bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of hormone replacement therapy on hemodynamic responses of postmenopausal women to passive heating
Authors: Dunbar Stacey L. , Kenney W. Larry
Published: December 2017

To examine the influence of chronic hormone replacement therapy (HRT) on the central and peripheral cardiovascular responses of postmenopausal women to direct passive heating, seven women taking estrogen replacement therapy, seven women taking estrogen and progesterone therapy, and seven women not taking HRT were passively heated with water-perfused suits to their individual limit of thermal tolerance. Measurements included heart rate (HR), cardiac output, blood pressure, skin blood flow, splanchnic blood flow, renal blood flow, esophageal temperature, and mean skin temperature. Cardiac output was higher in women taking estrogen and progesterone therapy than in women not taking HRT (7.12 ± 0.70 vs. 5.02 ± 0.57 l/min at the limit of thermal tolerance, respectively; P < 0.05) because of a higher HR. However, when the HR data were plotted as a percentage of the maximum HR or percentage of HR reserve, there were no differences among the three groups of women. Neither splanchnic nor renal blood flow differed among the groups of women. These data suggest that HRT has little effect on the cardiovascular responses to direct passive heating.
Mechanism of reduced maximal expiratory flow with aging
Authors: Babb T. G. , Rodarte J. R.
Published: December 2017

To investigate the determinants of maximal expiratory flow (MEF) with aging, 17 younger (7 men and 10 women, 39 ± 4 yr, mean ± SD) and 19 older (11 men and 8 women, 69 ± 3 yr) subjects with normal pulmonary function were studied. For further comparison, we also studied 10 middle-aged men with normal lung function (54 ± 6 yr) and 15 middle-aged men (54 ± 7 yr) with mild chronic airflow limitation (CAL; i.e., forced expiratory volume in 1 s/forced vital capacity = 63 ± 8%). MEF, static lung elastic recoil pressure (Pst), and the minimal pressure for maximal flow (Pcrit) were determined in a pressure-compensated, volume-displacement body plethysmograph. Values were compared at 60, 70, and 80% of total lung capacity. In the older subjects, decreases in MEF ( P < 0.01) and Pcrit ( P < 0.05), compared with the younger subjects, were explained mainly by loss of Pst ( P < 0.05). In the CAL subjects, MEF and Pcrit were lower ( P < 0.05) than in the older subjects, but Pst was similar. Thus decreases in MEF and Pcrit were greater than could be explained by the loss of Pst and appeared to be related to increased upstream resistance. These data indicate that the loss of lung recoil explains the decrease in MEF with aging subjects, but not in the mild CAL patients that we studied.
Treadmill economy in girls and women matched for height and weight
Authors: Allor K. M. , Pivarnik J. M. , Sam L. J. , Perkins C. D.
Published: December 2017

We investigated differences in walking (80 m/min) and running (147 m/min) economy [submaximal oxygen consumption (V˙o 2 submax)] between adolescent girls ( n = 13; age = 13.3 ± 0.9 yr) and young women ( n = 23; age = 21.0 ± 1.5 yr). Subjects were matched for height (158.7 ± 2.9 cm) and weight (52.1 ± 3.0 kg). Anthropometric measures (height, weight, breadths, skinfolds) and preexercise oxygen consumption were obtained on all subjects before submaximal and maximal treadmill exercise. Anthropometric measures were similar between groups, as was maximal oxygen consumption (girls, 47.7 ± 5.2; women, 47.5 ± 5.7 ml · kg−1 · min−1).V˙o 2 submax was significantly greater ( P < 0.0002) in girls compared with women during both walking (16.4 ± 1.7 vs. 14.4 ± 1.1 ml · kg−1 · min−1) and running (38.1 ± 3.7 vs. 33.9 ± 2.4 ml · kg−1 · min−1). Preexercise oxygen consumption (4.4 vs. 3.9 ml · kg−1 · min−1) accounted for only a fraction of the differences found in exercise economy. Although heart rate and respiratory frequency were greater in the girls in both walking (118 ± 11 vs. 104 ± 12 beats/min and 31 ± 3 vs. 25 ± 4 breaths/min, respectively; P < 0.002) and running (180 ± 15 vs. 163 ± 17 beats/min and 47 ± 11 vs. 38 ± 8 breaths/min; P < 0.005), this did not likely account for a large part of the difference inV˙o 2 submax between groups.
Body composition techniques and the four-compartment model in children
Authors: Fields David A. , Goran Michael I.
Published: December 2017

The purpose of this study was to compare the accuracy, precision, and bias of fat mass (FM) as assessed by dual-energy X-ray absorptiometry (DXA), hydrostatic weighing (HW), air-displacement plethysmography (PM) using the BOD POD body composition system and total body water (TBW) against the four-compartment (4C) model in 25 children (11.4 ± 1.4 yr). The regression between FM by the 4C model and by DXA deviated significantly from the line of identity (FM by 4C model = 0.84 × FM by DXA + 0.95 kg; R2= 0.95), as did the regression between FM by 4C model and by TBW (FM by 4C model = 0.85 × FM by TBW − 0.89 kg; R2= 0.98). The regression between FM by the 4C model and by HW did not significantly deviate from the line of identity (FM by 4C model = 1.09 × FM by HW + 0.94 kg; R2= 0.95) and neither did the regression between FM by 4C (using density assessed by PM) and by PM (FM by 4C model = 1.03 × FM by PM + 0.88; R2= 0.97). DXA, HW, and TBW all showed a bias in the estimate of FM, but there was no bias for PM. In conclusion, PM was the only technique that could accurately, precisely, and without bias estimate FM in 9- to 14-yr-old children.
Tolerance of SP-A-deficient mice to hyperoxia or exercise
Authors: Ikegami Machiko , Jobe Alan H. , Whitsett Jeffrey , Korfhagen Thomas
Published: December 2017

Mice carrying a null mutation of the surfactant-associated protein A (SP-A) gene have normal respiratory function, but their surfactant lacks tubular myelin, is sensitive to protein inactivation in vitro, and contains decreased pool sizes of the biophysically active large-aggregate surfactant. We hypothesized that SP-A-deficient mice would be more susceptible to exercise-induced stress and O2-induced lung injury. SP-A-(−/−) and SP-A-(+/+) mice tolerated 1 h of swimming or 45 min of running on a treadmill at 15 m/min equivalently, without alterations of the amount of alveolar saturated phosphatidylcholine. After 3 days of hyperoxia, SP-A-(−/−) mice had increased alveolar protein, but pressure-volume curves were not different between groups. Alveolar protein concentration was similarly increased in SP-A-(−/−) and SP-A-(+/+) mice after 4 days of exposure to hyperoxia. Survival rates were similar after 4 days of hyperoxia. SP-A-(−/−) mice were equally tolerant to exercise and 4 days of hyperoxia, indicating that the SP-A-dependent alterations in surfactant did not result in functional deficits.
Changes in respiratory control in humans induced by 8 h of hyperoxia
Authors: Ren Xiaohui , Fatemian Marzieh , Robbins Peter A.
Published: December 2017

In humans, 8 h of isocapnic hypoxia causes a progressive rise in ventilation associated with increases in the acute ventilatory responses to hypoxia (AHVR) and hypercapnia (AHCVR). To determine whether 8 h of hyperoxia causes the converse of these effects, three 8-h protocols were compared in 14 subjects: 1) poikilocapnic hyperoxia, with end-tidal Po 2 (Pet O2 ) = 300 Torr and end-tidal Pco 2(Pet CO2 ) uncontrolled; 2) isocapnic hyperoxia, with Pet O2 = 300 Torr and Pet CO2 maintained at the subject's normal air-breathing level; and 3) control. Ventilation was measured hourly. AHVR and AHCVR were determined before and 0.5 h after each exposure. During isocapnic hyperoxia, after an initial increase, ventilation progressively declined ( P< 0.01, ANOVA). After exposure to hyperoxia, 1) AHVR declined ( P < 0.05); 2) ventilation at fixed Pet CO2 decreased ( P< 0.05); and 3) air-breathing Pet CO2 increased ( P < 0.05); but 4) no significant changes in AHCVR or intercept were demonstrated. In conclusion, 8 h of hyperoxia have some effects opposite to those found with 8 h of hypoxia, indicating that there may be some “acclimatization to hypoxia” at normal sea-level values of Po 2.
Pulmonary gas exchange during exercise in women: effects of exercise type and work increment
Authors: Hopkins Susan R. , Barker Rebecca C. , Brutsaert Tom D. , Gavin Timothy P. , Entin Pauline , Olfert Ivan M. , Veisel Susan , Wagner Peter D.
Published: December 2017

Exercise-induced arterial hypoxemia (EIAH) has been reported in male athletes, particularly during fast-increment treadmill exercise protocols. Recent reports suggest a higher incidence in women. We hypothesized that 1-min incremental (fast) running (R) protocols would result in a lower arterial Po 2 (PaO2 ) than 5-min increment protocols (slow) or cycling exercise (C) and that women would experience greater EIAH than previously reported for men. Arterial blood gases, cardiac output, and metabolic data were obtained in 17 active women [mean maximal O2 uptake (V˙o 2 max) = 51 ml · kg−1 · min−1]. They were studied in random order (C or R), with a fastV˙o 2 max protocol. After recovery, the women performed 5 min of exercise at 30, 60, and 90% ofV˙o 2 max (slow). One week later, the other exercise mode (R or C) was similarly studied. There were no significant differences in V˙o 2 maxbetween R and C. Pulmonary gas exchange was similar at rest, 30%, and 60% of V˙o 2 max. At 90% ofV˙o 2 max, PaO2 was lower during R (mean ± SE = 94 ± 2 Torr) than during C (105 ± 2 Torr, P < 0.0001), as was ventilation (85.2 ± 3.8 vs. 98.2 ± 4.4 l/min btps, P < 0.0001) and cardiac output (19.1 ± 0.6 vs. 21.1 ± 1.0 l/min, P < 0.001). Arterial Pco 2 (32.0 ± 0.5 vs. 30.0 ± 0.6 Torr, P < 0.001) and alveolar-arterial O2 difference (A-aDo 2; 22 ± 2 vs. 16 ± 2 Torr, P < 0.0001) were greater during R. PaO2 and A-aDo 2 were similar between slow and fast. Nadir PaO2 was ≤80 Torr in four women (24%) but only during fast-R. In all subjects, PaO2 atV˙o 2 max was greater than the lower 95% prediction limit calculated from available data in men ( n = 72 C and 38 R) for both R and C. These data suggest intrinsic differences in gas exchange between R and C, due to differences in ventilation and also efficiency of gas exchange. The PaO2 responses to R and C exercise in our 17 subjects do not differ significantly from those previously observed in men.
Aging reduces adaptive capacity and stress protein expression in the liver after heat stress
Authors: Hall D. M. , Xu L. , Drake V. J. , Oberley L. W. , Oberley T. D. , Moseley P. L. , Kregel K. C.
Published: December 2017

A decline in an organism's ability to cope with stress through acute response protein expression may contribute to stress intolerance with aging. We investigated the influence of aging on stress tolerance and the capacity to synthesize the 70-kDa heat shock protein (HSP70) in young and old rats exposed to an environmental heating protocol. Livers were assessed for injury and HSP70 expression after heat stress by use of immunohistochemical and immunoblotting techniques. The inducible HSP70 response in the cytoplasm and nucleus was markedly reduced with age at several time points over a 48-h recovery period, although senescent rats were able to strongly express HSP70 early in recovery. Older animals had extensive zone-specific liver injury, which corresponded to the diminished HSP70 response observed in these regions, and a significant reduction in thermotolerance compared with their young counterparts. These data highlight the regional nature of stress-induced injury and HSP70 expression in the liver and the impact of aging on these responses. Furthermore, the results suggest a functional link between the age-related decrements in the expression of inducible HSP70 and the pathophysiological responses to heat stress.
Exercise in the heat is limited by a critical internal temperature
Authors: Walters T. J. , Ryan K. L. , Tate L. M. , Mason P. A.
Published: December 2017

We examined whether fatigue during exertional heat stress occurred at a critical internal temperature independent of the initial temperature at the start of exercise. Microwaves (2.1 GHz; 100 mW/cm2) were used to rapidly (3–8 min) heat rats before treadmill exercise to exhaustion. In a repeated-measures design, food-restricted male Sprague-Dawley rats ( n = 11) were preheated to three levels (low, medium, and high). In addition, two sham exposures, Sham 1 and Sham 2, were administered at the beginning and end of the study, respectively. At the initiation of exercise, hypothalamic (Thyp) and rectal (Trec) temperatures ranged from 39.0°C to 42.8°C (Thyp) and 42.1°C (Trec). The treadmill speed was 17 m/min (8° grade), and the ambient temperature during exercise was 35°C. Each treatment was separated by 3 wk. Run time to exhaustion was significantly reduced after preheating. There was a significant negative correlation between run time and initial Thyp and Trec ( r = 0.73 and 0.74, respectively). The temperatures at exhaustion were not significantly different across treatments, with a range of 41.9–42.2°C (Thyp) and 42.2–42.5°C (Trec). There were no significant differences in run time in the sham runs administered at the start and end of the investigation. No rats died as a result of exposure to any of the treatments, and body weight the day after each treatment was unaffected. These results support the concept that a critical temperature exists that limits exercise in the heat.
Physiology of a Microgravity Environment Selected Contribution: Effects of spaceflight during pregnancy on labor and birth at 1 G
Authors: Ronca April E. , Alberts Jeffrey R.
Published: December 2017

The events of parturition (labor, delivery, maternal care, placentophagia, and onset of nursing) were analyzed in female Norway rats (Rattus norvegicus) flown on either 11- or 9-day-long spaceflights beginning at the approximate midpoint of their pregnancies. Each space shuttle flight landed on the 20th day of the rats' pregnancies, just 48–72 h before parturition. After spaceflight, dams were continuously monitored and recorded by time-lapse videography throughout the completion of parturition and onset of nursing ( days 22 and 23). Analyses of parturition revealed that, compared with ground controls, flight dams displayed twice the number of lordosis contractions, the predominant labor contraction type in rats. The number of vertical contractions (those that immediately precede expulsion of a pup from the womb), the duration of labor, fetal wastage, number of neonates born, neonatal birth weights, placentophagia, and maternal care during parturition, including the onset of nursing, were comparable in flight and ground control dams. Our findings indicate that, with the exception of labor contractions, mammalian pregnancy and parturition remain qualitatively and quantitatively intact after spaceflight during pregnancy.
Selected Contribution: PKC activation inhibits Ca2+signaling in tracheal epithelial cells kept in simulated microgravity
Authors: Felix Jennifer A. , Dirksen Ellen R. , Woodruff Michael L.
Published: December 2017

Microgravity has been shown to alter protein kinase C (PKC) activity; therefore, we investigated whether microgravity influences mechanically stimulated Ca2+signaling and ATP-induced Ca2+oscillations, both of which are modulated by PKC. Rabbit tracheal epithelial outgrowth cultures or suspended epithelial sheets were rotated in bioreactors to simulate microgravity. Mechanical stimulation of a single cell increased the cytosolic Ca2+concentration in 35–55 cells of both outgrowth cultures and epithelial sheets kept at unit gravity (G) or in simulated microgravity (sμG). In outgrowth cultures, 12- O-tetradecanoylphorbol-13-acetate (TPA; 80 nM), a PKC activator, restricted Ca2+“waves” to about 10 cells in unit G and to significantly fewer cells in sμG. TPA only slightly reduced the spread of Ca2+waves in epithelial sheets kept in sμG but did not inhibit Ca2+waves of sheets kept in unit G. In both cell preparations from both conditions, TPA inhibited ATP-induced Ca2+oscillations; however, the effect was more pronounced in cells kept in sμG. These results suggest that PKC activation is more robust in cells subjected to sμG.
Acoustic rhinometry: validation by three-dimensionally reconstructed computer tomographic scans
Authors: Terheyden Hendrik , Maune Steffen , Mertens Jürgen , Hilberg Ole
Published: December 2017

The aim of the present study was a validation of acoustic rhinometry (AR) by computed tomography (CT). Six healthy subjects were examined by CT and AR. The CT data were processed in a computer program (AutoCAD), and a virtual three-dimensional model of each nasal cavity was constructed. This model permitted an individual prediction of the center line of the sound wave propagation through the air volume of the nasal cavity with the cross-sectional areas oriented perpendicularly to this line. The area-distance curves derived from AR and CT were compared. Linear regression analysis revealed a reasonable agreement of AR and CT in the anterior nose below a mean of 6 cm distance from the nostrils [ r = 0.839, P < 0.01, m = 1.123, b= −0.113 (AR = m × CT + b)]. The measuring accuracy using CT as gold standard revealed a mean error at the nasal valve of <0.01 cm2 (4.52%) and at the nasal isthmus of 0.02 cm2 (1.87%). Beyond 6 cm, the correlation decreased ( r = 0.419), and overestimation of the true area occurred (>100%). In conclusion, the measurements were reasonably accurate for diagnostic use up to the turbinate head region. Certain factors induce an overestimation of the true areas beyond this region. However, these factors are constant and reproducible in a single subject, and intraindividual comparative measurements are possible beyond the turbinate head region.
HSP72 gene expression progressively increases in human skeletal muscle during prolonged, exhaustive exercise
Authors: Febbraio M. A. , Koukoulas I.
Published: December 2017

To examine the effect of exercise on heat shock protein (HSP) 72 mRNA expression in skeletal muscle, five healthy humans (20 ± 1 yr; 64 ± 3 kg; peak O2uptake of 2.55 ± 0.2 l/min) cycled until exhaustion at a workload corresponding to 63% peak O2uptake. Muscle was sampled from the vastus lateralis, and muscle temperature was measured at rest (R), 10 min of exercise (Min10), ∼40 min before fatigue (F-40 = 144 ± 7 min), and fatigue (F = 186 ± 15 min). Muscle samples were analyzed for HSP72 mRNA expression, as well as glycogen and lactate concentration. Muscle temperature increased ( P < 0.05) during the first 10 min of exercise but then remained constant for the duration of the exercise. Similarly, lactate concentration increased ( P < 0.05) when Min10 was compared with R but decreased ( P < 0.05) thereafter, such that concentrations at F-40 and F were not different from those at R. In contrast, muscle glycogen concentration fell progressively throughout exercise (486 ± 74 vs. 25 ± 7 mmol/kg dry weight for R and F, respectively; P < 0.05). HSP72 mRNA was detected at R but did not increase by Min10. However, HSP72 mRNA increased ( P < 0.05) 2.2 ± 0.5- and 2.6 ± 0.9-fold, respectively, when F-40 and F were compared with R. These data demonstrate that HSP72 mRNA increases progressively during acute cycling, suggesting that processes that take place throughout concentric exercise are capable of initiating a stress response.
Sprint training restores normal contractility in postinfarction rat myocytes
Authors: Zhang Lian-Qin , Zhang Xue-Qian , Musch Timothy I. , Moore Russell L. , Cheung Joseph Y.
Published: December 2017

The significance of 6–8 wk of high-intensity sprint training (HIST) on contractile abnormalities of myocytes isolated from rat hearts with prior myocardial infarction (MI) was investigated. Compared with the sedentary (Sed) condition, HIST attenuated myocyte hypertrophy observed post-MI primarily by reducing cell lengths but not cell widths. At high extracellular Ca2+ concentration (5 mM) and low pacing frequency (0.1 Hz), conditions that preferentially favored Ca2+ influx over efflux, MI-Sed myocytes shortened less than Sham-Sed myocytes did. HIST significantly improved contraction amplitudes in MI myocytes. Under conditions that favored Ca2+ efflux, i.e., low extracellular Ca2+ concentration (0.6 mM) and high pacing frequency (2 Hz), MI-Sed myocytes contracted more than Sham-Sed myocytes. HIST did not appreciably affect contraction amplitudes of MI myocytes under these conditions. Compared with MI-Sed myocytes, HIST myocytes showed significant improvement in time required to reach one-half maximal contraction amplitude shortening, maximal myocyte shortening and relengthening velocities, and half time of relaxation. Our results indicate that HIST instituted shortly after MI improved cellular contraction in surviving myocytes. Because our previous studies demonstrated that, in post-MI myocytes, HIST improved intracellular Ca2+ dynamics, enhanced sarcoplasmic reticulum Ca2+ uptake and Ca2+ content, and restored Na+/Ca2+ exchange current toward normal, we hypothesized that improvement in MI myocyte contractile function by HIST was likely mediated by normalization of cellular Ca2+ homeostatic mechanisms.
Nasal resistance and flow resistive work of nasal breathing during exercise: effects of a nasal dilator strip
Authors: Gehring J. M. , Garlick S. R. , Wheatley J. R. , Amis T. C.
Published: December 2017

Using posterior rhinomanometry, we measured nasal airflow resistance (Rn) and flow-resistive work of nasal breathing (WONB), with an external nasal dilator strip (ENDS) and without (control), in 15 healthy adults (6 men, 9 women) during exclusive nasal breathing and graded (50–230 W) exercise on a cycle ergometer. ENDS decreased resting inspiratory and/or expiratory Rn (at 0.4 l/s) by >0.5 cmH2O · l−1· s in 11 subjects (“responders”). Inspired ventilation (V˙i) increased with external work rate, but tended to be greater with ENDS. Inspiratory and expiratory Rn (at 0.4 l/s) decreased asV˙i increased but, in responders, tended to remain lower with ENDS. Inspiratory (but not expiratory) Rn at peak nasal airflow (V˙n) increased as V˙i increased but, again, was lower with ENDS. At a V˙i of ∼35 l/min, ENDS decreased flow limitation and hysteresis of the inspiratory transnasal pressure-flow curve. In responders, ENDS reduced inspiratory WONB per breath and inspiratory nasal power values during exercise. We conclude that ENDS stiffens the lateral nasal vestibule walls and, in responders, may reduce the energy required for nasal ventilation during exercise.
Protein- and carbohydrate-induced augmentation of whole body creatine retention in humans
Authors: Steenge G. R. , Simpson E. J. , Greenhaff P. L.
Published: December 2017

This study investigated the effect of creatine supplementation in conjunction with protein and/or carbohydrate (CHO) ingestion on plasma creatine and serum insulin concentrations and whole body creatine retention. Twelve men consumed 4 × 5 g of creatine on four occasions in combination with 1) 5 g of CHO, 2) 50 g of protein and 47 g of CHO, 3) 96 g of CHO, or 4) 50 g of CHO. The increase in serum insulin was no different when the protein-CHO and high-CHO treatments were compared, but both were greater than the response recorded for the low-CHO treatment (both P < 0.05). As a consequence, body creatine retention was augmented by ∼25% for protein-CHO and high-CHO treatments compared with placebo treatment. The areas under creatine- and insulin-time curves were related during the first oral challenge ( r = −0.920, P < 0.05) but not after the fourth ( r = −0.342). It is concluded, first, that the ingestion of creatine in conjunction with ∼50 g of protein and CHO is as effective at potentiating insulin release and creatine retention as ingesting creatine in combination with almost 100 g of CHO. Second, the stimulatory effect of insulin on creatine disposal was diminished within the initial 24 h of supplementation.
Bronchial hyperreactivity is associated with enhanced grain dust-induced airflow obstruction
Authors: Kline Joel N. , Jagielo Paul J. , Watt Janet L. , Schwartz David A.
Published: December 2017

Bronchial hyperreactivity (BHR) is associated with the presence of airway inflammation in asthma and is seen in individuals occupationally exposed to grain dust. To better understand the relationship between BHR and pulmonary inflammation after grain dust exposure, we carried out an inhalation challenge to corn dust extract (CDE) on seven subjects with BHR [a 20% or greater decrease in forced expiratory volume in 1 s (FEV1) compared with diluent FEV1 with a cumulative dose of histamine ≤47.3 breath units] and compared their physiological and inflammatory responses with those of seven matched control subjects. BHR subjects were exposed to nebulized CDE (target dose of 0.16 μg/kg endotoxin) as tolerated; matched controls received equal amounts of CDE. Subjects with BHR complained of chest tightness and dyspnea within the 2 h after inhalation of CDE significantly more frequently than controls. Similarly, subjects with BHR developed significantly greater percent declines in FEV1 at time points up to 4 h after exposure to CDE. Significant increases in total cells, neutrophils, tumor necrosis factor-α, interleukin-6, and interleukin-8 were detected in bronchoalveolar lavage fluid 4 h after inhalation of CDE in all subjects, but no differences were detected between the control and BHR groups. These results suggest that, although subjects with BHR develop a more precipitous decline in FEV1 after exposure to CDE, the inflammatory response to CDE is similar in subjects with and without BHR.
Effects of transdermal nicotine treatment on structure and function of coronary artery bypass grafts
Authors: Clouse William D. , Yamaguchi Hiroki , Phillips Michael R. , Hurt Richard D. , Fitzpatrick Lorraine A. , Moyer Thomas P. , Rowland Charles , Schaff Hartzell V. , Miller Virginia M.
Published: December 2017

Smoking is a major risk factor for failure of coronary artery bypass grafts (CABG). Experiments were designed to determine effects of transdermal nicotine, independent of smoking, on structure and function of CABG. Saphenous veins were placed as CABG in untreated dogs (control) or in dogs treated with transdermal nicotine (one 11-mg or two 22-mg patches/day) for 5 wk. Serum nicotine and plasma nitric oxide were measured. Grafts were removed and prepared for organ chamber studies and histology. Serum nicotine averaged 12.1 and 118.7 ng/ml in the 11 mg/day and 44 mg/day groups, respectively. Plasma nitric oxide was higher in dogs treated with 11 mg/day doses compared with controls. In organ chamber studies, endothelium-dependent relaxations to thrombin and A-23187 and endothelium-independent relaxations to nitric oxide were greatest in grafts from dogs treated with 11 mg/day doses. Intimal thickness of the grafts were similar among groups. However, staining for bone sialoprotein was increased in the media of grafts from the 11 mg/day treatment group. These data suggest that transdermal nicotine in doses comparable and double to those used for conventional smoking cessation treatment in humans does not adversely affect early patency of canine CABG up to 4 wk postoperatively. Transdermal nicotine, however, may increase production of and response to nitric oxide in bypass grafts.
Oxygen uptake kinetics in treadmill running and cycle ergometry: a comparison
Authors: Carter Helen , Jones Andrew M. , Barstow Thomas J. , Burnley Mark , Williams Craig A. , Doust Jonathan H.
Published: December 2017

The purpose of the present study was to comprehensively examine oxygen consumption (V˙o 2) kinetics during running and cycling through mathematical modeling of the breath-by-breath gas exchange responses to moderate and heavy exercise. After determination of the lactate threshold (LT) and maximal oxygen consumption (V˙o 2 max) in both cycling and running exercise, seven subjects (age 26.6 ± 5.1 yr) completed a series of “square-wave” rest-to-exercise transitions at running speeds and cycling power outputs that corresponded to 80% LT and 25, 50, and 75%Δ (Δ being the difference between LT andV˙o 2 max).V˙o 2 responses were fit with either a two- (LT) exponential model. The parameters of theV˙o 2 kinetic response were similar between exercise modes, except for the V˙o 2 slow component, which was significantly ( P < 0.05) greater for cycling than for running at 50 and 75%Δ (334 ± 183 and 430 ± 159 ml/min vs. 205 ± 84 and 302 ± 154 ml/min, respectively). We speculate that the differences between the modes are related to the higher intramuscular tension development in heavy cycle exercise and the higher eccentric exercise component in running. This may cause a relatively greater recruitment of the less efficient type II muscle fibers in cycling.
Activation of human quadriceps femoris muscle during dynamic contractions: effects of load on fatigue
Authors: Lee Samuel C. K. , Becker Cara N. , Binder-Macleod Stuart A.
Published: December 2017

Muscle fatigue is both multifactorial and task dependent. Electrical stimulation may assist individuals with paralysis to perform functional activities [functional electrical stimulation (FES), e.g., standing or walking], but muscle fatigue is a limiting factor. One method of optimizing force is to use stimulation patterns that exploit the catchlike property of skeletal muscle [catchlike-inducing trains (CITs)]. Although nonisometric (dynamic) contractions are important parts of both normal physiological activation of skeletal muscles and FES, no previous studies have attempted to identify the effect that the load being lifted by a muscle has on the fatigue produced. This study examined the effects of load on fatigue during dynamic contractions and the augmentation produced by CITs as a function of load. Knee extension in healthy subjects was electrically elicited against three different loads. The highest load produced the least excursion, work, and average power, but it produced the greatest fatigue. CIT augmentation was greatest at the highest load and increased with fatigue. Because CITs were effective during shortening contractions for a variety of loads, they may be of benefit during FES applications.
Catecholamine release, growth hormone secretion, and energy expenditure during exercise vs. recovery in men
Authors: Pritzlaff Cathy J. , Wideman Laurie , Blumer Jeffrey , Jensen Michael , Abbott Robert D. , Gaesser Glenn A. , Veldhuis Johannes D. , Weltman Arthur
Published: December 2017

We examined the relationship between energy expenditure (in kcal) and epinephrine (Epi), norepinephrine (NE), and growth hormone (GH) release. Ten men [age, 26 yr; height, 178 cm; weight, 81 kg; O2uptake at lactate threshold (LT), 36.3 ml · kg−1 · min−1; peak O2uptake, 49.5 ml · kg−1 · min−1] were tested on six randomly ordered occasions [control, 5 exercise: at 25 and 75% of the difference between LT and rest (0.25LT, 0.75LT), at LT, and at 25 and 75% of the difference between LT and peak (1.25LT, 1.75LT) (0900–0930)]. From 0700 to 1300, blood was sampled and assayed for GH, Epi, and NE. Carbohydrate (CHO) expenditure during exercise and fat expenditure during recovery rose proportionately to increasing exercise intensity ( P = 0.002). Fat expenditure during exercise and CHO expenditure during recovery were not affected by exercise intensity. The relationship between exercise intensity and CHO expenditure during exercise could not be explained by either Epi ( P = 1.00) or NE ( P = 0.922), whereas fat expenditure during recovery increased with Epi and GH independently of exercise intensity ( P = 0.028). When Epi and GH were regressed against fat expenditure during recovery, only GH remained statistically significant ( P < 0.05). We conclude that a positive relationship exists between exercise intensity and both CHO expenditure during exercise and fat expenditure during recovery and that the increase in fat expenditure during recovery with higher exercise intensities is related to GH release.
Upper airway muscle responsiveness to rising Pco2during NREM sleep
Authors: Pillar Giora , Malhotra Atul , Fogel Robert B. , Beauregard Josee , Slamowitz David I. , Shea Steven A. , White David P.
Published: December 2017

Although pharyngeal muscles respond robustly to increasing Pco2during wakefulness, the effect of hypercapnia on upper airway muscle activation during sleep has not been carefully assessed. This may be important, because it has been hypothesized that CO2-driven muscle activation may importantly stabilize the upper airway during stages 3 and 4 sleep. To test this hypothesis, we measured ventilation, airway resistance, genioglossus (GG) and tensor palatini (TP) electromyogram (EMG), plus end-tidal Pco2(PetCO2) in 18 subjects during wakefulness, stage 2, and slow-wave sleep (SWS). Responses of ventilation and muscle EMG to administered CO2(PetCO2= 6 Torr above the eupneic level) were also assessed during SWS ( n = 9) or stage 2 sleep ( n = 7). PetCO2increased spontaneously by 0.8 ± 0.1 Torr from stage 2 to SWS (from 43.3 ± 0.6 to 44.1 ± 0.5 Torr, P < 0.05), with no significant change in GG or TP EMG. Despite a significant increase in minute ventilation with induced hypercapnia (from 8.3 ± 0.1 to 11.9 ± 0.3 l/min in stage 2 and 8.6 ± 0.4 to 12.7 ± 0.4 l/min in SWS, P < 0.05 for both), there was no significant change in the GG or TP EMG. These data indicate that supraphysiological levels of PetCO2(50.4 ± 1.6 Torr in stage 2, and 50.4 ± 0.9 Torr in SWS) are not a major independent stimulus to pharyngeal dilator muscle activation during either SWS or stage 2 sleep. Thus hypercapnia-induced pharyngeal dilator muscle activation alone is unlikely to explain the paucity of sleep-disordered breathing events during SWS.
Postexercise rehydration: effect of Na+ and volume on restoration of fluid spaces and cardiovascular function
Authors: Mitchell J. B. , Phillips M. D. , Mercer S. P. , Baylies H. L. , Pizza F. X.
Published: December 2017

Our purpose was to study the interaction between Na+ content and fluid volume on rehydration (RH) and restoration of fluid spaces and cardiovascular (CV) function. Ten men completed four trials in which they exercised in a 35°C environment until dehydrated by 2.9% body mass, were rehydrated for 180 min, and exercised for an additional 20 min. Four RH regimens were tested: low volume (100% fluid replacement)-low (25 mM) Na+ (LL), low volume-high (50 mM) Na+ (LH), high volume (150% fluid replacement)-low Na+ (HL), and high volume-high Na+ (HH). Blood and urine samples were collected and body mass was measured before and after exercise and every hour during RH. Before and after the dehydration exercise and during the 20 min of exercise after RH, cardiac output was measured. Fluid compartment (intracellular and extracellular) restoration and percent change in plasma volume were calculated using the Cl− and hematocrit/Hb methods, respectively. RH was greater ( P < 0.05) in HL and HH (102.0 ± 15.2 and 103.7 ± 14.7%, respectively) than in LL and LH (70.7 ± 10.5 and 75.9 ± 6.3%, respectively). Intracellular RH was greater in HL (1.12 ± 0.4 liters) than in all other conditions (0.83 ± 0.3, 0.69 ± 0.2, and 0.73 ± 0.3 liter for LL, LH, and HH, respectively), whereas extracellular RH (including plasma volume) was greater in HL and HH (1.35 ± 0.8 and 1.63 ± 0.4 liters, respectively) than in LL and LH (0.83 ± 0.3 and 1.05 ± 0.4 liters, respectively). CV function (based on stroke volume, heart rate, and cardiac output) was restored equally in all conditions. These data indicate that greater RH can be achieved through larger volumes of fluid and is not affected by Na+content within the range tested. Higher Na+ content favors extracellular fluid filling, whereas intracellular fluid benefits from higher volumes of fluid with lower Na+. Alterations in Na+ and/or volume within the range tested do not affect the degree of restoration of CV function.
Inhaled porcine pancreatic elastase causes bronchoconstriction via a bradykinin-mediated mechanism
Authors: Scuri M. , Forteza R. , Lauredo I. , Sabater J. R. , Botvinnikova Y. , Allegra L. , Abraham W. M.
Published: December 2017

Neutrophil elastase has been linked to inflammatory lung diseases such as chronic obstructive pulmonary disease, adult respiratory distress syndrome, emphysema, and cystic fibrosis. In guinea pigs, aerosol challenge with human neutrophil elastase causes bronchoconstriction, but the mechanism by which this occurs is not completely understood. Our laboratory previously showed that human neutrophil elastase releases tissue kallikrein (TK) from cultured tracheal gland cells. TK has been identified as the major kininogenase of the airway and cleaves both high- and low-molecular weight kininogen to yield lysyl-bradykinin. Because inhaled bradykinin causes bronchoconstriction and airway hyperresponsiveness in asthmatic patients and allergic sheep, we hypothesized that elastase-induced bronchoconstriction could be mediated by bradykinin. To test this hypothesis, we measured lung resistance (Rl) in sheep before and after inhalation of porcine pancreatic elastase (PPE) alone and after pretreatment with a bradykinin B2antagonist (NPC-567), the specific human elastase inhibitor ICI 200,355, the histamine H1-antagonist diphenhydramine hydrochloride, the cysteinyl leukotriene 1 receptor antagonist montelukast, or the cyclooxygenase inhibitor indomethacin. Inhaled PPE (125–1,000 μg) caused a dose-dependent increase in Rl. Aerosol challenge with a single 500 μg dose of PPE increased Rlby 132 ± 8% over baseline. This response was blocked by pretreatment with NPC-567 and ICI-200,355 ( n = 6; P < 0.001), whereas treatment with dyphenhydramine hydrochloride, montelukast, or indomethacin failed to block the PPE-induced bronchoconstriction. Consistent with pharmacological data, TK activity in bronchial lavage fluid increased 134 ± 57% over baseline ( n = 5; P < 0.02). We conclude that, in sheep, PPE-induced bronchoconstriction is in part mediated by the generation of bradykinin. Our findings suggest that elastase-kinin interactions may contribute to changes in bronchial tone during inflammatory diseases of the airways.
Echocardiographic criteria for detection of postinfarction congestive heart failure in rats
Authors: Sjaastad Ivar , Sejersted Ole M. , Ilebekk Arnfinn , Bjørnerheim Reidar
Published: December 2017

We evaluated postinfarction myocardial function in rats and determined echocardiographic criteria for congestive heart failure (CHF) using high performance echocardiography. Extensive myocardial infarction (MI) was induced in rats by left coronary occlusion. Sham-operated animals served as controls. Five weeks later, high-frame rate (∼200 Hz), fully digitized, shallow-focus (10–25 mm), two-dimensional, M-mode and Doppler echocardiography was performed. A J-tree cluster analysis was performed using parameters indicative of CHF. Reproducibility was examined. The cluster analysis joined the animals into one Sham and two MI clusters. One of the MI clusters had clinical characteristics of CHF and elevated left ventricular end diastolic pressure. Among the echocardiographic variables, only posterior wall shortening velocity separated the failing and nonfailing MI clusters. We conclude that, by high frame rate echocardiography, it is possible to obtain high- quality recordings in rats. It is feasible to distinguish MI rats with CHF due to myocardial dysfunction from those without failure and to perform longitudinal studies on myocardial function.
Exercise elevates plasma levels but not gene expression of IL-1β, IL-6, and TNF-α in blood mononuclear cells
Authors: Moldoveanu Andrei I. , Shephard Roy J. , Shek Pang N.
Published: December 2017

Physical activity induces a subclinical inflammatory response, mediated in part by leukocytes, and manifested by elevated concentrations of circulating proinflammatory cytokines, including interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α). However, the source of the cytokines that appear during exercise remains unknown. In this study, we examined exercise-induced changes in plasma cytokine concentrations and their corresponding mRNA expression in peripheral blood mononuclear cells. Ten healthy [peak oxygen uptake = 48.8 ± 6.5 (SD) ml · kg−1· min−1] but untrained men [age = 25 ± 5 (SD) yr] undertook 3 h of exercise (cycling and inclined walking) at 60–65% peak oxygen uptake. Circulating leukocyte subset counts were elevated during and 2 h postexercise but returned to normal within 24 h. Plasma concentrations of IL-1β, IL-6, and TNF-α peaked at the end of exercise and remained elevated at 2 h (IL-6) and up to 24 h (IL-1β and TNF-α) postexercise. Cytokine gene expression in circulating mononuclear cells was measured by using the reverse transcriptase-polymerase chain reaction; mRNA accumulation did not change with exercise. In conclusion, mRNA accumulation of IL-1β, IL-6, and TNF-α in circulating mononuclear cells is not affected by 3 h of moderate endurance exercise and does not seem to account for the observed increases in plasma cytokines.
Vascular perturbations in the chronic orthostatic intolerance of the postural orthostatic tachycardia syndrome
Authors: Stewart Julian M. , Weldon Amy
Published: December 2017

Chronic orthostatic intolerance is often related to the postural orthostatic tachycardia syndrome (POTS). POTS is characterized by upright tachycardia. Understanding of its pathophysiology remains incomplete, but edema and acrocyanosis of the lower extremities occur frequently. To determine how arterial and venous vascular properties account for these findings, we compared 13 patients aged 13–18 yr with 10 normal controls. Heart rate and blood pressure were continuously recorded, and strain-gauge plethysmography was used to measure forearm and calf blood flow, venous compliance, and microvascular filtration while the subject was supine and to measure calf blood flow and calf size change during head-up tilt. Resting venous pressure was higher in POTS compared with control (16 vs. 10 mmHg), which gave the appearance of decreased compliance in these patients. The threshold for edema formation decreased in POTS patients compared with controls (8.3 vs. 16.3 mmHg). With tilt, early calf blood flow increased in POTS patients (from 3.4 ± 0.9 to 12.6 ± 2.3 ml · 100 ml−1 · min−1) but did not increase in controls. Calf volume increased twice as much in POTS patients compared with controls over a shorter time of orthostasis. The data suggest that resting venous pressure is higher and the threshold for edema is lower in POTS patients compared with controls. Such findings make the POTS patients particularly vulnerable for edema fluid collection. This may signify a redistribution of blood to the lower extremities even while supine, accounting for tachycardia through vagal withdrawal.
Scientific approach to the 1-h cycling world record: a case study
Authors: Padilla Sabino , Mujika Iñigo , Angulo Francisco , Goiriena Juan Jose
Published: December 2017

The purpose of this study was to describe the physiological and aerodynamic characteristics and the preparation for a successful attempt to break the 1-h cycling world record. An elite professional road cyclist (30 yr, 188 cm, 81 kg) performed an incremental laboratory test to assess maximal power output (W˙max) and power output (W˙OBLA), estimated speed ( V OBLA), and heart rate (HROBLA) at the onset of blood lactate accumulation (OBLA). He also completed an incremental velodrome (cycling track) test (VT1), during which V OBLAVT1 and HROBLAVT1 were measured and W˙OBLAVT1 was estimated. W˙maxwas 572 W, W˙OBLA 505 W, V OBLA52.88 km/h, and HROBLA 183 beats/min. V OBLAVT1, HROBLAVT1, andW˙OBLAVT1 were 52.7 km/h, 180 beats/min, and 500.6 W, respectively. Drag coefficient and shape coefficient, measured in a wind tunnel, were 0.244 and 0.65 m2, respectively. The cyclist set a world record of 53,040 m, with an estimated average power output of 509.5 W. Based on direct laboratory data of the power vs. oxygen uptake relationship for this cyclist, this is slightly higher than the 497.25 W corresponding to his oxygen uptake at OBLA (5.65 l/min). In conclusion, 1) the 1-h cycling world record is the result of the interaction between physiological and aerodynamic characteristics; and 2) performance in this event can be predicted using mathematical models that integrate the principal performance-determining variables.
pHiresponses to osmotic cell shrinkage in the presence of open-system buffers
Authors: Heming Thomas A. , Boyarsky Gregory , Tuazon Divina M. , Bidani Akhil
Published: December 2017

Changes in plasma volume in vivo cause rapid changes in extracellular pH by altering the plasma bicarbonate concentration at a constant Pco2(Garella S, Chang BS, and Kahn SI. Kidney Int 8: 279, 1975). Few studies have examined the possibility that changes in cell volume produce comparable changes in intracellular pH (pHi). In the present study, alveolar macrophages were exposed to hyperosmotic medium in the absence or presence of the open-system buffers CO2-HCO3−, propionic acid-propionate, or NH3-NH4+. In the absence of open-system buffers, exposure to twice-normal osmolarity (2T) produced a slow cellular alkalinization [change in pHi(ΔpHi) ≈ 0.38; exponential time constant (τ) ≈ 120 s]. In the presence of 5% CO2, 2T caused a biphasic pHiresponse: a rapid increase (ΔpHi≈ 0.10, τ ≈ 15 s) followed by a slower pHiincrease. Identical rapid pHiincreases were produced by 2T in the presence of propionic acid (20 mM). Conversely, 2T caused a rapid pHidecrease (ΔpHi≈ −0.21, τ ≈ 10 s) in the presence of NH3(20 mM). Thus osmotic cell shrinkage caused rapid pHichanges of opposite direction in the presence of a weak acid buffer (contraction alkalosis with CO2or propionic acid) vs. a weak base buffer (contraction acidosis with NH3). Graded ΔpHiwere produced by varying extracellular osmolarity in the presence of open-system buffers; osmolarity increases of as little as 5–10% produced significant ΔpHi. The rapid pHiresponses to 2T were insensitive to inhibitors of membrane H+transport (ethylisopropylamiloride and bafilomycin A1). The results are consistent with shrinkage-induced disequilibria in the total cellular buffer system (i.e., intrinsic buffers plus added weak acid-base buffer).
Influence of lung volume on pulmonary microvascular pressure-volume characteristics
Authors: Topulos George P. , Brown Richard E. , Butler James P.
Published: December 2017

The pressure-volume (P-V) characteristics of the lung microcirculation are important determinants of the pattern of pulmonary perfusion and of red and white cell transit times. Using diffuse light scattering, we measured capillary P-V loops in seven excised perfused dog lobes at four lung volumes, from functional residual capacity (FRC) to total lung capacity (TLC), over a wide range of vascular transmural pressures (Ptm). At Ptm 5 cmH2O, specific compliance of the microvasculature was 8.6%/cmH2O near FRC, decreasing to 2.7%/cmH2O as lung volume increased to TLC. At low lung volumes, the vasculature showed signs of strain stiffening (specific compliance fell as Ptm rose), but stiffening decreased as lung volume increased and was essentially absent at TLC. The P-V loops were smooth without sharp transitions, consistent with vascular distension as the primary mode of changes in vascular volume with changes in Ptm. Hysteresis was small (0.013) at all lung volumes, suggesting that, although surface tension may set basal capillary shape, it does not strongly affect capillary compliance.