Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Controversy exists as to whether plasma volume (PV) expansion has the potential to increase maximal oxygen uptake (VO2max). In the present study, VO2max and exercise time to fatigue were measured in nine untrained men when plasma volume (PV) was normal and then again on the next day following two levels of PV expansion. Resting PV was expanded (via intravenous infusion of a 6% dextran solution) by 282 +/- 16 ml (i.e., PVX-1) and then by 624 +/- 26 ml (i.e., PVX-2). PVX-1 increased stroke volume (CO2 rebreathing) during submaximal exercise by 15% (P less than 0.05) above normal levels. VO2max following PVX-1 was increased 4% (P less than 0.05; 3.78 to 3.92 l/min) despite a 4% reduction in hemoglobin concentration. Exercise time to fatigue was also increased (P less than 0.05). PVX-2 resulted in an 11% (P less than 0.05) reduction in hemoglobin concentration during maximal exercise and a return of VO2max and exercise time to normal levels. In summary, we have observed in untrained men that 200-300 ml of PV expansion increases SV, measured during submaximal exercise, yet causes only a small amount of hemodilution. As a result, VO2max is increased slightly and performance is improved. Further PV expansion to levels 500-600 ml above normal results in an excessive hemodilution and a subsequent decline in VO2max and performance to normal levels. There is an optimal PV for eliciting VO2max in untrained men which appears to be approximately 200-300 ml above their normal levels.
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PMID:Maximal oxygen uptake relative to plasma volume expansion. 169 70

Dual chamber pacemaker programmability allows the possibility of atrially-tracked ventricular pacing in patients who would otherwise have intrinsic atrioventricular (AV) conduction. Thirteen patients with permanent AV sequential pacemakers (ages 50-79) were evaluated with paired exercise tests to determine the cardiopulmonary effects of pacemaker induced right ventricular activation compared with normal AV and intraventricular conduction. Peak oxygen uptake (VO2), oxygen pulse (O2P), respiratory rate (RR), and respiratory exchange ratio (RER) were determined using breath-by-breath analysis of expired gases. Patients exercised to fatigue and exercise tests were performed in random sequence. For patients with intrinsic AV conduction (group I, n = 8) the AV delay was programmed to preserve intrinsic conduction during one study; the alternate test used AV delay programming to produce ventricular pacing. Five patients with chronic AV block (group II) acted as a control for the effects of a rate adaptive AV delay compared to a fixed AV delay. Paired t-testing showed a significantly lower peak VO2 (P less than 0.015) and O2P (P less than 0.01) in patients with atrially-tracked ventricular pacing compared to intrinsic conduction. In contrast, group II showed a significant improvement in peak VO2 with rate adaptive AV delay compared to fixed AV delay programming (P less than 0.05). In conclusion, intrinsic conduction should be preserved in patients with dual chamber pacemakers whenever possible.
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PMID:Intrinsic conduction maximizes cardiopulmonary performance in patients with dual chamber pacemakers. 172 Nov 76

Inhibition of endogenous long chain fatty acids oxidation by tetradecylglycidate (TDGA) impeded gluconeogenesis from lactate or from low concentrations of pyruvate (less than 0.5 mM). The inhibitory effect of TDGA was overcome by medium and short chain fatty acid or by concentrations of pyruvate about 0.5 mM, but not by 10-fold higher concentrations of lactate. Despite decreased energy demand when gluconeogenesis was inhibited by TDGA, the pyruvate-induced increase in hepatic oxygen consumption was similar to the control, indicating that pyruvate transport across the mitochondrial membrane and/or its decarboxylation was not altered, and therefore can not be responsible for the inhibition of gluconeogenesis. Neither does a deficiency of acetyl-CoA explain the decrease in the gluconeogenic flux since high pyruvate loads (greater than 0.5 mM), beta-hydroxybutyrate or even ethanol was capable of overcoming the inhibitory effect of TDGA in the absence of significant changes in the hepatic content of acetyl-CoA. At low (less than 0.3 mM), presumably physiological, pyruvate concentrations, its rate of mitochondrial utilization is limited by the activity of the monocarboxylate transporter. Agents that reduced the mitochondrial NAD system, and therefore reduced flux through pyruvate dehydrogenase, like beta-hydroxybutyrate or ethanol, stimulated gluconeogenesis when fatty acid oxidation was inhibited. The latter observations indicate that the primary role of endogenous fatty acid, when substrate availability is limiting, is to spare mitochondrial pyruvate by decreasing its oxidation, and therefore shifting the partitioning between the carboxylation and decarboxylation reactions toward the former.
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PMID:Role of endogenous fatty acids in the control of hepatic gluconeogenesis. 172 53

To clarify the influence of body position on exercise prescription, 14 men (mean age +/- standard deviation 60.0 +/- 6.1 years) with coronary artery disease who underwent randomized recumbent and upright cycle ergometer tests to volitional fatigue were studied. At 100 watts, heart rate (HR), systolic blood pressure, oxygen consumption (VO2), rate pressure product and rating of perceived exertion were greater (p less than 0.05) in the upright than in the recumbent position. At peak exercise, however, these variables were not significantly different. Regressions of relative HR versus VO2 for recumbent and upright cycle ergometry were comparable: y = 1.24x - 32.7 and y = 1.26x - 31.5, respectively, where y = % maximal VO2, and x = % maximal HR. These findings indicate that recumbent exercise prescriptions may be based on the peak HR and VO2 values obtained during upright cycle ergometry, and vice versa. However, differences in the cardiorespiratory responses at submaximal exercise preclude the interchangeability of upright and recumbent training work rates.
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PMID:Physiologic responses to recumbent versus upright cycle ergometry, and implications for exercise prescription in patients with coronary artery disease. 172 65

The improvement in arterial blood gas tensions following assisted ventilation in chronic obstructive pulmonary disease (COPD) has usually been attributed to the relief of incipient or established respiratory muscle fatigue. The contribution of changes in the load placed upon and the drive to the respiratory muscle pump have not been evaluated. We have investigated the contribution of changes in respiratory muscle strength, the ventilatory response to CO2 and ventilatory function to changes in arterial blood gas tensions in eight patients with severe COPD completing six months domiciliary nasal intermittent positive pressure ventilation. Six patients showed a reduction and two an increase in arterial carbon dioxide tension (PaCO2), median (range) for eight patients, -0.9 kPa (-1.5 to +0.4) (p less than 0.05) and seven showed an improvement in arterial oxygen tension (PaO2), +0.7 kPa (-0.4 to +1.7) (p less than 0.05) during daytime spontaneous breathing. The reduction in PaCO2 was not related to increased inspiratory muscle strength but was correlated with a decrease in gas trapping (Spearman rank correlation coefficient (r(S)) 0.85, p less than 0.05) and in the residual volume (r(s) 0.78, p less than 0.05), suggesting reduced small airway obstruction and, therefore, a reduction in load. The change in PaCO2 also correlated with the increase in ventilation at an end-tidal CO2 of 8 kPa during rebreathing (r(s) -0.76, p less than 0.05) suggesting improved chemosensitivity to CO2. Our data do not support the hypothesis that improvements were due to the relief of muscle fatigue. We suggest that the contribution of changes in load and central drive warrant further investigation.
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PMID:Domiciliary nocturnal nasal intermittent positive pressure ventilation in COPD: mechanisms underlying changes in arterial blood gas tensions. 175 37

This review addresses current understanding of oxygen radical mechanisms as they relate to the brain during ischemia and reperfusion. The mechanism for radical production remains speculative in large part because of the difficulty of measuring radical species in vivo. Breakdown of lipid membranes during ischemia leads to accumulation of free fatty acids. Decreased energy stores during ischemia result in the accumulation of adenine nucleotides. During reperfusion, metabolism of free fatty acids via the cyclooxygenase pathway and metabolism of adenine nucleotides via the xanthine oxidase pathway are the most likely sources of oxygen radicals. Although leukocytes have been found to accumulate in some models of ischemia and reperfusion, their mechanistic role remains in question. Therapeutic strategies aimed at decreasing brain injury have included administration of radical scavengers at the time of reperfusion. Efficacy of traditional oxygen radical scavengers such as superoxide dismutase and catalase may be limited by their inability to cross the blood-brain barrier. Lipid-soluble antioxidants appear more efficacious because of their ability to cross the blood-brain barrier and because of their presence in membrane structures where peroxidative reactions can be halted.
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PMID:Oxygen radical mechanisms of brain injury following ischemia and reperfusion. 175 40

Given that individuals with disabilities may be unable to achieve maximal oxygen uptake in an exercise test and that maximal exercise testing may cause increased fatigue, pain, and muscle weakness, we examined the role of submaximal exercise testing and training based on objective as well as subjective parameters in polio survivors. Experimental (N = 7) and control subjects (N = 13) were tested before and after a 6-week period. The experimental subjects participated in a 6-week exercise training program for 30 to 40 minutes, three times a week. The program consisted of treadmill walking at 55% to 70% of age-predicted maximum heart rates; however, exercise intensity was modified to minimize discomfort/pain and fatigue. Neither objective nor subjective exercise responses were significantly different in the control group over the 6 weeks. No change was observed in cardiorespiratory conditioning in the experimental group. However, movement economy, which is related to the energy cost of walking, was significantly improved; and walking duration was significantly increased at the end of training. Modified aerobic training may have a role in enhancing endurance and reducing fatigue during activities of daily living in polio survivors.
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PMID:Effect of modified aerobic training on movement energetics in polio survivors. 175 91

The aim of physical exercise retraining in patients with chronic obstructive lung disease undergoing rehabilitation is to increase the anaerobic work capacity with a rise in VO2 max. Exercise programmes must take into account the duration, frequency and intensity of exercise. In these patients, numerous factors limit physical exercise, including (a) decreased ventilatory capacity and respiratory muscles fatigue; (b) decreased efficacy of the pulmonary gas exchanges; (c) altered pulmonary vascular bed with altered cardiovascular response. The most widely used training methods are walking (or running), practising on a conveyor belt and using an ergometric bicycle. The last named seems to be the best method to evaluate the physiological effects of exercise or for experimental studies. Patients who are fit to participate in a retraining programme must be in a stable period and have a stable pharmacological regimen; they must be subjected to a preliminary exercise test in order to evaluate the main physiological parameters and to obtain information on their tolerance to exercise, on the presence of lactic acidosis and on the degree of hypoxaemia and hypercapnia. In the absence of contra-indications, a training programme can be set up with 30 to 45 minutes of exercise per day at least 3 to 5 times a week during 5 to 8 weeks, with a load amounting to 50-60% of VO2 max. Two questions remain to be answered: (a) is oxygen therapy useful during retraining; (b) what effect has training on survival?
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PMID:[Indications and results of exercise rehabilitation in patients with chronic obstructive lung diseases]. 177 75

Pulse oximeters are being widely used for non-invasive, simultaneous assessment of haemoglobin oxygen saturation. They are reliable, accurate, relatively inexpensive and portable. Pulse oximeters are often used for estimating heart rate at rest and during exercise. However, at present the data available to validate their use as heart rate monitors are not sufficient. We evaluated the accuracy of two oximeters (Radiometer, ear and finger probe; Ohmeda 3700, ear probe) in monitoring heart rate during incremental exercise by comparing the pulse oximeters with simultaneous ECG readings. Data were collected on eight men (713 heart rate readings) during graded cycle ergometer and treadmill exercise to volitional fatigue. Analysis by linear regression revealed that general oximeter readings significantly correlated with those of ECG (r = 0.91, P less than 0.0001). However, comparison of heart rate at each level of work showed that oximeter readings significantly (P less than 0.05) under-estimated rates above 155 beats/min. These results indicate that the use of pulse oximeters as heart rate monitors during strenuous exercise is questionable. This inaccuracy may well originate from the instability of the probes, sweating, other artefacts during exercise, and measurement of different components in the cardiovascular cycle.
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PMID:Accuracy of pulse oximeters in estimating heart rate at rest and during exercise. 177 87

We used in situ gastrocnemius muscle of anaesthetized dogs to test the hypothesis that O2 radical production during muscle contraction contributes to fatigue. Muscle tension was measured with a force transducer and blood flow was monitored with an electromagnetic flow probe. Muscle contractions were produced by stimulating the nerve for 15 min at 20 Hz, 12 trains/min, and a duty cycle of 0.25. Three groups of seven animals were given an infusion of 0.2 mL.min-1 of either saline, low-dose oxygen radical scavengers (250 IU.mL-1 superoxide dismutase, 640 IU.mL-1 polyethylene glycol (PEG)-catalase, 0.25 mg.mL-1 deferoxamine, and 0.1 mg.mL-1 oxypurinol), or high-dose oxygen radical scavengers (3300 IU.mL-1 superoxide dismutase, 6600 IU.mL-1 PEG-catalase, 2.5 mg.mL-1 deferoxamine, and 0.1 mg.mL-1 oxypurinol). Blood flow and vascular resistance of the gastrocnemius muscle during stimulation did not differ among groups. After 15 min of stimulation, the developed tension (represented as a percentage of initial tension developed) was 66 +/- 7% in the saline treated group, 70 +/- 6% in the low-dose group, and 70 +/- 4% in the high-dose group. The change in tension during recovery was not significant in the control or low-dose groups. However, there was partial recovery in the high-dose group. In conclusion, in this preparation, oxygen radical scavengers did not delay the development of decreased muscle tension.
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PMID:Failure of oxygen radical scavengers to modify fatigue in electrically stimulated muscle. 177 47


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