bluuebunny/crossref_metadata_2025 huggingface dataset:
Life sciences space missions. Overview
Authors: Sulzman F. M.
Published: December 2017

It has been known for many years that weightlessness induces changes in numerous physiological systems: the cardiovascular system declines in both aerobic capacity and orthostatic tolerance; there is a reduction in fluid and electrolyte balance, hematocrit, and certain immune parameters; bone and muscle mass and strength are reduced; various neurological responses include space motion sickness and posture and gate alterations. These responses are caused by the hypokinesia of weightlessness, the cephalic fluid shift, the unloading of the vestibular system, stress, and the altered temporal environment.
IGF-I, growth hormone, and/or exercise effects on non-weight-bearing soleus of hypophysectomized rats
Authors: Roy R. R. , Tri C. , Grossman E. J. , Talmadge R. J. , Grindeland R. E. , Mukku V. R. , Edgerton V. R.
Published: December 2017

The effects of insulin-like growth factor (IGF-I) or growth hormone (GH) with and without exercise on predominantly slow muscles of hypophysectomized hindlimb-suspended (HS) rats were determined. HS resulted in a 21, 23, and 30% decrease in soleus, adductor longus, and vastus intermedius masses, respectively, compared with ambulatory rats. Compared with values in HS rats, IGF-I increased the vastus intermedius mass and GH or exercise alone increased both the soleus and vastus intermedius masses. There was a strong interactive effect between GH, but not IGF-I, and exercise in all three muscles of HS rats. The soleus fiber type distribution of HS rats was not affected by any treatment. HS resulted in a 24, 18 (P > 0.05), 32, and 20% (P > 0.05) decrease in the size of soleus fibers containing type I, IIa, I + IIa, and IIa + IIx myosin heavy chains, respectively, compared with ambulatory hypophysectomized rats. Hormone or exercise alone had no effect on fiber size in HS rats. However, all fiber sizes (except for type IIa + IIx in IGF-I with exercise rats) were larger in HS rats treated with GH or IGF-I and exercise than those in HS rats. These data indicate an interactive effect of both GH and IGF-I with exercise in maintaining fiber size of chronically non-weight-bearing predominantly slow muscles. Furthermore, the results suggest that the myosin heavy-chain phenotype in rats deficient in all pituitary factors is unresponsive to short-term administration of either GH or IGF-I or to exercise or HS.
Bromide dilution in adults: optimal equilibration time after oral administration
Authors: Van Marken Lichtenbelt W. D. , Kester A. , Baarends E. M. , Westerterp K. R.
Published: December 2017

Extracellular water is often estimated by bromide dilution. The time interval between oral administration of the dose and blood sampling varies considerably among studies. Because at least two processes are involved during equilibration (distribution of the dose and bromide leaving the body), we performed a bromide-dilution experiment and analyzed the decay data by fitting a biexponential curve. The experiment was carried out in 11 healthy adults (8 women and 3 men, age 21–39 yr). Bromide ingestion (60 mg Br/l estimated total body water) was followed by blood sampling at 2, 3, 4, 6, 10, 25, and 105 (or 170) h. The bromide concentration in serum ultrafiltrate was determined with high-performance liquid chromatography. The bromide concentration in serum after dose intake showed a significant decrease over time. One-exponent functions significantly fitted the data. The two-exponent functions fitted the data significantly better (F-test, P < 0.0001). A model combining the data from all subjects fitted just as well. Equilibration time can be defined as the time at which the first exponential function, which represents distribution of the dose, has decreased to 5% of its starting value. According to this model, the equilibration time of orally administered bromide should be 8.5–11.7 h. This can be achieved by an overnight equilibration.
Effects of fatiguing stimulation on intracellular Na+ and K+ in frog skeletal muscle
Authors: Balog E. M. , Fitts R. H.
Published: December 2017

The purpose of this study was to describe the alterations in the intracellular concentrations of sodium ([Na+]i) and potassium ([K+]i) and the membrane potential (Em) as a result of fatiguing stimulation of the frog semitendinosus muscle and to relate these changes to the alterations in the sarcolemma action potential and force-generating ability of the muscle. [Na+]i and [K+]i were measured by using ion-selective microelectrodes. Before stimulation (100-ms trains at 150 Hz, 1 stimulus/s for 5 min), [Na+]i, [K+]i, and Em were 16 +/- 1 mM, 142 +/- 5 mM, and -83 +/- 1 mV, respectively. As a result of stimulation, [Na+]i rose to 49 +/- 6 mM and recovered to 16 +/- 2 mM with a time constant (tau) of 70 s.[K+]i fell to 97 +/- 8 mM as a result of stimulation, then recovered to 148 +/- 5 mM with tau = 56 s. Em depolarized to -74 +/- 3 mV then recovered to -83 +/- 2 mV with tau = 53 s. The Na+/K+ permeability ratio of the resting membrane fell 3%, whereas at the peak of the action potential the permeability ratio fell 38%. A previous study using the same muscle and stimulation protocol showed force to recover with a fast initial phase (approximately 2 min) and a much slower second phase (approximately 50 min). The recovery of [Na+]i, [K+]i, and Em was similar to the fast phase of force recovery; thus the altered Na+ and K+ concentration gradient across the sarcolemma and t-tubular membrane may contribute to this component of fatigue. The possible fatigue mechanisms induced by the altered ionic gradients include 1) complete block of the action potential propagation; 2) depolarization-induced inactivation of t-tubular charge movement; and 3) a reduced magnitude of the t-tubular charge due to the lower action potential spike potential.
Air hunger induced by acute increase in PCO2 adapts to chronic elevation of PCO2 in ventilated humans
Authors: Bloch-Salisbury E. , Shea S. A. , Brown R. , Evans K. , Banzett R. B.
Published: December 2017

Brief increases in arterial PCO2 (PaCO2) (lasting several minutes) produce a sensation of respiratory discomfort (air hunger). It is not known whether air hunger adapts to chronic changes in PaCO2. This study tested whether the level of end-tidal PCO2 (PETCO2) required to evoke air hunger would increase with chronic elevation of PETCO2 (lasting several days). Four ventilator-dependent subjects participated in a 2-wk study during which they were ventilated with air (placebo) or air rich in CO2 (CO2 exposure). Average resting PETCO2 during control periods was 25 Torr (typical for such patients); PETCO2 was 15 Torr higher during CO2 exposure. Ventilation and arterial PO2 did not differ between conditions. Periodically, we performed tests in which subjects rated the intensity of air hunger induced by brief increases in PETCO2. The increase in PETCO2 required to elicit a given air hunger rating during CO2 exposure also increased by approximately 15 Torr. That is, subjects' sensation of air hunger fully adapted to the chronic increase in PETCO2. Arterial pH did not fully return to control values during CO2 exposure. Accommodation in the chemoreceptors and neural pathways that subserve air hunger sensation may explain the adaptation of air hunger.
Capacity of circulating neutrophils to produce reactive oxygen species after exhaustive exercise
Authors: Suzuki K. , Sato H. , Kikuchi T. , Abe T. , Nakaji S. , Sugawara K. , Totsuka M. , Sato K. , Yamaya K.
Published: December 2017

To investigate the cause of disagreement within the large body of literature concerning the effect of exercise on the capacity of circulating neutrophils to produce reactive oxygen species (ROS), 10 male endurance-trained athletes underwent maximal exercise. The generation of superoxide radical (O2-.) by neutrophils was first detected on a cell-by-cell basis by using histochemical nitro blue tetrazolium tests performed directly on fresh unseparated blood, which showed that responsive neutrophils under several stimulatory conditions relatively decreased after exercise. Similarly, O2-. detected with bis-N-methylacridinium nitrate (lucigenin)-dependent chemiluminescence (CL) of a fixed number of purified neutrophils on stimulation with opsonized zymosan was decreased slightly after exercise. In contrast, the 5-amino-2,3-dihydro-1,4-phthalazinedione (luminol)-dependent CL response of the neutrophils indicative of the myeloperoxidase (MPO)-mediated formation of highly reactive oxidants was significantly enhanced after exercise. It therefore suggests that the pathway of neutrophil ROS metabolism might be forwarded from the precursor O2-. production to the stages of more reactive oxidant formation due to the facilitation of MPO degranulation. In addition, these phenomena were closely associated with the exercise-induced mobilization of neutrophils from the marginated pool into the circulation, which was mediated by the overshooting of catecholamines during exercise. These findings indicate that the use of different techniques for detecting ROS or the different stages of neutrophil ROS metabolism could explain some of the disparate findings of the previous studies.
Energy expenditure and requirement while climbing above 6,000 m
Authors: Pulfrey S. M. , Jones P. J.
Published: December 2017

Humans survive the low barometric pressure of altitudes above 6,000 m only by making a complex series of adaptations. However, the effects of such adaptations on energy metabolism have not been widely studied. To determine daily energy requirement at extreme altitude, energy expenditure (EE) was measured by doubly labeled water (DLW) and energy intake-balance (IB) methods in five men and one woman while climbing between 5,900 and 8,046 m over a 7-day period. Energy intakes were determined by dietary record (13.8 +/- 2.0 MJ/day). Change in body energy stores, estimated from differences in body weight, skinfold thickness, limb circumference, and isotope-dilution techniques, was -5.1 +/- 1.6 MJ/day. DLW (19.4 +/- 1.2 MJ/day) and IB (18.9 +/- 2.7 MJ/day) measurements of EE provided similar estimates of group mean EE. These results suggest that IB and DLW techniques can yield comparable estimates of group mean EE at extreme altitude. It is concluded that problems of meeting energy requirements while climbing at extreme altitude are related to energy intakes amounting to only roughly 70% of EE.
Inhibitory effect of an intellectual task on breathing after voluntary hyperventilation
Authors: Chin K. , Ohi M. , Fukui M. , Kita H. , Tsuboi T. , Noguchi T. , Otsuka N. , Hirata H. , Mishima M. , Kuno K.
Published: December 2017

We investigated the effects of an intellectual task on posthyperventilation (PHV) breathing by using a video game. Eight normal subjects were placed in a supine positions. The game task by itself led to increase ventilation compared with the control tasks via an increase in the average inspiratory flow rate (P < 0.01) and the respiratory frequency (P < 0.001). After hypocapnic voluntary hyperventilation (VHV), the task led to a decrease in the 1-min PHV breathing level compared with the control tasks after VHV [after VHV, first 60 s average minute ventilation while watching television and while playing a video game are 5.54 +/- 2.91 (SD) and 2.05 +/- 1.40 l/min, respectively; P < 0.01]. Only one subject showed PHV apnea for at least 10 s during the control protocol, whereas seven of the same eight subjects showed PHV apnea while performing the task. After isocapnic VHV, the task still led to a decrease in PHV breathing compared with the control tasks. However, this decrease was smaller than in the hypocapnic studies and was only significant during the first 15 s of recovery. These results suggest that increased activity in the higher centers of the central nervous system has an inhibitory effect on PHV breathing at a time when the effects of short-term potentiation after VHV, hypocapnia, and perhaps other mechanisms would be expected to be acting on breathing.
Electrochemical nitric oxide and nitrogen dioxide analyzer for use with inhaled nitric oxide
Authors: Nelin L. D. , Christman N. T. , Morrisey J. F. , Dawson C. A.
Published: December 2017

The use of inhaled nitric oxide (NO) in research and clinical applications requires the monitoring of NO and its autooxidation product nitrogen dioxide (NO2) in inspired gas and in the ambient environment. We describe an inexpensive electrochemical NO and NO2 analyzer that uses a critical orifice constant-flow controller and a microprocessor crossover correction for the measurement of NO and NO2 in the concentration range relevant to the use of inhaled NO. The analyzer proved to have good accuracy and precision for NO and NO2 in the range of concentrations relevant to studies of inhaled NO. In this range, the performance was similar to that of a chemiluminescence analyzer, and the response characteristics were not affected by varying the O2 concentration of the mixtures analyzed.
Effect of heat stress on glucose kinetics during exercise
Authors: Hargreaves Mark , Angus Damien , Howlett Kirsten , Conus Nelly Marmy , Febbraio Mark
Published: December 2017

Hargreaves, Mark, Damien Angus, Kirsten Howlett, Nelly Marmy Conus, and Mark Febbraio. Effect of heat stress on glucose kinetics during exercise. J. Appl. Physiol. 81(4): 1594–1597, 1996.—To identify the mechanism underlying the exaggerated hyperglycemia during exercise in the heat, six trained men were studied during 40 min of cycling exercise at a workload requiring 65% peak pulmonary oxygen uptake (V˙o 2 peak) on two occasions at least 1 wk apart. On one occasion, the ambient temperature was 20°C [control (Con)], whereas on the other, it was 40°C [high temperature (HT)]. Rates of glucose appearance and disappearance were measured by using a primed continuous infusion of [6,6-2H]glucose. No differences in oxygen uptake during exercise were observed between trials. After 40 min of exercise, heart rate, rectal temperature, respiratory exchange ratio, and plasma lactate were all higher in HT compared with Con ( P < 0.05). Plasma glucose levels were similar at rest (Con, 4.54 ± 0.19 mmol/l; HT, 4.81 ± 0.19 mmol/l) but increased to a greater extent during exercise in HT (6.96 ± 0.16) compared with Con (5.45 ± 0.18; P < 0.05). This was the result of a higher glucose rate of appearance in HT during the last 30 min of exercise. In contrast, the glucose rate of disappearance and metabolic clearance rate were not different at any time point during exercise. Plasma catecholamines were higher after 10 and 40 min of exercise in HT compared with Con ( P < 0.05), whereas plasma glucagon, cortisol, and growth hormone were higher in HT after 40 min. These results indicate that the hyperglycemia observed during exercise in the heat is caused by an increase in liver glucose output without any change in whole body glucose utilization.
Combined heart rate and activity improve estimates of oxygen consumption and carbon dioxide production rates
Authors: Moon Jon K. , Butte Nancy F.
Published: December 2017

Moon, Jon K., and Nancy F. Butte. Combined heart rate and activity improve estimates of oxygen consumption and carbon dioxide production rates. J. Appl. Physiol.81(4): 1754–1761, 1996.—Oxygen consumption (V˙o 2) and carbon dioxide production (V˙co 2) rates were measured by electronically recording heart rate (HR) and physical activity (PA). Mean daily V˙o 2 andV˙co 2 measurements by HR and PA were validated in adults ( n = 10 women and 10 men) with room calorimeters. Thirteen linear and nonlinear functions of HR alone and HR combined with PA were tested as models of 24-h V˙o 2 andV˙co 2. Mean sleepV˙o 2 andV˙co 2 were similar to basal metabolic rates and were accurately estimated from HR alone [respective mean errors were −0.2 ± 0.8 (SD) and −0.4 ± 0.6%]. The range of prediction errors for 24-h V˙o 2 andV˙co 2 was smallest for a model that used PA to assign HR for each minute to separate active and inactive curves (V˙o 2, −3.3 ± 3.5%; V˙co 2, −4.6 ± 3%). There were no significant correlations betweenV˙o 2 orV˙co 2 errors and subject age, weight, fat mass, ratio of daily to basal energy expenditure rate, or fitness. V˙o 2,V˙co 2, and energy expenditure recorded for 3 free-living days were 5.6 ± 0.9 ml ⋅ min−1 ⋅ kg−1, 4.7 ± 0.8 ml ⋅ min−1 ⋅ kg−1, and 7.8 ± 1.6 kJ/min, respectively. Combined HR and PA measured 24-h V˙o 2 andV˙co 2 with a precision similar to alternative methods.
Dextromethorphan affects ventilation differently in male and female rats
Authors: Schlenker Evelyn H.
Published: December 2017

Schlenker, Evelyn H. Dextromethorphan affects ventilation differently in male and female rats. J. Appl. Physiol. 81(5): 1911–1916, 1996.—Subcutaneous administration of aspartic acid results in a long-lasting but reversible depression of ventilation in male but not in female rats. Aspartic acid acts on N-methyl-d-aspartate receptors. The present study tested the hypothesis that a noncompetitive N-methyl-d-aspartate-receptor antagonist, dextromethorphan (Dex), would depress ventilation in female rats and stimulate it in male rats. Moreover, Dex administered prior to aspartic acid should prevent the aspartic acid-induced depression of ventilation in male rats. In female rats, Dex caused a 30% depression of ventilation relative to saline at 5 and 10 mg/kg ( P < 0.01) but not at the highest dose (20 mg/kg). In male rats, Dex had no effect on ventilation. At a dose of 20 mg/kg, Dex depressed oxygen consumption to 50% of the saline value at all time points in female rats ( P < 0.001) and in male rats 45 and 60 min after administration. The time points when Dex depressed ventilation and oxygen consumption were different in female rats, suggesting that the depression of ventilation was not the result of a depression in oxygen consumption. During a hypercapnic challenge (7% CO2), female rats treated with 5 and 10 mg/kg of Dex exhibited a smaller increase in ventilatory response relative to saline treatment. At a dose of 20 mg/kg, the hypercapnic responsiveness of male rats was markedly stimulated (85.8 ± 8.95 ml/min) relative to saline (50.6 ± 9.14 ml/min; P < 0.001). Finally, Dex administered before aspartic acid prevented the aspartic acid-induced depression of ventilation in male rats. Thus, in rats, Dex has gender-specific effects on ventilation and these effects are not associated with changes in oxygen consumption.
Endothelin blockade augments pulmonary vasodilation in the ovine fetus
Authors: Dunbar Ivy D. , Kinsella John P. , Abman Steven H.
Published: December 2017

Ivy, D. Dunbar, John P. Kinsella, and Steven H. Abman.Endothelin blockade augments pulmonary vasodilation in the ovine fetus. J. Appl. Physiol. 81(6): 2481–2487, 1996.—The physiological role of endothelin-1 (ET-1) in regulation of vascular tone in the perinatal lung is controversial. Recent studies suggest that ET-1 contributes to high basal pulmonary vascular resistance in the normal fetus, but its role in the modulation of pulmonary vascular tone remains uncertain. We hypothesized that high ET-1 activity opposes the vasodilator response to some physiological stimuli such as increased pressure. To test the hypothesis that ET-1 modulates fetal pulmonary vascular responses to acute and prolonged physiological stimuli, we performed a series of experiments in the late-gestation ovine fetus. We studied the hemodynamic effects of two ET-1 antagonists, BQ-123 (a selective ETA-receptor antagonist) and phosphoramidon (a nonselective ET-1-converting enzyme inhibitor) during mechanical increases in pressure due to partial ductus arteriosus compression in chronically prepared late-gestation fetal lambs. In control studies, partial ductus arteriosus compression decreased the ratio of pulmonary arterial pressure to pulmonary artery flow in the left lung 34 ± 6% from baseline. Intrapulmonary infusions of BQ-123 (0.5 μg/min for 10 min; 0.025 μg/min for 2 h) or phosphoramidon (1.0 mg/min for 10 min) augmented the peak vasodilator response during ductus arteriosus compression (52 ± 3 and 49 ± 6% from baseline, respectively, P < 0.05 vs. control). In addition, unlike the transient vasodilator response to ductus arteriosus compression in control studies, ET-1 blockade with BQ-123 or phosphoramidon prolonged the increase in flow caused by ductus arteriosus compression. In summary, ETA-receptor blockade and ET-1-converting enzyme inhibition augment and prolong fetal pulmonary vasodilation during partial compression of the ductus arteriosus. We conclude that ET-1 activity modulates acute and prolonged responses of the fetal pulmonary circulation to changes in vascular pressure. We speculate that ET-1 contributes to regulation and maintenance of high pulmonary vascular resistance in the normal ovine fetal lung.
Windchill and the risk of tissue freezing
Authors: Danielsson Ulf
Published: December 2017

Danielsson, Ulf. Windchill and the risk of tissue freezing. J. Appl. Physiol. 81(6): 2666–2673, 1996.—Low air temperatures and high wind speeds are associated with an increased risk of freezing of the exposed skin. P. A. Siple and C. F. Passel ( Proc. Am. Phil. Soc. 89: 177–199, 1945) derived their windchill index from cooling experiments on a water-filled cylinder to quantify the risk of frostbite. Their results are reexamined here. It is found that their windchill index does not correctly describe the convective heat transfer coefficient (hc) for such a cylinder; the effect of the airspeed ( v) is underestimated. New risk curves have been developed, based on the convection equations valid for cylinders in a cross flow, hc ∝ v 0.62, and tissue freezing data from the literature. An analysis of the data reveals a linear relationship between the frequency of finger frostbite and the surface temperature. This relation closely follows a normal distribution of finger-freezing temperatures, with an SD of 1°C. As the skin surface temperature falls from −4.8 to −7.8°C, the risk of frostbite increases from 5 to 95%. These data indicate that the risk of finger frostbite is minor above an air temperature of −10°C, irrespective of v, but below −25°C there is a pronounced risk, even at low v.
Acute alveolar hypoxia increases blood-to-tissue albumin transport: role of atrial natriuretic peptide
Authors: Albert T. S. E. , Tucker V. L. , Renkin E. M.
Published: December 2017

Albert, T. S. E., V. L. Tucker, and E. M. Renkin. Acute alveolar hypoxia increases blood-to-tissue albumin transport: role of atrial natriuretic peptide. J. Appl. Physiol. 82(1): 111–117, 1997.—Plasma immunoreactive atrial natriuretic peptide (irANP) and blood-to-tissue clearance of 131I-labeled rat serum albumin (CRSA) were examined in anesthetized rats during hypoxic ventilation ( n = 5–7/group). Hypoxia (10 min) increased irANP from 211 ± 29 (room air) to 229 ± 28 (15% O2, not significant), 911 ± 205 (10% O2), and 4,374 ± 961 pg/ml (8% O2), respectively. Graded increases in CRSA were significant at 8% O2 in fat (3.6-fold), ileum (2.2-fold), abdominal muscles (2.0-fold), kidney (1.8-fold), and jejunum (1.4-fold). CRSA was decreased in back skin and testes; heart, brain, and lungs were unaffected. The increases in CRSAwere related to irANP and not to arterial[Formula: see text]. Circulating plasma volume was negatively correlated with whole body CRSA. Graded increases in extravascular water content (EVW) were found in the kidney, left heart, and cerebrum and were positively related to CRSA in the kidney. EVW decreased in gastrointestinal tissues; the magnitude was inversely related to CRSA. We conclude that ANP-induced protein extravasation contributes to plasma volume contraction during acute hypoxia.
Short- and long-term effects of testosterone on diaphragm in castrated and normal male rats
Authors: Prezant David J. , Karwa Manoj L. , Kim Helen H. , Maggiore Diane , Chung Virginia , Valentine David E.
Published: December 2017

Prezant, David J., Manoj L. Karwa, Helen H. Kim, Diane Maggiore, Virginia Chung, and David E. Valentine. Short- and long-term effects of testosterone on diaphragm in castrated and normal male rats. J. Appl. Physiol. 82(1): 134–143, 1997.—The effects of short- and long-term testosterone absence or treatment on the diaphragm were studied in castrated and sexually normal male rats. Compared with control rats (untreated normal males), testosterone absence or treatment did not significantly affect costal weight. In untreated castrated males, there were significant decreases in specific forces, type II fiber cross-sectional area, and myosin heavy chain (MHC) isoform 2B after 2.5 wk. In castrated males that received testosterone, there were significant increases in specific forces, type II total fiber proportional area, and relative expression of all adult diaphragm fast MHC isoforms (MHC-2all) after 2.5 wk. In normal males that received testosterone, the only significant finding was an increase in MHC-2B after 2.5 wk. Across all groups, there was close correlation between increases in maximum tetanic forces and MHC-2all. Changes in diaphragm function and composition were closely related to changes in serum testosterone levels at 2.5 wk. The lack of significant change in diaphragm function at 10 wk occurred despite changes in serum testosterone levels and diaphragm composition similar to those at 2.5 wk. These findings support our hypothesis that the effects of testosterone are dependent on basal circulating androgen levels and study duration.
Diaphragm disuse reduces Ca2+uptake capacity of sarcoplasmic reticulum
Authors: Howell Sandra , Zhan Wen-Zhi , Sieck Gary C.
Published: December 2017

Howell, Sandra, Wen-Zhi Zhan, and Gary C. Sieck.Diaphragm disuse reduces Ca2+uptake capacity of sarcoplasmic reticulum. J. Appl. Physiol. 82(1): 164–171, 1997.—Chronic phrenic tetrodotoxin (TTX) blockade and phrenic denervation (Dnv) of hamster diaphragm result in decreased maximum specific tension, prolonged contraction time, and improved fatigue resistance (W. Z. Zhan and G. C. Sieck. J. Appl. Physiol. 72: 1445–1453, 1992). An underlying increased relative contribution of type I fibers to total muscle mass appears to be consistent with, but does not completely account for, changes in contractile and fatigue properties. The present study was designed to evaluate a potential role for altered cellular Ca2+metabolism in the adaptive response of the diaphragm to chronic disuse. An analytic method based on simulation and modeling of long-term45Ca2+efflux data was used to estimate Ca2+ contents (nmol Ca2+/g wet wt tissue) and exchange fluxes (nmol Ca2+ ⋅ min−1 ⋅ g−1) for extracellular and intracellular compartments in the in vitro hamster hemidiaphragm after prolonged disuse. Three groups were compared: control (Con, n = 5), phrenic TTX blockade (TTX, n = 5), and phrenic denervation (Dnv, n = 5). Experimental muscles were loaded with45Ca2+for 1 h, and efflux data were collected for 8 h by using a flow-through tissue chamber. Compartmental analysis of efflux data estimated that the Ca2+ contents and Ca2+ exchange fluxes of the largest and slowest intracellular compartment (putative longitudinal reticulum) were reduced by ∼50% in TTX and Dnv muscle groups compared with Con. In addition, the kinetic model predicted significant decreases in total intracellular Ca2+ and total diaphragm Ca2+ in TTX and Dnv muscles. We conclude that the data support the hypothesis that the capac- ity of the sarcoplasmic reticulum for Ca2+ sequestration is reduced in chronic diaphragm disuse. The impact of this effect on diaphragm contractile and fatigue properties is discussed.
Respiratory transfer impedance between 8 and 384 Hz in guinea pigs before and after bronchial challenge
Authors: Sobh Jamil F. , Lilly Craig M. , Drazen Jeffrey M. , Jackson Andrew C.
Published: December 2017

Sobh, Jamil F., Craig M. Lilly, Jeffrey M. Drazen, and Andrew C. Jackson. Respiratory transfer impedance between 8 and 384 Hz in guinea pigs before and after bronchial challenge. J. Appl. Physiol. 82(1): 172–181, 1997.—We report a forced oscillatory technique for noninvasively measuring respiratory transfer impedance (Ztr) between 8 and 384 Hz in guinea pigs. This technique uses a device consisting of two chambers: one surrounding the animal’s head that is used as a plethysmograph to measured flow through the airway opening and the other that surrounds the animal’s body and is used to apply pressure oscillations to the body surface. Ztr was measured in spontaneously breathing awake guinea pigs and while the animals were anesthetized in normal and methacholine-challenged conditions. An eight-element model consisting of an airway compartment separated from a tissue compartment by a shunt gas compression compartment was fit to the data. Anesthesia increased central and peripheral airway resistance and bronchial airway wall compliance by 13, 31, and 44%, respectively, whereas it decreased tissue compliance by 37%. Compared with the unanesthetized condition, the methacholine challenge (20 μg/kg) resulted in an increase in central and peripheral airway resistance (69 and 319%, respectively) and a decrease in bronchial airway wall and tissue compliance (37 and 79%, respectively). This technique is capable of measuring Ztr in anesthetized and awake guinea pigs. Analysis of these data with this eight-element model provides reasonable estimates of airway and tissue parameters.
Alveolar liquid clearance in multiple nonperfused canine lung lobes
Authors: Grimme John D. , Lane Susan M. , Maron Michael B.
Published: December 2017

Grimme, John D., Susan M. Lane, and Michael B. Maron.Alveolar liquid clearance in multiple nonperfused canine lung lobes. J. Appl. Physiol. 82(1): 348–353, 1997.—We evaluated the ability of canine isolated nonperfused lung lobes to absorb fluid from their air spaces by simultaneously measuring alveolar liquid clearance (ALC) in three lobes removed from the same dog. Autologous plasma was instilled in the air spaces of each lobe, and the increase in plasma protein concentration resulting from fluid reabsorption was used to calculate ALC. ALC after 4 h was 16.5 ± 0.6% (SE) of the instilled fluid volume under baseline conditions and was 30.2 ± 1.3% after terbutaline (10−5M) administration. These values were similar to those previously reported for intact dogs. Propranolol (10−4M) and ouabain (10−3M) reduced ALC in terbutaline-stimulated lobes to 20.4 ± 0.8 and 3.9 ± 1.4%, respectively. There was no significant difference in ALC among the three lobes under either baseline conditions or after terbutaline administration. These data indicate that the sodium and water transport mechanisms of the canine alveolar epithelium remain viable during 4 h of nonperfusion and that there are no intrinsic differences in the transport properties of individual lung lobes. The ability to study several lobes simultaneously without the need for perfusion will allow for the design of experiments in which multiple interventions can be studied by using lung lobes from the same animal.
Effect of chronic resistive loading on hypoxic ventilatory responsiveness
Authors: Greenberg Harly E. , Rao Rammohan S. , Sica Anthony L. , Scharf Steven M.
Published: December 2017

Greenberg, Harly E., Rammohan S. Rao, Anthony L. Sica, and Steven M. Scharf. Effect of chronic resistive loading on hypoxic ventilatory responsiveness. J. Appl. Physiol. 82(2): 500–507, 1997.—Depression of ventilation mediated by endogenous opioids has been observed acutely after resistive airway loading. We evaluated the effects of chronically increased airway resistance on hypoxic ventilatory responsiveness shortly after load imposition and 6 wk later. A circumferential tracheal band was placed in 200-g rats, tripling tracheal resistance. Sham surgery was performed in controls. Ventilation and the ventilatory response to hypoxia were measured by using barometric plethysmography at 2 days and 6 wk postsurgery in unanesthetized rats during exposure to room air and to 12% O2-5% CO2-balance N2. Trials were performed with and without naloxone (1 mg/kg ip). Room air arterial blood gases demonstrated hypercapnia with normoxia in obstructed rats at 2 days and 6 wk postsurgery. During hypoxia, a 30-Torr fall in[Formula: see text] occurred with no change in[Formula: see text]. Hypoxic ventilatory responsiveness was suppressed in obstructed rats at 2 days postloading. Naloxone partially reversed this suppression. However, hypoxic responsiveness at 6 wk was not different from control levels. Naloxone had a small effect on ventilatory pattern at this time with no overall effect on hypoxic responsiveness. This was in contrast to previously demonstrated long-term suppression of CO2sensitivity in this model, which was partially reversible by naloxone only during the immediate period after load imposition. Endogenous opioids apparently modulate ventilatory control acutely after load imposition. Their effect wanes with time despite persistence of depressed CO2sensitivity.
Esophageal stimulation by hydrochloric acid causes neurogenic inflammation in the airways in guinea pigs
Authors: Hamamoto Junji , Kohrogi Hirotsugu , Kawano Osamu , Iwagoe Hajime , Fujii Kazuhiko , Hirata Nahomi , Ando Masayuki
Published: December 2017

Hamamoto, Junji, Hirotsugu Kohrogi, Osamu Kawano, Hajime Iwagoe, Kazuhiko Fujii, Nahomi Hirata, and Masayuki Ando.Esophageal stimulation by hydrochloric acid causes neurogenic inflammation in the airways in guinea pigs. J. Appl. Physiol. 82(3): 738–745, 1997.—To investigate whether tachykinins are released in the airways in response to stimulation of the esophagus, we studied the airway plasma extravasation induced by intraesophageal HCl in the presence or absence of neutral endopeptidase inhibitor phosphoramidon and NK1-receptor antagonist FK-888 in anesthetized guinea pigs. The airway plasma leakage was evaluated by measuring extravasated Evans blue dye in the animals pretreated with propranolol and atropine. Infusion of 1 N HCl into the esophagus significantly increased plasma extravasation in the trachea. Phosphoramidon significantly potentiated plasma extravasation in the trachea and main bronchi, whereas FK-888 significantly inhibited that extravasation in a dose-related manner. In the capsaicin-treated animals, airway plasma extravasation was completely inhibited even in the presence of phosphoramidon. Tracheal plasma extravasation potentiated by phosphoramidon was significantly inhibited in the bilateral vagotomized animals. These results suggest that 1) tachykinin-like substances are released to cause plasma extravasation in the airways as a result of intraesophageal HCl stimulation and 2) there are neural pathways communicating between the esophagus and airways, including the vagus nerve.
Effects of adenosine on pressure-flow relationships in an in vitro model of compartment syndrome
Authors: Shrier Ian , Baratz Ari , Magder Sheldon
Published: December 2017

Shrier, Ian, Ari Baratz, and Sheldon Magder. Effects of adenosine on pressure-flow relationships in an in vitro model of compartment syndrome. J. Appl. Physiol. 82(3): 755–759, 1997.—Blood flow through skeletal muscle is best modeled with a vascular waterfall at the arteriolar level. Under these conditions, flow is determined by the difference between perfusion pressure (Pper) and the waterfall pressure (Pcrit), divided by the arterial resistance (Ra). By pump perfusing an isolated canine gastrocnemius muscle ( n = 6) after it was placed within an airtight box, with and without adenosine infusion, we observed an interaction between the pressure surrounding a muscle (as occurs in compartment syndrome) and baseline vascular tone. We titrated adenosine concentration to double baseline flow. We measured Pcrit and Ra at box pressures (Pbox), which resulted in 100 (Pbox = 0), 90, 75, and 50% flow without adenosine; and 200, 180, 150, 100, and 50% flow with adenosine. Without adenosine, each 10% decline in flow was associated with a 5.7 mmHg increase in Pcrit ( P < 0.01). With adenosine, the same decrease in flow was associated with a 2.6-mmHg increase in Pcrit ( P < 0.01). Values of Pcrit at 50% of flow were almost identical. Each 10% decrease in flow was also associated with 2.2% increase in Ra with or without adenosine ( P < 0.001). Ra decreased with adenosine infusion ( P < 0.05), and there was no interaction between adenosine and flow ( P > 0.9). We conclude that increases in pressure surrounding a muscle limit flow primarily through changes in Pcrit with and without adenosine-induced vasodilation. The interaction between Pbox and adenosine with respect to Pcrit but not Ra suggests that Pbox affects the tone of the vessels responsible for Pcrit but not Ra.
Influence of age and breed on the binding of oxygen to red blood cells of bovine calves
Authors: Gustin P. , Detry B. , Robert A. , Cao M. L. , Lessire F. , Cambier C. , Katz V. , Ansay M. , Frans A. , Clerbaux T.
Published: December 2017

Gustin, P., B. Detry, A. Robert, M. L. Cao, F. Lessire, C. Cambier, V. Katz, M. Ansay, A. Frans, and T. Clerbaux.Influence of age and breed on the binding of oxygen to red blood cells of bovine calves. J. Appl. Physiol. 82(3): 784–790, 1997.—The influence of somatic growth and genetic selection on the whole blood oxygen equilibrium curve (OEC) was measured under standard conditions in double-muscled and dairy calves during their first 3 mo of life. Crossbreed animals were also investigated. Hemoglobin, 2,3-diphosphoglycerate (DPG), Cl, and Piconcentrations were also measured. The percentage of fetal hemoglobin (HbF) was determined. The influence of exogenous Cl, Pi, and pH on the OEC was also assessed. The[Formula: see text] at 50% hemoglobin saturation (P50) increased during somatic growth, probably because of the increase in DPG recorded in double-muscled neonates and to the progressive disappearance of HbF in both breeds. The oxygen exchange fraction (OEF%) was used to assess the combined influence of the OEC shift and OEC shape changes on blood oxygen desaturation under standard conditions, when the[Formula: see text] decreases within a physiological range. The OEF% showed an increase during the first month, then a stabilization. The effects of Cl, Pi, and pH in Friesian calves were similar as in adult cattle. Double-muscled neonates had a lower P50, OEF% values, and DPG concentrations and higher hemoglobin and Cl concentrations than Friesian neonates. The Piconcentration and the percentage of HbF were similar in both breeds. The pH and the Cl concentration had significantly less effect on the OEC in double-muscled than in Friesian calves. Crossbreed animals exhibited intermediate parameter values, between those recorded for double-muscled and Friesian calves. All differences between breeds progressively disappeared during the first month. These data show that blood function changes markedly in calves during the first month of life and that genetic selection can alter blood function.
Intravenous vs. oral rehydration: effects on subsequent exercise-heat stress
Authors: Castellani John W. , Maresh Carl M. , Armstrong Lawrence E. , Kenefick Robert W. , Riebe Deborah , Echegaray Marcos , Casa Douglas , Castracane V. Daniel
Published: December 2017

Castellani, John W., Carl M. Maresh, Lawrence E. Armstrong, Robert W. Kenefick, Deborah Riebe, Marcos Echegaray, Douglas Casa, and V. Daniel Castracane. Intravenous vs. oral rehydration: effects on subsequent exercise-heat stress. J. Appl. Physiol. 82(3): 799–806, 1997.—This study compared the influence of intravenous vs. oral rehydration after exercise-induced dehydration during a subsequent 90-min exercise bout. It was hypothesized that cardiovascular, thermoregulatory, and hormonal variables would be the same between intravenous and oral rehydration because of similar restoration of plasma volume (PV) and osmolality (Osmo). Eight non-heat-acclimated men received three experimental treatments (counterbalanced design) immediately after exercise-induced dehydration (33°C) to −4% body weight loss. Treatments were intravenous 0.45% NaCl (iv; 25 ml/kg), no fluid (NF), and oral saline (Oral; 25 ml/kg). After rehydration and rest (2 h total), subjects walked at 50% maximal O2 consumption for up to 90 min at 36°C. The following observations were made: 1) heart rate was higher ( P < 0.05) in Oral vs. iv at minutes 45, 60, and 75 of exercise; 2) rectal temperature, sweat rate, percent change in PV, and change in plasma Osmo were similar between iv and Oral; 3) change in plasma norepinephrine decreased less ( P < 0.05) in Oral compared with iv at minute 45; 4) changes in plasma adrenocorticotropic hormone and cortisol were similar between iv and Oral after exercise was initiated; and 5) exercise time was similar between iv (77.4 ± 5.4 min) and Oral (84.2 ± 2.3 min). These data suggest that after exercise-induced dehydration, iv and Oral were equally effective as rehydration treatments. Thermoregulation, change in adrenocorticotropic hormone, and change in cortisol were not different between iv and Oral after exercise began; this is likely due to similar percent change in PV and change in Osmo.
Exogenous glucose oxidation during exercise in endurance-trained and untrained subjects
Authors: Jeukendrup A. E. , Mensink M. , Saris W. H. M. , Wagenmakers A. J. M.
Published: December 2017

Jeukendrup, A. E., M. Mensink, W. H. M. Saris, and A. J. M. Wagenmakers. Exogenous glucose oxidation during exercise in endurance-trained and untrained subjects. J. Appl. Physiol. 82(3): 835–840, 1997.—To investigate the effect of training status on the fuel mixture used during exercise with glucose ingestion, seven endurance-trained cyclists (Tr; maximum O2 uptake 67 ± 2.3 ml ⋅ kg−1 ⋅ min−1) and eight untrained subjects (UTr; 48 ± 2 ml ⋅ kg−1 ⋅ min−1) were studied during 120 min of exercise at ∼60% maximum O2 uptake. At the onset of exercise, 8 ml ⋅ kg−1 ⋅ min−1of an 8% naturally enriched [13C]glucose solution was ingested and 2 ml/kg every 15 min thereafter. Energy expenditure was higher in Tr subjects compared with UTr subjects (3,404 vs. 2,630 kJ; P < 0.01). During the second hour, fat oxidation was higher in Tr subjects (37 ± 2 g) compared with UTr subjects (23 ± 1 g), whereas carbohydrate oxidation was similar (116 ± 8 g in Tr subjects vs. 114 ± 4 g in UTr subjects). No differences were observed in exogenous glucose oxidation (50 ± 2 g in Tr subjects and 45 ± 3 g in UTr subjects, respectively). Peak exogenous glucose oxidation rates were similar in the two groups (0.95 ± 0.07 g/min in Tr subjects and 0.96 ± 0.03 g/min in UTr subjects). It is concluded that the higher energy expenditure in Tr subjects during exercise at the same relative exercise intensity is entirely met by a higher rate of fat oxidation without changes in the rates of exogenous and endogenous carbohydrates.
Myosin heavy chain mRNA transform to faster isoforms in immobilized skeletal muscle: a quantitative PCR study
Authors: Jänkälä Heidi , Harjola Veli-Pekka , Petersen Niels Erik , Härkönen Matti
Published: December 2017

Jänkälä, Heidi, Veli-Pekka Harjola, Niels Erik Petersen, and Matti Härkönen. Myosin heavy chain mRNA transform to faster isoforms in immobilized skeletal muscle: a quantitative PCR study. J. Appl. Physiol. 82(3): 977–982, 1997.—A quantitative polymerase chain reaction (PCR) method was used to measure the quantities of type I, IIa, IIx, and IIb myosin heavy chain (MHC) mRNA in total RNA preparations of the soleus, gastrocnemius, and plantaris muscles of normal and hindlimb-immobilized rats. Type IIx and even type IIb MHC mRNA were demonstrated at extremely low levels in normal soleus, 2.1 ± 0.4 × 105and 5.0 ± 0.2 × 105molecules of mRNA per microgram total RNA, respectively. Immobilization for 1 wk significantly altered the gene expression of MHC isoforms. In soleus, both type IIx and IIb MHC genes became significantly upregulated, 24-fold ( P < 0.005) and 2.6-fold ( P < 0.05), respectively. In gastrocnemius, the level of type IIa MHC mRNA decreased by 51% ( P < 0.01) and the level of type IIx MHC mRNA increased by 140% ( P < 0.05). In plantaris, the level of type IIa MHC mRNA decreased by 58% ( P < 0.005). In conclusion, immobilization changed the MHC mRNA profile in three different types of skeletal muscle toward faster isoforms. The quantitative results permit reliable evaluation of changes in mRNA levels.
N-acetylcysteine administration alters the response to inspiratory loading in oxygen-supplemented rats
Authors: Supinski G. S. , Stofan D. , Ciufo R. , Dimarco A.
Published: December 2017

Supinski, G. S., D. Stofan, R. Ciufo, and A. DiMarco. N-acetylcysteine administration alters the response to inspiratory loading in oxygen-supplemented rats. J. Appl. Physiol. 82(4): 1119–1125, 1997.—Based on recent studies, it has been suggested that free radicals are elaborated in the respiratory muscles during strenuous contractions and contribute to the development of muscle fatigue. If this theory is correct, then it should be possible to attenuate the development of diaphragm fatigue and/or delay the onset of respiratory failure during loaded breathing by administering a free radical scavenger. The purpose of the present experiment was, therefore, to examine the effect of N-acetylcysteine (NAC), a free radical scavenger and glutathione precursor, on the evolution of respiratory failure in decerebrate unanesthetized rats breathing against a large inspiratory resistive load. We compared the inspiratory volume and pressure generation over time in animals pretreated with either saline or NAC (150 mg/kg) and then loaded until respiratory arrest. After arrest, the diaphragm was excised, and samples were assayed for reduced (GSH) and oxidized glutathione. As a control, we also assessed respiratory function and glutathione concentrations in groups of nonloaded saline- and NAC-treated animals. We found that NAC-treated animals were able to tolerate loading better than the saline-treated group, maintaining higher inspiratory pressures and sustaining higher inspired volumes. Administration of NAC also increased the time that animals could tolerate loading before the development of respiratory arrest. In addition, although saline-treated loaded animals had significant reductions in diaphragmatic GSH levels compared with unloaded controls, the magnitude of this reduction was blunted by NAC administration (i.e., GSH averaged 965 ± 113, 568 ± 83, 907 ± 39, and 784 ± 61 nmol/g for unloaded-saline, loaded-saline, unloaded-NAC, and loaded-NAC groups, P< 0.05, with the value for the loaded-saline group lower than the values for the two unloaded groups; GSH for the loaded-NAC group was not different, however, from unloaded controls). These data demonstrate that administration of NAC, a free radical scavenger, slows the rate of development of respiratory failure during inspiratory resistive loading.
Effects of diet on muscle triglyceride and endurance performance
Authors: Starling Raymond D. , Trappe Todd A. , Parcell Allen C. , Kerr Chad G. , Fink William J. , Costill David L.
Published: December 2017

Starling, Raymond D., Todd A. Trappe, Allen C. Parcell, Chad G. Kerr, William J. Fink, and David L. Costill. Effects of diet on muscle triglyceride and endurance performance. J. Appl. Physiol. 82(4): 1185–1189, 1997.—The purpose of this investigation was to examine the effects of diet on muscle triglyceride and endurance performance. Seven endurance-trained men completed a 120-min cycling bout at 65% of maximal oxygen uptake. Each subject then ingested an isocaloric high-carbohydrate (Hi-CHO; 83% of energy) or a high-fat (Hi-Fat; 68% of energy) diet for the ensuing 12 h. After a 12-h overnight fast, a 1,600-kJ self-paced cycling bout was completed. Muscle triglyceride measured before (33.0 ± 2.3 vs. 37.0 ± 2.1 mmol/kg dry wt) and after (30.9 ± 2.4 vs. 32.8 ± 1.6 mmol/kg dry wt) the 120-min cycling bout was not different between the Hi-CHO and Hi-Fat trials, respectively. After the 24-h dietary-fasting period, muscle triglyceride was significantly higher for the Hi-Fat (44.7 ± 2.4 mmol/kg dry wt) vs. the Hi-CHO (27.5 ± 2.1 mmol/kg dry wt) trial. Furthermore, self-paced cycling time was significantly greater for the Hi-Fat (139.3 ± 7.1 min) compared with the Hi-CHO (117.1 ± 3.2 min) trial. These data demonstrate that there was not a significant difference in muscle triglyceride concentration before and after a prolonged moderate-intensity cycling bout. Nevertheless, a high-fat diet increased muscle triglyceride concentration and reduced self-paced cycling performance 24 h after the exercise compared with a high-carbohydrate diet.