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

Variations of intracellular concentrations of isocitrate and NADP+ were measured throughout all growth phases of the marine bacterium Pseudomonas nautica. The intracellular isocitrate concentration tracked the intracellular protein concentration throughout all phases of growth. It rapidly increased in early exponential phase to a maximum and fell to nearly zero in parallel with pyruvate exhaustion in the culture medium. The intracellular NADP+ and protein concentrations increased in parallel during the exponential phase but were poorly correlated. Even after carbon exhaustion, the intracellular NADP+ concentration stayed high, as did protein levels. The results demonstrated that the intracellular isocitrate concentration, but not the intracellular NADP+ concentration, was affected by the carbon availability in the culture. They also suggest that, because of its variability, isocitrate, but not NADP+, plays the larger role in the control of the respiratory CO2 production rate (RCO2). From initial rate studies, bisubstrate Michaelis constants and the dissociation constant were determined for NADP+-specific isocitrate dehydrogenase (IDH) from P. nautica. These studies support the hypothesis that the mechanism of IDH's activity involves the ordered addition of the substrates, D-isocitrate and NADP+. Furthermore, the results support the use of a bisubstrate enzyme kinetic equation to model RCO2 in P. nautica.
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PMID:NADP-Isocitrate dehydrogenase from Pseudomonas nautica: kinetic constant determination and carbon limitation effects on the pool of intracellular substrates. 983 89

Work capacity and cardiopulmonary performance were studied in a group of 11 young obese subjects (BMI 39.9 kg/m2) and a group of 10 young normal subjects (BMI 22 kg/m2). First of all they underwent an incremental cycle ergometer test up to exhaustion. Subsequently, every subject of the two groups performed a constant work rate test at different work loads to estimate cardiac output (Q) below anaerobic threshold (AT) by a 20-second CO2 rebreathing method. Obese subjects had a significantly lower AT (79 vs. 109 W). The ratio between oxygen uptake and heart rate (VO2/HR) (O2 pulse) was higher in the obese group; nevertheless, this variable became significantly lower if we took into consideration the ratio between O2 pulse and kilogram fat-free body mass or kilogram body weight. Both these observations suggest that their reduced work tolerance is linked with a reduced oxygen supply to the muscles in activity. Q increased in similar ways in obese and normal subjects at the preset work rates. The ratio Q/body surface (cardiac index; CI) that we considered in order to try to minimize the differences in body sizes between the two groups, increased less in response to increasing work rates in our obese subjects than in normal subjects. As a whole, these data appear to be in line with a relatively less efficient cardiac performance during progressive work rates in obese subjects.
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PMID:Oxygen uptake and cardiac performance in obese and normal subjects during exercise. 997 87

Breathing frequency (fb), tidal volume (VT), and respiratory timing during slow (SR, 8 W min-1) and fast (FR, 65 W min-1) ramp exercise to exhaustion on a cycle ergometer was examined in seven healthy male subjects. Expiratory ventilation (VE), pulmonary gas exchange (VO2 and VCO2) and end-tidal gas tensions (PET,O2 and PET,CO2) were determined using breath-by-breath techniques. Arterialized venous blood was sampled from a dorsal hand vein at 2 min intervals during SR and 30 s intervals during FR and analysed for arterial plasma PCO2 (PaCO2). PET,CO2 increased with increasing work rates (WRs) below the ventilatory threshold (VT); at WRs > or = 90% VO2,max, PET,CO2 was reduced (P < 0.05) below 0 W values in SR but not in FR.fb and VT were similar for SR and FR at all submaximal WRs, resulting in a similar VE. At exhaustion VE was similar but fb was higher (P < 0.05) and VT was lower (P < 0.05) in SR (fb, 51 +/- 10 breaths min-1; VT, 2590 +/- 590 ml) than in FR (fb, 42 +/- 8 breaths min-1; VT, 3050 +/- 470 ml). The time of expiration (TE) decreased with increasing WR, but there was no difference between SR and FR. The time of inspiration (TI) decreased at exercise intensities > or = VT; at exhaustion, TI was shorter (P < 0.05) during SR (0.512 +/- 0.097 s) than during FR (0.753 +/- 0.100 s). The TI to total breath duration (TI/TTot) and the inspiratory flow (VT/TI) were similar during SR and FR at all submaximal exercise intensities; at VO2,max, TI/TTot was lower (P < 0.05) and VT/TI was higher (P < 0.05) during SR (TI/TTot, 0.473 +/- 0.030; VT/TI, 5.092 +/- 0.377 l s-1) than during FR (TI/TTot, 0.567 +/- 0.050; VT/TI, 4.117 +/- 0.635 l s-1). These results suggest that during progressive exercise, breathing pattern and respiratory timing may be determined, at least at submaximal work rates, independently of alveolar and arterial PCO2.
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PMID:Breathing patterns during slow and fast ramp exercise in man. 1008 11

The effect of a COPD crisis on arterial blood gases, heart rate, lactate and indices of oxidative stress were investigated before, during and 1 h after a 'run up to fatigue' in 6 COPD horses. They were investigated twice, randomly: once in acute crisis (C) and once in clinical remission (R). Arterial and mixed venous blood samples were collected and analysed for partial pressures in O2 and CO2. The mixed venous blood was also analysed for plasma lactate (LA) and packed cell volume (PCV), as well as for indices of oxidative stress, i.e. reduced glutathione, glutathione disulphide, glutathione redox ratio (GRR) and lipid hydroperoxides (LPH). The exercise test was an effort of increasing intensity on a treadmill at 0% slope, which was stopped when the horses showed signs of exhaustion. Their performance was evaluated by the number of steps and the running time in the last step. Heart rate was monitored continuously during the test. Blood sampling was performed before, just after and 1 h after the end of the test. The COPD crisis significantly reduced the time to fatigue. However, despite the fact that the exercise intensity and length were lower, peak HR and peak LA were similar in C and R, while arterial hypoxaemia and hypercapnia, and PCV were significantly higher in C, indicating a higher physiological stress in this condition. By contrast, the oxidative stress seemed to be higher in R than in C as suggested by the fact that, 1 h after exercise, GRR and LPH were significantly increased with regards to their pre-exercise values in R and not in C. The fact that exercise did not induce an oxidative stress in C could be partly related to (1) the lower exercise intensity reached by the horses, and (2) to the more severe hypoxaemia experienced in this condition. In conclusion, COPD horses in acute crisis show a significant decrease in performance. The reasons for this exercise intolerance remain unclear, but do not appear to be related to any increase of the oxidative stress in C.
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PMID:Cardiorespiratory measurements and indices of oxidative stress in exercising COPD horses. 1065 28

The so-called excess-CO2 in physical exertion results stoichiometrically directly from the quantity of protons bound in bicarbonate buffering. This situation is used in determining the ventilatory threshold (VT). However, the extent to which the degree and increase characteristics of excess-CO2 can be used as an equivalent to blood lactate concentrations is uncertain. To investigate this relationship, 21 healthy men exercised on a cycle ergometer (starting at 50 watt, increases of 50 watt every 3 minutes) to subjective exhaustion. To evaluate the characteristics of this increase, a slope constant lambda was calculated in relation to performance for both the blood lactate concentration (lambda lactate) and the cumulated excess-CO2 (lambda CO2 excess). The start of the lactate increase (LT) and excess-CO2 (VT) showed good intercorrelation (VT=2.27+0.98 x LT; r=0.914; P<0.001). Mean lambda lactate and lambda CO2 excess were of similar dimensions in all subjects (69.3 +/- 39.8 watt vs. 80.11 +/- 15.7 watt), but a minority of the subjects (n=7) showed a considerably more gradual increase for the excess-CO2 to the maximum. Since in addition there was no significant correlation between the absolute values for maximum lactate concentrations and the cumulative excess-CO2, an interindividual prediction of lactate concentrations from the excess-CO2 would be difficult. It is an open question, however, whether perhaps additional performance-limiting factors, such as the ventilation or the buffering capacity, may be included when measuring the excess-CO2 so that this parameter could be more a measure for the formation rate of new lactate than the blood lactate concentration alone.
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PMID:Increase characteristics of the cumulated excess-CO2 and the lactate concentration during exercise. 1096 17

The aim of this longitudinal study was to analyze the changes in several metabolic and neuromuscular variables in response to endurance training during three defined periods of a full sports season (rest, precompetition and competition). The study population was formed by thirteen professional cyclists (age +/- SEM: 24+/-1 years; mean V(O2 max) approximately 74 ml kg(-1) min(-1)). In each testing session, subjects performed a ramp test until exhaustion on a cycle ergometer (workload increases of 25 W min(-1)). The following variables were recorded every 100 W until the tests: oxygen consumption (V(O2) in l min(-1)), respiratory exchange ratio (RER in V(CO2) V(O2)(-1)) and blood lactate, pH and bicarbonate concentration [HCO3(-)]. Surface electromyography (EMG) recordings were also obtained from the vastus lateralis to determine the variables: root mean square voltage (rms-EMG) and mean power frequency (MPF). RER and lactate values both showed a decrease (p<0.05) throughout the season at exercise intensities corresponding to submaximal workloads. In contrast, no significant differences were found in mean pH or [HCO(3-)]. Finally, rms-EMG tended to increase during the season, with significant differences (p<0.05) observed mainly between the competition and rest periods at most workloads. In contrast, precompetition MPF values increased (p<0.05) with respect to resting values at most submaximal workloads but fell (p<0.05) during the competition period. Our findings suggest that endurance conditioning induces the following general adaptations in elite athletes: (1) lower circulating lactate and increased reliance on aerobic metabolism at a given submaximal intensity, and possibly (2) an enhanced recruitment of motor units in active muscles, as suggested by rms-EMG data.
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PMID:Metabolic and neuromuscular adaptations to endurance training in professional cyclists: a longitudinal study. 1101 88

The pulmonary ventilation-O2 uptake (VE-VO2) relationship during incremental exercise has two inflection points: one at a lower VO2, termed the ventilatory threshold (VT); and another at a higher VO2, the respiratory compensation point (RCP). The individuality of RCP was studied in relation to those of the chemosensitivities of the central and peripheral chemoreceptors, which were assessed by resting estimates of hypercapnic ventilatory response (HCVR) and hypoxic ventilatory response (HVR), respectively, and the rate of lactic acid increase during exercise, which was estimated as a slope difference (delta slope) between a lower slope of VCO2-VO2 relationship (VCO2:CO2 output) obtained at work rates below VT and a higher slope at work rates between VT and RCP. Twenty-two male and sixteen female subjects underwent a 1 min incremental exercise test until exhaustion, in which VT, RCP and delta slope were determined. All measures were normalized for body surface area. In the males, the individual difference in RCP was inversely correlated with those of HVR and delta slope (p < 0.05), and in the females, similar tendencies persisted, while the correlation did not reach statistically significant levels (0.05 < p < 0.1). There was no significant correlation between RCP and HCVR in either sex. A multiple linear regression analysis showed that 40 to 50% of the variance of RCP was accounted for by those of HVR and delta slope, both of which were related linearly and additively to RCP, this relation being manifested in the males but not in the females without consideration of the menstrual cycle. These results suggest that the individuality of RCP depends partly on the chemosensitivity of the carotid bodies and the rate of lactic acid increase during incremental exercise.
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PMID:Respiratory compensation point during incremental exercise as related to hypoxic ventilatory chemosensitivity and lactate increase in man. 1108 44

We previously observed an increase in minute ventilation (V E) with resistive unloading (He-O2 breathing) in healthy elderly subjects with normal pulmonary function. To investigate the effects of resistive unloading in elderly subjects with mild chronic airflow limitation (FEV(1)/FVC: 61 +/- 4%), we studied 10 elderly men and women 70 +/- 3 yr of age. These subjects performed graded cycle ergometry to exhaustion, once breathing room air and once breathing a He-O2 gas mixture (79% He, 21% O2). V E, pulmonary mechanics, and PET(CO2) were measured during each 1-min increment in work rate. Data were analyzed by paired t test at rest, at ventilatory threshold (VTh), and during maximal exercise. V E was significantly (p < 0.05) increased at VTh (3.4 +/- 4.0 L/min or 12 +/- 15% increase) and maximal exercise (15.2 +/- 9.7 L/min or 22 +/- 13% increase) while breathing He-O2. Concomitant to the increase in V E, PET(CO2) was decreased at all levels (p < 0.01), whereas total work of breathing against the lung was not different. We concluded that V E is increased during He-O2 breathing because of resistive unloading of the airways and the maintenance of the relationship between the work of breathing and exercise work rate.
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PMID:Breathing He-O2 increases ventilation but does not decrease the work of breathing during exercise. 1131 48

The aim of this study was double: to compare two different incremental stress protocols and to obtain reference values for a standardised exercise test in healthy workers. Firstly, eighty healthy male workers, 40 coal miners and 40 hospital workers, aged 19-54, performed in 2 different days 2 cycle ergometer tests up to exhaustion, increasing the work load respectively by 30 watts every 3 minutes (protocol A) and by 30 watts each minute (protocol B). Ventilatory and gas exchange measurements were done by a breath-by-breath apparatus equipped with a turbine and fast gas analysers for O2 and CO2. For each test the ventilatory anaerobic threshold (VAT) was blindly determined as oxygen uptake (V'O2 VAT) using standardised gas exchange and ventilatory indices (V'CO2, V'E, V'E/V'O2) that were found giving comparable results with those derived from the blood lactacte curve. Significant differences were observed between the two protocols only concerning the average work load at exhaustion and at the VAT: the highest being with the protocol B. Conversely, either the maximal oxygen uptake (V'O2 max) and the V'O2 VAT were comparable between protocols, as well as the other cardio-respiratory parameters were at these exercise levels. Oxygen uptake and heart rate increased in average linearly with the work load with very similar slopes in both protocols. Comparable results between protocols were found also as what concerns the slopes of the other physiological variables (V'E, V'CO2) analysed against the V'O2, particularly for exercise levels lower or equal to the individual VAT. Thus, these results suggest a very good comparability between the two protocols, concerning both the levels of maximal and sub-maximal aerobic capacity (V'O2 max, V'O2 VAT) and the cardio-respiratory pattern related to the oxygen uptake. Reference values for the 30 watts/3 minutes cycle ergometer stress test were achieved in other 320 healthy Sardinian workers concerning both the maximal (V'O2 max) and sub-maximal (V'O2 VAT) aerobic capacity and the range of normality for the cardio-respiratory pattern during the test, particularly for completely aerobic work loads, namely work loads not above the V'O2 VAT. These prediction equations can be useful for the evaluation of working capacity of workers employed in manual jobs characterised by moderate-to-high dynamic energy expenditure.
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PMID:[Incremental stress test: comparison between protocols and cardiorespiratory reference values in healthy workers]. 1138 87

Shredded straw of Miscanthus was composted in 800-L boxes with different amounts of pig slurry added as nitrogen source. The impact of the different initial C/N ratios (11, 35, 47, 50, and 54) on the composting process and the end product was evaluated by examining chemical and microbiological parameters during 12 months of composting. Low initial C/N ratios caused a fast degradation of fibers during the first three months of composting (hemicellulose: 50-80%, cellulose: 40-60%), while high initial C/N ratios resulted in 10-20% degradation of both hemicellulose and cellulose. These differences were reflected in the microbial biomass and respiration, which initially were higher in low C/N treatments than in high C/N treatments. After 12 months of composting, this situation was reversed. Composts with high initial C/N ratios had high microbial biomass (15-20 mg ATP g-1 OM) and respiration rates (200 mg CO2 h-1 g-1 OM) compared to treatments with low initial C/N ratios (less than 10 mg ATP g-1 OM and 25 mg CO2 h-1 g-1 OM). This could be explained by the microorganisms being nitrogen limited in the high C/N ratio treatments. In the low C/N ratio treatments, without nitrogen limitation, the high activity in the beginning decreased with time because of exhaustion of easily available carbon. Different nitrogen availability was also seen in the nitrification patterns, since nitrate was only measured in significant amounts in the treatments with initial C/N ratios of 11 and 35. The microbial community structure (measured as phospholipid fatty acid, PLFA, profile) was also affected by the initial C/N ratios, with lower fungal/bacterial ratios in the low compared to the high C/N treatments after 12 months of composting. However, in the low C/N treatments higher levels of PLFAs indicative of thermophilic gram-positive bacteria were found compared to the high C/N treatments. This was caused by the initial heating phase being longer in the low than in the high C/N treatments. The different fungal/bacterial ratios could also be explained by the initial heating phase, since a significant correlation between this ratio and heat generated during the initial composting phase was found.
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PMID:Influence of Initial C/N Ratio on Chemical and Microbial Composition during Long Term Composting of Straw. 1139 65


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