia caused an increase in VT and a decrease in f. At 5 degrees C VE was increased by CO2, at 35 degrees C VE decreased, and at 20 degrees C the results were variable. The data were examined in the light of theories relating to the relative contributions of inputs from brain stem and from pulmonary stretch receptors, in response to body temperature and CO2 partial pressure. It was concluded that hypercapnia stimulates an increase in VT via the brain stem, whereas at the same time removing a hypocapnic drive which, along with central thermal inputs, stimulates f.
Generation and regulation of breathing in utero: fetal CO2 response test
Authors: Moss I. R. , Scarpelli E. M.
Published: December 2017

Breathing responses to increasing fetal arterial CO2 pressure (PaCO2) were measured in 15 mature fetal lambs in utero during hyperoxic CO2 rebreathing in the ewe. Fetal breathing was expressed as 1) respiratory drive (RD), i.e., the early slope of intratracheal pressure during inspiration, and 2) ventilation equivalent (VEq), i.e., the product of intratracheal pressure and frequency of breathing. RD and VEq increased linearly with increasing PaCO2. CO2 threshold beyond which apneic fetuses started breathing was higher than the extrapolated CO2 threshold in spontaneously breathing fetuses. Afferent sciatic nerve stimulation, which induced regular breathing in apneic fetuses, lowered their CO2 threshold but did not alter their sensitivity to CO2. Naloxone resulted in initiation of fetal breathing, decreased CO2 threshold, and increased sensitivity to CO2. These studies demonstrate that respiratory center responsivity can be quantified in the lamb fetus in utero, that nonspecific somatic stimulation lowers fetal breathing threshold to CO2, and that endogenous opioid peptides could participate in the physiological suppression of breathing in fetal life.
Lung inflation and longitudinal distribution of pulmonary vascular resistance during hypoxia
Authors: Dawson C. A. , Grimm D. J. , Linehan J. H.
Published: December 2017

Using the low-viscosity bolus method, we examined the influence of lung inflation on the longitudinal distribution of vascular resistance during hypoxia in isolated cat lungs. During hypoxia, increasing transpulmonary pressure decreased vascular resistance but did not change the volume into the lung at which the maximum local resistance was located. This was in contrast to the normoxic situation in which inflation caused an increase in resistance over much of the transpulmonary pressure range studied and moved the maximum local resistance downstream. These results indicate that during hypoxia the major increase in resistance was in extra-alveolar vessels and that distension of these vessels by lung inflation decreased the magnitude of the pressor response. The increase in resistance in alveolar vessels, which occurred on inflation, was similar during control and hypoxic conditions but was a smaller part of the total resistance during hypoxia because of the much larger extra-alveolar vessel resistance.
Effects of normal and loaded spontaneous inspiration on cardiovascular function
Authors: Scharf S. M. , Brown R. , Saunders N. , Green L. H.
Published: December 2017

To assess the hemodynamic effects of spontaneous inspiration, we studied 12 anesthetized mongrel dogs during normal and loaded inspiration, before and after bilateral cervical vagotomy. Peak aortic flow fell (15--20%) whereas peak pulmonary artery flow rose (15--20%) under all conditions. When aortic flow fell, left ventricular diastolic size decreased whereas aortic and left atrial transmural pressures increased slightly. Right ventricular diastolic size and right atrial transmural pressure increased. During inspiratory loading transmural pressures rose more, but the fall in aortic flow remained the same. After vagotomy, inspiration was prolonged, allowing aortic flow to return to preinspiratory levels. At this time left ventricular diastolic size was increased compared to preinspiratory levels and there were further increases in left atrial and aortic transmural pressures. We have concluded that at least two factors affect aortic flow during inspiration: 1) a decrease in left ventricular preload that is associated with decreased left ventricular compliance, and 2) increased impedance to left ventricular emptying as reflected by the increase in aortic transmural pressure. This may play a greater role during inspiratory loading and when inspiration is prolonged.
Role of skin temperature in the control of sweating
Authors: McCaffrey T. V. , Wurster R. D. , Jacobs H. K. , Euler D. E. , Geis G. S.
Published: December 2017

In five male subjects tympanic membrane temperature (Tty), rectal temperature, skin temperatures at 12 sites were simultaneously recorded. Local sweating rate was measured at six sites using resistance hygrometry. After steady-state sweating was established, the lower body was heated at ambient temperatures of 50, 60, 70, and 80 degrees C or cooled at an ambient temperature of 29 degrees C while the upper body remained at a constant ambient temperature. During lower body heating or cooling, Tty was maintained constant by the drinking of cold (10 degrees C) or warm (45 degrees C) water. Sweating rate on both upper and lower body surfaces was proportional to lower body skin temperature. The regression coefficients for sweating rate versus mean lower body skin temperature varied from 0.03 to 0.09 mg/cm2.min. degrees C between subjects, but were not significantly different from each other (P greater than 0.05). This study demonstrates an influence of cutaneous thermoreceptors on sweating rate under steady-state conditions.
Pulmonary surface film stability and composition
Authors: Hildebran J. N. , Goerke J. , Clements J. A.
Published: December 2017

Stability of pulmonary alveoli at end expiration requires a very low air-water surface tension (e.g., less than 10 mN.m-1). Another important requirement is that the surface film maintain this low surface tension for a sufficiently long time at fixed lung volume. We measured monolayer collapse rates at 37 degrees C of lung surface-active material (SAM) and certain lipids found in this material and compared them with alveolar monolayer collapse rates calculated from published lung compliance changes. We found collapse rates for purified SAM or a mixture of dipalmitoyl lecithin (DPPC):monoenoic lecithin (PC):cholesterol (CHOL) (3.03:1.65:1 molar ratios) to be much greater than collapse rates of alveolar films estimated from indirect measurements. Monolayers of pure DPPC or DPPC with 10 mol% monoenoic PC and/or CHOL had collapse rates equal to or less than those estimated from lungs. We conclude that the alveolar monolayer is enriched in DPPC to the extent of 90 mol% or greater. Enrichment may exclude more mobile components from the monolayer during expiration when surface tension reaches verry low values.
Pulmonary pressure-flow curves measured by a data-averaging circuit
Authors: Lisboa C. , Ross W. R. , Jardim J. , Macklem P. T.
Published: December 2017

We measured pulmonary pressure-flow curves in nine normal nonsmoking subjects using a data-averaging circuit. With this method we obtained mean pressure flow curves of 20 consecutive breaths free of cardiac artifacts. Within-observer and within-subject-within-day reproducibility were good especially for the inspiratory limb of the curve. Within-subject-between-day variability in curvilinearity was substantial. In most subjects there was a continuous increase in resistance throughout the course of expiration even though the airways did not become dynamically compressed. This resulted in a mean value of expiratory resistance that was greater than during inspiration. Resistance early in expiration, however, was identical to that during inspiration. The data-averaging circuit allows for a more accurate assessment of the slope and the curvilinearity of pulmonary pressure-flow curves than other methods described before.
Measurement of transdiaphragmatic pressure with a single gastric-esophageal probe
Authors: Gilbert R. , Peppi D. , Auchincloss J. H.
Published: December 2017

A single gastric-esophageal probe, 5 mm in diam, with two transducers mounted near the tip has been used to measure transdiaphragmatic pressure in human subjects. The transducers are linear up to at least 200 cmH2O pressure and provide equal deflections for both positive and negative pressures. The method is shown to give results comparable to the standard procedure using two balloon-tipped catheters, one in the stomach and one in the esophagus.
Evidence for increased intrathoracic fluid volume in man at high altitude
Authors: Jaeger J. J. , Sylvester J. T. , Cymerman A. , Berberich J. J. , Denniston J. C. , Maher J. T.
Published: December 2017

To determine if subclinical pulmonary edema occurs commonly at high altitude, 25 soldiers participated in two consecutive 72-h field exercises, the first at low altitude (200–875 m) and the second at high altitude (3,000–4,300 m). Various aspects of ventilatory function and pulmonary mechanics were measured at 0, 36, and 72 h of each exercise. Based on physical examination and chest radiographs there was no evidence of pulmonary edema at high altitude. There was, however, an immediate and sustained decrease in vital capacity and transthoracic electrical impedance as well as a clockwise rotation of the transpulmonary pressure-volume curve. In contrast, closing capacity and residual volume did not change immediately upon arrival at high altitude but did increase later during the exposure. These observations are consistent with an abrupt increase in thoracic intravascular fluid volume upon arrival at high altitude followed by a more gradual increase in extravascular fluid volume in the peribronchial spaces of dependent lung regions.
Recovery from maximal effort exercise: lactate disappearance and subsequent performance
Authors: Weltman A. , Stamford B. A. , Fulco C.
Published: December 2017

The effects of differing recovery patterns following maximal exercise on blood lactate disappearance and subsequent performance were examined. Nine subjects completed four randomly assigned experimental sessions. Each session consisted of a 5-min maximal effort performance test conducted on a Monark bicycle ergometer (T1) followed by 20 min of recovery and a second 5-min maximal effort performance test (T2). Blood lactate levels were measured during min 5, 10, 15, and 20 of recovery. Recovery patterns consisted of passive recovery (PR), active recovery below anaerobic threshold (AR less than AT), active recovery above anaerobic threshold (AR greater than AT), and active recovery above anaerobic threshold while breathing 100% oxygen (AR greater than AT + O2). Blood lactate levels prior to T2 were significantly different across treatments (P less than 0.05). Comparison among treatments and between T1 and T2 revealed no significant differences in work output. It was concluded that while lactate disappearance following severe exercise can be affected by varying the recovery pattern, elevated levels of blood lactate exert no demonstrable effect on maximal effort performance of 5-min duration.
Aerobic and glycolytic metabolism in arm exercise
Authors: Pendergast D. , Cerretelli P. , Rennie D. W.
Published: December 2017

Eight kayakers (K) and 3 sedentary subjects (S) performed arm cranking and pedaling while erect or supine at each of several work loads from submaximal to the highest they could sustain for 2 min and for intervals varying from 10 s to 5 min. From measurements of VO2 and blood lactate concentration, the aerobic and glycolytic energy release in arm work was assessed. For steady-state aerobic work all subjects had a mechanical efficiency averaging 0.24 independent of posture or exercise mode. Per unit fat-free limb volume, arm VO2max of group K was 1.5-fold that of group S, whereas leg VO2max was the same in each group. Compared to group S, glycolytic arm work in group K was characterized by: 1) higher thresholds for release of lactate at the onset of submaximal work, 2) lower blood lactate concentrations during comparable absolute or relative submaximal work, 3) higher conventional anaerobic thresholds for absolute, but not relative work loads, 4) higher maximal rates of lactate release, and 5) the same maximal blood lactate concentrations. Measurement of the early lactate threshold, which occurred at considerably lower arm work loads than did anaerobic threshold, but which was greatly increased by specific muscle training, may provide a simple, sensitive, and nontraumatic evaluation of muscle training.
Plasma volume changes during rest and exercise in different postures in a hot humid environment
Authors: Diaz F. J. , Bransford D. R. , Kobayashi K. , Horvath S. M. , McMurray R. G.
Published: December 2017

Plasma volume shifts were investigated in five male subjects who rested and exercised in the upright, low-sit, and supine postures in a hot humid environment (49.5 degrees C, 28.9 Torr). The resting and exercise periods were each 45 min in duration. Weight losses during rest were 0.3% with an additional weight loss of 1.1% during exercise. During exercise subjects worked at either 360 or 540 kpm.min-1 in each of three postures. Each experiment was preceded by a 30-min control period in the supine posture at an ambient temperature of 22 degrees C. At rest plasma volume was reduced 17.3% in the upright, 9.0% in the low-sit, and 2.2% in the supine postures (using the end of the supine rest as the zero reference point). Supine exercise resulted in a plasma volume decrease of 11%, the low-sit 7.1%, and the upright 2.7%. The total reduction in plasma volume during the rest and exercise period was 20% in the upright, 16.1% in the low-sit, and 13.3% in the supine. No significant differences in plasma volume shifts were observed between the high and low work loads. The results indicate that the plasma volume shifts observed during rest and exercise in the heat are qualitatively similar to those observed in a cool environment.
Aortic body chemoreceptor responses to changes in PCO2 and PO2 in the cat
Authors: Lahiri S. , Mulligan E. , Nishino T. , Mokashi A.
Published: December 2017

Responses of aortic chemoreceptor afferents to a range of arterial carbon dioxide tension (Paco2) changes at various levels of arterial oxygen tension (Pao2) were investigated in 18 cats anesthetized with alpha-chloralose and maintained at 38 degrees C. Aortic chemoreceptor activity, end-tidal oxygen pressure, end-tidal carbon dioxide pressure, and arterial blood pressure were continuously monitored. Arterial blood gases were measured in steady states. Single or a few clearly identifiable afferents were studied during changes and steady states of Pao2 and Paco2. All the aortic chemoreceptor afferent discharge rates increased with Paco2 increases from hypercapnia (10–15 Torr) to normocapnia and moderate hypercapnia (30–50 Torr) and with Pao2 decreases from above 400 to 30 Torr. Hypoxia augmented the response to Paco2 most effectively in the range of 10–40 Torr. At any Pao2, the discharge rate reached a plateau with sufficient intensity of hypercapnia. The Paco2 stimulus threshold at a Pao2 of 440 Torr was about 15 Torr, and at a Pao2 of 60 Torr it was 10 Torr. In the transition from hypocapnia to hypercapnia, responses increased gradually, usually without an overshoot. The steady-state responses to Paco2 of the majority of aortic chemoreceptors resembled those of carotid chemoreceptors. The responses of both receptors can be attributed to the same basic type of mechanism.
Airway closure during anesthesia: a comparison between resident-gas and argon-bolus techniques
Authors: Hedenstierna G. , Santesson J.
Published: December 2017

Airway closure was measured in awake and then anesthetized supine healthy subjects with the argon-bolus and the resident-gas (nitrogen) techniques simultaneously. The preinspiratory lung volume for the closing volume maneuver was varied from residual volume to closing capacity (CC). Comparative measurements were also performed in the upright and supine positions in awake subjects. Closing volume (CV) was consistently larger with the bolus technique in supine subjects both when awake and when anesthetized (difference between methods 0.1--0.2 l, P less than 0.01), whereas no difference between the methods was noted in upright subjects. The lower “nitrogen CV” in supine subjects may be due to a shorter vertical lung height with a smaller range of nitrogen concentrations, resulting in a less abrupt onset of phase IV (taken to indicate CV). CV was not significantly affected by the preinspiratory lung volume with either technique, and CC was unchanged when anesthesia was instituted. Functional residual capacity (FRC) was reduced with anesthesia (mean reduction: 0.6 l, P less than 0.01) and FRC-CC became negative in all subjects with either technique. This implies intermittent or continuous airway closure during anesthesia and the possibility of increased venous admixture.
Influence of exercise hyperthermia on exercise breathing pattern
Authors: Martin B. J. , Morgan E. J. , Zwillich C. W. , Weil J. V.
Published: December 2017

Passive elevation of the body core temperature (Tc) induces rapid, shallow breathing in resting man. We wondered if exercise-induced Tc elevation would also lead to decreased tidal volume (VT) and increased breathing frequency (f) during exercise. To investigate this question, 10 subjects each performed 47 min of cycle ergometer exercise at 50--60% of the maximal aerobic capacity, with the work rate adjusted to maintain ventilation (VE) constant. This long ride raised mean Tc (rectal) 0.8 degrees C. Before and immediately after the long ride, ranges of VE and VT were obtained from short 6-min rides that progressed from unloaded pedaling to the anaerobic threshold. At the constant VE of the long ride, f rose and VT fell as Tc rose (P less than 0.05). The fall in VT was associated with a fall in inspiratory time (TI); drive (VT/TI) and timing (TI/Ttot)components of VE were unchanged. These effects were consistent over the entire range of VE obtained from the short 6-min rides. Passive heating in warm water to produce equal Tc elevation in the same subjects yielded similar exercise breathing-pattern changes. These findings suggest that increased Tc mediates the VT fall during prolonged exercise, possibly through stimulation of the central respiratory pacemaker.
Role of cerebellum on ventilatory change due to muscle-receptor stimulation in the dog
Authors: Panda A. , Senapati J. M. , Parida B. , Fahim M.
Published: December 2017

The role of the cerebellum in reflex increase of ventilation due to muscle-receptor stimulation was studied in dogs anesthetized with pentobarbital sodium. Stimulilike pressure application or stretch of gastrocnemius muscle produced increase in ventilation. Ablation or cooling of the anterior lobe of cerebellum significantly reduced this ventilatory response to application of the same degree of pressure or stretch of the gastrocnemius muscle. Ablation or cooling of the posterior lobe of the cerebellum did not have any effect on ventilation due to muscle-receptor stimulation. It was concluded that the anterior lobe of the cerebellum is in some way concerned with the ventilatory change produced by muscle-receptor activation.
Arterial-expired PCO2 differences in the dog during acute hypercapnia
Authors: Scheid P. , Meyer M. , Piiper J.
Published: December 2017

A recent report (J. Appl. Physiol. 38: 382-388, 1975) suggests that negative blood-gas CO2 partial pressure (PCO2) differences exist in the dog during hypercapnia, as mean expired PCO2 exceeded arterial PCO2 by more than 10 Torr when the CO2 fraction in inspired gas (FICO2) was 0.1. We have reinvestigated this problem in anesthetized dogs breathing spontaneously room air or hypercapnic mixtures (FICO2 = 0.05 or 0.10). During steady state, arterial blood samples were analyzed with electrodes, care being taken to keep the electrode temperature within +/- 0.2 degrees C at the actual aortic temperature of the animal. Respired gas was measured at the tracheostomy by a sensitive low-noise respiratory mass spectrometer. During room air breathing, the arterial-end-expired PCO2 difference, P(a-E')CO2, averaged +5 Torr and decreased to +0.9 Torr and to +0.1 Torr with FICO2 = 0.05 and 0.1, respectively. Hypoxia (FIO2 = 0.10) had no apparent effect on the P(a-E')CO2 difference. We ascribe the decrease in P(a-E')CO2 with hypercapnia to the diminishing effects of alveolar dead space, whereby end expired PCO2 approached arterial PCO2. We then conclude that in blood-gas equilibration lungs, PCO2 in end-capillary blood comes close to alveolar PCO2, and that the negative blood-gas PCO2 differences reported earlier are probably caused by deficiencies in the techniques used.
Postcapillary pH disequilibrium after gas exchange in isolated perfused liver
Authors: O'Brasky J. E. , Mauro T. , Crandall E. D.
Published: December 2017

pH equilibration after gas exchange in a systemic vascular bed was investigated using an isolated guinea pig liver preparation perfused with a blood-free Krebs-Ringer-bicarbonate solution. Effluent perfusate was withdrawn into a stopped-flow apparatus in which pH and temperature were continuously monitored. A decrease in pH of the perfusate after exit from the liver was observed. Addition of acetazolamide to inflowing perfusate had little effect on this fall in effluent fluid pH, while the addition of carbonic anhydrase completely abolished the decrease in pH. These results suggest that: 1) after the addition of metabolically produced CO2, the reaction CO2 leads to H2CO3 leads to H+ + HCO3- in the perfusate did not reach equilibrium during passage through the liver; 2) acetazolamide had little effect on the magnitude of the pH disequilibrium; and 3) carbonic anhydrase accelerated the reaction to equilibrium. We conclude that little or no catalysis of the conversion of perfusate CO2 to H2CO3 takes place within the hepatic circulation and that the presence of slow postcapillary blood pH changes in vivo may be dependent on the specific species and organ vascular bed from which the blood exited after participating in gas exchange.
Incorporating the gas analyzer response time in gas exchange computations
Authors: Mitchell R. R.
Published: December 2017

A simple method for including the gas analyzer response time in the breath-by-breath computation of gas exchange rates is described. The method uses a difference equation form of a model for the gas analyzer in the computation of oxygen uptake and carbon dioxide production and avoids a numerical differentiation required to correct the gas fraction wave forms. The effect of not accounting for analyzer response time is shown to be a 20% underestimation in gas exchange rate. The present method accurately measures gas exchange rate, is relatively insensitive to measurement errors in the analyzer time constant, and does not significantly increase the computation time.
Evaluation of a hot-wire respiratory flowmeter for clinical applicability
Authors: Yoshiya I. , Shimada Y. , Tanaka K.
Published: December 2017

A hot-wire flowmeter was evaluated for clinical applicability. 1) Calibration with a syringe could be done if emptying duration was 1-15 s. 2) Outputs linearly decreased with decreasing concentration of N2 in O2. Outputs with CO2 in O2 and N2O in O2 represented nonlinear convex relationships with varying concentrations of CO2 and N2O. Correction for each gas mixture to be measured is required. 3) Outputs linearly decreased with decreasing barometric pressure. 4) Stability assessed with a piston respirator was excellent (within +/- 2% of syringe volume) after 15 min warmup time. However, daily calibrations are recommended in clinical situations. 5) Nebulization, if not excessive, was acceptable if the expired gas was measured at the mouth. 6) Hot-wire burning, which occurred when it was partially in contact with materials whose specific heat differed with air, was successfully protected with a simple shutoff circuit. 7) The possibility of producing nitrogen oxides by the catalytic action of the platinum hot-wire was denied by colorimetric determination. Interchangeability and sterilizability of transducers and improved mechanical strength with platinum-rhodium alloy are also discussed.
Effect of Sindbis birus infection on survival of mice in the cold
Authors: Moore R. N. , Shackleford G. M. , Garry R. F. , Berry L. J.
Published: December 2017

Mice infected with 10(9) plaque-forming units (PFU) of Sindbis virus 9 h prior to exposure to cold (5 degrees C) died more rapidly after entering the new environment than saline-injected control mice. The early deaths occurred in animals singly housed without bedding and only when food was withheld. Because deaths could be prevented by providing the infected animals with food, it was concluded that metabolic alteractions resulting from the virus infection were responsible for the deaths. As evidence, corticosteroid-inducible hepatic enzymes did not respond to hydrocortisone administration in virus-infected mice housed at 5 degrees C. Phosphoenolpyruvate carboxykinase (PEPCK) (EC 4.1.1.32) was induced significantly in control mice held at 5 degrees C for 5 h, but failed to induce in infected mice in the cold. Tryptophan oxygenase (TO) (EC 1.13.11.11) activity was also induced in control mice at 5 degrees C, but was too low to be measured in livers of all infected mice including those exposed to cold. The conclusion that Sindbis virus-infected mice were unable to make the metabolic adjustments required for survival at 5 degrees C was further indicated by severe hypoglycemia and rapid drop in rectal temperature that occurred in infected mice after 5 h in the cold.
Reflex bronchoconstriction induced by capsaicin in the dog
Authors: Russell J. A. , Lai-Fook S. J.
Published: December 2017

To determine whether receptors stimulated by the injection of capsaicin into the pulmonary circulation cause reflex changes in airway size, six dogs were anesthetized with chloralose, paralyzed with succinylcholine, and mechanically ventilated (2 cm H2O PEEP). Intrapulmonary airways were outlined with tantalum dust, and diameters were determined by taking serial roentgenograms at end expiration. Capsaicin (20 micrograms/kg) injected into the right ventricle significantly decreased airway diameter (20%), heart rate, aortic pressure, and pulmonary artery pressure. In contrast, capsaicin injected into the left ventricle did not alter airway diameter or aortic pressure, although heart rate and pulmonary artery pressure decreased but to a lesser extent than after right ventricular injection. After vagotomy, capsaicin had no effect on airway diameter or heart rate but aortic pressure and pulmonary artery pressure increased slightly. Results suggest that pulmonary receptors sensitive to capsaicin and accessible via the pulmonary circulation produce reflex bronchoconstriction. One possible function of this vagal reflex is to assist fluid movement from microvasculature to peribronchial space by reducing peribronchial pressure.
Effect of training and heat acclimation on exercise responses of sedentary females
Authors: Fortney S. M. , Senay L. C.
Published: December 2017

In an attempt to explain why females experience greater strain than males during exercise in the heat, we studied the responses of nine females to moderate exercise (40% VO2 max) on a cycle ergometer in a cool (16--20 degrees C, 30% rh) and a hot (45 degrees C, 30% rh) environment. Venous blood was sampled during rest, at the 40th min of exercise, and 25 min after exercise. Test runs were then performed during a 4-wk training program (phase 2) and during heat acclimation (phase 3). Except for K+, changes in plasma constituents during exercise were not altered by training or acclimation. A greater mean decrease in plasma volume occurred during exercise in a hot (11.9%) than in a cool (3.9%) environment. Plasma osmolality and protein concentration increased due to the loss of plasma water. The most striking response to training was a significant expansion of resting plasma volume (9.7%) and total protein content (11.6%). During acclimation, sweat rates increased and mean skin temperatures significantly decreased. Hemodilution reported in heat-acclimated men was not seen. The factor primarily responsible for improved cardiovascular fitness in these women during acclimation may have been the maintenance of a larger central blood volume.
Ventilation in dogs on cardiopulmonary bypass with and without lungs
Authors: Vanderhoeft P. , de Francquen P. , Gelin M. , Van Stratum M. , Joris M. , Servais N. , Jank K. , Grevisse P. , Demeester M. , Smets P.
Published: December 2017

In 13 anesthetized or awake dogs, on cardiopulmonary bypass, we varied PaO2 and PaCO2 while continuously monitoring ventilatory responses and mechanics, to assess the dog's ability to maintain eupneic ventilation for any chemical drive. In a second group of 13 dogs on cardiopulmonary bypass we repeated the tests after removal of both lungs, to assess the importance of pulmonary feedback and mechanics. The VE/PO2 plot formed two hyperbolas, asymptotic to 39 Torr PO2 with lungs, and to 27 without; both intercepted zero ventilation near 200 Torr. Hyperoxic apnea occurred at, or below, PCO2 30 +/- 7 Torr under barbiturate and 20 +/- 4 Torr under morphine. Steady-state low PCO2 (10 Torr) turned off hypoxic drives as low as 20 Torr PO2. Empty-chest dogs had a low respiratory frequency (18 vs. 40), and near zero dynamic elastance; ventilatory work per minute and airway resistance were the same with and without lungs. Chest wall ventilatory responses are grossly independent of the presence of absence of lungs.
Reflex control of skin blood flow by skin temperature: role of core temperature
Authors: Johnson J. M. , Park M. K.
Published: December 2017

Two protocols were used to discover whether the reflex response in skin blood flow (SkBF) to rising skin temperature (Tsk) was dependent on the level of internal temperature. Part I. In five subjects, Tsk (controlled with water-perfused suits) was raised to 37 degrees C prior to, between 2 and 5 min, or between 10 and 17 min of exercise. The associated SkBF elevation per degree rise in Tsk averaged 0.20, 1.28, and 1.75 ml/100 ml . min, respectively. When Tsk was raised during the first 5 min of exercise, esophageal temperature (Tes) rose markedly (0.39 degrees C), but transiently fell if Tsk was raised after 10 min of exercise. Part II. In six subjects, different work loads were used to develop different levels of internal temperature. Tsk was elevated to 37 degrees C after 10--15 min at light (50--75 W) or moderate (100--150 W) work loads. At the heavier work load (and higher Tes), the rise in forearm SkBF per degree rise in Tsk averaged 2.33 +/- 0.38 (SE) times that observed at the light work load. These data strongly suggest that the reflex response of SkBF to rising Tsk is dependent on the level of internal temperature.
Maximal work capacity of women during acute hypoxia
Authors: Wagner J. A. , Miles D. S. , Horvath S. M. , Reyburn J. A.
Published: December 2017

Six healthy women (22--34 yr of age) performed maximal bicycle work in a hypobaric chamber at sea level and at simulated altitudes of 2,130 and 3,050 m (barometric pressures, 758, 586, and 523 Torr). Maximal oxygen uptake (VO2max) decreased 10 and 15% from sea-level values at 2,130 and 3,050 m, respectively. At these altitudes minute ventilation (VEBTPS) increased 17 and 22% respectively, a consequence of increased respiratory rate (fR). Respiratory exchange ratios increased 10 and 14%, and oxygen pulse decreased 9 and 12%, respectively, at 2,130 and 3,050 m. Maximal blood lactates, heart rates, cardiac outputs, and plasma volume shifts were unaffected by these altitudes. Although during maximal work the percentage increases in VEBTPS, fR, and R that resulted from altitude exposure were greater in women than those previously reported for men, the decrements in VO2max were comparable to those in men. The results show that relative to their performance at sea level, men and women have equal ability to perform maximal work at altitudes up to 3,050 m.
Estimating central and peripheral respiratory resistance: an alternative analysis
Authors: Slutsky A. S. , Drazen J. M.
Published: December 2017

Pimmel et al (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 45: 375--380, 1978) recently presented an analysis of the frequency dependence of respiratory resistance (Rrs) based on a simple electrical analog of the respiratory system that allows estimation of the central (Rc) and peripheral (Rp) components of Rrs. The method by which they determine these parameters from the experimental data is based on a number of unproven assumptions. Using the same electrical analog, we present an analysis that allows calculation of these parameters, as well as the corner frequency of the network (f1), without need for similar assumptions. Our technique is based on fitting the resistances (RTh) measured over a range of frequencies (f) to the exact solution of the network given by RTh = Rc + Rpf1(2)/f2 + f1(2)). Using the transformation X = 1/(f2 + f1(2), the equation becomes a linear relationship between RTh and X allowing the resistances to be determined by linear regression. Reanalysis of Pimmel et al.'s data demonstrated that the assumptions of a constant f1, and the equivalence of RTh at 0 Hz to RTh at 1 Hz in invalid under certain conditions. Thus, if one is to use the electrical analog to partition Rrs into its central and peripheral components, one should use the analytic approach suggested here that does not rely on these assumptions.
Effects of centrifugation stress on pituitary-gonadal function in male rats
Authors: Gray G. D. , Smith E. R. , Damassa D. A. , Davidson J. M.
Published: December 2017

The effects of centrifugation for various lengths of time were investigated on circulating levels of luteinizing hormone (LH) and testosterone in male rats. In a chronic 52-day experiment, centrifugation at 4.1 G significantly reduced LH and testosterone levels for the entire period. Centrifugation at 2.3 G had less effect inasmuch as LH levels were not significantly decreased and testosterone levels were significantly reduced only during the first few days of centrifugation. In more acute experiments, centrifugation at 4.1 G for 4 h resulted in reduced testosterone levels, whereas centrifugation for 15 min did not significantly alter the hormone levels. These results indicate that centrifugation can decrease circulating LH and testosterone levels if the gravitational force is of sufficient magnitude and is maintained for a period of hours. Chronic centrifugation may also inhibit the acute excitatory response of LH to handling and ether stress.
Catecholamine-fuel interrelationships during exercise in fasting men
Authors: Pequignot J. M. , Peyrin L. , Peres G.
Published: December 2017

Adrenergic response to exercise and the relationships between plasma catecholamines and blood energetic substrates were studied in sedentary men after 15 h of fasting. Subjects pedaled a bicycle ergometer until exhaustion at a work load approximating 80% maximal oxygen consumption. Working ability was diminished by the fast (P less than 0.025). Resting plasma norepinephrine level was increased by fasting. During exercise plasma epinephrine (E) and norepinephrine (NE) concentrations were more elevated in fasting subjects than in fed subjects. Plasma catecholamine (CA) levels in fasting men correlated with blood glucose, blood lactate, and plasma glycerol concentrations. There was no significative correlation between CA and plasma free fatty acid (FFA) levels. The increased adrenergic activity in fasting subjects correlated with reduced endurance time. This study emphasizes the role of CA release, probably combined with other hormonal factors, in the mobilization of energy substrates during submaximal exercise.
Airway transepithelial electric potential in vivo: species and regional differences
Authors: Boucher R. C. , Bromberg P. A. , Gatzy J. T.
Published: December 2017

A technique for measurement of transmural bioelectric potential difference (PD) in vivo was adapted for use in mammalian airways. PD was measured between a Ringer-perfused exploring bridge positioned on the airway furface and a reference Ringer-agar bridge in the subcutaneous space. The in vivo PD of canine trachea from 50 dogs was 30.8 +/- 9.5 (SD) mV, lumen negative, indistinguishable from the peak in vitro transmural PD of the excised canine trachea. Liquid junction potentials between bridge perfusate and tracheal liquid were negligible. The response pattern to drugs applied to the mucosal surface in vivo was similar to that observed in vitro. The PD in canine bronchi 3-6 cm distal to the carina were substantially lower. Tracheal PDs of rabbit (-23 mV), guinea pig (-8 mV), and rat (-14 mV) were higher than bronchial PDs of the same species. PD across airway epithelia can be accurately and reliably measured in vivo and the lower bronchial PD suggests regional differences in electrolyte transport and/or permeability.
Applied physiology for wheelchair design
Authors: Glaser R. M. , Sawka M. N. , Young R. E. , Suryaprasad A. G.
Published: December 2017

The purpose of this study was to evaluate potential wheelchair design changes that may reduce operational energy cost and cardiopulmonary responses. Design changes, which were simulated with a wheelchair ergometer, allowed two techniques of hand-rim propulsion: the usual synchronous application of force (sync), and an asynchronous technique where force was applied one hand at a time in a reciprocal fashion (async). Three hand-rim drive ratios were also simulated: low, normal, and high. Combinations of these force application-drive ratio simulations were evaluated at power output (PO) levels of 30 and 60 kpm.min-1. The async-high combination was found to elicit significantly lower (P less than 0.01) gross caloric output, pulmonary ventilation, and heart rate values, and provide the greatest advantage over conventional sync-normal operation at both PO levels. It appeared that async propulsion and high drive ratio resulted in less wasted movements. Although the async-high combination was superior under these test conditions, other combinations may be necessary to better match various locomotive tasks to individuals of different capabilities
Vital capacity, exercise performance, and blood gases at altitude as related to age
Authors: Dill D. B. , Hillyard S. D. , Miller J.
Published: December 2017

Vital capacity (VC) rarely may decrease 35-60% in healthy mountain climbers associated with high-altitude pulmonary edema (HAPE). In the age range 58-71 yr, five of six men during a week or more on White Mt. in 1962 had decreases in VC from 20 to 32% without frank symptoms of HAPE, Dill, one of the five, had decreases in VC again on White Mt. in 1977 and 1978. Yet none of 11 young climbers on White Mt. studied by Hultgren (personal communication) had a significant decrease in VC. Dill's arterial O2 saturation at age 87 at 485 Torr was about 79% in rest and 74% when VO2 was 0.74 ml/min.kg. His aerobic capacity at age 87 yr was 18 ml/min.kg at 695 Torr and 15 at 485 Torr.
Analysis of rebreathing measurements of pulmonary tissue volume in pulmonary edema
Authors: Friedman M. , Kaufman S. H. , Wilkins S. A.
Published: December 2017

A rebreathing method (usood volume (VTPC) was evaluated in 13 dogs. In seven, pulmonary edema was induced by oleic acid injection. Six dogs served as controls. Values of VTPC calculated by three algorithms were compared to postmortem lung water. The first algorithm uses the C18O intercept to determine time 0 and all data to construct the alveolar disappearance curves. The second uses the beginning of inspiration as time 0. The last uses data only during the last third of expiration. The best correlation (r = 0.90) between VTPC and total lung water was obtained utilizing the first algorithm. In the control animals, mean VTPC was 188 ml, and in the edema dogs was 278 ml. Mean VTPC for all dogs was 96 +/- 14% of total lung water using the first algorithm. Another algorithm (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 44: 782-795, 1978) was evaluated inthe edema dog group. This method gave values of VTPC 53% higher than those obtained by the first algorithm.
Exercise thermoregulation after 14 days of bed rest
Authors: Greenleaf J. E. , Reese R. D.
Published: December 2017

Rectal (Tre) and mean skin (Tsk) temperatures and sweating responses were measured during 70-min submaximal supine exercise (relative VO2 43-48%) in seven men (19-22 yr) during an ambulatory-control (AC) period and after three 2-wk bed-rest (BR) periods separated by 3-wk ambulatory recovery periods. During each of the three BR periods they performed isometric exercises (IME) or isotonic exercises (ITE) for 1 h/day or no prescribed exercise (NOE). Mean basal oral temperature decreased from 36.0 to 35.7 degrees C in the last 10 days of the control-recovery periods, but it varied between 35.7 and 35.9 degrees C during BR. In the exercise-temperature test the equilibrium level of Tre for the IME (37.92 degrees C) and NOE (37.75 degrees C) regimens were higher (P less than 0.05) than the AC level of 37.51 degrees C. Mean skin temperatures with the IME and ITE regimens increased by only 0.4 degrees C during exercise, and both equilibrium Tsk values, 31.98 degrees C and 31.87 degrees C, respectively, were lower (P less than 0.05) than the AC values of 32.71 degrees C. There were no significant differences between any of the sweat rates (range, 438-565 g/h) in the four experiments, but calculated skin heat conductances (Hsk) correlated +0.86 with equilibrium levels of Tsk. It was concluded that the excessive increase in Tre during submaximal exercise following BR deconditioning could be influenced by changes in Hsk, but inhibition of sweating may also be a factor.
Regional distribution of cerebral blood flow during exercise in dogs
Authors: Gross P. M. , Marcus M. L. , Heistad D. D.
Published: December 2017

This study was performed to determine whether exercise produces vasodilatation in regions of the brain that are associated with motor functions despite the associated vasoconstrictor effect of hypocapnia. Total and regional cerebral blood flow (CBF) were measured with microspheres in dogs during treadmill exercise of moderate intensity. Flow was also measured at rest after stimulation of ventilation with doxapram. During moderate exercise, total CBF was not changed significantly, but regional flow was increased in structures associated with motor-sensory control; blood flow to motor-sensory cortex, neocerebellar and paleocerebellar cortex, and spinal cord increased 30 +/- 7%, 39 +/- 8%, and 29 +/- 4%, respectively (P less than 0.05). After doxapram, which increased arterial blood pressure and decreased arterial PCO2 to levels similar to those during exercise, total CBF decreased and there was no redistribution of CBF. These results indicate that exercise in conscious dogs increases blood flow in regions of the brain associated with movement despite the associated vasoconstrictor stimulus of arterial hypocapnia. Thus, during exercise, local dilator influences that presumably result from increases in metabolism predominate over a potent constrictor stimulus in regulation of cerebral vascular resistance.
Maximal oxygen uptake during free, tethered, and flume swimming
Authors: Bonen A. , Wilson B. A. , Yarkony M. , Belcastro A. N.
Published: December 2017

The purpose of this study was 1) to compare the maximal oxygen uptake (VO2max) obtained in swimmers during tethered swimming, free swimming, and flume swimming, and 2) to determine whether an arm-ergometer test would provide comparable results. In the first experiments the VO2max for tethered swimming (2.67 +/- 0.26 l/min) and flume swimming (2.62 +/- 0.26 l/min) were not different (P greater than 0.05) and were highly correlated (r = 0.99). However, with arm ergometry a significantly lower VO2max (2.36 +/- 0.24 l/min) occurred from those found in the two swimming tests (P less than 0.05). Other experiments demonstrated that the tethered swimming VO2max (3.53 +/- 0.27 l/min) and the free swimming VO2max (3.55 +/- 0.28 l/min) also provide results that were similar (P greater than 0.05) and highly correlated with each other (r = 0.99). Differences between tethered and flume swimming, and tethered and free swimming were small, being 1.2 +/- 1.6% and 0.6 +/- 0.9%, respectively. Differences between tethered swimming and arm ergometry VO2max were large, 14.7 +/- 2.4%, despite the high correlation (r = 0.97) between these measurements. Predictions of a swimming VO2max from the arm-ergometer data yielded a considerable error (+/-7.1% and +/-7.4%). The present results indicate that flume swimming, free swimming, and tethered swimming yield essentially identical VO2max results.
Initial renal responses of nonhuman primate to immersion and intravascular volume expansion
Authors: Peterson T. V. , Gilmore J. P. , Zucker I. H.
Published: December 2017

Experiments were performed in anesthetized Macaca fascicularis monkeys to determine if the initial renal responses of these animals to head-out vertical water immersion and isoncotic, isotonic volume expansion are similar, especially with regard to the onset of any changes in solute or water excretion. Significant increases in urine flow, sodium excretion, and osmolar clearance occurred after 10 min of immersion but not until 30 min after volume expansion. Potassium excretion increased during immersion but decreased after volume expansion. Mean arterial blood pressure increased after 30 min of immersion but was unchanged after volume expansion. Indices of vascular filling, central venous pressure in the immersed animals and left ventricular end-diastolic pressure in the volume-expanded animals, increased immediately after the intervention. Effective renal plasma flow increased in both groups but glomerular filtration rate was not consistently elevated. These results suggest that, in the nonhuman primate, immersion and volume expansion exert their renal effects through different afferent and/or efferent mechanisms and should not be considered as similar volume stimuli.
Characteristics of sustained graded inspiratory inhibition by phasic lung volume changes
Authors: Baker J. P. , Remmers J. E.
Published: December 2017

The dynamic characteristics of graded reversible inspiratory inhibition by vagal feedback were investigated in pentobarbital-anesthetized paralyzed cats, ventilated with a servo respirator. The volume and time associated with various levels of graded inhibition were determined by using a series of constant-flow lung inflations. Protracted phrenic inhibition was produced by lung inflation, which was arrested when the phrenic discharge was partially inhibited. Thereafter, the volume was withdrawn along a trajectory that approximately paralleled the fall in inhibitory threshold. This volume-withdrawal trajectory would be expected to produce a sustained nearly constant level of inhibition based on the results determined from the constant-flow inflations. However, the observed inhibition exceeded that expected, increasing to a maximum and then decreasing to expected values over a period ranging from 1 to 2 s in most animals. This excess inhibition cannot be attributed to the known dynamic properties of pulmonary stretch receptors; their activity should be reduced, for any particular lung volume, during the volume withdrawal maneuver. These results suggest a central integrative processing of vagal afferent activity that causes inhibition to lag volume. This delay acts to promote inspiratory off-switching because it prevents the development of a protracted period of reversible inhibition.