bluuebunny/crossref_metadata_2025 huggingface dataset:
Contraction-induced increase inVmaxof palmitate uptake and oxidation in perfused skeletal muscle
Authors: Turcotte Lorraine P. , Petry Carsten , Kiens Bente , Richter Erik A.
Published: December 2017

To evaluate the effects of contractions on the kinetics of uptake and oxidation of palmitate in a physiological muscle preparation, rat hindquarters were perfused with glucose (6 mmol/l), albumin-bound [1-14C]palmitate, and varying amounts of albumin-bound palmitate (200–2,200 μmol/l) at rest and during muscle contractions. When plotted against the unbound palmitate concentration, palmitate uptake and oxidation displayed simple Michaelis-Menten kinetics with estimated maximal velocity ( Vmax) and Michaelis-Menten constant ( Km) values of 42.8 ± 3.8 (SE) nmol ⋅ min−1⋅ g−1and 13.4 ± 3.4 nmol/l for palmitate uptake and 3.8 ± 0.4 nmol ⋅ min−1⋅ g−1and 8.1 ± 2.9 nmol/l for palmitate oxidation, respectively, at rest. Whereas muscle contractions increased the Vmaxfor both palmitate uptake and oxidation to 91.6 ± 10.1 and 16.5 ± 2.3 nmol ⋅ min−1⋅ g−1, respectively, the Kmremained unchanged. Vmaxand Kmestimates obtained from Hanes-Woolf plots (substrate concentration/velocity vs. substrate concentration) were not significantly different. In the resting perfused hindquarter, an increase in palmitate delivery from 31.9 ± 0.9 to 48.7 ± 1.2 μmol ⋅ g−1⋅ h−1by increasing perfusate flow was associated with a decrease in the fractional uptake of palmitate so that the rates of uptake and oxidation of palmitate remained unchanged. It is concluded that the rates of uptake and oxidation of long-chain fatty acids (LCFA) saturate with an increase in the concentration of unbound LCFA in perfused skeletal muscle and that muscle contractions, but not an increase in plasma flow, increase the Vmaxfor LCFA uptake and oxidation. The data are consistent with the notion that uptake of LCFA in muscle may be mediated in part by a transport system.
Effect of arterial occlusion on responses of group III and IV afferents to dynamic exercise
Authors: Adreani Christine M. , Kaufman Marc P.
Published: December 2017

Our laboratory has shown previously that a low level of dynamic exercise induced by electrical stimulation of the mesencephalic locomotor region (MLR) stimulated group III and IV muscle afferents in decerebrate unanesthetized cats (C. M. Adreani, J. M. Hill, and M. P. Kaufman. J. Appl. Physiol. 83: 1811–1817, 1997). In the present study, we have extended these findings by examining the effect of occluding the arterial supply to the dynamically exercising muscles on the afferents’ responses to MLR stimulation. In decerebrate cats, we found that arterial occlusion increased the responsiveness to a low level of dynamic exercise in 44% of the group III and 47% of the group IV afferents tested. Occlusion, compared with the freely perfused state, did not increase the concentrations of either hydrogen ion or lactate ion in the venous effluent from the exercising muscles. We conclude that arterial occlusion caused some unspecified substance to accumulate in the working muscles to increase the sensitivity of equal percentages of group III and IV afferents to dynamic exercise.
Effects of high-intensity intermittent swimming on glucose transport in rat epitrochlearis muscle
Authors: Kawanaka Kentaro , Tabata Izumi , Tanaka Ayumi , Higuchi Mitsuru
Published: December 2017

Recently (K. Kawanaka, I. Tabata, and M. Higuchi. J. Appl. Physiol. 83: 429–433, 1997), we demonstrated that glucose transport activity after repeated 10-s-long in vitro tetani in rat epitrochlearis (Epi) muscle was negatively correlated with the postcontraction muscle glycogen concentration. Therefore, we examined whether high-intensity intermittent swimming, which depletes muscle glycogen to a lower level than that observed after ten 10-s-long in vitro tetani, elicits higher glucose transport than that observed after ten 10-s-long in vitro tetani, which has been regarded as the exercise-induced maximal stimulus for glucose transport. In male rats, 2-deoxy-d-glucose transport rate in Epi muscle after eight bouts of high-intensity intermittent swimming with a weight equal to 18% of body mass (exercise duration: 20 s, rest duration between exercise bouts: 40 s) was higher than that observed after the ten 10-s-long tetani (2.25 ± 0.08 vs. 1.02 ± 0.16 μmol ⋅ ml intracellular water−1⋅ 20 min−1). Muscle glycogen concentration in Epi after eight bouts of high-intensity intermittent swimming was significantly lower than that observed after ten 10-s-long in vitro tetani (7.6 ± 0.5 vs. 14.8 ± 1.4 μmol glucose/g muscle). These observations show that the high-intensity intermittent swimming increases glucose transport in rat Epi to a much higher level than that induced by ten 10-s-long in vitro tetani, which has been regarded as the exercise-related maximal stimulus for glucose transport. Furthermore, this finding suggests that the lower muscle glycogen level after high-intensity intermittent swimming than after in vitro tetani may play a role, because there was a significant negative correlation between glucose transport and muscle glycogen concentration in Epi after high-intensity swimming and in vitro tetani.
Hyperhydration: tolerance and cardiovascular effects during uncompensable exercise-heat stress
Authors: Latzka William A. , Sawka Michael N. , Montain Scott J. , Skrinar Gary S. , Fielding Roger A. , Matott Ralph P. , Pandolf Kent B.
Published: December 2017

This study examined the efficacy of glycerol and water hyperhydration (1 h before exercise) on tolerance and cardiovascular strain during uncompensable exercise-heat stress. The approach was to determine whether 1-h preexercise hyperhydration (29.1 ml H2O/kg lean body mass with or without 1.2 g/kg lean body mass of glycerol) provided a physiological advantage over euhydration. Eight heat-acclimated men completed three trials (control euhydration before exercise, and glycerol and water hyperhydrations) consisting of treadmill exercise-heat stress (ratio of evaporative heat loss required to maximal capacity of climate = 416). During exercise (∼55% maximal O2 uptake), there was no difference between glycerol and water hyperhydration methods for increasing ( P < 0.05) total body water. Glycerol hyperhydration endurance time (33.8 ± 3.0 min) was longer ( P < 0.05) than for control (29.5 ± 3.5 min), but was not different ( P > 0.05) from that of water hyperhydration (31.3 ± 3.1 min). Hyperhydration did not alter ( P > 0.05) core temperature, whole body sweating rate, cardiac output, blood pressure, total peripheral resistance, or core temperature tolerance. Exhaustion from heat strain occurred at similar core and skin temperatures and heart rates in each trial. Symptoms at exhaustion included syncope and ataxia, fatigue, dyspnea, and muscle cramps ( n = 11, 10, 2, and 1 cases, respectively). We conclude that 1-h preexercise glycerol hyperhydration provides no meaningful physiological advantage over water hyperhydration and that hyperhydration per se only provides the advantage (over euhydration) of delaying hypohydration during uncompensble exercise-heat stress.
Smaller lungs in women affect exercise hyperpnea
Authors: McClaran Steven R. , Harms Craig A. , Pegelow David F. , Dempsey Jerome A.
Published: December 2017

We subjected 29 healthy young women (age: 27 ± 1 yr) with a wide range of fitness levels [maximal oxygen uptake (V˙o2 max): 57 ± 6 ml ⋅ kg−1⋅ min−1; 35–70 ml ⋅ kg−1⋅ min−1] to a progressive treadmill running test. Our subjects had significantly smaller lung volumes and lower maximal expiratory flow rates, irrespective of fitness level, compared with predicted values for age- and height-matched men. The higher maximal workload in highly fit (V˙o2 max> 57 ml ⋅ kg−1⋅ min−1, n = 14) vs. less-fit (V˙o2 max< 56 ml ⋅ kg−1⋅ min−1, n = 15) women caused a higher maximal ventilation (V˙e) with increased tidal volume (Vt) and breathing frequency (fb) at comparable maximal Vt/vital capacity (VC). More expiratory flow limitation (EFL; 22 ± 4% of Vt) was also observed during heavy exercise in highly fit vs. less-fit women, causing higher end-expiratory and end-inspiratory lung volumes and greater usage of their maximum available ventilatory reserves. HeO2(79% He-21% O2) vs. room air exercise trials were compared (with screens added to equalize external apparatus resistance). HeO2increased maximal expiratory flow rates (20–38%) throughout the range of VC, which significantly reduced EFL during heavy exercise. When EFL was reduced with HeO2, Vt, fb, andV˙e (+16 ± 2 l/min) were significantly increased during maximal exercise. However, in the absence of EFL (during room air exercise), HeO2had no effect onV˙e. We conclude that smaller lung volumes and maximal flow rates for women in general, and especially highly fit women, caused increased prevalence of EFL during heavy exercise, a relative hyperinflation, an increased reliance on fb, and a greater encroachment on the ventilatory “reserve.” Consequently, Vt andV˙e are mechanically constrained during maximal exercise in many fit women because the demand for high expiratory flow rates encroaches on the airways’ maximum flow-volume envelope.
Single soleus muscle fiber function after hindlimb unweighting in adult and aged rats
Authors: Thompson L. V. , Johnson S. A. , Shoeman J. A.
Published: December 2017

This investigation compared how hindlimb unweighting (HU) affected the contractile function of single soleus muscle fibers from 12- and 30-mo-old Fischer 344 Brown Norway F1 Hybrid rats. After 1 wk of HU, functional properties of single permeabilized fibers were studied, and, subsequently, the fiber type was established by myosin heavy chain (MHC) analysis. After HU, the relative mass of soleus declined by 12 and 19% and the relative mass of the gastrocnemius declined by 15 and 13% in 12- and 30-mo-old animals, respectively. In 12-mo-old animals, the peak active force (5.0 ± 0.2 ×10−4vs. 3.8 ± 0.2 ×10−4N) and the peak specific tension (92 ± 4 vs. 78 ± 3 kN/m2) were significantly reduced in the MHC type I fibers by 24 and 15%, respectively. In 30-mo-old animals, the peak active force declined by 40% (4.7 ± 0.2 ×10−4vs. 2.8 ± 0. 3 ×10−4N) and the peak specific tension declined by 30% (79 ± 5 vs. 55 ± 4 kN/m2). The maximal unloaded shortening velocity of the MHC type I fibers increased in 12-mo-old animals (from 1.65 ± 0.12 to 2.59 ± 0.26 fiber lengths/s) and in 30-mo-old animals (from 0.90 ± 0.09 to 1.50 ± 0.10 fiber lengths/s) after HU. Collectively, these data suggest that the effects of HU on single soleus skeletal muscle fiber function occur in both age groups; however, the single MHC type I fibers from the older animals show greater changes than do single MHC type I fibers from younger animals.
Protein kinase C modulation of ventilatory response to hypoxia in nucleus tractus solitarii of conscious rats
Authors: Gozal Evelyne , Roussel Anisha L. , Holt Gregory A. , Gozal Lyad , Gozal Yair M. , Torres José E. , Gozal David
Published: December 2017

This study aimed to determine the role of protein kinase C (PKC) in signal transduction mechanisms underlying ventilatory regulation in the nucleus tractus solitarii (NTS). Microinjection of phorbol 12-myristate 13-acetate into the commissural NTS of nine chronically instrumented, unrestrained rats elicited significant cardiorespiratory enhancements that lasted for at least 4 h, whereas administration of vehicle ( n = 15) or the inactive phorbol ester 4α-phorbol 12,13-didecanoate ( n = 7) did not elicit minute ventilation (V˙e) changes. Peak hypoxic V˙eresponses (10% O2-balance N2) were measured in 19 additional animals after NTS microinjection of bisindolylmaleimide (BIM) I, a selective PKC inhibitor ( n= 12), BIM V (inactive analog; n = 7), or vehicle (Con; n = 19). In Con,V˙e increased from 139 ± 9 to 285 ± 26 ml/min in room air and hypoxia, respectively, and similar responses occurred after BIM V. BIM I did not affect room airV˙e but markedly attenuated hypoxia-induced V˙e increases (128 ± 12 to 167 ± 18 ml/min; P < 0.02 vs. Con and BIM V). When BIM I was microinjected into the cerebellum ( n = 4), cortex ( n = 4), or spinal cord ( n = 4),V˙e responses were similar to Con. Western blots of subcellular fractions of dorsocaudal brain stem lysates revealed translocation of PKCα, β, γ, δ, ε, and ι isoenzymes during acute hypoxia, and enhanced overall PKC activity was confirmed in the particulate fraction of dorsocaudal brain stem lysates harvested after acute hypoxia. These studies suggest that, in the adult rat, PKC activation in the NTS mediates essential components of the acute hypoxic ventilatory response.
Modeling bronchial circulation with application to soluble gas exchange: description and sensitivity analysis
Authors: Bui Thien D. , Dabdub Donald , George Steven C.
Published: December 2017

The steady-state exchange of inert gases across an in situ canine trachea has recently been shown to be limited equally by diffusion and perfusion over a wide range (0.01–350) of blood solubilities (βblood; ml ⋅ ml−1 ⋅ atm−1). Hence, we hypothesize that the exchange of ethanol (βblood = 1,756 at 37°C) in the airways depends on the blood flow rate from the bronchial circulation. To test this hypothesis, the dynamics of the bronchial circulation were incorporated into an existing model that describes the simultaneous exchange of heat, water, and a soluble gas in the airways. A detailed sensitivity analysis of key model parameters was performed by using the method of Latin hypercube sampling. The model accurately predicted a previously reported experimental exhalation profile of ethanol ( R 2= 0.991) as well as the end-exhalation airstream temperature (34.6°C). The model predicts that 27, 29, and 44% of exhaled ethanol in a single exhalation are derived from the tissues of the mucosa and submucosa, the bronchial circulation, and the tissue exterior to the submucosa (which would include the pulmonary circulation), respectively. Although the concentration of ethanol in the bronchial capillary decreased during inspiration, the three key model outputs (end-exhaled ethanol concentration, the slope of phase III, and end-exhaled temperature) were all statistically insensitive ( P > 0.05) to the parameters describing the bronchial circulation. In contrast, the model outputs were all sensitive ( P < 0.05) to the thickness of tissue separating the core body conditions from the bronchial smooth muscle. We conclude that both the bronchial circulation and the pulmonary circulation impact soluble gas exchange when the entire conducting airway tree is considered.
Catecholaminergic modulation of respiratory rhythm in an in vitro turtle brain stem preparation
Authors: Johnson Rebecca A. , Johnson Stephen M. , Mitchell Gordon S.
Published: December 2017

An in vitro brain stem preparation from adult turtles was used to determine effects of dopamine (DA) and norepinephrine (NE) on the pattern of respiratory motor output recorded from hypoglossal nerve roots (XII). Bath-applied DA (10–200 μM) increased the frequency of respiratory bursts (peaks) from 0.9 ± 0.2 to 2.4 ± 0.3 (SE) peaks/min, resulting in a 99 ± 9% increase in neural minute activity. R[+]-SCH-23390 (10 μM, D1antagonist) and eticlopride (20 μM, D2antagonist) attenuated the DA-mediated increase in peak frequency by 52 and 59%, respectively. On the other hand, the DA-receptor agonists apomorphine (D1, D2), quinelorane (D2), and SKF-38393 (D1) had no effect on peak frequency. Prazosin, an α1-adrenergic antagonist (250 nM) abolished the DA-mediated frequency increase. Although NE (10–200 μM) and phenylephrine (10–200 μM, α1-adrenergic agonist) increased peak frequency from 0.5 ± 0.1 to 1.2 ± 0.3 peaks/min and from 0.6 ± 0.1 to 1.0 ± 0.2 peaks/min, respectively, these effects were not as large as that with DA alone. The data suggest that both dopaminergic and adrenergic receptor activation in the brain stem increase respiratory frequency in turtles, but the DA receptor-mediated increase is dependent on coactivation of α1-adrenergic receptors.
Effects of posture on cardiovascular responses to lower body positive pressure at rest and during dynamic exercise
Authors: Nishiyasu Takeshi , Nagashima Kei , Nadel Ethan R. , Mack Gary W.
Published: December 2017

We tested the hypothesis that cardiovascular responses to lower body positive pressure (LBPP) would be dependent on the posture of the subject and also on the background condition (rest or exercise). We measured heart rate (HR), mean arterial blood pressure (MAP), and cardiac stroke volume in eight subjects at rest and during cycle ergometer exercise (76 ± 3 W) with and without LBPP (25, 50, and 75 mmHg) in the supine and upright positions. At rest, the increase in MAP was proportional to the increase in LBPP and was greater in the supine (6 ± 2, 15 ± 3, and 26 ± 3 mmHg) than in the upright (2 ± 3, 9 ± 3, and 17 ± 3 mmHg) position. During dynamic exercise, the increases in MAP evoked by 25, 50, and 75 mmHg LBPP were greater in the supine (13 ± 2, 28 ± 3, and 40 ± 3 mmHg) than in the upright (7 ± 3, 12 ± 3, and 25 ± 3 mmHg) position. We conclude that the systemic pressure response to LBPP is clearly dependent on the body position, with the larger pressure responses being associated with the supine position both at rest and during dynamic leg exercise.
Mechanical work of breathing during maximal voluntary ventilation
Authors: Milic-Emili Joseph , Orzalesi Marcello M.
Published: December 2017

With the use of the esophageal balloon technique, the working capacity of the respiratory muscles was assessed in four normal subjects by measuring the work per breath (W) and respiratory power (W˙) during maximal voluntary ventilation with imposed respiratory frequencies (f) ranging from 20 to 273 cycles/min. Measurements were made in a body plethysmograph to assess the work wasted as a result of alveolar gas compressibility (Wg′). In line with other types of human voluntary muscle activity, W decreased with increasing f, whereasW˙ exhibited a maximum at f of ∼100 cycles/min. Up to this f value, Wg′ was small relative to W. With further increase in f, the Wg′/W ratio increased progressively, amounting to 8–22% of W˙ at f of 200 cycles/min.
Architectural and functional features of human triceps surae muscles during contraction
Authors: Kawakami Yasuo , Ichinose Yoshiho , Fukunaga Tetsuo
Published: December 2017

Architectural properties of the triceps surae muscles were determined in vivo for six men. The ankle was positioned at 15° dorsiflexion (−15°) and 0, 15, and 30° plantar flexion, with the knee set at 0, 45, and 90°. At each position, longitudinal ultrasonic images of the medial (MG) and lateral (LG) gastrocnemius and soleus (Sol) muscles were obtained while the subject was relaxed (passive) and performed maximal isometric plantar flexion (active), from which fascicle lengths and angles with respect to the aponeuroses were determined. In the passive condition, fascicle lengths changed from 59, 65, and 43 mm (knee, 0°; ankle, −15°) to 32, 41, and 30 mm (knee, 90° ankle, 30°) for MG, LG, and Sol, respectively. Fascicle shortening by contraction was more pronounced at longer fascicle lengths. MG had greatest fascicle angles, ranging from 22 to 67°, and was in a very disadvantageous condition when the knee was flexed at 90°, irrespective of ankle positions. Different lengths and angles of fascicles, and their changes by contraction, might be related to differences in force-producing capabilities of the muscles and elastic characteristics of tendons and aponeuroses.
Effect of aerosolized acetylcholine on bronchial blood flow
Authors: Charan Nirmal B. , Carvalho Paula , Johnson Shane R. , Thompson William H. , Lakshminarayan S.
Published: December 2017

We studied the effects of aerosolized as well as intravenous infusion of acetylcholine on bronchial blood flow in six anesthetized sheep. Intravenous infusion of acetylcholine, at a dose of 2 μg/kg, increased bronchial blood flow from 45 ± 15 (SE) to 74 ± 30 ml/min, and vascular conductance increased by 76 ± 22%. In contrast, aerosolized acetylcholine at doses of 2 and 20 μg/kg decreased bronchial vascular conductance by ∼10%. At an aerosolized dose of 200 μg/kg, the bronchial vascular conductance increased by ∼15%, and there was no further increase in conductance when the aerosolized dose was increased to 2,000 μg/kg. Pretreatment of animals with a nitric oxide synthase inhibitor, N ω-nitro-l-arginine methyl ester hydrochloride, partially blocked the vasodilatory effects of intravenous acetylcholine and completely blocked the vasodilatory effects of high-dose aerosolized acetylcholine. These data suggest that aerosolized acetylcholine does not readily penetrate the vascular wall of bronchial circulatory system and, therefore, has minimal vasodilatory effects on the bronchial vasculature.
Crural diaphragm activation during dynamic contractions at various inspiratory flow rates
Authors: Beck Jennifer , Sinderby Christer , Lindström Lars , Grassino Alex
Published: December 2017

The purpose of this study was to evaluate the influence of velocity of shortening on the relationship between diaphragm activation and pressure generation in humans. This was achieved by relating the root mean square (RMS) of the diaphragm electromyogram to the transdiaphragmatic pressure (Pdi) generated during dynamic contractions at different inspiratory flow rates. Five healthy subjects inspired from functional residual capacity to total lung capacity at different flow rates while reproducing identical Pdi and chest wall configuration profiles. To change the inspiratory flow rate, subjects performed the inspirations while breathing across two different inspiratory resistances (10 and 100 cmH2O ⋅ l−1 ⋅ s), at mouth pressure targets of −10, −20, −40, and −60 cmH2O. The diaphragm electromyogram was recorded and analyzed with control of signal contamination and electrode positioning. RMS values obtained for inspirations with identical Pdi and chest wall configuration profiles were compared at the same percentage of inspiratory duration. At inspiratory flows ranging between 0.1 and 1.4 l/s, there was no difference in the RMS for the inspirations from functional residual capacity to total lung capacity when Pdi and chest wall configuration profiles were reproduced ( n = 4). At higher inspiratory flow rates, subjects were not able to reproduce their chest wall displacements and adopted different recruitment patterns. In conclusion, there was no evidence for increased demand of diaphragm activation when healthy subjects breathe with similar chest wall configuration and Pdi profiles, at increasing flow rates up to 1.4 l/s.
Chronic hormone replacement therapy does not alter resting or maximal skin blood flow
Authors: Brooks-Asplund E. M. , Kenney W. L.
Published: December 2017

Postmenopausal women on estrogen replacement therapy (ERT) regulate body core temperature at a lower baseline level at rest in a thermoneutral environment. We conducted a series of studies to test whether, in a thermoneutral environment, chronic (≥2 yr) oral ERT significantly alters baseline skin blood flow (SkBF) and cutaneous vascular conductance (CVC) and whether ERT alters maximal CVC (CVCmax) and SkBF in postmenopausal women. In the first set of studies, forearm blood flow (FBF) was measured by venous-occlusion plethysmography in 24 postmenopausal women: 8 not taking exogenous hormone therapy (No HRT group), 8 on ERT, and 8 receiving combination of estrogen and progesterone therapy, at rest and during prolonged (1 h) local heating of the forearm at 42°C. Mean arterial pressure (MAP) was measured by brachial auscultation before each set of FBF measurements to calculate forearm vascular conductance (FVC = FBF/MAP). SkBF was measured by laser-Doppler flowmetry (LDF), and CVC was calculated as LDF/MAP and standardized as %CVCmax. Baseline FVC, %CVCmax, and maximal FVC were not significantly different among the three groups of women. In the second set of experiments, LDF in ERT and No HRT groups was measured at rest in both thermoneutral and warm environments. %CVCmax was again not significantly different between ERT and No HRT groups at thermoneutral ambient temperatures and increased similarly in the warm environment. Therefore, chronic exogenous ERT does not appear to influence either baseline or maximal SkBF.
Effect of heating on vascular reactivity in rat mesenteric arteries
Authors: Massett Michael P. , Lewis Stephen J. , Bates James N. , Kregel Kevin C.
Published: December 2017

Vasoconstriction in the viscera is one of the primary cardiovascular adjustments to heating. Local temperature can influence vascular responsiveness to catecholamines and sympathetic nerve activity. Therefore, we hypothesized that heating would alter vascular reactivity in rat mesenteric arteries. Concentration-response curves to norepinephrine, phenylephrine, potassium chloride (KCl), calcium, acetylcholine, and sodium nitroprusside were obtained in vascular ring segments from rat mesenteric arteries at 37 and 41°C. In some rings, basal tension increased slightly during heating. Heating to 41°C did not alter the contractile responses to norepinephrine in endothelium-intact or -denuded rings but augmented the responses to KCl and calcium in endothelium-intact rings. The potentiating effect of heating on the responses to KCl and calcium was eliminated after endothelium removal. In contrast, the relaxant responses to acetylcholine and sodium nitroprusside were significantly attenuated at 41°C. Collectively, these results demonstrate that heating alters vascular reactivity in rat mesenteric arteries. Furthermore, these data imply that heating reduces the ability of vascular smooth muscle to relax, possibly due to a decrease in sensitivity to nitric oxide.
Force treadmill for measuring vertical and horizontal ground reaction forces
Authors: Kram Rodger , Griffin Timothy M. , Donelan J. Maxwell , Chang Young Hui
Published: December 2017

We constructed a force treadmill to measure the vertical, horizontal and lateral components of the ground-reaction forces (Fz, Fy, Fx, respectively) and the ground-reaction force moments (Mz, My, Mx), respectively exerted by walking and running humans. The chassis of a custom-built, lightweight (90 kg), mechanically stiff treadmill was supported along its length by a large commercial force platform. The natural frequencies of vibration were >178 Hz for Fzand >87 Hz for Fy, i.e., well above the signal content of these ground-reaction forces. Mechanical tests and comparisons with data obtained from a force platform runway indicated that the force treadmill recorded Fz, Fy,Mxand Myground-reaction forces and moments accurately. Although the lowest natural frequency of vibration was 88 Hz for Fx, the signal-to-noise ratios for Fxand Mzwere unacceptable. This device greatly decreases the time and laboratory space required for locomotion experiments and clinical evaluations. The modular design allows for independent use of both treadmill and force platform.
Sarcomere lesion damage occurs mainly in slow fibers of reloaded rat adductor longus muscles
Authors: Vijayan Kalpana , Thompson Joyce L. , Riley Danny A.
Published: December 2017

Sarcomere lesions were previously observed with reloading of rat adductor longus muscles after spaceflight and hindlimb unloading (HU). Spaceflown rats displayed more lesioned fibers in the “slow-fiber” region, suggesting a damage-susceptible fiber type. Unloading induces fast myosin expression in some slow fibers, generating hybrid fibers. We examined whether lesion damage differed among slow-, hybrid-, and fast-fiber types in HU-reloaded adductor longus muscles. Temporal HU for 5, 8, 11, 14, and 17 days revealed that hybrid fiber percent, detected by antimyosin immunostaining, peaked at 29 ± 12% by 14 days. A 14-day HU followed by 12–14 h of voluntary reloading was performed to induce lesions. χ2 analysis showed that slow fibers were preferentially damaged, accounting for 92 ± 5% of lesioned fibers; hybrid and fast fibers accounted for 7 ± 4 and <0.5%, respectively. Atrophy did not explain differential lesion damage across fiber types, as slow and hybrid fibers atrophied to a similar extent. Because active myofiber contractions are requisite for lesion formation, selective recruitment of slow fibers most likely explains their damage susceptibility.
Energy requirements and physical activity in free-living older women and men: a doubly labeled water study
Authors: Starling Raymond D. , Toth Michael J. , Carpenter William H. , Matthews Dwight E. , Poehlman Eric T.
Published: December 2017

Determinants of daily energy needs and physical activity are unknown in free-living elderly. This study examined determinants of daily total energy expenditure (TEE) and free-living physical activity in older women ( n = 51; age = 67 ± 6 yr) and men ( n = 48; age = 70 ± 7 yr) by using doubly labeled water and indirect calorimetry. Using multiple-regression analyses, we predicted TEE by using anthropometric, physiological, and physical activity indexes. Data were collected on resting metabolic rate (RMR), body composition, peak oxygen consumption (V˙o 2 peak), leisure time activity, and plasma thyroid hormone. Data adjusted for body composition were not different between older women and men, respectively (in kcal/day): TEE, 2,306 ± 647 vs. 2,456 ± 666; RMR, 1,463 ± 244 vs. 1,378 ± 249; and physical activity energy expenditure, 612 ± 570 vs. 832 ± 581. In a subgroup of 70 women and men, RMR andV˙o 2 peakexplained approximately two-thirds of the variance in TEE ( R 2 = 0.62; standard error of the estimate = ±348 kcal/day). Crossvalidation of this equation in the remaining 29 women and men was successful, with no difference between predicted and measured TEE (2,364 ± 398 and 2,406 ± 571 kcal/day, respectively). The strongest predictors of physical activity energy expenditure ( P < 0.05) for women and men were V˙o 2 peak( r = 0.43), fat-free mass ( r = 0.39), and body mass ( r = 0.34). In summary, RMR andV˙o 2 peak are important independent predictors of energy requirements in the elderly. Furthermore, cardiovascular fitness and fat-free mass are moderate predictors of physical activity in free-living elderly.
Platelet-activating factor modulates pulmonary vasomotor tone in the perinatal lamb
Authors: Ibe Basil O. , Hibler Sue , Raj J. Usha
Published: December 2017

Eight near-term fetal lambs were studied acutely in utero to determine role of platelet-activating factor (PAF) in the regulation of vasomotor tone in systemic and pulmonary circulations in the immediate perinatal period. Four fetal lambs were studied predelivery and 2 h postdelivery to determine circulating PAF levels. Aortic and pulmonary arterial pressures and cardiac output were measured continuously, and systemic and pulmonary vascular resistances were calculated. Left pulmonary arterial blood flow was also measured in four fetal lambs. After delivery and oxygenation, circulating PAF levels fell significantly. When WEB-2170, a specific PAF-receptor antagonist, was infused to block effect of endogenous PAF in the eight near-term fetal lambs, systemic vascular resistance fell 30% but pulmonary vascular resistance fell dramatically by 68%. Specificity of WEB-2170 was tested in juvenile lambs and was found to be very specific in lowering vasomotor tone only when tone was elevated by action of PAF. Our data show that endogenous PAF levels in the fetus contribute to maintain a high basal systemic and pulmonary vasomotor tone and that a normal fall in circulating PAF levels after birth and oxygenation may facilitate fall in pulmonary vascular resistance at birth.
O2 extraction maintains O2 uptake during submaximal exercise with β-adrenergic blockade at 4,300 m
Authors: Wolfel Eugene E. , Selland Mark A. , Cymerman A. , Brooks George A. , Butterfield Gail E. , Mazzeo Robert S. , Grover Robert F. , Reeves John T.
Published: December 2017

Whole body O2 uptake (V˙o 2) during maximal and submaximal exercise has been shown to be preserved in the setting of β-adrenergic blockade at high altitude, despite marked reductions in heart rate during exercise. An increase in stroke volume at high altitude has been suggested as the mechanism that preserves systemic O2 delivery (blood flow × arterial O2 content) and thereby maintainsV˙o 2 at sea-level values. To test this hypothesis, we studied the effects of nonselective β-adrenergic blockade on submaximal exercise performance in 11 normal men (26 ± 1 yr) at sea level and on arrival and after 21 days at 4,300 m. Six subjects received propranolol (240 mg/day), and five subjects received placebo. At sea level, during submaximal exercise, cardiac output and O2 delivery were significantly lower in propranolol- than in placebo-treated subjects. Increases in stroke volume and O2 extraction were responsible for the maintenance of V˙o 2. At 4,300 m, β-adrenergic blockade had no significant effect onV˙o 2, ventilation, alveolar Po 2, and arterial blood gases during submaximal exercise. Despite increases in stroke volume, cardiac output and thereby O2 delivery were still reduced in propranolol-treated subjects compared with subjects treated with placebo. Further reductions in already low levels of mixed venous O2 saturation were responsible for the maintenance ofV˙o 2 on arrival and after 21 days at 4,300 m in propranolol-treated subjects. Despite similar workloads and V˙o 2, propranolol-treated subjects exercised at greater perceived intensity than subjects given placebo at 4,300 m. The values for mixed venous O2 saturation during submaximal exercise in propranolol-treated subjects at 4,300 m approached those reported at simulated altitudes >8,000 m. Thus β-adrenergic blockade at 4,300 m results in significant reduction in O2delivery during submaximal exercise due to incomplete compensation by stroke volume for the reduction in exercise heart rate. Total bodyV˙o 2 is maintained at a constant level by an interaction between mixed venous O2 saturation, the arterial O2-carrying capacity, and hemodynamics during exercise with acute and chronic hypoxia.
Effects of lung volume on diaphragm EMG signal strength during voluntary contractions
Authors: Beck Jennifer , Sinderby Christer , Lindström Lars , Grassino Alex
Published: December 2017

The use of esophageal recordings of the diaphragm electromyogram (EMG) signal strength to evaluate diaphragm activation during voluntary contractions in humans has recently been criticized because of a possible artifact created by changes in lung volume. Therefore, the first aim of this study was to evaluate whether there is an artifactual influence of lung volume on the strength of the diaphragm EMG during voluntary contractions. The second aim was to measure the required changes in activation for changes in lung volume at a given tension, i.e., the volume-activation relationship of the diaphragm. Healthy subjects ( n = 6) performed contractions of the diaphragm at different transdiaphragmatic pressure (Pdi) targets (range 20–160 cmH2O) while maintaining chest wall configuration constant at different lung volumes. The diaphragm EMG was recorded with a multiple-array esophageal electrode, with control of signal contamination and electrode positioning. The effects of lung volume on the EMG were studied by comparing the crural diaphragm EMG root mean square (RMS), an index of crural diaphragm activation, with an index of global diaphragm activation obtained by normalizing Pdi to the maximum Pdi at the given muscle length (Pdi/P[Formula: see text]) at the different lung volumes. We observed a direct relationship between RMS and Pdi/P[Formula: see text]independent of diaphragm length. The volume-activation relationship of the diaphragm was equally affected by changes in lung volume as the volume-Pdi relationship (60% change from functional residual capacity to total lung capacity). We conclude that the RMS of the diaphragm EMG is not artifactually influenced by lung volume and can be used as a reliable index of diaphragm activation. The volume-activation relationship can be used to infer changes in the length-tension relationship of the diaphragm at submaximal activation/contraction levels.
Muscle use during dynamic knee extension: implication for perfusion and metabolism
Authors: Ray Chester A. , Dudley Gary A.
Published: December 2017

Dynamic one-legged knee extension (DKE) is commonly used to examine physiological responses to “aerobic” exercise. Muscle blood flow during DKE is often expressed relative to quadriceps femoris muscle mass irrespective of work rate. This is contrary to the notion that increased force is achieved by recruitment in large muscles. The purpose of this study, therefore, was to determine muscle use during DKE. Six subjects had magnetic resonance images taken of their quadriceps femoris before and after 4 min of DKE at 20 and 40 W. Muscle use was determined by shifts in T2. The cross-sectional area of quadriceps femoris that had an elevated T2 was 16 ± 1% (mean ± SE) preexercise, and 54 ± 5 and 94 ± 4% after 20- and 40-W DKE, respectively. Volume of quadriceps femoris increased 11.4 ± 0.2% ( P = 0.006), from 2,230 ± 233 cm3before exercise to 2,473 ± 232 cm3 after 40-W DKE. Extrapolation of these data indicates that 1,301 ± 111 cm3 of quadriceps femoris were engaged during 20-W DKE compared with 2,292 ± 154 cm3 during 40-W DKE. By using muscle blood flow data for submaximal DKE at 20 W [P. Andersen and B. Saltin. J. Physiol. (Lond.)366: 233–249, 1985; and L. B. Rowell, B. Saltin, B. Kiens, and N. J. Christensen. Am. J. Physiol. 251 ( Heart Circ. Physiol. 20): H1038–H1044, 1986] and estimating muscle use in those studies from our data (total muscle mass × 0.54), extrapolated blood flow to active muscle (263 and 278 ml ⋅ min−1 ⋅ 100 g−1, respectively) is comparable to that obtained during peak aerobic DKE when expressed relative to total muscle mass (243 and 250 ml ⋅ min−1 ⋅ 100 g−1, respectively). These findings indicate that increased power during aerobic DKE is achieved by recruitment. Additionally, they suggest that blood flow to the active quadriceps femoris muscle does not increase with increases in submaximal work rate but instead is maximal to support aerobic metabolism. Thus increases in muscle blood flow are directed to newly recruited muscle, not to increased perfusion of muscle already engaged.
Pulmonary vagal innervation is required to establish adequate alveolar ventilation in the newborn lamb
Authors: Wong Kevin A. , Bano Ather , Rigaux Anita , Wang Bing , Bharadwaj Baikhunth , Schürch Samuel , Green Francis , Remmers John E. , Hasan Shabih U.
Published: December 2017

To investigate the effects of bilateral intrathoracic vagotomy on the establishment of continuous breathing and effective gas exchange at birth, we studied 8 chronically instrumented, unanesthetized, sham-operated and 14 vagotomized newborn lambs after a spontaneous, unassisted vaginal delivery. Fetal lambs were instrumented in utero to record sleep states, diaphragmatic electromyogram, blood pressure, arterial pH, and blood-gas tensions. Six of eight sham-operated lambs established effective gas exchange within 10 min of birth, whereas 12 of 14 vagotomized animals developed respiratory acidosis and hypoxemia ( P= 0.008). Breathing frequency in vagotomized newborns was significantly lower during the entire postnatal period compared with sham-operated newborns. Vagotomized subjects also remained hypothermic during the entire postnatal period ( P < 0.05). Bronchoalveolar lavage indicated an increased minimum surface tension, whereas lung histology showed perivascular edema and partial atelectasis in the vagotomized group. We conclude that stimulation of breathing and effective gas exchange are critically dependent on intact vagal nerves during the transition from fetal to neonatal life.
Genetic and other determinants of AMP deaminase activity in healthy adult skeletal muscle
Authors: Norman Barbara , Mahnke-Zizelman Donna K. , Vallis Amy , Sabina Richard L.
Published: December 2017

AMPD1 genotype, relative fiber type composition, training status, and gender were evaluated as contributing factors to the reported variation in AMP deaminase enzyme activity in healthy skeletal muscle. Multifactorial correlative analyses demonstrate that AMPD1 genotype has the greatest effect on enzyme activity. An AMPD1 mutant allele frequency of 13.7 and a 1.7% incidence of enzyme deficiency was found across 175 healthy subjects. Homozygotes for the AMPD1 normal allele have high enzyme activities, and heterozygotes display intermediate activities. When examined according to genotype, other factors were found to affect variability as follows: AMP deaminase activity in homozygotes for the normal allele exhibits a negative correlation with the relative percentage of type I fibers and training status. Conversely, residual AMP deaminase activity in homozygotes for the mutant allele displays a positive correlation with the relative percentage of type I fibers. Opposing correlations in different homozygous AMPD1 genotypes are likely due to relative fiber-type differences in the expression of AMPD1 and AMPD3 isoforms. Gender also contributes to variation in total skeletal muscle AMP deaminase activity, with normal homozygous and heterozygous women showing only 85–88% of the levels observed in genotype-matched men.
Endurance in high-fat-fed rats: effects of carbohydrate content and fatty acid profile
Authors: Helge Jørn W. , Ayre Kerry , Chaunchaiyakul Suwadee , Hulbert Anthony J. , Kiens Bente , Storlien Leonard H.
Published: December 2017

The purpose of this experiment was to study endurance performance and substrate storage and utilization in fat- or carbohydrate-fed rats. Ninety-nine rats were randomly divided into three groups and over 4 wk were fed either a carbohydrate-rich [CHO; 10% total energy content in the diet (E%) fat, 20 E% protein, 70 E% carbohydrate] diet or one of two fat-rich diets (65 E% fat, 20 E% protein, 15 E% carbohydrate) containing either saturated (Sat) or monounsaturated fatty acids (Mono). Each dietary group was randomly assigned to a trained (6 days/wk, progressive to 60 min, 28 m/min at a 10% incline) or a sedentary group. Rats were killed either before or after a treadmill endurance run to exhaustion. Training increased endurance (206%), but diet composition did not affect endurance in either trained or sedentary rats. β-Hydroxyacyl-CoA dehydrogenase activity was increased in fat-fed but not carbohydrate-fed rats ( P < 0.05). Respiratory exchange ratio during the initial phase of exercise was lower after the Mono compared with the Sat diet ( P < 0.05) and higher after the CHO than the Sat diet ( P < 0.05). Thus adaptation to a high-fat diet containing a moderate amount of carbohydrates did not induce enhanced endurance in either trained or untrained rats; however, substrate utilization was modulated by both amount and type of dietary fat during the initial stage of exercise in trained and sedentary rats.
Faster adjustment of O2delivery does not affect V˙o 2 on-kinetics in isolated in situ canine muscle
Authors: Grassi Bruno , Gladden L. Bruce , Samaja Michele , Stary Creed M. , Hogan Michael C.
Published: December 2017

The mechanism(s) limiting muscle O2 uptake (V˙o 2) kinetics was investigated in isolated canine gastrocnemius muscles ( n = 7) during transitions from rest to 3 min of electrically stimulated isometric tetanic contractions (200-ms trains, 50 Hz; 1 contraction/2 s; 60–70% of peakV˙o 2). Two conditions were mainly compared: 1) spontaneous adjustment of blood flow (Q˙) [control, spontaneousQ˙ (C Spont)]; and 2) pump-perfusedQ˙, adjusted ∼15 s before contractions at a constant level corresponding to the steady-state value during contractions in C Spont [faster adjustment of O2 delivery (Fast O2 Delivery)]. During Fast O2 Delivery, 1–2 ml/min of 10−2 M adenosine were infused intra-arterially to prevent inordinate pressure increases with the elevated Q˙. The purpose of the study was to determine whether a faster adjustment of O2 delivery would affectV˙o 2 kinetics.Q˙ was measured continuously; arterial ([Formula: see text]) and popliteal venous ([Formula: see text]) O2 contents were determined at rest and at 5- to 7-s intervals during contractions; O2 delivery was calculated asQ˙ ⋅ [Formula: see text], and V˙o 2 was calculated asQ˙ ⋅ arteriovenous O2 content difference. Times to reach 63% of the difference between baseline and steady-stateV˙o 2 during contractions were 23.8 ± 2.0 (SE) s in C Spont and 21.8 ± 0.9 s in Fast O2 Delivery (not significant). In the present experimental model, elimination of any delay in O2 delivery during the rest-to-contraction transition did not affect muscleV˙o 2 kinetics, which suggests that this kinetics was mainly set by an intrinsic inertia of oxidative metabolism.
Exercise-training-induced alterations in hepatic function in mares
Authors: Dyke T. M. , Sams R. A. , Hinchcliff K. W.
Published: December 2017

The effects of exercise training on hepatic function in horses were determined by studying the plasma clearance of antipyrine (20 mg/kg iv) in adult mares that either underwent treadmill training for 5 wk ( n = 7) or remained in box stalls for the same time period ( n = 6). Training consisted of treadmill exercise at 60% (12 min/day) and 90% (3 min/day) of pretraining maximal oxygen consumption (V˙o2 max) for 6 days/wk for 5 wk.V˙o2 maxand velocity to obtain a blood lactate concentration of 4 mmol/l were significantly increased (from 129 to 149 ml ⋅ min−1⋅ kg−1and from 5.6 to 6.1 m/s, respectively) as a result of training. The plasma clearance and volume of distribution of antipyrine increased significantly in the trained group (from 5.5 to 6.4 ml ⋅ min−1⋅ kg−1and from 813 to 881 ml/kg, respectively) and decreased significantly in the untrained group. Elimination half-lives did not change as a result of training or box rest. Increases in plasma antipyrine clearance were indicative of an increase in hepatic metabolism of antipyrine. Increases in the volume of distribution of antipyrine suggest that total body water increases as a result of exercise training.
Effect of prolonged, heavy exercise on pulmonary gas exchange in athletes
Authors: Hopkins Susan R. , Gavin Timothy P. , Siafakas Nikos M. , Haseler Luke J. , Olfert Ivan M. , Wagner Harrieth , Wagner Peter D.
Published: December 2017

During maximal exercise, ventilation-perfusion inequality increases, especially in athletes. The mechanism remains speculative. We hypothesized that, if interstitial pulmonary edema is involved, prolonged exercise would result in increasing ventilation-perfusion inequality over time by exposing the pulmonary vascular bed to high pressures for a long duration. The response to short-term exercise was first characterized in six male athletes [maximal O2 uptake (V˙o 2 max) = 63 ml ⋅ kg−1 ⋅ min−1] by using 5 min of cycling exercise at 30, 65, and 90%V˙o 2 max. Multiple inert-gas, blood-gas, hemodynamic, metabolic rate, and ventilatory data were obtained. Resting log SD of the perfusion distribution (log SDQ˙) was normal [0.50 ± 0.03 (SE)] and increased with exercise (log SDQ˙ = 0.65 ± 0.04, P < 0.005), alveolar-arterial O2 difference increased (to 24 ± 3 Torr), and end-capillary pulmonary diffusion limitation occurred at 90%V˙o 2 max. The subjects recovered for 30 min, then, after resting measurements were taken, exercised for 60 min at ∼65%V˙o 2 max. O2 uptake, ventilation, cardiac output, and alveolar-arterial O2difference were unchanged after the first 5 min of this test, but log SDQ˙ increased from 0.59 ± 0.03 at 5 min to 0.66 ± 0.05 at 60 min ( P < 0.05), without pulmonary diffusion limitation. Log SDQ˙ was negatively related to total lung capacity normalized for body surface area ( r = −0.97, P < 0.005 at 60 min). These data are compatible with interstitial edema as a mechanism and suggest that lung size is an important determinant of the efficiency of gas exchange during exercise.