Showing papers in "Journal of Applied Physiology in 1994"
TL;DR: This paper illustrates how recurrence plots can take single physiological measurements, project them into multidimensional space by embedding procedures, and identify time correlations (recurrences) that are not apparent in the one-dimensional time series.
Abstract: Physiological systems are best characterized as complex dynamical processes that are continuously subjected to and updated by nonlinear feedforward and feedback inputs. System outputs usually exhibit wide varieties of behaviors due to dynamical interactions between system components, external noise perturbations, and physiological state changes. Complicated interactions occur at a variety of hierarchial levels and involve a number of interacting variables, many of which are unavailable for experimental measurement. In this paper we illustrate how recurrence plots can take single physiological measurements, project them into multidimensional space by embedding procedures, and identify time correlations (recurrences) that are not apparent in the one-dimensional time series. We extend the original description of recurrence plots by computing an array of specific recurrence variables that quantify the deterministic structure and complexity of the plot. We then demonstrate how physiological states can be assessed by making repeated recurrence plot calculations within a window sliding down any physiological dynamic. Unlike other predominant time series techniques, recurrence plot analyses are not limited by data stationarity and size constraints. Pertinent physiological examples from respiratory and skeletal motor systems illustrate the utility of recurrence plots in the diagnosis of nonlinear systems. The methodology is fully applicable to any rhythmical system, whether it be mechanical, electrical, neural, hormonal, chemical, or even spacial.
1,327 citations
TL;DR: The data suggest that skeletal muscle adaptations that may contribute to strength gains of the lower extremity are similar for men and women during the early phase of resistance training and, with the exception of changes in the fast fiber type composition, that they occur gradually.
Abstract: An 8-wk progressive resistance training program for the lower extremity was performed twice a week to investigate the time course for skeletal muscle adaptations in men and women. Maximal dynamic strength was tested biweekly. Muscle biopsies were extracted at the beginning and every 2 wk of the study from resistance-trained and from nontrained (control) subjects. The muscle samples were analyzed for fiber type composition, cross-sectional area, and myosin heavy chain content. In addition, fasting blood samples were measured for resting serum levels of testosterone, cortisol, and growth hormone. With the exception of the leg press for women (after 2 wk of training) and leg extension for men (after 6 wk of training), absolute and relative maximal dynamic strength was significantly increased after 4 wk of training for all three exercises (squat, leg press, and leg extension) in both sexes. Resistance training also caused a significant decrease in the percentage of type IIb fibers after 2 wk in women and 4 wk in men, an increase in the resting levels of serum testosterone after 4 wk in men, and a decrease in cortisol after 6 wk in men. No significant changes occurred over time for any of the other measured parameters for either sex. These data suggest that skeletal muscle adaptations that may contribute to strength gains of the lower extremity are similar for men and women during the early phase of resistance training and, with the exception of changes in the fast fiber type composition, that they occur gradually.
826 citations
TL;DR: The crossover point is the power output at which energy from CHO-derived fuels predominates over energy from lipids, with further increases in power eliciting a relative increment in CHO utilization and a decrement in lipid oxidation.
Abstract: The “crossover” concept represents a theoretical means by which one can understand the effects of exercise intensity and prior endurance training on the balance of carbohydrate (CHO) and lipid meta...
793 citations
TL;DR: 760-800 nm absorption is closely correlated with venous oxygen saturation, minimally affected by skin blood flow, altered by changes in limb perfusion, and primarily derived from deoxygenated hemoglobin and not myoglobin.
Abstract: Near-infrared (NIR) spectroscopy is a noninvasive technique that uses the differential absorption properties of hemoglobin to evaluate skeletal muscle oxygenation. Oxygenated and deoxygenated hemog...
685 citations
TL;DR: The observations reviewed here suggest that adenosine and agents that act throughadenosine are excellent candidates for development as anti-inflammatory agents.
Abstract: Adenosine receptors are present on most cells and organs, yet, although the physiological effects of adenosine were first described over 60 years ago, the potential therapeutic uses of adenosine ha...
650 citations
TL;DR: The role of myosin heavy-chain (MHC) isoforms in skeletal muscle motility has been investigated by correlated biochemical-physiological studies on single skinned fibers, in agreement with results from in vitro motility assays as mentioned in this paper.
Abstract: Skeletal muscles of different mammalian species contain four major myosin heavy-chain (MHC) isoforms: the "slow" or beta-MHC and the three "fast" IIa-, IIx-, and IIb-MHCs; and three major myosin light-chain (MLC) isoforms, the "slow" MLC1s and the two "fast" MLC1f and MLC3f. The differential distribution of the MHCs defines four major fiber types containing a single MHC isoform and a number of intermediate hybrid fiber populations containing both beta/slow- and IIa-MHC, IIa- and IIx-MHC, or IIx- and IIb-MHC. The IIa-, IIx-, and IIb-MHCs were first detected in neonatal muscles, and their expression in developing and adult muscle is regulated by neural, hormonal, and mechanical factors. The transcriptional mechanisms responsible for the fiber type-specific regulation of MHC and MLC gene expression are not known and are presently being explored by in vivo transfection experiments. The functional role of MHC isoforms has been in part clarified by correlated biochemical-physiological studies on single skinned fibers: these studies, in agreement with results from in vitro motility assays, indicate that both MHC and MLC isoforms determine the maximum velocity of shortening of skeletal muscle fibers.
510 citations
TL;DR: The data indicate that NO is released from an incubated skeletal muscle preparation and presents the possibility that muscle-derived NO may play an important metabolic role and reduce both basal 2-deoxyglucose transport and NO efflux.
Abstract: To determine whether nitric oxide (NO) synthase activity exists in rat skeletal muscle, media from incubated rat extensor digitorum longus muscle preparations were assayed for NO with a chemiluminescent detection system. Although small amounts of NO were detected in media alone, the addition of muscle increased NO concentration in the media by 30-fold. The release of NO into the media diminished over time. Either arginine (10(-6) M), sodium nitroprusside (10(-6) M), or prior electrical stimulation in vivo caused 50-200% increases (P < 0.05) in NO concentration. NG-monomethyl-L-arginine monoacetate (10(-6) M), an NO synthase inhibitor, decreased both basal 2-deoxyglucose transport and NO efflux, indicating that NO may play a role in modulating skeletal muscle carbohydrate metabolism. These data indicate that NO is released from an incubated skeletal muscle preparation and presents the possibility that muscle-derived NO may play an important metabolic role.
412 citations
TL;DR: Results are interpreted as demonstrating that the optimal musculotendinous stiffness for maximum concentric and isometric activities was toward the stiff end of the elasticity continuum.
Abstract: The purpose of this study was to quantify the relationship between musculotendinous stiffness and performance in eccentric, isometric, and concentric activities. Thirteen trained subjects performed...
379 citations
TL;DR: It is indicated that a heavy-resistance strength-training program increases RMR in healthy older men, perhaps by increasing FFM and sympathetic nervous system activity.
Abstract: Resting metabolic rate (RMR) decreases with age, largely because of an age-related decline in fat-free mass (FFM). We hypothesized that a strength-training program capable of eliciting increases in...
311 citations
TL;DR: The results demonstrate that NIRS provides the particular advantage of obtaining the contemporary evaluation of blood flow and VO2, allowing correlation of these two variables by a single maneuver without discomfort for the subject.
Abstract: We applied near-infrared spectroscopy (NIRS) for the simultaneous measurement of forearm blood flow (FBF) and oxygen consumption (VO2) in the human by inducing a 50-mmHg venous occlusion. Eleven healthy subjects were studied both at rest and after hand exercise during vascular occlusion. FBF was also measured by strain-gauge plethysmography. FBF measured by NIRS was 1.9 +/- 0.8 ml.100 ml-1.min-1 at rest and 8.2 +/- 2.9 ml.100 ml-1.min-1 after hand exercise. These values showed a correlation (r = 0.94) with those obtained by the plethysmography. VO2 values were 4.6 +/- 1.3 microM O2 x 100 ml-1.min-1 at rest and 24.9 +/- 11.2 microM O2 x 100 ml-1.min-1 after hand exercise. The scatter of the FBF and VO2 values showed a good correlation between the two variables (r = 0.93). The results demonstrate that NIRS provides the particular advantage of obtaining the contemporary evaluation of blood flow and VO2, allowing correlation of these two variables by a single maneuver without discomfort for the subject.
296 citations
TL;DR: It is demonstrated that strength training increases insulin action and lowers plasma insulin levels in middle-aged and older men.
Abstract: The insulin resistance associated with aging may be due, in part, to reduced levels of physical activity in the elderly. We hypothesized that strength training increases insulin action in older ind...
TL;DR: A clear and repeatable difference was found, supporting Morgan's prediction of more sarcomeres after decline running, although with some differences in response that depended on the age of the rats.
Abstract: Unaccustomed eccentric exercise, in which a muscle is lengthened while generating tension, is well known to cause injury and pain. A rapid training effect has been demonstrated in a number of eccen...
TL;DR: It is suggested that short-term resistance training reduces MR image contrast shift evoked by a given effort, thereby reflecting the use of less muscle to lift the load.
Abstract: This study examined the effect of resistance training on exercise-induced contrast shift in magnetic resonance (MR) images. It was hypothesized that a given load could be lifted after training with...
TL;DR: The discharge rate of most motor units declined despite an increase in the excitatory drive to the motoneuron pool during the fatigue task, and the direction of the change in discharge rate could not be predicted from the threshold force of recruitment or the variability of interimpulse intervals.
Abstract: The activity of 50 single motor units was recorded in the biceps brachii muscle of human subjects while they performed submaximal isometric elbow flexion contractions that were sustained to induce fatigue. The purposes of this study were to examine the influence of fatigue on motor unit threshold force and to determine the relationship between the threshold force of recruitment and the initial interimpulse interval on the discharge rates of single motor units during a fatiguing contraction. The discharge rate of most motor units that were active from the beginning of the contraction declined during the fatiguing contraction, whereas the discharge rates of most newly recruited units were either constant or increased slightly. The absolute threshold forces of recruitment and derecruitment decreased, and the variability of interimpulse intervals increased after the fatigue task. The change in motor unit discharge rate during the fatigue task was related to the initial rate, but the direction of the change in discharge rate could not be predicted from the threshold force of recruitment or the variability in the interimpulse intervals. The discharge rate of most motor units declined despite an increase in the excitatory drive to the motoneuron pool during the fatigue task.
TL;DR: This study reassessed the theory and methodology of BIA and describes a new technique for measuring segmental impedance that may resolve some major limitations associated with the current whole body impedance methodology.
Abstract: Bioelectrical impedance analysis (BIA) for body composition has been based on the volume conductor model that results in the mathematical relationship Ht2/R approximately FFM, where Ht is body height, R is whole body resistance or impedance, and FFM is fat-free mass. Although this relationship exists in the human subject, its strength and usefulness have been subject to conflicting reports. This study reassessed the theory and methodology of BIA and describes a new technique for measuring segmental impedance that may resolve some major limitations associated with the current whole body impedance methodology. By use of data from 200 adult subjects, a new theory and methodology for BIA were developed in four steps: 1) a rationale was presented for replacing the Ht2/R model by one based on electrical resistivity, 2) a practical six-electrode technique for segmental BIA that uses only peripheral electrode sites was described, 3) prediction equations for fat weight based on the new segmental BIA technique were developed, and 4) prediction equations for fat distribution, a potential new use of impedance methodology, were developed using a new measure of fat distribution, the impedance index.
TL;DR: The findings of concomitant increases in gene transcript levels forET-1 and the ETA and ETB receptors in lung, but not in the great vessels or any other organ examined, are consistent with the hypothesis that increased ET-1 synthesis in the lung contributes to pulmonary vascular remodeling and the maintenance of chronic hypoxic pulmonary hypertension.
Abstract: To test the hypothesis that endothelin (ET)-1 synthesis and ET receptor levels are increased selectively in the lung of rats with chronic hypoxic pulmonary hypertension, the current study examined the effects of exposure to chronic hypoxia (10% O2, 1 atm, 4 wk) on pulmonary arterial pressure, ET-1 levels in plasma and lung, and ET-1 and ETA and ETB receptor mRNA levels in lung, heart, pulmonary artery, aorta, kidney, spleen, and liver. Hypoxic exposure was associated with increases in pulmonary arterial pressure, plasma ET-1 levels, ET-1 mRNA in lung and pulmonary artery, and ET-1 stores and ETA and ETB receptor mRNA levels in lung. In thoracic aorta and the four heart chambers, ETA and ETB receptor mRNA levels were increased, but ET-1 mRNA levels were unchanged from air control levels. No change in ET-1 or ET receptor mRNA levels was seen in organs perfused by the systemic vascular bed, except in liver, where ETA receptor mRNA levels were decreased. The findings of concomitant increases in gene transcript levels for ET-1 and the ETA and ETB receptors in lung, but not in the great vessels or any other organ examined, are consistent with the hypothesis that increased ET-1 synthesis in the lung contributes to pulmonary vascular remodeling and the maintenance of chronic hypoxic pulmonary hypertension.
TL;DR: Findings can improve occupational safety guidelines for human heat exposure, as they provide further evidence that the incidence of exhaustion from heat strain can be predicted from core temperature.
Abstract: This study determined the influence of exercise intensity, protective clothing level, and climate on physiological tolerance to uncompensable heat stress. It also compared the relationship between core temperature and the incidence of exhaustion from heat strain for persons wearing protective clothing to previously published data of unclothed persons during uncompensable heat stress. Seven heat-acclimated men attempted 180-min treadmill walks at metabolic rates of approximately 425 and 600 W while wearing full (clo = 1.5) or partial (clo = 1.3) protective clothing in both a desert (43 degrees C dry bulb, 20% relative humidity, wind 2.2 m/s) and tropical (35 degrees C dry bulb, 50% relative humidity, wind 2.2 m/s) climate. During these trials, the evaporative cooling required to maintain thermal balance exceeded the maximal evaporative capacity of the environment and core temperature continued to rise until exhaustion from heat strain occurred. Our findings concerning exhaustion from heat strain are 1) full encapsulation in protective clothing reduces physiological tolerance as core temperature at exhaustion was lower (P < 0.05) in fully than in partially clothed persons, 2) partial encapsulation results in physiological tolerance similar to that reported for unclothed persons, 3) raising metabolic rate from 400 to 600 W does not alter physiological tolerance when subjects are fully clothed, and 4) physiological tolerance is similar when subjects are wearing protective clothing in desert and tropical climates having the same wet bulb globe thermometer. These findings can improve occupational safety guidelines for human heat exposure, as they provide further evidence that the incidence of exhaustion from heat strain can be predicted from core temperature.
TL;DR: The effects of a 16-wk strength-training program on total and regional body composition were assessed by dual-energy X-ray absorptiometry (DEXA), magnetic resonance imaging (MRI), and hydrodensitometry in 13 untrained healthy men.
Abstract: The effects of a 16-wk strength-training program on total and regional body composition were assessed by dual-energy X-ray absorptiometry (DEXA), magnetic resonance imaging (MRI), and hydrodensitometry in 13 untrained healthy men [60 +/- 4 (SD) yr]. Nine additional men (62 +/- 6 yr) served as inactive controls. The strength-training program resulted in substantial increases in both upper (39 +/- 8%; P < 0.001) and lower (42 +/- 14%; P < 0.001) body strength. Total fat-free mass (FFM) increased by 2 kg (62.0 +/- 7.1 to 64.0 +/- 7.2 kg; P < 0.001), and total fat mass decreased by the same amount (23.8 +/- 6.7 to 21.8 +/- 6.0 kg; P < 0.001) when measured by DEXA. When measured by hydrodensitometry, similar increases in FFM (61.3 +/- 7.8 to 63.0 +/- 7.6 kg; P < 0.01) and decreases in fat mass (23.8 +/- 7.9 to 22.1 +/- 7.7 kg; P < 0.001) were observed. When measured by DEXA, FFM was increased in the arms (6.045 +/- 0.860 to 6.418 +/- 0.803 kg; P < 0.01), legs (19.416 +/- 2.228 to 20.131 +/- 2.303 kg; P < 0.001), and trunk (29.229 +/- 4.108 to 30.134 +/- 4.184 kg; P < 0.01), whereas fat mass was reduced in the arms (2.383 +/- 0.830 to 2.128 +/- 0.714 kg; P < 0.01), legs (7.583 +/- 1.675 to 6.945 +/- 1.551 kg; P < 0.001), and trunk (12.216 +/- 4.143 to 11.281 +/- 3.653 kg; P < 0.01) as a result of training.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: The results indicate that, under the conditions employed in isolated muscle preparations, 2-DG uptake accurately reflects glucose transport activity and that 2- DG is the most appropriate glucose analogue for measurement of glucose Transport activity when transport rates are high.
Abstract: The purpose of this study was to evaluate the suitability of the glucose analogue 2-deoxyglucose (2-DG) for measurement of glucose transport activity in rat skeletal muscles in vitro when transport rates are high. The goal was to determine whether glucose phosphorylation rather than transport becomes limiting under experimental conditions normally employed in muscle incubation experiments. The rate of 2-DG uptake assayed in the presence of 8 mM 2-DG and a maximally effective concentration of insulin remained linear for > or = 60 min in the split soleus and 120 min in the epitrochlearis. Hexokinase activity assayed in skeletal muscle homogenates was not inhibited appreciably by 2-deoxyglucose 6-phosphate (2-DG-6-P) concentrations in the range of those achieved intracellularly during the linear phase of 2-DG uptake (i.e., 2-DG-6-P below approximately 30 mM). During this linear phase of 2-DG uptake, total intracellular 2-DG concentrations did not exceed 30 mM. The combined effects of contractions plus a maximally effective concentration of insulin on glucose transport activity measured at a near-saturating concentration of 2-DG were additive in the epitrochlearis and the soleus. Our results indicate that, under the conditions employed in our isolated muscle preparations, 2-DG uptake accurately reflects glucose transport activity and that 2-DG is the most appropriate glucose analogue for measurement of glucose transport activity when transport rates are high.
TL;DR: Findings indicate that macrophage subpopulations are associated with distinct stages during the recovery process from hindlimb suspension: ED1+ macrophages areassociated with muscle necrosis, whereas ED2+ cells are associatedWith muscle regeneration.
Abstract: The hypothesis that distinct populations of macrophages are associated with muscle necrosis and regeneration was examined in Wistar rat soleus muscle after 10 days of hindlimb suspension and 2, 4, ...
TL;DR: The elderly subjects reduced the variability in force at the lower target forces, which was not consistent with the hypothesis that the greater coefficient of variation for the force fluctuations is due to increased motor unit forces.
Abstract: The increase in motor unit force that occurs with aging has been hypothesized to cause a decline in the ability to maintain a constant submaximal force. To test this hypothesis, young and elderly subjects performed a 12-wk strength-training program that was intended to increase motor unit force. The training program caused similar increases (%initial) in the training load (137.4 +/- 17.2%), twitch force (23.1 +/- 7.4%), and maximum voluntary contraction force (39.2 +/- 6.8%) of the first dorsal interosseus muscle for the young and elderly subjects. The increase in strength was associated with a modest increase in muscle volume (7% of initial value) and a nonmonotonic increase in the surface-recorded electromyogram that was significant at week 8 but not at week 12. The elderly subjects reduced the variability in force at the lower target forces (2.5, 5.0, and 20.0% maximum voluntary contraction force). This improvement, however, was unrelated to changes in the distribution of motor unit forces, which was not consistent with the hypothesis that the greater coefficient of variation for the force fluctuations is due to increased motor unit forces.
TL;DR: GSH-deficient rats had approximately 50% reduced endurance, which suggests a critical role of endogenous GSH in the circumvention of exercise-induced oxidative stress and as a determinant of exercise performance.
Abstract: Glutathione (GSH) plays a central role in coordinating the synergism between different lipid- and aqueous-phase antioxidants. We documented 1) how exogenous GSH and N-acetylcysteine (NAC) may affec...
TL;DR: The greater reliance on carbohydrate as a fuel source during exercise in the heat appears to be partially reduced after acclimation, which is consistent with the observed changes in plasma epinephrine concentrations.
Abstract: Exercise metabolism was examined in 13 endurance athletes who exercised on three occasions for 40 min at 70% of maximal O2 uptake in an environmental chamber at either 20 degrees C and 20% relative humidity (RTT) or 40 degrees C and 20% relative humidity before (PRE ACC) or after (POST ACC) 7 days of acclimation. Exercise in the heat resulted in a lower (P < 0.05) mean O2 uptake (0.13 l/min) and higher (P < 0.01) heart rate and respiratory exchange ratio. Acclimation resulted in a lower (P < 0.01) mean heart rate and respiratory exchange ratio. Postexercise rectal temperature, muscle temperature, muscle and blood lactate, and blood glucose were higher (P < 0.01) in the PRE ACC than in the RTT trial, but all were reduced (P < 0.01) in the POST ACC compared with the PRE ACC trial. Muscle glycogenolysis and percentage of type I muscle fibers showing glycogen depletion were greater (P < 0.05) in the PRE ACC than in the RTT trial. Muscle glycogenolysis was unaffected by acclimation during exercise in the heat, although the percentage of depleted type I fibers was higher (P < 0.05) in the unacclimated state. Plasma epinephrine was higher (P < 0.01) during exercise in the heat in the unacclimated individual relative to RTT but was lower (P < 0.01) in the POST ACC than in the PRE ACC trial. The greater reliance on carbohydrate as a fuel source during exercise in the heat appears to be partially reduced after acclimation. These alterations are consistent with the observed changes in plasma epinephrine concentrations.
TL;DR: The results demonstrate that near-infrared spectroscopy can be used as a noninvasive bedside technique for both qualitative and quantitative evaluation of cerebral hemodynamics and oxygenation in adults.
Abstract: Near-infrared spectroscopy was used to measure global cerebral blood flow and volume in 10 healthy adult volunteers. High- and low-cerebral blood flow compartments were detected with mean flows for...
TL;DR: It is concluded that the pediatric airway behaved as predicted by the Starling resistor model and that Pcrit, a measure of airway collapsibility, correlated with the degree of upperAirway obstruction and was reduced postoperatively, consistent with increased upper airway stability.
Abstract: In adults, the critical nasal pressure (Pcrit) at which the upper airway collapses is higher in patients with the obstructive sleep apnea syndrome (OSAS) than in those with primary snoring. Pediatric OSAS differs clinically from adult OSAS. We therefore compared Pcrit between prepubertal children with OSAS and primary snoring. Pcrit was determined by correlating the maximal inspiratory airflow with the level of positive or negative nasal pressure applied via a nasal mask. As in adults, we found that the maximal inspiratory airflow varied in proportion to the upstream (nasal) rather than the downstream (esophageal) pressure changes. Pcrit was 1 +/- 3 cmH2O in OSAS compared with -20 +/- 9 cmH2O in primary snorers (P < 0.002). In three OSAS patients reevaluated after tonsillectomy and adenoidectomy, Pcrit declined to -7.2 +/- 4.0 cmH2O. We conclude that the pediatric airway behaved as predicted by the Starling resistor model and that Pcrit, a measure of airway collapsibility, correlated with the degree of upper airway obstruction and was reduced postoperatively, consistent with increased upper airway stability.
TL;DR: It is shown that replacing ordinary time derivatives with fractional time derivatives in the constitutive equation of conventional spring-dashpot systems naturally leads to power law relaxation function, the Fourier transform of which is the constant-phase impedance with alpha = 1 - beta.
Abstract: Recent studies indicated that lung tissue stress relaxation is well represented by a simple empirical equation involving a power law, t-beta (where t is time). Likewise, tissue impedance is well described by a model having a frequency-independent (constant) phase with impedance proportional to omega-alpha (where omega is angular frequency and alpha is a constant). These models provide superior descriptions over conventional spring-dashpot systems. Here we offer a mathematical framework and explore its mechanistic basis for using the power law relaxation function and constant-phase impedance. We show that replacing ordinary time derivatives with fractional time derivatives in the constitutive equation of conventional spring-dashpot systems naturally leads to power law relaxation function, the Fourier transform of which is the constant-phase impedance with alpha = 1 - beta. We further establish that fractional derivatives have a mechanistic basis with respect to the viscoelasticity of certain polymer systems. This mechanistic basis arises from molecular theories that take into account the complexity and statistical nature of the system at the molecular level. Moreover, because tissues are composed of long flexible biopolymers, we argue that these molecular theories may also apply for soft tissues. In our approach a key parameter is the exponent beta, which is shown to be directly related to dynamic processes at the tissue fiber and matrix level. By exploring statistical properties of various polymer systems, we offer a molecular basis for several salient features of the dynamic passive mechanical properties of soft tissues.
TL;DR: PCO2 measured in intestinal lumen can be used to detect dysoxia, indicating primarily aerobic appearance of PCO2 in venous blood, and portions of intestine that remained perfused at very low flow produced dissolved CO2 mainly by oxidative phosphorylation.
Abstract: Increased intestinal mucosal PCO2 is used to detect the condition of inadequate O2 delivery, i.e., “dysoxia.” However, mucosal PCO2 (PmCO2) can arise from oxidative phosphorylation, in which case i...
TL;DR: Simultaneous submental electromyography, respiratory plethysmography, and fiber-optic endoscopy revealed a well-timed pattern between physiological respiratory events and related swallowing events.
Abstract: The coordination of breathing and swallowing was studied in 13 young healthy adult subjects during the administration of graduated volumes of water (3, 10, and 20 ml). Simultaneous submental electromyography, respiratory plethysmography, and fiber-optic endoscopy revealed a well-timed pattern between physiological respiratory events and related swallowing events. Expiration was the phase of respiration that was most closely associated with deglutition. Respiration was usually maintained at the onset of deglutition and halted before the onset of laryngeal elevation. The apneic interval was approximately 1 s for the 3-, 10-, and 20-ml boluses. A large-volume (100-ml) straw swallow resulted in variable respiration-swallowing patterns and in statistically significant differences (P < 0.01) in the duration of apneic pause and laryngeal excursion. The expiratory phase of respiration resumed nearly 0.50 s before the completion of swallowing. Clinical implications of the findings are addressed and related to aspiration and pulmonary complications in dysphagic patients.
TL;DR: These results provide further evidence of functionally relevant reductions in parasympathetic and increases in sympathetic influences on arterial pressure control after spaceflight.
Abstract: Spaceflight is associated with decreased orthostatic tolerance after landing. Short-duration spaceflight (4–5 days) impairs one neural mechanism: the carotid baroreceptor-cardiac reflex. To underst...
TL;DR: The results indicate that the rate of ATP utilization may be increased during exercise in the heat but that this increased energy demand is predominantly met by an increase in anaerobic glycolysis and creatine phosphate hydrolysis, preventing a reduction in total adenine nucleotide pool.
Abstract: To examine the effect of heat stress on muscle energy metabolism during submaximal exercise, 12 endurance-trained men cycled on two occasions for approximately 40 min at 70% maximal O2 uptake in an environmental chamber at either 20 degrees C and 20% relative humidity (T20) or 40 degrees C and 20% relative humidity (T40). Trials were conducted > or = 1 wk apart in random order. No difference in mean O2 uptake was observed when exercise in T40 was compared with that in T20. In contrast, exercise in T40 resulted in a higher mean heart rate (P < 0.01) and respiratory exchange ratio (P < 0.05) compared with that in T20. Postexercise rectal and muscle temperatures were also higher (P < 0.01) in T40 than in T20. Lower (P < 0.01) postexercise creatine phosphate and higher creatine (P < 0.01) and ammonia (P < 0.05) were observed in muscle after exercise in T40 compared with T20. In addition, an increased (P < 0.01) muscle glycogenolysis and higher (P < 0.01) postexercise muscle lactate accumulation were observed during exercise in T40 compared with T20. In contrast, no differences were observed in postexercise concentrations of total adenine nucleotide pool (ATP+ADP+AMP), ATP/ADP ratio, or inosine 5'-monophosphate (IMP) when T40 was compared with T20. These results indicate that the rate of ATP utilization may be increased during exercise in the heat but that this increased energy demand is predominantly met by an increase in anaerobic glycolysis and creatine phosphate hydrolysis, preventing a reduction in total adenine nucleotide pool.(ABSTRACT TRUNCATED AT 250 WORDS)