bluuebunny/crossref_metadata_2025 huggingface dataset:
Pituitary-adrenal-gonadal responses to high-intensity resistance exercise overtraining
Authors: Fry A. C. , Kraemer W. J. , Ramsey L. T.
Published: December 2017

Weight-trained men [OT ; n = 11; age = 22.0 ± 0.9 (SE) yr] resistance trained daily at 100% one-repetition maximum (1-RM) intensity for 2 wk, resulting in 1-RM strength decrements and in an overtrained state. A control group (Con; n = 6; age = 23.7 ± 2.4 yr) trained 1 day/wk at a low relative intensity (50% 1 RM). After 2 wk, the OT group exhibited slightly increased exercise-induced testosterone (preexercise = 26.5 ± 1.3 nmol/l, postexercise = 29.1 ± 5.9 nmol/l) and testosterone-to-cortisol ratio (preexercise = 0.049 ± 0.007 nmol/l, postexercise = 0.061 ± 0.006 nmol/l) and decreased exercise-induced cortisol (preexercise = 656.1 ± 98.1 nmol/l, postexercise = 503.1 ± 39.7 nmol/l). Serum concentrations for growth hormone and plasma peptide F [preproenkephalin (107—140)] were similar for both groups throughout the overtraining period. This hormonal profile is distinctly different from what has been previously reported for other types of overtraining, indicating that high-relative-intensity resistance exercise overtraining may not be successfully monitered via circulating testosterone and cortisol. Unlike overtraining conditions with endurance athletes, altered resting concentrations of pituitary, adrenal, or gonadal hormones were not evident, and exercise-induced concentrations were only modestly affected.
Corticosteroid effects on diaphragm neuromuscular junctions
Authors: Sieck Gary C. , Van Balkom Roland H. H. , Prakash Y. S. , Zhan Wen-Zhi , Dekhuijzen P. N. Richard
Published: December 2017

The effects of corticosteroid (CS) treatment (prednisolone continuously administered subcutaneously at a flow rate of 2.5 μl/h, daily dose 5.6 mg/kg, for 3 wk) on neuromuscular junction (NMJ) morphology and neuromuscular transmission in rat diaphragm muscle (Dimus) were compared with weight-matched (Sham) and ad libitum fed control (Ctl) groups. Fibers were classified on the basis of myosin heavy chain (MHC) isoform expression. CS treatment caused significant atrophy of fibers expressing MHC2X(type IIx), either alone or with MHC2B(type IIx/b). Fibers expressing MHCslow(type I) and MHC2A(type IIa) were unaffected by CS. The planar areas of nerve terminals and motor endplates at type IIx/b fibers were smaller in CS-treated Dimuscompared with Sham and Ctl. However, CS-induced atrophy of type IIx/b fibers exceeded changes in NMJ morphology. Thus, when normalized for fiber diameter, NMJs were relatively larger in the CS-treated group compared with Ctl. Neuromuscular transmission failure, assessed in vitro by comparing force loss during repetitive (40 Hz) nerve vs. direct muscle stimulation, was less in CS-treated Dimus. These results indicate that alterations in NMJ morphology after CS treatment are dependent on fiber type and may contribute to improved neuromuscular transmission.
Effects of prolonged oxygen exposure at 1.5, 2.0, or 2.5 ATA on pulmonary function in men (Predictive Studies V)
Authors: Clark J. M. , Lambertsen C. J. , Gelfand R. , Flores N. D. , Pisarello J. B. , Rossman M. D. , Elias J. A.
Published: December 2017

As part of a study of human organ O2tolerance, lung flow-volume and spirometric measurements were performed repeatedly before, during, and after continuous O2exposures at 1.5, 2.0, and 2.5 ATA for average durations of 17.7, 9.0, and 5.7 h, respectively (effects of O2breathing at 3.0 ATA for 3.5 h were reported previously; J. M. Clark, R. M. Jackson, C. J. Lambertsen, R. Gelfand, W. D. B. Hiller, and M. Unger. J. Appl. Physiol. 71: 878–885, 1991). Additional measurements of pulmonary mechanical function, gas exchange, and alveolar inflammatory cells were obtained before and after O2exposure. Rates of pulmonary symptom development and lung volume reduction increased progressively with elevation of O2pressure. Average rates of vital capacity reduction over a useful range of O2pressures provided a valuable general description of pulmonary O2tolerance in humans. However, the existence of multiple pulmonary effects of O2toxicity and the complexity of their interactions require awareness that deviations from the average relationships may occur in different individuals or under varying conditions of O2exposure and subsequent recovery. The associated pulmonary function deficits may represent responses to a composite of direct and indirect effects of O2poisoning, along with related consequences and subsequent reactions to those effects.
Methacholine causes reflex bronchoconstriction
Authors: Wagner Elizabeth M. , Jacoby David B.
Published: December 2017

To determine whether methacholine causes vagally mediated reflex constriction of airway smooth muscle, we administered methacholine to sheep either via the bronchial artery or as an aerosol via tracheostomy into the lower airways. We then measured the contraction of an isolated, in situ segment of trachealis smooth muscle and determined the effect of vagotomy on the trachealis response. Administering methacholine to the subcarinal airways via the bronchial artery (0.5–10.0 μg/ml) caused dose-dependent bronchoconstriction and contraction of the tracheal segment. At the highest methacholine concentration delivered, trachealis smooth muscle tension increased an average of 186% over baseline. Aerosolized methacholine (5–7 breaths of 100 mg/ml) increased trachealis tension by 58% and airways resistance by 183%. As the bronchial circulation in the sheep does not supply the trachea, we postulated that the trachealis contraction was caused by a reflex response to methacholine in the lower airways. Bilateral vagotomy essentially eliminated the trachealis response and the airways resistance change after lower airways challenge (either via the bronchial artery or via aerosol) with methacholine. We conclude that 1) methacholine causes a substantial reflex contraction of airway smooth muscle and 2) the assumption may not be valid that a response to methacholine in humans or experimental animals represents solely the direct effect on smooth muscle.
Expression of fibroblast growth factor family during postnatal skeletal muscle hypertrophy
Authors: Mitchell Pamela , Steenstrup Tom , Hannon Kevin
Published: December 2017

The potential role of the fibroblast growth factor (FGF) family during stretch-induced postnatal skeletal muscle hypertrophy was analyzed by using an avian wing-weighting model. After 2 or 11 days of weighted stretch, anterior latissimus dorsi (ALD) muscles were, on average, 34 ( P < 0.01) and 85% ( P < 0.01) larger, respectively, than unweighted ALD control muscles. By using quantitative RT-PCR, FGF-1 mRNA expression was found to be significantly decreased in ALD muscles stretched for 2 or 11 days. In contrast, FGF-4 and FGF-10 mRNA expression was significantly increased 2 days after initiation of stretch. FGF-2, FGF-10, fibroblast growth factor receptor 1, and FREK mRNA expression was significantly increased at 11 days poststretch. Increases in FGF-2 and FGF-4 protein could be detected throughout the myofiber periphery after 11 days of stretch. On a cellular level, FGF-2 and FGF-4 proteins were differentially localized. This differential expression pattern and protein localization of the FGF family in response to stretch-induced hypertrophy suggest distinct roles for individual FGFs during the postnatal hypertrophy process.
Endogenous vasopressin does not mediate hypoxia-induced anapyrexia in rats
Authors: Steiner Alexandre A. , Carnio Evelin C. , Antunes-Rodrigues José , Branco Luiz G. S.
Published: December 2017

The present study was designed to test the hypothesis that arginine vasopressin (AVP) mediates hypoxia-induced anapyrexia. The rectal temperature of awake, unrestrained rats was measured before and after hypoxic hypoxia, AVP-blocker injection, or a combination of the two. Control animals received saline injections of the same volume. Basal body temperature was 36.52 ± 0.29°C. We observed a significant ( P < 0.05) reduction in body temperature of 1.45 ± 0.33°C after hypoxia (7% inspired O2), whereas systemic and central injections of AVP V1- and AVP V2-receptor blockers caused no change in body temperature. When intravenous injection of AVP blockers was combined with hypoxia, we observed a reduction in body temperature of 1.49 ± 0.41°C (V1-receptor blocker) and of 1.30 ± 0.13°C (V2-receptor blocker), similar to that obtained by application of hypoxia only. Similar results were observed when the blockers were injected intracerebroventricularly. The data indicate that endogenous AVP does not mediate hypoxia-induced anapyrexia in rats.
Soft palate muscle responses to negative upper airway pressure
Authors: Amis T. C. , O’Neill N. , Wheatley J. R. , van der Touw T. , di Somma E. , Brancatisano A.
Published: December 2017

The afferent pathways and upper airway receptor locations involved in negative upper airway pressure (NUAP) augmentation of soft palate muscle activity have not been defined. We studied the electromyographic (EMG) response to NUAP for the palatinus, tensor veli palatini, and levator veli palatini muscles in 11 adult, supine, tracheostomized, anesthetized dogs. NUAP was applied to the nasal or laryngeal end of the isolated upper airway in six dogs and to four to six serial upper airway sites from the nasal cavity to the subglottis in five dogs. When NUAP was applied at the larynx, peak inspiratory EMG activity for the palatinus and tensor increased significantly ( P< 0.05) and plateaued at a NUAP of −10 cmH2O. Laryngeal NUAP failed to increase levator activity consistently. Nasal NUAP did not increase EMG activity for any muscle. Consistent NUAP reflex recruitment of soft palate muscle activity only occurred when the larynx was exposed to the stimulus and, furthermore, was abolished by bilateral section of the internal branches of the superior laryngeal nerves. We conclude that soft palate muscle activity may be selectively modulated by afferent activity originating in the laryngeal and hypopharyngeal airway.
Norepinephrine response to exercise at the same relative intensity before and after endurance exercise training
Authors: Greiwe Jeffrey S. , Hickner Robert C. , Shah Suresh D. , Cryer Philip E. , Holloszy John O.
Published: December 2017

It is well documented that endurance exercise training results in a blunted norepinephrine (NE) response to exercise of a given absolute exercise intensity. However, it is not clear what effect training has on the catecholamine response to exercise of the same relative intensity because previous studies have provided conflicting results. The purpose of the present study was, therefore, to determine the catecholamine response to exercise of the same relative exercise intensity before and after endurance exercise training. Six women and three men [age 28 ± 8 (SD) yr] performed 10 wk of training. Maximal O2 uptake (V˙o 2 max) was determined during treadmill exercise. Fifteen-minute treadmill exercise bouts were performed at 60, 65, 70, 75, 80, and 85% ofV˙o 2 max before and after training.V˙o 2 max was increased by 20% (from 39.2 ± 7.7 to 46.9 ± 8.1 ml ⋅ kg−1 ⋅ min−1; P < 0.05) in response to training. Plasma NE concentrations were higher ( P < 0.05) during exercise at the same relative intensity after, compared with before, training at 65–85% ofV˙o 2 max .Differences between heart rates and plasma epinephrine concentrations after, compared with before, training were not statistically significant. These results provide evidence that the NE response to exercise is dependent on the absolute as well as the relative intensity of the exercise.
Effect of increasing central venous pressure during passive heating on skin blood flow
Authors: Crandall C. G. , Levine B. D. , Etzel R. A.
Published: December 2017

Whole body heating in humans increases skin blood flow (SkBF) and decreases central venous pressure (CVP). This study sought to identify whether elevations in SkBF are augmented during passive heating if CVP is increased during the heat stress. Seven subjects were exposed to passive heating. Once SkBF was substantially elevated, 15 ml/kg warm saline were rapidly infused intravenously. Whole body heating significantly increased cutaneous vascular conductance and decreased CVP from 7.7 ± 0.6 to 4.9 ± 0.5 mmHg ( P < 0.05). Saline infusion returned CVP to pre-heat-stress pressures (7.9 ± 0.6 mmHg; P > 0.05) and significantly increased cutaneous vascular conductance relative to the period before saline administration. Moreover, saline infusion did not alter mean arterial pressure, pulse pressure, or esophageal temperature (all P > 0.05). To serve as a volume control, 15 ml/kg saline were rapidly infused intravenously in normothermic subjects. Saline infusion increased CVP ( P < 0.05) without affecting mean arterial pressure, pulse pressure, or cutaneous vascular conductance (all P > 0.05). These data suggest that cardiopulmonary baroreceptor unloading during passive heating may attenuate the elevation in SkBF in humans, whereas loading cardiopulmonary baroreceptors in normothermia has no effect on SkBF.
Mathematical models of diffusion-limited gas bubble dynamics in tissue
Authors: Srinivasan R. Srini , Gerth Wayne A. , Powell Michael R.
Published: December 2017

Mathematical models of bubble evolution in tissue have recently been incorporated into risk functions for predicting the incidence of decompression sickness (DCS) in human subjects after diving and/or flying exposures. Bubble dynamics models suitable for these applications assume the bubble to be either contained in an unstirred tissue (two-region model) or surrounded by a boundary layer within a well-stirred tissue (three-region model). The contrasting premises regarding the bubble-tissue system lead to different expressions for bubble dynamics described in terms of ordinary differential equations. However, the expressions are shown to be structurally similar with differences only in the definitions of certain parameters that can be transformed to make the models equivalent at large tissue volumes. It is also shown that the two-region model is applicable only to bubble evolution in tissues of infinite extent and cannot be readily applied to bubble evolution in finite tissue volumes to simulate how such evolution is influenced by interactions among multiple bubbles in a given tissue. Two-region models that are incorrectly applied in such cases yield results that may be reinterpreted in terms of their three-region model equivalents but only if the parameters in the two-region model transform into consistent values in the three-region model. When such transforms yield inconsistent parameter values for the three-region model, results may be qualitatively correct but are in substantial quantitative error. Obviation of these errors through appropriate use of the different models may improve performance of probabilistic models of DCS occurrence that express DCS risk in terms of simulated in vivo gas and bubble dynamics.
Simultaneous determination of muscle31P and O2 uptake kinetics during whole body NMR spectroscopy
Authors: Whipp B. J. , Rossiter H. B. , Ward S. A. , Avery D. , Doyle V. L. , Howe F. A. , Griffiths J. R.
Published: December 2017

Our understanding of O2 uptake (V˙o 2) control mechanisms during exercise may be improved by the simultaneous determination of the kinetics of intramuscular high-energy phosphate turnover and pulmonary V˙o 2. We therefore developed a technique for remote gas-exchange analysis while subjects exercised in a whole body 1.5-T NMR system. Knee-extension exercise was performed against restraining rubber bands in the prone position. Free induction decays were acquired every 1,875 ms by using a transmit-receive coil, which was placed under the quadriceps. This allowed 31P spectra of intramuscular ATP, Pi, and creatine phosphate dynamics to be determined every 15 s. Airflow was measured with a custom-designed turbine and a 45-ft.-long cable to reach the volume-measuring module. This was located in an adjacent radio-frequency-shielded room, as was the respiratory mass spectrometer, which also used a 45-ft.-long sampling line. The respired gas profiles were not discernibly different from those that used the standard inlet; the increase in the delay was readily incorporated into the breathby-breath algorithm, allowing theV˙o 2 kinetics to be determined in concert with those of intramuscular phosphate metabolism.
Oximetry of retinal vessels by dual-wavelength imaging: calibration and influence of pigmentation
Authors: Beach J. M. , Schwenzer K. J. , Srinivas S. , Kim D. , Tiedeman J. S.
Published: December 2017

A method for noninvasive measurement of Hb O2 saturation (So 2) in retinal blood vessels by digital imaging was developed and tested. Images of vessels were recorded at O2-sensitive and O2-insensitive wavelengths (600 and 569 nm, respectively) by using a modified fundus camera with an image splitter coupled to an 18-bit digital camera. Retinal arterial So 2 was varied experimentally by having subjects breathe mixtures of O2 and N2 while systemic arterial So 2 was monitored with a pulse oximeter. Optical densities (ODs) of vascular segments were determined using a computer algorithm to track the path of reflected light intensity along vessels. During graded hypoxia the OD ratio (ODR = OD600/OD569) bore an inverse linear relationship to systemic So 2. Compensation for the influence of choroidal pigmentation significantly reduced variation in the arterial So 2measurements among subjects. An O2sensitivity of 0.00504 ± 0.00029 (SE) ODR units/%So 2was determined. Retinal venous So 2 at normoxia was 55 ± 3.38% (SE). Breathing 100% O2 increased venous So 2 by 19.2 ± 2.9%. This technique, when combined with blood flow studies in human subjects, will enable the study of retinal O2 utilization under experimental and various disease conditions.
Estimation of rat muscle blood flow by microdialysis probes perfused with ethanol, [14C]ethanol, and3H2O
Authors: Stallknecht B. , Donsmark M. , Enevoldsen L. H. , Fluckey J. D. , Galbo H.
Published: December 2017

We used the perfused rat hindquarter to evaluate whether the microdialysis ethanol technique can be used to qualitatively estimate nutritive skeletal muscle blood flow. Four microdialysis probes were inserted in different hindlimb muscles in each of 16 rats. Hindquarters were perfused at blood flow rates ranging from 0 to 21 ml ⋅ 100 g−1 ⋅ min−1. The microdialysis probes were perfused at 2 μl/min with perfusate containing ethanol, [14C]ethanol, and3H2O. Within and between experiments outflow-to-inflow ratios (o/i) generally varied inversely with blood flow. When a low flow or no flow was maintained in hindquarters, o/i ratios first increased with time (for at least 60 min) and then leveled off. The long time constant impaired detection of rapid oscillations in blood flow, especially at low blood flow rates. Contractions per se apparently decreased o/i ratios independent of blood flow. Ethanol and [14C]ethanol o/i ratios did not differ.3H2O o/i paralleled ethanol and [14C]ethanol o/i ratios but it was significantly lower. In conclusion, differences in skeletal muscle blood flow can be detected by the microdialysis technique. However, the slow changes in o/i, in particular at low blood flow rates, limit the usefulness of the technique for measuring dynamic changes in blood flow; caution must also be exerted during muscle contractions.3H2O and [14C]ethanol are good alternatives to ethanol in the determination of blood flow by microdialysis.
Resistance training affects GLUT-4 content in skeletal muscle of humans after 19 days of head-down bed rest
Authors: Tabata Izumi , Suzuki Youji , Fukunaga Tetsuo , Yokozeki Toshiko , Akima Hiroshi , Funato Kazuo
Published: December 2017

This study assessed the effects of inactivity on GLUT-4 content of human skeletal muscle and evaluated resistance training as a countermeasure to inactivity-related changes in GLUT-4 content in skeletal muscle. Nine young men participated in the study. For 19 days, four control subjects remained in a −6° head-down tilt at all times throughout bed rest, except for showering every other day. Five training group subjects also remained at bed rest, except during resistance training once in the morning. The resistance training consisted of 30 isometric maximal voluntary contractions for 3 s each; leg-press exercise was used to recruit the extensor muscles of the ankle, knee, and hip. Pauses (3 s) were allowed between bouts of maximal contraction. Muscle biopsy samples were obtained from the lateral aspect of vastus lateralis (VL) muscle before and after the bed rest. GLUT-4 content in VL muscle of the control group was significantly decreased after bed rest (473 ± 48 vs. 398 ± 66 counts ⋅ min−1 ⋅ μg membrane protein−1, before and after bed rest, respectively), whereas GLUT-4 significantly increased in the training group with bed rest (510 ± 158 vs. 663 ± 189 counts ⋅ min−1 ⋅ μg membrane protein−1, before and after bed rest, respectively). The present study demonstrated that GLUT-4 in VL muscle decreased by ∼16% after 19 days of bed rest, and isometric resistance training during bed rest induced a 30% increase above the value of GLUT-4 before bed rest.
Effects of impaired Ca2+homeostasis on contraction in postinfarction myocytes
Authors: Zhang Xue-Qian , Musch Timothy I. , Zelis Robert , Cheung Joseph Y.
Published: December 2017

The significance of altered Ca2+ influx and efflux pathways on contractile abnormalities of myocytes isolated from rat hearts 3 wk after myocardial infarction (MI) was investigated by varying extracellular Ca2+concentration ([Ca2+]o, 0.6–5.0 mM) and pacing frequency (0.1–5.0 Hz). Myocytes isolated from 3-wk MI hearts were significantly longer than those from sham-treated (Sham) hearts (125 ± 1 vs. 114 ± 1 μm, P < 0.0001). At high [Ca2+]oand low pacing frequency, conditions that preferentially favored Ca2+ influx over efflux, Sham myocytes shortened to a greater extent than 3-wk MI myocytes. Conversely, under conditions that favored Ca2+ efflux (low [Ca2+]oand high pacing frequency), MI myocytes shortened more than Sham myocytes. At intermediate [Ca2+]oand pacing frequencies, differences in steady-state contraction amplitudes between Sham and MI myocytes were no longer significant. Collectively, the interpretation of these data was that Ca2+ influx and efflux pathways were subnormal in MI myocytes and that they contributed to abnormal cellular contractile behavior. Because Na+/Ca2+exchange activity, but not whole cell Ca2+ current, was depressed in 3-wk MI rat myocytes, our results on steady-state contraction are consistent with, but not proof of, the hypothesis that depressed Na+/Ca2+exchange accounted for abnormal contractility in MI myocytes. The effects of depressed Na+/Ca2+exchange on MI myocyte mechanical activity were further evaluated in relaxation from caffeine-induced contractures. Because Ca2+ uptake by sarcoplasmic reticulum was inhibited by caffeine and with the assumption that intracellular Na+ and membrane potential were similar between Sham and MI myocytes, myocyte relaxation from caffeine-induced contracture can be taken as an estimate of Ca2+ extrusion by Na+/Ca2+exchange. In MI myocytes, in which Na+/Ca2+exchange activity was depressed, the half time of relaxation (1.54 ± 0.14 s) was significantly ( P < 0.02) prolonged compared with that measured in Sham myocytes (1.10 ± 0.10 s).
Acinar flow irreversibility caused by perturbations in reversible alveolar wall motion
Authors: Tsuda Akira , Otani Yoshio , Butler James P.
Published: December 2017

Mixing associated with “stretch-and-fold” convective flow patterns has recently been demonstrated to play a potentially important role in aerosol transport and deposition deep in the lung (J. P. Butler and A. Tsuda. J. Appl. Physiol. 83: 800–809, 1997), but the origin of this potent mechanism is not well characterized. In this study we hypothesized that even a small degree of asynchrony in otherwise reversible alveolar wall motion is sufficient to cause flow irreversibility and stretch-and-fold convective mixing. We tested this hypothesis using a large-scale acinar model consisting of a T-shaped junction of three short, straight, square ducts. The model was filled with silicone oil, and alveolar wall motion was simulated by pistons in two of the ducts. The pistons were driven to generate a low-Reynolds-number cyclic flow with a small amount of asynchrony in boundary motion adjusted to match the degree of geometric (as distinguished from pressure-volume) hysteresis found in rabbit lungs (H. Miki, J. P. Butler, R. A. Rogers, and J. Lehr. J. Appl. Physiol. 75: 1630–1636, 1993). Tracer dye was introduced into the system, and its motion was monitored. The results showed that even a slight asynchrony in boundary motion leads to flow irreversibility with complicated swirling tracer patterns. Importantly, the kinematic irreversibility resulted in stretching of the tracer with narrowing of the separation between adjacent tracer lines, and when the cycle-by-cycle narrowing of lateral distance reached the slowly growing diffusion distance of the tracer, mixing abruptly took place. This coupling of evolving convective flow patterns with diffusion is the essence of the stretch-and-fold mechanism. We conclude that even a small degree of boundary asynchrony can give rise to stretch-and-fold convective mixing, thereby leading to transport and deposition of fine and ultrafine aerosol particles deep in the lung.
Role of L-selectin in physiological manifestations after burn and smoke inhalation injury in sheep
Authors: Sakurai Hiroyuki , Schmalstieg Frank C. , Traber Lillian D. , Hawkins Hal K. , Traber Daniel L.
Published: December 2017

The effects of a monoclonal antibody against L-selectin [leukoctye adhesion molecule (LAM)1–3] on microvascular fluid flux were determined in conscious sheep subjected to a combined injury of 40% third-degree burn and smoke inhalation. This combined injury induced a rapid increase in systemic prefemoral lymph flow (sQ˙lymph) from the burned area and a delayed-onset increase in lung lymph flow. The initial increase in sQ˙lymphwas associated with an elevation of the lymph-to-plasma oncotic pressure ratio; consequently, it leads to a predominant increase in the systemic soft tissue permeability index (sPI). In an untreated control group, the increased sPI was sustained beyond 24 h after injury. Pretreatment with LAM1–3 resulted in earlier recovery from the increased sPI, although the initial responses in sQ˙lymphand sPI were identical to those in the nontreatment group. The delayed-onset lung permeability changes were significantly attenuated by pretreatment with LAM1–3. These findings indicate that both leukocyte-dependent and -independent mechanisms are involved in the pathogenesis that occurs after combined injury with burn and smoke inhalation.
V˙o2recovery kinetics in the horse following moderate, heavy, and severe exercise
Authors: Langsetmo I. , Poole D. C.
Published: December 2017

At the onset of exercise, horses exhibit O2uptake (V˙o2) kinetics that are qualitatively similar to those of humans. In humans, there is a marked dissymmetry between on- and off-kinetics forV˙o2. This investigation sought to formally characterize the off-transient (recovery)V˙o2kinetics in the horse within the moderate (M), heavy (H), and severe (S) exercise domains. Six horses were run on a high-speed treadmill at M, H, and S exercise intensities (i.e., that speed which yielded ∼50, 85, 100% peakV˙o2, respectively, on the maximal incremental test). The time courses for the recovery were modeled by using a three-phase model with a single-exponential (fast component) or double-exponential (fast and slow component) phase 2. The single-exponential phase 2 model provided an excellent fit to the off-transient data, with the exception of one horse in the H domain which was best modeled by a double exponential. The time delay elicited no domain dependency (M, 18.0 ± 1.0; H, 17.6 ± 1.1; S, 17.8 ± 2.0 s; P > 0.05), as was the case for the fast-component time constants (M, 16.3 ± 2.0 s; H, 13.5 ± 1.0 s; S, 14.6 ± 0.3 s; P > 0.05). In the H and S (but not M) domains, the V˙o2following resolution of the fast component was elevated above the preexercise baseline (H, 3.0 ± 1.0 l/min; S, 5.7 ± 1.1 l/min). This additional postexerciseV˙o2was correlated to the end-exercise increase in lactate ( r = 0.94, P < 0.001) but not the end-exercise pulmonary arterial blood temperature ( r = 0.45, P > 0.05). These data indicate that the time delay and subsequent kinetic response of the primary (fast-component) phase of exerciseV˙o2recovery in the horse is independent of the preceding exercise-intensity domain. However, in the H and S domains, the fast component resolves to an elevated baseline.
Role of nitric oxide in the vascular effects of local warming of the skin in humans
Authors: Kellogg D. L. , Liu Y. , Kosiba I. F. , O’Donnell D.
Published: December 2017

Local warming of skin induces vasodilation by unknown mechanisms. To test whether nitric oxide (NO) is involved, we examined effects of NO synthase (NOS) inhibition with N G-nitro-l-arginine methyl ester (l-NAME) on vasodilation induced by local warming of skin in six subjects. Two adjacent sites on the forearm were instrumented with intradermal microdialysis probes for delivery ofl-NAME and sodium nitroprusside. Skin blood flow was monitored by laser-Doppler flowmetry (LDF) at microdialysis sites. Local temperature (Tloc) of the skin at both sites was controlled with special LDF probe holders. Mean arterial pressure (MAP; Finapres) was measured and cutaneous vascular conductance calculated (CVC = LDF/MAP = mV/mmHg). Data collection began with a control period (Tloc at both sites = 34°C). One site was then warmed to 41°C while the second was maintained at 34°C. Local warming increased CVC from 1.44 ± 0.41 to 4.28 ± 0.60 mV/mmHg ( P < 0.05). Subsequent l-NAME administration reduced CVC to 2.28 ± 0.47 mV/mmHg ( P < 0.05 vs. heating), despite the continued elevation of Tloc. At a Tloc of 34°C,l-NAME reduced CVC from 1.17 ± 0.23 to 0.75 ± 0.11 mV/mmHg ( P < 0.05). Administration of sodium nitroprusside increased CVC to levels no different from those induced by local warming. Thus NOS inhibition attenuated, and sodium nitroprusside restored, the cutaneous vasodilation induced by elevation of Tloc; therefore, the mechanism of cutaneous vasodilation by local warming requires NOS generation of NO.
Physiological responses of exercised-fatigued individuals exposed to wet-cold conditions
Authors: Tikuisis P. , Ducharme M. B. , Moroz D. , Jacobs I.
Published: December 2017

Thirteen healthy and fit men [age = 27 ± 8 (SD) yr, height = 177 ± 5 cm, mass = 75 ± 7 kg, body fat = 14 ± 5%, maximal O2 consumption = 51 ± 4 ml ⋅ kg−1 ⋅ min−1] participated in an experiment designed to test their thermoregulatory response to a challenging cold exposure after 5 h of demanding mixed exercise during which only water was consumed. Subjects expended 7,314 ± 741 kJ on cycling, rowing, and treadmill-walking machines, performed 8,403 ± 1,401 kg ⋅ m of mechanical work during resistance exercises, and completed 120 inclined sit-ups. Subjects then assumed a seated position in a 10°C air environment while wearing shorts, T-shirt, rain hat, and neoprene gloves and boots. After 30 min the subjects were showered continuously with cold water (∼920 ml/min at 10°C) on their backs accompanied by a 6 km/h wind for up to 4 h. Blood samples were taken from the nondominant arm every 30 min during the exposure and assayed for energy metabolites, hormones, indexes of hydration, and neurotransmitters. Counterbalanced control trials without prior exercise were also conducted. Blood insulin was higher during the control trial, whereas values of glycerol, nonesterified fatty acids, β-hydroxybutyrate, lactate, cortisol, free triiodothyronine, and thyroxine were lower. Three subjects lasted the maximum duration of 4.5 h for control and fatigue trials, with final rectal temperatures of 36.43 ± 0.21 and 36.08 ± 0.49°C, respectively. Overall, the duration of 172 ± 68 (SD) min for the fatigue trial was not significantly different from that of the control trial (197 ± 72 min) and, therefore, was not affected by the preexposure exercise. Although duration was positively correlated to body fatness and shivering intensity, the latter was not correlated to any physical characteristic or the fitness level of the individual.
Eosinophils in the bronchial mucosa in relation to methacholine dose-response curves in atopic asthma
Authors: Möller Gertrude M. , Overbeek Shelley E. , van Helden-Meeuwsen Cornelia G. , Hoogsteden Henk C. , Bogaard Jan M.
Published: December 2017

Asthma is characterized by both local infiltration of eosinophils in the bronchial mucosa and bronchial hyperreactivity (BHR). A detailed characterization of BHR implies analysis of a histamine or methacholine dose-response curve yielding not only the dose at 20% fall of baseline forced expiratory volume in 1 s (FEV1), but also a plateau (P) representing the maximal narrowing response in terms of percent change in FEV1and reactivity as the steepest slope at 50% of P (%FEV1/doubling dose). In the baseline condition, the specific airway conductance (sGaw) may be considered closely related to airway lumen diameter. In 20 nonsmoking asthmatic patients, methacholine dose-response curves were obtained, and a sigmoid model fit yielded the BHR indexes. Immunohistochemistry with the monoclonal antibodies (EG1and EG2) was used to recognize the total number of eosinophils and activated eosinophils, respectively. The number of activated eosinophils was significantly correlated to both P ( r = 0.62; P < 0.05) and sGaw ( r = −0.52; P < 0.05), whereas weaker and nonsignificant correlations were found for dose at 20% fall of baseline FEV1and the total number of eosinophils. We conclude that the number of activated eosinophils can be considered a marker of the inflammation-induced decrease of airway lumen diameter as represented by the plateau index and sGaw.
Length dependence of active force production in skeletal muscle
Authors: Rassier D. E. , MacIntosh B. R. , Herzog W.
Published: December 2017

The sliding filament and cross-bridge theories of muscle contraction provide discrete predictions of the tetanic force-length relationship of skeletal muscle that have been tested experimentally. The active force generated by a maximally activated single fiber (with sarcomere length control) is maximal when the filament overlap is optimized and is proportionally decreased when overlap is diminished. The force-length relationship is a static property of skeletal muscle and, therefore, it does not predict the consequences of dynamic contractions. Changes in sarcomere length during muscle contraction result in modulation of the active force that is not necessarily predicted by the cross-bridge theory. The results of in vivo studies of the force-length relationship suggest that muscles that operate on the ascending limb of the force-length relationship typically function in stretch-shortening cycle contractions, and muscles that operate on the descending limb typically function in shorten-stretch cycle contractions. The joint moments produced by a muscle depend on the moment arm and the sarcomere length of the muscle. Moment arm magnitude also affects the excursion (length change) of a muscle for a given change in joint angle, and the number of sarcomeres arranged in series within a muscle fiber determines the sarcomere length change associated with a given excursion.
Effect of NO, vasodilator prostaglandins, and adenosine on skeletal muscle angiogenic growth factor gene expression
Authors: Benoit H. , Jordan M. , Wagner H. , Wagner P. D.
Published: December 2017

Exercise training results in several muscle adaptations, one of which is angiogenesis. Acutely, exercise leads to release of nitric oxide, prostacyclin (PGI2), and adenosine (A) in the skeletal muscles. In this paper, we asked whether any of these locally released vasodilators, as well as other known dilator prostaglandins (PGE1 and PGE2), have the potential to increase angiogenic growth factor gene expression in resting skeletal muscle. Seven groups of 5–7 female Wistar rats (age 8–12 wk, weight 250 ± 10 g) were anesthetized and instrumented for carotid artery pressure and electromagnetic femoral artery blood flow measurement. One group acted as control while the other groups each received one of the following six agents by constant arterial infusion (dose in μg/min): A (200), nitroprusside (NP, 4.2), acetylcholine (100), PGE1 (1.9), PGE2 (1.7), and PGI2 (1.7). Each agent reduced peripheral vascular resistance to a similar extent (at least twofold). Densitometric mRNA/18S levels for vascular endothelial growth factor (VEGF) were increased 50% by NP and acetylcholine, were unaffected by PGE1 and PGE2, and were reduced 40% by PGI2. For basic fibroblast growth factor, only PGI2 had any effect, reducing mRNA/18S ∼25%. For transforming growth factor-β1, A, NP, and PGE1 led to reduced mRNA/18S, whereas PGE2 slightly increased mRNA/18S. For the principal putative angiogenic growth factor, VEGF, these data suggest that naturally secreted vasodilators in contracting skeletal muscle could be involved in regulation of gene expression, namely, nitric oxide in a positive and PGI2 in a negative direction.
Sympathetic adaptations to one-legged training
Authors: Ray Chester A.
Published: December 2017

The purpose of the present study was to determine the effect of leg exercise training on sympathetic nerve responses at rest and during dynamic exercise. Six men were trained by using high-intensity interval and prolonged continuous one-legged cycling 4 day/wk, 40 min/day, for 6 wk. Heart rate, mean arterial pressure (MAP), and muscle sympathetic nerve activity (MSNA; peroneal nerve) were measured during 3 min of upright dynamic one-legged knee extensions at 40 W before and after training. After training, peak oxygen uptake in the trained leg increased 19 ± 2% ( P < 0.01). At rest, heart rate decreased from 77 ± 3 to 71 ± 6 beats/min ( P< 0.01) with no significant changes in MAP (91 ± 7 to 91 ± 11 mmHg) and MSNA (29 ± 3 to 28 ± 1 bursts/min). During exercise, both heart rate and MAP were lower after training (108 ± 5 to 96 ± 5 beats/min and 132 ± 8 to 119 ± 4 mmHg, respectively, during the third minute of exercise; P < 0.01). MSNA decreased similarly from rest during the first 2 min of exercise both before and after training. However, MSNA was significantly less during the third minute of exercise after training (32 ± 2 to 22 ± 3 bursts/min; P < 0.01). This training effect on MSNA remained when MSNA was expressed as bursts per 100 heartbeats. Responses to exercise in five untrained control subjects were not different at 0 and 6 wk. These results demonstrate that exercise training prolongs the decrease in MSNA during upright leg exercise and indicates that attenuation of MSNA to exercise reported with forearm training also occurs with leg training.
Nasal vestibule wall elasticity: interactions with a nasal dilator strip
Authors: Amis T. C. , Kirkness J. P. , di Somma E. , Wheatley J. R.
Published: December 2017

We studied the effect of an adhesive external nasal dilator strip (ENDS) on external nasal geometry in 20 healthy Caucasian adults (10 men, 10 women; age 21–45 yr). The recoil force exerted by ENDS was estimated by bending the device ( n = 10) with known weights. In the horizontal direction, a small/medium-sized ENDS in situ exerted a unilateral recoil force of 21.4–22.6 g. Application of ENDS resulted in a displacement of the lateral nasal vestibule walls that had both anterosuperior and horizontal components and that was maintained over an 8-h period. The resultant unilateral nasal vestibule wall displacement at the tip of the device was at 47.6 ± 2.0° to the horizontal (as related to the plane of the device when in situ) and had a magnitude of 3.5 ± 0.1 mm. ENDS increased external nasal cross-sectional area by 23.0–65.3 mm2. Nasal vestibule wall compliance was estimated at 0.05–0.16 mm/g. Thus ENDS applies a relatively constant abducting force irrespective of nasal width. Variable responsiveness to ENDS may be related to differences in elastic properties of the nasal vestibule wall.
Electromyographic activity from human laryngeal, pharyngeal, and submental muscles during swallowing
Authors: Perlman A. L. , Palmer P. M. , McCulloch T. M. , Vandaele D. J.
Published: December 2017

The durations and temporal relationships of electromyographic activity from the submental complex, superior pharyngeal constrictor, cricopharyngeus, thyroarytenoid, and interarytenoid muscles were examined during swallowing of saliva and of 5- and 10-ml water boluses. Bipolar, hooked-wire electrodes were inserted into all muscles except for the submental complex, which was studied with bipolar surface electrodes. Eight healthy, normal, subjects produced five swallows of each of three bolus volumes for a total of 120 swallows. The total duration of electromyographic activity during the pharyngeal stage of the swallow did not alter with bolus condition; however, specific muscles did show a volume-dependent change in electromyograph duration and time of firing. Submental muscle activity was longest for saliva swallows. The interarytenoid muscle showed a significant difference in duration between the saliva and 10-ml water bolus. Finally, the interval between the onset of laryngeal muscle activity (thyroarytenoid, interarytenoid) and of pharyngeal muscle firing patterns (superior pharyngeal constrictor onset, cricopharyngeus offset) decreased as bolus volume increased. The pattern of muscle activity associated with the swallow showed a high level of intrasubject agreement; the presence of somewhat different patterns among subjects indicated a degree of population variance.
Differential lung mechanics are genetically determined in inbred murine strains
Authors: Tankersley Clarke G. , Rabold Richard , Mitzner Wayne
Published: December 2017

Genetic determinants of lung structure and function have been demonstrated by differential phenotypes among inbred mice strains. For example, previous studies have reported phenotypic variation in baseline ventilatory measurements of standard inbred murine strains as well as segregant and nonsegregant offspring of C3H/HeJ (C3) and C57BL/6J (B6) progenitors. One purpose of the present study is to test the hypothesis that a genetic basis for differential baseline breathing pattern is due to variation in lung mechanical properties. Quasi-static pressure-volume curves were performed on standard and recombinant inbred strains to explore the interactive role of lung mechanics in determination of functional baseline ventilatory outcomes. At airway pressures between 0 and 30 cmH2O, lung volumes are significantly ( P < 0.01) greater in C3 mice relative to the B6 and A/J strains. In addition, the B6C3F1/J offspring demonstrate lung mechanical properties significantly ( P < 0.01) different from the C3 progenitor but not distinguishable from the B6 progenitor. With the use of recombinant inbred strains derived from C3 and B6 progenitors, cosegregation analysis between inspiratory timing and measurements of lung volume and compliance indicate that strain differences in baseline breathing pattern and pressure-volume relationships are not genetically associated. Although strain differences in lung volume and compliance between C3 and B6 mice are inheritable, this study supports a dissociation between differential inspiratory time at baseline, a trait linked to a putative genomic region on mouse chromosome 3, and differential lung mechanics among C3 and B6 progenitors and their progeny.
Dextran restores albumin-inhibited surface activity of pulmonary surfactant extract
Authors: Kobayashi Tsutomu , Ohta Keisuke , Tashiro Katsumi , Nishizuka Kazuo , Chen Wei-Min , Ohmura Shigeo , Yamamoto Ken
Published: December 2017

We examined the effect of dextran (molecular weight 71,000) in counteracting the surfactant inhibitory action of plasma albumin. The surface adsorption time of 0.5 mg/ml modified natural surfactant (MNS; porcine lung extract consisting of phospholipids and hydrophobic surfactant proteins) with 7.5 mg/ml albumin decreased from 681 to 143 s by addition of dextran at a concentration of 10 mg/ml ( P < 0.01). The minimum surface tension of 2.0 mg/ml MNS with 30 mg/ml albumin decreased from over 21 mN/m to below 3 mN/m when dextran was added at a concentration of 10 mg/ml ( P < 0.01). Surfactant-deficient newborn rabbits given 10 ml/kg of a liquid containing 2.0 mg/ml MNS with 30 mg/ml albumin had a mean tidal volume ≤5 ml/kg after 5 min of mechanical ventilation, but, in those animals given the liquid containing 10 mg/ml dextran also, the volume was >13 ml/kg ( P < 0.05). Although the underlying mechanism remains to be elucidated, we conclude that dextran restores the albumin-inhibited surface activity of MNS.
Posture effects on timing of abdominal muscle activity during stimulated ventilation
Authors: Abe Tadashi , Yamada Takumi , Tomita Tomoyuki , Easton Paul A.
Published: December 2017

In humans during stimulated ventilation, substantial abdominal muscle activity extends into the following inspiration as postexpiratory expiratory activity (PEEA) and commences again during late inspiration as preexpiratory expiratory activity (PREA). We hypothesized that the timing of PEEA and PREA would be changed systematically by posture. Fine-wire electrodes were inserted into the rectus abdominis, external oblique, internal oblique, and transversus abdominis in nine awake subjects. Airflow, end-tidal CO2, and moving average electromyogram (EMG) signals were recorded during resting and CO2-stimulated ventilation in both supine and standing postures. Phasic expiratory EMG activity (tidal EMG) of the four abdominal muscles at any level of CO2 stimulation was greater while standing. Abdominal muscle activities during inspiration, PEEA, and PREA, were observed with CO2stimulation, both supine and standing. Change in posture had a significant effect on intrabreath timing of expiratory muscle activation at any level of CO2stimulation. The transversus abdominis showed a significant increase in PEEA and a significant decrease in PREA while subjects were standing; similar changes were seen in the internal oblique. We conclude that changes in posture are associated with significant changes in phasic expiratory activity of the four abdominal muscles, with systematic changes in the timing of abdominal muscle activity during early and late inspiration.
Effect of furosemide on pulmonary blood flow distribution in resting and exercising horses
Authors: Erickson Howard H. , Bernard Susan L. , Glenny Robb W. , Fedde M. Roger , Polissar Nayak L. , Basaraba Randall J. , Walther Sten M. , Gaughan Earl M. , McMurphy Rose , Hlastala Michael P.
Published: December 2017

We determined the spatial distribution of pulmonary blood flow (PBF) with 15-μm fluorescent-labeled microspheres during rest and exercise in five Thoroughbred horses before and 4 h after furosemide administration (0.5 mg/kg iv). The primary finding of this study was that PBF redistribution occurred from rest to exercise, both with and without furosemide. However, there was less blood flow to the dorsal portion of the lung during exercise postfurosemide compared with prefurosemide. Furosemide did alter the resting perfusion distribution by increasing the flow to the ventral regions of the lung; however, that increase in flow was abated with exercise. Other findings included 1) unchanged gas exchange and cardiac output during rest and exercise after vs. before furosemide, 2) a decrease in pulmonary arterial pressure after furosemide, 3) an increase in the slope of the relationship of PBF vs. vertical height up the lung during exercise, both with and without furosemide, and 4) a decrease in blood flow to the dorsal region of the lung at rest after furosemide. Pulmonary perfusion variability within the lung may be a function of the anatomy of the pulmonary vessels that results in a predominantly fixed spatial pattern of flow distribution.