bluuebunny/crossref_metadata_2025 huggingface dataset:
Regional differences in serotonergic input to canine parasternal intercostal motoneurons
Authors: Zhan Wen-Zhi , Mantilla Carlos B. , Zhan Phillip , Bitton Asaf , Prakash Y. S. , de Troyer Andre , Sieck Gary C.
Published: December 2017

There is a mediolateral gradient in activation of the parasternal intercostal (PI) muscle during inspiration. In the present study, we tested the hypotheses that serotonergic [5-hydroxytryptamine (5-HT)] input from descending central drive and/or intrinsic size-related properties of PI motoneurons leads to the differential activation of PI muscles. In dogs, PI motoneurons innervating the medial and lateral regions of the PI muscles at the T3–T5 interspaces were retrogradely labeled by intramuscular injection of cholera toxin B subunit. After a 10-day survival period, PI motoneurons and 5-HT terminals were visualized by using immunohistochemistry and confocal imaging. There were no differences in motoneuron morphology among motoneurons innervating the medial and lateral regions of the PI muscle. However, the number of 5-HT terminals and the 5-HT terminal density (normalized for surface area) were greater in motoneurons innervating the medial region of the PI muscle compared with the lateral region. These results suggest that differences in distribution of 5-HT input may contribute to regional differences in PI muscle activation during inspiration and that differences in PI motoneuron recruitment do not relate to size.
Simple contrivance “clamps” end-tidal P CO 2 and P O 2 despite rapid changes in ventilation
Authors: Banzett Robert B. , Garcia Ronald T. , Moosavi Shakeeb H.
Published: December 2017

The device described in this study uses functionally variable dead space to keep effective alveolar ventilation constant. It is capable of maintaining end-tidal[Formula: see text] and[Formula: see text] within ±1 Torr of the set value in the face of increases in breathing above the baseline level. The set level of end-tidal [Formula: see text] or[Formula: see text] can be independently varied by altering the concentration in fresh gas flow. The device comprises a tee at the mouthpiece, with one inlet providing a limited supply of fresh gas flow and the other providing reinspired alveolar gas when ventilation exceeds fresh gas flow. Because the device does not depend on measurement and correction of end-tidal or arterial gas levels, the response of the device is essentially instantaneous, avoiding the instability of negative feedback systems having significant delay. This contrivance provides a simple means of holding arterial blood gases constant in the face of spontaneous changes in breathing (above a minimum alveolar ventilation), which is useful in respiratory experiments, as well as in functional brain imaging where blood gas changes can confound interpretation by influencing cerebral blood flow.
Effect of contractile activity on protein turnover in skeletal muscle mitochondrial subfractions
Authors: Connor Michael K. , Bezborodova Olga , Escobar C. Patricia , Hood David A.
Published: December 2017

To determine the role of intramitochondrial protein synthesis (PS) and degradation (PD) in contractile activity-induced mitochondrial biogenesis, we evaluated rates of [35S]methionine incorporation into protein in isolated rat muscle subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria. Rates of PS ranged from 47 to 125% greater ( P < 0.05) in IMF compared with SS mitochondria. Intense, acute in situ contractile activity (10 Hz, 5 min) of fast-twitch gastrocnemius muscle resulted in a 50% decrease in PS ( P < 0.05) in SS but not IMF mitochondria. Recovery, or continued contractile activity (55 min), reestablished PS in SS mitochondria. In contrast, PS was not affected in either SS or IMF mitochondria after prolonged (60-min) contractile activity in the presence or absence of a recovery period. PD was not influenced by 5 min of contractile activity in the presence or absence of recovery but was reduced after 60 min of contractions followed by recovery. Chronic stimulation (10 Hz, 3 h/day, 14 days) increased muscle cytochrome- c oxidase activity by 2.2-fold but reduced PS in IMF mitochondria by 29% ( P < 0.05; n = 4). PS in SS mitochondria and PD in both subfractions were not changed by chronic stimulation. Thus acute contractile activity exerts differential effects on protein turnover in IMF and SS mitochondria, and it appears that intramitochondrial PS does not limit the extent of chronic contractile activity-induced mitochondrial biogenesis.
Comparative effects of α-receptor stimulation and nitrergic inhibition on bronchovascular tone
Authors: Carvalho Paula , Thompson William H. , Charan Nirmal B.
Published: December 2017

Adrenergic agonists are known to influence bronchial blood flow and bronchovascular resistance. Recently, the nitrergic system has also been implicated in the control of bronchovascular tone. In this study, we compared the effects of the nitric oxide synthase inhibitor N ω-nitro-l-arginine methyl ester (l-NAME) and the α1-receptor agonist phenylephrine on bronchovascular resistance in anesthetized sheep ( n = 9). Bronchial blood flow, cardiac output, and systemic and pulmonary arterial pressures were continuously monitored. Phenylephrine (1.2–3.4 μg ⋅ kg−1 ⋅ min−1) was infused intravenously to increase mean systemic arterial pressure above 95 Torr for 10 min and then was discontinued. When hemodynamic parameters returned to baseline, nebulized phenylephrine (10 mg) was given over 10 min. When parameters again normalized, l-NAME (30 mg/kg) was infused intravenously over 1 min. Intravenous phenylephrine increased systemic vascular resistance by 40% at 10 min with no concurrent increase in bronchovascular resistance, but inhaled phenylephrine increased bronchovascular resistance by 66% at 10 min. By comparison, intravenous l-NAME produced a rapid and sustained fivefold increase in bronchovascular resistance at 10 min. We conclude that, although α-agonist stimulation has some influence on bronchovascular resistance in sheep, the nitrergic system has predominant control of bronchovascular tone.
Exercise and bone mineral density in men: a meta-analysis
Authors: Kelley George A. , Kelley Kristi S. , Tran Zung Vu
Published: December 2017

The purpose of this study was to use the meta-analytic approach to examine the effects of exercise on bone mineral density (BMD) in men. A total of 26 effect sizes (ES) representing 225 subjects from 8 studies met the criteria for inclusion. When BMD sites assessed were specific to the sites loaded during exercise, increases of ∼2.6% (2.1% in the exercisers and −0.5% in the controls) were found. These results were statistically significant (ES = 0.213, 95% bootstrap confidence interval = 0.007–0.452). Statistically significant ES changes were found for older (>31 yr) but not younger (<31 yr) adults, with differences between groups statistically significant ( P = 0.04). Statistically significant changes were also observed at the femur, lumbar, and os calcis sites. The results of this study suggest that site-specific exercise may help improve and maintain BMD at the femur, lumbar, and os calcis sites in older men. However, the biological importance of the small changes observed for most outcomes, quality of studies, and limited data pool prevent us from forming any firm conclusion regarding the use of exercise for maintaining and/or improving BMD in men. Clearly, a need exists for additional studies.
Epinephrine inhibits exogenous glucose utilization in exercising horses
Authors: Geor Raymond J. , Hinchcliff Kenneth W. , McCutcheon Laura Jill , Sams Richard A.
Published: December 2017

This study examined the effects of preexercise glucose administration, with and without epinephrine infusion, on carbohydrate metabolism in horses during exercise. Six horses completed 60 min of treadmill exercise at 55 ± 1% maximum O2uptake 1) 1 h after oral administration of glucose (2 g/kg; G trial); 2) 1 h after oral glucose and with an intravenous infusion of epinephrine (0.2 μmol ⋅ kg−1⋅ min−1; GE trial) during exercise, and 3) 1 h after water only (F trial). Glucose administration (G and GE) caused hyperinsulinemia and hyperglycemia (∼8 mM). In GE, plasma epinephrine concentrations were three- to fourfold higher than in the other trials. Compared with F, the glucose rate of appearance was ∼50% and ∼33% higher in G and GE, respectively, during exercise. The glucose rate of disappearance was ∼100% higher in G than in F, but epinephrine infusion completely inhibited the increase in glucose uptake associated with glucose administration. Muscle glycogen utilization was higher in GE [349 ± 44 mmol/kg dry muscle (dm)] than in F (218 ± 28 mmol/kg dm) and G (201 ± 35 mmol/kg dm). We conclude that 1) preexercise glucose augments utilization of plasma glucose in horses during moderate-intensity exercise but does not alter muscle glycogen usage and 2) increased circulating epinephrine inhibits the increase in glucose rate of disappearance associated with preexercise glucose administration and increases reliance on muscle glycogen for energy transduction.
Age causes a redistribution of joint torques and powers during gait
Authors: DeVita Paul , Hortobagyi Tibor
Published: December 2017

At self-selected walking speeds, elderly compared with young adults generate decreased joint torques and powers in the lower extremity. These differences may be actual gait-limiting factors and neuromuscular adaptations with age or simply a consciously selected motor pattern to produce a slower gait. The purpose of the study was to compare joint torques and powers of young and elderly adults walking at the same speed. Twelve elderly and fourteen young adults (ages 69 and 21 yr) walked at 1.48 m/s over a force platform while being videotaped. Hip, knee, and ankle torques and powers were calculated from the reaction force and kinematic data. A support torque was calculated as the sum of the three joint torques. Extensor angular impulse during stance and positive work at each joint were derived from the torques and powers. Step length was 4% shorter and cadence was 4% higher in elderly adults (both P < 0.05) compared with young adults. Support angular impulse was nearly identical between groups, but elderly adults had 58% greater angular impulse and 279% more work at the hip, 50% less angular impulse and 39% less work at the knee, and 23% less angular impulse and 29% less work at the ankle compared with young adults ( t-test, all P < 0.05). Age caused a redistribution of joint torques and powers, with the elderly using their hip extensors more and their knee extensors and ankle plantar flexors less than young adults when walking at the same speed. Along with a reduction in motor and sensory functions, the natural history of aging causes a shift in the locus of function in motor performance.
Endocrine markers of semistarvation in healthy lean men in a multistressor environment
Authors: Friedl Karl E. , Moore Robert J. , Hoyt Reed W. , Marchitelli Louis J. , Martinez-Lopez Lester E. , Askew E. Wayne
Published: December 2017

We tested the hypothesis that key endocrine responses to semistarvation would be attenuated by changing only the food intake in a multistressor environment that also included sustained workload, inadequate sleep, and thermal strain. Serum hormones were compared within and between two groups of healthy young male volunteers participating in the 8-wk US Army Ranger course, with four repeated cycles of restricted energy intakes and refeeding: group 1 ( n = 49) and group 2 ( n = 48); energy deficits averaged 1,200 and 1,000 kcal/day, respectively. After 8 wk, most of group 1 achieved a minimum body fat, serum 3,5,3′-triiodothyronine (T3) was below normal (78 ± 20 ng/dl), testosterone (T) approached castrate levels (4.5 ± 3.9 nmol/l), insulin-like growth factor I (IGF-I) declined by one-half (75 ± 25 μg/l), and cholesterol rose from 158 ± 31 to 217 ± 39 mg/dl. Bioavailable T3 and T were further reduced by increases in their specific binding proteins in response to declining insulin. Refeeding, even with continuation of the other stressors, produced prompt recovery of T3, T, and IGF-I. Higher energy intakes in group 2 attenuated the subclinical hypothyroidism and hypercholesterolemia, whereas consistent luteinizing hormone suppression indicated centrally mediated threshold effects on gonadal hormone suppression. We conclude that low T, T3, and IGF-I remained reliable markers of acute energy deficits in the presence of other stressors; elevated cholesterol and cortisol provided information about chronic status, corresponding to diminishing body fat stores.
Effect of age on sleep onset-related changes in respiratory pump and upper airway muscle function
Authors: Worsnop Christopher , Kay Amanda , Kim Young , Trinder John , Pierce Robert
Published: December 2017

In normal young men, there is an abrupt fall in ventilation (V˙e), a rise in upper airway resistance (UAR), and falls in the activities of the diaphragm (Di), intercostals (IC), genioglossus (GG), and tensor palatini (TP) at sleep onset. On waking, there is an abrupt increase inV˙e and fall in UAR and an increase in the activities of Di, IC, GG, and TP. The aim of this study was to determine whether these changes are age dependent. Nine men aged 20 to 25 yr were compared with nine men aged 42 to 67 yr. Airflow, UAR, Di, and IC surface electromyograms (EMGs) and the intramuscular EMGs of GG and TP were recorded. It was found that the falls in IC, GG, and TP at the transition from α to θ electroencephalogram (EEG) activity were significantly greater in the older than in the younger men ( P < 0.05) and that the fall in Di was also greater, although this was only marginally significant ( P = 0.15). The rise in GG at θ-to-α transitions was also greater in the older than in the younger men, and there was a trend for TP to be higher.
Consequences of periodic augmented breaths on tongue muscle activities in hypoxic rats
Authors: Janssen Patrick L. , Williams James S. , Fregosi Ralph F.
Published: December 2017

This study was designed to investigate the influence of hypoxia-evoked augmented breaths (ABs) on respiratory-related tongue protrudor and retractor muscle activities and inspiratory pump muscle output. Genioglossus (GG) and hyoglossus (HG) electromyogram (EMG) activities and respiratory-related tongue movements were compared with peak esophageal pressure (Pes; negative change in pressure during inspiration) and minute Pes (Pes × respiratory frequency = Pes/min) before and after ABs evoked by sustained poikilocapnic, isocapnic, and hypercapnic hypoxia in spontaneously breathing, anesthetized rats. ABs evoked by poikilocapnic and isocapnic hypoxia triggered long-lasting (duration at least 10 respiratory cycles) reductions in GG and HG EMG activities and tongue movements relative to pre-AB levels, but Pes was reduced transiently (duration of <10 respiratory cycles) after ABs. Adding 7% CO2 to the hypoxic inspirate had no effect on the frequency of evoked ABs, but this prevented long-term declines in tongue muscle activities. Bilateral vagotomy abolished hypoxia-induced ABs and stabilized drive to the tongue muscles during each hypoxic condition. We conclude that, in the rat, hypoxia-evoked ABs 1) elicit long-lasting reductions in protrudor and retractor tongue muscle activities, 2) produce short-term declines in inspiratory pump muscle output, and 3) are mediated by vagal afferents. The more prolonged reductions in pharyngeal airway vs. pump muscle activities may lead to upper airway narrowing or collapse after spontaneous ABs.
Respiratory muscle activity measured with a noninvasive EMG technique: technical aspects and reproducibility
Authors: Maarsingh E. J. W. , van Eykern L. A. , Sprikkelman A. B. , Hoekstra M. O. , van Aalderen W. M. C.
Published: December 2017

A new method is being developed to investigate airway obstruction in young children by means of noninvasive electromyography (EMG) of diaphragmatic and intercostal muscles. The purpose of this study was to evaluate the reproducibility of the EMG measurements. Eleven adults, 39 school children (20 healthy, 19 asthmatic), and 16 preschool children were studied during tidal breathing on separate occasions: two for adults with a time interval of 3 wk and three for children with time intervals of 1 and 24 h. Single electrodes were placed on the second intercostal space left and right of the sternum and at the height of the frontal and the dorsal diaphragm. Bipolar electrode pairs were placed on the rectus abdominis muscle. A newly designed digital physiological amplifier without any analog filtering was used to measure the EMG signals. Except for the average dorsal diaphragm EMG derivation in healthy school children on the second occasion, a significant correlation between the mean peak-to-peak inspiratory activity of average diaphragmatic and intercostal EMG was found in the different age groups on the different measurement occasions ( P< 0.05). To assess the repeatability, we described the agreement between the repeated measurements within the same subjects. No significant differences were found between the measurements on the separate occasions. Our observations indicate that the EMG signals derived from the diaphragm and intercostal muscles are, in different age groups with and without asthma, reproducible during tidal breathing.
Effects of postexercise carbohydrate-protein feedings on muscle glycogen restoration
Authors: Carrithers John A. , Williamson David L. , Gallagher Philip M. , Godard Michael P. , Schulze Kimberley E. , Trappe Scott W.
Published: December 2017

The purpose of this investigation was to determine the effects of postexercise eucaloric carbohydrate-protein feedings on muscle glycogen restoration after an exhaustive cycle ergometer exercise bout. Seven male collegiate cyclists [age = 25.6 ± 1.3 yr, height = 180.9 ± 3.2 cm, wt = 75.4 ± 4.0 kg, peak oxygen uptake (V˙o 2 peak) = 4.20 ± 0.2 l/min] performed three trials, each separated by 1 wk: 1) 100% α-d-glucose [carbohydrate (CHO)], 2) 70% carbohydrate-20% protein (PRO)-10% fat, and 3) 86% carbohydrate-14% amino acid (AA). All feedings were eucaloric, based on 1.0 g ⋅ kg body wt− 1 ⋅ h− 1of CHO, and administered every 30 min during a 4-h muscle glycogen restoration period in an 18% wt/vol solution. Muscle biopsies were obtained immediately and 4 h after exercise. Blood samples were drawn immediately after the exercise bout and every 0.5 h for 4 h during the restoration period. Increases in muscle glycogen concentrations for the three feedings (CHO, CHO-PRO, CHO-AA) were 118 mmol/kg dry wt; however, no differences among the feedings were apparent. The serum glucose and insulin responses did not differ throughout the restoration period among the three feedings. These results suggest that muscle glycogen restoration does not appear to be enhanced with the addition of proteins or amino acids to an eucaloric CHO feeding after exhaustive cycle exercise.
Ozone uptake in the intact human respiratory tract: relationship between inhaled dose and actual dose
Authors: Rigas Marc L. , Catlin Sandra N. , Ben-Jebria Abdellaziz , Ultman James S.
Published: December 2017

Inhaled concentration (C), minute volume (MV), and exposure duration (T) are factors that may affect the uptake of ozone (O3) within the respiratory tract. Ten healthy adult nonsmokers participated in four sessions, inhaling 0.2 or 0.4 ppm O3 through an oral mask while exercising continuously to elicit a MV of 20 l/min for 60 min or 40 l/min for 30 min. In each session, fractional absorption (FA) was determined on a breath-by-breath basis as the ratio of O3 uptake to the inhaled O3 dose. The mean ± SD value of FA for all breaths was 0.86 ± 0.06. Although C, MV, and T all had statistically significant effects on FA ( P < 0.0001, P = 0.004, and P = 0.026, respectively), the magnitudes of these effects were small compared with intersubject variability. For an average subject, a 0.05 change in FA would require that C change by 1.3 ppm, MV change by 46 l/min, or T change by 1.7 h. It is concluded that inhaled dose is a reasonable surrogate for the actual dose delivered to a particular subject during O3 exposures of <2 h, but it is not a reasonable surrogate when comparisons are made between individuals.
Plasma leptin in female athletes: relationship with body fat, reproductive, nutritional, and endocrine factors
Authors: Thong Farah S. L. , McLean Cyndy , Graham Terry E.
Published: December 2017

The relationship of leptin to thyroid and sex hormones, insulin, energy intake, exercise energy expenditure, and reproductive function was assessed in 39 female athletes. They comprised elite athletes who were either amenorrheic (EAA; n = 5) or cyclic (ECA; n = 8) and recreationally active women who were either cyclic (RCA; n= 13) or taking oral contraceptives (ROC; n = 13). Leptin was significantly lower in EAA (1.7 ± 0.2 ng/ml) than in ECA (2.9 ± 0.3 ng/ml), RCA (5.8 ± 0.9 ng/ml), and ROC (7.4 ± 1.3 ng/ml). Hypoleptinemia in EAA was paralleled by reductions ( P < 0.05) in caloric intake, insulin, estradiol, and thyroid hormones. Leptin increased by 40–46% ( P < 0.05) in the luteal phase of the menstrual cycle in RCA and ECA. Plasma leptin was similar in the placebo and active pill phases in ROC despite a significant increase in ethinylestradiol. Leptin correlated ( P < 0.05) with triiodothyronine and insulin but not with estrogen, energy intake, or exercise energy expenditure. These data suggest that in female athletes 1) leptin may be a metabolic signal that provides a link between adipose tissue, energy availability, and the reproductive axis and 2) sex hormones do not directly regulate leptin secretion.
Thoracoabdominal asynchrony failed to grade airway obstructions in foals
Authors: Miller Carrie , Hoffman Andrew M. , Hunter Janice
Published: December 2017

Respiratory inductive plethysmography (RIP) can be used to obtain a valid measure of tidal volume in humans. This device also compares the contributions to ventilation of the thorax and abdomen. Although thoracoabdominal asynchrony is a prominent clinical feature for patients with airway obstruction, the accuracy of the RIP device to assess the severity of obstruction is unclear. This study analyzes how well RIP variables reflect the degree of a fixed external inspiratory plus expiratory resistive load in foals. Foals were employed because the species and age group are commonly afflicted with respiratory disease. Eight conscious, sedated (xylazine 1.25 mg/kg body wt) foals were subjected to randomly ordered resistive loads at the airway opening and, on a separate day, to histamine aerosol challenge. During resistive loading, phase angle changed significantly, as did phase relation ( P ≤ 0.05). However, no significant correlation was found between the degree of change in resistive load and the degree to which phase angle or relation was altered ( rs= 0.41 and 0.25, respectively). In addition, neither phase angle nor relation changed significantly with histamine challenge. We conclude that, although RIP variables changed markedly with fixed upper airway resistive loading, the degree to which they changed was erratic and therefore not useful for grading these obstructions. Furthermore, RIP variables were insensitive measures of histamine-induced bronchoconstriction.
Force-frequency relationship and potentiation in mammalian skeletal muscle
Authors: MacIntosh Brian R. , Willis Janine C.
Published: December 2017

Repetitive activation of a skeletal muscle results in potentiation of the twitch contractile response. Incompletely fused tetanic contractions similar to those evoked by voluntary activation may also be potentiated by prior activity. We aimed to investigate the role of stimulation frequency on the enhancement of unfused isometric contractions in rat medial gastrocnemius muscles in situ. Muscles set at optimal length were stimulated via the sciatic nerve with 50-μs duration supramaximal pulses. Trials consisted of 8 s of repetitive trains [5 pulses (quintuplets) 2 times per second or 2 pulses (doublets) 5 times per second] at 20, 40, 50, 60, 70, and 80 Hz. These stimulation frequencies represent a range over which voluntary activation would be expected to occur. When the frequency of stimulation was 20, 50, or 70 Hz, the peak active force (highest tension during a contraction − rest tension) of doublet contractions increased from 2.2 ± 0.2, 4.1 ± 0.4, and 4.3 ± 0.5 to 3.1 ± 0.3, 5.6 ± 0.4, and 6.1 ± 0.7 N, respectively. Corresponding measurements for quintuplet contractions increased from 2.2 ± 0.2, 6.1 ± 0.5, and 8.7 ± 0.7 to 3.2 ± 0.3, 7.3 ± 0.6, and 9.0 ± 0.7 N, respectively. Initial peak active force values were 27 ± 1 and 61.5 ± 5% of the maximal (tetanic) force for doublet and quintuplet contractions, respectively, at 80 Hz. With doublets, peak active force increased at all stimulation frequencies. With quintuplets, peak active force increased significantly for frequencies up to 60 Hz. Twitch enhancement at the end of the 8 s of repetitive stimulation was the same regardless of the pattern of stimulation during the 8 s, and twitch peak active force returned to prestimulation values by 5 min. These experiments confirm that activity-dependent potentiation is evident during repeated, incompletely fused tetanic contractions over a broad range of frequencies. This observation suggests that, during voluntary motor unit recruitment, derecruitment or decreased firing frequency would be necessary to achieve a fixed (submaximal) target force during repeated isometric contractions over this time period.
Cerebral and intestinal perfusion and metabolism in normocythemic hyperviscous hypoxic newborn pigs
Authors: Goldstein Marshall , Rehan Virender K. , Oh William , Stonestreet Barbara S.
Published: December 2017

We studied the effects of hypoxia on cerebral cortical and intestinal perfusion and metabolism in normocythemic hyperviscous newborn pigs. Seven pigs were made hyperviscous by an injection of cryoprecipitate, increasing viscosity from 5.8 ± 0.9 to 9.0 ± 1.2 (SD) cycles/s. Six normoviscous pigs received 0.9% NaCl. Reducing the inspired O2decreased the arterial O2content ([Formula: see text]) from 9.5 ± 1.6 to 3.6 ± 1.3 ml O2/100 ml. Increases in brain and decreases in gastrointestinal blood flow at the lower[Formula: see text] values were similar between the groups. During hypoxia, blood flow to stomach, distal intestinal mucosa, and large intestines was lower (−50, −23, and −28%, respectively) in the hyperviscous than normoviscous group. At the lower [Formula: see text] values, cerebral cortical vascular resistance decreased in both groups and intestinal vascular resistance increased (+257%) in the hyperviscous but not in the normoviscous group. During hypoxia, systemic oxygen delivery decreased, extraction increased, and uptake did not change; cerebral cortical O2delivery, extraction, and uptake did not change; and intestinal O2delivery decreased, extraction increased, and uptake did not change in both groups. Our study demonstrated that 1) during hypoxia, increases in systemic O2extraction compensated for decreases in delivery and systemic uptake did not change; vasodilation sustained cerebral cortical O2delivery and preserved metabolism; increases in intestinal oxygen extraction offset decreases in delivery and uptake was preserved; and 2) nonpolycythemic hyperviscosity did not have a major influence on cardiovascular or metabolic responses to hypoxia, except for modest effects on intestinal resistance and perfusion to certain gastrointestinal regions. We conclude that, under normocythemic conditions, a moderate increase in viscosity does not have a major impact on hemodynamic or metabolic adjustments to hypoxia in newborn pigs.
Treadmill exercise training blunts suppression of splenic natural killer cell cytolysis after footshock
Authors: Dishman R. K. , Warren J. M. , Hong S. , Bunnell B. N. , Mougey E. H. , Meyerhoff J. L. , Jaso-Friedmann L. , Evans D. L.
Published: December 2017

This study extended to treadmill exercise training our prior report (Dishman RK, Warren JM, Youngstedt SD, Yoo H, Bunnell BN, Mougey EH, Meyerhoff JL, Jaso-Friedmann L, and Evans DL. J Appl Physiol78: 1547–1554, 1995) that activity wheel running abolished the suppression of footshock-induced natural killer (NK) cell cytolysis. Twenty-four male Fischer 344 rats were assigned to one of three groups ( n = 8, all groups): 1) a home-cage control group, 2) a sedentary treatment group, or 3) a treadmill-running group (0° incline, 25 m/min, 35 min/day, 6 days/wk). After 6 wk, the treadmill and sedentary groups received 2 days of footshock. Splenic NK cytotoxicity was determined by standard 4-h 51Cr release assay. Percentages of lymphocytes were determined by flow cytometry. Plasma levels of ACTH, corticosterone, and prolactin concentration were measured by radioimmunoassay. After footshock, percentage of lysis relative to home-cage controls was 40% and 80% for sedentary and treadmill-trained animals, respectively ( P < 0.05). Our results indicate that the protective effect of chronic exercise on innate cellular immunity in the Fischer 344 male rat is not restricted to activity wheel running, nor is it explained by elevations in basal NK activity, increased percentages of splenic NK and cytotoxic T cells, or increased plasma levels of ACTH, corticosterone, and prolactin.
Evaluation of the cerebral hemodynamic response to rhythmic handgrip
Authors: Giller Cole A. , Giller Angela M. , Cooper Christopher R. , Hatab Mustapha R.
Published: December 2017

The response of the cerebral circulation to exercise has been studied with transcranial Doppler ultrasound (TCD) because this modality provides continuous measurements of blood velocity and is well suited for the exercise environment. The use of TCD as an index of cerebral blood flow, however, requires the assumption that the diameter of the insonated vessel is constant. Here, we examine this assumption for rhythmic handgrip using a spectral index designed to measure trends in vessel flow. Nineteen normal subjects were studied during 5 min of volitional maximum rhythmic right handgrip at 1 Hz. TCD velocities from both middle arteries (left and right), blood pressure, and end-tidal Pco 2 were recorded every 10 s. A spectral weighted sum was also calculated as a flow index (FI). Averages were computed from the last 2 min of handgrip. Relative changes in velocity, FI, and pressure were calculated. The validity of FI was tested by comparing the change in diameter derived from equations relating flow and diameter. Mean blood pressure increased 23.8 ± 17.8% (SD), and velocity increased 13.3 ± 9.8% (left) and 9.6 ± 8.3% (right). Although the mean change in FI was small [2.0 ± 18.2% (left) and 4.7 ± 29.7% (right)], the variation was high: some subjects showed a significant increase in FI and others a significant decrease. Diameter estimates from two equations relating flow and luminal area were not significantly different. Decreases in FI were associated with estimated diameter decreases of 10%. Our data suggest that the cerebral blood flow (CBF) response to rhythmic handgrip is heterogeneous and that middle cerebral artery flow can decrease in some subjects, in agreement with prior studies using the Kety-Schmidt technique. We speculate that the velocity increase is due to sympathetically mediated vasoconstriction rather than a ubiquitous flow increase. Our data suggest that the use of ordinary TCD velocities to interpret the CBF response during exercise may be invalid.
Aortic input impedance in infants and children
Authors: Sharp M. Keith , Pantalos George M. , Minich Luann , Tani Lloyd Y. , McGough Edwin C. , Hawkins John A.
Published: December 2017

Flow and pressure measurements were performed in the ascending aortas of six pediatric patients ranging in age from 1 to 4 yr and in weight from 7.2 to 16.4 kg. From these measurements, input impedance was calculated. It was found that total vascular resistance decreased with increasing patient weight and was approximately one to three times higher than those of adults. Conductance per unit weight was relatively constant but was approximately three times higher than for adults. Strong inertial character was observed in the impedance of four of the six patients. Among a three-element and two four-element lumped-parameter models, the model with characteristic aortic resistor (Rc) and inertance in series followed by parallel peripheral resistor (Rp) and compliance fitted the data best. Rpdecreased with increasing patient weight and was one to three times higher than in adults, and Rc decreased with increasing patient weight and was 2 to 15 times higher. The Rp-to-Rc ratio differed significantly between infants and children vs. adults. The results suggested that Rp developed more rapidly with patient weight than did Rc. Compliance values increased with increasing patient weight and were 3 to 16 times lower than adult values.
Effects of length oscillation on the subsequent force development in swine tracheal smooth muscle
Authors: Wang Lu , Paré Peter D. , Seow Chun Y.
Published: December 2017

It has been shown that deep inspiration (DI) taken before application of bronchoconstricting stimuli causes a reduction in the subsequent bronchoconstriction; a fast DI has a greater inhibitory effect than a slow DI. We hypothesize that periodic length changes imposed on a relaxed airway smooth muscle (ASM) would attenuate subsequent bronchoconstriction by disrupting the organization of the contractile apparatus, and this could be an important mechanism for the observed bronchoprotective effect of DI and tidal breathing. Length oscillations of different amplitude, frequency, and duration were applied to a relaxed muscle. The effects of such perturbations on force development were then assessed. Results show that oscillations reduce the subsequent force generation and that the magnitude of force reduction is proportional to amplitude and duration of the length oscillation. After the oscillation, isometric force recovered to the preoscillation level in a series of isometric contractions, and the rate of recovery was facilitated by frequent stimulation. The in vitro behavior of ASM found in this study could account for the observed temporary reduction in bronchoconstriction subsequent to a DI.
Developmental aspects of oxygen sensing by the carotid body
Authors: Donnelly David F.
Published: December 2017

The carotid body chemoreceptors, the major hypoxia sensory organs for the respiratory system, undergo a significant increase in their hypoxia responsiveness in the postnatal period. This is manifest by a higher level of afferent nerve activity for a given level of arterial oxygen tension. The mechanism for the enhanced sensitivity is unresolved, but most work has focused on the glomus cell, a secretory cell apposed to the afferent nerve ending and believed to be the site of hypoxia transduction. The glomus cell secretory response to hypoxia increases postnatally, and this is correlated with an enhanced calcium rise in response to hypoxia and an increase in oxygen-sensitive potassium currents. These changes are sensitive to the level of hypoxia in the postnatal period, and significant impairment of organ function is observed with postnatal hypoxia as well as postnatal hyperoxia. Although many questions remain, especially with regard to the coupling of glomus cells to nerve endings, the use of cellular and molecular techniques should offer resolution in the near future.
Genetic determinants of acute hypoxic ventilation: patterns of inheritance in mice
Authors: Tankersley Clarke G. , Elston Robert C. , Schnell Audrey H.
Published: December 2017

Acutely lowering ambient O2tension increases ventilation in many mammalian species, including humans and mice. Inheritance patterns among kinships and between mouse strains suggest that a robust genetic influence determines individual hypoxic ventilatory responses (HVR). Here, we tested specific genetic hypotheses to describe the inheritance patterns of HVR phenotypes among two inbred mouse strains and their segregant and nonsegregant progeny. Using whole body plethysmography, we assessed the magnitude and pattern of ventilation in C3H/HeJ (C3) and C57BL/6J (B6) progenitor strains at baseline and during acute (3–5 min) hypoxic [mild hypercapnic hypoxia, inspired O2fraction ([Formula: see text]) = 0.10] and normoxic (mild hypercapnic normoxia,[Formula: see text] = 0.21) inspirate challenges in mild hypercapnia (inspired CO2fraction = 0.03). First- and second-filial generations and two backcross progeny were also studied to assess response distributions of HVR phenotypes relative to the parental strains. Although the minute ventilation (V˙e) during hypoxia was comparable between the parental strains, breathing frequency (f) and tidal volume were significantly different; C3 mice demonstrated a slow, deep HVR relative to a rapid, shallow phenotype of B6 mice. The HVR profile in B6C3F1/J mice suggested that this offspring class represented a third phenotype, distinguishable from the parental strains. The distribution of HVR among backcross and intercross offspring suggested that the inheritance patterns for f and V˙e during mild hypercapnic hypoxia are consistent with models that incorporate two genetic determinants. These results further suggest that the quantitative genetic expression of alleles derived from C3 and B6 parental strains interact to significantly attenuate individual HVR in the first- and second-filial generations. In conclusion, the genetic control of HVR in this model was shown to exhibit a relatively simple genetic basis in terms of respiratory timing characteristics.
Skeletal muscle attenuation determined by computed tomography is associated with skeletal muscle lipid content
Authors: Goodpaster Bret H. , Kelley David E. , Thaete F. Leland , He Jing , Ross Robert
Published: December 2017

The purpose of this investigation was to validate that in vivo measurement of skeletal muscle attenuation (MA) with computed tomography (CT) is associated with muscle lipid content. Single-slice CT scans performed on phantoms of varying lipid concentrations revealed good concordance between attenuation and lipid concentration ( r2= 0.995); increasing the phantom's lipid concentration by 1 g/100 ml decreased its attenuation by ∼1 Hounsfield unit (HU). The test-retest coefficient of variation for two CT scans performed in six volunteers was 0.51% for the midthigh and 0.85% for the midcalf, indicating that the methodological variability is low. Lean subjects had significantly higher ( P < 0.01) MA values (49.2 ± 2.8 HU) than did obese nondiabetic (39.3 ± 7.5 HU) and obese Type 2 diabetic (33.9 ± 4.1 HU) subjects, whereas obese Type 2 diabetic subjects had lower MA values that were not different from obese nondiabetic subjects. There was also good concordance between MA in midthigh and midcalf ( r = 0.60, P < 0.01), psoas ( r = 0.65, P < 0.01), and erector spinae ( r = 0.77, P < 0.01) in subsets of volunteers. In 45 men and women who ranged from lean to obese (body mass index = 18.5 to 35.9 kg/m2), including 10 patients with Type 2 diabetes mellitus, reduced MA was associated with increased muscle fiber lipid content determined with histological oil red O staining ( P = −0.43, P < 0.01). In a subset of these volunteers ( n = 19), triglyceride content in percutaneous biopsy specimens from vastus lateralis was also associated with MA ( r = −0.58, P = 0.019). We conclude that the attenuation of skeletal muscle in vivo determined by CT is related to its lipid content and that this noninvasive method may provide additional information regarding the association between muscle composition and muscle function.
Postischemic recovery of heart metabolism and function: role of mitochondrial fatty acid transfer
Authors: Montessuit Christophe , Papageorgiou Irène , Tardy-Cantalupi Isabelle , Rosenblatt-Velin Nathalie , Lerch René
Published: December 2017

Postischemic recovery of contractile function is better in hearts from fasted rats than in hearts from fed rats. In this study, we examined whether feeding-induced inhibition of palmitate oxidation at the level of carnitine palmitoyl transferase I is involved in the mechanism underlying impaired recovery of contractile function. Hearts isolated from fasted or fed rats were submitted to no-flow ischemia followed by reperfusion with buffer containing 8 mM glucose and either 0.4 mM palmitate or 0.8 mM octanoate. During reperfusion, oxidation of palmitate was higher after fasting than after feeding, whereas oxidation of octanoate was not influenced by the nutritional state. In the presence of palmitate, recovery of left ventricular developed pressure was better in hearts from fasted rats. Substitution of octanoate for palmitate during reperfusion enhanced recovery of left ventricular developed pressure in hearts from fed rats. However, the chain length of the fatty acid did not influence diastolic contracture. The results suggest that nutritional variation of mitochondrial fatty acid transfer may influence postischemic recovery of contractile function.
Effect of resistance training on single muscle fiber contractile function in older men
Authors: Trappe Scott , Williamson David , Godard Michael , Porter David , Rowden Greg , Costill David
Published: December 2017

The purpose of this study was to examine single cell contractile mechanics of skeletal muscle before and after 12 wk of progressive resistance training (PRT) in older men ( n = 7; age = 74 ± 2 yr and weight = 75 ± 5 kg). Knee extensor PRT was performed 3 days/wk at 80% of one-repetition maximum. Muscle biopsy samples were obtained from the vastus lateralis before and after PRT (pre- and post-PRT, respectively). For analysis, chemically skinned single muscle fibers were studied at 15°C for peak tension [the maximal isometric force (Po)], unloaded shortening velocity ( Vo), and force-velocity parameters. In this study, a total of 199 (89 pre- and 110 post-PRT) myosin heavy chain (MHC) I and 99 (55 pre- and 44 post-PRT) MHC IIa fibers were reported. Because of the minimal number of hybrid fibers identified post-PRT, direct comparisons were limited to MHC I and IIa fibers. Muscle fiber diameter increased 20% (83 ± 1 to 100 ± 1 μm) and 13% (86 ± 1 to 97 ± 2 μm) in MHC I and IIa fibers, respectively ( P < 0.05). Powas higher ( P < 0.05) in MHC I (0.58 ± 0.02 to 0.90 ± 0.02 mN) and IIa (0.68 ± 0.02 to 0.85 ± 0.03 mN) fibers. Muscle fiber Vowas elevated 75% (MHC I) and 45% (MHC IIa) after PRT ( P < 0.05). MHC I and IIa fiber power increased ( P < 0.05) from 7.7 ± 0.5 to 17.6 ± 0.9 μN · fiber lengths · s−1and from 25.5 to 41.1 μN · fiber lengths · s−1, respectively. These data indicate that PRT in elderly men increases muscle cell size, strength, contractile velocity, and power in both slow- and fast-twitch muscle fibers. However, it appears that these changes are more pronounced in the MHC I muscle fibers.
Chronically and acutely exercised rats: biomarkers of oxidative stress and endogenous antioxidants
Authors: Liu Jiankang , Yeo Helen C. , Övervik-Douki Eva , Hagen Tory , Doniger Stephanie J. , Chu Daniel W. , Brooks George A. , Ames Bruce N.
Published: December 2017

The responses to oxidative stress induced by chronic exercise (8-wk treadmill running) or acute exercise (treadmill running to exhaustion) were investigated in the brain, liver, heart, kidney, and muscles of rats. Various biomarkers of oxidative stress were measured, namely, lipid peroxidation [malondialdehyde (MDA)], protein oxidation (protein carbonyl levels and glutamine synthetase activity), oxidative DNA damage (8-hydroxy-2′-deoxyguanosine), and endogenous antioxidants (ascorbic acid, α-tocopherol, glutathione, ubiquinone, ubiquinol, and cysteine). The predominant changes are in MDA, ascorbic acid, glutathione, cysteine, and cystine. The mitochondrial fraction of brain and liver showed oxidative changes as assayed by MDA similar to those of the tissue homogenate. Our results show that the responses of the brain to oxidative stress by acute or chronic exercise are quite different from those in the liver, heart, fast muscle, and slow muscle; oxidative stress by acute or chronic exercise elicits different responses depending on the organ tissue type and its endogenous antioxidant levels.
Supine lower body negative pressure exercise during bed rest maintains upright exercise capacity
Authors: Watenpaugh Donald E. , Ballard Richard E. , Schneider Suzanne M. , Lee Stuart M. C. , Ertl Andrew C. , William Jacqueline M. , Boda Wanda L. , Hutchinson Karen J. , Hargens Alan R.
Published: December 2017

Bed rest and spaceflight reduce exercise fitness. Supine lower body negative pressure (LBNP) treadmill exercise provides integrated cardiovascular and musculoskeletal stimulation similar to that imposed by upright exercise in Earth gravity. We hypothesized that 40 min of supine exercise per day in a LBNP chamber at 1.0–1.2 body wt (58 ± 2 mmHg LBNP) maintains aerobic fitness and sprint speed during 15 days of 6° head-down bed rest (simulated microgravity). Seven male subjects underwent two such bed-rest studies in random order: one as a control study (no exercise) and one with daily supine LBNP treadmill exercise. After controlled bed-rest, time to exhaustion during an upright treadmill exercise test decreased 10%, peak oxygen consumption during the test decreased 14%, and sprint speed decreased 16% (all P < 0.05). Supine LBNP exercise during bed rest maintained all the above variables at pre-bed-rest levels. Our findings support further evaluation of LBNP exercise as a countermeasure against long-term microgravity-induced deconditioning.
Detecting lung overdistention in newborns treated with high-frequency oscillatory ventilation
Authors: Weber Kaye , Courtney Sherry E. , Pyon Kee H. , Chang Gordon Y. , Pandit Paresh B. , Habib Robert H.
Published: December 2017

Positive airway pressure (Paw) during high-frequency oscillatory ventilation (HFOV) increases lung volume and can lead to lung overdistention with potentially serious adverse effects. To date, no method is available to monitor changes in lung volume (ΔVl) in HFOV-treated infants to avoid overdistention. In five newborn piglets (6–15 days old, 2.2–4.2 kg), we investigated the use of direct current-coupled respiratory inductive plethysmography (RIP) for this purpose by evaluating it against whole body plethysmography. Animals were instrumented, fitted with RIP bands, paralyzed, sedated, and placed in the plethysmograph. RIP and plethysmography were simultaneously calibrated, and HFOV was instituted at varying Paw settings before (6–14 cmH2O) and after (10–24 cmH2O) repeated warm saline lung lavage to induce experimental surfactant deficiency. Estimates of ΔVl from both methods were in good agreement, both transiently and in the steady state. Maximal changes in lung volume (ΔVlmax) from all piglets were highly correlated with ΔVl measured by RIP (in ml) = 1.01 × changes measured by whole body plethysmography − 0.35; r2= 0.95. Accuracy of RIP was unchanged after lavage. Effective respiratory system compliance (Ceff) decreased after lavage, yet it exhibited similar sigmoidal dependence on ΔVlmaxpre- and postlavage. A decrease in Ceff (relative to the previous Paw setting) as ΔVlmaxwas methodically increased from low to high Paw provided a quantitative method for detecting lung overdistention. We conclude that RIP offers a noninvasive and clinically applicable method for accurately estimating lung recruitment during HFOV. Consequently, RIP allows the detection of lung overdistention and selection of optimal HFOV from derived Ceff data.