bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of resistance exercise on postprandial lipemia
Authors: Petitt Darby S. , Arngrímsson Sigurbjörn Á. , Cureton Kirk J.
Published: March 2015

The purpose of this study was to examine the effect of resistance exercise on postprandial lipemia. Fourteen young men and women participated in each of three treatments: 1) control (Con), 2) resistance exercise (RE), and 3) aerobic exercise (AE) estimated to have an energy expenditure (EE) equal that for RE. Each trial consisted of performing a treatment on day 1 and ingesting a fat-tolerance test meal 16 h later ( day 2). Resting metabolic rate and fat oxidation were measured at baseline and at 3 and 6 h postprandial on day 2. Blood was collected at baseline and at 0.5, 1, 2, 3, 4, 5, and 6 h after meal ingestion. RE and AE were similar in EE [1.7 ± 0.1 vs. 1.6 ± 0.1 (SE) MJ, respectively], as measured by using the Cosmed K4b2. Baseline triglycerides (TG) were significantly lower after RE than after Con (19%) and AE (21%). Furthermore, the area under the postprandial response curve for TG, adjusted for baseline differences, was significantly lower after RE than after Con (14%) and AE (18%). Resting fat oxidation was significantly greater after RE than after Con (21%) and AE (28%). These results indicate that resistance exercise lowers baseline and postprandial TG, and increases resting fat oxidation, 16 h after exercise.
Determinants of exercise performance in normal men with externally imposed expiratory flow limitation
Authors: Iandelli Iacopo , Aliverti Andrea , Kayser Bengt , Dellacà Raffaele , Cala Stephen J. , Duranti Roberto , Kelly Susan , Scano Giorgio , Sliwinski Pawel , Yan Sheng , Macklem Peter T. , Pedotti Antonio
Published: March 2015

To understand how externally applied expiratory flow limitation (EFL) leads to impaired exercise performance and dyspnea, we studied six healthy males during control incremental exercise to exhaustion (C) and with EFL at ∼1. We measured volume at the mouth (Vm), esophageal, gastric and transdiaphragmatic (Pdi) pressures, maximal exercise power (W˙max) and the difference (Δ) in Borg scale ratings of breathlessness between C and EFL exercise. Optoelectronic plethysmography measured chest wall and lung volume (Vl). From Campbell diagrams, we measured alveolar (Pa) and expiratory muscle (Pmus) pressures, and from Pdi and abdominal motion, an index of diaphragmatic power (W˙di). Four subjects hyperinflated and two did not. EFL limited performance equally to 65%W˙max with Borg = 9–10 in both. At EFLW˙max, inspiratory time (Ti) was 0.66s ± 0.08, expiratory time (Te) 2.12 ± 0.26 s, Pmus ∼40 cmH2O and ΔVl-ΔVm = 488.7 ± 74.1 ml. From Pa and Vl, we calculated compressed gas volume (Vc) = 163.0 ± 4.6 ml. The difference, ΔVl-ΔVm-Vc (estimated blood volume shift) was 326 ml ± 66 or 7.2 ml/cmH2O Pa. The high Pmus and long Te mimicked a Valsalva maneuver from which the short Ti did not allow recovery. Multiple stepwise linear regression revealed that the difference between C and EFL Pmus accounted for 70.3% of the variance in ΔBorg. ΔW˙di added 12.5%. We conclude that high expiratory pressures cause severe dyspnea and the possibility of adverse circulatory events, both of which would impair exercise performance.
Recombinant α1-proteinase inhibitor blocks antigen- and mediator-induced airway responses in sheep
Authors: Scuri Mario , Botvinnikova Yelena , Lauredo Isabel T. , Abraham William M.
Published: March 2015

α1-Proteinase inhibitor (α1-PI) is a natural serine protease inhibitor. Although mainly thought to protect the airways from neutrophil elastase, α1-PI may also regulate the development of airway hyperresponsiveness (AHR), as indicated by our previous findings of an inverse relationship between lung α1-PI activity and the severity of antigen-induced AHR. Because allergic stimulation of the airways causes release of elastase, tissue kallikrein, and reactive oxygen species (ROS), all of which can reduce α1-PI activity and contribute to AHR, we hypothesized that administration of exogenous α1-PI should protect against pathophysiological airway responses caused by these agents. In untreated allergic sheep, airway challenge with elastase, xanthine/xanthine oxidase (which generates ROS), high-molecular-weight kininogen, the substrate for tissue kallikrein, and antigen resulted in bronchoconstriction. ROS and antigen also induced AHR to inhaled carbachol. Treatment with 10 mg of recombinant α1-PI (rα1-PI) blocked the bronchoconstriction caused by elastase, high-molecular-weight kininogen, and ROS, and the AHR induced by ROS and antigen. One milligram of rα1-PI was ineffective. These are the first in vivo data demonstrating the effects of rα1-PI. Our results are consistent with and extend findings obtained with human plasma-derived α1-PI and suggest that α1-PI may be important in the regulation of airway responsiveness.
Effects of physical activity, body fat, and salivary cortisol on mucosal immunity in children
Authors: Cieslak Thomas J. , Frost Gail , Klentrou Panagiota
Published: March 2015

This study examined relationships among physical activity, body composition, and stress- and immunity-related variables in fifth grade children (10–11 yr) in Southern Ontario. The 29 boys and 32 girls, who participated in the study, performed a 20-m shuttle run for prediction of aerobic fitness. Bioelectrical impedance was used to assess relative body fat. Standardized questionnaires were used to determine physical activity-related variables and frequency of upper respiratory tract infection (URTI). Resting saliva samples were collected and tested for resting cortisol and resting secretory immunoglobulin A (SIgA). Subjects wore a pedometer for 48 h to estimate their average total distance traveled per day. SIgA was significantly correlated with reported URTIs but was not related to salivary cortisol, physical activity, fitness level, or relative body fat. Children who spent more time in sport activities and had higher aerobic fitness reported fewer “sick” days. Children with body fat higher than 25% reported significantly ( P < 0.05) more sick days than the rest of the cohort. There were no gender differences in SIgA, URTI frequency, and cortisol levels. The test-retest reproducibility for salivary cortisol was 0.66 ( P < 0.01), whereas long-term SIgA reproducibility was nonsignificant for repeated measurements taken after 6 wk. Resting secretory immunity was not strongly related to fitness and physical activity, but there was evidence that reduced physical activity and excess body fat can result in higher URTI incidence.
Laryngeal elevation achieved by neuromuscular stimulation at rest
Authors: Burnett Theresa A. , Mann Eric A. , Cornell Sonia A. , Ludlow Christy L.
Published: March 2015

During swallowing, airway protection is achieved in part by laryngeal elevation. Although multiple muscles are normally active during laryngeal elevation, neuromuscular stimulation of select muscles was evaluated to determine which single muscle or muscle pair best elevates the larynx and should be considered during future studies of neuromuscular stimulation in dysphagic patients. Hooked-wire monopolar electrodes were inserted into mylohyoid, thyrohyoid, and geniohyoid muscle regions in 15 healthy men selected for having a highly visible thyroid prominence for videotaping. During trials of single, bilateral, and combined muscle stimulations, thyroid prominence movements were video recorded, digitized, and normalized relative to elevation during a 2-ml water swallow. Individual muscle stimulation induced ∼30% of the elevation observed during a swallow and ∼50% of swallow velocity, whereas paired muscle stimulation resulted in ∼50% of the elevation and ∼80% of the velocity produced during a swallow. Paired muscle stimulation produced significantly greater elevation than single muscle stimulation and could assist with laryngeal elevation in dysphagic patients with reduced or delayed laryngeal elevation.
Profiles of connectin (titin) in atrophied soleus muscle induced by unloading of rats
Authors: Goto Katsumasa , Okuyama Ryoko , Honda Masanori , Uchida Hiroshi , Akema Tatsuo , Ohira Yoshinobu , Yoshioka Toshitada
Published: March 2015

Responses of the properties of connectin molecules in the slow-twitch soleus (Sol) and fast-twitch extensor digitorum longus muscles of rats to 3 days of unloading with or without 3-day reloading were investigated. The wet weight (relative to body wt) of Sol, not of extensor digitorum longus, in the unloaded group was significantly less than in the age-matched control ( P < 0.05). Immunoelectron microscopic analyses showed that a monoclonal antibody against connectin (SM1) bound to the I-band region close to the edge of the A band at resting length and moved reversibly away from the Z line as the muscle fibers were stretched. In Sol, the displacement of the SM1-bound dense spots in response to stretching decreased after hindlimb suspension. There were no changes in the molecular weights and the percent distributions of α- and β-connectin in both muscles after hindlimb suspension. A significant increment of percent β-connectin in Sol was observed after 3 days of reloading after hindlimb suspension ( P < 0.05). It is suggested that the elasticity of connectin filaments in the I-band region of the atrophied Sol fibers was reduced relative to that of the control fibers. The lack of the elasticity in atrophied muscle fibers may cause a decrease in contractile function.
Effect of upper airway negative pressure and lung inflation on laryngeal motor unit activity in rabbit
Authors: Ryan Stephen , McNicholas Walter T. , O'Regan Ronan G. , Nolan Philip
Published: March 2015

10.1152/japplphysiol.00413.2001.—Distortion of the upper airway by negative transmural pressure (UANP) causes reflex vagal bradycardia. This requires activation of cardiac vagal preganglionic neurons, which exhibit postinspiratory (PI) discharge. We hypothesized that UANP would also stimulate cranial respiratory motoneurons with PI activity. We recorded 32 respiratory modulated motor units from the recurrent laryngeal nerve of seven decerebrate paralyzed rabbits and recorded their responses to UANP and to withholding lung inflation using a phrenic-triggered ventilator. The phasic inspiratory ( n = 17) and PI ( n = 5) neurons detected were stimulated by −10 cmH2O UANP and by withdrawal of lung inflation ( P < 0.05, Friedman's ANOVA). Expiratory-inspiratory units ( n = 10) were tonically active but transiently inhibited in postinspiration; this inhibition was more pronounced and prolonged during UANP stimuli and during no-inflation tests ( P < 0.05). We conclude that, in addition to increasing inspiratory activity in the recurrent laryngeal nerve, UANP also stimulates units with PI activity.
Effect of stimulus cycle time on acute respiratory responses to intermittent hypercapnic hypoxia in unsedated piglets
Authors: Waters Karen A. , Tinworth Kellie D.
Published: March 2015

To determine whether stimulus frequency affects physiological compensation to an intermittent respiratory stimulus, we studied piglets ( n = 43) aged 14.8 ± 2.4 days. A 24-min total hypercapnic hypoxia (HH) (10% O2-6% CO2-balance N2 = HH) was delivered in 24-, 8-, 4-, or 2-min cycles alternating with air. Controls ( n = 10) breathed air continuously. Minute ventilation and temperature were not different between the 2-min and 24-min groups, with neither different from controls during recovery. Piglets exposed to 8-min cycles had ventilatory stimulation, whereas those exposed to 4-min cycles had significant depression of ventilation. Despite this, piglets in these intermediate intermittent HH (IHH) groups (8- and 4-min cycles) showed more severe acidosis and attenuated temperature changes ( P < 0.001 and P < 0.01 for pH and temperature vs. 24 min, respectively). Cycle time affected the ability of young piglets to tolerate IHH. More severe respiratory acidosis developed when IHH was delivered in intermediate (4 min or 8 min) cycles compared with the same total dose as a single episode or in short (2 min) cycles.
Effects of transmural pressure on brachial artery mean blood velocity dynamics in humans
Authors: Lott Mary E. J. , Herr Michael D. , Sinoway Lawrence I.
Published: March 2015

The effects of changes in transmural pressure on brachial artery mean blood velocity (MBV) were examined in humans. Transmural pressure was altered by using a specially designed pressure tank that raised or lowered forearm pressure by 50 mmHg within 0.2 s. Brachial MBV was measured with Doppler directly above the site of forearm pressure change. Pressure changes were evoked during resting conditions and after a 5-s handgrip contraction at 25% maximal voluntary contraction. The handgrip protocol selected was sufficiently vigorous to limit flow and sufficiently brief to prevent autonomic engagement. Changes in transmural pressure evoked directionally similar changes in MBV within 2 s. This was followed by large and rapid adjustments [−2.14 ± 0.24 cm/s (vasoconstriction) during negative pressure and +2.14 ± 0.45 cm/s (vasodilatation) during positive pressure]. These adjustments served to return MBV to resting levels. This regulatory influence remained operative after 5-s static handgrip contractions. Of note, changes in transmural pressure were capable of altering the timing of the peak MBV response (5 ± 0, 2 ± 0, 6 ± 1 s ambient, negative, and positive pressure, respectively) as well as the speed of MBV adjustment (−2.03 ± 0.18, −2.48 ± 0.15, −0.84 ± 0.19 cm · s−1 · s−1ambient, negative, and positive pressure, respectively) after handgrip contractions. Vascular responses, seen with changes in transmural pressure, provide evidence that the myogenic response is normally operative in the limb circulation of humans.
Aging induces muscle-specific impairment of endothelium-dependent dilation in skeletal muscle feed arteries
Authors: Woodman Christopher R. , Price Elmer M. , Laughlin M. Harold
Published: March 2015

We tested the hypothesis that aging decreases endothelium-dependent vasodilation in feed arteries perfusing rat skeletal muscle. In addition, we tested the hypothesis that attenuated vasodilator responses are associated with decreased endothelial nitric oxide synthase (eNOS) and superoxide dismutase-1 (SOD-1) expression. Soleus feed arteries (SFA) and gastrocnemius feed arteries (GFA) were isolated from young (4 mo) and old (24 mo) male Fischer 344 rats. Feed arteries from the right hindlimb were cannulated with two glass micropipettes for examination of endothelium-dependent [acetylcholine (ACh)] and endothelium-independent [adenosine (Ado) or sodium nitroprusside (SNP)] vasodilator function. Feed arteries from the left hindlimb were frozen and used to assess eNOS and SOD-1 protein and mRNA expression. In SFA, endothelium-dependent dilation to ACh was reduced in old rats (0.9 ± 0.04 vs. 0.8 ± 0.03), whereas dilator responses to Ado and SNP were similar in SFA of young and old rats. In GFA, vasodilator responses to ACh, Ado, and SNP were not altered by age. eNOS and SOD-1 protein expression declined with age in SFA (−71 and −54%, respectively) but not in GFA. eNOS and SOD-1 mRNA expression were not altered by age in SFA or GFA. Collectively, these data indicate aging induces muscle-specific impairment of endothelium-dependent vascular function in SFA.
Dynamic time course of hemodynamic responses after passive head-up tilt and tilt back to supine position
Authors: Toska Karin , Walløe Lars
Published: March 2015

Mechanisms involved in the control of arterial pressure during postural changes were studied by analysis of the dynamic time course of cardiovascular changes during head-up tilt (HUT) and tilt back to supine position (TB). Beat-to-beat values of cardiovascular variables were recorded continuously before, during, and after passive HUT to 30° in seven healthy humans. Left cardiac stroke volume (SV, Doppler ultrasound), mean arterial blood pressure (MAP), heart rate (HR), cardiac output (CO), and total peripheral conductance (TPC) were recorded. During HUT, MAP at the level of the carotid baroreceptors decreased by ∼5 mmHg. There was a striking asymmetry between the time courses of cardiovascular changes on HUT and on TB. Adjustments generally took up to 30 s after HUT, whereas most changes were completed during the first 10 s after TB. Cardiovascular reflex adjustments of HR and TPC were more symmetrical. After HUT, SV was maintained during the first 4–6 s and then decreased steadily during the next 30 s to a stable level ∼25% below its pretilt value. However, after TB, SV increased rapidly to its pretilt value in <10 s. This asymmetry in SV dynamics may be explained in part by a more rapid change in left cardiac filling after TB than after HUT. On TB, there must be a rapid inflow of stagnant blood from the legs, whereas venous valves will impede backward filling of veins in the lower body on HUT. In conclusion, we have revealed a characteristic asymmetry in cardiovascular responses to inverse variations in gravity forces in humans. This asymmetry can be explained in part by nonlinear, hydrodynamic factors, such as the one-way effect of venous valves in the lower part of the body.
Translational Physiology: Porcine models of human coronary artery disease: implications for preclinical trials of therapeutic angiogenesis
Authors: Hughes G. Chad , Post Mark J. , Simons Michael , Annex Brian H.
Published: March 2015

“Therapeutic angiogenesis” describes an emerging field of cardiovascular medicine whereby new blood vessels are induced to grow to supply oxygen and nutrients to ischemic cardiac or skeletal muscle. Various methods of producing therapeutic angiogenesis have been employed, including mechanical means, gene therapy, and the use of growth factors, among others. The use of appropriate large-animal models is essential if these therapies are to be critically evaluated in a preclinical setting before their use in humans, yet little has been written comparing the various available models. Over the past decade, swine have been increasingly used in studies of chronic ischemia because of their numerous similarities to humans, including minimal preexisting coronary collaterals as well as similar coronary anatomy and physiology. Consequently, this review describes the most commonly used swine models of chronic myocardial ischemia with special attention to regional myocardial blood flow and function and critically evaluates the strengths and weaknesses of each model in terms of utility for preclinical trials of angiogenic therapies.
Modulation of phrenic motoneuron excitability by ATP: consequences for respiratory-related output in vitro
Authors: Miles Gareth B. , Parkis Marjorie A. , Lipski Janusz , Funk Gregory D.
Published: March 2015

On the basis of the high level of P2X receptor expression found in phrenic motoneurons (MN) in rats (Kanjhan et al., J Comp Neurol407: 11–32, 1999) and potentiation of hypoglossal MN inspiratory activity by ATP (Funk et al., J Neurosci 17: 6325–6337, 1997), we tested the hypothesis that ATP receptor activation also modulates phrenic MN activity. This question was examined in rhythmically active brain stem-spinal cord preparations from neonatal rats by monitoring effects of ATP on the activity of spinal C4 nerve roots and phrenic MNs. ATP produced a rapid-onset, dose-dependent, suramin- and pyridoxal-phosphate-6-azophenyl-2′,4′-disulphonic acid 4-sodium-sensitive increase in C4 root tonic discharge and a 22 ± 7% potentiation of inspiratory burst amplitude. This was followed by a slower, 10 ± 5% reduction in burst amplitude. ATPγS, the hydrolysis-resistant analog, evoked only the excitatory response. ATP induced inward currents (57 ± 39 pA) and increased repetitive firing of phrenic MNs. These data, combined with persistence of ATP currents in TTX and immunolabeling for P2X2 receptors in Fluoro-Gold-labeled C4 MNs, implicate postsynaptic P2 receptors in the excitation. Inspiratory synaptic currents, however, were inhibited by ATP. This inhibition differed from that seen in root recordings; it did not follow an excitation, had a faster onset, and was induced by ATPγS. Thus ATP inhibited activity through at least two mechanisms: 1) a rapid P2 receptor-mediated inhibition and 2) a delayed P1 receptor-mediated inhibition associated with hydrolysis of ATP to adenosine. The complex effects of ATP on phrenic MNs highlight the importance of ATP as a modulator of central motor outflows.
Physical and pubertal development in young male gymnasts
Authors: Gurd Brendon , Klentrou Panagiota
Published: March 2015

The purpose of this study was to evaluate the effect of intense training on physical growth and sexual maturation in young male gymnasts. Physical development, pubertal development, testosterone levels, energy expenditure, and relative body fat were examined in 21 circumpubertal male gymnasts (13.3 ± 0.3 yr) and 24 age-matched controls (13.5 ± 0.3 yr). Subjects completed a self-assessment of genital and pubic hair development with the use of the Tanner scale. All subjects were measured for height, weight, and salivary testosterone levels (T). The Physical Activity Questionnaire for Adolescents was used to estimate weekly energy expenditure in metabolic equivalents. Percent body fat (%BF) was assessed by using bioelectrical impedance analysis. Developmental stages and T, as well as height and weight, were not different between groups. Energy expenditure was significantly higher ( P ≤ 0.05) and %BF was lower ( P ≤ 0.05) in athletes than in controls, but lean body mass was not significantly different between groups. Energy expenditure was negatively correlated ( P ≤ 0.05) with %BF but not related to T. Developmental stages were strongly ( P ≤ 0.05) related to T but not to energy expenditure or %BF. It is concluded that, although there is a higher energy expenditure accompanying intense training in young male athletes, their body composition is not necessarily affected, and there is no determined effect on their physical and pubertal development.
Effect of positive pressure on venous return in volume-loaded cardiac surgical patients
Authors: Van Den Berg Paul C. M. , Jansen Jos R. C. , Pinsky Michael R.
Published: March 2015

The hemodynamic effects of increases in airway pressure (Paw) are related in part to Paw-induced increases in right atrial pressure (Pra), the downstream pressure for venous return, thus decreasing the pressure gradient for venous return. However, numerous animal and clinical studies have shown that venous return is often sustained during ventilation with positive end-expiratory pressure (PEEP). Potentially, PEEP-induced diaphragmatic descent increases abdominal pressure (Pabd). We hypothesized that an increase in Paw induced by PEEP would minimally alter venous return because the associated increase in Pra would be partially offset by a concomitant increase in Pabd. Thus we studied the acute effects of graded increases of Paw on Pra, Pabd, and cardiac output by application of inspiratory-hold maneuvers in sedated and paralyzed humans. Forty-two patients were studied in the intensive care unit after coronary artery bypass surgery during hemodynamically stable, fluid-resuscitated conditions. Paw was progressively increased in steps of 2 to 4 cmH2O from 0 to 20 cmH2O in sequential 25-s inspiratory-hold maneuvers. Right ventricular (RV) cardiac output (COtd) and RV ejection fraction (EFrv) were measured at 5 s into the inspiratory-hold maneuver by the thermodilution technique. RV end-diastolic volume and stroke volume were calculated from EFrvand heart rate data, and Pra was measured from the pulmonary artery catheter. Pabd was estimated as bladder pressure. We found that, although increasing Paw progressively increased Pra, neither COtdnor RV end-diastolic volume changed. The ratio of change (Δ) in Paw to ΔPra was 0.32 ± 0.20. The ratio of ΔPra to ΔCOtdwas 0.05 ± 00.15 l · min−1· mmHg−1. However, Pabd increased such that the ratio of ΔPra to ΔPabd was 0.73 ± 0.36, meaning that most of the increase in Pra was reflected in increases in Pabd. We conclude that, in hemodynamically stable fluid-resuscitated postoperative surgical patients, inspiratory-hold maneuvers with increases in Paw of up to 20 cmH2O have minimal effects on cardiac output, primarily because of an in-phase-associated pressurization of the abdominal compartment associated with compression of the liver and squeezing of the lungs.
Exercise training preserves coronary flow and reduces infarct size after ischemia-reperfusion in rat heart
Authors: Brown David A. , Jew Korinne N. , Sparagna Genevieve C. , Musch Timothy I. , Moore Russell L.
Published: March 2015

The effect of endurance training on the resistance of the heart to left ventricular (LV) functional deficit and infarction after a transient regional ischemia and subsequent reperfusion was examined. Female Sprague-Dawley rats were randomly assigned to an endurance exercise training (Tr) group or a sedentary (Sed) control group. After 20 wk of training, hearts were excised, perfused, and instrumented for assessment of LV mechanical function, and the left anterior descending coronary artery was occluded to induce a transient regional ischemia (1 h) that was followed by 2 h of reperfusion. Throughout much of the regional ischemia-reperfusion protocol, coronary flow rates, diastolic function, and LV developed pressure were better preserved in hearts from Tr animals. During the regional ischemia, coronary flow to myocardium outside the ischemic zone at risk (ZAR) was maintained in Tr hearts, whereas it progressively fell in Sed hearts. On release of the coronary artery ligature, flow to the ZAR was greater in Tr than in Sed hearts. Infarct size, expressed as a percentage of the ischemic ZAR, was significantly smaller in hearts from Tr rats (24 ± 3 vs. 32 ± 2% of ZAR, P < 0.05). Mn- and CuZn-SOD protein expression were higher in the LV myocardium of Tr animals ( P < 0.05 for both isoforms). Our data indicate that long-term exercise training leads to infarct sparing and better maintenance of coronary flow and mechanical function after ischemia-reperfusion.
Effects of surface grade on proximal hindlimb muscle strain and activation during rat locomotion
Authors: Gillis Gary B. , Biewener Andrew A.
Published: March 2015

Sonomicrometry and electromyography were used to determine how surface grade influences strain and activation patterns in the biceps femoris and vastus lateralis of the rat. Muscle activity is generally present during much of stance and is most intense on an incline, intermediate on the level, and lowest on a decline, where the biceps remains inactive except at high speeds. Biceps fascicles shorten during stance, with strains ranging from 0.07–0.30 depending on individual, gait, and grade. Shortening strains vary significantly among grades ( P = 0.05) and average 0.21, 0.16, and 0.14 for incline, level, and decline walking, respectively; similar trends are present during trotting and galloping. Vastus fascicles are stretched while active over the first half of stance on all grades, and then typically shorten over the second half of stance. Late-stance shortening is highest during galloping, averaging 0.14, 0.10, and 0.02 in the leading limb on incline, level, and decline surfaces, respectively. Our results suggest that modulation of strain and activation in these proximal limb muscles is important for accommodating different surface grades.
Addition of inspiratory resistance increases the amplitude of the slow component of O2 uptake kinetics
Authors: Carra J. , Candau R. , Keslacy S. , Giolbas F. , Borrani F. , Millet G. P. , Varray A. , Ramonatxo M.
Published: March 2015

The contribution of respiratory muscle work to the development of the O2consumption (V˙o 2) slow component is a point of controversy because it has been shown that the increased ventilation in hypoxia is not associated with a concomitant increase inV˙o 2 slow component. The first purpose of this study was thus to test the hypothesis of a direct relationship between respiratory muscle work andV˙o 2 slow component by manipulating inspiratory resistance. Because the conditions for aV˙o 2 slow component specific to respiratory muscle can be reached during intense exercise, the second purpose was to determine whether respiratory muscles behave like limb muscles during heavy exercise. Ten trained subjects performed two 8-min constant-load heavy cycling exercises with and without a threshold valve in random order. V˙o 2 was measured breath by breath by using a fast gas exchange analyzer, and the V˙o 2 response was modeled after removal of the cardiodynamic phase by using two monoexponential functions. As anticipated, when total work was slightly increased with loaded inspiratory resistance, slight increases in baseV˙o 2, the primary phase amplitude, and peak V˙o 2 were noted (14.2%, P < 0.01; 3.5%, P > 0.05; and 8.3%, P < 0.01, respectively). The bootstrap method revealed small coefficients of variation for the model parameter, including the slow-component amplitude and delay (15 and 19%, respectively), indicating an accurate determination for this critical parameter. The amplitude of the V˙o 2 slow component displayed a 27% increase from 8.1 ± 3.6 to 10.3 ± 3.4 ml · min−1 · kg−1( P < 0.01) with the addition of inspiratory resistance. Taken together, this increase and the lack of any differences in minute volume and ventilatory parameters between the two experimental conditions suggest the occurrence of aV˙o 2 slow component specific to the respiratory muscles in loaded condition.
In situ rat fast skeletal muscle is more efficient at submaximal than at maximal activation levels
Authors: Abbate F. , De Ruiter C. J. , Offringa C. , Sargeant A. J. , De Haan A.
Published: March 2015

The influence of stimulation frequency on efficiency (= total work output/high-energy phosphate consumption) was studied using in situ medial gastrocnemius muscle tendon complexes of the rat. The muscles performed 20 repeated concentric contractions (2/s) at 34°C. During these repeated contractions, the muscle was stimulated via the severed sciatic nerve with either 60, 90, or 150 Hz. The muscle was freeze-clamped immediately after these contractions, and high-energy phosphate consumption was determined by measuring intramuscular chemical change relative to control muscles. The average values (±SD) of efficiency calculated for 60, 90, and 150 Hz were 18.5 ± 1.5 ( n = 7), 18.6 ± 1.5 ( n = 9), and 14.7 ± 1.3 mJ/μmol phosphate ( n = 9). The results indicate that the efficiency of the muscles that were submaximally activated (60 or 90 Hz) was higher (+26%, P < 0.05) than that of those maximally activated (150 Hz). Additional experiments showed that the low efficiency at maximal activation levels is unlikely to be the result of a higher energy turnover by the Ca2+-ATPase relative to the total energy turnover. Therefore, alternative explanations are discussed.
Increased antioxidant capacity does not attenuate muscle atrophy caused by unweighting
Authors: Koesterer T. J. , Dodd S. L. , Powers Scott
Published: March 2015

Previous studies have increased antioxidant capacity in skeletal muscle to attenuate oxidative stress and muscle atrophy during limb immobilization (Appell HJ, Duarte JAR, and Soares JMC. Int J Sports Med 18: 157–160, 1997; Kondo H, Miura M, Nakagaki I, Sasaki S, and Itokawa Y. Am J Physiol Endocrinol Metab 262: E583–E590, 1992). The purpose of this study was to determine the level of oxidative stress in muscle during hindlimb unweighting (HLU) and whether antioxidant supplementation can attenuate the atrophy and changes in contractile properties resulting from 14 days of unweighting. Muscle unweighting caused a 44% decrease in soleus (Sol) and a 30% decrease in gastrocnemius (GS) mass, a 7% decrease in body weight, and 28% decrease in tetanic force in the GS. Protein carbonyls increased by 44% in the Sol with HLU. Antioxidant supplementation did not attenuate the GS or Sol atrophy or the decrease in GS force generation during HLU. Sol and GS protein concentration was not different between groups. The GS was also subjected to three different oxidative challenges to determine whether the supplement increased the antioxidant capacity of the muscle. In all cases, muscles exhibited an increased antioxidant capacity. These data indicate that antioxidant supplementation was not an effective countermeasure to the atrophy associated with HLU.
Influence of surface chemistry and topography of particles on their immersion into the lung's surface-lining layer
Authors: Geiser Marianne , Schürch Samuel , Gehr Peter
Published: March 2015

Inhaled and deposited spherical particles, 1–6 μm in diameter and of differing surface chemistry and topography, were studied in hamster intrapulmonary conducting airways and alveoli by electron microscopy. Polystyrene and Teflon particles, as well as puffball spores, were found submersed in the aqueous lining layer and adjacent to epithelial cells. The extent of particle immersion promoted by a surfactant film was assessed in a “floating-drop-surface balance” by light microscopy. Teflon and polystyrene spheres were immersed into the subphase by 50–60% at film surface tensions of 25 and 30 mJ/m2, respectively, and totally submersed at 15 and 25 mJ/m2, respectively. Puffball spores were immersed by ∼50% at 22 mJ/m2 and totally submersed at film surface tensions of ≤15 mJ/m2. These results suggest that the surface tension in the intrapulmonary conducting airways of hamsters may reach ≤15 mJ/m2 and that respirable particles (<10 μm in diameter) are wetted and displaced into the surface lining layer, which may facilitate interactions with many lung cells.
Hindlimb unloading-induced muscle atrophy and loss of function: protective effect of isometric exercise
Authors: Hurst J. E. , Fitts R. H.
Published: March 2015

The primary objective of this study was to determine the effectiveness of isometric exercise (IE) as a countermeasure to hindlimb unloading (HU)-induced atrophy of the slow (soleus) and fast (plantaris and gastrocnemius) muscles. Rats were assigned to either weight-bearing control, 7-day HU (H7), H7 plus IE (I7), 14-day HU (H14), or H14 plus IE (I14) groups. IE consisted of ten 5-s maximal isometric contractions separated by 90 s, administered three times daily. Contractile properties of the soleus and plantaris muscles were measured in situ. The IE attenuated the HU-induced decline in the mass and fiber diameter of the slow-twitch soleus muscle, whereas the gastrocnemius and plantaris mass were not protected. These results are consistent with the mean electromyograph recordings during IE that indicated preferential recruitment of the soleus over the gastrocnemius and plantaris muscles. Functionally, the IE significantly protected the soleus from the HU-induced decline in peak isometric force (I14, 1.49 ± 0.12 vs. H14, 1.15 ± 0.07 N) and peak power (I14, 163 ± 17 vs. H14, 75 ± 11 mN·fiber length·s-1). The exercise protocol showed protection of the plantaris peak isometric force at H7 but not H14. The IE also prevented the HU-induced decline in the soleus isometric contraction time, which allowed the muscle to produce greater tension at physiological motoneuron firing frequencies. In summary, IE resulted in greater protection from HU-induced atrophy in the slow soleus than in the fast gastrocnemius or plantaris.
Effect of naloxone on perceived exertion and exercise capacity during maximal cycle ergometry
Authors: Sgherza Anthony L. , Axen Kenneth , Fain Randi , Hoffman Robert S. , Dunbar Christopher C. , Haas François
Published: March 2015

We assessed the effects of naloxone, an opioid antagonist, on exercise capacity in 13 men and 5 women (mean age = 30.1 yr, range = 21–35 yr) during a 25 W/min incremental cycle ergometer test to exhaustion on different days during familiarization trial and then after 30 mg (iv bolus) of naloxone or placebo (Pl) in a double-blind, crossover design. Minute ventilation (V˙e), O2 consumption (V˙o 2), CO2 production, and heart rate (HR) were monitored. Perceived exertion rating (0-10 scale) and venous samples for lactate were obtained each minute. Lactate and ventilatory thresholds were derived from lactate and gas-exchange data. Blood pressure was obtained before exercise, 5 min postinfusion, at maximum exercise, and 5 min postexercise. There were no control-Pl differences. The naloxone trial demonstrated decreased exercise time (96% Pl; P < 0.01), total cumulative work (96% Pl; P < 0.002), peakV˙o 2 (94% Pl; P < 0.02), and HR (96% Pl; P < 0.01). Other variables were unchanged. HR and V˙e were the same at the final common workload, but perceived exertion was higher (8.1 ± 0.5 vs. 7.1 ± 0.5) after naloxone than Pl ( P < 0.01). The threshold for effort perception amplification occurred at ∼60 ± 4% of Pl peakV˙o 2. Thus we conclude that peak work capacity was limited by perceived exertion, which can be attenuated by endogenous opioids rather than by physiological limits.
Density-dependent reduction of nitric oxide diffusing capacity after pneumonectomy
Authors: Hsia Connie C. W. , Yan Xiao , Dane D. Merrill , Johnson Robert L.
Published: March 2015

Airway lengthening after pneumonectomy (PNX) may increase diffusive resistance to gas mixing (1/DG); the effect is accentuated by increasing acinar gas density but is difficult to detect from lung CO-diffusing capacity (Dl CO). Because lung NO-diffusing capacity (Dl NO) is three- to fivefold that of Dl CO, whereas 1/DG for NO and CO are similar, we hypothesized that a density-dependent fractional reduction would be greater for Dl NO than for Dl CO. We measured Dl NOand Dl CO at two tidal volumes (Vt) and with three background gases [helium (He), nitrogen (N2), and sulfur hexafluoride (SF6)] in immature dogs 3 and 9 mo after right PNX (5 and 11 mo of age). At maturity (11 mo), background gas density had no effect on Dl NO, Dl CO, or Dl NO-to-Dl CO ratio in sham controls. In PNX animals, Dl NO declined 25–50% in SF6 relative to He and N2, and Dl NO/Dl CO declined ∼50% in SF6 relative to He at a Vt of 15 ml/kg, consistent with a significant 1/DG. At 5 mo of age, Dl NO/Dl CO declined 25–45% in SF6 relative to He and N2 in both groups, but Dl CO increased paradoxically in SF6 relative to N2 or He by 20–60%. Findings suggest that SF6, besides increasing 1/DG, may redistribute ventilation and/or enhance acinar penetration of the convective front.
Gender differences in the endocrine and metabolic responses to hypoxic exercise
Authors: Sandoval Darleen A. , Matt Kathleen S.
Published: March 2015

This study tested the hypothesis that women would have blunted physiological responses to acute hypoxic exercise compared with men. Fourteen women taking oral contraceptives (28 ± 0.9 yr of age) and 15 men (30 ± 1.0 yr of age) with similar peak O2 consumption (V˙o 2 peak) values (56 ± 1.1 vs. 57 ± 0.8 ml · kg fat-free mass−1 · min−1) were studied under hypoxic (H; fraction of inspired oxygen = 13%) vs. normoxic (fraction of inspired oxygen = 20.93%) conditions. Cardiopulmonary, metabolic, and neuroendocrine measures were taken before, during, and 30 min after three 5-min consecutive workloads at 30, 45, and 60% V˙o 2 peak. In women compared with men, glucose levels were greater during recovery from H ( P < 0.05) and lactate levels were lower at 45%V˙o 2 peak, 60%V˙o 2 peak, and up to 20 min of recovery ( P < 0.05), regardless of trial ( P < 0.0001). Although the women had greater baseline levels of cortisol and growth hormone ( P < 0.0001), gender did not affect these hormones during H or exercise. Catecholamine responses to H were also similar between genders. Thus the endocrine response to hypoxia per se was not blunted in women as we had hypothesized. Other mechanisms must be at play to cause the gender differences in metabolic substrates in response to hypoxia.
Online recording of ethane traces in human breath via infrared laser spectroscopy
Authors: von Basum Golo , Dahnke Hannes , Halmer Daniel , Hering Peter , Mürtz Manfred
Published: March 2015

A method is described for rapidly measuring the ethane concentration in exhaled human breath. Ethane is considered a volatile marker for lipid peroxidation. The breath samples are analyzed in real time during single exhalations by means of infrared cavity leak-out spectroscopy. This is an ultrasensitive laser-based method for the analysis of trace gases on the sub-parts per billion level. We demonstrate that this technique is capable of online quantifying of ethane traces in exhaled human breath down to 500 parts per trillion with a time resolution of better than 800 ms. This study includes what we believe to be the first measured expirograms for trace fractions of ethane. The expirograms were recorded after a controlled inhalation exposure to 1 part per million of ethane. The normalized slope of the alveolar plateau was determined, which shows a linear increase over the first breathing cycles and ends in a mean value between 0.21 and 0.39 liter-1. The washout process was observed for a time period of 30 min and was modelled by a threefold exponential decay function, with decay times ranging from 12 to 24, 341 to 481, and 370 to 1,770 s. Our analyzer provides a promising noninvasive tool for online monitoring of the oxidative stress status.
Increases in maximal accumulated oxygen deficit after high-intensity interval training are not gender dependent
Authors: Weber Clare L. , Schneider Donald A.
Published: March 2015

Gender differences in maximal accumulated oxygen deficit (MAOD) were examined before and after 4 and 8 wk of high-intensity interval training. Untrained men ( n = 7) and women ( n = 7) cycled at 120% of pretraining peak oxygen uptake (V˙o 2 peak) to exhaustion (MAOD test) pre-, mid-, and posttraining. A posttraining timed test was also completed at the MAOD test power output, but this test was stopped at the time to exhaustion achieved during the pretraining MAOD test. The 14.3 ± 5.2% increase in MAOD observed in men after 4 wk of training was not different from the 14.0 ± 3.0% increase seen in women ( P > 0.05). MAOD increased by a further 6.6 ± 1.9% in men, and this change was not different from the additional 5.1 ± 2.3% increase observed in women after the final 4 wk of training. V˙o 2 peak measured during incremental cycling increased significantly ( P < 0.01) in male but not in female subjects after 8 wk of training. Moreover, the accumulated oxygen (AO2) uptake was higher in men during the posttraining timed test compared with the pretraining MAOD test ( P < 0.01). In contrast, the AO2uptake was unchanged from pre- to posttraining in female subjects. The increase in MAOD with training was not different between men and women, suggesting an enhanced ability to produce ATP anaerobically in both groups. However, the increase inV˙o 2 peak and AO2 uptake obtained in male subjects after training indicates improved oxidative metabolism in men but not in women. We conclude that there are basic gender differences that may predispose men and women to specific metabolic adaptations after a period of intense interval training.
Desiccation and hypertonicity of the airway surface fluid and thermally induced asthma
Authors: Kotaru Chakradhar , Hejal Rana B. , Finigan J. H. , Coreno Albert J. , Skowronski Mary E. , Brianas Lori , McFadden E. R.
Published: March 2015

To determine whether drying and hypertonicity of the airway surface fluid (ASF) are involved in thermally induced asthma, nine subjects performed isocapnic hyperventilation (HV) (minute ventilation 62.2 ± 8.3 l/min) of frigid air (−8.9 ± 3.3°C) while periciliary fluid was collected endoscopically from the trachea. Osmolality was measured by freezing-point depression. The baseline 1-s forced expiratory volume was 73 ± 4% of predicted and fell 26.4% 10 min postchallenge ( P > 0.0001). The volume of ASF collected was 11.0 ± 2.2 μl at rest and remained constant during and after HV as the airways narrowed (HV 10.6 ± 1.9, recovery 6.5 ± 1.7 μl; P = 0.18). The osmolality also remained stable throughout (rest 336 ± 16, HV 339 ± 16, and recovery 352 ± 19 mosmol/kgH2O, P = 0.76). These data demonstrate that airway desiccation and hypertonicity of the ASF do not develop during hyperpnea in asthma; therefore, other mechanisms must cause exercise- and hyperventilation-induced airflow limitation.
Selected Contribution: Neuroplasticity in nucleus tractus solitarius neurons after episodic ozone exposure in infant primates
Authors: Chen Chao-Yin , Bonham Ann C. , Plopper Charles G. , Joad Jesse P.
Published: March 2015

Acute ozone exposure evokes adverse respiratory responses, particularly in children. With repeated ozone exposures, however, despite the persistent lung inflammation and increased sensory nerve excitability, the central nervous system reflex responses, i.e., rapid shallow breathing and decreased lung function, adapt, suggesting changes in central nervous system signaling. We determined whether repeated ozone exposures altered the behavior of nucleus tractus solitarius (NTS) neurons where reflex respiratory motor outputs are first coordinated. Whole cell recordings were performed on NTS neurons in brain stem slices from infant monkeys exposed to filtered air or ozone (0.5 ppm, 8 h/day for 5 days every 14 days for 11 episodes). Although episodic ozone exposure depolarized the membrane potential, increased the membrane resistance, and increased neuronal spiking responses to depolarizing current injections ( P < 0.05), it decreased the excitability to vagal sensory fiber activation ( P < 0.05), suggesting a diminished responsiveness to sensory transmission, despite overall increases in excitability. Substance P, implicated in lung and NTS signaling, contributed to the increased responsiveness to current injections but not to the diminished sensory transmission. The finding that NTS neurons undergo plasticity with repeated ozone exposures may help to explain the adaptation of the respiratory motor responses.
Magnitude estimation of inspiratory resistive loads by double-lung transplant recipients
Authors: Zhao Weiying , Martin A. Daniel , Davenport Paul W.
Published: March 2015

The purpose of this study was to investigate the role of afferent input from the lung and lower airways in magnitude estimation of inspiratory resistive loads (R). To assess the role of lung vagal afferents in respiratory sensation, sensations related to inspiratory R, reflected by subjects' percentage of handgrip responses (HG%), were compared between double-lung transplant (DLT) recipients with normal lung function and healthy control (Nor) subjects. Perceptual sensitivity to the external load was measured as the slope of HG% as a function of peak mouth pressure (Pm), and the slope of HG% as a function of R, after a log-log transformation. The results showed that the DLT group had a similar HG% response, as well as the slopes of log HG%-log Pm and log HG%-log R, compared with the Nor group. Furthermore, the ventilatory responses to external loads were also similar between the two groups. These results suggest that lung vagal afferents do not play a significant role in magnitude estimation of inspiratory resistive loads in humans.
Sex differences in hepatic gene expression in a rat model of ethanol-induced liver injury
Authors: Tadic Stasa D. , Elm Mary S. , Li Ha-Sheng , Van Londen Gijsberta J. , Subbotin Vladimir M. , Whitcomb David C. , Eagon Patricia K.
Published: March 2015

Sex differences in susceptibility to alcohol-induced liver injury have been observed in both humans and experimental animal models. Using a standard model of alcohol-induced fatty liver injury and microarray analysis, we have identified differential expression of hepatic genes in both sexes. The genes that exhibit differential expression are of three types: those that are changed only in male rats fed alcohol, those that change in only female rats fed alcohol, and those that change in both sexes, although not always in the same manner. Certain of the differentially expressed genes have previously been identified as participants in the induction of alcohol-induced liver injury. However, this analysis has identified a number of genes that heretofore have not been implicated in alcoholic liver injury; such genes may provide new areas of investigation into the pathogenesis of this disease.