bluuebunny/crossref_metadata_2025 huggingface dataset:
Impaired calcium pump function does not slow relaxation in human skeletal muscle after prolonged exercise
Authors: Booth John , McKenna Michael J. , Ruell Patricia A. , Gwinn Tom H. , Davis Glen M. , Thompson Martin W. , Harmer Alison R. , Hunter Sandra K. , Sutton John R.
Published: December 2017

Booth, John, Michael J. McKenna, Patricia A. Ruell, Tom H. Gwinn, Glen M. Davis, Martin W. Thompson, Alison R. Harmer, Sandra K. Hunter, and John R. Sutton. Impaired calcium pump function does not slow relaxation in human skeletal muscle after prolonged exercise. J. Appl. Physiol. 83(2): 511–521, 1997.—This study examined the effects of prolonged exercise on human quadriceps muscle contractile function and homogenate sarcoplasmic reticulum Ca2+uptake and Ca2+-adenosinetriphosphatase activity. Ten untrained men cycled at 75 ± 2% (SE) peak oxygen consumption until exhaustion. Biopsies were taken from the right vastus lateralis muscle at rest, exhaustion, and 20 and 60 min postexercise. Peak tension and half relaxation time of the left quadriceps muscle were measured during electrically evoked twitch and tetanic contractions and a maximal voluntary isometric contraction at rest, exhaustion, and 10, 20, and 60 min postexercise. At exhaustion, homogenate Ca2+uptake and Ca2+adenosinetriphosphatase activity were reduced by 17 ± 4 and 21 ± 5%, respectively, and remained depressed after 60 min recovery ( P ≤ 0.01). Muscle ATP, creatine phosphate, and glycogen were all depressed at exhaustion ( P ≤ 0.01). Peak tension during a maximal voluntary contraction, a twitch, and a 10-Hz stimulation were reduced after exercise by 28 ± 3, 45 ± 6, 65 ± 5%, respectively ( P ≤ 0.01), but no slowing of half relaxation times were found. Thus fatigue induced by prolonged exercise reduced muscle Ca2+uptake, but this did not cause a slower relaxation of evoked contractions.
Airway thermal volume in humans and its relation to body size
Authors: Serikov Vladimir B. , Jerome E. Heidi , Fleming Neal W. , Moore Peter G. , Stawitcke Frederick A. , Staub Norman C.
Published: December 2017

Serikov, Vladimir B., E. Heidi Jerome, Neal W. Fleming, Peter G. Moore, Frederick A. Stawitcke, and Norman C. Staub.Airway thermal volume in humans and its relation to body size. J. Appl. Physiol. 83(2): 668–676, 1997.—The objective of this study was to investigate the influence of volume ventilation (V˙e) and cardiac output (Q˙) on the temperature of the expired gas at the distal end of the endotracheal tube in anesthetized humans. In 63 mechanically ventilated adults, we used a step decrease in the humidity of inspired gas to cool the lungs. After change from humid to dry gas ventilation, the temperature of the expired gas decreased. We evaluated the relationship between the inverse monoexponential time constant of the temperature fall (1/τ) and eitherV˙e orQ˙. WhenV˙e was increased from 5.67 ± 1.28 to 7.14 ± 1.60 (SD) l/min ( P = 0.02), 1/τ did not change significantly [from 1.25 ± 0.38 to 1.21 ± 0.51 min−1, P = 0.81]. In the 11 patients in whom Q˙ changed during the study period (from 5.07 ± 1.81 to 7.38 ± 2.45 l/min, P = 0.02), 1/τ increased correspondingly from 0.89 ± 0.22 to 1.52 ± 0.44 min−1( P = 0.003). We calculated the airway thermal volume (ATV) as the ratio of the measured valuesQ˙ to 1/τ and related it to the body height (BH): ATV (liters) = 0.086 BH (cm) − 9.55 ( r = 0.90).
Exercise performance, red blood cell deformability, and lipid peroxidation: effects of fish oil and vitamin E
Authors: Oostenbrug G. S. , Mensink R. P. , Hardeman M. R. , De Vries T. , Brouns F. , Hornstra G.
Published: December 2017

Oostenbrug, G. S., R. P. Mensink, M. R. Hardeman, T. De Vries, F. Brouns, and G. Hornstra. Exercise performance, red blood cell deformability, and lipid peroxidation: effects of fish oil and vitamin E. J. Appl. Physiol. 83(3): 746–752, 1997.—Previous studies have indicated that fish oil supplementation increases red blood cell (RBC) deformability, which may improve exercise performance. Exercise alone, or in combination with an increase in fatty acid unsaturation, however, may enhance lipid peroxidation. Effects of a bicycle time trial of ∼1 h on RBC characteristics and lipid peroxidation were, therefore, studied in 24 trained cyclists. After 3 wk of fish oil supplementation (6 g/day), without or with vitamin E (300 IU/day), trial performance, RBC characteristics, and lipid peroxidation were measured again. RBC deformability appeared to decrease during endurance exercise. After correction for hemoconcentration, plasma total tocopherol concentrations decreased by 0.77 μmol/l ( P = 0.012) or 2.9% and carotenoid concentrations by 0.08 μmol/l ( P = 0.0008) or 4.5%. Endurance exercise did not affect the lag time and rate of in vitro oxidation of low-density lipoproteins (LDLs), but the maximum amount of conjugated dienes formed decreased by 2.1 ± 1.0 μmol/mmol LDL cholesterol ( P= 0.042) or 1.2%. Fish oil supplementation with and without vitamin E did not affect RBC characteristics or exercise performance. Both supplements decreased the rate of LDL oxidation, and fish oil supplementation with vitamin E delayed oxidation. The amount of dienes, however, was not affected. The supplements also did not change effects of exercise. We conclude that the changes observed during endurance exercise may indicate increased oxidative stress, but further research is necessary to confirm this. Fish oil supplementation does not improve endurance performance, but it also does not cause or augment changes in antioxidant levels or LDL oxidation during exercise.
Contractions of specific abdominal muscles in postural tasks are affected by respiratory maneuvers
Authors: Hodges Paul W. , Gandevia Simon C. , Richardson Carolyn A.
Published: December 2017

Hodges, Paul W., Simon C. Gandevia, and Carolyn A. Richardson. Contractions of specific abdominal muscles in postural tasks are affected by respiratory maneuvers. J. Appl. Physiol. 83(3): 753–760, 1997.—The influence of respiratory activity of the abdominal muscles on their reaction time in a postural task was evaluated. The electromyographic (EMG) onsets of the abdominal muscles and deltoid were evaluated in response to shoulder flexion initiated by a visual stimulus occurring at random throughout the respiratory cycle. Increased activity of the abdominal muscles was produced by inspiratory loading, forced expiration below functional residual capacity, and a static glottis-closed expulsive maneuver. During quiet breathing, the latency between activation of the abdominal muscles and deltoid was not influenced by the respiratory cycle. When respiratory activity of the abdominal muscles increased, the EMG onset of transversus abdominis and internal oblique, relative to deltoid, was significantly earlier for movements beginning in expiration, compared with inspiration [by 97–107 ms ( P < 0.01) and 64–90 ms ( P < 0.01), respectively]. However, the onset of transversus abdominis EMG was delayed by 31–54 ms ( P < 0.01) when movement was performed during a static expulsive effort, compared with quiet respiration. Thus changes occur in early anticipatory contraction of transversus abdominis during respiratory tasks but they cannot be explained simply by existing activation of the motoneuron pool.
Thermoregulatory control during pregnancy and lactation in rats
Authors: Eliason Heather L. , Fewell James E.
Published: December 2017

Eliason, Heather L., and James E. Fewell.Thermoregulatory control during pregnancy and lactation in rats. J. Appl. Physiol. 83(3): 837–844, 1997.—Although the mechanisms remain unknown, maternal core temperature (Tc) decreases near term of pregnancy and is increased throughout lactation in rats. The purpose of our present experiments was to determine whether pregnancy and lactation shift the thermoneutral zone of rats and to investigate whether the changes in maternal Tcduring pregnancy and lactation result from “forced” or “regulated” thermoregulatory responses. Conscious, chronically instrumented nonpregnant and pregnant and lactating rats were studied both in a thermocline (a chamber with a linear temperature gradient from 12 to 36°C) and in a metabolic chamber to determine the influence of pregnancy and lactation on selected ambient temperature as well as the thermoregulatory response to changes in ambient temperature. We found that selected ambient temperature, oxygen consumption, and thermal conductance did not change in rats studied in a thermocline as Tc decreased near term of pregnancy. There was, however, a downward shift in the thermoneutral zone of rats studied in a metabolic chamber near term of pregnancy. During lactation, selected ambient temperature decreased in rats studied in a thermocline as oxygen consumption and Tc increased. The thermoneutral zone of lactating rats was not different from that of nonpregnant animals. Thus our data provide evidence that the decrease in Tc near term of pregnancy in rats results from a regulated thermoregulatory response, whereas the increase in Tc during lactation results from a forced thermoregulatory response.
Efficiency of human skeletal muscle in vivo: comparison of isometric, concentric, and eccentric muscle action
Authors: Ryschon T. W. , Fowler M. D. , Wysong R. E. , Anthony A.-R. , Balaban R. S.
Published: December 2017

Ryschon, T. W., Fowler, R. E. Wysong, A.-R. Anthony, and R. S. Balaban. Efficiency of human skeletal muscle in vivo: comparison of isometric, concentric, and eccentric muscle action. J. Appl. Physiol. 83(3): 867–874, 1997.—The purpose of this study was to estimate the efficiency of ATP utilization for concentric, eccentric, and isometric muscle action in the human tibialis anterior and extensor digitorum longus in vivo. A dynamometer was used to quantitate muscle work, or tension, while simultaneous31P-nuclear magnetic resonance data were collected to monitor ATP, phosphocreatine, inorganic phosphate, and pH. The relative efficiency of the actions was estimated in two ways: steady-state effects on high-energy phosphates and a direct comparison of ATP synthesis rates with work. In the steady state, the cytosolic free energy dropped to the lowest value with concentric activity, followed by eccentric and isometric action for comparative muscle tensions. Estimates of ATP synthesis rates revealed a mechanochemical efficiency [i.e., ATP production rate/work (both in J/s)] of 15.0 ± 1.3% in concentric and 34.7 ± 6.1% in eccentric activity. The estimated maximum ATP production rate was highest in concentric action, suggesting an activation of energy metabolism under these conditions. By using direct measures of metabolic strain and ATP turnover, these data demonstrate a decreasing metabolic efficiency in human muscle action from isometric, to eccentric, to concentric action.
Normalized metabolic stress for31P-MR spectroscopy studies of human skeletal muscle: MVC vs. muscle volume
Authors: Fowler M. D. , Ryschon T. W. , Wysong R. E. , Combs C. A. , Balaban R. S.
Published: December 2017

Fowler, M. D., T. W. Ryschon, R. E. Wysong, C. A. Combs, and R. S. Balaban. Normalized metabolic stress for31P-MR spectroscopy studies of human skeletal muscle: MVC vs. muscle volume. J. Appl. Physiol. 83(3): 875–883, 1997.—A critical requirement of submaximal exercise tests is the comparability of workload and associated metabolic stress between subjects. In this study, 31P-magnetic resonance spectroscopy was used to estimate metabolic strain in the soleus muscle during dynamic, submaximal plantar flexion in which target torque was 10 and 15% of a maximal voluntary contraction (MVC). In 10 healthy, normally active adults, (PCr + Pi)/PCr, where PCr is phosphocreatine, was highly correlated with power output normalized to the volume of muscle in the plantar flexor compartment ( r = 0.89, P < 0.001). The same variable was also correlated, although less strongly ( r = 0.78, P < 0.001), with power normalized to plantar flexor cross-sectional area. These findings suggest that comparable levels of metabolic strain can be obtained in subjects of different size when the power output, or stress, for dynamic plantar flexion is selected as a function of plantar flexor muscle volume. In contrast, selecting power output as a function of MVC resulted in a positive linear relationship between (PCr + Pi)/PCr and the torque produced, indicating that metabolic strain was increasing rather than achieving constancy as a function of MVC. These findings provide new insight into the design of dynamic muscle contraction protocols aimed at detecting metabolic differences between subjects of different body size but having similar blood flow capacity and mitochondrial volume per unit of muscle.
Femoral arterial injection of adenosine in humans elevates MSNA via central but not peripheral mechanisms
Authors: Maclean D. A. , Saltin B. , Rådegran G. , Sinoway L.
Published: December 2017

MacLean, D. A., B. Saltin, G. Rådegran, and L. Sinoway. Femoral arterial injection of adenosine in humans elevates MSNA via central but not peripheral mechanisms. J. Appl. Physiol. 83(4): 1045–1053, 1997.—The purpose of the present study was to examine the effects of femoral arterial injections of adenosine on muscle sympathetic nerve activity (MSNA) under three different conditions. These conditions were adenosine injection alone, adenosine injection after phenylephrine infusion, and adenosine injection distal to a thigh cuff inflated to arrest the circulation. The arterial injection of adenosine alone resulted in a fourfold (255 ± 18 U/min) increase above baseline (73 ± 12 U/min; P< 0.05) in MSNA with an onset latency of 15.8 ± 0.8 s from the time of injection. The systemic infusion of phenylephrine resulted in an increase ( P < 0.05) in mean arterial pressure of ∼10 mmHg and a decrease ( P < 0.05) in heart rate of 8–10 beats/min compared with baseline values before phenylephrine infusion. After adenosine injection, the onset latency for the increase in MSNA was delayed to 19.2 ± 2.1 s and the magnitude of increase was attenuated by ∼50% (123 ± 20 U/min) compared with adenosine injection alone ( P < 0.05). When a cuff was inflated to 220 mmHg to arrest the circulation and adenosine was injected into the leg distal to the inflated cuff, there were no significant changes in MSNA or any of the other measured variables. However, on deflation of the cuff, there was a rapid increase ( P < 0.05) in MSNA, with an onset latency of 9.1 ± 0.9 s, and the magnitude of increase (276 ± 28 U/min) was similar to that observed for adenosine alone. These data suggest that ∼50% of the effects of exogenously administered adenosine are a result of baroreceptor unloading due to a drop in blood pressure. Furthermore, the finding that adenosine did not directly result in an increase in MSNA while it was trapped in the leg but that it needed to be released into the circulation suggests that adenosine does not directly stimulate thin fiber muscle afferents in the leg of humans. In contrast, it would appear that adenosine exerts its effects via some other chemically sensitive pool of afferents.
Patterns of shortening and thickening of the human diaphragm
Authors: Wait J. L. , Johnson R. L.
Published: December 2017

Wait, J. L., and R. L. Johnson. Patterns of shortening and thickening of the human diaphragm. J. Appl. Physiol. 83(4): 1123–1132, 1997.—To study how the human diaphragm changes configuration during inspiration, we simultaneously measured diaphragm thickening using ultrasound and inspired volumes using a pneumotachograph. Diaphragm length was assessed by chest radiography. We found that thickening and shortening were greatest during a breath taken primarily with the abdomen. However, the degree of thickening was greater than expected for fiber shortening, assuming parallel muscle fibers and no shear. So, to clarify this unexpected finding, we considered geometric models of the diaphragm. How a muscle thickens as its fibers shorten is critically dependent on geometry. Thus, if a flat rectangular sheet of muscle shortens along one dimension, surface area-to-length ratio along this dimension should remain constant, and thickness would be inversely proportional to length during shortening. The simplest model of the diaphragm, however, is a cylindrical sheet of muscle in the zone of apposition capped by a dome; the ratio of surface area to radial fiber length in the dome is substantially less than the ratio of area to length of the cylindrical zone of apposition; hence, as the zone of apposition shortens while the dome radius remains constant, the ratio of total surface area to combined length (i.e., dome + zone of apposition) must decrease and thickening of the muscle correspondingly must increase more than expected for a simple rectangular strip. A similar relationship can be derived between thickening and length in a muscle sheet with a wedge-shaped insertion into a thin flat tendon. Comparison of calculations with these types of models to data from human subjects indicates that the unexpected thickening in the zone of apposition is explained by the peculiar geometry of the diaphragm. The greater thickening of the diaphragm in the zone of apposition suggests that more of the muscle mass and more sarcomeres are retained in the zone of apposition as the dome descends. Physiologically, this greater thickening may have importance by reducing wall stress in the zone of apposition and reducing the work or energy requirements per sarcomere.
Hemodynamics, cerebral circulation, and oxygen saturation in Cheyne-Stokes respiration
Authors: Franklin Karl A. , Sandström Erik , Johansson Göran , Bålfors Eva M.
Published: December 2017

Franklin, Karl A., Erik Sandström, Göran Johansson, and Eva M. Bålfors. Hemodynamics, cerebral circulation, and oxygen saturation in Cheyne-Stokes respiration. J. Appl. Physiol. 83(4): 1184–1191, 1997.—Because cardiovascular disorders and stroke may induce Cheyne-Stokes respiration, our purpose was to study the interaction among cerebral activity, cerebral circulation, blood pressure, and blood gases during Cheyne-Stokes respiration. Ten patients with heart failure or a previous stroke were investigated during Cheyne-Stokes respiration with recordings of daytime polysomnography, cerebral blood flow velocity, intra-arterial blood pressure, and intra-arterial oxygen saturation with and without oxygen administration. There were simultaneous changes in wakefulness, cerebral blood flow velocity, and respiration with accompanying changes in blood pressure and heart rate ∼10 s later. Cerebral blood flow velocity, blood pressure, and heart rate had a minimum occurrence in apnea and a maximum occurrence during hyperpnea. The apnea-induced oxygen desaturations were diminished during oxygen administration, but the hemodynamic alterations persisted. Oxygen desaturations were more severe and occurred earlier according to intra-arterial measurements than with finger oximetry. It is not possible to explain Cheyne-Stokes respiration by alterations in blood gases and circulatory time alone. Cheyne-Stokes respiration may be characterized as a state of phase-linked cyclic changes in cerebral, respiratory, and cardiovascular functions probably generated by variations in central nervous activity.
Rib cage mechanics during quiet breathing and exercise in humans
Authors: Kenyon C. M. , Cala S. J. , Yan S. , Aliverti A. , Scano G. , Duranti R. , Pedotti A. , Macklem Peter T.
Published: December 2017

Kenyon, C. M., S. J. Cala, S. Yan, A. Aliverti, G. Scano, R. Duranti, A. Pedotti, and Peter T. Macklem. Rib cage mechanics during quiet breathing and exercise in humans. J. Appl. Physiol. 83(4): 1242–1255, 1997.—During exercise, large pleural, abdominal, and transdiaphragmatic pressure swings might produce substantial rib cage (RC) distortions. We used a three-compartment chest wall model ( J. Appl. Physiol. 72: 1338–1347, 1992) to measure distortions of lung- and diaphragm-apposed RC compartments (RCp and RCa) along with pleural and abdominal pressures in five normal men. RCp and RCa volumes were calculated from three-dimensional locations of 86 markers on the chest wall, and the undistorted (relaxation) RC configuration was measured. Compliances of RCp and RCa measured during phrenic stimulation against a closed airway were 20 and 0%, respectively, of their values during relaxation. There was marked RC distortion. Thus nonuniform distribution of pressures distorts the RC and markedly stiffens it. However, during steady-state ergometer exercise at 0, 30, 50, and 70% of maximum workload, RC distortions were small because of a coordinated action of respiratory muscles, so that net pressures acting on RCp and RCa were nearly the same throughout the respiratory cycle. This maximizes RC compliance and minimizes the work of RC displacement. During quiet breathing, plots of RCa volume vs. abdominal pressure were to the right of the relaxation curve, indicating an expiratory action on RCa. We attribute this to passive stretching of abdominal muscles, which more than counterbalances the insertional component of transdiaphragmatic pressure.
Changes in skeletal muscle biochemistry and histology relative to fiber type in rats with heart failure
Authors: Delp Michael D. , Duan Changping , Mattson John P. , Musch Timothy I.
Published: December 2017

Delp, Michael D., Changping Duan, John P. Mattson, and Timothy I. Musch. Changes in skeletal muscle biochemistry and histology relative to fiber type in rats with heart failure. J. Appl. Physiol. 83(4): 1291–1299, 1997.—One of the primary consequences of left ventricular dysfunction (LVD) after myocardial infarction is a decrement in exercise capacity. Several factors have been hypothesized to account for this decrement, including alterations in skeletal muscle metabolism and aerobic capacity. The purpose of this study was to determine whether LVD-induced alterations in skeletal muscle enzyme activities, fiber composition, and fiber size are 1) generalized in muscles or specific to muscles composed primarily of a given fiber type and 2) related to the severity of the LVD. Female Wistar rats were divided into three groups: sham-operated controls ( n = 13) and rats with moderate ( n = 10) and severe ( n = 7) LVD. LVD was surgically induced by ligating the left main coronary artery and resulted in elevations ( P < 0.05) in left ventricular end-diastolic pressure (sham, 5 ± 1 mmHg; moderate LVD, 11 ± 1 mmHg; severe LVD, 25 ± 1 mmHg). Moderate LVD decreased the activities of phosphofructokinase (PFK) and citrate synthase in one muscle composed of type IIB fibers but did not modify fiber composition or size of any muscle studied. However, severe LVD diminished the activity of enzymes involved in terminal and β-oxidation in muscles composed primarily of type I fibers, type IIA fibers, and type IIB fibers. In addition, severe LVD induced a reduction in the activity of PFK in type IIB muscle, a 10% reduction in the percentage of type IID/X fibers, and a corresponding increase in the portion of type IIB fibers. Atrophy of type I fibers, type IIA fibers, and/or type IIB fibers occurred in soleus and plantaris muscles of rats with severe LVD. These data indicate that rats with severe LVD after myocardial infarction exhibit 1) decrements in mitochondrial enzyme activities independent of muscle fiber composition, 2) a reduction in PFK activity in type IIB muscle, 3) transformation of type IID/X to type IIB fibers, and 4) atrophy of type I, IIA, and IIB fibers.
Adrenergic β1- and β1+2-receptor blockade suppress the natural killer cell response to head-up tilt in humans
Authors: Klokker M. , Secher N. H. , Madsen P. , Pedersen M. , Pedersen B. K.
Published: December 2017

Klokker, M., N. H. Secher, P. Madsen, M. Pedersen, and B. K. Pedersen. Adrenergic β1- and β1+2-receptor blockade suppress the natural killer cell response to head-up tilt in humans. J. Appl. Physiol. 83(5): 1492–1498, 1997.—To evaluate stress-induced changes in blood leukocytes with emphasis on the natural killer (NK) cells, eight male volunteers were followed during three trials of head-up tilt with adrenergic β1- (metoprolol) and β1+2- (propranolol) blockade and with saline (control) infusions. The β1- and β1+2-receptor blockade did not affect the appearance of presyncopal symptoms, but the head-up tilt induced a transient lymphocytosis that was abolished by β1+2-receptor blockade but not by β1-receptor blockade. Head-up tilt also resulted in delayed neutrophilia, which was insensitive to β-receptor blockade. Lymphocyte subset analysis revealed that the head-up tilt resulted in a twofold increase in the percentage and absolute number of CD3−/CD16+and CD3−/CD56+NK cells in peripheral blood and that this increase was partially blocked by metoprolol and abolished by propranolol. The NK cell activity on a per NK cell basis did not change during head-up tilt, indicating that the cytotoxic capability of NK cells recruited to circulation is unchanged. The data suggest that the head-up tilt-induced lymphocytosis was due mainly to CD16+and CD56+NK cells and that their recruitment to the blood was inhibited by β1- and especially β1+2-receptor blockade. Thus stress-induced recruitment of lymphocytes, and of NK cells in particular, is mediated by epinephrine through activation of β-receptors on the lymphocytes.
Nitric oxide decreases lung liquid production in fetal lambs
Authors: Cummings James J.
Published: December 2017

Cummings, James J. Nitric oxide decreases lung liquid production in fetal lambs. J. Appl. Physiol. 83(5): 1538–1544, 1997.—To examine the effect of nitric oxide on fetal lung liquid production, I measured lung liquid production in fetal sheep at 130 ± 5 days gestation (range 122–137 days) before and after intrapulmonary instillation of nitric oxide. Thirty-one studies were done in which net lung luminal liquid production ( Jv) was measured by plotting the change in lung luminal liquid concentration of radiolabeled albumin, an impermeant tracer that was mixed into the lung liquid at the start of each study. To see whether changes in Jv might be associated with changes in pulmonary hemodynamics, pulmonary and systemic pressures were measured and left pulmonary arterial flow was measured by an ultrasonic Doppler flow probe. Variables were measured during a 1- to 2-h control period and for 4 h after a small bolus of isotonic saline saturated with nitric oxide gas (10 or 100%) was instilled into the lung liquid. Control (saline) instillations ( n = 6) caused no change in any variable over 6 h. Nitric oxide instillation significantly decreased Jv and increased pulmonary blood flow; these effects were sustained for 1–2 h. There was also a significant but transient decrease in pulmonary arterial pressure. Thus intrapulmonary nitric oxide causes a significant decrease in lung liquid and is associated with a decrease in pulmonary vascular resistance. In a separate series of experiments either amiloride or benzamil, which blocks Na+transport, was mixed into the lung liquid before nitric oxide instillation; still, there was a similar reduction in lung liquid production. Thus the reduction in lung liquid secretion caused by nitric oxide does not appear to depend on apical Na+ efflux.
Age and gender comparisons of muscle strength in 654 women and men aged 20–93 yr
Authors: Lindle R. S. , Metter E. J. , Lynch N. A. , Fleg J. L. , Fozard J. L. , Tobin J. , Roy T. A. , Hurley B. F.
Published: December 2017

Lindle, R. S., E. J. Metter, N. A. Lynch, J. L. Fleg, J. L. Fozard, J. Tobin, T. A. Roy, and B. F. Hurley. Age and gender comparisons of muscle strength in 654 women and men aged 20–93 yr. J. Appl. Physiol. 83(5): 1581–1587, 1997.—To assess age and gender differences in muscle strength, isometric, concentric (Con), and eccentric (Ecc) peak torque was measured in the knee extensors at a slow (0.52 rad/s) and fast (3.14 rad/s) velocity in 654 subjects (346 men and 308 women, aged 20–93 yr) from the Baltimore Longitudinal Study of Aging. Regression analysis revealed significant ( P < 0.001) age-related reductions in Con and Ecc peak torque for men and women at both velocities, but no differences were observed between the gender groups or velocities. Age explained losses in Con better than Ecc peak torque, accounting for 30% (Con) vs. 19% (Ecc) of the variance in men and 28% (Con) vs. 11% (Ecc) in women. To assess age and gender differences in the ability to store and utilize elastic energy, the stretch-shortening cycle was determined in a subset of subjects ( n = 47). The older women (mean age = 70 yr) showed a significantly greater enhancement in the stretch-shortening cycle, compared with men of similar age ( P < 0.01) and compared with younger men and women (each P < 0.05). Both men and women showed significant declines in muscle quality for Con peak torque ( P < 0.01), but no gender differences were observed. Only the men showed a significant decline in muscle quality ( P < 0.001) for Ecc peak torque. Thus both men and women experience age-related losses in isometric, Con, and Ecc knee extensor peak torque; however, age accounted for less of the variance in Ecc peak torque in women, and women tend to better preserve muscle quality with age for Ecc peak torque. In addition, older women have an enhanced capacity to store and utilize elastic energy compared with similarly aged men as well as with younger women and men.
Glucose transporter content and enzymes of metabolism in nerve-repair grafted muscle of aging Fischer 344 rats
Authors: Larkin Lisa , Leiendecker Eric R. , Supiano Mark , Halter Jeffrey
Published: December 2017

Larkin, Lisa, Eric R. Leiendecker, Mark Supiano, and Jeffrey Halter. Glucose transporter content and enzymes of metabolism in nerve-repair grafted muscle of aging Fischer 344 rats. J. Appl. Physiol. 83(5): 1623–1629, 1997.—Aging and grafting are associated with decreased ability of muscle to sustain power, likely reflecting diminished fuel availability. To assess mechanisms that may contribute to availability of glucose, we studied GLUT-1 and GLUT-4 protein as well as mRNA contents and enzymes of glucose metabolism in grafted and control medial gastrocnemius (MG) muscles of 6-, 12-, and 24-mo-old male Fischer 344 rats. There was no effect of age or grafting on MG GLUT-4 content. There was both an age- and graft-associated increase in GLUT-1 content ( P = 0.0044 and 0.0063, respectively). There was no effect of aging or grafting on hexokinase and phosphofructokinase activity or on protein and glycogen content. Muscle mass and citrate synthase activity were significantly diminished with grafting. Citrate synthase activity was significantly greater in the 12-mo-old compared with the 6- and 24-mo-old animals. Grafting in combination with aging had no impact on any of the parameters measured. We conclude that diminished glucose transporter expression cannot explain the decreased ability of aged muscle to sustain power. In addition, we conclude that the diminished ability of the grafted MG muscle to sustain power may be explained, in part, by a decrease in energy available from oxidative metabolism.
Changes in stroke volume with β-blockade before and after 10 days of exercise training in men and women
Authors: Mier Constance M. , Domenick Melissa A. , Wilmore Jack H.
Published: December 2017

Mier, Constance M., Melissa A. Domenick, and Jack H. Wilmore. Changes in stroke volume with β-blockade before and after 10 days of exercise training in men and women. J. Appl. Physiol. 83(5): 1660–1665, 1997. We sought to determine whether 10 days of training would be a sufficient stimulus for cardiac adaptations that would allow a greater compensatory stroke volume during β-blockade. We also sought to determine whether men and women had a similar cardiac reserve capacity for increasing stroke volume with β-blockade during submaximal exercise. Eight men (age 29 ± 2 yr, mean ± SE) and eight women (25 ± 2 yr) cycled at 65% of peak O2 consumption (unblocked) under placebo-control and β-blockade (100 mg atenolol) conditions performed on separate days. These tests were repeated at the same power output after training (10 consecutive days, 1 h of cycling per day). Before training, β-blockade significantly ( P < 0.05) decreased heart rate (HR) and cardiac output and increased stroke volume in both men and women. After training, the increase in stroke volume and decrease in HR with β-blockade was significantly less while cardiac output was reduced more. There were no gender differences in the effects of β-blockade on HR, stroke volume, or cardiac output. These data indicate that, during exercise with β-blockade, exercise training for 10 days does not enhance the compensatory increase in stroke volume and that men and women have a similar cardiac reserve capacity for increasing stroke volume.
High vascular and airway pressures increase interstitial protein mRNA expression in isolated rat lungs
Authors: Parker James C. , Breen Ellen C. , West John B.
Published: December 2017

Parker, James C., Ellen C. Breen, and John B. West.High vascular and airway pressures increase interstitial protein mRNA expression in isolated rat lungs. J. Appl. Physiol. 83(5): 1697–1705, 1997.—We hypothesized that wall stresses produced by high peak airway (Paw) and venous (Ppv) pressures would increase mRNA levels for structural proteins of the interstitial matrix in isolated rat lungs. Groups of lungs ( n = 6) were perfused for 4 h at a peak Paw of 35 cmH2O (HiPaw), cyclical peak Ppv of 28 cmH2O (HiPv), or baseline vascular and airway pressures (LoPress). In two separate groups, comparable peak pressures increased capillary filtration coefficient fourfold in each group. Northern blots were probed for mRNA of α1(I), α1(III), and α2(IV) procollagen chains, laminin B chain, fibronectin, and transforming growth factor-β1, and densities were normalized to 18S rRNA. mRNA was significantly higher in the HiPv group for type I (4.3-fold) and type III (3.8-fold) procollagen and laminin B chain (4.8-fold) and in the HiPaw group for type I (2.4-fold) and type IV (4.5-fold) procollagen and laminin B chain (2.3-fold) than in the LoPress group. Only fibronectin mRNA was significantly increased (3.9-fold) in the LoPress group relative to unperfused lungs. Estimated wall stresses were highest for alveolar septa in the HiPaw group and for capillaries in the HiPv group. The different patterns of mRNA expression are attributed to different regional stresses or extent of injury.
Human growth hormone response to repeated bouts of aerobic exercise
Authors: Kanaley J. A. , Weltman J. Y. , Veldhuis J. D. , Rogol A. D. , Hartman M. L. , Weltman A.
Published: December 2017

Kanaley, J. A., J. Y. Weltman, J. D. Veldhuis, A. D. Rogol, M. L. Hartman, and A. Weltman. Human growth hormone response to repeated bouts of aerobic exercise. J. Appl. Physiol. 83(5): 1756–1761, 1997.—We examined whether repeated bouts of exercise could override growth hormone (GH) auto-negative feedback. Seven moderately trained men were studied on three occasions: a control day (C), a sequential exercise day (SEB; at 1000, 1130, and 1300), and a delayed exercise day (DEB; at 1000, 1400, and 1800). The duration of each exercise bout was 30 min at 70% maximal O2 consumption (V˙o 2 max) on a cycle ergometer. Standard meals were provided at 0600 and 2200. GH was measured every 5–10 min for 24 h (0800–0800). Daytime (0800–2200) integrated GH concentrations were ∼150–160% greater during SEB and DEB than during C: 1,282 ± 345, 3,192 ± 669, and 3,389 ± 991 min ⋅ μg ⋅ l−1for C, SEB, and DEB, respectively [SEB > C ( P < 0.06), DEB > C ( P < 0.03)]. There were no differences in GH release during sleep (2300–0700). Deconvolution analysis revealed that the increase in 14-h integrated GH concentration on DEB was accounted for by an increase in the mass of GH secreted per pulse (per liter of distribution volume, lv): 7.0 ± 2.9 and 15.9 ± 2.6 μg/lv for C and DEB, respectively ( P < 0.01). Comparison of 1.5-h integrated GH concentrations on the SEB and DEB days (30 min exercise + 60 min recovery) revealed that, with each subsequent exercise bout, GH release apparently increased progressively, with a slightly greater increase on the DEB day [SEB vs. DEB: 497 ± 162 vs. 407 ± 166 ( bout 1), 566 ± 152 vs. 854 ± 184 ( bout 2), and 633 ± 149 vs. 1,030 ± 352 min ⋅ μg ⋅ l−1( bout 3), P < 0.05]. We conclude that the GH response to acute aerobic exercise is augmented with repeated bouts of exercise.
Effects of surfactant proteins SP-B and SP-C on dynamic and static mechanics of immature lungs
Authors: Kobayashi Tsutomu , Tashiro Katsumi , Yamamoto Ken , Nitta Shunichi , Ohmura Shigeo , Suzuki Yasuhiro
Published: December 2017

Kobayashi, Tsutomu, Katsumi Tashiro, Ken Yamamoto, Shunichi Nitta, Shigeo Ohmura, and Yasuhiro Suzuki. Effects of surfactant proteins SP-B and SP-C on dynamic and static mechanics of immature lungs. J. Appl. Physiol. 83(6): 1849–1856, 1997.—To investigate the effects of surfactant proteins B (SP-B) and C (SP-C) on lung mechanics, we compared tidal and static lung volumes of immature rabbits anesthetized with pentobarbital sodium and given reconstituted test surfactants (RTS). With a series of RTS having various SP-B concentrations (0–0.7%) but a fixed SP-C concentration (1.4%), both the tidal volume with 25-cmH2O insufflation pressure and the static volume deflated to 5-cmH2O airway pressure increased, significantly correlating with the SP-B concentration: the former increased from 6.5 to 26.0 ml/kg (mean), and the latter increased from 6.4 to 31.8 ml/kg. With another series of RTS having a fixed SP-B concentration (0.7%) but various SP-C concentrations (0–1.4%), the tidal volume increased from 5.1 to 24.8 ml/kg, significantly correlating with the SP-C concentration, whereas the static volume increased from 3.4 to 32.0 ml/kg, the ceiling value, in the presence of a minimal concentration of SP-C (0.18%). In conclusion, certain doses of SP-B and SP-C were indispensable for optimizing dynamic lung mechanics; the static mechanics, however, required significantly less SP-C.
Isoproterenol attenuates high vascular pressure-induced permeability increases in isolated rat lungs
Authors: Parker James C. , Ivey Claire L.
Published: December 2017

Parker, James C., and Claire L. Ivey.Isoproterenol attenuates high vascular pressure-induced permeability increases in isolated rat lungs. J. Appl. Physiol. 83(6): 1962–1967, 1997.—To separate the contributions of cellular and basement membrane components of the alveolar capillary barrier to the increased microvascular permeability induced by high pulmonary venous pressures (Ppv), we subjected isolated rat lungs to increases in Ppv, which increased capillary filtration coefficient ( K fc) without significant hemorrhage (31 cmH2O) and with obvious extravasation of red blood cells (43 cmH2O). Isoproterenol (20 μM) was infused in one group (Iso) to identify a reversible cellular component of injury, and residual blood volumes were measured to assess extravasation of red blood cells through ruptured basement membranes. In untreated lungs (High Ppv group), K fc increased 6.2 ± 1.3 and 38.3 ± 15.2 times baseline during the 31 and 43 cmH2O Ppv states. In Iso lungs, K fc was 36.2% ( P < 0.05) and 64.3% of that in the High Ppv group at these Ppv states. Residual blood volumes calculated from tissue hemoglobin contents were significantly increased by 53–66% in the high Ppv groups, compared with low vascular pressure controls, but there was no significant difference between High Ppv and Iso groups. Thus isoproterenol significantly attenuated vascular pressure-induced K fc increases at moderate Ppv, possibly because of an endothelial effect, but it did not affect red cell extravasation at higher vascular pressures.
Optical measurement of isolated canine lung filtration coefficients at normal hematocrits
Authors: Klaesner Joseph W. , Pou N. Adrienne , Parker Richard E. , Finney Charlene , Roselli Robert J.
Published: December 2017

Klaesner, Joseph W., N. Adrienne Pou, Richard E. Parker, Charlene Finney, and Robert J. Roselli. Optical measurement of isolated canine lung filtration coefficients at normal hematocrits. J. Appl. Physiol. 83(6): 1976–1985, 1997.—In this study, lung filtration coefficient ( K fc) values were measured in eight isolated canine lung preparations at normal hematocrit values using three methods: gravimetric, blood-corrected gravimetric, and optical. The lungs were kept in zone 3 conditions and subjected to an average venous pressure increase of 10.24 ± 0.27 (SE) cmH2O. The resulting K fc(ml ⋅ min−1 ⋅ cmH2O−1 ⋅ 100 g dry lung wt−1) measured with the gravimetric technique was 0.420 ± 0.017, which was statistically different from the K fc measured by the blood-corrected gravimetric method (0.273 ± 0.018) or the product of the reflection coefficient (ςf) and K fc measured optically (0.272 ± 0.018). The optical method involved the use of a Cellco filter cartridge to separate red blood cells from plasma, which allowed measurement of the concentration of the tracer in plasma at normal hematocrits (34 ± 1.5). The permeability-surface area product was measured using radioactive multiple indicator-dilution methods before, during, and after venous pressure elevations. Results showed that the surface area of the lung did not change significantly during the measurement of K fc. These studies suggest that ςf K fccan be measured optically at normal hematocrits, that this measurement is not influenced by blood volume changes that occur during the measurement, and that the optical ςf K fcagrees with the K fc obtained via the blood-corrected gravimetric method.
Modification of active cutaneous vasodilation by oral contraceptive hormones
Authors: Charkoudian Nisha , Johnson John M.
Published: December 2017

Charkoudian, Nisha, and John M. Johnson. Modification of active cutaneous vasodilation by oral contraceptive hormones. J. Appl. Physiol. 83(6): 2012–2018, 1997.—It is not clear whether the altered thermoregulatory reflex control of the cutaneous circulation seen among phases of the menstrual cycle also occurs with the synthetic estrogen and progesterone in oral contraceptive pills and whether any such modifications include altered control of the cutaneous active vasodilator system. To address these questions, we conducted controlled whole body heating experiments in seven women at the end of the third week of hormone pills (HH) and at the end of the week of placebo/no pills (LH). A water-perfused suit was used to control body temperature. Laser Doppler flowmetry was used to monitor cutaneous blood flow at a control site and at a site at which noradrenergic vasoconstrictor control had been eliminated by iontophoresis of bretylium (BT), isolating the active cutaneous vasodilator system. The oral temperature (Tor) thresholds for cutaneous vasodilation were higher in HH at both control [37.09 ± 0.12 vs. 36.83 ± 0.07°C (LH), P < 0.01] and BT-treated [37.19 ± 0.05 vs. 36.88 ± 0.12°C (LH), P < 0.01] sites. The Tor threshold for sweating was similarly shifted (HH: 37.15 ± 0.11°C vs. LH: 36.94 ± 0.11°C, P < 0.01). A rightward shift in the relationship of heart rate to Tor was seen in HH. The sensitivities (slopes of the responses vs. Tor) did not differ statistically between phases. The similar threshold shifts at control and BT-treated sites suggest that the hormones shift the function of the active vasodilator system to higher internal temperatures. The similarity of the shifts among thermoregulatory effectors suggests a centrally mediated action of these hormones.
Neural mechanism of the pressor response to obstructive and nonobstructive apnea
Authors: Katragadda Srinivas , Xie Ailiang , Puleo Dominic , Skatrud James B. , Morgan Barbara J.
Published: December 2017

Katragadda, Srinivas, Ailiang Xie, Dominic Puleo, James B. Skatrud, and Barbara J. Morgan. Neural mechanism of the pressor response to obstructive and nonobstructive apnea. J. Appl. Physiol. 83(6): 2048–2054, 1997.—Obstructive and nonobstructive apneas elicit substantial increases in muscle sympathetic nerve activity and arterial pressure. The time course of change in these variables suggests a causal relationship; however, mechanical influences, such as release of negative intrathoracic pressure and reinflation of the lungs, are potential contributors to the arterial pressure rise. To test the hypothesis that apnea-induced pressor responses are neurally mediated, we measured arterial pressure (photoelectric plethysmography), muscle sympathetic nerve activity (peroneal microneurography), arterial O2 saturation (pulse oximeter), and end-tidal CO2 tension (gas analyzer) during sustained Mueller maneuvers, intermittent Mueller maneuvers, and simple breath holds in six healthy humans before, during, and after ganglionic blockade with trimethaphan (3–4 mg/min, titrated to produce complete disappearance of sympathetic bursts from the neurogram). Ganglionic blockade abolished the pressor responses to sustained and intermittent Mueller maneuvers (−4 ± 1 vs. +15 ± 3 and 0 ± 2 vs. +15 ± 5 mmHg) and breath holds (0 ± 3 vs. +11 ± 3, all P < 0.05). We conclude that the acute pressor response to obstructive and nonobstructive voluntary apnea is sympathetically mediated.
Arterial baroreflex modulation of heat-induced vasodilation in the rabbit ear
Authors: Ryan Kathy L. , Taylor W. Fred , Bishop Vernon S.
Published: December 2017

Ryan, Kathy L., W. Fred Taylor, and Vernon S. Bishop.Arterial baroreflex modulation of heat-induced vasodilation in the rabbit ear. J. Appl. Physiol. 83(6): 2091–2097, 1997.—The purpose of this study was to determine whether nonthermal baroreflexes arising from cardiopulmonary and/or arterial baroreceptors modulate rabbit ear blood flow (EBF) during hyperthermia. Intact and sinoaortic-denervated (SAD) rabbits were chronically instrumented with a Doppler ultrasonic flow probe for measurement of EBF velocity (kHz). During whole body heating in conscious rabbits, EBF and ear vascular conductance (EVC) increased as core temperature increased until maximal plateau levels of EBF and EVC were reached. The maximal plateau level of EVC attained during heat stress was lower in SAD than in intact rabbits. Subsequent intrapericardial administration of procaine at maximal EBF blocked cardiac afferents but did not alter EVC in either animal group. In a second experiment, ramp decreases in mean arterial pressure were produced by vena caval occlusion at maximal EBF. In intact rabbits, EBF and EVC decreased linearly as mean arterial pressure fell, but EBF and EVC did not decrease during vena caval occlusion in SAD rabbits. Thus neither pharmacological nor mechanical unloading of cardiac baroreceptors results in reflex vasoconstriction in the heat-stressed rabbit ear. However, baroreflexes arising from arterial baroreceptors may modulate EBF in heat-stressed rabbits.
Is urodilatin the missing link in exercise-dependent renal sodium retention?
Authors: Schmidt W. , Bub A. , Meyer M. , Weiss T. , Schneider G. , Maassen N. , Forssmann W. G.
Published: December 2017

Schmidt, W., A. Bub, M. Meyer, T. Weiss, D. Schneider, N. Maassen, and W. G. Forssmann. Is urodilatin the missing link in exercise-dependent renal sodium retention? J. Appl. Physiol. 84(1): 123–128, 1998.—The purpose of the present study was to investigate the behavior of plasma atrial natriuretic peptide [ANP-(99—126)] concentration ([ANP]) and renal urodilatin [Uro; ANP-(95—126)] excretion during and after exercise and their possible effects on renal Na+retention. Ten male subjects performed a cycle ergometer test for 60 min at 60% of maximum workload. Blood and urine samples were collected before, during, and up to 24 h after exercise. During exercise, plasma [ANP] and renal Uro excretion were oppositely affected: whereas [ANP] increased from 46.5 ± 5.1 to 124.1 ± 10.6 pg/ml, urinary Uro excretion decreased from 120.8 ± 16.0 to 49.5 ± 9.8 fmol/min and remained at a lower level until 1 h after exercise. Glomerular filtration rate showed lowest values during exercise (from 164.9 ± 15.3 to 75.8 ± 10.1 ml/min), and urine flow and the fractional excretion rate of Na+([Formula: see text]) and Cl−([Formula: see text]) had their nadir during the first hour after exercise. Positive relationships were observed between Uro excretion and[Formula: see text]( P < 0.05) and[Formula: see text], whereas a tendency toward a negative correlation was obtained between [ANP] and[Formula: see text]. It seems possible that Uro may be, among other factors, involved in the exercise-related regulation of renal Na+retention. The specific roles Uro and ANP play during exercise, however, remain to be investigated.