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Biomedical subjects

H G Welch

Publications and source records attributed to H G Welch.

At least 109 records · Page 6Linked to original sources
PubMed1983

Lactate accumulation during incremental exercise with varied inspired oxygen fractions.

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.

Adult↗
PubMed1982

Hyperoxia and human performance: a brief review.

The intent of this review was to examine the effects of hyperoxic gas mixtures on human performance. The evidence seems clear that performance is enhanced when O2-enriched gases are inhaled during exercise; however, the physiological mechanisms responsible for the improvement remain obscure. Increased pressure has a detrimental effect on performance, so that studies using hyperbaric oxygenation are ambiguous if the intent is to understand the effects of increased PO2. The large increases in maximal O2 uptake with hyperoxia reported in the literature may be erroneous because of problems encountered with the Douglas bag technique when gases with elevated O2 fractions are used. These apparent increases cannot be easily reconciled with published values for cardiac output and blood gas concentrations during exercise with hyperoxia. The effects of elevated PO2 are apparently widespread and, to a degree, independent; these include effects on pulmonary ventilation, on vascular smooth muscle, and on cellular metabolism. The available data do not lend strong support to the hypothesis that improvement in O2 delivery is responsible for the enhanced performance with hyperoxia. There are effects of hyperoxia on the pulmonary responses to exercise and on the acid-base responses. There is evidence that one or both of these mechanisms could play an important role in the changes in performance with hyperoxia.

Blood Gas Analysis↗
PubMed1981

Measurement of metabolic rate in hyperoxia.

The conventional Douglas bag calculation for estimating O2 uptake (VO2) during exercise in normoxia and hyperoxia, VO2 = VE . (FIO2 . FEN2/FIN2 - FEO2), was tested against two other valid calculations: the Fick equation, VO2 = VI . FIO2 - VE . FEO2, and the equation VO2 = VI - VE - VCO2 (VE and VI are expired and inspired ventilation, respectively; FEO2 and FIO2 are expired and inspired O2 contents, respectively; FEN2 and FIN2 are expired and inspired N2 contents, respectively; and VCO2 is CO2 production.). These calculations are based on different assumptions, in part, and are affected to a varying degree of errors in volume or gas fraction measurements. With the conventional Douglas bag technique, we found evidence of an overestimate of VO2 during hyperoxia. After the introduction of a mixing chamber for sampling expired air, the means of the three methods were not significantly different. The variability among the methods was least with the conventional calculation but increased with higher O2 fractions. The average VO2 for submaximal exercise in hyperoxia was not significantly different from that of normoxia. VO2 max was significantly higher in hyperoxia. The increased variability of the Douglas bag method in hyperoxia may lead to overestimates of VO2 max unless special precautions are taken.

Humans↗
PubMed1980

Oxygen uptake, acid-base status, and performance with varied inspired oxygen fractions.

Six subjects rode a bicycle ergometer on three occasions breathing 17, 21, or 60% oxygen. In addition to rest and recovery periods, each subject worked for 10 min at 55% of maximal oxygen uptake (VO2 max) and then to exhaustion at approximately 90% VO2 max. Performance time, inspired and expired gas fractions, ventilation, and arterialized venous oxygen tension (PO2), carbon dioxide tension (PCO2), lactate, and pH were measured. VO2, carbon dioxide output, [H+]a, and [HCO3-]a were calculated. Performance times were longer in hyperoxia than in normoxia or hypoxia. However, VO2 was not different at exhaustion in normoxia compared with hypoxia or hyperoxia. During exercise, hypoxia was associated with increased lactate levels and decreased [H+]a, PCO2, and [HCO3-]a. The opposite trends were generally associated with hyperoxia. At exhaustion, [H+]a was not different under any inspired oxygen fraction. These results support the contention that oxygen is not limiting for exercise of this intensity and duration. The results also suggest that [H+] is a possible limiting factor and that the effect of oxygen on performance is perhaps related to control of [H+].

Acid-Base Equilibrium↗
PubMed1980

Effects of varying concentrations of N2/O2 and He/O2 on exercise tolerance in man.

Hyperoxic gas mixtures improve exercise tolerance in humans. It is not clear whether this improvement is due to 1) a decreased anaerobiosis in the working cell, 2) a decreased cost of breathing resulting from the relative hypoventilation in hyperoxia, 3) the reduction of a possible metabolic depressant-N2, or a combination of these. This study made use of He/O2 breathing mixtures to gather data relative to #2 and #3, primarily. Ten subjects ran to exhaustion on a treadmill breathing one of four mixtures-20 O2/80 N2, 20 O2/80 He, 80 O2/20 N2, 80 O2/20 He. Running time to exhaustion, minute ventilation, respiratory frequency, tidal volume, and heart rate were measured. Performance increased significantly on hyperoxic mixtures (P < .001) and He/O2 mixtures (P < .001). Although the peak ventilatory volumes were higher on He/O2 mixtures, the ventilatory mass moved was significantly less (P < .001) on those mixtures conceivably resulting in a decreased cost of breathing. These data did not reject any of the hypotheses but offered the greatest support for hypothesis #2.

Adult↗
PubMed1978

Efficiency of anaerobic work.

This study was undertaken to compare the efficiency of aerobic and anaerobic work. Nine subjects worked at approximately 100% VO2 max for 2 min while inspiring gas mixtures with O2 fractions ranging from 0.13 to 0.21. Exercise O2 uptake, recovery O2 uptake, and blood lactate concentration were measured. Steady level O2 uptake was measured in normoxia at submaximal loads of about 30, 50, and 70% of VO2 max. Fast recovery O2 uptake did not change as PIO2 was varied. Exercise O2 uptake and blood lactate concentrations were linearly related to PIO2. The ratio of the slopes of these lines provided an empirical expression of the O2 equivalent of blood lactate. This ratio was constant, suggesting that it is not less efficient to use ATP synthesized anaerobically. Energy input from lactate was calculated using this factor. Efficiency decreased as power output increased even at the submaximal work rates. This may result from either 1) a decrease in muscle efficiency, 2) an increase in metabolism that is not directly related to the external work, or 3) some combination of 1 and 2.

Adult↗
PubMed1977

Effects of hyperoxia on leg blood flow and metabolism during exercise.

These experiments were designed to investigate the effects of O2 breathing on limb blood flow and metabolism during exercise. Six subjects took part in the study. Four subjects breathed air or 100% O2 while pedaling a Krogh bicycle at 150 W (55-70% of maximal aerobic capacity). Two subjects breathed either 60% or 100% O2 while working at a power output at or slightly in excess of their maximal aerobic capacities. The major findings of the study were 1) leg blood flow is reduced during exercise when comparing hyperoxia with normoxia; 2) VO2 of the exercising limb is not different during hyperoxia; 3) O2 delivery to the leg (the product of blood flow and arteriovenous O2 difference) is not significantly different in the two conditions; and 4) blood pressure is not markedly affected in the experiments at 150 W. Since BP was not different during hyperoxia, at a time when flow was reduced by 11%, this suggests an increased resistance to flow in the exercising limb. In general, these findings are consistent with those reported for the in situ dog muscle but are at variance with results of experiments with humans, especially the reports indicating substantial increases in O2 uptake during hypertoxic conditions.

Blood Glucose↗
PubMed1975

Effects of hyperoxic gas mixtures on energy metabolism during prolonged work.

These experiments were designed to study selected respiratory and metabolic responses to exercise in hyperoxia. Four subjects were examined during 30-min bicycle ergometer rides at both 40% and 80% of their aerobic maximum. The VO2 was significantly increased at both work levels breathing 60% O2 versus 21% O2, while VCO2 showed no significant change during the 40% exercise tests but was significantly decreased during the 80% intensity rides. The average increase in the volume of O2 taken up during 30 min of hyperoxic exercise, compared with normoxia, was 3.3 liters at the 40% exercise level and 5.6 liters at the 80% level. Neither the magnitude of the O2 nor the CO2 storage calculated for the exercise bouts could explain these increases. Steady-state criteria for the gas stores were established by the stable values of PETCO2, VO2, VCO2, and VI from minute 6 through 30 at both work levels. R values decreased during the hyperoxic tests suggesting the possibility of a shift toward increased fatty acid metabolism.

Adult↗
PubMed1975

Effects of hyperoxic gas mixtures on exercise tolerance in man.

This study was undertaken to determine the effects of O2-enriched gases on performance. Nine trained subjects ran to exhaustion on the treadmill on five different occasions breathing one of a range of hyperoxic gas mixtures--20%, 40%, 60%, 80%, or 100% O2. Each subject worked at a workload determined to be 110% of that necessary to elicit his maximum O2 uptake. The exercise bouts were scheduled one week apart to minimize the effects of training and fatigue. The subjects were given no cues as to the mixtures being breathed or to their running times. The parameters measured included running time, minute ventilation, and heart rate. The results indicate that the maximum performance time increases significantly as the O2 fraction of the gas is increased. Contrary to other published literature, 100% O2 increases performance significantly over 60% O2. Ventilation at any point in time is decreased when breathing hyperoxic mixtures. This decrease appears to be more a function of breathing frequency than of tidal volume. Terminal heart rates are not significantly different regardless of the O2 fraction of the inspired gas.

Adult↗