bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative physiology of the high-pressure neurological syndrome--compression rate effects
Authors: Brauer R. W. , Beaver R. W. , Lahser S. , McCall R. D. , Venters R.
Published: December 2017

The effect of compression rate on onset of high-pressure convulsions has been studied in 14 vertebrate species, as well as in 10 mouse strains and 4 rat strains. Compression rate effects were observed in 9 of the 14 species. They appear to be independent of exposure temperature, correlate only very loosely with phylogenetic position, and appear to reflect species-specific compensatory mechanisms grafted onto an underlying convulsion-producing effect of high hydrostatic pressure. Five vertebrate species distributed among three of the four classes tested failed to show a significant degree of compression rate dependence of high-pressure neurological syndrome (HPNS) convulsion thresholds. The implications of this finding for the formulation of hypotheses regarding the biophysical basis for HPNS convulsions has been discussed. Comparison of intrinsic HPNS susceptibility in different species, in the light of these findings, requires that the comparison be made at a common compression rate. Four of the five lower vertebrate species fall consistently into the category showing high HPNS convulsion threshold pressures regardless of the compression rate employed, whereas the two primates and the one carnivore tested equally consistently fall in the low convulsion threshold pressure category. The data suggest a parallel between the degree of brain development and the relative HPNS susceptibility of a given species and contrast with the inverse relations observed during maturation of newborn mice and rats. The results are compared with data for other convulsants and suggest grouping HPNS and pentylenetetrazole seizures as against electroshock, hyperoxic, flurothyl, strychine, or picrotoxin convulsions.
Hydroxyl radical formation in phagocytic cells of the rat
Authors: Drath D. B. , Karnovsky M. L. , Huber G. L.
Published: December 2017

Polymorphonuclear leukocytes (PMN) and macrophages, harvested from the peritoneum and lung, release superoxide (O-.2) and hydrogen peroxide (H2O2) during phagocytosis. These two agents are thought to react with each other to produce a highly active oxidative substance known as hydroxyl radical (OH.). We present evidence suggesting that these radicals are generated by phagocytic cells of the rat. Our findings are based upon an assay where ethylene gas is generated from methional by the action of this radical. Ethylene generation was shown to be inhibited by superoxide dismutase, catalase, and scavengers of OH.. Of the cells examined, PMN generated the most ethylene from methional, exhibiting a fourfold increase during phagocytosis. Pulmonary and peritoneal macrophages caused smaller amounts of this gas to be formed. Regardless of cell type, an intact cell was required for ethylene generation. Zymosan appeared to be the most effective particle for all cells in ethylene formation from methional, although opsonization was critical only for PMN. Ethylene generation was dependent on cell concentration to an extent and increased with time.
Chronic response of rat brain norepinephrine and serotonin levels to endurance training
Authors: Brown B. S. , Payne T. , Kim C. , Moore G. , Krebs P. , Martin W.
Published: December 2017

Norepinephrine (NE) and serotonin (5-HT) concentrations were determined in three areas of the rat brain following 8 wk exposure to differing physical activity and dietary regimens. Animals were divided into sedentary and exercise groups, and one-half of each received either a normal or atherogenic diet. The exercise consisted of 30 min of treadmill running, 5 days/wk, for 8 wk. Brains were weighed and sectioned into cerebral cortex, cerebellum, and remainder (midbrain), and fluorometrically analyzed for NE and 5-HT content. In most brain areas, NE and 5-HT levels were significantly greater among exercise-normal diet and exercise-fat diet compared to both sedentary groups. In the cerebral cortex, exercise-normal diet rats possessed higher levels of NE and lower concentrations of 5-HT than sedentary animals. The atherogenic diet did not affect amine levels other than 5-HT in the cortex among exercise rats. The NE results are consistent with prior research indicating its control of sympathetic function. Increased levels of 5-HT in the midbrain may be the neurotransmittal adaptation responsible for decreased appetite and enhanced weight loss following chronic endurance exercise.
Effects of sitting up on pulmonary blood pressure, flow, and volume in man
Authors: Fournier P. , Mensch-Dechene J. , Ranson-Bitker B. , Valladares W. , Lockhart A.
Published: December 2017

Pulmonary vascular pressure, blood flow, and blood volume were measured in the supine and sitting positions in eight subjects with localized lung carcinoma associated with moderate airway obstruction. Supine cardiac output, pulmonary wedge (Ppw) and artery (Ppa) pressure, and pulmonary vascular resistance (PVR) were normal. Circulatory changes in sitting position were also normal: heart rate increased 13 +/- 9% (mean +/- SD); stroke volume fell 21 +/- 15%; cardiac output fell 13 +/- 19%; and arteriovenous O2 difference increased 37 +/- 21%. Neither the difference between mean Ppa and mean Ppw nor the rise of PVR from 92 +/- 25 to 122 +/- 49 dyn.s.cm-5 in sitting position were significant. Pulmonary blood volume (PBV) as measured by a dye-bolus-injection technique fell from 517 +/- 122 ml supine to 360 +/- 43 ml sitting (P less than 0.01). This decrease is best explained by closure of alveolar vessels in the upper part of the lung and by the concomitant cessation of flow in corresponding extra-alveolar vessels, which would prevent distribution of dye in the region. Circumstantial evidence suggests the latter vessels remain open under the large expanding stresses that prevail in the upper lung.
Accentuated hypoxemia at high altitude in subjects susceptible to high-altitude pulmonary edema
Authors: Hyers T. M. , Scoggin C. H. , Will D. H. , Grover R. F. , Reeves J. T.
Published: December 2017

To investigate the hypotheses that activated coagulation, catecholamine release, or arginine vasopressin release are involved in the pathogenesis of high-altitude pulmonary edema (HAPE), we measured these variables in seven subjects susceptible to HAPE and in nine control subjects at an altitude of 1,600 m, and after 6 and 12 h at a simulated altitude of 4,150 m. Each subject was studied twice, once after 3 days of placebo medication and once after 3 days of premedication with aspirin and dipyridamole. At high altitude, HAPE-susceptible subjects showed significantly exaggerated hypoxemia and a slightly higher end-tidal carbon dioxide partial pressure that did not account fully for the hypoxemia. Fibrinolytic activity was significantly accelerated in both groups at high altitude, whereas other coagulation measurements, catecholamines and arginine vasopressin levels, and pulmonary function tests were not significantly changed. Similar findings were obtained after both placebo and platelet-inhibitor premedication. The results indicate that none of the three hypothesized mechanisms, i.e., activated coagulation, excessive catecholamine release, or antidiuresis, would account for HAPE susceptibility. Instead, HAPE-susceptible subjects exhibited exaggerated hypoxemia associated with relative hypoventilation and a widened alveolar-arterial gas pressure difference.
Inhibition of converting enzyme activity by acute hypoxia in dogs
Authors: Stalcup S. A. , Lipset J. S. , Legant P. M. , Leuenberger P. J. , Mellins R. B.
Published: December 2017

We studied the effect of a change in oxygen tension on converting enzyme activity in anesthetized, paralyzed, catheterized dogs ventilated with room air, 100% O2, and hypoxic gas mixtures. Bradykinin was continuously infused into the femoral vein and simultaneous samples drawn from the pulmonary artery and left atrium; bradykinin was extracted into ethanol and measured by radioimmunoassay. Clearance of bradykinin by lung converting enzyme decreased from 96% at PaO2 levels above 95 Torr to 0% below 26 Torr. Inhibition of enzyme activity was rapid in onset (less than 2 min), closely correlated with PaO2 (r = 0.92, P less than 0.001), and reversible within 2 min after return to room air breathing. Converting enzyme activity of the systemic vascular bed was also inhibited by hypoxia; kininase I activity was unaffected by oxygen tension. Although arterial bradykinin concentrations in the range of 0.5 ng/ml produced hypotension in normoxic animals, elevations to 30 ng/ml had no hypotensive effect in hypoxic dogs. During acute hypoxia, venous bradykinin will pass through the lung unmetabolized, and local levels of angiotensin II and bradykinin will vary in vascular beds with different oxygen tensions, providing a finely-graded mechanism for blood flow regulation.
Influence of cardiac output on intrapulmonary shunt
Authors: Lynch J. P. , Mhyre J. G. , Dantzker D. R.
Published: December 2017

The effect of changing cardiac output on intrapulmonary shunt was studied in the setting of hemorrhagic pulmonary edema induced by intravenous oleic acid in 17 alpha-chloralose-anesthetized dogs. The dogs were mechanically ventilated and cardiac output was alternately depressed and augmented using either pharmacologic means or mechanical alteration of venous return. Following oleic acid, the measured ventilation-perfusion distributions, as measured by the multiple inert gas elimination technique, demonstrated a two-compartment blood flow distribution consisting of shunt and normal units. Changes in cardiac output were not associated with change in the shape of the distributions but there was a significant linear correlation between the level of cardiac output and the shunt fraction. The shunt fraction also varied directly with the mixed venous partial oxygen pressure and inversely with the pulmonary vascular resistance. These data suggest that shunt and nonshunt vessels behave differently in response to alterations of blood flow and emphasize that any interpretation of changes in shunt in the setting of diffuse lung injury must be interpreted in light of changes in cardiac output.
Wind speed limits to work under hot environments for clothed men
Authors: Kamon E. , Avellini B.
Published: December 2017

Four heat-acclimated clothed young adult men exercised (treadmill) at metabolic rate of 191 W.m-2 (27% VO2 max), under five air temperatures (Ta) between 36 and 53 degrees C and three wind velocities (v), 1, 2, and 4 m.s-1, for 2 h. The 2nd h of each experiment involved progressive increases in the ambient vapor pressure (Pa) to force an upward inflection of the rectal temperature (Tre). The Tre point of inflection identified the critical Pa (Pcrit) for each Ta. The average mean skin temperature (Tsk = 36 degrees C for all Pcrit. Straight-line isotherms for Tsk = 36 degrees C, which agreed with the negative regressions of the Pcrit on Ta, represented the limits of exposure for Ta less than or equal to 44 degrees C. The slope characteristics of the isotherms corresponded with skin wettedness (w) of 0.94, 0.71, and 0.58, respectively, for v of 1, 2, and 4 m.s-1. For Ta greater than 44 degrees C the limit line corresponded with steeper negative regressions indicating a lower w than for Ta less than or equal to 44 degrees C. Despite the increase in the ambient evaporative capacity due to the higher v the limit lines describing exposure limits were not significantly different either at Ta less than or equal to 44 degrees C for v of 2 and 4 m.s-1 or at Ta greater than 44 degrees C for all three v.
Effect of a mild exercise program on myocardial function and the development of hypertrophy
Authors: Cutilletta A. F. , Edmiston K. , Dowell R. T.
Published: December 2017

Cardiac function and the development of myocardial hypertrophy were studied in rats conditioned by an exercise program consisting of 8 wk of running on a treadmill. At the end of the training period a group of exercised and sedentary rats was subjected to hemodynamic evaluation under general anesthesia. Except for a slight elevation in the heart rates of the exercised animals there were no significant differences between the exercised and sedentary rats at rest. Following an increase in afterload or a period of hypoxia, the cardiac index of the exercised animals remained significantly higher than that of the sedentary controls. These differences were related to changes in stroke volume. Another group of exercised and sedentary animals underwent either constriction of the ascending aorta or a sham operation. Sedentary rats developed significant hypertrophy at 3 days but had no hypertrophy at 1 day after aortic constriction. Exercised rats, however, developed significant myocardial hypertrophy by 1 day after pressure overload. These data suggest that the heart from an exercised animal is better able to tolerate increases in afterload and hypoxia and can respond with compensatory myocardial hypertrophy more rapidly than the heart of a sedentary animal.
Acid-base curve nomogram for chimpanzee blood and comparison with human blood characteristics
Authors: Takano N. , Lever M. J. , Lambertsen C. J.
Published: December 2017

An acid-base nomogram for chimpanzee blood was constructed. Blood was drawn from eight lightly anesthetized chimpanzees. Each sample of blood was oxygenated and nine aliquots were prepared with three different concentrations of hemoglobin and three different amounts of added acid or base. Each aliquot was equilibrated at two PCO2 levels and the pH was measured and plotted on pH-logPCO2 coordinates. Using the intersection point of these pH-logPCO2 lines as a point of equal hemoglobin-independent “base excess” for each condition, values for true base excess were plotted. Connecting these values provided a Cartesian PCO2-pH base excess nomogram for the chimpanzee comparable to that devised by Siggaard-Andersen for humans. Examination of blood from normal human subjects by the same methods showed no appreciable differences from the original Siggaard-Andersen nomogram. However, the PCO2-pH-base excess nomogram for chimpanzee blood deviated slightly from that for human blood. It is possible that the deviation is related to an arterial bicarbonate concentration in the chimpanzee slightly higher than that in human.
Circulatory regulation during exercise in different ambient temperatures
Authors: Nadel E. R. , Cafarelli E. , Roberts M. F. , Wenger C. B.
Published: December 2017

Three relatively fit subjects performed duplicate 20- to 25-min cycle ergometer exercise bouts at moderate and heavy intensities (40% and 70% Vo2 max) in ambient temperatures of 20, 26, and 36 degrees C. They approached a steady state in internal body temperature (Tes) in all but the heavy exercise in the heat, where Tes rose consistently, averaging 38.84 degrees C at the termination of exercise. Cardiac output (Q), estimated by a rebreathing technique, was proportional to Vo2 and independent of the body temperatures, except during the lower exercise intensity in the heart, where Q averaged 1.31 . min -1 higher throughout. In any environment, forearm blood flow was linearly related to Tes above the Tes threshold for vasodilation, but during heavy exercise in the heat this relationship was severely attenuated above a Tes around 38.0 degrees C, when forearm blood flow exceeded 15 ml.min -1 .100 ml -1. Plasma volume decreases during exercise were primarily a function of the intensity of exercise. During heavy exercise in the heat the relative vasconstriction contributes to the maintenance of an adequate stroke volume preventing a fall in Q. In this case, circulatory regulation has precedence over temperature regulation.
Muscle strength and speed of movement in relation to age and muscle morphology
Authors: Larsson L. , Grimby G. , Karlsson J.
Published: December 2017

Maximum values for isometric strength, dynamic strength, and speed of movement (MEV) in the quadriceps muscle were measured in 114 male subjects who were between 11 and 70 yr. Biopsy samples were taken from the quadriceps muscle in 51 of the subjects (22–65 yr. old). Isometric and dynamic strength increased up to the third decade, remained almost constant to the fifth decade, and then decreased with increasing age. However, no measurable external atrophy of the quadriceps muscle, explaining the decline in strength, could be seen in old age. Histochemical changes in the muscle tissue such as decreased proportion of type II fibers and a selective atrophy of type II fibers, were seen with increasing age. The strength decline in old age was also observed to correlate significantly with the type II fiber area. Multiple regression analyses indicated, however, that mechanisms other than the type II fiber atrophy might be responsible for the decline in strength performance during aging. The implications of these findings are discussed.
Flow-volume curves of excised right and left rabbit lungs
Authors: Yokoyama E.
Published: December 2017

Static pressure-volume (PV) curves and flow-volume (VV) curves of excised right and left rabbit lungs obtained by forced and passive deflation were compared. Deflation PV curves in which the volume was expressed as either ml/lung weight or percent total lung capacity were nearly identical between right and left lungs. Descending limbs of the forced VV curves in which the flow divided by vital capacity (VC) was plotted against %VC generally agreed between right and left lungs, although peak flow tended to be higher in left lungs. However, the flow obtained during passive deflation was higher in left lungs over most of the deflation suggesting that the resistance of proximal airways per unit volume is lower in left than in right lungs.
Mean alveolar gases and alveolar-arterial gradients in pulmonary patients
Authors: Luft U. C. , Loeppky J. A. , Mostyn E. M.
Published: December 2017

In view of uncertainties about the best way to estimate mean alveolar gases in patients with ventilation-perfusion inequalities, three different methods were evaluated on 54 patients. 1) O2 and CO2 were recorded by mass spectrometer on an O2 (x)-CO2 (y) diagram. The coordinates at the intersect of the expiratory record with the mixed expired R line (RE) ives the mean alveolar values (PAo2 and PAco2. 2)pa'co2 was calculated with the Bohr equation using a predicted anatomic dead space and PA'o2 was derived with the alveolar equation. 3) End-tidal (ET) P02 were averaged over 1 min at rest in steady state. Mean RET calculated from 3 was identical with RE. Mean values for PAco2, PA'CO2. and PETco2 differed by less that 1 Torr, but the variance was least with the end-tidal method. There was a highly significant correlation between delta aAPco2 using PETco2 and VD/VT, better than with either of the other methods. The end-tidal measurement appears to give the best approximation of mean alveolar gas in pulmonary patients.
A method for continuous measurement of ammonia in respiratory airways
Authors: Larson T. V. , Covert D. S. , Frank R.
Published: December 2017

A method has been developed that can continuously measure respiratory NH3 with a detection limit of 30 parts per billion by volume (ppbv) at an averaging time of 1 s. The method is based on the chemiluminescent detection of NO, which is produced by oxidizing NH3 at 850 degrees C. A polyethylene sampling probe, incorporating a heated capillary tip bathed in dry, NH3-free diluent air, minimizes NH3 losses due to absorption in breath condensate. In one subject, flow and tidal volume were monitored during quiet mouth breathing while NH3 and CO2 were sampled at the lips. In 10 subjects, NH3, and CO2 were sampled at the lips during quiet mouth breathing ranged from 280 to 1,280 ppbv (mean plus or minus SE, 540 PLUS OR MINUS 85 PPBV).
Catecholamines in dogs during cold adaptation by repeated immersions
Authors: Therminarias A. , Chirpaz M. F. , Lucas A. , Tanche M.
Published: December 2017

Dogs were immersed in cold water 1 h/day for 30 consecutive days. During the first immersion, oxygen uptake increased approximately sevenfold and colonic temperature decreased; a large increase in plasma epinephrine and norepinephrine concentrations was found; plasma glucose, lactic acid, and free fatty acid (FFA) concentrations were also increased. An adaptative response to cold was evidenced during the 10th immersion by a further increase in oxygen uptake and a reduction in the fall of colonic temperature; plasma epinephrine, glucose, and lactic acid were diminished whereas FFA were higher. Consequently 10 h spent in cold are sufficient to induce an improved capacity for heat production. An enhanced ability to produce nonshivering thermogenesis mediated by epinephrine or norepinephrine is not obvious because after the 30th immersion no enhanced calorigenic response to epinephrine or norepinephrine infusion was found. In dogs mechanisms other than norepinephrine-enhanced sensitivity might be involved in this kind of cold adaptation.
Graded inspiratory inhibition: specific effects of flow rate
Authors: Baker J. P. , Remmers J. E. , Younes M. K.
Published: December 2017

The effect of inspiratory flow rate on graded inspiratory inhibition was examined in barbiturate-anesthetized paralyzed cats normally ventilated by a phrenic-driven servorespirator. Periodically, the animals were inflated, for a single breath, by a constant-flow volume ramp begun at one of several delays following phrenic onset. The phrenic activity during these volume-ramp test inflations was compared with phrenic activity in the absence of volume feedback. The relation between volume and phrenic inhibition was determined for two different flow rates. Inhibition of phrenic activity began when volume above functional residual capacity (FRC) exceeded a time-dependent threshold and, beyond this threshold, continued in a graded fashion. The threshold for the first detectable inhibition declined as inspiratory time progressed both in intact animals and in pneumotaxic-lesioned animals when phrenic activity reached an apneustic plateau. Inspiratory inhibition was associated with similar lung volume above FRC regardless of whether volume resulted from high or low flow rates, suggesting that the processing of the receptor feedback information offsets flow effects on receptor firing.
Intermittent flow in tendon capillary bundles
Authors: Hills B. A.
Published: December 2017

The capillary bed has been observed in the Achilles tendon of 40 bullfrogs and 10 guinea pigs for periods of up to 2 h. The opening and closing of adjacent capillaries in a perfused area follows the pattern originally described by Krogh for skeletal muscle but the frequency is slower, as anticipated from the lower metabolic rate of tendon. However, superimposed on this "flickering is a much slower process whereby whole bundles of 20–147 capillaries open and close with little overlap in the tissue areas perfused by each. Periods of no flow averaged 39 min in 70 bundles followed in bullfrogs and 43 min in 34 bundles followed in guinea pigs, although a few failed to open in 100 min. This bundle phenomenon is discussed in relation to the serious implications in mathematically modeling the exchange of gases and nutrients between blood and tissue and the possible errors in assuming time averaging when determining blood perfusion rates. Also mentioned are the likely effects of decompression on closed bundles and the notion is introduced that the bundle phenomenon may be a factor determining which tissues can be injured by decompression.
Fluid shifts during initial phase of immersion diuresis in man
Authors: Khosla S. S. , DuBois A. B.
Published: December 2017

The object was to study fluid shifts in man during the 1st h of immersion diuresis. Control experiments were done on subjects lying down in air for 4 h with and without vasopressin. During immersion up to the neck, seven of nine subjects had significant diuresis and natriuresis. In the first 20 min of sitting in 33 degress C water, a hemodilution of 2% of blood volume was observed. As diuresis progressed, hemoconcentration began. When vasopressin was given just before immersion to prevent the diuresis, the hemodilution observed was greater and lasted longer. Thus the hematocrit fell by 1.7 U, plasma osmolality by 6.0 mosmol/kg, plasma proteins by 0.33 g/100 ml, and plasma sodium by 5.0 meq/l. We conclude that a hemodilution of about 4% of blood volume occurs during the early plasma of immersion and the degree of hyposmolality observed suggests that the fluid shifted was more hyposmotic than the interstitial fluid alone, possibly because some intracellular water may have shifted into the bloodstream during immersion.
Training-induced changes in hormonal and metabolic responses to submaximal exercise
Authors: Winder W. W. , Hickson R. C. , Hagberg J. M. , Ehsani A. A. , McLane J. A.
Published: December 2017

Plasma glucagon and catecholamines increase during prolonged submaximal exercise, but the magnitude of the increase is less in endurance-trained individuals than in untrained subjects. We have studied the rapidity at which this adaptation occurs. Six initially untrained healthy subjects exercised vigorously (on bicycle ergometers and by running) 30–50 min/day, 6 days/wk, for 9 wk. Prior to the beginning of training and at 3-wk intervals thereafter, participants were subjected to 90-min bicycle ergometer test work loads that elicited 58 +/- 2% of the subjects' initial maximal oxygen consumption. The major proportion of the training-induced decrement in plasma glucagon and catecholamine responses to exercise was seen after 3 wk of training. We conclude that the hormonal component of the training adaptation occurs very early in the course of a vigorous endurance training program.
Longitudinal mixing in pulmonary airways: comparison of inspiration and expiration
Authors: Ultman J. S. , Thomas M. W.
Published: December 2017

The increase in dispersion of an inert tracer bolus of helium (He) or sulfur hexafluoride (SF6) was used as a direct and noninvasive measure of longitudinal mixing in the conducting airways. Over a 0- to 260-ml range of bolus penetration, a change in the inspiratory flow from 0.35 to 1.2 l/s did not affect the dispersion of He and SF6, this implies that pure convective dispersion is the dominant inspiratory mixing process. The same change in expiratory flow caused a significant increase in SF6 dispersion only; this indicates that Taylor dispersion is important during expiration. In experiments performed at a fixed penetration of 160 ml and with SF6 only, the inspiratory and the expiratory flows were independently varied from 0.18 to 5.4 l/s. Though the bolus dispersion exhibited a mildly negative correlation with inspiratory flow, it was linearly correlated with expiratory flow. From the former result we conclude that although inspiratory mixing occurs primarily by convective dispersion, there is also a small degree of turbulent dispersion. The latter result confirms that expiratory mixing is primarily due to Taylor dispersion.
Influence of expiratory flow rate on "closing volume" measurement
Authors: Osmanliev D. P. , Popov P. K.
Published: December 2017

The influence of expiratory flow rate (VE) on the onset of phase IV was studied in 15 normal subjects. VE was controlled voluntarily and varied between 0.2 and 2.5 l/s. All subjects showed significantly higher values for CV/VC, % at expiratory flow rate of 1.0 and 1.5 l/s, compared to those estimated at 0.2 l/s. The correlation between CV and volume of flow limitation (VFL) was also studied. For most of the subjects a considerable disagreement between the two values at very low VE was found. At higher flows, however, CV and VFL agreed well. Our results indicate that CV measurement is markedly influenced by VE in the range 0.2--1.5 l/s. This finding gives further support to the hypothesis that CV is determined in part by dynamic flow-limiting properties of the lung as well as by true airway closure.
Tonometer for calibration and evaluation of oxygen microelectrodes
Authors: Proctor K. G. , Bohlen H. G.
Published: December 2017

A temperature-controlled tonometer for the calibration of oxygen microelectrodes is described. The tonometer equilibrated a fluid with a known gas tension within 30 s and has eliminated many problems previously associated with microelectrode evaluation.
Dynamic mechanisms determine functional residual capacity in mice, Mus musculus
Authors: Vinegar A. , Sinnett E. E. , Leith D. E.
Published: December 2017

Awake mice (22.6--32.6 g) were anesthetized intravenously during head-out body plethysmography. One minute after pentobarbital sodium anesthesia, tidal volume had fallen from 0.28 +/- 0.04 to 0.14 +/- 0.02 ml and frequency from 181 +/- 20 to 142 +/- 8. Functional residual capacity (FRC) decreased by 0.10 +/- 0.02 ml. Expiratory flow-volume curves were linear, highly repeatable, and submaximal over substantial portions of expiration in awake and anesthetized mice; and expiration was interrupted at substantial flows that abruptly fell to and crossed zero as inspiration interrupted relaxed expiration. FRC is maintained at a higher level in awake mice due to a higher tidal volume and frequency coupled with expiratory braking (persistent inspiratory muscle activity or increased glottal resistance). In anesthetized mice, the absence of braking, coupled with reductions in tidal volume and frequency and a prolonged expiratory period, leads to FRCs that approach relaxation volume (Vr). An equation in derived to express the difference between FRC and Vr in terms of the portion of tidal volume expired without braking, the slope of the linear portion of the expiratory flow-volume curve expressed as V/V, the time fraction of one respiratory cycle spent in unbraked expiration, and respiratory frequency.
Ventilation and gas exchange during phasic hindlimb exercise in the dog
Authors: Weissman M. L. , Wasserman K. , Huntsman D. J. , Whipp B. J.
Published: December 2017

To investigate the importance of the major neural afferent component from the exercising extremities in exercise hyperpnea, rhythmic contraction of hindlimb muscles was produced in the dog, by electrically stimulating the peripheral cut ends of the sciatic and femoral nerves, bilaterally, for 4- to 5-min periods. VE, VCO2, and VO2 were computed breath-by-breath and PaCO2 was monitored continuously with an indwelling arterial electrode. During exercise, VO2 and VCO2 were approximately doubled in the steady state, rising with t1/2 of 25 +/- 2 and 35 +/- 4 s, respectively. VE increased within five breaths after exercise onset, and thereafter rose to a steady state with a t1/2 of 37 +/- 5 s. Mean PaCO2 increased transiently within the 1st min of stimulation but was not significantly different from control in the steady state. We conclude that the major neural afferent component from the contracting muscles is not an obligatory requirement for normal ventilatory response in the steady state of phasic exercise.
Physical performance and peak aerobic power at different body temperatures
Authors: Bergh U. , Ekblom B.
Published: December 2017

In eight male subjects we studied the effect of different core (esophageal, (Tes 34.9--38.4 degrees C) and muscle (Tm 35.1--39.3 degrees C) temperature on 1) physical performance (time to exhaustion at a standard maximal rate of work, WT), 2) aerobic power (VO2), 3) heart rate (HR), and 4) blood lactate (LA) concentration during exhaustive combined arm and leg exercise. In three subjects the effects at different mean skin temperatures (Tsk 27 and 31 degrees C, respectively) were also studied. Peak VO2 was positively correlated to both Tes (r = 0.88) and Tm (r = 0.91). None of the subjects attained control VO2max at Tes and Tm lower than 37.5 and 38.0 degrees C, respectively. HR was correlated to both Tes (r = 0.97) and Tm (r = 0.95). Different Tsk did not affect peak VO2 and HR at subnormal body temperatures. Pulmonary ventilation was independent of Tes and Tm in all experimental situations. LA was significantly higher at Tes 37.5 degrees C compared to both Tes 34.9 and 38.5 degrees C, respectively. At Tes less than 37.5 degrees C and Tm less than 38.0 degrees C, there was a linear reduction in WT (20%.degrees C-1), peak VO2 (5--6%.degrees C-1), and HR (8 beats.min-1.degrees C-1) with lowered Tes and Tm.
Glucose metabolism in rat lung during exposure to hyperbaric O2
Authors: Bassett D. J. , Fisher A. B.
Published: December 2017

Lung metabolism on exposure to hyperbaric oxygen was studied in rat lungs perfused with artificial media and ventilated with O2 at 0.2, 1, or 5 ATA. During the first 80 min of exposure to O2 at 5 ATA, glucose utilization increased 55%, lactate plus pyruvate production increased 45%, total CO2 production increased 47%, tissue ATP decreased 17%, and the ATP/ADP decreased 29% compared with 0.2 ATA O2. The increased CO2 production was due to a nearly twofold stimulation of pentose cycle activity whereas mitochondrial CO2 production did not change significantly. There were no significant differences in metabolism between lungs studied at 0.2 and 1 ATA O2. During the next hour of perfusion, there was a marked increase in mitochondrial CO2 production of control lungs but tissue ATP/ADP did not change significantly. With oxygen at 5 ATA, mitochondrial CO2 production increased only slightly, tissue ATP/ADP decreased further, and lungs demonstrated accumulation of edema fluid. The results indicate that exposure of lungs to hyperbaric oxygen results in stimulation of NADPH turnover through the pentose cycle and increased ATP generation, although the increased rate was not sufficient to maintain normal ATP/ADP.
Mechanism of decreased blood flow to atelectatic lung
Authors: Benumof J. L.
Published: December 2017

This study examined the relative contribution of passive mechanical forces vs. hypoxic pulmonary vasoconstriction as mechanisms of blood flow reduction through atelectatic canine lung. Selective atelectasis of the left lower lobe caused the electromagnetically measured lobar blood flow to decrease 59% from control levels. Reexpansion and ventilation of the left lower lobe with 95% N2–5% CO2, which should terminate any passive mechanical contribution to the decreased test lobe blood flow, did not cause any significant increase in left lower lobe blood flow. Ventilation of the left lower lobe with 100% O2, which should terminate any hypoxic pulmonary vasoconstriction contribution to the decreased test lobe blood flow, increased blood flow back to levels not significantly different from control. Differences between degree of hypoxia, magnitude of transpulmonary pressure, and absolute pulmonary vascular pressure during left lower lobe atelectasis and ventilation with N2 were considered to be minor influences. I conclude that the mechanism of decreased blood flow to an atelectatic lobe is hypoxic pulmonary vasoconstriction.
Thermoregulation in unrestrained rats during and after exposure to 1.5--4 G
Authors: Giacchino J. , Horwitz B. A. , Horowitz J. M.
Published: December 2017

Unrestrained rats were exposed to cold for 1 h during and immediately after exposure to hypergravic fields (1.5--4 G) to determine if they recover their ability to thermoregulate on reentry to 1-G conditions. In contrast to the decreased body temperatures observed when cold exposure occurred concurrently with acceleration, hypothalamic, carotid, and brown fat temperatures did not fall when rats were exposed to cold immediately after return to 1 G. These results support the hypothesis that the thermoregulatory alterations seen under hypergravic conditions are manifestations of an effect of ongoing exposure to hypergravity and can be reversed on termination of acceleration. The reversibility of the thermoregulatory impairment is apparently unaffected by the magnitude of the acceleration field over a range of 1.5--4 G.
Determinants of gas exchange kinetics during exercise in the dog
Authors: Casaburi R. , Weissman M. L. , Huntsman D. J. , Whipp B. J. , Wasserman K.
Published: December 2017

Following exercise onset, CO2 output (VCO2) and O2 uptake (VO2) increase exponentially, but with appreciably different time constants. To determine the sensitivity of the time courses of these variables to altered ventilatory kinetics, rhythmic exercise was induced abruptly in anesthetized dogs by bilateral stimulation of the peripheral ends of the cut sciatic and femoral nerves. This increased the metabolic rate by 83 +/- 25 (SD) %. The dogs were ventilated with a constant-volume pump, the frequency of which was changed exponentially from the start of the exercise up to the ventilation that returned arterial CO2 and O2 pressure (PCO2 and PO2) in the steady state to resting levels. The time constant (tau) of the increase in ventilation (VE) was varied among trials. VCO2, VO2, end-tidal PCO2 and PO2, and arterial PCO2 were measured breath by breath. tauVO2 was constant at approximately 18 s regardless of alterations in tauVE. In contrast, tauVCO2 was strongly dependent on tauVE, apparently due to the larger body stores for CO2; the transitions were isocapnic when tau VE was approximately 40 s. We conclude that ventilatory dynamics can markedly influence the dynamics of CO2 exchange during exercise, but has no appreciable effect on O2 uptake dynamics.
Thermoregulation in swimmers and runners
Authors: McMurray R. G. , Horvath S. M.
Published: December 2017

Thermoregulatory responses of six trained swimmers and five runners to cold and heat were evaluated during 30 min of exercise (60% VO2max) while immersed to the neck in 20, 25, 30, and 35 degrees C water. Mean oxygen uptake was similar for both groups during all four trials. Changes in metabolic rate during the 8th to 28th min were significantly greater for the runners in 20 degrees C water, and swimmers in 30 and 35 degrees C water. Heart rates, Tsk, delta Tre, Tb, body heat content, and heat storage were dependent on water temperature. Runners were able to attain higher sweat rates than swimmers in 35 degrees C water. Swimmers had significantly greater tissue conductance values in the 35 degrees C exposure. Swimmers thermoregulated better in 20 degrees C water than runners, possibly due to a larger surface area-to-volume ratio, percentage body fat, subcutaneous fat, or improved vasomotor control. Exercise in the heat was better tolerated by runners. Physical training in water does not improve heat acclimatization to the extent of training in air, but does improve cold tolerance.
Acceleration forces at eye level experienced with rotation on the horizontal bar
Authors: Beck G. R. , Rabinovitch P. , Brown A. C.
Published: December 2017

Negative acceleration forces (-Gz) experienced at eye level have been associated with preretinal hemorrhage and headache. These signs and symptoms were found in individuals who experienced negative (toward the head) force while rotating on a horizontal bar or hanging from a trapeze. Lightweight accelerometers were used to measure -Gz experienced at eye level in children and adult gymnasts performing a single-knee backswing on a horizontal bar. Rate of onset of -Gz, peak -Gz, time experiencing -Gz, area of curve (G.second), and mean force (area/time) were calculated. There was no significant difference between the children and the adult gymnasts in any of the above parameters. The best gymnast had a maximum rate of onset of 38.15 G/s and the maximum negative force experienced was 5.52 G. The maximum rate of onset for a child was 41.56 G/s and the maximum negative force experienced was 5.73 G. Compared with -Gz tolerance curves generated on a centrifuge the best gymnast would have become symptomatic while performing this maneuver in 6 s. The best child would have become symptomatic in 25 s. These tolerance limits can be easily exceeded by gymnasts and by the monkey-bar enthusiast.
Hypopnea consequent to reduced pulmonary blood flow in the dog
Authors: Stremel R. W. , Whipp B. J. , Casaburi R. , Huntsman D. J. , Wasserman K.
Published: December 2017

The ventilatory responses to diminished pulmonary blood flow (Qc), as a result of partial cardiopulmonary bypass (PCB), were studied in chloralose-urethan-anesthetized dogs. Qc was reduced by diverting vena caval blood through a membrane gas exchanger and returning it to the ascending aorta. PCB flows of 400--1,600 ml/min were utilized for durations of 2--3 min. Decreasing Qc, while maintaining systemic arterial blood gases and perfusion, results in a significant (P less than 0.05) decrease in expiratory ventilation (VE) (15.9%) and alveolar ventilation (VA) (31.0%). The ventilatory decreases demonstrated for this intact group persist after bilateral cervical vagotomy (Vx), carotid body and carotid sinus denervation (Cx), and combined Vx and Cx. The changes in VE and VA were significantly (P less than 0.001) correlated with VCO2 changes, r = 0.80 and r = 0.93, respectively. These ventilatory changes were associated with an overall average decrease in left ventricular PCO2 of 2.1 Torr; this decrease was significant (P less than 0.05) only in the intact and Cx groups. Decreasing pulmonary blood flow results in a decrease in ventilation that may be CO2 related; however, the exact mechanism remains obscure but must have a component that is independent of vagally mediated cardiac and pulmonary afferents and peripheral baroreceptor and chemoreceptor afferents.
Real-time moment analysis of pulmonary nitrogen washout
Authors: Saniie J. , Saidel G. M. , Chester E. H.
Published: December 2017

A real-time moment analysis was applied to multibreath nitrogen-washout dynamics of the lung. Because the analysis accounts for breathing pattern variations, subjects could perform the washout with spontaneous breathing. The real-time digital processing of the nitrogen and flow signals incorporates filtering, delay compensation, and corrections for the effects of gas composition and temperature changes. In our study, moment analysis of the multibreath washout was evaluated for 37 subjects: 6 normal nonsmokers, 4 “normal” smokers, 6 asthmatics, 12 with diffuse interstitial disease, and 9 with chronic obstructive pulmonary disease. Moments were computed from end-tidal and breath-averaged nitrogen fractions. The ratio of 1st-to-0th moments was found to yield distinctions among subjects with different degrees of ventilation inhomogeneity, even between normal nonsmokers and “normal” smokers. With minimal computational facilities, this moment analysis not only provides a sensitive index of ventilatory dysfunction, but also a cost-effective tool.
Temperature regulation and hypohydration: a singular view
Authors: Senay L. C.
Published: December 2017

Body temperatures of exercising humans who have been denied water are elevated when compared to hydrated controls. The simplest “explanation” for the elevated temperature is a decrease in sensitivity of the sweating mechanism. This and similar “explanations” do not direct attention to basic causes but only the result(s) of more fundamental aspects of regulatory physiology. Among the items considered in this speculative presentation are influences of changes in osmolarity, specific ions, peptide hormones, fluid shifts, and muscular contractions during exercise. A hypothesis is offered for consideration in explaining elevations of body temperature in exercise with and without water replacement. In general, the hypothesis relates changes in hypothalamic osmotic pressure and/or ionic constituents with fluid and ionic events in muscle during exercise. The fluid and ionic shifts are probably proportional to the amount of lean body mass engaged in dynamic exercise. Since blood volume has also been shown to be related to lean body mass, similar relative work loads should lead to similar changes in the osmotic and/or ionic environment of the hypothalamus, thus resulting in similar increases in body temperature during exercise. Hypohydration is superimposed on this basic response. Increases in body temperature of resting hypohydrated subjects appear to be due to increases in osmotic pressure and/or specific ion concentrations. During exercise, these changes are added to those induced by muscle contraction. The focal point of all such ionic and osmotic changes is thought to be neural processes within the hypothalamus.
Vagal effects on histamine, carbachol, and prostaglandin F2 alpha responsiveness in the dog
Authors: Snapper J. R. , Drazen J. M. , Loring S. H. , Braasch P. S. , Ingram R. H.
Published: December 2017

To investigate whether an individual dog's responsiveness to histamine correlates with its responsiveness to other bronchoconstrictor agents and to investigate whether varying vagal effects account for the previously described range of histamine responsiveness, we compared dose-effect relationships of histamine to those of two pharmacological dissimilar agents, carbachol and prostaglandin F2 alpha before and after vagal blockade. There was a highly significant correlation between histamine and both carbachol (P less than 0.001) and prostaglandin F2 alpha (P less than 0.001) responsiveness. The range of responsiveness to prostaglandin F2 alpha was greater than that for histamine or carbachol. When histamine and carbachol were given simultaneously, a purely additive effect was found. Vagal blockade had no significant effect on histamine or carbachol responsiveness, but significantly diminished the responsiveness to prostaglandin F2 alpha; however, it neither narrowed the range nor changed the rank order of responsiveness. We conclude that the range of responsiveness is not specific for any one agent and that vagal mechanisms do not play a role in producing this range.
Heat and acute dehydration effects on acceleration response in man
Authors: Nunneley S. A. , Stribley R. F.
Published: December 2017

Though heat and dehydration each impair acceleration tolerance, interactions among these stresses have not previously been studied. Seven men were dehydrated in heat by 0, 1, and 3% of body weight before a series of +Gz, gradual-onset centrifuge runs with the capsule first 38 degrees C, then 20 degrees C. Heat alone raised heart rate by 6.5 beats/min independent of other stresses. Dehydration and acceleration appeared to act synergistically in raising HR. Heat lowered relaxed G tolerance by 0.3 G; dehydration tended to lower G tolerance and increased the variability of response to heat. A high-tolerance subgroup (n = 4) could normally sustain +7 Gz for 60 s with anti-G suit and straining, but 3% dehydration reduced mean time to 35 s. Dehydration was associated with a decrease in the loss of plasma volume at 7 G. Heat-induced tolerance loss appears similar for both gradual- and rapid-onset centrifuge profiles. In contrast, dehydration effects are greater in rapid-onset runs, evidence that normal anti-G protective mechanisms can partly counteract the effect of fluid deficit. The results are relevant for crew members of high-performance aircraft, where unexpected diminution of their normally high G tolerance can have disastrous consequences.
Effects of endurance training on left ventricular dimensions in healthy men
Authors: Wolfe L. A. , Cunningham D. A. , Rechnitzer P. A. , Nichol P. M.
Published: December 2017

Echocardiography was employed to measure the serial effects of jogging on resting left ventricular dimensions and function. Twelve men were exercised (mean age 36.8 yr) and 10 served as controls (mean age 34.8 yr). Increases of 14 and 18% were observed for predicted aerobic capacity in the training group (TG) after 3 and 6 mo of training, respectively; the control group (CG) displayed a small detraining effect. Echocardiographic findings included a significant (P less than 0.05) reduction in resting heart rate and a moderate increase in stroke volume (SV) in the TG compared to the CG. The increased SV appeared to be due to increased end-diastolic dimensions (LVIDd, LVEDV), secondary to greater ventricular filling rather than a more vigorous ventricular contraction. Posterior wall thickness, septal thickness, and calculated left ventricular muscle mass were not significantly increased in the TG compared to CG after either 3 or 6 mo training. It was concluded that left ventricular structure and resting contractile status are not altered by 6 mo of jogging training in healthy, previously sedentary men.