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Biomedical subjects

J A Davis

Publications and source records attributed to J A Davis.

At least 235 records · Page 13Linked to original sources
PubMed1981

A test to determine parameters of aerobic function during exercise.

A short-duration cycle ergometer exercise test has been developed that allows four parameters of aerobic function to be discerned. These are the maximum O2 uptake, anaerobic threshold, work efficiency, and the time constant for O2 uptake kinetics. The test form is a ramp of 4-8 min duration to the limit of tolerance. The parameters determined from the ramp faithfully reproduced those obtained from several standard procedures. We conclude that a profile of aerobic function in man can be obtained from a single short-duration ramp test.

Adult↗
PubMed1981

Effect of CO2 set point on ventilatory response to exercise.

The ventilatory response to exercise was determined in seven normal adults during induced chronic metabolic acidosis, chronic metabolic alkalosis, and a control state. Incremental and constant-load exercise tests were performed in each condition on a cycle ergometer. Ventilation and gas exchange variables were determined breath by breath, and CO2 partial pressure (PCO2), pH, and HCO3 were determined from arterialized venous blood (Pa-VCO2). During chronic metabolic acidosis PaVCO2 was lower than control (36.3 +/- 2.1 and 43.7 +/- 2.9 Torr, respectively) and during alkalosis it was elevated to 47.1 +/- 1.3 Torr. The new PCO2 levels caused by chronic acid-base alterations were unchanged during moderate exercise. The ventilatory response (VE) to the same metabolic rate increment was therefore larger (delta VE = 20.6 +/- 2.91/min) when PCO2 was lower than the control level (delta VE = 14.5 +/- 2.01/min. VE also increased more steeply in response to incremental exercise tests when PCO2 was reduced. Thus the hyperpnea of moderate exercise reflects the level at which arterial PCO2 is regulated at rest, as well as the metabolic load (VCO2).

Acidosis↗
PubMed1980

The relation of ventilation to metabolic rate during moderate exercise in man.

To characterize more precisely the relationship between ventilation (VE) and CO2 output (VCO2) during incremental exercise, 35 healthy males were studied at rest and during upright cycle ergometry, with the work rate incremented every 4 min up to each subject's anaerobic threshold (Oan). Twenty-one subjects had arterial blood sampled at rest and in the steady state at each work rate to determine the relationship between physiological dead space ventilation (VD) and VCO2. At these work rates arterial PCO2 was regulated at the resting, control value. VE (BTPS) was linearly related to VCO2 from rest Oan with a slope of 24.6. However, the regression had a significant positive intercept of 3.2 L/min-1. This causes the ventilatory equivalent for CO2 (i.e., VE/VCO2) to decrease with increasing work rates. VD also increased linearly with increasing VCO2. However, this was consequent to increased breathing frequency as VD remained constant. Thus, the observed fall in VE/VCO2 with increasing work rates is due to the positive intercept but the inherent relationship between VE and VCO2, reflected by the linear regression slope, remains unchanged from rest through moderate exercise.

Adult↗
PubMed1980

Physiological alterations consequent to 20-week conditioning programs of bicycling, tennis, and jogging.

This study investigated the efficacy of free-wheel bicycling and tennis as endurance conditioning activities. The subjects were 38 sedentary, middle-aged male volunteers, who were randomly assigned to one of four groups: bicyling (N=9); tennis (N=10); jogging (N=9); and control (N=10). Each subject was tested twice at the beginning and once at the conclusion of the 20-week study. Each training group exercised 3 days/week for 30 min/day, following 15 minutes of formal warm-up. The bicycling, tennis and jogging groups had an average attendance of 3.0, 2.7, and 2.8 days/week, and maintained theri exercise intensity at 83, 65, and 85% of HR max respectively. Using analysis of covariance, only the bicycle and jogging groups significantly increased treadmill Vo2max (14.8 and 13.3% respectively) even though there was a 5.7% improvement for the tennis group. The control group did not change. Vo2max was also assessed on a cycle ergometer for the bicycle and jogging groups, and increased significantly by 17.4 and 14.0% respectively, thus, specificity of the training response was not identified. VEmax increased significantly in the bicycling and jogging groups, while resting blood pressure did not change for any of the four groups. Relative to body composition, only the bicycle group increased lean body weight. The bicycle and jogging groups had substantial decreases in relative and absolute body fat, but these changes were not statistically significant due to changes in the control group. In conclusion, bicycling and jogging appear to provide comparable physiological benefits. Tennis produced only modest increases in endurance capacity but, since the duration of each training session was only 30 to 50% of a typical time period for playing tennis, the results of the present study may, in fact, be underestimating changes in Vo2max due to the interaction of intensity and duration in facilitating change.

Body Composition↗
PubMed1979

Case report 84.

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Aged↗