bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of dry swallows and wet swallows of different volumes on esophageal peristalsis
Authors: Hollis J. B. , Castell D. O.
Published: December 2017

The effect of dry swallows and wet swallows of various volumes on esophageal function was studied in normal subjects. An intraesophageal transducer assembly was used to measure the dynamics of esophageal peristalsis. The strength of esophageal contraction (amplitude) following a 1-ml liquid bolus was similar to that following a dry swallow but was significantly less than that following a wet swallow of a larger volume. There was no difference in strength of esophageal squeeze following swallows ranging from 2 to 20 ml. In addition, a wet swallow was associated with slower wave speed, greater duration of the contraction wave, and later time of appearance of the peristaltic wave in the distal esophagus than a dry swallow. Futhermore, the incidence of peristalsis was greater with a wet swallow than a dry swallow. The results of our studies indicate that although the act of swallowing alone in man initiates peristalsis, afferent information contributes to the regulation of primary peristalsis.
Effect of resistive loading on ventilatory response to hypoxia
Authors: Rebuck A. S. , Juniper E. F.
Published: December 2017

Ventilatory responses to hypoxia, with and without an inspiratory resistive load, were measured in eight normal subjects, using a rebreathing technique. During the studies, the end-tidal P-CO2 was kept constant at mixed venous level (Pv-CO2) by drawing expired gas through a variable CO2-absorbing bypass. The initial bag O2 concentration was 24% and rebreathing was continued until the O2 concentration in the bag fell to 6% or the subject's arterial oxygen saturation (Sa-O2), monitored continuously by ear oximetry, fell to 70%. Studies with and without the load were performed in a formally randomized order for each subject. Linear regressions for rise in ventilation against fall in Sa-O2 were calculated. The range of unloaded responses was 0.78–3.59 1/min per 1% fall in Sa-O2 and loaded responses 0.37–1.68 1/min per 1% fall in Sa-O2. In each subject, the slope of the response curve during loading fell by an almost constant fraction of the unloaded response, such that the ratio of loaded to unloaded slope in all subjects ranged from 0.41 to 0.48. However, the extrapolated intercept of the response curve on the Sa-O2 axis did not alter significantly indicating that the P-CO2 did not alter between experiments. These results suggest that the change in ventilatory response to hypoxia during inspiratory resistive loading is related to the mechanical load applied, with the loaded slope being directly proportional to the unloaded one.
Human air space shapes, sizes, areas, and volumes
Authors: Hansen J. E. , Ampaya E. P.
Published: December 2017

The geometry of an enlarged reconstructed human acinus (i.e., a terminal bronchiole and distal airways and air spaces) was studied. Alveoli were categorized in six shapes: three-fourths of a spheroid, a slightly truncated cone, one-fourth of a spheroid, a cylindroid with a hemispherical bottom, a shallow cylindroid with a flat bottom, and a truncated deep ellipsoid. Sacs were usually either hemispheroids or shallow truncated cones. Ducts of eight generations were spheroid and gradually decreased in diameter (D) and length (L) as the generation number (z) increased. Considering the terminal bronchiole as the 15th generation and using Weibel's data for the first 10 generations, the dimensions, in mm, for z of 1–10 and 10–26 were reasonably described by D-z = 12e-(0.27–0.005z)z and L-z = 25e-0.187z. The predicted volume of the acinus at three-fourths total lung volume was 182.8 mm3, a volume equivalent to that of a sphere 7.04 mm in diameter. The reconstruction demonstrated a great increase in respiratory bronchiolar and ductal cross-sectional area and alveolar surface area, considerably more rapid than predicted by Weibel's model A.
Oxygen uptake/heart rate relationship in leg and arm exercise, sitting and standing
Authors: Vokac Z. , Bell H. , Bautz-Holter E. , Rodahl K.
Published: December 2017

The effect of leg exercise and of arm exercise in sitting and standing body positions on energy output and on some cardiorespiratory parameters was studied in seven male subjects. Oxygen uptake (VO2), heart rate (fH), pulmonary ventilation (VE) and respiratory frequency were measured at rest, in the 7–8th min of submaximal work (300, 600, 900 kpm/min), and at maximal effort. Significantly higher Vo2, fH, and VE in arm cranking than in cycling were found at submaximal work loads above 300 kpm/min. Though the maximal work load in arm exercise was 50–60% of that in cycling, Vo2 in arm work was at maximal effort only 22% lower than in leg exercise while the difference in fH was insignificant. No differences were found in arm work between the results obtained at any work level in sitting and standing body positions. The only postural difference in arm work was a 13% higher work load achieved at maximal effort when standing than when sitting. Differences in fH between arm and leg exercise were much smaller for the same Vo2 than for the same work load and were time dependent. While fH quickly leveled off in leg exercise, fH in arm cranking rose steadily during the first 6 min of work which created the fH differences observed in the 7–8 min of submaximal arm arm and leg exercise. At submaximal work levels a tendency to synchronize the respiratory frequency with the frequency of the rotatory movements was more apparent in arm cranking than in cycling.
Skinfolds and resting heat loss in cold air and water: temperature equivalence
Authors: Smith R. M. , Hanna J. M.
Published: December 2017

Fourteen male subjects with unweighted mean skinfolds (MSF) of 10.23 mm underwent several 3-h exposures to cold water and air of similar velocities in order to compare by indirect calorimetry the rate of heat loss in water and air. Measurements of heat loss (excluding the head) at each air temperature (Ta = 25, 20, 10 degrees C) and water temperature (Tw = 29–33 degrees C) were used in a linear approximation of overall heat transfer from body core (Tre) to air or water. We found the lower critical air and water temperatures to fall as a negative linear function of MSF. The slope of these lines was not significantly different in air and water with a mean of minus 0.237 degrees C/mm MSF. Overall heat conductance was 3.34 times greater in water. However, this value was not fixed but varied as an inverse curvilinear function of MSF. Thus, equivalent water-air temperatures also varied as a function of MSF. Between limits of 100–250% of resting heat loss the followingrelationships between MSF and equivalent water-air temperatures were found (see article).
Sleep patterns afted graded exercise
Authors: Shapiro C. M. , Griesel R. D. , Bartel P. R. , Jooste P. L.
Published: December 2017

The effects of six graded and measured exercise activities on sleep patterns were investigated in two healthy young men. Electrophysiological recording were made continuously throughout the night to distinguish sleep states. This experiment was designed to test the hypothesis of a relation between physical activity and slow-wave sleep (SWS: stages 3 and 4 of non-REM sleep). A progressive increase in SWS over the whole-night sleep record was found with progressively increasing physical fatigue. A fall in rapid-eye-movement (REM) sleep and at higher exercise levels, of stage 2 sleep, was found. The results support the hypothesis that SWS is involved in the recovery process from fatigue.
Effect of gas density on dynamic pulmonary compliance
Authors: Forkert L. , Wood L. D. , Cherniack R. M.
Published: December 2017

We measured dynamic pulmonary compliance (Cdyn( in nine asymptomatic young men breathing gases of different density. When corrected for gas inertia, Cdyn was significantly lower during dense gas breathing (sulfur hexafluoride) than during air breathing. At higher breathing frequencies (60–90 breaths/min), Cdyn was greater on helium than on air. Static compliance was not different while breathing the three gas mixtures. These results may be explained by a density dependence of airways resistance in parallel lung units which contribute to frequency dependence of dynamic compliance. We conclude that most frequency-dependent behavior occurs among intraregional lung units subtended from airways between segmental bronchi and peripheral airways.
Pulmonary response to antigen infusion in the sensitized guinea pig: modification by atropine
Authors: Drazen J. M. , Austen K. F.
Published: December 2017

Alterations in pulmonary conductance, dynamic compliance, respiratory frequency, minute volume, mean arterial pressure, pulse rate, relaxation volume-to-dry weight ratio, and wet-to-dry weight ratio resulting from antigen infusion in sensitized guinea pigs was examined with and without atropine treatment. In untreated animals 3 min after antigen infusion there were significant decreases in dynamic compliance and pulmonary conductance with an increase in relaxation volume-to-dry weight ratio while other parameters were not altered. In atropine-treated animals antigen infusion resulted in a decreased dynamic compliance and an increased relaxation volume-to-dry weight ratio but no significant change in pulmonary conductance. This suggests that the alterations in large and central airway tone resulting from antigen infusion are mediated predominantly by secondary cholinergic mechanisms while peripheral airway effects are mainly noncholinergic.
Metabolic and cardiovascular adjustment to work in air and water at 18, 25, and 33 degrees C
Authors: McArdle W. D. , Magel J. R. , Lesmes G. R. , Pechar G. S.
Published: December 2017

By use of successive increments of discontinuous work with an arm-leg cycle ergometer the VO2, Q, SV, and HR were studied in six male subjects at rest and during exercise in air and in water at 18, 25, and 33 degrees C. The Q values obtained by CO2 rebreathing were reproducible. VO2 was linearly related to work with the plots for air and 33 degrees C water being similar. However, during work in 25 and 18 degrees C water, the VO2 averaged 9.0% (150 ml) and 25.3% (400 ml) higher, respectively, than values observed in 33 degrees C water, with the largest differences observed in leaner subjects. The plot of HR-VO2 was linear and almost identical during work in air and 33 degrees C water, but shifted significantly to the right in cooler water. VO2 averaged 250–700 ml higher in cold water compared to air and 33 degrees C water at a given mean heart rate. The Q vs. VO2 line was similar during work in air and in water with no effect of water or temperature. At similar levels of VO2, SV was significantly larger (P less than 0.05) in 25 and 18 degrees C water than in air or 33 degrees C water. Consequently, the reduction in heart rate during work in cold water was entirely compensated for by a proportionate increase in the SV of the heart. Q was therefore maintained at similar levels of energy expenditure in air and in 18, 25, and 30 degrees C water.
Collection of normal canine tracheobronchial secretions
Authors: Adams G. K. , Aharonson E. F. , Reasor M. J. , Proctor D. F.
Published: December 2017

A technique is described for the collection of tracheobronchial secretions from the upper trachea of anesthetized dogs. The method is simple, relatively quantitative, and provides secretory material in quantity suitable for biochemical or rheological studies. In 42 experiments comprising 184 individual samples we have found the collection rate of tracheobronchial secretions to be 1.0 ± 0.1 mg/min per kg (mean ± SEM).

airway mucus; trachea; anesthetized dogs

Submitted on June 11, 1975
Single-breath oxygen tests for individual lungs in awake man
Authors: Frazier A. R. , Rehder K. , Sessler A. D. , Rodarte J. R. , Hyatt R. E.
Published: December 2017

Single-breath oxygen (SBO2) tests for individual lungs were performed in five healthy awake volunteers. In the supine position, all subjects consistently showed a closing volume (CV) for both lungs. In the lateral position, CV was demonstrated in all analyzable SBO2 tests for the dependent and in 20 of 28 for the nondependent lung. CV consistently occurred in the dependent before it occurred in the nondependent lung (asynchronous onset of CV). After CV had been reached in the nondependent lung, a mean of 77 ml of gas was still expired from the dependent lung. No changes in CV for individual lungs were demonstrated with changes in body position. Expiratory flow limitation consistently occurred first in the dependent lung (asynchronous onset of flow limitation). In the lateral position, at high lung volumes, the dependent lung achieved higher flow rates; later in expiration, the nondependent lung contributed progressively more gas to the total expirate (asynchronous emptying). In general, our findings are consistent with both the “asynchronous flow limitation” and the “airway closure” interpretations of CV. However, some of the results are not consistent with either theory.
Effect of hypoxia on the pressure developed by inspiratory muscles during airway occlusion
Authors: Kelsen S. G. , Altose M. D. , Stanley N. N. , Levinson R. S. , Cherniack N. S. , Fishman A. P.
Published: December 2017

The effect of progressive isocapnic hypoxia on the pressure generated by the inspiratory muscle during airway occlusion was studied in 10 awake subjects during normal and obstructed breathing. Isocapnic hypoxia was produced by rebreathing a gas mixture of 6% CO2 in air while the expired gas was passed through a CO2 scrubber so as to maintain PACO2 constant (42.6 mmHg +/- 2.2 SE). Occlusion of the airway was performed randomly for a single breath at FRC. In all 10 subjects maximal pressure (Ppeak) and the pressures measured 100, 200, 300, and 400 ms after the onset of inspiration increased during hypoxia. Furthermore, good correlation was noted between the occlusion pressure response to hypoxia (delta P/DELTA[1/PO2-32]) and simultaneous changes in ventilatory response to hypoxia (delta VI/DELTA[1/PO2-32]). The occlusion pressure response to hypoxia therefore seems to be a reliable measure of respiratory center output. When rebreathing was repeated during inspiratory resistive loading, the occlusion pressure at any given PO2 and delta P/DELTA(1PO2-32) measured in the first 400 ms of inspiration increased in 9 of 10 subjects. Since PACO2 and PAO2 during both control and loaded experiments were the same, the increase in occlusion pressure in the presence of flow-resistive loading appeared to represent a neurally mediated increase in inspiratory motoneuron activity.
Physiological responses of men working in 25.5 degrees C water, breathing air or helium tri-mix
Authors: Hoar P. F. , Raymond L. W. , Langworthy H. C. , Johnsonbaugh R. E. , Sode J.
Published: December 2017

Fourteen scuba divers in swim trunks did ergometer work while breathing air at 3 m in 25.5 degrees C water. They were stressed by work and cold. Exercise produced increases in heart rate, minute ventilation (VE), oxygen consumption (VO2), and catecholamine excretion. Cold lowered rectal temperature (Tre) despite exercise, and contributed to the increase in VO2 and catecholamine excretion. Immersion, cutaneous vasoconstriction, work, and scuba breathing contributed to a brisk diuresis, probably by centralizing blood volume and thus stimulating central vascular volume receptors. Similar exercise in 25.5 degrees C water, breathing helium tri-mix (gas density less than air), produced higher VE but lower VO2 when compared to air breathing. Tri-mix scuba breathing resulted in a smaller diuresis, perhaps because its lower density leads to lesser atrial distension during work. The fall in Tre during work in 25.5 degrees C water was identical whether air or helium tri-mix was respired, since helium does not accentuate respiratory convective heat transfer.
An experimental model for the study of exercise-induced skeletal muscle hypertrophy
Authors: Gonyea W. J. , Ericson G. C.
Published: December 2017

A procedure for training laboratory cats to perform weight-lifting exercise has been developed. This program consists of operantly conditioning adult cats to move a bar a specific distance with their right forelimb to receive a food reward. Weights attached to the bar via a pully are lifted as the bar is moved. The cat is then exercised at the same load for 5 days before the weight is increased. A linear potentiometer, attached to the hinged bar, produces an analog voltage proportional to the bar movement. This voltage is then monitored by a general purpose computer using a real-time behavioral program. In this way, the numbber of times the cat moves the bar, the time required to move the bar, and the time between bar movements are all recorded. The total physical work accomplished and the average power expended by the cat during the weight-lifting exercise regimen can then be calculated. This procedure has the advantage of inducing significant gross muscle hypertrophy (from 7 to 34%) and muscle fiber hypertrophy in one limb, while the muscles of the opposite limb can be utilized for comparative studies. The striking morphological and histochemical transformations that occur during physiological hypertrophy are now available for experimental investigation using this model.
Threshold temperatures for shivering in acute and chronic hypercapnia
Authors: Schaefer K. E. , Wunnenberg W.
Published: December 2017

Threshold temperatures for shivering in acute and chronic hypercapnia were determined in guinea pigs by measuring the time course of cervical cord temperature, skin temperature, oxygen consumption (Vo2), and electrical muscle activity during cold exposure (15 degrees C). Prior to acute exposure to CO2, the shivering threshold was determined in each animal during controlconditions breathing air. With increasing CO2 concentrations (5,7.5, and 15% CO2) the shivering thresholds fell to lower temperatures, decreasing by approximately 40 degrees C at 15% CO2. The shift of the shivering threshold to lower values found during acute exposure to 15% CO2 was reversed after chronic exposure to 15% CO2 for 3 days, which marks the time of metabolic adaptation to CO2.
Papain inhibition by serum
Authors: Fisher M. J. , Jay R. E. , Haugh L. D. , Sander E. G.
Published: December 2017

Sera from seven animal species (rat, cow, cat, dog, human, rabbit, and hamster) were tested and found to inhibit the papain-catalyzed hydrolysis of alpha-N-benzoyl-L-arginine-p-nitroaniline-HCl (L-BAPA). The relative concentration of inhibitor in each serum sample was expressed in terms of its papain inhibitory capacity (PIC) defined as the number of units of papain inhibited per ml of serum. Rat serum contained the highest concentration of inhibitor while hamster serum contained the lowest concentration. The inhibitor appears to be competitive with respect to L-BAPA and is heat labile and nondialyzable. Antipapain activity can be separated from antitrypsin activity by (NH4)2SO4 fractionation.
Adaptation of anesthetized men to breathing through an inspiratory resistor
Authors: Whitelaw W. A. , Derenne J. P. , Couture J. , Milic-Emili J.
Published: December 2017

Normal men anesthetized with methoxyflurane rebreathed carbon dioxide under two conditions. In one case they breathed most of the time through a low-resistance circuit and an inspiratory resistor of 40.4 cmH2O/1-s-1 was applied at intervals. In another case they breathed most of the time through the resistor and were allowed occasional free breaths. There were no differences between the two types of runs in tidal volume, respiratory frequency, duration of inspiration of loaded or unloaded breaths, or in amplitude or shape of occlusion pressure waves. It is concluded that the reaction of conscious men to an inspiratory resistive load, consisting of a compensatory augmentation of neural drive to respiratory muscles that does not depend on a chemical stimulus, is absent in anesthetized men.
Plasma angiotensin II levels in hypoxic and hypovolemic stress in unanesthetized rabbits
Authors: Zakheim R. M. , Molteni A. , Mattioli L. , Park M.
Published: December 2017

Plasma levels of angiotensin II were determined by radioimmunoassay in unanesthetized white rabbits exposed to acute hypoxia (FIO2 10% for 10 min),chronic hypoxia (0.5 atm up to 16 days), or hypovolemic stress (bleeding 20ml/kg). Angiotensin II levels significantly decreased after 10 min of acutehypoxia in normal rabbits and significantly increased when the same procedure was applied to animals previously exposed to hypoxia by 6–8 days of permanence in the hypobaric chamber or sodium deprivation. Chronic hypoxia resulted in a temporary increase of angiotensin II already evident on the 3rd day, but maximal at the 9th day with return to normal values within 16 days.Hypovolemic stress resulted in the expected rise of angiotensin II levels 10 min postbleeding both in normal and acclimatized rabbits. The responseof the renin-angiotensin-aldosterone system to hypoxic and hypovolemic stress is different. The direction and magnitude of the response to hypoxia depends on the underlying state of activation of the system and the cardiovascular condition of the animal at the time of hypoxic stress.
Relationship between viscoelastic properties of the rectum and anal pressure in man
Authors: Arhan P. , Faverdin C. , Persoz B. , Devroede G. , Dubois F. , Dornic C. , Pellerin D.
Published: December 2017

Viscoelastic properties of the rectal wall and anal sphincter pressure were studied simultaneously in 25 normal children. During rectal distension for 60 s, with varying volumes of air, the rectal pressure varied as the sum of two exponential functions of the time plus an asymptotic constant. A rectoanal inhibitory reflex was elicited during these distensions. The exponential decrease of the rectal pressure corresponded exactly to the return of the upper anal canal pressure to the resting value in some subjects. In others, the upper anal canal remained relaxed as long as the rectal ampulla was distended, except with smaller volumes. The results obtained may be explained by an analogical rheological linear model.
Curve-fitting analysis of pressure-volume characteristics of the lungs
Authors: Pengelly L. D.
Published: December 2017

The pressure-volume relationship of the mammalian lung is markedly curvilinear and in the normal lung, can be shown to fit an exponential function of the form V = V0(1 - K 0e-K1P) in the range of lung volume from FRC to TLC. A method is presented, using a programmable calculator, of determining the parameters V0, K0, and K1, and of deriving related constants of greater physiological significance. Values calculated from pressure-volume curves of 20 normal human subjects are listed, together with coefficients of determination, to demonstrate the adequacy of fit of the method. Half-inflation pressure (h- ln 2/K1), ranged from 2.65 to 9.21 and coefficients of determination (r2) ranged from 0.851 to 0.9998.
Relative contributions of hypocarbia and hyperpnea as mechanisms in postexercise asthma
Authors: McFadden E. R. , Stearns D. R. , Ingram R. H. , Leith D. E.
Published: December 2017

The purpose of this investigation was to assess the relative contributions of hyperpnea and hypocapnia in the induction of postexercise asthma. To achieve these ends, eight young asthmatics were exercised on a treadmill while minute ventilations (VE) and end-tidal CO2 (PET CO2) tensions were continuously recorded. The subjects were then restudied using a partial rebreathing technique that allowed separation of minute and alveolar ventilations so that independent evaluations could be made of the relative effects of bulk airflow on pulmonary mechanics as well as a systematic study of hypocapnia in a dose-response fashion. Sustained hyperpnea with VEidentical to those recorded during exercise was totally without effect when the mean PET CO2 was isocapnic or lowered to approximately 30 Torr. Reduction in PETCO2 to 21.3 +/-0.9 Torr brought about significant changes in mechanics, but in every variable measured, exercise produced the greatest alterations and did so at PETCO2 values that had no effect when studied in a controlled fashion. Consequently, neither high VE per se, nor hypocapnia can be considered as the mechanisms underlying exercise induced asthma.
Reflex control of expiratory airflow and duration
Authors: Remmers J. E. , Bartlett D.
Published: December 2017

Unanesthetized, unrestrained cats were studied repeatedly after placement of a permanent tracheostomy, catheters for respiratory pressure measurements, and respiratory muscle EMG electrodes. The tracheostomy was opened or closed by a remote mechanism. Opening the tracheostomy reduced tracheal pressure to zero and diverted flow from the upper airway; closing the tracheostomy reestablished the normal pathway for airflow. Opening the tracheostomy during expiration evoked reflex responses in the diaphragm, in the laryngeal abductor and in abdominal expiratory muscles. These were sustained compensatory (“tracking”) responses which, in each case, acted to offset loss of expiratory braking by the upper airway. Occlusion of the tracheostomy during expiration produced the opposite responses. Responses to tracheostomy opening usually overcompensated for the loss of upper airway resistance, suggesting that extrathoracic tracheal receptors may participate in tracking. Changes in the expiratory time course of lung volume were accompanied by changes in the duration of expiration. These “triggering” responses were shown to operate independently of the tracking responses though both were eliminated by vagotomy.
Hemodynamic response to graded exercise after chronic beta-adrenergic blockade
Authors: Reybrouck T. , Amery A. , Billiet L.
Published: December 2017

The effect of sustained beta-adrenergic blockade (BB) on the hemodynamic response to graded exercise has been studied in 31 patients with high blood pressure. Hemodynamic investigations were conducted during a control period and were repeated after 1 mo of BB. Similar readjustments were observed at rest and during submaximal and maximal exercise. No significant change occurred in maximal physical working capacity during beta blockade. This resulted from hemodynamic readjustments. Maximal exercise heart rate was reduced by 34%, and this was compensated for by a 31% enhancement in stroke index. Consequently cardiac index decreased by only 14%. In the Fick equation the decrease in cardiac index was further compensated by an increase of the total arteriovenous O2 difference of 8%, thereby maintaining O2 delivery to the tissues. At maximal exercise mean brachial artery pressure dropped 14.5%, while mean pulmonary artery pressure increased by 20%. It is concluded that the compensatory action of the stroke volume, resulting from the interaction of an increased preload and a decreased impedance, played a major role in the hemodynamic readjustments following chronic BB to maintain maximal working capacity.
Mechanism of change in pulmonary shunt flow with hemorrhage
Authors: Colley P. S. , Cheney F. W. , Butler J.
Published: December 2017

In the presence of regional atelectasis, hemorrhage increases the pulmonary shunt fraction (Qs/Qt). We wanted to determine if the increase in Qs/Qt occurs due to inhibition of hypoxic vasoconstriction or due to hydrostatic effects associated with a collapsed lung and decrease in cardiac output. We compared the effects of hemorrhage on flow to a hypoxic lung (Qh) produced in two ways in anesthetized dogs. In six dogs atelectasis of one lung was produced by bronchial occlusion and in a second group of six dogs one lung was ventilated with 100% nitrogen. The other lung in each group was ventilated with 100% nitrogen. The other lung in each group was ventilated with 100% O2. Hemorrhage (20 ml/kg) had no effect on Qh/Qt in dogs with a nitrogen-ventilated lung suggesting that hemorrhage did not inhibit hypoxic vasoconstriction. In contrast, hemorrhage caused a marked increase in Qh/Qt in dogs with a collapsed lung because the flow to the inflated ventilated lung fell, while flow to the collapsed lung did not change. The increase in Qs/Qt in the dogs with atelectasis can be explained solely on the basis of mechanical effects produced by the differences in lung heights and alveolar pressures between ventilated and atelectatic lung.
Effects of intravenous histamine on pulmonary mechanics in nonasthmatic and asthmatic subjects
Authors: Brown R. , Ingram R. H. , Wellman J. J. , McFadden E. R.
Published: December 2017

Histamine is thought to be one of the primary mediators of the airways response in allergic asthma. We have studied in detail in nonasthmatic and asthmatic volunteers the effects of its intravenous infusion on pulmonary mechanics. The doses used were similar in both groups and limited by vascular rather than pulmonary effects. Measurements were made of lung resistance, the subdivisions of lung volume, maximal flow, density dependence, lung elastic recoil and dynamic compliance. The only mean group changes were a decrease in dynamic compliance and increase in frequency dependence of compliance in the nonasthmatics. Although in nonasthmatic individuals, statistically significant changes occasionally occurred in some parameters, the response was variable on repeated studies and sufficiently small to be of questionable physiological significance. Some of the asthmatics developed larger changes, but these only occurred in those individuals whose preinfusion pulmonary function was abnormal. Our results suggest the possibility that altered prechallenge pulmonary function rather than an unusual sensitivity to histamine may determine the greater responses observed in asthmatics.
Fluid shifts during thermal stress with and without fluid replacement
Authors: Myhre L. G. , Robinson S.
Published: December 2017

Six unacclimatized men rested for 4 h in a hot, dry environment (Ta 50 degrees C, Tw 26 degrees C; wind speed 0.5 m/s) without fluid replacement (DH). Another group of six men were exposed to the same thermal stress, replacing evaporative fluid loss with warm 0.1% NaCl solution (FRP). Total grams of circulating hemoglobin, determined by CO immediately prior to and again during the last minutes of heat exposure, increased an insignificant 1.6 and 1.3% during DH and FRP, respectively. With DH, body weight loss of 2.6% was accompanied by a 7.8% reduction in calculated plasma volume (PV). Even when body weight was maintained (FRP), PV decreased 2.9% during the heat exposure. Total circulating serum protein did not change as a result of the heat stress with either DH or FRP. In a test-retest series of experiments on four men, DH was not detrimental to sweat rate which averaged 251 g/m2-h compared with 239 g/m2-h with FRP. It was concluded that hemodilution is not a general response to acute heat exposure, and the disproportionately large reduction in PV during thermal dehydration was confirmed.
Ventilatory and gas exchange dynamics in response to sinusoidal work
Authors: Casaburi R. , Whipp B. J. , Wasserman K. , Beaver W. L. , Koyal S. N.
Published: December 2017

The dynamic relationships between ventilation and gas exchange variables during exercise were determined utilizing frequency analysis techniques. Five subjects exercised on a cycle ergometer for 30 min at work rates which fluctuated sinusoidally between 25 W and 80% of the anaerobic threshold at sinusoidal periods of 0.7, 1,2,4,6, and 10 min. VE, VCO2, VO2, and HR were computed and displayed breath-by-breath. From these and steady-state response data, digital computer routines extracted amplitude and phase relations between each variable and the perturbing work load. These response characteristics were well described by first-order linear dynamics with time constants for VE, VCO2, VO2, and HR averaging 1.4, 1.2, 0.8, and 0.8 min, respectively. The time constants of VE and VCO2 were strongly correlated among subjects (r = 0.97). Further, there was no evidence that neural afferents from the exercising limbs induced fast components in the ventilatory response to these forcings. These results are consistent with the hypothesis that exercise hyperpnea is linked to metabolism via carbon dioxide production.
Effect of functional overload on enzyme levels in different types of skeletal muscle
Authors: Baldwin K. M. , Cheadle W. G. , Martinez O. M. , Cooke D. A.
Published: December 2017

The effects of bilateral functional overload on enzyme changes in fast-twitch plantaris muscles were studied on different groups of rats: 1) normal-control; 2) normal-exercise; 3) overload-control; and 4) overload-exercise. Overload was accomplished by surgical elimination of synergists. Exercising groups walked up a 65% grade, 3 m/min, 2 h/day. Peak muscle enlargement of the overload groups was reached after 5 wk. Citrate synthase, phosphofructokinase, and myofibril ATPase activities were consistantly depressed by approximately 30%, 40%, and 18%, respectively, in overload as compared to normal groups. Daily exercise prevented the decrease in only citrate synthase activity. Unilateral overload of medial gastrocnemius muscle indicated that both fast-twitch oxidative-glycogenolytic and fast-twitch glycogenolytic fiber types undergo enzyme changes in response to the functional stress. However, changes in the former were in closer agreement with the net changes seen in the plantaris than the latter. Soleus muscle responded to overload primarily with marked reductions in respiratory capacity. These findings suggest that certain enzyme systems are altered with functional overload in different fiber types. However, the alterations in certain enzyme systems may, in part, be independent of the process of hypertrophy.
Can alveolar pCO2 exceed pulmonary end-capillary CO2? No
Authors: Forster R. E.
Published: December 2017

The exchanges and chemical reactions of CO2 within the blood are not complete during its transit time through the alveolar capillaries, so that theoretically alveolar PCO2 cannot exactly equal end-capillary blood PCO2. However, as a practical matter, the technical errors in determining alveolar and peripheral arterial PCO2 are so large in comparison with the difference between pulmonary arterial PCO2 and pulmonary venous PCO2, owing to the large effective solubility of CO2 in blood, that for this reason alone any difference between alveolar and end-capillary PCO2 can be neglected. The hypothetical mechanism that was originally proposed by Gurtner, Song, and Farhi for the production of an alveolar PCO2 greater than end-capillary PCO2 during rebreathing and depends on the existence of a radial gradient of H+ X HCO3- in the capillary blood near the wall appears unlikely because a) it would require a significant separation of charged ions over a large proportion of the capillary length and for a large proportion of the blood transit time and b) it would require a large radial gradient of PCO2 within the blood which on thermodynamic grounds would in turn require an unreasonable amount of energy to maintain.
Carotid and aortic chemoreceptor function in the rat
Authors: Sapru H. N. , Krieger A. J.
Published: December 2017

Carotid and aortic chemoreceptor function was studied in normal Wistar rats. Sodium cyanide, lobeline HCl, and doxapram HCl in the doses of 2–400 mug/kg injected into the external carotid artery stimulated respiration significantly. Injections of the drugs into the ascending aorta produced less effects which were abolished after section of the carotid sinus nerves. The drugs produced a significant increase in the carotid sinus nerve activity but failed to do so in the aortic depressor or recurrent laryngeal nerves. These results indicate that the carotid chemoreceptor function in Wistar rats in normal while functional aortic chemoreceptors are absent in them.
Mechanisms responsible for decreased glomerular filtration in hibernation and hypothermia
Authors: Tempel G. E. , Musacchia X. J. , Jones S. B.
Published: December 2017

Mechanisms underlying the elimination or marked depression of renal function in hibernation and hypothermia were investigated through measurements of blood pressure, heart rate, red blood cell and plasma volumes, and relative distribution of cardiac output. Hamsters (Mesocricetus auratus) were made hypothermic (rectal temperature (Tre), 7 degrees C) by exposure to helox and cold, or permitted to hibernate with several weeks of cold exposure (Ta approximately 5 degrees C). Mean arterial pressure, 120 Torr in normothermic control animals, demonstrated a 55% and 60% decrease during hibernation and hypothermia, respectively. As the animals rewarmed from hypothermia or aroused from hibernation, blood pressure increased rapidly at 8–12 degrees C, more gradually at 12–17 degrees C, and plateaued thereafter. Blood pressure rapidly returned to near control levels whereas heart rate remained at less than one-half control value at the highest temperature examined. Red blood cell volume, 26.2 +/- 0.6 ml/kg body wt in the control animals appeared unaffected by hypothermia. Plasma volume, by contrast, decreased from control values of 33.0 +/- 0.8 to 21.3 +/- 0.6 ml/kg body wt in hypothermia, a decrease of approximately 35%. Distribution of cardiac output to various organs in hibernation and hypothermia followed a similar pattern. Relative flow to the heart, lung, diaphragm, and brown fat increased while the fraction distributed to the visceral organs appeared to decrease. The normothermic control kidney received approximately 16% of the cardiac output while the hibernating and hypothermic kidneys received approximately 10% and 6%, respectively. The data are discussed in terms of the determinants of glomarular filtration rate and explain, in part, the elimination or marked reduction in renal function observed in depressed metabolic states.
Airway responses to inhaled histamine in asymptomatic smokers and nonsmokers
Authors: Brown N. E. , McFadden E. R. , Ingram R. H.
Published: December 2017

Bronchia reactivity to inhaled histamine was assessed in asymptomatic cigarette smokers and in nonsmoking atopic and nonatopic subjects. The only prechallenge between-group difference was the ratio of maximal flow on 80% helium-20% oxygen (Vmax HeO2) to maximal flow on air (Vmax air) from partial expiratory flow volume curves at 25% vital capacity (25% VC PEFV): Mean +/- SEM for smokers 1.18 /+- 0.06, atopics 1.45 +/- 0.08, nonatopics 1.51 +/- 0.03. This suggests that prior to inhalation to total lung capacity, the predominant site of resistance at flow limitation was in smaller airways of the smokers and in larger airways of both groups of nonsmokers. Following inhalation of histamine, smokers and nonatopics had similar changes in lung volumes and Vmax air which were less than in atopics. The Vmax HeO2/Vmax air ratios at 25% VC PEFV increased in smokers and decreased in nonsmokers: smokers 1.48 +/- 0.08, atopics 1.22 +/- 0.10, nontopics 1.16 +/- 0.06. This suggests a predominant large airway response in smokers and a prominent small airway response in nonsmokers. These responses may reflect differences in the predominant site of aerosol deposition rather than in airway reactivity.
Extension of pulmonary O2 tolerance in man at 2 ATA by intermittent O2 exposure
Authors: Hendricks P. L. , Hall D. A. , Hunter W. L. , Haley P. J.
Published: December 2017

To study extension of O2 tolerance by interruption of hyperoxic exposure, as compared to previous studies of continuous oxygen exposure, five healthy volunteers were exposed to oxygen at 2 ATA on an intermittent schedule of 20 min breathing O2, alternating with 5 min on a normoxic N2-O2 mixture. The cycle was repeated until symptoms or signs of O2 toxicity caused cessation of the experiment. Tracheal irritation and burning on inspiration occurred after 6–9 “oxygen hours” of exposure and progressed to severe tracheobronchial burning sensation, chest pain, and dyspnea after 11–15 h of O2. Average duration of exposure was 13.7 O2 h, inducing a mean vital capacity decrease of 10.3%. The decrease began soon after onset of symptoms. With intermittent O2 administration, nearly a doubling of the average duration of actual oxygen breathing was required to induce marked vital capacity change (greater than 10%) as compared to the previous studies of continuous O2 exposure. The increased duration of tolerable O2 exposure in man resembles the extension of O2 tolerance known to occur in animals exposed to intermittent hyperoxia.
H+ transport from CNS in hypercapnia and regulation of CSF [HCO3-]
Authors: Kazemi H. , Choma L.
Published: December 2017

CSF HCO3- increases more than plasma HCO3- in hypercapnia, and there are at least two sources for the CSF HCO3- increase--one derived from the simultaneous increase in plasma HCO3-, and the other, HCO3-formed from hydration of CO2 in the choroid plexus and glia and susceptible to inhibition by acetazolamide (J. Appl. Physiol. 38: 504–512, 1975). It was proposed that the H+ formed in the CNS in CO2 hydration is actively exchanged for plasma Na+ utilizing the Na-K ATPase pump. H+ transport from the CNS was therefore studied in four groups of dogs breathing 5% CO2 at constant VA for 4 h with repeated injections of saline, acetazolamide 5 mg/ml, ouabain 0.1 mg/ml, and acetazolamide and ouabain together into lateral cerebral ventricles. Arterial HCO3-increased 2.5 meq/l at 4 h of hypercapnia in all groups. CSF HCO3-increased 5.8 meq/l in the saline-injected animals, but it increased only about 2 meq/l and equaled plasma HCO3- rise in the other three groups. Therefore CNS HCO3- formation in hypercapnia can be blocked by inhibiting the CO2 hydration reaction with acetazolamide or by blocking H+ removal by inhibiting Na-K ATPase with ouabain. The data support the thesis of active H+ removal from the CNS in exchange for plasma Na+ in hypercapnia.
Effects of plasma ascorbic acid levels on heat acclimatization in man
Authors: Kotze H. F. , van der Walt W. H. , Rogers G. G. , Strydom N. B.
Published: December 2017

Thirteen male volunteers were heat acclimatized for 4 h/day for 10 consecutive days. Three to four hours before each heat exposure, four of the subjects received an oral dose of 250 ascorbic acid, five received 500 mg ascorbic acid, and the remaining four a placebo. Rectal temperature, heart rate, and sweat rate were measured hourly during exposure. Venous blood samples were collected before each administration of drug or placebo. On days 1, 2, 3, 5, 8, and 10, blood samples were also collected just prior to heat exposure and after two and four hours of exposure. In the subjects receiving ascorbic acid, total circulating plasma ascorbic acid increased over the first three or four days to a plateau level some fourfold higher than in the subjects receiving the placebo. The plateau level was the same in the subjects receiving 250 mg and 500 mg ascorbic acid. The increased ascorbic acid concentration was shown to be associated with a reduction in total sweat output, independent of rectal temperature, and a reduction in rectal temperature, independent of total sweat output. The results indicate that ascorbic acid may be effective in reducing heat strain in unacclimatized individuals.
Systematic design of cantilever beams for muscle research
Authors: McLaughlin R. J.
Published: December 2017

Experimental studies of muscle contraction often involve difficult problems in the design of cantilever beams for movable levers, transducers, or mechanical supports. Equations are presented for the calculation of mass, inertia, stress distribution, strain, deflection curve, compliance, and resonant frequency of uniform or nonuniform cantilever beams made of structural materials of different density or elastic modulus. Formulas are listed for solid, thick-wall, and thin-wall uniform beams of rectangular and circular cross section. Physical properties including density, elastic and torsional moduli, stress and strain limits, thermal expansion coefficients, Poisson's ratio, and certain elastic-modulus-to-density ratios are tabulated for structural materials including common metals, glass, plastic, and wood. A graphical design procedure is presented based on a chart containing loci of constant beam parameter values as a function of beam length and height or diameter, for the simple geometries. The choice of structural material is discussed for design problems with typical constraints, and examples are given of the design of beams of nonuniform cross section. Methods for extending the design chart to other geometries and materials are included.
Rat model of acute heatstroke mortality
Authors: Hubbard R. W. , Bowers W. D. , Matthew W. T. , Curtis F. C. , Criss R. E. , Sheldon G. M. , Ratteree J. W.
Published: December 2017

A total of 252 untrained, unacclimatized, and unanesthetized laboratory rats weighing between 485 and 545 g were fasted and either run to exhaustion at 5, 20, 23, or 26 degrees C or were restrained and heated at an ambient temperature of 41.5 degrees C. The incidence of mortality associated with a wide range of work-induced hyperthermias was compared to the lethality of equivalent heat loads in the absence of physical effort. The severity of hyperthermia was calculated in degree-minutes above a base-line core temperature of 40.4 degrees C. The LD25′s of run-exhausted versus restrained-heated rats were 16.8 and 30.1 deg-min, respectively. Survivors had a faster cooling rate than fatalities, but run-exhausted survivors had a slower cooling rate than restrained-heating survivors. Results indicate that 1) both the incidence of mortality and the survival time can be predicted from the severity of core heating, 2) work-related factors contribute to an increased rate of heatstroke death at low thermal loads, and 3) retrospectively, both heat-sensitive and heat-resistant groups were identified.
Relationship of lung recoil to lung volume and maximum expiratory flow in normal children
Authors: Mansell A. L. , Bryan A. C. , Levison H.
Published: December 2017

Thirty-one normal children, aged 6--18 yr, were studied by measurements of static lung volumes, static expiratory pressure-volume (PV) curves, and maximum expiratory flow-volume (MEFV) curves. A theoretical standard volume was used to compare children of differing size and this showed that total lung capacity (TLC) is also a valid standard volume. The shape of the PV curve was found to change so that static elastic recoil at a fixed proportion of TLC was higher in older than in younger children. This was also true of static recoil at functional residual capacity (FRC) and an associated increase in the ratio of FRC to TLC was interpreted as evidence for increase in outward recoil of the chest wall during childhood. Since static recoil at “closing capacity” (CC) remained constant, a decrease in the ratio of CC to TLC was quantitatively explained by the PV shift during childhood. Although maximum expiratory flow at various lung volumes increased in constant proportion to TLC, “upstream conductance” decreased relative to TLC. It was concluded that maturation of the respiratory system is disproportionate in several features during childhood and that these disproportions are likely to be even more prominent during infancy and early childhood.