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Query: UMLS:C0392674 (exhaustion)
 13,658 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The addition of methanol to a cell suspension of Methanosarcina barkeri resulted in an increase of the intracellular ATP concentration from 1 nmol/mg to 10 nmol/mg protein and in the formation of a proton-motive force delta p of -130 mV. delta p consisted of more than 90% of the membrane potential delta psi. These values were similar under N2 and under H2. The addition of the uncoupler tetrachlorosalicylanilide to the above system under N2 led to a drastic decrease of both, the ATP concentration and the delta p and to a stop of methanogenesis. With methanol and H2, however, methane formation continued, although the effect of the uncoupler on the ATP pool and on delta p was a under N2. The proton-translocating ATPase inhibitor N,N'-dicyclohexylcarbodiimide caused a rapid exhaustion of the ATP pool and a discontinuation of methane synthesis, whereas delta p was unaffected. Inhibition of methane formation under these conditions could be relieved by the addition of the uncoupler tetrachlorosalicylanilide. These results demonstrate that methane formation according to the equation CH3OH + H2----H2----CH4 + H2O was coupled to ATP synthesis by a chemiosmotic mechanism and was under the control of delta psi: Methane formation only proceeded if the delta psi generated was used for ATP synthesis or if an uncoupler was present. Under N2, methane formation according to the equation 4CH3OH ----CO2 + 3CH4 + 2H2O was abolished by an uncoupler, because one step in the oxidation of methanol to 1 CO2 apparently depended on an energized state of the membrane.
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PMID:Coupling of ATP synthesis and methane formation from methanol and molecular hydrogen in Methanosarcina barkeri. 632 9

There were studied transitional processes accompanying the beginning of growth under glucose addition and stopping of growth under glucose exhaustion in pure and mixed aerobic cultures of Escherichia coli and Serratia marcescens. Continued record of Eh, pH, and CO2 showed that these processes sharply differ from each other in their character in pure and mixed cultures, it is particularly related to the changes of the redox potential. There is no characteristic change in the redox potential in pure culture of E. coli at growth termination in the case when S. marcescens cells are present in the culture.
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PMID:[Changes in redox potentials during transitional processes in pure and mixed cultures of Escherichia coli and Serratia marcescens]. 637 72

In an effort to examine the effects of maternal exercise on the fetus we measured maternal and fetal temperatures and blood gases and calculated uterine O2 consumption in response to three different treadmill exercise regimens in 12 chronically catheterized near-term sheep. We also measured fetal catecholamine concentrations, heart rate, blood pressure, cardiac output, blood flow distribution, blood volume, and placental diffusing capacity. Maternal and fetal temperatures increased a mean maximum of 1.5 +/- 0.5 (SE) and 1.3 +/- 0.1 degrees C, respectively. We corrected maternal and fetal blood gas values for the temperatures in vivo. Maternal arterial partial pressure of O2 (PO2), near exhaustion during prolonged (40 min) exercise at 70% maximal O2 consumption, increased 13% to a maximum of 116.7 +/- 4.0 Torr, whereas partial pressure of CO2 (PCO2) decreased by 28% to 27.6 +/- 2.2 Torr. Fetal arterial PO2 decreased 11% to a minimum of 23.2 +/- 1.6 Torr, O2 content by 26% to 4.3 +/- 0.6 ml X dl -1, PCO2 by 8% to 49.6 +/- 3.2 Torr, but pH did not change significantly. Recovery was virtually complete within 20 min. During exercise total uterine O2 consumption was maintained despite the reduction in uterine blood flow because of hemoconcentration and increased O2 extraction. The decrease of 3 Torr in fetal arterial PO2 and 1.5 ml X dl -1 in O2 content did not result in major cardiovascular changes or catecholamine release. These findings suggest that maternal exercise does not represent a major stressful or hypoxic event to the fetus.
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PMID:Exercise responses in pregnant sheep: blood gases, temperatures, and fetal cardiovascular system. 641 12

To examine the effect of naloxone (an opiate antagonist) on exercise performance, six normal females (20-28 yr) walked on a treadmill (93.8 m/min) with the grade increasing 2.5% every 4 min until exhaustion. Each subject completed three trials: naloxone infusion (0.4 mg/ml saline), saline infusion (1 ml), and an infusion control. The order of trials was randomized and double blind. Each subject responded similarly at each submaximal stage for all three trials. The results during maximal exertion were different. Time to exhaustion was similar for all conditions, averaging 32.6 +/- 3.0 min with a maximal O2 uptake of 38.8 +/- 2.8 ml X kg-1 X min-1 and a lactate of 9.1 +/- 1.1 mmol/l. Maximal ventilation (BTPS) was 7.9 l/min less during the naloxone treatment when compared with either control or placebo trials (P less than 0.05). This difference was attributed to a 4-breath/min reduction in respiratory frequency (P less than 0.05). End-tidal CO2 partial pressure was approximately 4 Torr higher at maximum after naloxone injection. Maximal heart rates averaged 190.8 +/- 3.8 beats/min for both control and placebo trials. This was significantly greater (P less than 0.05) than the 185 +/- 2.4 beats/min recorded for the naloxone trials. Ratings of perceived exertion were 17.0 +/- 1.3 units at maximum, similar for all three trials. Despite these statistically significant cardiorespiratory differences, naloxone produced no effect on maximum O2 uptake or exercise duration.
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PMID:Effects of naloxone on maximal stress testing in females. 642 86

Individuals with chronic airflow obstruction (CAO) are thought to have limited exercise tolerance primarily because of impaired ventilatory mechanics. We studied the effects of added external dead space (DS) on exercise capacity [maximum O2 consumption (VO2max)], maximum exercise ventilation (VEmax), and blood gases (arterial PO2, PCO2, pH) in 22 patients with CAO [forced expired volume at 1 s (FEV1) = 0.96 +/- 0.41 liter]. Maximum exercise testing (Emax) was performed by incremental cycle ergometry. Patients exercised at base line (BL) and with DS (0.25 liter if FEV1 less than 0.8, and 0.50 liter if FEV1 greater than 0.8 liter), in random-order single-blind fashion. DS resulted in a 12.2% increase in VEmax (P less than 0.001); tidal volume increased (P less than 0.025) while respiratory frequency was unchanged. The VO2max and maximum CO2 production decreased (P less than 0.001) with DS. Arterial PCO2 at rest and at exhaustion increased with DS (P less than 0.001). The pH and arterial PO2 showed small declines at rest and at Emax. Thus, at the lower maximum work load achieved with DS, the patients ventilated more and tolerated a higher arterial PCO2 and a lower arterial PO2 and pH before stopping from dyspnea as compared with the BL exercise run. In contrast, the VO2max of nine normal control subjects was unaffected by the addition of DS. Although VEmax can be increased in CAO patients with DS, this increase is not sufficient to prevent further CO2 retention or a decrease in exercise capacity. We conclude that exercise performance is limited primarily by impaired ventilatory mechanics in CAO.
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PMID:Exercise performance with added dead space in chronic airflow obstruction. 642 44

Six healthy male subjects performed three exercise tests in which the power output was increased by 100 kpm/min each minute until exhaustion. The studies were carried out after oral administration of CaCO3 (control), NH4Cl (metabolic acidosis), and NaHCO3 (metabolic alkalosis). Ventilation (VE), O2 intake (VO2), and CO2 output (VCO2) were monitored continuously. Arterialized-venous blood samples were drawn at specific times and analyzed for pH, PCO2, and lactate concentration. Resting pH (mean +/- SE) was lowest in acidosis (7.29 +/- 0.01) and highest in alkalosis (7.46 +/- 0.02). A lower peak power output (kpm/min) was achieved in acidosis (1,717 +/- 95) compared with control (1,867 +/- 120) alkalosis (1,867 +/- 125). Submaximal VO2 and VCO2 were similar, but peak VO2 and VCO2 were lower in acidosis. Plasma lactate concentration was lower at rest and during exercise in acidosis. Although lactate accumulation was reduced in acidosis, increases in hydrogen ion concentration were similar in the three conditions. We conclude that acid-base changes influence the maximum power output that may be sustained in incremental dynamic exercise and modify plasma lactate appearance, but have little effect on hydrogen ion appearance in plasma.
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PMID:Effect of pH on metabolic and cardiorespiratory responses during progressive exercise. 652 52

Anaerobic threshold has been defined as the oxygen uptake (VO2) at which blood lactate (La) begins to rise systematically during graded exercise (Davis et al. 1982). It has become common practice in the literature to estimate the anaerobic threshold by using ventilatory and/or gas exchange alterations. However, confusion exists as to the validity of this practice. The purpose of this study was to examine the precision with which ventilatory and gas exchange techniques for determining anaerobic threshold predicted the anaerobic threshold resolved by La criteria. The anaerobic threshold was chosen using three criteria: (1) systematic increase in blood La (ATLa), (2) systematic increase in ventilatory equivalent for O2 with no change in the ventilatory equivalent for CO2 (ATVE/VO2), and (3) non-linear increase in expired ventilation graphed as a function of VO2 (ATVE). Thirteen trained male subjects performed an incremental cycle ergometer test to exhaustion in which the load was increased by 30 W every 3 minutes. Ventilation, gas exchange measures, and blood samples for La analysis were obtained every 3rd min throughout the test. In five of the thirteen subjects tested the anaerobic threshold determined by ventilatory and gas exchange alterations did not occur at the same VO2 as the ATLa. The highest correlation between a gas exchange anaerobic threshold and ATLa was found for ATVE/VO2 and was r = 0.63 (P less than 0.05). These data provide evidence that the ATLa and ATVE do not always occur simultaneously and suggest limitations in using ventilatory or gas exchange measures to estimate the ATLa.
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PMID:Precision of ventilatory and gas exchange alterations as a predictor of the anaerobic threshold. 653 32

Twenty-four patients suffering from chronic obstructive pulmonary disease (COPD) exercised on a bicycle with a progressive increase in load (30 W/min) until dyspnea or exhaustion occurred. Seven subjects were CO2 retainers: PaCO2 greater than or equal to 45 mm Hg at rest and/or during exercise. Fifteen normal subjects were submitted to the same protocol. To make comparison possible, all the parameters studied were calculated at 60 watts. It was concluded that CO2 retention during exercise is not secondary to a decreased respiratory drive but mainly to a lesser increase in VE and to higher VD/VT ratios.
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PMID:Control of breathing during exercise in patients with chronic airflow limitation with or without hypercapnia. 662 8

Six subjects pedaled a stationary cycle ergometer to exhaustion on three separate occasions while breathing gas mixtures of 17, 21, or 60% O2 in N2. Each subject rode for 3 min at work rates of 60, 90, 105 W, followed by 15-W increases every 3 min until exhaustion. Inspired and expired gas fractions, ventilation (V), heart rate, and blood lactate were measured. O2 uptake (VO2) and CO2 output (VCO2) were calculated for the last minute of each work rate; blood samples were drawn during the last 5 s. "Break points" for lactate, V, VCO2, V/VO2, and expired oxygen fraction (FEO2) were mathematically determined. VO2 was not significantly different at any work rate among the three different conditions. Nor did maximal VO2 differ significantly among the three treatments (P greater than 0.05). Lactate concentrations were significantly lower during hyperoxia and significantly higher during hypoxia compared with normoxia. Lactate values at exhaustion were not significantly different among the three treatments. Four subjects were able to work for a longer period of time during hyperoxic breathing. The variations in lactate accumulation as reported in this study cannot be explained on the basis of differences in VO2. The results of this research lend support to the hypothesis that differences in the performance of subjects breathing altered fractions of inspired oxygen may be caused by differences in lactate (or H+) accumulation.
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PMID:Lactate accumulation during incremental exercise with varied inspired oxygen fractions. 662 44

Twelve normal men performed 1-min incremental exercise tests to exhaustion in approximately 10 min on both treadmill and cycle ergometer. The maximal O2 uptake (VO2 max) and anaerobic threshold (AT) were higher (6 and 13%, respectively) on the treadmill than the cycle; the AT was reached at about 50% of VO2 max on both ergometers. Maximal CO2 output, heart rate, and O2 pulse were also slightly, but significantly higher on the treadmill. Maximal ventilation, gas exchange ratio, and ventilatory equivalents for O2 and CO2 for both forms of exercise were not significantly different. To determine the optimum exercise test for both treadmill and cycle, we exercised five of the subjects at various work rate increments on both ergometers in a randomized design. The treadmill increments were 0.8, 1.7, 2.5, and 4.2%/min at a constant speed of 3.4 mph, and 1.7 and 4.2%/min at 4.5 mph. Cycle increments were 15, 30, and 60 W/min. The VO2 max was significantly higher on tests where the increment magnitude was large enough to induce test durations of 8-17 min, but the AT was independent of test duration. Thus, for evaluating cardiopulmonary function with incremental exercise testing by either treadmill or cycle, we suggest selecting a work rate increment to bring the subject to the limit of his tolerance in about 10 min.
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PMID:Optimizing the exercise protocol for cardiopulmonary assessment. 664 91


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