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Biomedical subjects

E T Howley

Publications and source records attributed to E T Howley.

54 records · Page 3Linked to original sources
PubMed1983

Effects of various levels of hypoxia on plasma catecholamines at rest and during exercise.

The purpose of this study was to investigate the relationship between hypoxia and heart rate (HR), pulmonary ventilation, plasma epinephrine (E) and norepinephrine (NE) at rest and during exercise at 40% of maximal oxygen uptake. Six subjects were exposed to inspired gas mixtures containing 21%, 19%, 17%, 15%, and 13% O2. The duration of exposure to each mixture was 10 continuous min at rest, followed by 10 continuous min during exercise. The order of the inspired gas mixtures was randomized. During the exercise test, HR was elevated with exposure to 15% and 13% O2 (p less than 0.001). Pulmonary ventilation was higher at 13% O2 than at the higher O2 percents (p less than 0.001). There were no significant changes in plasma E or NE at rest or during exercise in response to the gas treatments. These results indicate that acute exposure to hypoxic gas mixtures at rest and during light work does not result in significant increases in sympathetic nervous system activity, as judged by the plasma E and NE response.

Adult↗
PubMed1982

A differential catecholamine response during prolonged exercise and passive heating.

Plasma catecholamines (Ca) increase over time during prolonged exercise at a constant work rate. Possible reasons for this include hypoglycemia, dehydration, increased perceived exertion, and rising body temperature. In an effort to ascertain the contribution of elevated core temperature on the plasma Ca response to prolonged exercise four trained men were studied under two thermal conditions during 45 min of bicycle exercise (approximately 60% Vo2max) and during passive heating. On one testing day each subject was heat-stressed during exercise wearing a nylon pullover shell and cotton pants, (heat stress treatment); on the second day fans were directed on the subjects exercising in a thermoneutral environment (fan treatment). The passive heating experiment was conducted in a hot water bath (41 degrees C). The exercise heat stress treatment produced a higher plasma norepinephrine (NE) concentration (P less than 0.05) in all subjects than the fan treatment. The plasma epinephrine (E) concentration was not significantly (P greater than 0.05) different during exercise in the heat stress treatment from that found during fan treatment. A rise in rectal temperature (Tre) during passive heating resulted in quantitatively small changes in plasma E and NE. The heat load combined with the exercise task produced an increase in plasma NE concentration greater than the sum of the values measured during exercise in the thermoneutral environment and passive heating. This suggested that the combination of stressors caused an augmentation of the sympathetic nervous system's response. Finally, the added heat load caused changes in plasma NE and little change in plasma E, suggesting a differential Ca response with heat stress.

Adult↗
PubMed1982

Change in plasma cAMP and catecholamines in men subjected to the same relative amount of physical work stress.

This study has shown, for the first time, that the change in plasma adenosine 3',5' cyclic monophosphate (cAMP), from accommodation or trough levels, correlates highly in both progressive and continuous work stress experiments with epinephrine (E) at 0.990 and 0.898, and norepinephrine (NE) at 0.954 and 0.927, respectively, in men subjected to the same relative, rather than absolute, stress levels. All three analytes increased significantly (p less than 0.05) by the time each subject had reached 80% of their Vo2 max in the progressive experiments and after working at 80% of their Vo2 max continuously for 10 min. In no case did plasma cAMP rise before the catecholamines. The possible significance of these observations to net perceived relative physiological stress are discussed.

Adult↗
PubMed1981

Efficiency of trained subjects differing in maximal oxygen uptake and type of training.

This study was undertaken to examine the relationship between energy expenditure and work rate on a bicycle ergometer in five sprinters and five distance runners who differed in maximal oxygen uptake (VO2max) and type of training. Each subject performed at work rates of 30, 60, 90, 120, and 150 watts (W). The relationship between energy expenditure and work rates was most accurately described by a quadratic curve for both groups: for sprinters, energy expenditure (kJ) = 11.57 + 0.1812 (W) + 0.00046 (W)2; for distance runners, energy expenditure (kJ) = 11.74 + 0.1386 (W) + 0.00060 (W)2. Delta efficiency (delta work accomplished divided by delta energy expended X 100%) decreased as work rate increased. Statistical analyses revealed no significant differences between groups in delta efficiency at the same work rate (P greater than 0.25) or at the same relative work rate (P greater than 0.75). These results suggest that differences in VO2max and/or type of training have little or no causal effect on the decrease in delta efficiency with increasing work rate. The observed decrease in delta efficiency may be due to increases in metabolism not directly related to the performance of the external work or to an increasing amount of unmeasured work as work rate increases on a bicycle ergometer.

Adult↗
PubMed1977

Preparation of matched reagents for use with the Scholander gas analyzer.

Scholander's method of gas analysis requires that the solutions for CO2 absorber, O2 absorber, and acid-rinse be matched in terms of water vapor tension throughout the analysis. Any difference in vapor pressure between either or both of the absorbing solutions and the indicator drop (composed of acid-rinse) will produce a measurable volume change which cannot be attributed to the presence of absorbable gases. This paper describes a practical and quantitative method for preparing reagents whose vapor pressures are matched. A fixed acid-rinse formulation was used throughout. A CO2 absorber prepared from 1.35 N KOH and an O2 absorber prepared from 0.76 N KOH were both matched in terms of vapor pressure with Scholander's acid-rinse solution. Analysis of atmospheric air provided a check on the accuracy of the technique. The values obtained were O2 20.94%, CO2 0.03%, and N2 (balance) 79.04%.

Carbon Dioxide↗
PubMed1977

Oxygen cost of running in trained and untrained men and women.

The purpose of this study was to compare the oxygen cost of running as it relates to speed of running among the following four groups: trained male distance runners, trained female distance runners, untrained but active men and women. Each subject was given a series of treadmill tests during which Vo2 was measured at submaximal work loads. The linear regression equation was utilized to compute the relationship between Vo2 and running speed for each groups. The results indicated that the rate of increase in Vo2 for a given increase in running speed could be represented as a straight line and was the same for all groups (P greater than .05). The trained male runners had a significantly lower Vo2 (P less than .05) than those of the other three groups at any measured speed. The trained females and untrained males had significantly lower Vo2s than the untrained females (P less than .05) at any of the given range of speeds. No significant differences were observed between the untrained mean and trained women (P greater than .05). It was concluded that there were differences in the oxygen cost of running not only between the trained and untrained groups but also between males and females.

Adult↗
PubMed1976

The effect of different intensities of exercise on the excretion of epinephrine and norepinephrine.

Anticipation of a potentially stressful situation can alter the activity of the sympathetic nervous system. The purpose of this study was to measure the effect of three different intensities of exercise on epinephrine (E) and norepinephrine (NE) excretion when the work test order was randomly assigned and the subjects were not informed of the test order. Six subjects exercised at work loads which averaged 49%, 65%, and 82% Vo2max. Each subject showed an increased rate of NE excretion as the work load increased. The differences among work loads were significant (P less than 0.01). The E response was less consistent. Two subjects showed the greatest rate of excretion at the lowest work load, and one subject showed no increase above his pre-exercise resting value. While NE excretion was closely related to the work load, factors other than exercise appeared to exert considerable influence on the rate of E excretion during exercise.

Adult↗
PubMedDate not supplied

Skeletal muscle fibre type and capillary density in college-aged blacks and whites.

The purpose of this study was to compare muscle fibre type proportions and capillary density in untrained, college-aged blacks (n = 14) and whites (n = 14). Both groups were similar in terms of peak oxygen uptake (VO2peak), measured during cycle ergometry (blacks: 42.6 +/- 4, whites: 44.3 +/- 4 ml.kg-1 min-1, mean +/- SD). Muscle samples were obtained from the quadriceps femoris (vastus lateralis) by the needle biopsy technique. Fibre type was determined by myosin ATPase stain (pH = 4.54) and capillaries were identified by amylase-periodic acid Schiff (PAS) stain. The percentage of type I, IIa, and IIb fibres in the blacks was 39.5 +/- 11.5, 40.0 +/- 8.4, and 22.8 +/- 9.8, respectively. In whites the percentage of type I, IIa, and IIb fibres was 44.9 +/- 8.5, 36.6 +/- 6.9, and 18.3 +/- 9.6, respectively. No significant differences were noted between the two racial groups for type I, IIa, or IIb fibres. Capillary density was 277 +/- 39/mm2 in the blacks compared to 289 +/- 32/mm2 in the whites. Capillary density was positively correlated to percentage of type I fibres (r = 0.497) and negatively correlated to percentage of type IIa fibres (r = -0.389), in the overall study population. These data suggest that if racial differences in fibre type do exist, such differences are small compared to the variability in this measure.

Adolescent↗
PubMedDate not supplied

Cardiovascular and plasma catecholamine response to static exercise in normotensive blacks and whites.

OBJECTIVES: The objectives of the present study were (1) to evaluate the pressor response to an isometric handgrip exercise in normotensive black and white males; (2) to measure plasma catecholamine levels pre- and post-exercise, as an index of sympathetic nervous system activity; and (3) to quantify the pressor response to bolus intravenous injections of phenylephrine (an alpha-specific agonist). METHODS: Cardiovascular and catecholamine responses to an isometric handgrip exercise (3 minutes at 30% MVC) were measured in 15 normotensive blacks and whites. In another phase of the study, pressor responses to bolus injections of phenylephrine were assessed to evaluate alpha-adrenergic sensitivity. RESULTS: The blood pressure in the blacks increased from 119/69 to 160/120 mm HG during isometric exercise, while in the whites it increased from 118/67 to 153/110 mm HG. The blacks exhibited a greater diastolic blood pressure reactivity, as evidenced by a significant race x time interaction (p < 0.05). The heart rate responses were not significantly different between the two groups. The plasma levels of norepinephrine were similar at rest, but were 25% lower in the blacks than in the whites following isometric exercise (p < 0.01). Black subjects also demonstrated an increased pressor response to intravenous injections of phenylephrine at rest (p < 0.05). CONCLUSIONS: The enhanced vascular sensitivity to norepinephrine may have contributed to the greater exercise pressor response in the blacks.

Adrenergic alpha-Agonists↗