bluuebunny/crossref_metadata_2025 huggingface dataset:
Ventilatory adaptations to resistive loading during wakefulness and non-REM sleep
Authors: Iber C. , Berssenbrugge A. , Skatrud J. B. , Dempsey J. A.
Published: December 2017

Ventilatory and timing responses to repetitive and sustained inspiratory resistive loading were assessed in six naive male subjects during wakefulness (AW) and non-REM sleep (NREM). In five of six subjects, tidal volume (VT) was maintained or increased with repetitive five-breath loading periods during wakefulness. In these five subjects, mouth occlusion pressure (P100) increased with loading during AW (1.8 +/- 0.5 control vs. 2.2 +/- 0.4 cmH2O loaded, P less than 0.05), but not during NREM (2.1 +/- 1.5 control vs. 2.1 + 1.5 cmH2O loaded). For each state, VT and frequency (f) responses to sustained loads were similar to responses to five-breath loads. During sustained loading; a) VT increased 35% during AW, decreased 28% during NREM, b) f decreased 35% during AW, increased 6% during NREM, c) minute ventilation (VE) decreased 12% during AW, decreased 23% during NREM. Ventilatory responses persisted until arousal (0.4--1.7 min) in NREM. With repetitive loading: a) inspiratory duration (TI) increased during AW but did not change during NREM, b) “duty cycle” (TI/TT) increased with loading in both states. These findings suggest that a) NREM abolishes between-breath augmentations in P100, b) within-breath load compensation is operant during both AW (preserved VT) and NREM (failure of predicted TI prolongation) by differing mechanisms, c) arousal may be a ventilatory compensation to inspiratory resistive loading in NREM.
Distribution of cardiac output during static exercise in the conscious cat
Authors: Diepstra G. , Gonyea W. , Mitchell J. H.
Published: December 2017

Blood flows to major organs were measured in conscious cats to study the changes in the distribution of cardiac output during voluntary static (isometric) exercise. Five animals were operantly conditioned to hold a bar against a fixed resistance for 30 s. Organ flows were measured during rest and exercise by injecting 25-micrometer radioactive microspheres into the left atrium or left ventricle. Increases were observed during exercise in heart rate (18%), mean arterial pressure (25%), left ventricular systolic pressure (17%), and rate of left ventricular development (26%). Static exercise produced significant changes in flow (ml . min-1 .g-1) to the kidneys (-1.09 +/- 0.24), spleen (-0.85 +/- 0.21), and exercising muscles (+0.13 +/- 0.08), while flows to liver, heart, brain, and nonexercising muscle were not significantly changed from control levels. Denervation of the left kidney abolished the decrease in flow to that kidney during exercise. Thus, static exercise appears to produce a significant increase in blood flow to exercising muscles and significant reductions in blood flow to spleen and kidneys. The reduction in renal blood flow is mediated by a neural mechanism.
Recovery time course in contractile function of fast and slow skeletal muscle after hindlimb immobilization
Authors: Witzmann F. A. , Kim D. H. , Fitts R. H.
Published: December 2017

Contractile properties were evaluated in rats remobilized after 6 wk of hindlimb casting to evaluate the regenerative capacity of fast and slow skeletal muscles. Contractile parameters were determined in vitro (22 degrees C) in the type I soleus (SOL), type IIA and IIB extensor digitorum longus (EDL), and the type IIB superficial vastus lateralis (SVL). Immobilization (IM) shortened the SOL isometric twitch duration after which contraction time and half-relaxation time required 4 and 7 days to recover, respectively. In contrast, IM prolonged the twitch in the EDL and SVL and recovery required 14 and 7 days, respectively. Peak tetanic tension (g/cm2) fell in the SOL and EDL with IM and full recovery required 28 days. In this regard, the SVL remained unaltered. Rates of tension development and decline remained essentially unaltered in the fast muscles after IM but fell in the SOL, requiring 14 days to fully recover. Maximal shortening velocity, which had been elevated in all three muscles by IM, recovered rapidly. The present results demonstrate that both fast and slow muscle have the ability to completely recover from 6 weeks of IM.
Infant birth weight is related to maternal arterial oxygenation at high altitude
Authors: Moore L. G. , Rounds S. S. , Jahnigen D. , Grover R. F. , Reeves J. T.
Published: December 2017

Infant birth weight is reported to decrease at high altitude as a reulst of fetal growth retardation (McCullough, Reeves, and Liljegren. Arch. Environ, Health. 32: 36--39, 1977) but not all babies born at high altitude are small. We hypothesized that maternal characteristics acting to lower arterial O2 content would contribute to smaller infant birth weight. To test this hypothesis, we measured arterial oxygenation serially during pregnancy and again postpartum in 44 residents of Leadville, CO (elevation 3,100 m). We identified three maternal characteristics--ventilation, hemoglobin concentration, and smoking habits--that were related to the birth weight of the offspring. Mothers of smaller babies (less than 2,900 g) compared to mothers of larger babies (greater than 3,500 g) were characterized by hypoventilation, no change or a decrease in ventilation and arterial O2 saturation from early to late gestation, and a falling hemoglobin concentration that combined to lower arterial O2 content in the 3rd trimester. Maternal smoking at 3,100 m was associated with a two to threefold greater reduction in infant birth weight (-546 g) than reported from sea level. Thus, maternal arterial oxygenation during pregnancy may be important for predicting fetal growth retardation and the process of adaptation to high altitude.
Thermoregulatory responses in the rat to exercise in the heat following prolonged heat exposure
Authors: Francesconi R. , Hubbard R. , Mager M.
Published: December 2017

To determine the effects of prolonged exposure to severe thermal stress on the subsequent ability to exercise in the heat, rats were exposed to a hot (35 degrees C) environment for 1, 2, 3, or 4 wk. At each of these weekly intervals the rats ran on a treadmill to hyperthermic exhaustion (41.5--43.0 degrees C), and tail-skin (Tt-sk) and rectal (Tre) temperatures were monitored. The results indicated that prolonged heat exposure did not enhance the rats' endurance capacity. Further, as the period of heat stress increased, there was a concomitant significant decrement in tail-skin vasodilation; indeed, after 3 and 4 wk at 35 degrees C Tt-sk reflects a complete shutdown of blood flow to the tail during exercise. Additionally, slight evaporative cooling from exogenous fluid (saliva or urine from the treadmill surface) might account for the low Tt-sk in relation to Tre and Ta. Hematocrit ratios ordinarily decreased from week to week during heat exposure, whereas body weights remained very consistent throughout the 4-wk interval. The mechanism of this decrement in vasodilation is undergoing further study.
Effect of thoracic deafferentation on load-compensating mechanisms in humans
Authors: Axen K. , Haas S. S.
Published: December 2017

First-breath responses to graded elastic (delta E) and resistive (delta R) loads in 29 cervical cord-injured and 80 normal men were compared with those predicted assuming identical respiratory muscle pressure (Pmus) wave forms in the unloaded and loaded states. The cord-injured group's mean actual and predicted inspiratory duration (TI) responses were equal, indicating that the average duration of their phrenic discharge remained constant during both delta E and delta R. Their mean expiratory duration (TE) responses fell short of predictions with delta E but exceeded predictions with delta R, signifying that a neural mechanism hastened inspiration following delta E but postponed it following delta R. TE/(pred TE) values (an index of phrenic timing) from different loads were proportional to concomitant TI responses but not to indices of diaphragmatic force [peak Pmus, (VT/TI)/(pred VT/TI)], movement (VT, VT/TI), or duration of contraction [TI/(pred TI)]. These findings suggest that oropharyngeal and/or pulmonary receptors signaling airflow duration, rather than diaphragmatic length or tension receptors, adjust phrenic motoneuron timing during mechanical loading. The cord-injured group produced a normal tidal volume (VT) defense coupled with a depressed frequency (f) response to delta E and, conversely, a weak VT defense coupled with a normal f response to delta R. Since both groups' VT/TI responses surpassed predictions equally, the cord-injured group's deficit was attributable entirely to impaired regulation of TE during delta E and TI during delta R. Thus chest wall receptors modulate duration and timing, but probably not average intensity, of the phrenic output during loading. Nearly one-third of the normal, but virtually none of the cord-injured, samples prolonged TI against large delta R and shortened TI agaist large delta E, suggesting that thoracic deafferentation impairs human ability to distinguish large delta R from delta E. These latter findings support the hypothesis that chest wall afferents subserve perception of respiratory force or position in humans.
Measuring ventilatory muscle endurance in humans as sustainable inspiratory pressure
Authors: Nickerson B. G. , Keens T. G.
Published: December 2017

We have devised a method for measuring ventilatory muscle endurance as the sustainable inspiratory pressure (SIP), which is the highest pressure a subject can generate in each breath for 10 min. We used a weighted plunger as an inspiratory valve. This both ensures that a constant pressure is generated with each breath and allows the subject to vary his tidal volume freely. Fifteen normal subjects, ages 5--75 yr, had SIP of 82 +/- 6 (SE) cmH2O or 68 +/- 3% of their maximum inspiratory pressure. The respiratory rate was 13 +/- 1 breaths/min with 52 +/- 4% of the respiratory cycle spent in inspiration; end-tidal CO2 pressure increased by 3.3 +/- 1.0 Torr during runs at SIP. Oxygen consumption measured in two subjects rose with increasing pressure below SIP. There was no further increase in oxygen consumption when these subjects breathed with inspiratory pressures above SIP. Our method allows reproducible measurement of ventilatory muscle endurance without dependence on the subject's flow rates or the resistance chosen.
Changes in respiratory movements of the human vocal cords during hyperpnea
Authors: England S. J. , Bartlett D.
Published: December 2017

Five healthy young subjects were studied to assess the changes in vocal cord movements that occur between resting breathing and hyperpnea. Both hypercapnia and exercise induced decreases in the extent of narrowing of the glottic aperture occurring during expiration. In addition, four of the subjects showed a significant positive rank correlation between the extent of narrowing of the glottis and the observed length of the expiratory phase of the respiratory cycle. These results indicate that the braking of expiratory airflow by movements of the vocal cords toward the midline is reduced during hyperpnea at the same time that expiratory time is decreased.
No effect of naloxone on hypoxia-induced ventilatory depression in adults
Authors: Kagawa S. , Stafford M. J. , Waggener T. B. , Severinghaus J. W.
Published: December 2017

The ventilatory response to acute isocapnic hypoxia is prompt but is not maintained at its peak. Within 10 min, it begins to fall, and by 30 min has reached an approximately steady level, usually still above control. We used naloxone to test in four men the hypothesis that this fade is hypoxic depression mediated by endogenous opioid peptides, e.g, endorphins. Breath by breath minute ventilation was recorded during a hyperoxic control period (FIO2 = 0.3) to establish control alveolar PCO2. After 15 min. of isocapnic hypoxia (end-tidal PO2 = 45 Torr), naloxone injection (1.2 or 10 mg, iv) failed to alter the slow decrement of ventilation. Hypoxic ventilatory depression appears not to be mediated by endorphins in adults.
Functional diagrams of flow and volume for the dog's lung
Authors: Moffatt D. S. , Guyton A. C. , Adair T. H.
Published: December 2017

Quantitative diagrams have been constructed from data obtained in isolated perfused dog lungs for the multiple interrelationships among pressure, volume, and flow characteristics of the pulmonary vasculature. These characteristics are described in the form of functional diagrams for flows from 0.3 to 1.0 l . min-1 . 100 g wet lung weight-1 (WLW), for venous pressures from -8 to +14 Torr, and for arterial pressures from 16 to 30 Torr. The quantitative relationships were shown not to change significantly as the transpulmonary pressure changes within the range from 3 to 10 Torr. The change in blood volume with arterial pressure, called the “distributed arterial compliance,” averaged 1.5 g . Torr-1 . 100 g WLW-1. This compliance was nearly constant over the range of arterial pressure studied. On the other hand, the change in blood volume with venous pressure, called the 'distributed venous compliance” was different for different levels of venous pressures. Its maximum value was 1.04 g . Torr-1 . 100 g WLW-1 when the venous pressure was near 2 Torr. At venous pressures both above and below this pressure level this compliance decreased. These distributed compliances are described as resulting to a significant extent from changes in flow patterns through the pulmonary circulation rather than being direct indications of the true vascular compliances.
Chemoreceptor involvement in cortisol responses to hypoxia in ventilated dogs
Authors: Raff H. , Tzankoff S. P. , Fitzgerald R. S.
Published: December 2017

Changes in cortisol secretion rate (CSR) in response to hypoxic hypoxia (HH) and to carbon monoxide hypoxia (COH) were assessed in mongrel dogs that had intact chemoreceptors (INT); surgically deafferented carotid bodies (CBD) or aortic bodies (ABD); or both carotid and aortic chemoreceptors denervated (SAD). All dogs were anesthetized, paralyzed, ventilated, and maintained normocapnic. In the INT and ABD groups, CSR responded “maximally” to HH, whereas in CBD and SAD animals, the CSR was attenuated but not eliminated. COH, which does not stimulate the carotid body, caused a submaximal increase in CSR regardless of chemoreceptor status. It is concluded that 1) the carotid bodies are the principal chemoreceptor influence on CSR during HH and 2) there is a nonchemoreceptor-mediated increase in CSR during hypoxia.
Chylomicron triglyceride metabolism in resting and exercising fed dogs
Authors: Terjung R. L. , Budohoski L. , Nazar K. , Kobryn A. , Kaciuba-Uscilko H.
Published: December 2017

The turnover of circulating triglycerides (TG) was determined in dogs during rest, following ingestion of food that included corn oil, and in the final period of a 1-h treadmill exercise of moderate intensity (72–84 m/min). In all cases the loss of [14C]TG from the plasma followed a first-order process. The fractional removal rate constant at rest was 26.5 +/- 1.9% (SE) n = 10) of the circulating pool size per minute, and it was increased slightly to 33.8 +/- 3.6% (n = 7) per minute during exercise. The uptake of plasma TG-derived fatty acids (5 min postinjection) was increased (P less than 0.05) in working muscle, whereas the TG uptake in fat tended to decrease. Further, the percent of TG-derived fatty acids found in the muscle's acylglyceride pool was less (90.0 +/- 3.6 vs. 53.5 +/- 1.8%), while that in the muscle's free fatty acid pool was greater (12.3 +/- 36.1 +/- 4.7%) in working compared with resting muscle. Thus the fourfold greater quantity of plasma TG-derived fatty acids found in the working muscle's free fatty acid pool could account for the entire increased TG uptake caused by exercise. This suggests that, in the fed state, circulating TG could represent a potential source of fatty acids for beta-oxidation in working muscle. However, the importance of plasma TG-derived fatty acids as an energy substrate during muscle use in a postprandial state has yet to be determined quantitatively.
Respiratory muscle fatigue after marathon running
Authors: Loke J. , Mahler D. A. , Virgulto J. A.
Published: December 2017

Respiratory muscle fatigue has been demonstrated in the laboratory as well as in pathological states, but whether it occurs in healthy individuals under physiological conditions is unknown. To determine whether fatigue of the respiratory muscles may develop with endurance exercise, we measured spirometry and respiratory muscle strength and endurance in four runners before and after completion of a marathon race (42.2 km). Strength was assessed by measuring maximal inspiratory (PImax) and expiratory (PEmax) pressures and transdiaphragmatic pressure during inspiratory capacity (PdiIC); endurance was determined by measuring maximal voluntary ventilation (MVV). After marathon running (mean time, 3 h 24 min) there was no change in forced vital capacity, inspiratory capacity, or flow rates from prerace values. Decreases were observed between pre- and postrace PImax (165.8 +/- 11.0 vs. 138.5 +/- 7.6 cmH2O; P less than 0.01) PEmax (240.0 +/- 20.4 vs. 173.0 +/- 22.6 cmH2O; P less than 0.05), PdiIC (78.8 +/- 11.6 vs. 63.3 +/- 7.0 cmH2O; P less than 0.10), and MVV (178 +/- 24.2 vs. 161.2 +/- 23.2 l/min; P less than 0.005). The decrements in respiratory muscle strength and endurance suggest the development of respiratory muscle fatigue after marathon running.
Bronchodilatation, lung recoil, and density dependence of maximal expiratory flow
Authors: Weiss J. W. , McFadden E. R. , Ingram R. H.
Published: December 2017

Using normal human subjects we have measured maximal expiratory flow rates with air (Vmaxair) and after a washin of 80% He-20% O2 (VmaxHeO2) and static elastic recoil pressures of the lung [Pst(L)] both before and after administration of a beta-agonist, terbutaline. The effects of inhaled drug were compared with those of the subcutaneously administered agent, each given in doses to produce maximal bronchodilatation as assessed by increases in Vmaxair in the mid-vital capacity. Although there was a significant yet modest decrease in Pst(L) only after injection of the agent, density dependence (DD), assessed as the ratio of VmaxHeO2 to Vmaxair, increased significantly and comparably after either route of administration. A modest decrease in Pst(L), therefore, did not affect the changes in DD.
Effects of exposure to acid on alveolar epithelial water and solute transport
Authors: Kim K. J. , Crandall E. D.
Published: December 2017

Water and solute transport properties of normal and acid-exposed bullfrog alveolar epithelium were determined under controlled conditions. Paired lungs from the same animal were studied in Ussing chambers. Tissue bioelectric parameters, permeabilities of water and solutes, and hydraulic conductivity were measured. Results from control lungs were compared with those observed after the alveolar epithelium was exposed to acid (pH 2.0–4.0) for variable periods of time (1–60 min). Acid exposure appears to initially damage tissue active transport mechanisms, causing a marked fall in potential difference at pH less than or equal to 3.0. Increases in tissue conductance and permeability to solutes occurred after a variable time lag. Water permeability did not change after acid exposure. Equivalent homogeneous pore radius increased as time of exposure to acid increased. It is concluded that the bullfrog alveolar epithelium, normally resistant to water and solute flux, loses its ability to transport ions actively and gradually becomes leaky after exposure to acid (pH less than or equal to 3.0). The pathway for movement of water across alveolar epithelium may be different from that for solutes.
Problems in measurement of thoracic gas volume in infancy
Authors: Beardsmore C. S. , Stocks J. , Silverman M.
Published: December 2017

Thoracic gas volume (TGV) was measured with a whole-body plethysmograph in 20 infants at functional residual capacity (FRC) and at a series of higher lung volumes achieved by artificial inflation of the lungs with known volumes of air after airway occlusion. There was a discrepancy between the corrected values of TGV measured at high and low lung volumes in nine infants; in six cases TGV measured at high lung volumes exceeded that measured at FRC, and in three cases it was reduced when compared with the measurement made at FRC. These changes were not related to age, size, or clinical status and could be explained by airway closure at FRC, combined with an uneven distribution of pleural pressure.
Mechanical properties of rat lung during prolonged hypercapnia
Authors: Lai Y. L. , Lamm W. J. , Hildebrandt J.
Published: December 2017

Young adult rats were exposed to short-term (2 or 4 h) and prolonged (1 day to 3 wk) 5% CO2 to determine whether changes in lung mechanical properties might contribute to ventilatory adaptation. Anaesthetized rats were tracheotomized for measurement of functional residual capacity (FRC) and respiratory rates (chest intact), and for pressure-volume (PV) curves (chest open). Total lung capacity, minimal volume, lung compliance, and lung wet weight-to-dry weight ratio did not change significantly (P greater than 0.05) from air control values with CO2 exposure. From 4 h to 3 wk of hypercapnia, FRC was increased significantly (P less than 0.01) by about 25%; some of this rise could be associated with dynamic factors such as increased breathing frequency. Lung PV curves showed a small (0.5 cmH2O) left shift early in the short exposure period; this reversed into a slight (0.5 cmH2O) right shift after prolonged CO2. It is unlikely that these relatively small changes in FRC and lung recoil could contribute significantly to the previously reported long-term ventilatory adaptation to CO2.
Dynamics of cardiac, respiratory, and metabolic function in men in response to step work load
Authors: Miyamoto Y. , Hiura T. , Tamura T. , Nakamura T. , Higuchi J. , Mikami T.
Published: December 2017

Stroke volume, heart rate, cardiac output, tidal volume, respiratory frequency, minute ventilation, end-tidal tensions of O2 and CO2, O2 uptake, CO2 output, and respiratory exchange ratio were measured simultaneously in healthy male volunteers before, during, and after upright bicycle exercise from 0 to 360 and 720 kpm/min. The circulatory variables were determined continuously once per 20 cardiac cycles and the respiratory variables breath by breath using separate computer-based systems in which an impedance pneumograph and an impedance cardiograph were incorporated. Stroke volume, heart rate, and cardiac output started to increase without measurable delay at the onset of exercise. Stroke volume increased by 20% from resting control value in response to the mildest exercise and essentially leveled off with a further increase in work load. Time constant for cardiac output increased with the increasing work load. Time constant for minute ventilation was much longer than that for cardiac output and independent of work intensity. A good synchronization between the ventilation and cardiac output responses at an initial period of transitions from rest to exercise and from exercise to rest seems to support the concept of cardiodynamic hyperpnea.
Hemodynamic and vasoactive mediator response to experimental respiratory failure
Authors: O'Brodovich H. M. , Stalcup S. A. , Pang L. M. , Mellins R. B.
Published: December 2017

We determined the changes in hemodynamics and circulating concentrations of endogenous vasoactive mediators during acute respiratory failure in chronically catheterized unanesthetized sheep. Inhalation of a hypercarbic-hypoxic gas mixture for 2 h (pHa = 7.16, PaCO2 = 84 Torr, PaO2 = 48 Torr, n = 5) resulted in a doubling of cardiac output (thermodilution) and systemic and pulmonary hypertension. Systemic vascular resistance decreased, whereas pulmonary vascular resistance gradually increased throughout the 2-h experimental gas period. Pulmonary hypertension persisted for 45 min after return to room air breathing. Plasma renin activity tripled, and circulating bradykinin concentration increased 25-fold (radioimmunoassay). Plasma norepinephrine and epinephrine concentrations (radioenzymatic assay) dramatically increased with respective initial values (15 min) of 23.9 +/- 9.5 (SE) and 26.7 +/- 13.3 ng/ml (base line less than 0.2). Inhalation of hypoxic (n = 4) or hypercarbic-enriched O2 (n = 7) gas mixtures did not produce similar findings. We concluded that the hemodynamic response to experimental respiratory failure results from the combination of hypercarbic acidosis and hypoxia. These changes were mediated in part by increased sympathoadrenal activity and altered concentrations of H+, O2, and endogenous vasoactive mediators.
Reduction of the edema of acute hyperoxic lung injury by granulocyte depletion
Authors: Shasby D. M. , Fox R. B. , Harada R. N. , Repine J. E.
Published: December 2017

Increased numbers of granulocytes are found in lungs acutely injured by hyperoxia, but their contribution to lung injury remains unknown. We found that circulating granulocytes markedly increased (P less than 0.01) in rabbits exposed to hyperoxia for 72 h and that the numbers of granulocytes in lung lavages also increased and were correlated (r = 0.72, P less than 0.01) with the degree of edematous lung injury. Furthermore, when rabbits were treated with nitrogen mustard (1.75 mg/kg) and developed sustained granulocytopenia, exposure to hyperoxia for 72 h resulted in fewer granulocytes in lung lavages and less edematous lung injury. In contrast, when rabbits were similarly treated with nitrogen mustard but did not maintain sustained granulocytopenia throughout the exposure to hyperoxia, increased numbers of granulocytes were found in lung lavages and the degree of edematous lung injury increased to levels not different from those observed in oxygen-exposed rabbits that had not been treated with nitrogen mustard. These findings suggest that granulocytes may contribute to production of edema in acute oxygen toxicity.
Induced venous pooling and cardiorespiratory responses to exercise after bed rest
Authors: Convertino V. A. , Sandler H. , Webb P. , Annis J. F.
Published: December 2017

The purpose of this study was to deliberately induce venous pooling the lower extremities of bed-rested subjects to determine whether such distention may reverse the reduction in maximal O2 uptake that has regularly been observed. Bed-rest deconditioning was assessed in eight healthy male subjects by measuring submaximal and maximal O2 uptake (VO2 max), ventilation, and heart rate (HRmax) before and after 15 days of bed rest. During bed rest four subjects in the experimental group received daily treatments of venous pooling for 210 min/day with a reverse gradient garment (RGG), whereas the four subjects in the control group received no treatment. Compared with prebed-rest values, VO2max was reduced by 14.0 (P less than 0.05), HRmax was increased by 4.2 (P less than 0.05), and endurance time for the exercise test was decreased by 9.2% (P less than 0.05) in the control group. In the RGG group, VO2max, HRmax, and endurance time were essentially unchanged after bed rest. The plasma volume (PV) of the control group decreased by 16.7 (P less than 0.05) after bed rest compared with a 10.3% (not significant) reduction in the RGG group. The percent delta PV was related to the percent delta VO2 max (r = 0.75, P less than 0.05) and percent delta HR max (r = 0.65, P less than 0.05). The data support the hypothesis that the lack of venous pooling and associated fluid shifts contribute the decrement in VO2 max associated with bed-rest deconditioning.
Improvement in ventilatory muscle function with running
Authors: Robinson E. P. , Kjeldgaard J. M.
Published: December 2017

We studied the effects of running on ventilatory muscle strength and endurance in 11 adults enrolled in a physical fitness program. Twelve healthy volunteers were used as a control group. Maximum expiratory pressure (Paomax), maximum voluntary ventilation (MVV), peak inspiratory flow, forced expiratory volume in 1 s, forced vital capacity, and maximum sustainable ventilatory capacity for 15 min (MSVC) were measured at 0, 10, and 20 wk. At the end of the 10-wk program, the subject group demonstrated a significant increase in both MSVC and MVV. At the end of the 20-wk period, the subject group demonstrated a significant increase in expiratory Paomax (14.4%), MVV (13.6%), and MSVC (15.8%). There was no significant change at the end of the 20-wk period in any of the tests in the control group. These data indicate that running can improve ventilatory muscle strength and endurance in healthy, previously sedentary individuals.
Splanchnic vasoconstriction in heat-stressed men: role of renin-angiotensin system
Authors: Escourrou P. , Freund P. R. , Rowell L. B. , Johnson D. G.
Published: December 2017

We conducted a two-part study to determine whether the renin-angiotensin system contributes to the rise in splanchnic vascular resistance (SVR) during heat stress (rectal temperature was raised 1 degree C). In experiment 1 (control) seven men on a normal salt diet were directly heated (water-perfused suits) for 40–50 min. Arterial pressure (85 Torr) was unchanged; plasma renin activity (PRA) rose from 102 to 239 ng angiotensin I.100 ml-1.3 h-1; and SVR increased 73% (from 63 to 109 units). Experiment 2 was a repetition of experiment 1 on the same subjects, except that propranolol (10 mg iv) was given at the onset of heating to block renin release. Propranolol attenuated the rise in heart rate and reduced mean arterial pressure from 82 to 72 Torr; it blocked the rise in PRA with heating in two subjects, reduced it in three, but increased it in two. Although changes in SVR paralleled those in PRA in three subjects, SVR still rose 60% (from 58 to 99 units) after PRA rise was blocked. In both experiments, plasma norepinephrine concentration rose indicating increased sympathetic nervous activity. During mild heat stress, increased PRA is not a major factor in the increase of SVR.
Effects of lung inflation on alveolar epithelial solute and water transport properties
Authors: Kim K. J. , Crandall E. D.
Published: December 2017

Paired hollow bullfrog lungs (Rana catesbeiana) were used to study the effects of lung inflation on alveolar epithelial transport of water and hydrophilic solutes. Frogs were double pithed and the lungs were removed after bronchial placement of a Lucite plug. Three openings in the plug accommodated the insertion of two agar-Ringer bridges (for electrical potential measurement and passage of direct current) and the injection and removal of alveolar bathing fluid. Ringer solution containing a tracer quantity of radioactive solute was instilled into the lung sacs (5 ml or 50 ml) and the lungs were suspended in baths of Ringer solution containng appropriate cold solutes (5 mM). Permeability properties of each solute (and water) were determined from the rate of radiotracer concentration change in the bath. The spontaneous potential difference, tissue resistance, and solute permeability properties determined in these experiments showed no significant differences between the 5- and 50-ml lungs. Assuming homogeneous, cylindrical water-filled pores to be present in the tissue, the equivalent pore radii estimated from the rates of solute and water fluxes were 1.1 (for 5-ml lungs) and 0.9 nm (for 50-ml lungs). After overinflation of the lung (to greater than 80 ml), experiments at 50 ml yielded a pore radius of 3.4 nm. These data suggest that passive alveolar epithelial transport properties do not change with degrees of lung inflation normally encountered in vivo but that overinflation can lead to increased leakiness of the barrier.
Parameters of ventilatory and gas exchange dynamics during exercise
Authors: Whipp B. J. , Ward S. A. , Lamarra N. , Davis J. A. , Wasserman K.
Published: December 2017

To determine the precise nonsteady-state characteristics of ventilation (VE), O2 uptake (VO2), and CO2 output (VCO2) during moderate-intensity exercise, six subjects each underwent eight repetitions of 100-W constant-load cycling. The tests were preceded either by rest or unloaded cycling (“0” W). An early component of VE, VO2, and VCO2 responses, which was obscured on any single test by the breath-to-breath fluctuations, became apparent when the several repetitions were averaged. These early responses were abrupt when the work was instituted from rest but were much slower and smaller from the 0-W base line and corresponded to the phase of cardiodynamic gas exchange. Some 20 s after the onset of the work a further monoexponential increase to steady state occurred in all three variables, the time constants of which did not differ between the two types of test. Consequently, the exponential behavior of VE, VO2, and VCO2 in response to moderate exercise is best described by a model that incorporates only the second phase of the response.
Physical training in diabetic rats: effect on glucose tolerance and serum lipids
Authors: Tan M. H. , Bonen A. , Garner J. B. , Belcastro A. N.
Published: December 2017

The effect of 10 wk of treadmill training on glucose tolerance, serum lipids, tissue lipoprotein lipase (LPL) activities, and triglyceride secretion rates (TGSR) were studied in normal and diabetic rats. Training had little effect on the glucose tolerance of the normal rats but ameliorated the deterioration of glucose intolerance seen in the sedentary diabetic rats. Trained diabetic and normal rats had lower serum triglycerides than their sedentary counterparts [diabetic 34 +/- 5 vs. 61 +/- 4 (means +/- SE); normal 34 +/- 3 vs. 50 +/- 3 mg/dl]. This hypotriglyceridemic effect was associated with a reduction in the TGSR in the trained rats (diabetics 0.34 +/- 0.05 vs. 0.51 +/- 0.02; normal 0.48 +/- 0.05 vs. 0.53 +/- 0.04 mg/min). There were no differences in the tissue LPL activities (soleus, gastrocnemius, epididymal fat, and heart) between the trained and sedentary rats in both groups. Training also did not affect the serum cholesterol and the high-density lipoprotein cholesterol levels in both groups of rats.
Effect of oleic acid injury on lung-heart interaction during ventricular filling
Authors: Lloyd T. C.
Published: December 2017

Part of ventricular filling pressure is expended in deforming the lungs and oleic acid lung injury, which reduces lung compliance, might be expected to change the magnitude of this effect. Left ventricular pressure-volume curves from 13 treated and 13 uninjured dogs were compared. Curves were obtained by inflating a balloon in the flaccid left ventricle of the freshly dead dog. The extracardiac compliance component was determined by subtracting ventricular pressures observed when lungs were collapsed from those observed during inflation to levels duplicating both airway pressure and lung volume of uninjured dogs. We found that the respiratory system compliance opposing ventricular filling is much less than is predicted from the compliance opposing tidal ventilation. This suggests that cardiac filling imposes a local shape change rather than a general lung volume change. Injury only slightly decreased cardiac filling compliance although it markedly reduced lung inflating compliance. These results are consistent with citations showing that edema increases lung compliance by altering surface properties and airway closure with little change in tissue deformability. Thus, while edema may alter cardiac performance by changing pleural pressure, it has little influence on the pulmonary component of diastolic compliance.
Forced noise mechanical parameters during inspiration and expiration
Authors: Miller T. K. , Pimmel R. L.
Published: December 2017

Using the forced random noise technique we collected three 5-min records of pressure and flow signals in five clinically normal nonsmoking adults. Each recording was analyzed to obtain respiratory impedance spectra from data obtained during continuous sampling, midinspiration, and midexpiration. Estimates of respiratory resistance, inertance, and compliance were obtained by regression analysis on each impedance spectrum. Mean expiratory resistance and compliance were significantly (P less than 0.01) greater than corresponding mean inspiratory values, while mean expiratory inertance was significantly (P less than 0.001) less than the mean inspiratory value. Parameters from continuous sampling agreed fairly well with inspiratory resistance and inertance and with expiratory compliance. The coefficient of variation of parameters from continuous data were similar to, or smaller than, those from inspiratory or expiratory data. Thus continuous sampling appears to be an acceptable approach for collecting random noise data.
Comparison of pulmonary and extrapulmonary extraction of biogenic amines
Authors: Pitt B. R. , Hammond G. L. , Gillis C. N.
Published: December 2017

Multiple indicator-dilution technique was used to study the effect of altered blood flow and imipramine (8 mg/kg) on extraction (E) of trace amounts of 5-hydroxy[14C]tryptamine (5-[14C]HT) and [3H]norepinephrine ([3H]NE) in pulmonary (n = 6) and hindlimb (n = 6) circulations of anesthetized dogs. Increasing cardiac output (via right-heart bypass) from 63 to 112 ml.min-1.kg-1 did not significantly affect pulmonary amine extraction [E(5-[14C]-HT), 73 +/- 4%; E([3H]NE), 51 +/- 3%], whereas decreasing cardiac output to 13 ml.min-1.kg-1 led to significant increases in extraction of either amine (P less than 0.05). Imipramine significantly decreased pulmonary amine extraction with greatest inhibition noted at the lowest cardiac output. Hindlimb E(5-[14C]HT) and E([3H]NE) was 49 +/- 6 and 33 +/- 3%, respectively, at hindlimb blood flow of 104 ml/min and was not affected by changes in hindlimb blood flow from 47 to 202 ml/min. Although hindlimb (5-[14C]HT) was significantly less than pulmonary E(5-[14C]-HT), it was similar in that imipramine significantly decreased hindlimb E(5][14C]HT) to 26% (P less than 0.01) suggesting that part of hindlimb 5-HT extraction may involve a drug-sensitive carrier-mediated process as has been shown in lung. The difference in magnitude between the two beds may be a function of decreased endothelial cell surface area in the hindlimb compared with lung. Since pulmonary and hindlimb extraction of trace amounts of these amines appears to be insensitive to changes in blood flow near normal regional blood flow, indicator-dilution techniques appear to be useful in evaluating alterations in the metabolic capacity of the microcirculation of intact animals.
Effects of horizontal body casting on the baroreceptor reflex control of heart rate
Authors: Billman G. E. , Dickey D. T. , Sandler H. , Stone H. L.
Published: December 2017

The purpose of this study was to investigate the effects of long-term horizontal body position on baroreceptor reflex control of heart rate. Six male rhesus monkeys (6.2–9.4 kg) were given bolus injections of 4.0 micrograms/kg phenylephrine during each of the following conditions: awake, anesthetized (10 mg/kg ketamine HCl), and after beta-blockade (1 mg/kg propranolol HCl) before, 7, 14, and 28 days after being placed in a horizontal body cast. R-R interval vs. systolic arterial pressure was plotted, and the slope was determined by least-squares-fit linear regression. Baroreceptor slope was significantly reduced by 7 days of horizontal body position and remained attenuated throughout the 28-day restraint period both before and after beta-receptor blockade. These data are consistent with the thesis that prolonged exposure to a zero-gravity environment impairs autonomic reflex regulation of the cardiovascular system.
Exercise performance after ventilatory work
Authors: Martin B. , Heintzelman M. , Chen H. I.
Published: December 2017

Although increased ventilation is one of the most readily observed physiological responses to exercise, it is uncertain how severely this hyperpnea stresses the ventilatory muscles. As one approach to this question, we compared short-term maximal running performance in nine subjects with and without prior ventilatory work designed to reduce ventilatory muscle endurance. This work consisted of 150 min of sustained maximum ventilation performed isocapnically while the subjects were seated. Both the level of sustained expired minute ventilation and the O2 uptake associated with it slowly declined with time during this 150-min period. On the average, subjects were able to maintain two-thirds of their 12-s maximum voluntary ventilation (MVV) during this long-term breathing test. The test had no effect on subsequently measured vital capacity, forced expiratory volume in 1 s, or the MVV. However, in short-term maximal running, at constant speed upgrades increased 1% each minute until volitional exhaustion, performance after prior breathing work was reduced as compared with control (6.5 vs. 7.6 min; P less than 0.01). Subjects ceased work at significantly lower ventilation (117 vs. 124 1.min-1 BTPS; P less than 0.05) and heart rate (179 vs. 187 beats.min-1; P less than 0.01) and reached significantly lower peak O2 uptake (3.07 vs. 3.24 1.min-1 STPD; P less than 0.05) during maximal running after ventilatory work. We conclude that reduced ventilatory muscle endurance alone is sufficient to decrease short-term maximal running performance.
Influence of joint position on ankle plantarflexion in humans
Authors: Sale D. , Quinlan J. , Marsh E. , McComas A. J. , Belanger A. Y.
Published: December 2017

The contractile properties of the triceps surae (medial and lateral gastrocnemii and soleus) have been studied in humans. In comparison with most other human muscles, the triceps complex had a slow twitch (mean contraction and half-relaxation times 112.4 +/- 11.1 and 99.6 +/- 14.4 ms, respectively) and a low tetanus fusion frequency (60 Hz). Stretching the muscle caused both the contraction and half-relaxation times to become longer. With the knee bent, the optimum length for torque development corresponded to almost full dorsiflexion of the ankle. Similar results were obtained with the knee extended. The optimum position of the ankle differed considerably from the position of the joint when the leg was at rest. Although the position of the ankle joint affected electromyographic (EMG) activity recorded during maximal voluntary contraction, there was little change in the EMG-to-M wave ratio.
Automatic dew-point temperature sensor
Authors: Graichen H. , Rascati R. , Gonzalez R. R.
Published: December 2017

A device is described for measuring dew-point temperature and water vapor pressure in small confined areas. The method is based on the deposition of water on a cooled surface when at dew-point temperature. A small Peltier module lowers the temperature of two electrically conductive plates. At dew point the insulating gap separating the plates becomes conductive as water vapor condenses. Sensors based on this principle can be made small and rugged and can be used for measuring directly the local water vapor pressure. They may be installed within a conventional ventilated sweat capsule used for measuring water vapor loss from the skin surface. A novel application is the measurement of the water vapor pressure gradients across layers of clothing worn by an exercising subject.
Lung inflation, lung solute permeability, and alveolar edema
Authors: Egan E. A.
Published: December 2017

A series of experiments in anesthetized rabbits were conducted to determine whether hyperinflation of the lung alone could produce a protein-permeable lung epithelium and whether a protein-permeable lung epithelium allowed accumulation of liquid in the alveolar space. Some animals had their entire lungs subjected to distending pressures; others had only an area of the lung subjected to the high distending pressure. Alveolar liquid was measured by dilution of radioactive solutes upon instillation of saline into atelectatic lung, and protein permeability was determined by the loss of labeled albumin from the alveolar space over 40–60 min. Inflation of the entire lung at 40 cmH2O for 20 min increases air-space gas volume three- to fourfold, does not produce a protein-permeable epithelium, and does not result in accumulation of alveolar liquid. Distension of a small area of the lung by 40 cmH2O pressure for 20 min increases the gas volume 6- to 12-fold and produces a protein-permeable epithelium, but does not result in liquid accumulation in the alveoli. It is concluded that only very high distending volumes cause the lung epithelium to become permeable to protein and that a protein-permeable epithelium alone does not induce alveolar edema.
A rapid technique for dynamic calibration of electromagnetic flowmeters
Authors: Hill R. D.
Published: December 2017

A new technique for the dynamic calibration of electromagnetic flowmeters has been developed that uses a simple transistor circuit and is suitable for both sine- and square-wave flowmeters. The magnet current is amplitude modulated using a square wave at a frequency of 1 Hz to provide a suitable input to the flowmeter. This input simulates the input that would have been generated is a square-wave oscillatory flow had been passed through a flow probe. The modulating square wave together with the square wave from the flowmeter output are sampled using a digital computer, and comparison of the Fourier transforms of the two waveforms yields a calibration of amplitude attentuation and phase lag for frequencies up to 50 Hz. The technique is very fast and thus allows multiple determinations of the calibration, which in turn lead to a more accurate calibration that has been achieved by other methods. The calibration of a Statham SP2202 flowmeter is presented providing an example of the technique.
Fibrinopeptide A after strenuous physical exercise at high altitude
Authors: Bartsch P. , Schmidt E. K. , Straub P. W.
Published: December 2017

To examine hemostasis after physical exercise at altitudes easily accessible to tourists by public transport, 20 young male volunteers were exposed to 3,457 m above sea level. Ten of them were subjected to an exhaustive exercise for about 8 min on a bicycle ergometer. The preexercise samples (n = 20) taken 1 h after arrival showed no significant alteration of coagulation compared with control values at 600 m. After the exercise the clotting times (P less than 0.001) and euglobulin lysis times (P less than 0.001) were shortened, whereas factor VIII activity (P less than 0.001) was elevated. There was, however, no significant difference in fibrinopeptide A levels between the exercise and the control group. Ethanol gelation test remained negative. We found no rise in fibrin(ogen) degradation products and fibrin(ogen) fragment E and thus conclude that there is no evidence for clinically relevant intravascular coagulation after short-term strenuous physical exercise at altitude.
Determination of ventilatory pattern in REM sleep in normal infants
Authors: Haddad G. G. , Lai T. L. , Mellins R. B.
Published: December 2017

Using methods that we devised for detecting and counting eye movements on the electrooculogram (EOG), we studied tidal volume (VT) and total respiratory cycle time (Ttot) as a function of the frequency of rapid eye movements (REM) during REM sleep in nine normal infants at 1 mo of age. In each of the nine infants, the mean VT and mean Ttot decreased with increasing frequency of eye movements. Instantaneous minute ventilation (VT/Ttot or V), however, did not change with the frequency of eye movements. In addition, there was no consistent change in the variability of VT, Ttot, or V when studied as a function of the frequency of eye movements. Our data support the notion that the ventilatory pattern in REM sleep depends in part on mechanisms that are inherent to REM sleep.