bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of elastomer arterial models with specified compliance
Authors: Stevanov M. , Baruthio J. , Eclancher B.
Published: December 2017

A simple way of making elastic tubes using a mechanical lathe for precise control of the wall thickness is proposed in this study. These tubes are particularly useful for modeling properties of large arteries. Tubes with different geometric parameters and hence different elastic behavior have been made with a silicon elastomer (Rhodorsil RTV 1556). They have been created to be used for compliance measurements in hemodynamics research. Within a limited range of pressures, depending on the wall thickness, such tubes can be used to study models in which the compliance value is assumed to be constant.
Methodological and physiological variability within the ventilatory response to hypoxia in humans
Authors: Zhang Shu , Robbins Peter A.
Published: December 2017

Measurement of the acute hypoxic ventilatory response (AHVR) requires careful choice of the hypoxic stimulus. If the stimulus is too brief, the response may be incomplete; if the stimulus is too long, hypoxic ventilatory depression may ensue. The purpose of this study was to compare three different techniques for assessing AHVR, using different hypoxic stimuli, and also to examine the between-day variability in AHVR. Ten subjects were studied, each on six different occasions, which were ≥1 wk apart. On each occasion, AHVR was assessed using three different protocols: 1) protocol SW, which uses square waves of hypoxia; 2) protocol IS, which uses incremental steps of hypoxia; and 3) protocol RB, which simulates an isocapnic rebreathing test. Mean values for hypoxic sensitivity were 1.02 ± 0.48, 1.15 ± 0.55, and 0.93 ± 0.60 (SD) l ⋅ min− 1 ⋅ %− 1for protocols SW, IS, and RB, respectively. These differed significantly ( P < 0.01). The coefficients of variation for measurement of AHVR were 20, 23, and 36% for the three protocols, respectively. These were not significantly different. There was a significant physiological variation in AHVR ( F 50,100 = 3.9, P < 0.001), with a coefficient of variation of 26%. We conclude that there was relatively little systematic variation between the three protocols but that AHVR varies physiologically over time.
Oxygen sensing by the carotid body chemoreceptors
Authors: Prabhakar Nanduri R.
Published: December 2017

Carotid bodies are sensory organs that detect changes in arterial blood oxygen, and the ensuing reflexes are critical for maintaining homeostasis during hypoxemia. During the past decade, tremendous progress has been made toward understanding the cellular mechanisms underlying oxygen sensing at the carotid body. The purpose of this minireview is to highlight some recent concepts on sensory transduction and transmission at the carotid body. A bulk of evidence suggests that glomus (type I) cells are the initial site of transduction and that they release transmitters in response to hypoxia, which causes depolarization of nearby afferent nerve endings, leading to an increase in sensory discharge. There are two main hypotheses to explain the transduction process that triggers transmitter release. One hypothesis assumes that a biochemical event associated with a heme protein triggers the transduction cascade. The other hypothesis suggests that a K+ channel protein is the oxygen sensor and that inhibition of this channel by hypoxia leading to depolarization is a seminal event in transduction. Although there is body of evidence supporting and questioning each of these, this review will try to point out that the truth lies somewhere in an interrelation between the two. Several transmitters have been identified in glomus cells, and they are released in response to hypoxia. However, their precise roles in sensory transmission remain uncertain. It is hoped that future studies involving transgenic animals with targeted disruption of genes encoding transmitters and their receptors may resolve some of the key issues surrounding the sensory transmission at the carotid body. Further studies are necessary to identify whether a single sensor or multiple oxygen sensors are needed for the transduction process.
Centrally administered MTII affects feeding, drinking, temperature, and activity in the Sprague-Dawley rat
Authors: Murphy B. , Nunes C. N. , Ronan J. J. , Hanaway M. , Fairhurst A. M. , Mellin T. N.
Published: December 2017

MTII, an agonist of melanocortinergic receptors, is a well-documented anorexigenic agent in rats. Many investigators have reported its effects on feeding without considering concurrent alterations in other behaviors. Accordingly, we performed studies to simultaneously measure nocturnal feeding, drinking, activity, and temperature of rats after intracerebroventricular (third ventricle) administration of a wide dose range of MTII (0.05–500 ng). We observed that MTII modulates these physiological parameters in a dose-dependent manner. Low doses of MTII (0.05 ng) caused reductions in feeding without alterations in body temperature, drinking, or activity. In contrast, hyperthermia and disrupted drinking patterns, along with food intake reductions, were evident at doses exceeding 50 ng. The fact that low doses altered only feeding, whereas higher doses affected a range of parameters, suggests that certain melanocortin-induced behavioral changes may be mediated by distinct populations of melanocortin receptors with varying affinities or that those changes seen at higher doses may be nonspecific in nature.
Measurement of fat mass using DEXA: a validation study in elderly adults
Authors: Salamone Loran M. , Fuerst Thomas , Visser Marjolein , Kern Marialice , Lang Thomas , Dockrell Maurice , Cauley Jane A. , Nevitt Michael , Tylavsky Francis , Lohman Tim G.
Published: December 2017

The accuracy of total body fat mass and leg fat mass measurements by fan-beam dual-energy X-ray absorptiometry (DEXA) was assessed in 60 healthy elderly subjects (aged 70–79 yr). Total fat and leg fat mass at four leg regions (total leg, thigh, midthigh, and calf) were measured with the QDR 4500A (Hologic, Waltham, MA). The four-compartment model and multislice computed tomography scans were selected as criterion methods for total fat and leg fat mass, respectively. Total fat mass from DEXA was positively associated with fat mass from the four-compartment model with a standard error of the estimate ranging from 1.4 to 1.6 kg. DEXA fan-beam tended to overestimate fat mass for total leg and total thigh fat mass, whereas only marginal differences in fat mass measurements at the midthigh and calf were demonstrated (≤0.08 kg, P< 0.0005). Although there were significant differences between DEXA fan beam and the criterion methods, these differences were of small magnitude, suggesting that DEXA is an accurate method for measurement of fat mass for the elderly.
Does gender influence human cardiovascular and renal responses to water immersion?
Authors: Watenpaugh Donald E. , Pump Bettina , Bie Peter , Norsk Peter
Published: December 2017

We hypothesized that women and men exhibit similar cardiovascular and renal responses to thermoneutral water immersion (WI) to the neck. Ten women and nine men underwent two sessions in random order: 1) seated nonimmersed for 5.5 h (control) and 2) WI for 3 h, with subjects seated nonimmersed for 1.5 h pre- and 1 h postimmersion. We measured left atrial diameter, heart rate, arterial pressure, urine volume and osmolality, and urinary endothelin, urodilatin, sodium, and potassium excretion. No significant difference existed between groups in cardiovascular responses. The groups also exhibited mostly similar renal responses to immersion after adjustment for body mass. However, female urodilatin excretion per kilogram during immersion was over twofold that of men, and the female kaliuretic response to immersion was delayed and less pronounced relative to that in men. Men may excrete more potassium than women during immersion because men possess greater lean body mass (potassium per kilogram). Results obtained in men during WI may be cautiously extrapolated to women, yet urodilatin and potassium responses exhibit gender differences.
Glucose uptake is increased in trained vs. untrained muscle during heavy exercise
Authors: Kristiansen Søren , Gade Jon , Wojtaszewski Jørgen F. P. , Kiens Bente , Richter Erik A.
Published: December 2017

Endurance training increases muscle content of glucose transporter proteins (GLUT-4) but decreases glucose utilization during exercise at a given absolute submaximal intensity. We hypothesized that glucose uptake might be higher in trained vs. untrained muscle during heavy exercise in the glycogen-depleted state. Eight untrained subjects endurance trained one thigh for 3 wk using a knee-extensor ergometer. The subjects then performed two-legged glycogen-depleting exercise and consumed a carbohydrate-free meal thereafter to keep muscle glycogen concentration low. The next morning, subjects performed dynamic knee extensions with both thighs simultaneously at 60, 80, and until exhaustion at 100% of each thigh's peak workload. Glucose uptake was similar in both thighs during exercise at 60% of thigh peak workload. At the end of 80 and at 100% of peak workload, glucose uptake was on average 33 and 22% higher, respectively, in trained compared with untrained muscle ( P < 0.05). Training increased the muscle content of GLUT-4 by 66% ( P < 0.05). At exhaustion, glucose extraction correlated significantly ( r = 0.61) with total muscle GLUT-4 protein. Thus, when working at a high load with low glycogen concentrations, muscle glucose uptake is significantly higher in trained than in untrained muscle. This may be due to the higher GLUT-4 protein concentration in trained muscle.
Lower limb skeletal muscle mass: development of dual-energy X-ray absorptiometry prediction model
Authors: Shih Rick , Wang Zimian , Heo Moonseong , Wang Wei , Heymsfield Steven B.
Published: December 2017

Although magnetic resonance imaging (MRI) can accurately measure lower limb skeletal muscle (SM) mass, this method is complex and costly. A potential practical alternative is to estimate lower limb SM with dual-energy X-ray absorptiometry (DXA). The aim of the present study was to develop and validate DXA-SM prediction equations. Identical landmarks (i.e., inferior border of the ischial tuberosity) were selected for separating lower limb from trunk. Lower limb SM was measured by MRI, and lower limb fat-free soft tissue was measured by DXA. A total of 207 adults (104 men and 103 women) were evaluated [age 43 ± 16 (SD) yr, body mass index (BMI) 24.6 ± 3.7 kg/m2]. Strong correlations were observed between lower limb SM and lower limb fat-free soft tissue ( R 2 = 0.89, P < 0.001); age and BMI were small but significant SM predictor variables. In the cross-validation sample, the differences between MRI-measured and DXA-predicted SM mass were small (−0.006 ± 1.07 and −0.016 ± 1.05 kg) for two different proposed prediction equations, one with fat-free soft tissue and the other with added age and BMI as predictor variables. DXA-measured lower limb fat-free soft tissue, along with other easily acquired measures, can be used to reliably predict lower limb skeletal muscle mass.
Comparison of thermoregulatory responses between men and women immersed in cold water
Authors: Tikuisis P. , Jacobs I. , Moroz D. , Vallerand A. L. , Martineau L.
Published: December 2017

Eleven women (age = 24.4 ± 6.3 yr, mass = 65.0 ± 7.8 kg, height = 167 ± 8 cm, body fatness = 22.4 ± 5.9%, mean ± SD) were immersed to neck level in 18°C water for up to 90 min for comparison of their thermal responses with those of men ( n = 14) in a previous similarly conducted protocol. Metabolic rate increased about three times resting levels in men and women, whereas the rate of rectal temperature cooling (ΔTre/Δ t) in women (0.47°C/h) was about one-half that in men. With use of all data, ΔTre/Δ t correlates with the ratio of body surface area to size and the metabolic rate of shivering correlates inversely to the square root of body fatness. No significant gender differences in total metabolic heat production normalized for body mass or surface area were found among subjects who completed 90 min of immersion (9 women and 7 men). Nor was there a gender difference in the overall percent contribution (∼60%) of fat oxidation to total heat production. Blood concentrations of free fatty acids, glycerol, β-hydroxybutyrate, and lactate increased significantly during the 90-min immersion, whereas muscle glycogen sampled from the right quadriceps femoris vastus lateralis decreased (free fatty acids, glycerol, and β-hydroxybutyrate were higher in women). When the subjects were subgrouped according to similar body fatness and 60 min of immersion (6 women and 5 men), no significant gender differences emerged in ΔTre/Δ t, energy metabolism, and percent fat oxidation. These findings suggest that no gender adjustments are necessary for prediction models of cold response if body fatness and the ratio of body surface area to size are taken into account and that a potential gender advantage with regard to carbohydrate sparing during cold water immersion is not supported.
Description and validation of a novel liquid metal-free device for venous congestion plethysmography
Authors: Christ F. , Bauer A. , Brügger D. , Niklas M. , Gartside I. B. , Gamble J.
Published: December 2017

We present a newly developed electromechanical sensor with automated calibration for strain-gauge plethysmography (filtrass) and compare it to a conventional mercury-in-Silastic strain-gauge plethysmograph (MSG). Fluid filtration capacity ( K f) and isovolumetric venous pressure (Piv) of the limb were assessed noninvasively with both devices in 29 healthy volunteers. We found significantly higher Kf and Piv values with MSG [4.6 ± 2.0 × 10−3ml · min−1 · mmHg−1 · 100 ml tissue−1 ( K f units; K fU) and 21.2 ± 8.1 mmHg for Pvi], than with filtrass, giving values of 3.1 ± 0.8 K fU and 15.1 ± 7.1 mmHg. Because K f and Piv are profoundly influenced by the calibration, we investigated the quality of the calibration signal and its impact on the obtained values. We could show that the reproducibility of repeated calibrations was higher with filtrass (58% lower mean ± SD). The data were grouped according to the quality of calibration, and we found no significant difference in K f and Piv between filtrass (3.0 ± 0.7 K fU and 15.9 ± 6.9 mmHg, respectively) and MSG with good calibration signal (3.3 ± 0.8 K fU and 18.6 ± 7.1 mmHg, respectively; no significant difference). However, we obtained significantly higher MSG values (5.6 ± 2.0 K fU and 23.1 ± 8.4 mmHg, respectively; P < 0.001) in the group with a bad calibration signal. We suggest that the filtrass sensor, which performs an automatic, standardized calibration procedure and shows a linear signal response to stretch, gives highly reproducible and reliable results and thus is more suitable for routine application.
Effect of systemic nitric oxide synthase inhibition on postexercise hypotension in humans
Authors: Halliwill John R. , Minson Christopher T. , Joyner Michael J.
Published: December 2017

An acute bout of aerobic exercise results in a reduced blood pressure that lasts several hours. Animal studies suggest this response is mediated by increased production of nitric oxide. We tested the extent to which systemic nitric oxide synthase inhibition [ N G-monomethyl-l-arginine (l-NMMA)] can reverse the drop in blood pressure that occurs after exercise in humans. Eight healthy subjects underwent parallel experiments on 2 separate days. The order of the experiments was randomized between sham (60 min of seated upright rest) and exercise (60 min of upright cycling at 60% peak aerobic capacity). After both sham and exercise, subjects received, in sequence, systemic α-adrenergic blockade (phentolamine) and l-NMMA. Phentolamine was given first to isolate the contribution of nitric oxide to postexercise hypotension by preventing reflex changes in sympathetic tone that result from systemic nitric oxide synthase inhibition and to control for alterations in resting sympathetic activity after exercise. During each condition, systemic and regional hemodynamics were measured. Throughout the study, arterial pressure and vascular resistances remained lower postexercise vs. postsham despite nitric oxide synthase inhibition (e.g., mean arterial pressure afterl-NMMA was 108.0 ± 2.4 mmHg postsham vs. 102.1 ± 3.3 mmHg postexercise; P < 0.05). Thus it does not appear that postexercise hypotension is dependent on increased production of nitric oxide in humans.
A human acinar structure for simulation of realistic alveolar plateau slopes
Authors: Dutrieue Brigitte , Vanholsbeeck Frederique , Verbanck Sylvia , Paiva Manuel
Published: December 2017

We simulated the intra-acinar contribution to phase III slope ( S acin) for gases of differing diffusivities (He and SF6) by solving equations of diffusive and convective gas transport in multi-branch-point models (MBPM) of the human acinus. We first conducted a sensitivity study of S acin to asymmetry and its variability in successive generations. S acin increases were greatest when asymmetry and variability of asymmetry were increased at the level of the respiratory bronchioles (generations 17–18) for He and at the level of the alveolar ducts (generations 20–21) for SF6, corresponding to the location of their respective diffusion fronts. On the basis of this sensitivity study and in keeping with reported acinar morphometry, we built a MBPM that actually reproduced experimental S acin values obtained in normal subjects for He, N2, and SF6. Ten variants of such a MBPM were constructed to estimate intrinsic S acin variability owing to peripheral lung structure. The realistic simulation of S acin in the normal lung and the understanding of how asymmetry affects S acin for different diffusivity gases make S acin a powerful tool to detect structural alterations at different depths in the lung periphery.
Ventilatory response to incremental and constant-workload exercise in the presence of a thoracic restriction
Authors: O'Connor Sinéad , McLoughlin Paul , Gallagher Charles G. , Harty Helen R.
Published: December 2017

In the presence of an externally applied thoracic restriction, conflicting ventilatory responses to exercise have been reported, which could be accounted for by differences in exercise protocol. Seven male subjects performed two incremental and two constant-workload ergometer tests either unrestricted or in the presence of an inelastic corset. Ventilatory variables and arterial estimates of Pco 2 were obtained breath by breath. Subjects hyperventilated in the presence of restriction during the constant-workload test (38.4 ± 3.0 vs. 32.8 ± 3.0 l/min for the average of the last 3 min of exercise, P < 0.05), whereas, at an equivalent workload during the incremental test, ventilation was similar to unrestricted values (unrestricted = 26.3 ± 1.6 vs. restricted = 27.9 ± 2.3 l/min, P = 0.36). We used a first-order linear model to describe the effects of change in workload on minute ventilation (24). When the time constants and minute ventilation values measured during unrestricted and restricted constant-workload exercise were used to predict the ventilatory response to the respective incremental exercise tests, no significant difference was observed. This suggests that hyperventilation is not seen in the restricted incremental test because the temporal dynamics of the ventilatory response are altered.
N-3 polyunsaturated fatty acids do not affect cytokine response to strenuous exercise
Authors: Toft Anders Dyhr , Thorn Mette , Ostrowski Kenneth , Asp Sven , Møller Kirsten , Iversen Susanne , Hermann Claus , Søndergaard Sisse Rye , Pedersen Bente Klarlund
Published: December 2017

The aim of the present study was to investigate whether fish oil supplementation was able to modulate the acute-phase response to strenuous exercise. Twenty male runners were randomized to receive supplementation ( n = 10) with 6.0 g fish oil daily, containing 3.6 g n-3 polyunsaturated fatty acids (PUFA), for 6 wk or to receive no supplementation ( n = 10) before participating in The Copenhagen Marathon 1998. Blood samples were collected before the race, immediately after, and 1.5 and 3 h postexercise. The fatty acid composition in blood mononuclear cells (BMNC) differed between the fish oil-supplemented and the control group, showing incorporation of n-3 PUFA and less arachidonic acid in BMNC in the supplemented group. The plasma levels of tumor necrosis factor-α, interleukin-6, and transforming growth factor-β1 peaked immediately after the run, the increase being 3-, 92-, and 1.1-fold, respectively, compared with resting samples. The level of interlukin-1 receptor antagonist peaked 1.5 h after exercise, with the increase being 87-fold. However, the cytokine levels did not differ among the two groups. Furthermore, supplementation with fish oil did not influence exercise-induced increases in leucocytes and creatine kinase. In conclusion, 6 wk of fish oil supplementation had no influence on the acute-phase response to strenuous exercise.
Selected Contribution: Regulatory pathways involved in mechanical induction of c-fos gene expression in bone cells
Authors: Peake M. A. , Cooling L. M. , Magnay J. L. , Thomas P. B. M. , El Haj A. J.
Published: December 2017

The regulatory pathways involved in the rapid response of the AP-1 transcription factor, c- fos, to mechanical load in human primary osteoblast-like (HOB) cells and the human MG-63 bone cell line were investigated using a four-point bending model. HOB and MG-63 cells showed upregulation of c- fos expression on fibronectin and collagen type I substrates; however, MG-63 cells did not respond on laminin YIGSR substrates. Addition of cytochalasin D and Arg-Gly-Asp peptides during loading did not inhibit the response, whereas addition of β1-integrin antibodies inhibited the load response. The role of Ca2+ signaling has been demonstrated by blocking upregulation with addition of 2 mM EGTA, which chelates extracellular Ca2+, and gadolinium (10 μM), which inhibits stretch-activated channels. Addition of the Ca2+ ionophore A-23187 induced upregulation without loading; however, addition of nifedipine (10 μM), the L-type channel blocker, failed to prevent the load response. Inhibitors of downstream pathways indicated the involvement of protein kinase C. Our results demonstrate a key involvement of Ca2+ signaling pathways and integrin binding in the c- fos response to mechanical strain.
Performance of near-infrared spectroscopy in measuring local O2 consumption and blood flow in skeletal muscle
Authors: Van Beekvelt Mireille C. P. , Colier Willy N. J. M. , Wevers Ron A. , Van Engelen Baziel G. M.
Published: December 2017

The aim of this study was to investigate local muscle O2consumption (muscV˙o 2) and forearm blood flow (FBF) in resting and exercising muscle by use of near-infrared spectroscopy (NIRS) and to compare the results with the global muscV˙o 2 and FBF derived from the well-established Fick method and plethysmography. muscV˙o 2 was derived from 1) NIRS using venous occlusion, 2) NIRS using arterial occlusion, and 3) the Fick method [muscV˙o 2 (Fick)]. FBF was derived from 1) NIRS and 2) strain-gauge plethysmography. Twenty-six healthy subjects were tested at rest and during sustained isometric handgrip exercise. Local variations were investigated with two independent and simultaneously operating NIRS systems at two different muscles and two measurement depths. muscV˙o 2 increased more than fivefold in the active flexor digitorum superficialis muscle, and it increased 1.6 times in the brachioradialis muscle. The average increase in muscV˙o 2 (Fick) was twofold. FBF increased 1.4 times independent of the muscle or the method. It is concluded that NIRS is an appropriate tool to provide information about local muscV˙o 2 and local FBF because both place and depth of the NIRS measurements reveal local differences that are not detectable by the more established, but also more global, Fick method.
Airway resistance and tissue elastance from input or transfer impedance in bronchoconstricted monkeys
Authors: Black Kristin R. , Suki Bela , Madwed Jeffrey B. , Jackson Andrew C.
Published: December 2017

Ascaris suum (AS) challenge in nonhuman primates is used as an animal model of human asthma. The primary goal of this study was to determine whether the airways and respiratory tissues in monkeys that are bronchoconstricted by AS inhalation behave similarly to those in asthmatic humans. Airway resistance (Raw) and tissue elastance (Eti) were estimated from respiratory system input (Zin) or transfer (Ztr) impedance. Zin (0.4–20 Hz) and Ztr (2–128 Hz) were measured in anesthetized cynomolgus monkeys ( n = 10) under baseline (BL) and post-AS challenge conditions. Our results indicate that AS challenge in monkeys produces 1) predominately an increase in Raw and not tissue resistance, 2) airway wall shunting at higher AS doses, and 3) heterogeneous airway constriction resulting in a decrease of lung parenchyma effective compliance. We investigated whether the airway and tissue properties estimated from Zin and Ztr were similar and found that Raw estimated from Zin and Ztr were correlated [ r 2 = 0.76], not significantly different at BL (13.6 ± 1.4 and 13.1 ± 0.9 cmH2O · l−1 · s−1, respectively), but significantly different post-AS (20.5 ± 4.5 cmH2O · l−1 · s−1and 18.5 ± 5.2 cmH2O · l−1 · s−1). There was no correlation between Eti estimated from Zin and Ztr. The changes in lung mechanical properties in AS-bronchoconstricted monkeys are similar to those recently reported in human asthma, confirming that this is a reasonable model of human asthma.
Effects of high-intensity swimming training on GLUT-4 and glucose transport activity in rat skeletal muscle
Authors: Terada Shin , Yokozeki Toshiko , Kawanaka Kentaro , Ogawa Kishiko , Higuchi Mitsuru , Ezaki Osamu , Tabata Izumi
Published: December 2017

This study was performed to assess the effects of short-term, extremely high-intensity intermittent exercise training on the GLUT-4 content of rat skeletal muscle. Three- to four-week-old male Sprague-Dawley rats with an initial body weight ranging from 45 to 55 g were used for this study. These rats were randomly assigned to an 8-day period of high-intensity intermittent exercise training (HIT), relatively high-intensity intermittent prolonged exercise training (RHT), or low-intensity prolonged exercise training (LIT). Age-matched sedentary rats were used as a control. In the HIT group, the rats repeated fourteen 20-s swimming bouts with a weight equivalent to 14, 15, and 16% of body weight for the first 2, the next 4, and the last 2 days, respectively. Between exercise bouts, a 10-s pause was allowed. RHT consisted of five 17-min swimming bouts with a 3-min rest between bouts. During the first bout, the rat swam without weight, whereas during the following four bouts, the rat was attached to a weight equivalent to 4 and 5% of its body weight for the first 5 days and the following 3 days, respectively. Rats in the LIT group swam 6 h/day for 8 days in two 3-h bouts separated by 45 min of rest. In the first experiment, the HIT, LIT, and control rats were compared. GLUT-4 content in the epitrochlearis muscle in the HIT and LIT groups after training was significantly higher than that in the control rats by 83 and 91%, respectively. Furthermore, glucose transport activity, stimulated maximally by both insulin (2 mU/ml) (HIT: 48%, LIT: 75%) and contractions (25 10-s tetani) (HIT: 55%, LIT: 69%), was higher in the training groups than in the control rats. However, no significant differences in GLUT-4 content or in maximal glucose transport activity in response to both insulin and contractions were observed between the two training groups. The second experiment demonstrated that GLUT-4 content after HIT did not differ from that after RHT (66% higher in trained rats than in control). In conclusion, the present investigation demonstrated that 8 days of HIT lasting only 280 s elevated both GLUT-4 content and maximal glucose transport activity in rat skeletal muscle to a level similar to that attained after LIT, which has been considered a tool to increase GLUT-4 content maximally.
Reflex vascular defects in the orthostatic tachycardia syndrome of adolescents
Authors: Stewart Julian M. , Weldon Amy
Published: December 2017

Dependent pooling occurs in postural orthostatic tachycardia syndrome (POTS) related to defective vasoconstriction. Increased venous pressure (Pv) >20 mmHg occurs in some patients (high Pv) but not others (normal Pv). We compared 22 patients, aged 12–18 yr, with 13 normal controls. Continuous blood pressure and strain-gauge plethysmography were used to measure supine forearm and calf blood flow, resistance, venous compliance, and microvascular filtration, and blood flow and swelling during 70° head-up tilt. Supine, high Pv had normal resistance in arms (26 ± 2 mmHg · ml−1 · 100 ml · min) and legs (34 ± 3 mmHg · ml−1 · 100 ml · min) but low leg blood flow (1.5 ± 0.4 ml · 100 ml−1 · min−1). Supine leg Pv (30 ± 2 vs. 13 ± 1 mmHg in control) exceeded the threshold for edema (isovolumetric pressure = 19 ± 3 mmHg). Supine, normal Pv had high blood flow in arms (4.1 ± 0.2 vs. 3.5 ± 0.2 ml · 100 ml−1 · min−1 in control) and legs (3.8 ± 0.4 vs. 2.7 ± 0.3 ml · 100 ml−1 · min−1 in control) with low resistance. With tilt, calf blood flow increased steadily in POTS with high Pv and transiently increased in normal Pv. Calf volume increased in all POTS patients. Arm blood flow increased in normal Pv only with forearm maintained at heart level. These data suggest that there are (at least) two subgroups of POTS characterized by high Pv and low flow or normal Pv and high flow. These may correspond to abnormalities in local or baroreceptor-mediated vasoconstriction, respectively.
Renal hypertension prevents run training modification of cardiomyocyte diastolic Ca2+regulation in male rats
Authors: Palmer Bradley M. , Lynch Joshua M. , Snyder Steven M. , Moore Russell L.
Published: December 2017

The combined effects of endurance run training and renal hypertension on cytosolic Ca2+concentration ([Ca2+]c) dynamics and Na+-dependent Ca2+regulation in rat left ventricular cardiomyocytes were examined. Male Fischer 344 rats underwent stenosis of the left renal artery [hypertensive (Ht), n = 18] or a sham operation [normotensive (Nt), n = 20]. One-half of the rats from each group were treadmill trained for >16 wk. Cardiomyocyte fura 2 fluorescence ratio transients were recorded for 7 min during electrical pacing at 0.5 Hz, 2 mM extracellular Ca2+concentration, and 29°C. The rate of [Ca2+]cdecline was not changed by run training in the Nt group but was reduced in the Ht group. At 7 min, cardiomyocytes were exposed to 10 mM caffeine in the absence of Na+and Ca2+, which triggered sarcoplasmic reticular Ca2+release and suppressed Ca2+efflux via Na+/Ca2+exchanger. External Na+was then added, and Na+-dependent Ca2+efflux rate was recorded. Treadmill training significantly enhanced Na+-dependent Ca2+efflux rate under these conditions in the Nt group but not in the Ht group. These data provide evidence that renal hypertension prevents the normal run training-induced modifications in diastolic [Ca2+]cregulation mechanisms, including Na+/Ca2+exchanger.
Scaling peak V˙o 2 to body mass in young male and female distance runners
Authors: Eisenmann Joey C. , Pivarnik James M. , Malina Robert M.
Published: December 2017

This study examined age- and sex-associated variation in peak oxygen consumption (V˙o 2) of young male and female distance runners from an allometric scaling perspective. Subjects were from two separate studies of 9- to 19-yr-old distance runners from the mid-Michigan area, one conducted between 1982 and 1986 (Young Runners Study I, YRS I) and the other in 1999–2000 (Young Runners Study II, YRS II). Data from 27 boys and 27 girls from YRS I and 48 boys and 22 girls from the YRS II were included, and a total of 139 and 108 measurements of body size and peak V˙o 2 in boys and girls, respectively, were available. Subjects were divided into whole year age groups. A 2 × 9 (sex × age group) ANOVA was used to examine differences in peakV˙o 2. Intraindividual ontogenetic allometric scaling was determined in 20 boys and 17 girls measured annually for 3–5 yr. Allometric scaling factors were calculated using linear regression of log-transformed data. Results indicated that 1) absolute peak V˙o 2increases with age in boys and girls, 2) relative peakV˙o 2(ml · kg−1 · min−1) remains relatively stable in boys and in girls, 3) relative peakV˙o 2(ml · kg−0.75 · min−1) increases throughout the age range in boys and increases in girls until age 15 yr, and 4) peakV˙o 2 adjusted for body mass (ml/min) increases with age in boys and girls. The overall mean cross-sectional scaling factor was 1.01 ± 0.03 (SE) in boys and 0.85 ± 0.05 (SE) in girls. Significant age × sex interactions and significant scaling factors between sexes identify the progressive divergence of peak V˙o 2 between adolescent male and female distance runners. Mean ontogenetic allometric scaling factors were 0.81 [0.71–0.92, 95% confidence interval (CI)] and 0.61 (0.50–0.72, 95% CI) in boys and girls, respectively ( P = 0.002). There was considerable variation in individual scaling factors (0.51–1.31 and 0.28–0.90 in boys and girls, respectively). The results suggest that the interpretation of growth-related changes in peak V˙o 2 of young distance runners is dependent upon the manner of expressing peakV˙o 2 relative to body size and/or the statistical technique employed.
First-pass effect of an intravenous bolus of [13C]bicarbonate displayed breath-by-breath
Authors: Roecker K. , Landaw E. , Striegel H. , Mayer F. , Dickhuth H.-H.
Published: December 2017

The dilution of an intravenous bolus dose of [13C]bicarbonate is used as an estimate for the metabolic rate under certain conditions. It is a consistent finding in all studies that the total amount of intravenous [13C]bicarbonate cannot be recovered as breath 13CO2. In this study, we used a breath-by-breath analysis of 13CO2 to depict the washout of 13CO2 at a high temporal resolution to analyze the extent to which a probable first-pass effect is responsible for the reduced recovery. Eight healthy men were tested at seated rest and with bicycle exercise at a constant load relative to 40 and 75% maximal O2 consumption (V˙o 2 max). [13C]bicarbonate (0.0125 g/kg body wt) was administered as an intravenous bolus in each test. Respiratory mass spectrometry was used to derive the course of the end-tidal13CO2-to-12CO2 ratio from the breath-by-breath data. Approximately 2 min after13C administration, the washout curve could be fitted well by a two-exponential curve describing a two-compartment mammillary model. Immediately after administration of the bolus dose, an excess peak in the end-tidal13CO2-to-12CO2 ratio appeared. This peak could not be included in the two-exponential fitting. The area under the first peak resulted in 3.8 ± 1.3% of the total [13C]bicarbonate dose at rest, 11.5 ± 2.9% at moderate exercise (40%V˙o 2 max), and 16.9 ± 4.0% at intensive exercise (75% V˙o 2 max). The first-pass effect had an increasing impact of up to about two-thirds of the lacking bicarbonate with higher exercise intensity. The “loss” of tracer via this first-pass effect must be considered when the results of studies with parenteral administration of [13C]bicarbonate are considered, especially when it is given as a bolus dose and during exercise.
Alterations in a redox oxygen sensing mechanism in chronic hypoxia
Authors: Reeve H. L. , Michelakis E. , Nelson D. P. , Weir E. K. , Archer S. L.
Published: December 2017

The mechanism of acute hypoxic pulmonary vasoconstriction (HPV) may involve the inhibition of several voltage-gated K+channels in pulmonary artery smooth muscle cells. Changes in Po 2 can either be sensed directly by the channel(s) or be transmitted to the channel via a redox-based effector mechanism. In control lungs, hypoxia and rotenone acutely decrease production of activated oxygen species, inhibit K+channels, and cause constriction. Two-day and 3-wk chronic hypoxia (CH) resulted in a decrease in basal activated oxygen species levels, an increase in reduced glutathione, and loss of HPV and rotenone-induced constriction. In contrast, 4-aminopyridine- and KCl-mediated constrictions were preserved. After 3-wk CH, pulmonary arterial smooth muscle cell membrane potential was depolarized, K+ channel density was reduced, and acute hypoxic inhibition of whole cell K+ current was lost. In addition, Kv1.5 and Kv2.1 channel protein was decreased. These data suggest that chronic reduction of the cytosol occurs before changes in K+ channel expression. HPV may be attenuated in CH because of an impaired redox sensor.
Cotyledon and binucleate cell nitric oxide synthase expression in an ovine model of fetal growth restriction
Authors: Galan Henry L. , Regnault Timothy R. H. , Le Cras Timothy D. , Tyson R. Weslie , Anthony Russell V. , Wilkening Randall B. , Abman Steven H.
Published: December 2017

Heat exposure early in ovine pregnancy results in placental insufficiency and intrauterine growth restriction (PI-IUGR). We hypothesized that heat exposure in this model disrupts placental structure and reduces placental endothelial nitric oxide synthase (eNOS) protein expression. We measured eNOS protein content and performed immunohistochemistry for eNOS in placentas from thermoneutral (TN) and hyperthermic (HT) animals killed at midgestation (90 days). Placental histomorphometry was compared between groups. Compared with the TN controls, the HT group showed reduced delivery weights (457 ± 49 vs. 631 ± 21 g; P < 0.05) and a trend for reduced placentome weights (288 ± 61 vs. 554 ± 122 g; P = 0.09). Cotyledon eNOS protein content was reduced by 50% in the HT group ( P < 0.03). eNOS localized similarly to the vascular endothelium and binucleated cells (BNCs) within the trophoblast of both experimental groups. HT cotyledons showed a reduction in the ratio of fetal to maternal stromal tissue (1.36 ± 0.36 vs. 3.59 ± 1.2; P≤ 0.03). We conclude that eNOS protein expression is reduced in this model of PI-IUGR and that eNOS localizes to both vascular endothelium and the BNC. We speculate that disruption of normal vascular development and BNC eNOS production and function leads to abnormal placental vascular tone and blood flow in this model of PI-IUGR.
Role of nitric oxide in the regulation of glucose kinetics in response to endotoxin in dogs
Authors: Moeniralam H. S. , Sprangers F. , Endert E. , Ackermans M. T. , Van Lanschot J. J. B. , Sauerwein H. P. , Romijn J. A.
Published: December 2017

The purpose of the present in vivo study was to determine the role of nitric oxide (NO) in the regulation of glucose metabolism in response to endotoxin by blocking NO synthesis with NG-monomethyl-l-arginine (l-NMMA). In five dogs, the appearance and disappearance rates of glucose (by infusion of [6,6-2H2]glucose), plasma glucose concentration, and plasma hormone concentrations were measured on five different occasions: saline infusion, endotoxin alone ( E coli, 1.0 μg/kg iv), and endotoxin administration plus three different doses of primed, continuous infusion of l-NMMA. Endotoxin increased rate of appearance of glucose from 13.7 ± 1.6 to 23.6 ± 3.3 μmol · kg−1· min−1( P < 0.05), rate of disappearance of glucose from 13.9 ± 1.1 to 24.8 ± 3.1 μmol · kg−1· min−1( P < 0.001), plasma lactate from 0.5 ± 0.1 to 1.7 ± 0.1 mmol/l ( P < 0.01), and counterregulatory hormone concentrations. l-NMMA did not affect the rise in rate of appearance and disappearance of glucose, plasma lactate, or the counterregulatory hormone response to endoxin. Plasma glucose levels were not affected by endotoxin with or withoutl-NMMA. In conclusion, in vivo inhibition of NO synthesis by high doses of l-NMMA does not affect glucose metabolism in response to endotoxin, indicating that NO is not a major mediator of glucose metabolism during endotoxemia in dogs.
Effect of ventilation-perfusion inhomogeneity and N2O on oxygenation: physiological modeling of gas exchange
Authors: Peyton Philip J. , Robinson Gavin J. B. , Thompson Bruce
Published: December 2017

Ventilation-perfusion (V˙a/Q˙) inhomogeneity was modeled to measure its effect on arterial oxygenation during maintenance-phase anesthesia involving an inspired mixture of 30% O2 and either N2O or N2. A multialveolar compartment computer model was constructed based on a log normal distribution ofV˙a/Q˙ inhomogeneity. Increasing the log SD of the distribution of blood flow from 0 to 1.75 produced a progressive fall in arterial Po 2 (PaO2 ). The fall was less steep in the presence of N2O than when N2 was present instead. This was due mainly to the concentrating effect of N2O uptake on alveolar Po 2 in moderately lowV˙a/Q˙ compartments. The improvement in PaO2 when N2O was present instead of N2 was greatest when the degree ofV˙a/Q˙ inhomogeneity was in the range typically seen in anesthetized patients. Models based on distributions of expired and inspired alveolar ventilation give quantitatively different results for PaO2 . In the presence ofV˙a/Q˙ inhomogeneity, second-gas and concentrating effects may have clinically significant effects on arterial oxygenation even at “steady-state” levels of N2O uptake.
Muscle regeneration during hindlimb unloading results in a reduction in muscle size after reloading
Authors: Mozdziak P. E. , Pulvermacher P. M. , Schultz E.
Published: December 2017

The hindlimb-unloading model was used to study the ability of muscle injured in a weightless environment to recover after reloading. Satellite cell mitotic activity and DNA unit size were determined in injured and intact soleus muscles from hindlimb-unloaded and age-matched weight-bearing rats at the conclusion of 28 days of hindlimb unloading, 2 wk after reloading, and 9 wk after reloading. The body weights of hindlimb-unloaded rats were significantly ( P < 0.05) less than those of weight-bearing rats at the conclusion of hindlimb unloading, but they were the same ( P > 0.05) as those of weight-bearing rats 2 and 9 wk after reloading. The soleus muscle weight, soleus muscle weight-to-body weight ratio, myofiber diameter, number of nuclei per millimeter, and DNA unit size were significantly ( P< 0.05) smaller for the injured soleus muscles from hindlimb-unloaded rats than for the soleus muscles from weight-bearing rats at each recovery time. Satellite cell mitotic activity was significantly ( P < 0.05) higher in the injured soleus muscles from hindlimb-unloaded rats than from weight-bearing rats 2 wk after reloading, but it was the same ( P > 0.05) as in the injured soleus muscles from weight-bearing rats 9 wk after reloading. The injured soleus muscles from hindlimb-unloaded rats failed to achieve weight-bearing muscle size 9 wk after reloading, because incomplete compensation for the decrease in myonuclear accretion and DNA unit size expansion occurred during the unloading period.
Effects of 3-day bed rest on physiological responses to graded exercise in athletes and sedentary men
Authors: Smorawiński J. , Nazar K. , Kaciuba-Uscilko H. , Kamińska E. , Cybulski G. , Kodrzycka A. , Bicz B. , Greenleaf J. E.
Published: December 2017

To test the hypotheses that short-term bed-rest (BR) deconditioning influences metabolic, cardiorespiratory, and neurohormonal responses to exercise and that these effects depend on the subjects' training status, 12 sedentary men and 10 endurance- and 10 strength-trained athletes were submitted to 3-day BR. Before and after BR they performed incremental exercise test until volitional exhaustion. Respiratory gas exchange and heart rate (HR) were recorded continuously, and stroke volume (SV) was measured at submaximal loads. Blood was taken for lactate concentration ([LA]), epinephrine concentration ([Epi]), norepinephrine concentration ([NE]), plasma renin activity (PRA), human growth hormone concentration ([hGH]), testosterone, and cortisol determination. Reduction of peak oxygen uptake (V˙o 2 peak) after BR was greater in the endurance athletes than in the remaining groups (17 vs. 10%). Decrements in V˙o 2 peak correlated positively with the initial values ( r = 0.73, P < 0.001). Resting and exercise respiratory exchange ratios were increased in athletes. Cardiac output was unchanged by BR in all groups, but exercise HR was increased and SV diminished in the sedentary subjects. The submaximal [LA] and [LA] thresholds were decreased in the endurance athletes from 71 to 60%V˙o 2 peak ( P < 0.001); they also had an earlier increase in [NE], an attenuated increase in [hGH], and accentuated PRA and cortisol elevations during exercise. These effects were insignificant in the remaining subjects. In conclusion, reduction of exercise performance and modifications in neurohormonal response to exercise after BR depend on the previous level and mode of physical training, being the most pronounced in the endurance athletes.
Expression of heme oxygenase in the oxygen-sensing regions of the rostral ventrolateral medulla
Authors: Mazza Emilio , Thakkar-Varia Smita , Tozzi Carol A. , Neubauer Judith A.
Published: December 2017

Recently, unique regions in the rostral ventrolateral medulla (RVLM) have been found to be oxygen sensitive. However, the mechanism of sensing oxygen in these RVLM regions is unknown. Because heme oxygenase (HO) has been shown to be involved in the hypoxic responses of the carotid body and pulmonary artery, the aim of this study was to determine whether HO is present in the RVLM and whether expression of HO is altered by chronic hypoxia. Adult rats were exposed to hypoxia (10% O2) or normoxia (21% O2) for 10 days, and the mRNA for HO-1 and HO-2 was examined in the RVLM by using RT-PCR. Expression of HO-2 mRNA was seen in the RVLM of both control and hypoxic samples, whereas expression of HO-1 mRNA was only seen in the RVLM of hypoxic samples. HO-2 was immunocytochemically localized in brain sections (40 μm) to the C1 region and pre-Bötzinger complex of the RVLM. Together, these results indicate that HO-2 is present in the RVLM under control conditions and that HO-1 is induced in the RVLM during chronic hypoxia, consistent with a potential role for HO in the oxygen-sensing function of these cardiorespiratory RVLM regions.
Validity of estimating limb muscle volume by bioelectrical impedance
Authors: Miyatani Masae , Kanehisa Hiroaki , Masuo Yoshihisa , Ito Masamitsu , Fukunaga Tetsuo
Published: December 2017

The present study aimed to investigate the validity of estimating muscle volume by bioelectrical impedance analysis. Bioelectrical impedance and series cross-sectional images of the forearm, upper arm, lower leg, and thigh on the right side were determined in 22 healthy young adult men using a specially designed bioelectrical impedance acquisition system and magnetic resonance imaging (MRI) method, respectively. The impedance index ( L2/Z) for every segment, calculated as the ratio of segment length squared to the impedance, was significantly correlated to the muscle volume measured by MRI, with r= 0.902–0.976 ( P < 0.05). In these relationships, the SE of estimation was 38.4 cm3for the forearm, 40.9 cm3for the upper arm, 107.2 cm3for the lower leg, and 362.3 cm3for the thigh. Moreover, isometric torque developed in elbow flexion or extension and knee flexion or extension was significantly correlated to the L2/Z values of the upper arm and thigh, respectively, with correlation coefficients of 0.770–0.937 ( P < 0.05), which differed insignificantly from those (0.799–0.958; P < 0.05) in the corresponding relationships with the muscle volume measured by MRI of elbow flexors or extensors and knee flexors or extensors. Thus the present study indicates that bioelectrical impedance analysis may be useful to predict the muscle volume and to investigate possible relations between muscle size and strength capability in a limited segment of the upper and lower limbs.