Biomedical subjects

W L Kenney

Publications and source records attributed to W L Kenney.

61 records · Page 4Linked to original sources

PubMed1985

Decreased core-to-skin heat transfer in mild essential hypertensives exercising in the heat.

In previous reports (1,2) we examined the physiological responses of normotensive and essentially hypertensive men to steady state leg exercise (at 40% V02max) in a warm (38 degrees C dry-bulb, 28 degrees C wet-bulb) environment. Those results are reviewed. Additionally, in this paper we report relative core-to-skin heat transfer (HT) characteristics of these two groups, matched for age, aerobic fitness, and body composition, but differing in resting blood pressure. Forearm skin blood flow (as measured from changes in total forearm blood flow) was relatively reduced in the hypertensives. This resulted in a similar (but slightly compensated) reduction in HT, e.g., at minute 30, the hypertensives had 81% less skin blood flow and 56% less HT than their normotensive counterparts. This finding has important implications for unmedicated mild hypertensives exercising or working in hot environments.

Adult↗

PubMed1984

Comparative physiological responses of normotensive and essentially hypertensive men to exercise in the heat.

Six essentially hypertensive men (average resting arterial pressure of 150/97 mm Hg) and eight normotensive controls (average resting arterial pressure of 115/73 mm Hg) were tested during 1 h of dynamic leg exercise in a warm environment. The groups were well matched for age, VO2 max, body surface area, weight, and body fat. Environmental conditions were 38 degrees C dry-bulb, 28 degrees C wet-bulb; exercise intensity was approximately 40% VO2 max (85-90 W). There were no significant intergroup differences in core or mean skin temperatures, calculated heat exchange variables, heart, or sweat rates. Blood pressure differences between the groups were maintained (P less than 0.01). The hypertensive group responded with a significantly lower stroke index (P less than 0.01) and cardiac index (P less than 0.01), and a decreased slope of the rise in forearm blood flow (P less than 0.01) due to an higher vascular resistance (P less than 0.01). The combined heat load (M + R + C) presented was not sufficient to override the hypertensives' higher cutaneous vasoconstrictor tone. However, on a practical basis, the hypertensives were able to tolerate exercise in the heat as well as their normotensive counterparts.

Adult↗

PubMed1984

Effect of mild essential hypertension on control of forearm blood flow during exercise in the heat.

Six essential hypertensive (resting mean arterial pressure, MAP greater than 110 mmHg) and eight normotensive (resting MAP less than 95 mmHg) men, aged 30-58 yr, were tested during 1 h of dynamic leg exercise in the heat. Environmental conditions were fixed at 38 degrees C dry-bulb temperature and 28 degrees C wet-bulb temperature; exercise intensity was preset to approximate 40% of each subject's maximal aerobic capacity (actual range 38-43%). Forearm blood flow (FBF) was measured by impedance plethysmography. The intergroup difference in arterial pressure was maintained but not increased or decreased during exercise in the heat. FBF increased in both groups, but the increase was significantly less for the hypertensive subjects. FBF showed a significant linear correlation (different from 0) with core temperature in seven of eight control subjects but in none of the hypertensive subjects. The magnitude of FBF increase was inversely proportional to resting MAP (r = -0.89). It was concluded that essential hypertensive subjects respond to exercise in the heat with a diminished FBF response related to an alteration in control relative to central (core temperature) influences. This may be due to an imbalance between thermal and nonthermal (baroreflex) mechanisms controlling cutaneous blood flow.

Adult↗

PubMedDate not supplied

Physical activity in human hypertension. A mechanisms approach.

The concept of treating hypertension without medication is seen as an attractive alternative to the problems that can arise with the use of drug therapy. Weight loss, salt restriction, relaxation therapy, and exercise have been the non-pharmacological treatments for hypertension. The role of long term exercise in lowering resting arterial pressure in hypertension, and its use as a non-drug therapy have been studied. Epidemiological studies of athletic ability, occupation, and leisure-time activities have provided equivocal findings and the effect of training on chronic high blood pressure of hypertensives is still unclear. Further well-controlled studies (with respect to training intensities, weight loss, concurrent hypotensive medication, salt restriction, and hypertensive classification), with an emphasis on elucidating the physiological mechanisms involved, are required so that the contribution of exercise to hypertensive therapy can be determined.

Blood Pressure↗

PubMedDate not supplied

Physiological correlates of heat intolerance.

Although wide interindividual variation exists with respect to heat tolerance, research has pointed out common physical and physiological characteristics which are associated with a decreased ability to adapt to an imposed (internal or external) heat load. While it is difficult to predict individual responses, it is often desirable, e.g. in an industrial environment, to screen out those suspected heat-intolerant persons. Included among the correlates of heat intolerance are a history of heat illness, previous difficulty in acclimating or reacclimating to the heat, low aerobic fitness level, age, hypertension, body size and composition (high adiposity, small size), and drug use (prescription and narcotic) and alcohol consumption.

Adrenergic beta-Antagonists↗

PubMedDate not supplied

Heat tolerance, thermoregulation and ageing.

Older individuals, regardless of how one classifies 'old', are the most rapidly growing portion of the population. Statistics from heat waves and other morbidity-mortality data strongly suggest that older persons are at greater risk of developing life-threatening manifestations of heat stress such as heat stroke. Most laboratory studies have found that ageing is associated with decreased heat tolerance and alterations in thermoregulatory effector responses. What is not so clear is the role of ageing per se in this decreased heat tolerance (as opposed to some concomitant functional decline, e.g. decreasing VO2max, which accompanies ageing across a population). Studies have shown decrements in resting heat tolerance and responses to thermal transients in older adults. With exercise in warm environments, most research has focused on the sweating response and it appears that whether or not sweating rate declines in the elderly is dependent upon the environment studied. In hot dry environments, older persons (of both sexes) consistently secrete sweat at a lower rate than their younger counterparts. However, as humidity of the environment increases, this difference tends to disappear. A key issue which deserves further attention is that of hydration in the elderly, both in terms of body water content and compartmentalisation, and of skin water content. Finally, ageing is often accompanied by other conditions (e.g. hypertension, diabetes, cardiovascular insufficiencies, long term therapeutic drug modalities) which further affect heat tolerance and thermoregulation.

Adult↗

PubMedDate not supplied

Changes in iron status during competitive season in female collegiate swimmers.

We examined changes in iron status in 25 female varsity collegiate swimmers over the course of a competitive season via weekly capillary blood sampling. We also studied the effectiveness of moderate iron supplementation (39 mg/day) in preventing expected changes in iron status via a double-blinded crossover design. On entry into the study, 17 of the swimmers had depleted iron stores (plasma ferritin < 12 micrograms/L) and 5 were anemic (Hb < 120 g/L). After 5 wk of placebo treatment, hemoglobin decreased (> or = 6 g/L) in 44% and increased in 12% of the subjects. After 5 wk of iron supplementation, hemoglobin decreased in 16% and increased in 24% of the subjects. Likewise, after placebo treatment, plasma ferritin decreased (> or = 5 micrograms/L) in 24% and increased in 4% of the subjects, whereas iron supplementation resulted in decreases in 4% and increases in 68% of the subjects. In the absence of iron supplementation, hemoglobin levels decreased despite mean dietary iron intakes of 16.3 mg/day. These results show that moderate iron supplementation is effective in preventing decline in the iron status of female collegiate swimmers during a competitive season, but a higher dose of iron may be necessary to reverse their iron-deficient state.

Adolescent↗