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Biomedical subjects

K C Light

Publications and source records attributed to K C Light.

At least 73 records · Page 4Linked to original sources
PubMed1990

Temporal stability of the hemodynamics of cardiovascular reactivity.

Cardiovascular responses to a competitive reaction-time task were monitored in 13 male subjects tested twice, 3 months apart. The temporal stability of blood pressure responses was in line with previous reports. However, in this study impedance cardiography permitted the investigation of the hemodynamic adjustments underlying the observed blood pressure responses. Analyses revealed that cardiac output and total peripheral resistance responses displayed temporal stability, indicating that subjects' blood pressure responses on the two occasions were the result of similar hemodynamic responses. These data thus extend the literature by demonstrating that the hemodynamic response pattern itself represents a stable individual difference variable.

Adult↗
PubMed1990

Hemodynamics of blood pressure responses during active and passive coping.

This laboratory study was designed to address a number of interrelated issues regarding cardiovascular reactivity to psychological stress. One objective was to extend the previous research comparing cardiovascular responses during active versus passive coping, by comparing responses to two task conditions designed to be similar in all ways except the opportunity to make a response influencing the task's outcome. A second objective was to compare responses to two different passive film tasks, which differed in outcome uncertainty and the degree of vicarious active coping achieved through identification with the role portrayed by the actors. A third objective was to evaluate whether individuals are predisposed to exhibit a particular hemodynamic pattern underlying their blood pressure adjustments, independently of the task demands imposed. Ninety healthy young adult male subjects were tested in pairs on a series of tasks that included a competitive reaction-time task, an active as well as a passive phase of a team reaction-time task, and passive viewing of two film segments. The tasks demanding active coping responses tended to raise blood pressure due primarily to an increase in cardiac output, while vascular resistance fell. During passive coping demands cardiac output increased to a lesser extent, but vascular resistance also tended to increase, thereby raising blood pressure by their synergistic effects. However, these patterns were not typical of all participating subjects. On the basis of their cardiac output and vascular resistance responses to the competitive reaction-time task, one third of the subjects were categorized as being high myocardial reactors (n = 30) and another third high vascular reactors (n = 31). Post-hoc analyses of responses to the other tasks, based on these categorizations, indicated that the hemodynamic basis of reactivity is an individual characteristic only partially modified by coping demands. The active/passive coping dimension is discussed both conceptually and in relation to the role of stress in the etiology of hypertension.

Adaptation, Psychological↗
PubMed1989

Cardiovascular responses in the laboratory and in the natural environment: is blood pressure reactivity to laboratory-induced mental stress related to ambulatory blood pressure during everyday life?

Cardiovascular activity recorded at rest and during mental stress in the laboratory was studied in relation to ambulatory recorded cardiovascular activity at work and at home. Fifty-five Type A men (M = 42.4 years) underwent a standardized laboratory mental stress protocol in which systolic blood pressure, diastolic blood pressure, and heart rate were recorded at baseline and during a 15 min mental arithmetic task (MAT). On a subsequent day, ambulatory blood pressure and heart rate were recorded at 20 minute intervals for 12-14 hr during normal activities at home and at work. Subjects completed a behavioral diary concurrently with each cuff inflation. High and Low groups were identified based upon a median split of their cardiovascular response levels at baseline and during the MAT. Subjects with high systolic blood pressure levels during the MAT had high systolic blood pressure at home, at work, during physical activity, and when they reported being 'stressed'. Baseline systolic blood pressure in the laboratory was less consistently related to ambulatory systolic pressure across ambulatory conditions. Diastolic blood pressure at baseline was related to ambulatory diastolic blood pressure at work, at home, and when resting. Diastolic blood pressure during the MAT was associated with higher diastolic pressure at work and at home. Heart rate at baseline and during the MAT was related to heart rate at work and during physical activity. Change scores derived by subtracting mean values during the MAT from baseline resting levels were not associated with ambulatory blood pressures or heart rates under any daily conditions. In the best case, systolic blood pressure measured during the MAT was related to systolic blood pressure during physical activity, to systolic blood pressure and heart rate during mental stress, to systolic and diastolic blood pressure at rest, and to systolic blood pressure and heart rate at work but not at home. We conclude that levels of blood pressure and heart rate measured in the laboratory, but not reactivity (i.e, change scores) during the MAT, are related to blood pressure and heart rate levels recorded in the natural environment, especially in the work setting.

Activities of Daily Living↗
PubMed1989

Race, borderline hypertension, and hemodynamic responses to behavioral stress before and after beta-adrenergic blockade.

Blood pressure (BP) and hemodynamic responses (cardiac output [CO] and total peripheral resistance [TPR]) to a competitive reaction-time task, previously shown to increase beta-adrenergic activity, were compared in 20 Black and 20 White young men, once following infusion of saline placebo and later repeated after infusion of the nonselective beta-antagonist, propranolol. Both racial groups included subjects with marginal systolic BP (SBP) elevations (n = 6 Whites, n = 5 Blacks) and subjects with normal BP (n = 14 Whites, n = 15 Blacks). Blacks with marginal SBP elevations showed greater diastolic BP increases during the stressor than their White counterparts, both before and after beta-blockade. Both Blacks and Whites with marginal SBP elevations showed greater CO increases during the task than normotensives prior to blockade. Independent of BP status, Black subjects consistently showed higher TPR responses to the task than Whites (lesser decreases before blockade and greater increases after blockade). Blacks also showed greater diminution than Whites after blockade in ionotropic myocardial responses (stroke volume, pre-ejection period, and CO) to the stressor. The possible contributions of alpha-adrenergic and beta-adrenergic influences to these racial group differences are discussed.

Adolescent↗
PubMed1988

Short-term behavioral effects of beta-adrenergic medications in men with mild hypertension.

beta-Adrenergic-inhibiting drugs are widely prescribed for the treatment of hypertension. These drugs have previously been found to influence a variety of psychologic and behavioral functions and have, in some cases, been associated with serious psychiatric side effects. The present study examined psychologic changes associated with beta-blockade therapy. Twenty-six men with mild hypertension (diastolic blood pressure 90 to 110 mm Hg) were randomly assigned to receive either a selective beta 1-antagonist (atenolol), a nonselective beta 1- and beta 2-antagonist (propranolol), or a placebo. Both before and after a 2-week period of drug administration, subjects completed a comprehensive assessment of quality of life including measures of mood, memory performance, and side effects. In general, beta-blocker therapy was associated with relatively few adverse symptoms, particularly when compared with control subjects taking placebo. Reductions in negative emotional states (tension and anger) were observed for subjects receiving atenolol, and the largest improvements in memory performance were observed for subjects receiving propranolol. These results suggest that beta-blocker therapy is not invariably associated with negative side effects and that some behavioral functions may actually be improved.

Adult↗
PubMed1987

Effects of race and marginally elevated blood pressure on responses to stress.

A total of 228 men, aged 18 to 22 years (109 black and 119 white), underwent monitoring of heart rate (HR) and systolic (SBP) and diastolic blood pressure (DBP) responses during several stressor conditions and a 30-minute posttask rest period. Stressors included the cold pressor test and three reaction-time tasks: noncompetitive, competitive, and competitive plus money incentive. Substantial within-subject variations in blood pressure and heart rate were induced, varying from 119/70 to 148/94 mm Hg and from 63 to 91 beats/min on the average. Men (25 black and 39 white) with marginal SBP elevations during initial casual determinations had higher SBP under all conditions compared with men whose casual SBP levels were normal, and they also showed greater elevations over baseline levels in heart rate, SBP, and DBP during the stressors and the initial casual determination. Black and white subjects did not differ in their blood pressures at baseline or during the initial casual determinations, although blacks had slightly lower heart rates. Blacks did show greater SBP elevations over baseline levels than whites during the stressors, primarily because the blacks with marginally elevated SBP showed substantially greater stress-induced increases than whites with marginally elevated SBP. This enhanced pressor response to stress in blacks with marginal blood pressure elevations may be due to higher vascular resistance during enhanced sympathetic activity and could contribute to the higher incidence of hypertension among blacks.

Adult↗
PubMed1987

Psychosocial precursors of hypertension: experimental evidence.

This article reviews key experimental studies concerning the possible contribution of behavioral stress to the development of primary hypertension. In animal preparations, chronic exposure to stressors in conjunction with predisposing genetic factors of high sodium/low potassium intake can lead to hypertension and cardiac pathology. Studies with human subjects are less definitive, but several lines of evidence suggest that high heart rate and blood pressure reactivity to behavioral stressors may indicate an increased susceptibility to hypertension, including an association between high reactivity and both borderline hypertension and a positive family history of hypertension, observations that stressors involving active coping evoke enhanced beta-adrenergic myocardial activity, resulting in cardiac output that is excessive relative to overall tissue oxygen consumption, and observations of decreased short-term sodium and fluid excretion during stressors in some individuals and an association between high salt intake and increased peak blood pressure levels evoked by exposure to stress. Indicated directions for future animal research include studies of the interactive effects of chronic stress with other environmental factors, such as high and low calcium intake, while in humans, future studies should incorporate monitoring of cardiovascular responses to real-life events, and should also include long-term follow-up investigations to evaluate more directly the predictive significance of high cardiovascular reactivity to stress.

Adaptation, Psychological↗
PubMed1986

Memory performance by mild hypertensives following beta-adrenergic blockade.

Previous experiments have reported deficits in cognitive performance following the administration of beta-adrenoceptor antagonists. These deficits have not appeared consistently, however, and it is not clear from previous studies whether changes in the central nervous system, rather than end-organ functioning, are responsible. The present experiment investigated the effects of beta blockade in a memory-search paradigm that distinguished the relatively central process of memory comparison from the more peripheral processes of stimulus encoding and response selection. Twenty-six adult men with mild essential hypertension received either a placebo or a beta blocker (atenolol or propranolol) for 2 weeks. Although beta blockade did occur in the active drug groups, there were no significant effects of the drugs on memory-search performance.

Adult↗
PubMed1984

Sex differences in cardiovascular stress responses: modulation as a function of menstrual cycle phases.

An experiment was conducted to study the effects of two laboratory stresses (unsignalled shock-avoidance reaction time and cold pressor tasks) on cardiovascular responses of young adult women during the follicular or the luteal phases of the menstrual cycle. A comparison group of male subjects, matched for family history of hypertension and for time between stress and rest sessions, was also tested. Results showed reduced cardiovascular responsiveness to the reaction time task (heart rate and blood pressure) for the women in the follicular phase of their cycle as compared with those in the luteal phase or with the males. Cardiovascular hyperresponsivity to this task has been previously related to familial history of hypertension. No differential changes were observed during the cold pressor test. These results are discussed in terms of possible hormonal effects on blood pressure regulation, and with respect to methodological considerations for assessing stress reactivity among women.

Adolescent↗
PubMed1984

Vasopressin and urine flow rate responses to stress in conscious dogs.

Behavioral stress increases arterial pressure while decreasing urine flow rate; the urine flow rate response can be abolished by surgical renal denervation. In this study, the effects of infusion of alpha-adrenoceptor antagonists (intravenous phenoxybenzamine or prazosin) on the antidiuretic and plasma vasopressin responses to stress were examined. Without alpha-adrenoceptor blockade, 20 min of stress increased arterial pressure and decreased urine flow rate, but no change in urine osmolality or plasma vasopressin concentration occurred. Arterial pressure and urine flow rate returned to base-line level during a 20-min recovery period. With alpha-adrenoceptor blockade, which prevented the arterial pressure response to stress, urine flow rate still decreased during stress, but urine osmolality and plasma vasopressin concentration increased. The decrease in urine flow rate and increase in urine osmolality and plasma vasopressin concentration persisted into the first 20-min recovery period but returned to base-line level during a second 20-min recovery period. We conclude that the antidiuretic response to behavioral stress in conscious dogs with saline infusion alone is not mediated via a change in vasopressin release. In contrast, the antidiuretic response to behavioral stress with alpha-adrenoceptor antagonist infusion may be mediated via an increased release of vasopressin.

Animals↗
PubMed1983

Psychological stress induces sodium and fluid retention in men at high risk for hypertension.

Exposure to competitive mental tasks significantly reduced the urinary sodium and fluid excreted by young men with one or two hypertensive parents or with borderline hypertension. In this high-risk group, the degree of retention was directly related to the magnitude of heart rate increase during stress, suggesting common mediation by way of the sympathetic nervous system. Thus, psychological stress appears to induce changes in renal excretory functions that may play a critical role in long-term blood pressure regulation.

Adolescent↗
PubMed1983

Neural control of renal excretory function during behavioral stress in conscious dogs.

The renal and neural mechanisms underlying the excretory response to behavioral stress (aversive conditioning) were examined in 30 conscious dogs. Twenty-one dogs decreased urine flow more than 20% during stress, whereas 9 dogs showed less than a 10% decrease. In 11 of the 21 renal-reactive dogs, decreases in urine flow (42%) and sodium excretion (45%) were associated with unchanged glomerular filtration (-1.5%; GFR; inulin clearance) and effective renal blood flow (-4%; RBF; p-aminohippurate clearance). In the other 10 renal-reactive dogs, similar declines in urine flow (54%) and sodium excretion (52%) occurred with decreases in GFR (24%) and RBF (27%). Among all 30 dogs, greater increases in cardiovascular activity during stress were associated with greater decreases in renal excretion. Surgical renal denervation abolished the excretory response to stress in 4 of 5 dogs. These findings suggest that excretory responses in most dogs are mediated 1) primarily via increased tubular reabsorption rather than decreased GFR, 2) via central integration with cardiovascular responses, and 3) via the renal nerves.

Animals↗