bluuebunny/crossref_metadata_2025 huggingface dataset:
Gender-specific regional changes in genetic structure of muscularity in early adolescence
Authors: Loos R. , Thomis M. , Maes H. H. , Beunen G. , Claessens A. L. , Derom C. , Legius E. , Derom R. , Vlietinck R.
Published: December 2017

Loos, R., M. Thomis, H. H. Maes, G. Beunen, A. L. Claessens, C. Derom, E. Legius, R. Derom, and R. Vlietinck. Gender-specific regional changes in genetic structure of muscularity in early adolescence. J. Appl. Physiol. 82(6): 1802–1810, 1997.—Genetic and environmental influences on muscle circumference measurements of the extremities were estimated in 105 pairs of twins between 10 and 14 yr of age. Four circumferences, extended upper arm (EAC), forearm (FC), thigh (TC), and calf (CC), were measured. Univariate model fitting revealed that the largest part (87–95%) of the variance for all circumferences at most ages was explained by additive genetic factors. Sex differences were observed for some age categories. Multivariate analyses showed a different pattern evolving according to age and gender. In boys from 10 to 12 yr of age, one general genetic factor influenced all four circumferences. With increasing age, an arm-leg model emerged, one genetic factor influencing the arm and another genetic factor the leg circumferences. In young girls one genetic factor loaded on the proximal (EAC,TC) and another on the distal (FC,CC) circumferences. With subjects at age 14 yr, an arm-leg model was observed. High genetic correlations indicated that genetic factors related to EAC, FC, TC, and CC did not act independently. The age- and gender-specific changes in the genetic structure suggest pubertal influences. This study shows that muscle circumferences are highly heritable characteristics and are therefore a promising starting point at which to locate their genes. Gene mapping could validate the gender-specific change of the genetic structure with age and region.
Exercise-induced changes in circulating growth factors with cyclic variation in plasma estradiol in women
Authors: Hornum Mette , Cooper Dan M. , Brasel Jo Anne , Bueno Alina , Sietsema Kathy E.
Published: December 2017

Hornum, Mette, Dan M. Cooper, Jo Anne Brasel, Alina Bueno, and Kathy E. Sietsema. Exercise-induced changes in circulating growth factors and cyclic variation in plasma estradiol in women. J. Appl. Physiol. 82(6): 1946–1951, 1997.—The effect of 10 min of high-intensity cycling exercise on circulating growth hormone (GH), insulin-like growth factors I and II (IGF-I and -II), and insulin-like growth factor binding protein 3 (IGF BP-3) was studied in nine eumenorrheic women (age 19–48 yr) at two different phases of the menstrual cycle. Tests were performed on separate mornings corresponding to the follicular phase and to the periovulatory phase of the menstrual cycle, during which plasma levels of endogenous estradiol (E2) were relatively low (272 ± 59 pmol/l) and high (1,112 ± 407 pmol/l), respectively. GH increased significantly in response to exercise under both E2conditions. Plasma GH before exercise (2.73 ± 2.48 vs. 1.71 ± 2.09 μg/l) and total GH over 10 min of exercise and 1-h recovery (324 ± 199 vs. 197 ± 163 ng) were both significantly greater for periovulatory phase than for follicular phase studies. IGF-I, but not IGF-II, increased acutely after exercise. IGF BP-3, assayed by radioimmunoassay, was not significantly different at preexercise, end exercise, or at 30-min recovery time points and was not different between the two study days. When assayed by Western blot, however, there was a significant increase in IGF BP-3 30 min after exercise for the periovulatory study. These findings indicate that the modulation of GH secretion associated with menstrual cycle variations in circulating E2affects GH measured after exercise, at least in part, by an increase in baseline levels. The acute increase in IGF-I induced by exercise appears to be independent of the GH response and is not affected by menstrual cycle timing.
Thermal and circulatory responses during exercise: effects of hypohydration, dehydration, and water intake
Authors: Armstrong Lawrence E. , Maresh Carl M. , Gabaree Catherine V. , Hoffman Jay R. , Kavouras Stavros A. , Kenefick Robert W. , Castellani John W. , Ahlquist Lynn E.
Published: December 2017

Armstrong, Lawrence E., Carl M. Maresh, Catherine V. Gabaree, Jay R. Hoffman, Stavros A. Kavouras, Robert W. Kenefick, John W. Castellani, and Lynn E. Ahlquist. Thermal and circulatory responses during exercise: effects of hypohydration, dehydration, and water intake. J. Appl. Physiol. 82(6): 2028–2035, 1997.—This investigation examined the distinct and interactive effects of initial hydration state, exercise-induced dehydration, and water rehydration in a hot environment. On four occasions, 10 men performed a 90-min heat stress test (treadmill walking at 5.6 km/h, 5% grade, 33°C, 56% relative humidity). These heat stress tests differed in pretest hydration [2 euhydrated (EU) and 2 hypohydrated (HY) trials] and water intake during exercise [2 water ad libitum (W) and 2 no water (NW) trials]. HY + NW indicated greater physiological strain than all other trials ( P < 0.05–0.001) in heart rate, plasma osmolality (Posm), sweat sensitivity (g / °C ⋅ min), and rectal temperature. Unexpectedly, final HY + W and EU + W responses for rectal temperature, heart rate, and Posm were similar, despite the initial 3.9 ± 0.2% hypohydration in HY + W. We concluded that differences in pretest Posm (295 ± 7 and 287 ± 5 mosmol/kg for HY + W and EU + W, respectively) resulted in greater water consumption (1.65 and 0.31 liter for HY + W and EU + W, respectively), no voluntary dehydration (0.9% body mass increase), and attenuated thermal and circulatory strain during HY + W.
Chemical stimulation of cardiac receptors attenuates locomotion in mesencephalic cats
Authors: Pickar Joel G.
Published: December 2017

Pickar, Joel G. Chemical stimulation of cardiac receptors attenuates locomotion in mesencephalic cats. J. Appl. Physiol. 83(1): 113–119, 1997.—The purpose of the present investigation was to determine whether chemical stimulation of cardiac receptors is sufficient to inhibit locomotion. Decerebrate, unanesthetized cats were induced to walk on a treadmill by electrically stimulating the mesencephalic locomotor region (MLR). Cardiac receptors were stimulated by injecting nicotine (62.3 ± 8.6 μg/kg, mean ± SE) into the pericardial sac. Cardiac nerve activity was reversibly blocked by injecting procaine (2%) into the pericardial sac. Locomotion was monitored by using bipolar needle electrodes inserted into the lateral gastrocnemius (LG) and tibialis anterior (TA) muscles. Integrated electromyographic (iEMG) activity from each muscle was quantified on a step-by-step basis. Intrapericardial (ipc) nicotine inhibited locomotion and evoked the coronary chemoreflex. Blood pressure and heart rate decreased significantly by 45.6 ± 7.1 mmHg and 59.3 ± 12.3 beats/min, respectively. Nicotine ipc significantly reduced iEMG activity by 24–28% in the LG muscles. The TA muscles were not affected consistently by ipc nicotine. The locomotor inhibition and the depressor reflex paralleled each other and occurred within 5 s of nicotine injection. Procaine ipc blocked the nicotine-induced locomotor inhibition and depressor reflex. The effects of procaine were largely reversible, because ipc nicotine reduced iEMG activity in the LG (25–46%) but not in the TA muscles after washing procaine from the pericardial sac. These results demonstrate that cardiac receptors sensitive to nicotine inhibit MLR-induced locomotion in the decerebrate cat. These findings indicate the presence of a neural pathway from the heart whereby endogenous stimuli could reflexly alter motor control.
High lung inflation increases mRNA levels of ECM components and growth factors in lung parenchyma
Authors: Berg John T. , Fu Zhenxing , Breen Ellen C. , Tran Hung-Cuong , Mathieu-Costello Odile , West John B.
Published: December 2017

Berg, John T., Zhenxing Fu, Ellen C. Breen, Hung-Cuong Tran, Odile Mathieu-Costello, and John B. West. High lung inflation increases mRNA levels of ECM components and growth factors in lung parenchyma. J. Appl. Physiol. 83(1): 120–128, 1997.—Remodeling of pulmonary capillaries occurs after chronic increases in capillary pressure (e.g., mitral stenosis). Also, remodeling of pulmonary arteries begins within 4 h of increased wall stress and is endothelium dependent. We have previously shown that high lung inflation increases wall stress in pulmonary capillaries. This study was designed to determine whether high lung inflation induces remodeling of the extracellular matrix (ECM) in lung parenchyma. Open-chest rabbits were ventilated for 4 h with 9-cmH2O positive end-expiratory pressure (PEEP) on one lung and 1-cmH2O PEEP on the other (High-PEEP group), or with 2-cmH2O PEEP on both lungs (Low-PEEP group). An additional untreated control group was also included. We found increased levels of mRNA in both lungs of High-PEEP rabbits (compared with both the Low-PEEP and untreated groups) for α1(III) and α2(IV) procollagen, fibronectin, basic fibroblast growth factor, and transforming growth factor-β1. In contrast, α2(I) procollagen and vascular endothelial growth factor mRNA levels were not changed. We conclude that high lung inflation for 4 h increases mRNA levels of ECM components and growth factors in lung parenchyma.
Effects of dietary manipulations and glucose infusion on glucagon response during exercise in rats
Authors: Tadjoré Maurice , Bergeron Raynald , Latour Martin , Désy François , Warren Claude , Lavoie Jean-Marc
Published: December 2017

Tadjoré, Maurice, Raynald Bergeron, Martin Latour, François Désy, Claude Warren, and Jean-Marc Lavoie.Effects of dietary manipulations and glucose infusion on glucagon response during exercise in rats. J. Appl. Physiol. 83(1): 148–152, 1997.—The purpose of the present investigation was to test the hypothesis that blood glucose concentration is not always related to glucagon response during exercise. Three groups of rats were submitted to a prolonged (3-h) swimming exercise. Two groups of rats had their normal food intake restricted by 50% the night before the experiment. One of these two groups of rats was intravenously infused with glucose throughout exercise to maintain euglycemia. The third group of rats swam while under normal dietary conditions. Plasma glucose, sampled in arterial blood, was reduced ( P < 0.05) at 75, 105, 150, and 170 min of exercise (from ∼130 to 110 mg/dl) in the food-restricted animals without glucose infusion, whereas a significant ( P < 0.05) increase was measured in the two other groups during exercise. A significant ( P < 0.01) difference in the mean integrated areas under the glucose-concentration curve was found only between the fed and the two food-restricted groups. Plasma insulin concentrations decreased ( P < 0.05) similarly in all groups during exercise, whereas plasma epinephrine and norepinephrine concentrations increased significantly ( P < 0.01) in all groups. Despite differences between groups in plasma glucose response during exercise, and despite the absence of any decrease in exercising blood glucose levels in at least two of the three groups, plasma glucagon responses were increased ( P < 0.05) similarly in all groups (from ∼250 to 550 pg/ml) at the end of the exercise period. The increase in glucagon was significant after 90 min of exercise in the food-restricted groups, with or without glucose infusion, but only after 140 min in the fed group. These results indicate that the glucagon response during exercise is not always linked to the decrease in plasma glucose.
Age-related declines in maximal aerobic capacity in regularly exercising vs. sedentary women: a meta-analysis
Authors: Fitzgerald Margaret D. , Tanaka Hirofumi , Tran Zung V. , Seals Douglas R.
Published: December 2017

Fitzgerald, Margaret D., Hirofumi Tanaka, Zung V. Tran, and Douglas R. Seals. Age-related declines in maximal aerobic capacity in regularly exercising vs. sedentary women: a meta-analysis. J. Appl. Physiol. 83(1): 160–165, 1997.—Our purpose was to determine the relationship between habitual aerobic exercise status and the rate of decline in maximal aerobic capacity across the adult age range in women. A meta-analytic approach was used in which mean maximal oxygen consumption (V˙o 2 max) values from female subject groups (ages 18–89 yr) were obtained from the published literature. A total of 239 subject groups from 109 studies involving 4,884 subjects met the inclusion criteria and were arbitrarily separated into sedentary (groups = 107; subjects = 2,256), active (groups = 69; subjects = 1,717), and endurance-trained (groups = 63; subjects = 911) populations.V˙o 2 max averaged 29.7 ± 7.8, 38.7 ± 9.2, and 52.0 ± 10.5 ml ⋅ kg−1 ⋅ min−1, respectively, and was inversely related to age within each population ( r = −0.82 to −0.87, all P < 0.0001). The rate of decline inV˙o 2 max with increasing subject group age was lowest in sedentary women (−3.5 ml ⋅ kg−1 ⋅ min−1⋅ decade−1), greater in active women (−4.4 ml ⋅ kg−1 ⋅ min−1⋅ decade−1), and greatest in endurance-trained women (−6.2 ml ⋅ kg−1 ⋅ min−1 ⋅ decade−1) (all P < 0.001 vs. each other). When expressed as percent decrease from mean levels at age ∼25 yr, the rates of decline inV˙o 2 max were similar in the three populations (−10.0 to −10.9%/decade). There was no obvious relationship between aerobic exercise status and the rate of decline in maximal heart rate with age. The results of this cross-sectional study support the hypothesis that, in contrast to the prevailing view, the rate of decline in maximal aerobic capacity with age is greater, not smaller, in endurance-trained vs. sedentary women. The greater rate of decline inV˙o 2 max in endurance-trained populations may be related to their higher values as young adults (baseline effect) and/or to greater age-related reductions in exercise volume; however, it does not appear to be related to a greater rate of decline in maximal heart rate with age.
Effects of vigorous exercise training and β-agonist administration on bone response to hindlimb suspension
Authors: Bloomfield Susan A. , Girten Beverly E. , Weisbrode Steven E.
Published: December 2017

Bloomfield, Susan A., Beverly E. Girten, and Steven E. Weisbrode. Effects of vigorous exercise training and β-agonist administration on bone response to hindlimb suspension. J. Appl. Physiol. 83(1): 172–178, 1997.—The effectiveness of dobutamine (Dob) in preventing bone loss during 14 days of hindlimb suspension (Sus) was tested in exercise-trained (Ex; n = 25) and sedentary (Sed; n = 22) rats (age 155 days). One-half of each group was given Dob (2 mg ⋅ kg−1 ⋅ day−1) or saline (Sal). Histomorphometric measurements at midfemur revealed a 17% smaller cortical bone area (CBA) and a 32% lower periosteal mineral apposition rate (MAR) in suspended vs. nonsuspended Sed/Sal rats. Dob abolished this decline in CBA in Sed/Sus rats, probably via an attenuation of the decrease in periosteal MAR; similar but nonsignificant effects on cross-sectional moment of inertia were observed. Nonsuspended Ex rats had no change in bone CBA when CBA is indexed to body weight. Sus appeared to uncouple the relationship between soleus weight and CBA. Dob attenuated the 43% decline in soleus weight after Sus in Ex but not in Sed rats. In summary, vigorous Ex before Sus does not affect loss of bone mass due to unloading; Dob effectively maintains CBA in Sed rats subjected to suspension.
Inputs from upper airway affect firing of respiratory-associated midbrain neurons
Authors: Chen Zibin , Eldridge Frederic L.
Published: December 2017

Chen, Zibin, and Frederic L. Eldridge. Inputs from upper airway affect firing of respiratory-associated midbrain neurons. J. Appl. Physiol. 83(1): 196–203, 1997.—In 16 decerebrated unanesthetized cats, we studied effects of neural inputs from upper airway on firing of 62 mesencephalic neurons that also developed respiratory-associated (RA) rhythmic firing when respiratory drive was high [Z. Chen, F. L. Eldridge, and P.G. Wagner. J. Physiol. (Lond.) 437: 305–325, 1991] and on firing of 16 neurons that did not develop the rhythmic firing (non-RA neurons). Activity in RA neurons increased after mechanical expansion of pharynx (45% of those tested) or larynx (68%) and after stimulation of glossopharyngeal (50%) or superior laryngeal nerves (77%). The increased neuronal firing occurred despite decreases or abolition of respiratory activity (expressed in phrenic nerve). Neuronal firing also increased after mechanical stimulation of nasal mucosa (66%) or by jets of air directed into the nares (48%) and after light brushing of nasal skin (∼40%). Most stimuli led to decreased firing in a smaller number of neurons, and some neurons showed no response. None of the non-RA neurons developed an increase of firing after any of the stimuli, although one had decreased firing after stimulation of the superior laryngeal nerve. We conclude that inputs from the upper airway and nasal skin have independent modulatory effects on the same mesencephalic neurons that are stimulated by ascending rhythmic RA input from the medulla. These findings may have relevance to generation of the sensation of dyspnea.
Postnatal lung function and protein permeability after fetal or maternal corticosteroids in preterm lambs
Authors: Rebello Celso M. , Ikegami Machiko , Ervin M. Gore , Polk Daniel H. , Jobe Alan H.
Published: December 2017

Rebello, Celso M., Machiko Ikegami, M. Gore Ervin, Daniel H. Polk, and Alan H. Jobe. Postnatal lung function and protein permeability after fetal or maternal corticosteroids in preterm lambs. J. Appl. Physiol. 83(1): 213–218, 1997.—We evaluated postnatal lung function and intravascular albumin loss to tissues of 123-days-gestation preterm surfactant-treated and ventilated lambs 15 h after direct fetal ( n = 8) or maternal ( n = 9) betamethasone treatment or saline placebo ( n = 9). The betamethasone-treated groups had similar increases in dynamic compliances, ventilatory efficiency indexes, and lung volumes relative to controls ( P < 0.05). The losses of125I-labeled albumin from blood, a marker of intravascular integrity, and the recoveries of125I-albumin in muscle and brain were similar for control and betamethasone-exposed lambs. Betamethasone-treated lambs had lower recoveries of125I-albumin in lung tissues and in alveolar washes than did controls ( P < 0.01). Although blood pressures were higher for the treated groups ( P< 0.05), all groups had similar blood volumes, cardiac outputs, and organ blood flows. Maternal or fetal treatment with betamethasone 15 h before preterm delivery equivalently improved postnatal lung function, reduced albumin recoveries in lungs, and increased blood pressures. However, prenatal betamethasone had no effects on the systemic intravascular losses of albumin or did not change blood volumes.
Sequential arousal and airway-defensive behavior of infants in asphyxial sleep environments
Authors: Lijowska Anna S. , Reed Nevada W. , Chiodini Barbara A. Mertins , Thach Bradley T.
Published: December 2017

Lijowska, Anna S., Nevada W. Reed, Barbara A. Mertins Chiodini, and Bradley T. Thach. Sequential arousal and airway-defensive behavior of infants in asphyxial sleep environments. J. Appl. Physiol. 83(1): 219–228, 1997.—Infants are prone to accidental asphyxiation. Therefore, we studied airway-defensive behaviors and their relationship to spontaneous arousal behavior in 41 healthy sleeping infants (2–26 wk old), using two protocols: 1) infant was rebreathing expired air, face covered by bedding material; and 2) infant was exposed to hypercarbia, face uncovered. Multiple measurements of respiratory and motor activities were recorded (video, polygraph). The infants’ response to increasing hypercarbia consisted of four highly stereotyped behaviors: sighs (augmented breaths), startles, thrashing limb movements, and full arousal (eyes open, cry). These behaviors occurred abruptly in self-limited clusters of activity and always in the same sequence: first a sigh coupled with a startle, then thrashing, then full arousal. Incomplete sequences (initial behaviors only) occurred far more frequently than the complete sequence and were variably effective in removing the bedding covering the airway. In both protocols, as inspired CO2increased, incomplete arousal sequences recurred periodically and with increasing frequency and complexity until the infant either succeeded in clearing his/her airway or was completely aroused. Spontaneous arousal sequences, identical to those occurring during hypercarbia, occurred periodically during sleep. This observation suggests that the infant’s airway-defensive responses to hypercarbia consist of an increase in the frequency and complexity of an endogenously regulated, periodically occurring sequence of arousal behaviors.
Ventilatory response to helium-oxygen breathing during exercise: effect of airway anesthesia
Authors: Krishnan Bharath S. , Clemens Ron E. , Zintel Trevor A. , Stockwell Martin J. , Gallagher Charles G.
Published: December 2017

Krishnan, Bharath S., Ron E. Clemens, Trevor A. Zintel, Martin J. Stockwell, and Charles G. Gallagher. Ventilatory response to helium-oxygen breathing during exercise: effect of airway anesthesia. J. Appl. Physiol. 83(1): 82–88, 1997.—The substitution of a normoxic helium mixture (HeO2) for room air (Air) during exercise results in a sustained hyperventilation, which is present even in the first breath. We hypothesized that this response is dependent on intact airway afferents; if so, airway anesthesia (Anesthesia) should affect this response. Anesthesia was administered to the upper airways by topical application and to lower central airways by aerosol inhalation and was confirmed to be effective for over 15 min. Subjects performed constant work-rate exercise (CWE) at 69 ± 2 (SE) % maximal work rate on a cycle ergometer on three separate days: twice after saline inhalation ( days 1 and 3) and once after Anesthesia ( day 2). CWE commenced after a brief warm-up, with subjects breathing Air for the first 5 min (Air-1), HeO2 for the next 3 min, and Air again until the end of CWE (Air-2). The resistance of the breathing circuit was matched for Air and HeO2. Breathing HeO2 resulted in a small but significant increase in minute ventilation (V˙i) and decrease in alveolar [Formula: see text] in both the Saline (average of 2 saline tests; not significant) and Anesthesia tests. Although Anesthesia had no effect on the sustained hyperventilatory response to HeO2breathing, theV˙i transients within the first six breaths of HeO2 were significantly attenuated with Anesthesia. We conclude that theV˙i response to HeO2 is not simply due to a reduction in external tubing resistance and that, in humans, airway afferents mediate the transient but not the sustained hyperventilatory response to HeO2 breathing during exercise.
Transcapillary escape rate of albumin in humans during exercise-induced hypervolemia
Authors: Haskell Andrew , Nadel Ethan R. , Stachenfeld Nina S. , Nagashima Kei , Mack Gary W.
Published: December 2017

Haskell, Andrew, Ethan R. Nadel, Nina S. Stachenfeld, Kei Nagashima, and Gary W. Mack. Transcapillary escape rate of albumin in humans during exercise-induced hypervolemia. J. Appl. Physiol. 83(2): 407–413, 1997.—To test the hypotheses that plasma volume (PV) expansion 24 h after intense exercise is associated with reduced transcapillary escape rate of albumin (TERalb) and that local changes in transcapillary forces in the previously active tissues favor retention of protein in the vascular space, we measured PV, TERalb, plasma colloid osmotic pressure (COPp), interstitial fluid hydrostatic pressure (Pi), and colloid osmotic pressure in leg muscle and skin and capillary filtration coefficient (CFC) in the arm and leg in seven men and women before and 24 h after intense upright cycle ergometer exercise. Exercise expanded PV by 6.4% at 24 h (43.9 ± 0.8 to 46.8 ± 1.2 ml/kg, P< 0.05) and decreased total protein concentration (6.5 ± 0.1 to 6.3 ± 0.1 g/dl, P < 0.05) and COPp (26.1 ± 0.8 to 24.3 ± 0.9 mmHg, P < 0.05), although plasma albumin concentration was unchanged. TERalb tended to decline (8.4 ± 0.5 to 6.5 ± 0.7%/h, P = 0.11) and was correlated with the increase in PV ( r = −0.69, P < 0.05). CFC increased in the leg (3.2 ± 0.2 to 4.3 ± 0.5 μl ⋅ 100 g−1 ⋅ min−1 ⋅ mmHg−1, P < 0.05), and Pi showed a trend to increase in the leg muscle (2.8 ± 0.7 to 3.8 ± 0.3 mmHg, P = 0.08). These data demonstrate that TERalb is associated with PV regulation and that local transcapillary forces in the leg muscle may favor retention of albumin in the vascular space after exercise.
Contractile apparatus and sarcoplasmic reticulum function: effects of fatigue, recovery, and elevated Ca2+
Authors: Williams Jay H.
Published: December 2017

Williams, Jay H. Contractile apparatus and sarcoplasmic reticulum function: effects of fatigue, recovery, and elevated Ca2+. J. Appl. Physiol. 83(2): 444–450, 1997.—This investigation tested the notion that fatiguing stimulation induces intrinsic changes in the contractile apparatus and sarcoplasmic reticulum (SR) and that these changes are initiated by elevated intracellular Ca2+concentration ([Ca2+]i). Immediately after stimulation of frog semitendinosus muscle, contractile apparatus and SR function were measured. Despite a large decline in tetanic force (Po), maximal Ca2+-activated force (Fmax) of the contractile apparatus was not significantly altered. However, Ca2+sensitivity was increased. In conjunction, the rate constant of Ca2+uptake by the SR was diminished, and the caffeine sensitivity of Ca2+release was decreased. During recovery, Po, contractile apparatus, and SR function each returned to near-initial levels. Exposure of skinned fibers to 0.5 μM free Ca2+for 5 min depressed both Fmaxand Ca2+sensitivity of the contractile apparatus. In addition, caffeine sensitivity of Ca2+release was diminished. Results suggest that fatigue induces intrinsic alterations in contractile apparatus and SR function. Changes in contractile apparatus function do not appear to be mediated by increased [Ca2+]i. However, a portion of the change in SR Ca2+release seems to be due to elevated [Ca2+]i.
Chronic β-blockade increases skeletal muscle β-adrenergicreceptor density and enhances contractile force
Authors: Murphy René J. L. , Gardiner Phillip F. , Rousseau Guy , Bouvier Michel , Béliveau Louise
Published: December 2017

Murphy, René J. L., Phillip F. Gardiner, Guy Rousseau, Michel Bouvier, and Louise Béliveau. Chronic β-blockade increases skeletal muscle β-adrenergic-receptor density and enhances contractile force. J. Appl. Physiol.83(2): 459–465, 1997.—The effects of a chronic 14-day administration of a selective β2-adrenergic-receptor antagonist (ICI-118551) on skeletal muscle were evaluated in female Sprague-Dawley rats. Chronic ICI-118551 treatment did not modify muscle mass, oxidative potential, or protein concentration of the medial gastrocnemius muscle, suggesting that maintenance of these skeletal muscle characteristics is not dependent on β2-adrenergic-receptor stimulation. However, the drug treatment increased β-adrenergic-receptor density of the lateral gastrocnemius (42%) and caused an increase in specific (g/g) isometric in situ contractile forces of the medial gastrocnemius [twitch, 56%; tetanic (200 Hz), 28%]. The elevated contractile forces observed after a chronic treatment with ICI-118551 were completely abolished when the β2-adrenergic antagonist was also administered acutely before measurement of contractile forces, suggesting that this response is β2-adrenergic-receptor dependent. Possible mechanisms for the increased forces were studied. Caffeine administration potentiated twitch forces but had little effect on tetanic force in control animals. Administration of dibutyryl adenosine 3′,5′-cyclic monophosphate in control animals also resulted in small increases of twitch force but did not modify tetanic forces. We conclude that increases in β-adrenergic-receptor density and the stimulation of the receptors by endogenous catecholamines appear to be responsible for increased contractile forces but that the mechanism remains to be demonstrated.
Curtailed respiration by repeated vs. isolated hypoxia in maturing piglets is unrelated to NTS ME or SP levels
Authors: Waters Karen A. , Laferrière André , Paquette Julie , Goodyer Cynthia , Moss Immanuela R.
Published: December 2017

Waters, Karen A., André Laferrière, Julie Paquette, Cynthia Goodyer, and Immanuela R. Moss. Curtailed respiration by repeated vs. isolated hypoxia in maturing piglets is unrelated to NTS ME or SP levels. J. Appl. Physiol. 83(2): 522–529, 1997.—In early development, respiratory disorders can produce recurring hypoxic episodes during sleep. To examine possible effects of daily repeated vs. isolated hypoxic hypoxia, cardiorespiratory functions and central, respiratory-related neuromodulator levels in 21- to 32-day-old, chronically instrumented, unsedated piglets were compared between a fifth sequential daily hypoxia and an isolated hypoxia (10% O2-90% N2 for 30 min). Diaphragmatic electromyographic activity, heart rate and arterial pressure, and pH and gas tensions were measured. In vivo microdialysis, via chronically implanted guides, served to sample interstitial substance P (SP) and methionine-enkephalin (ME) at the level of the respiratory-related nucleus tractus solitarii (NTS). Compared with an isolated hypoxia, repeated hypoxia resulted in 1) lower respiratory frequency (f), ventilation equivalent, and arterial pH, higher arterial [Formula: see text]during hypoxia, and lower f in recovery from hypoxia; and 2) increased SP concentrations but no change in ME concentrations. We conclude that, in these maturing swine, repeated vs. isolated hypoxic exposure curtails respiratory responses to hypoxia by a mechanism(s) unrelated to SP or ME levels at the NTS.
Downstream effects of splanchnic ischemia-reperfusion injury on renal function and eicosanoid release
Authors: Rothenbach Patricia , Turnage Richard H. , Iglesias Jose , Riva Angela , Bartula Lori , Myers Stuart I.
Published: December 2017

Rothenbach, Patricia, Richard H. Turnage, Jose Iglesias, Angela Riva, Lori Bartula, and Stuart I. Myers. Downstream effects of splanchnic ischemia-reperfusion injury on renal function and eicosanoid release. J. Appl. Physiol.82(2): 530–536, 1997.—This study examines the hypothesis that intestinal ischemia-reperfusion (I/R) injury contributes to renal dysfunction by altered renal eicosanoid release. Anesthetized Sprague-Dawley rats underwent 60 min of sham or superior mesenteric artery (SMA) occlusion with 60 min of reperfusion. The I/R groups received either allopurinol, pentoxifylline, 1-benzylimidazole, or carrier before SMA occlusion. In vivo renal artery blood flow was measured by Transonic flow probes, the kidneys were then perfused in vitro for 30 min, and the effluent was analyzed for eicosanoid release and renal function. Intestinal I/R caused a twofold increase in the ratio of renal release of thromboxane B2to prostaglandin E2and to 6-ketoprostaglandin F1αcompared with the sham level, with a corresponding 25% decrease in renal sodium and inulin clearance and renal blood flow. Pentoxifylline or allopurinol pretreatment restored renal eicosanoid release and renal sodium and inulin clearance to the sham level but did not alter renal blood flow. Pretreatment with 1-benzylimidazole restored renal function, eicosanoid release, and renal blood flow to sham levels. These data suggest that severe intestinal I/R contributes to the downregulation of renal function. The decrease in renal function is due in part to toxic oxygen metabolites, which occur in the milieu of altered renal eicosanoid release, reflecting a decrease in vasodilator and an increase in vasoconstrictor eicosanoids.
EEG and sleep disturbances during dives at 450 msw in helium-nitrogen-oxygen mixture
Authors: Rostain J. C. , Gardette-Chauffour M. C. , Naquet R.
Published: December 2017

Rostain, J. C., M. C. Gardette-Chauffour, and R. Naquet. EEG and sleep disturbances during dives at 450 msw in helium-nitrogen-oxygen mixture. J. Appl. Physiol. 83(2): 575–582, 1997.—To study the effects of nitrogen addition to the breathing mixture on sleep disturbances at pressure, two dives were performed in which helium-nitrogen-oxygen mixture was used up to 450 m sea water (msw). In total, sleep of 12 professional divers was analyzed (i.e., 184 night records). Sleep was disrupted by compression and by stay at 450 msw: we observed an increase in awake periods and in sleep stages I and II and a decrease in stages III and IV and in rapid-eye-movement sleep periods. These changes, which were more intense at the beginning of the stay, began to decrease from the seventh day of the stay, but the return to control values was recorded only during the decompression at depths below 200 msw. These changes were equivalent to those recorded in other experiments with helium-oxygen mixture in the same range of depths and were independent of the intensity of changes recorded in electroencephalographic activities in awake subjects.
Heat strain models applicable for protective clothing systems: comparison of core temperature response
Authors: Gonzalez R. R. , McLellan T. M. , Withey W. R. , Chang S. K. , Pandolf K. B.
Published: December 2017

Gonzalez, R. R., T. M. McLellan, W. R. Withey, S. K. Chang, and K. B. Pandolf. Heat strain models applicable for protective clothing systems: comparison of core temperature response. J. Appl. Physiol. 83(3): 1017–1032, 1997.—Core temperature (Tc) output comparisons were analyzed from thermal models applicable to persons wearing protective clothing. The two models evaluated were the United States (US) Army Research Institute of Environmental Medicine (USARIEM) heat strain experimental model and the United Kingdom (UK) Loughborough (LUT25) model. Data were derived from collaborative heat-acclimation studies conducted by three organizations and included an intermittent-work protocol (Canada) and a continuous-exercise/heat stress protocol (UK and US). Volunteers from the US and the UK were exposed to a standard exercise/heat stress protocol (ambient temperature 35°C/50% relative humidity, wind speed 1 m/s, level treadmill speed 1.34 m/s). Canadian Forces volunteers did an intermittent-work protocol (15 min moderate work/15 min rest at ambient temperature of 40°C/30% relative humidity, wind speed ≈0.4 m/s). Each model reliably predicted Tc responses (within the margin of error determined by 1 root mean square deviation) during work in the heat with protective clothing. Models that are analytically similar to the classic Stolwijk-Hardy model serve as robust operational tools for prediction of physiological heat strain when modified to incorporate clothing heat-exchange factors.
Analysis of perfluorochemical elimination from the respiratory system
Authors: Shaffer Thomas H. , Foust Raymond , Wolfson Marla R. , Miller Thomas F.
Published: December 2017

Shaffer, Thomas H., Raymond Foust IIII, Marla R. Wolfson, and Thomas F. Miller, Jr. Analysis of perfluorochemical elimination from the respiratory system. J. Appl. Physiol. 83(3): 1033–1040, 1997.—We describe a simple apparatus for analysis of perfluorochemicals (PFC) in expired gas and thus a means for determining PFC vapor and liquid elimination from the respiratory system. The apparatus and data analysis are based on thermal conduction and mass transfer principles of gases. In vitro studies were conducted with the PFC vapor analyzer to determine calibration curves for output voltage as a function of individual respiratory gases, respiratory gases saturated with PFC vapor, and volume percent standards for percent PFC saturation (%PFC-Sat) in air. Voltage-concentration data for %PFC-Sat of the vapor from the in vitro tests were accurate to within 2.0% from 0 to 100% PFC-Sat, linear ( r = 0.99, P < 0.001), and highly reproducible. Calculated volume loss of PFC liquid over time correlated well with actual loss by weight ( r = 0.99, P < 0.001). In vivo studies with neonatal lambs demonstrated that PFC volume loss and evaporation rates decreased nonlinearly as a function of time. These relationships were modulated by changes in PFC physical properties, minute ventilation, and postural repositioning. The results of this study demonstrate the sensitivity and accuracy of an on-line method for PFC analysis of expired gas and describe how it may be useful in liquid-assisted ventilation procedures for determining PFC volume loss, evaporation rate, and optimum dosing and ventilation strategy.
Reduction of allergic airway responses in P-selectin-deficient mice
Authors: De Sanctis George T. , Wolyniec Walter W. , Green Francis H. Y. , Qin Shixin , Jiao Aiping , Finn Patricia W. , Noonan Thomas , Joetham Anthony A. , Gelfand Erwin , Doerschuk Claire M. , Drazen Jeffrey M.
Published: December 2017

De Sanctis, George T., Walter W. Wolyniec, Francis H. Y. Green, Shixin Qin, Aiping Jiao, Patricia W. Finn, Thomas Noonan, Anthony A. Joetham, Erwin Gelfand, Claire M. Doerschuk, and Jeffrey M. Drazen. Reduction of allergic airway responses in P-selectin-deficient mice. J. Appl. Physiol. 83(3): 681–687, 1997.—P-selectin is an adhesion receptor that has been shown to be important in the recruitment of eosinophils and lymphocytes in a variety of inflammatory conditions. Because cellular recruitment is thought to be a critical event in allergen-induced changes in airway responsiveness, we reasoned that P-selectin-deficient mice would exhibit reduced airway responsiveness and cellular trafficking noted in wild-type (+/+) mice. Both (+/+) and P-selectin-deficient (−/−) mice sensitized and challenged with ovalbumin (OVA/OVA) exhibited the same capacity to produce increased titers of total and OVA-specific immunoglobulin E. Airway responsiveness to methacholine was significantly greater in the (+/+) (OVA/OVA) animals than it was in the respective (−/−) (OVA/OVA) group or control groups ( P = 0.0016). Bronchoalveolar lavage fluid from (−/−) (OVA/OVA) mice contained significantly fewer eosinophils and lymphocytes compared with the (+/+) (OVA/OVA) mice ( P < 0.05). These results suggest that the predominant role of P-selectin in OVA-induced airway hyperresponsiveness is to promote the airway inflammatory response to allergen inhalation.
Mechanisms for the mechanical response of airway smooth muscle to length oscillation
Authors: Shen X. , Wu M. F. , Tepper R. S. , Gunst S. J.
Published: December 2017

Shen, X., M. F. Wu, R. S. Tepper, and S. J. Gunst. Mechanisms for the mechanical response of airway smooth muscle to length oscillation. J. Appl. Physiol. 83(3): 731–738, 1997.—Airway smooth muscle tone in vitro is profoundly affected by oscillations in muscle length, suggesting that the effects of lung volume changes on airway tone result from direct effects of stretch on the airway smooth muscle. We analyzed the effect of length oscillation on active force and length-force hysteresis in canine tracheal smooth muscle at different oscillation rates and amplitudes during contraction with acetylcholine. During the shortening phase of the length oscillation cycle, the active force generated by the smooth muscle decreased markedly below the isometric force but returned to isometric force as the muscle was lengthened. Results indicate that at rates comparable to those during tidal breathing, active shortening and yielding of contractile elements contributes to the modulation of force during length oscillation; however, the depression of force during shortening cannot be accounted for by cross-bridge properties, shortening-induced cross-bridge deactivation, or active relaxation. We conclude that the depression of contractility may be a function of the plasticity of the cellular organization of contractile filaments, which enables contractile element length to be reset in relation to smooth muscle cell length as a result of smooth muscle stretch.
Superior laryngeal nerve section alters responses to upper airway distortion in sleeping dogs
Authors: Curran Aidan K. , Eastwood Peter R. , Harms Craig A. , Smith Curtis A. , Dempsey Jerome A.
Published: December 2017

Curran, Aidan K., Peter R. Eastwood, Craig A. Harms, Curtis A. Smith, and Jerome A. Dempsey. Superior laryngeal nerve section alters responses to upper airway distortion in sleeping dogs. J. Appl. Physiol. 83(3): 768–775, 1997.—We investigated the effect of superior laryngeal nerve (SLN) section on expiratory time (Te) and genioglossus electromyogram (EMGgg) responses to upper airway (UA) negative pressure (UANP) in sleeping dogs. The same dogs used in a similar intact study (C. A. Harms, C. A., Y.-J. Zeng, C. A. Smith, E. H. Vidruk, and J. A. Dempsey. J. Appl. Physiol. 80: 1528–1539, 1996) were bilaterally SLN sectioned. After recovery, the UA was isolated while the animal breathed through a tracheostomy. Square waves of negative pressure were applied to the UA from below the larynx or from the mask (nares) at end expiration and held until the next inspiratory effort. Section of the SLN increased eupneic respiratory frequency and minute ventilation. Relative to the same dogs before SLN section, sublaryngeal UANP caused less Te prolongation while activation of the genioglossus required less negative pressures. Mask UANP had no effect on Te or EMGgg activity. We conclude that the SLN 1) is not obligatory for the reflex prolongation of Te and activation of EMGgg activity produced by UANP and 2) plays an important role in the maintenance of UA stability and the pattern of breathing in sleeping dogs.
Phrenic motoneuron firing rates before, during, and after prolonged inspiratory resistive loading
Authors: Road J. D. , Cairns A. M.
Published: December 2017

Road, J. D., and A. M. Cairns. Phrenic motoneuron firing rates before, during, and after prolonged inspiratory resistive loading. J. Appl. Physiol. 83(3): 776–783, 1997.—Phrenic motoneuron firing rates during brief inspiratory resistive loading (IRL) are high, and nearly all the motoneurons are recruited. Diaphragmatic fatigue has been difficult to demonstrate during IRL. Furthermore, evidence from studies in limb muscles has shown variable motoneuron responses to prolonged high-intensity loads. We studied phrenic motoneuron firing rates before, during, and after prolonged IRL in anesthetized rabbits. Of 117 phrenic axons, only 2 axons were not recruited; 41 axons were silent during unloaded breathing but were recruited at higher loads. Silent axons showed a more rapid increase in firing rate as the load increased. Phrenic motoneuron firing rates increased throughout the period of loading, whereas airway pressure swings did not. After prolonged IRL, higher motoneuron firing rates were needed during brief loads to produce the same airway pressure. No evidence of a decline in motoneuron firing rates was seen at any point. We conclude that the respiratory muscles can be shown to demonstrate physiological responses consistent with fatigue during prolonged IRL, and activation rates are high and remain so throughout this prolonged loading.
Interaction of cross-sectional area, driving pressure, and airflow of passive velopharynx
Authors: Isono Shiroh , Feroah Thom R. , Hajduk Eric A. , Brant Rollin , Whitelaw William A. , Remmers John E.
Published: December 2017

Isono, Shiroh, Thom R. Feroah, Eric A. Hajduk, Rollin Brant, William A. Whitelaw, and John E. Remmers. Interaction of cross-sectional area, driving pressure, and airflow of passive velopharynx. J. Appl. Physiol. 83(3): 851–859, 1997.—Previous studies have shown that, when the pharyngeal muscles are relaxed, the velopharynx is a highly compliant segment of the pharynx. Thus, under these circumstances, cross-sectional area of the velopharynx ( A VP), driving pressure across the velopharynx (ΔP), and inspiratory airflow (V˙i) will be mutually interdependent variables. The purpose of the present investigation was to describe the interrelation among these three variables during inspiration. We studied 15 sleeping patients with obstructive sleep apnea/hypopnea when the pharyngeal muscles were rendered hypotonic by applying continuous positive airway pressure to the nasal airway. A VP, determined by endoscopic imaging, was significantly greater at onset ofV˙i limitation than at minimum oropharyngeal pressure ( P < 0.01). Snoring was never observed duringV˙ilimitation. In a subgroup of six patients, values for ΔP,V˙i, and A VP were obtained at 0.1-s intervals at various levels of mask pressure. For these six patients, the mathematical expressionV˙i = 0.657( A VP/ A max) ⋅ ΔP0.332, where A max is maximal A VP, described the relationship among the three variables ( R 2 = 0.962) for flow-limited and non-flow-limited inspirations. The impedance of the passive velopharynx, defined as ΔP0.33/V˙, was inversely related to A VP and increased dramatically when A VP was <0.3 cm2. In summary, we observed a progressive decrease in A VP during flow-limited inspiration in patients with obstructive sleep apnea. This constriction of the velopharynx contributes to an increase in velopharyngeal impedance that, in turn, counterbalances the increase in ΔP during flow limitation.
Cardiovascular responses to treadmill and cycle ergometer exercise in children and adults
Authors: Turley Kenneth R. , Wilmore Jack H.
Published: December 2017

Turley, Kenneth R., and Jack H. Wilmore. Cardiovascular responses to treadmill and cycle ergometer exercise in children and adults. J. Appl. Physiol. 83(3): 948–957, 1997.—This study was conducted to determine whether submaximal cardiovascular responses at a given rate of work are different in children and adults, and, if different, what mechanisms are involved and whether the differences are exercise-modality dependent. A total of 24 children, 7 to 9 yr old, and 24 adults, 18 to 26 yr old (12 males and 12 females in each group), participated in both submaximal and maximal exercise tests on both the treadmill and cycle ergometer. With the use of regression analysis, it was determined that cardiac output (Q˙) was significantly lower ( P ≤ 0.05) at a given O2 consumption level (V˙o 2, l/min) in boys vs. men and in girls vs. women on both the treadmill and cycle ergometer. The lower Q˙ in the children was compensated for by a significantly higher ( P ≤ 0.05) arterial-mixed venous O2difference to achieve the same or similarV˙o 2. Furthermore, heart rate and total peripheral resistance were higher and stroke volume was lower in the children vs. in the adult groups on both exercise modalities. Stroke volume at a given rate of work was closely related to left ventricular mass, with correlation coefficients ranging from r = 0.89–0.92 and r = 0.88–0.93 in the males and females, respectively. It was concluded that submaximal cardiovascular responses are different in children and adults and that these differences are related to smaller hearts and a smaller absolute amount of muscle doing a given rate of work in the children. The differences were not exercise-modality dependent.
Nonlinear systems identification: autocorrelation vs. autoskewness
Authors: Sammon Michel , Curley Frederick
Published: December 2017

Sammon, Michel, and Frederick Curley. Nonlinear systems identification: autocorrelation vs. autoskewness. J. Appl. Physiol. 83(3): 975–993, 1997.—Autocorrelation function ( C 1) or autoregressive model parameters are often estimated for temporal analysis of physiological measurements. However, statistical approximations truncated at linear terms are unlikely to be of sufficient accuracy for patients whose homeostatic control systems cannot be presumed to be stable local to a single equilibrium. Thus a quadratic variant of C 1[autoskewness function ( C 2)] is introduced to detect nonlinearities in an output signal as a function of time delays. By use of simulations of nonlinear autoregressive models, C 2 is shown to identify only those nonlinearities that “break” the symmetry of a system, altering the mean and skewness of its outputs. Case studies of patients with cardiopulmonary dysfunction demonstrate a range of ventilatory patterns seen in the clinical environment; whereas testing of C 1reveals their breath-by-breath minute ventilation to be significantly autocorrelated, the C 2 test concludes that the correlation is nonlinear and asymmetrically distributed. Higher-order functionals [e.g., autokurtosis ( C 3)] are necessary for global analysis of metastable systems that continuously “switch” between multiple equilibrium states and unstable systems exhibiting nonequilibrium dynamics.