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Biomedical subjects

W R Lovallo

Publications and source records attributed to W R Lovallo.

At least 19 recordsLinked to original sources
PubMed1992

Hemodynamic characteristics of young men at risk for hypertension at rest and during laboratory stressors.

Examined hemodynamic activity--at rest, during mental arithmetic, and during hand cold pressor--in young men varying in risk for hypertension. Classification into low-risk (n = 72), moderate-risk (n = 20), and high-risk (n = 13) groups was based on resting systolic blood pressure (SBP) and parental history of essential hypertension (PH). Dependent variables were SBP, diastolic BP (DBP), heart rate, and rate-pressure product (RPP). Progressively greater hemodynamic activity was seen across risk groups at rest and during the tasks. Risk groups differed significantly in SBP, DBP, and RPP at baseline (ps less than .003) and in size of response to mental arithmetic (ps less than .05) but not to cold pressor. These relationships were either absent or weaker when using either risk factor alone to form risk groups. These findings suggest that hemodynamic reactivity to mental stress is predicted better by a combination of resting SBP and PH than by either risk factor alone and that physiological reactivity may be an important accompaniment of increased risk for hypertension.

Adult↗
PubMed1992

Cardiovascular responses to occupational stress in male medical students: a paradigm for ambulatory monitoring studies.

Hemodynamic responses to systematic variations in occupational stress were examined using ambulatory blood pressure monitors (ABPMs). The goals of this study were (a) to illustrate the effectiveness of employing naturally occurring, controlled variations in psychological stress levels in studies incorporating ABPMs and (b) to document the patterns of cardiovascular responses to acute examination stress in medical students. Heart rate, systolic blood pressure, diastolic blood pressure, rate-pressure product, and mood states were measured before, during, and after low-stress (lecture) and high-stress (examination) work in 44 healthy male medical students. The lecture day was characterized by stable patterns of cardiovascular activity across all three periods. Hemodynamic activity and reports of activation and distress were greater on the examination day than on the lecture day. Cardiovascular activity during the preexamination period was as high as that seen during the examination period itself, indicating an anticipatory stress effect. Pressor activity decreased after the examination, although some residual chronotropic activity was seen. Systematic changes in physiological responses to controlled variations in the level of this naturalistic stressor support the use of this paradigm for other ABPM studies. The elevations in preexamination responses seen here suggest the need to consider prestressor experiences in such studies.

Achievement↗
PubMed1991

Psychophysiological activity and neuropsychological test performance in alcoholics.

This study examined electromyogram (EMG) and skin conductance level (SCL) as mediators of neuropsychological test performance of alcoholics. Alcoholics and controls with high EMG performed less well than low EMG subjects on 12 measures of neuropsychological performance. For SCL, the alcoholics and controls in the Low Group did not differ from those in the High Group on any measure. Analyses that used information intake (Low EMG and High SCL) and rejection (High EMG and Low SCL) information postures (IPs) demonstrated that the intake group outperformed the rejection group on 10 neuropsychological measures. Subjects with intake IPs reported more stimulation, concentration, and interest during the tasks than did subjects with rejection IPs. Results suggest that IPs can be used to identify alcoholics with neuropsychological deficits.

Alcoholism↗
PubMed1991

Antihypertensive efficacy of guanfacine and methyldopa in patients with mild to moderate essential hypertension.

Guanfacine, an alpha-2 adrenoceptor agonist, was compared with methyldopa as step-2 therapy for patients with mild-to-moderate essential hypertension in a 12-week, double-blind, randomized, parallel evaluation of efficacy and safety. The study consisted of a 2-week screening/weaning period (phase I), a 3-week treatment period with a diuretic (phase II), and a 12-week treatment period with a diuretic plus methyldopa or guanfacine (phase III). Patients were weaned from prior anti-hypertensive medication during the screening/weaning period and began receiving chlorthalidone 25 mg every morning. Patients received only 25 mg of chlorthalidone each morning during the phase II period. Those who had an average seated diastolic blood pressure (BP) of 95-114 mm Hg at the end of the phase II period were eligible to enter the phase III period and were randomly assigned to chlorthalidone plus guanfacine, 1 mg every night, or methyldopa, 250 mg tid. Seated and standing systolic and diastolic BP and pulses were measured biweekly for 12 weeks after randomization. Of the 112 patients who were randomly assigned to guanfacine or methyldopa, 87% completed the entire study. The mean seated systolic and diastolic BP were reduced 13/13 mm Hg by guanfacine administration and 15/13 mm Hg by methyldopa administration. No significant changes in seated pulse were seen in either group. Similar changes occurred in the standing position. Very few adverse effects were reported during the study, the most prevalent side effect was xerostomia (13% guanfacine, 9% methyldopa). No significant differences were observed between treatment groups for the incidence of cardiac arrhythmias after methyldopa or guanfacine administration was stopped.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Effects of caffeine on pressor regulation during rest and exercise in men at risk for hypertension.

Caffeine-induced blood pressure elevations are well documented in habitual consumers, occurring through both vasoconstrictive and cardiostimulatory actions. Whether caffeine hinders pressor regulation during exercise has been uncertain, particularly in those at risk for hypertension. Thus effects of caffeine versus placebo were studied during supine bicycle exercise in healthy men (ages 20 to 35). Hypertension risk was defined during screening: high risk (HRISK) = 135 to 154/85 to 94 mm Hg plus parental hypertension (n = 20); low risk (LRISK) = less than or equal to 132/84 mm Hg and no parental hypertension (n = 14). Exaggerated pressor responses (greater than or equal to 230/100 mm Hg) seen during exercise after placebo identified a subgroup of seven HRISKs indistinguishable at rest from the remaining HRISK men. This subgroup showed a larger resting diastolic response to caffeine (p less than 0.05) than LRISKs and other HRISKs. Compared with placebo, caffeine increased the number of LRISK (0% to 36%) and HRISK (35% to 50%) men reaching abnormal exercise blood pressures, and blunted normal increments in cardiac index at higher workloads among HRISK men (p = 0.05). Thus restriction of caffeine before exercise might benefit persons with either risk for hypertension or unusual sensitivity to caffeine.

Adult↗
PubMed1991

Hypertension risk and caffeine's effect on cardiovascular activity during mental stress in young men.

Examined the cardiovascular effects of caffeine plus behavioral stress in men low versus high in risk of essential hypertension. Caffeine (3.3 mg/kg, equivalent to 2 to 3 cups of coffee) or placebo was given on alternate days to 19 low-risk men (negative for parental hypertension and low-normal resting blood pressure, BP) and 20 high-risk men (positive history, high-normal BP). Forty minutes later, each worked for 15 min on a demanding psychomotor task during which BP, cardiac output, and vascular resistance were determined. During rest, caffeine raised vascular resistance in both groups. During the task, it supra-additively increased the systolic BP response by enhancing the rise in cardiac output, producing equivalent BP rises in both groups. Due to the higher resting pressures of the high-risk men, caffeine plus the task resulted in 50% of these having transient BP of 140/90 mg Hg or greater. Caffeine in combination with mental stress may produce undesirable BP in those at risk for hypertension.

Adult↗
PubMed1991

Heart rate reactivity, behavior pattern, and parental hypertension as predictors of cardiovascular activity during cognitive challenge.

Hemodynamic responses were studied during work on serial subtraction and digits backwards tasks in 99 healthy male undergraduates jointly classified as high or low heart rate reactors, Type A or Type B behavior pattern, and as having positive or negative parental history of hypertension. Heart rate, systolic blood pressure, and diastolic blood pressure were recorded, and rate pressure product was calculated at rest and during the tasks. High heart rate reactors to a cold pressor task responded with relatively higher heart rate and rate pressure product during both cognitive tasks than low heart rate reactors. Type A subjects defined by Jenkins Activity Survey did not differ from Type Bs on any of these physiological variables, although behavioral evidence demonstrated greater effort and superior performance by the Type As. Subjects with a positive parental history of hypertension manifested greater systolic and diastolic pressures and rate pressure product responses to the cognitive challenge than those lacking such parental history. These results indicate that the individual difference variables of heart rate reactivity and parental history of hypertension predicted different hemodynamic response patterns to behavioral challenge.

Adult↗
PubMed1991

Blood pressure dysregulation associated with alcohol withdrawal.

Alcoholics' blood pressures (BP) are typically elevated during withdrawal. Do such elevations predict future blood pressure dysregulation or are they simply a transitory effect of alcohol toxicity? Thirty-two patients admitted to the hospital for alcohol detoxification were tested to examine the relationship between admission BP and response to isometric handgrip administered 4 to 5 days (session 1) and 3 to 4 weeks (session 2) postdetoxification. Alcoholics were divided into three groups based on admission BPs: Hypertensive (HT, greater than or equal to 160/95 mmHg), Borderline Hypertensive (BHT, 140/90-159/94 mmHg), and Normotensive (NT, less than 140/90 mmHg). In sessions 1 and 2, the groups no longer differed on resting BP or heart rate (HR) but did differ on BP and HR response to handgrip: Compared with the NT group, the HT and BHT groups had greater rises in systolic and diastolic BP and HR. There was a trend for HT alcoholics to report a positive parental history of hypertension (91%) compared to BHT and NT alcoholics (64% and 60%, respectively), suggesting the existence of premorbid factors to this exaggerated cardiovascular response. Further, alcohol consumption, based on a quantity-frequency index, was significantly higher in the HT group than in the NT group. The results suggest that transitory elevations in blood pressure observed during alcohol withdrawal may predict future BP abnormalities.

Adult↗
PubMed1990

Exaggerated pressure response to exercise in men at risk for systemic hypertension.

Normotensive persons at high risk of developing systemic hypertension have greater cardiovascular reactivity to mental and physical stressors. This study compared cardiovascular responses to exercise in normotensive men (aged 28 +/- 0.8 years [mean +/- standard error of the mean]) at high risk (positive parental history and high normal resting blood pressure [BP], n = 20) and at low risk (negative history, low normal BP, n = 15) of hypertension. All men had normal body weight and exercise tolerance. During graded supine bicycle exercise, 35% (7 of 20) of high-risk men had exaggerated BP responses (greater than or equal to 230/100 mm Hg) versus 0% of low-risk men, thus forming 3 groups (low risk, high-risk normal BP response, high-risk exaggerated response). Cardiac function was measured by nuclear cardiography. Cardiac index, peripheral resistance index, left ventricular ejection fraction and contractility index were measured at rest and during each exercise work load. High-risk exaggerated responders could not be distinguished from their high-risk normal-responding counterparts using resting BP or other cardiovascular variables. During exercise all 3 groups had equivalent increases in cardiac output. However, the high-risk exaggerated responders had blunting in peripheral resistance decline, resulting in excessive BP increases. This finding suggests an impaired capacity for exercise-induced vasodilation, indicating that the exaggerated response group may be at highest risk for future hypertension in these 3 groups.

Adult↗
PubMed1990

Effects of caffeine on blood pressure response during exercise in normotensive healthy young men.

The possible combined effects of caffeine and exercise on blood pressure (BP) regulation were examined in 34 healthy, normotensive (BP less than 135/85 mm Hg) young men (mean age 27 +/- 3 years) in a placebo-controlled, double-blind crossover design. Each subject performed submaximal and symptom-limited maximal supine bicycle exercise 1 hour apart after ingestion of placebo or caffeine (3.3 mg/kg). Heart rate, BP, cardiac output and peripheral vascular resistance were compared for placebo and caffeine days. Postdrug baseline showed that caffeine increased systolic and diastolic BP and peripheral vascular resistance (p less than 0.001 for each) and decreased heart rate (p less than 0.01) but did not change stroke volume or cardiac output. BP and vascular resistance effects of caffeine remained during submaximal exercise resulting in an additive increase in BP while negative chronotropic effects of caffeine disappeared. At maximal exercise substantially more subjects (15 on caffeine vs 7 on placebo, p less than 0.02) had systolic BP greater than or equal to 230 mm Hg and/or greater than or equal to 100 mm Hg for diastolic BP. Plasma norepinephrine levels were not significantly different across days, but epinephrine was higher at maximal exercise and cortisol was increased post-drug and throughout maximal exercise on caffeine days. Data indicate that caffeine increases BP additively during submaximal exercise and may cause excessive BP responses at maximal exercise for some individuals. The pressor effects of caffeine appear to be due to increasing vascular resistance rather than cardiac output.

Adult↗
PubMed1990

Methodological guidelines for impedance cardiography.

Impedance cardiography was introduced over 20 years ago as a noninvasive and unobtrusive technique for measuring systolic time intervals and cardiac output. Although our understanding of the physiological events reflected in the impedance cardiogram has become more refined, the technique's theoretical basis remains somewhat controversial and acceptance of its validity has relied heavily upon empirical validation. Largely as a consequence of this status, there have been inadequate grounds on which to develop sound methodological standardization. Currently, the methodological approaches that have been most frequently adopted may be viewed as representing the standard. The various aspects of impedance methodology are discussed, and alternative approaches described, with the objective of providing an informed basis for choosing among these methodological alternatives. It is recommended that studies utilizing impedance cardiography should be reported with clear and detailed methodological description. This should help clarify the extent to which methodological differences may underlie any discrepant research observations, as well as facilitate the emergence of improved methodological standards.

Cardiac Output↗
PubMed1989

Simultaneous measurement of stroke volume by impedance cardiography and nuclear ventriculography: comparisons at rest and exercise.

UNLABELLED: We have conducted four major impedance cardiography (ZCG) studies to provide data on validity, reproducibility, and sensitivity of response to interventions. The reference technique was quantitative nuclear ventriculography (NVG). Subjects were healthy young men in situations where minimally invasive and unobtrusive techniques were preferred. Interventions used included caffeine ingestion and exercise. Validity of ZCG estimates of stroke volume index (SVI, ml/m2) was tested in 35 men at rest. SVI was 49 +/- 9 by ZCG and 46 +/- 7 by NVG (r = 0.82). Measurements of SVI during bicycle exercise showed no overall difference by the two methods (F = 0.26, P = NS). Vascular resistance index (mean BP/CI) increased comparably by both techniques (+9.6% by ZCG and +9.7% by NVG) following caffeine (3.3 mg/kg). The reproducibility of ZCG was demonstrated in the day-to-day consistency of caffeine's effect on vascular resistance in 3 other studies (+11.9%, 12%, and 8.9%). Reliability across and within days was shown by repeated tests in the same subjects (SVI, r's = .96, .92). CONCLUSION: Impedance cardiography was shown to be a useful noninvasive technique for evaluation of cardiodynamics in biomedical research since it was highly reproducible and yielded equivalent results of relative changes produced by pharmacological and physical challenge. In addition, there was good agreement with NVG in absolute values for grouped data.

Cardiography, Impedance↗
PubMed1989

Caffeine may potentiate adrenocortical stress responses in hypertension-prone men.

The effect of caffeine on blood cortisol levels and blood pressures was examined during rest and in response to a challenging psychomotor task in men with a low versus high risk of essential hypertension. Thirty-four healthy men ages 21-35 years were selected such that 17 were at high risk for hypertension (positive parental history and screening blood pressures of 135/85-155/95 mm Hg) and 17 were at low risk (negative parental history and no pressures above 132/84 mm Hg). Testing consisted of quiet rest (20 minutes); oral placebo (grapefruit juice) or caffeine administration (3.3 mg/kg in grapefruit juice); rest during a postdrug absorption period (40 minutes); work on an unsignalled simple reaction time task (15 minutes); and quiet rest (20 minutes). Blood pressures were recorded at 2-minute intervals, and blood samples were withdrawn via an indwelling catheter at the end of the baseline, drug absorption, task, and recovery periods. The combination of task plus caffeine produced the highest blood pressures in men at risk for hypertension. Cortisol levels were found to be sustained during rest in members of the high risk group after they had consumed caffeine, whereas members of the low risk group showed a modest decline. The high risk subjects also showed a significant rise in cortisol during (+3.7 micrograms/dl) and after (+4.0 micrograms/dl) work on the reaction time task after caffeine consumption.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗
PubMed1988

Effect of behavior state on caffeine's ability to alter blood pressure.

Caffeine use during exposure to mental stress is an extremely common occurrence. Because both have been shown to alter blood pressure (BP) and its underlying hemodynamic mechanisms, the potential exists for additive or even synergistic effects. Changes in heart rate, BP and noninvasive thoracic impedance measures of left ventricular function were examined in young men (ages 20 to 36) at rest and during a demanding behavioral task performed 40 minutes after predosing with caffeine (3.3 mg/kg, equivalent to 2 to 3 cups of coffee) or placebo in a double-blind crossover design. All subjects were healthy young men without history of cardiovascular disease, regular use of nicotine, recreational or prescription drugs or caffeine intolerance. Caffeine abstinence was required for 12 hours before each test session. Systolic and diastolic BP were elevated by both caffeine and the behavioral task alone (p less than 0.01 for each); when combined, caffeine's pressor effects were additive to those of the behavioral task. However, caffeine's pressor effect was produced by different mechanisms depending on the behavioral state. Caffeine increased systemic vascular resistance (p less than 0.01) under resting conditions, but it enhanced cardiac output (p less than 0.01) during behavioral arousal associated with the task. The combined influence of caffeine and the task increased the number of men in whom peak systolic BP reached hypertensive levels, and also synergistically increased cardiac minute work (p less than 0.01) and the rate-pressure product estimate of myocardial oxygen demand (p less than 0.05). Implications of these findings are discussed for long standing theoretical disputes regarding caffeine, its health consequences, and for methodologic issues in behavioral and clinical studies.

Adult↗
PubMed1987

Caffeine enhances the physiological response to occupational stress in medical students.

Caffeine (3.3 mg/kg) was tested against a placebo in 20 male medical students during periods of low (no exams) versus high (final exams) work stress. On each of 8 test days, heart rate and blood pressure were measured at baseline and over a 40-min postdrug interval; immediately afterward, blood was drawn to test plasma cortisol and serum lipid concentrations. Exams increased heart rate (p less than .005) and systolic blood pressure (p less than .02). Caffeine decreased heart rate (p less than .0001) and increased systolic blood pressure (p less than .005), diastolic blood pressure (p less than .0001), plasma cortisol levels (p less than .01), and serum cholesterol levels (p less than .02). Caffeine effects were additive with those of exams, and together they increased the number of men showing systolic blood pressures in the borderline hypertensive range. Thus, caffeine use during periods of increased occupational stress may enhance the cumulative stress response.

Adult↗
PubMed1987

Physiological responses of type A and type B men during cognitive performance.

Twenty male medical students classified as Type A or Type B solved a Concept Identification (CI) problem while measurements were taken on cardiovascular and somatic activity. The As produced significantly more overall electromyogram (EMG) activity and greater vasomotor activity than the Bs at baseline and during the task. Both Type As and Bs showed significantly higher levels of Heart Rate (HR), systolic and diastolic blood pressures, skin conductance, frontal EMG, and lower levels of vasomotor activity during work on the problem than during pre- and post-problem baselines. Type As showed significant negative correlations between total errors during CI and level of vasomotor activity, and between postsolution response latency and skin conductance. Type Bs showed a strong positive association between presolution response time and heart rate that did not hold for the As. The As appear to have shown sympathetic activation associated with quality of problem-solving performance, while the B's showed a relationship that suggested an impaired efficiency of performance associated with cardiac activation.

Adult↗
PubMed1979

Randomness and the "streaking" phenomenon: attentional anomalies in performance on the Whitaker Index of Schizophrenic Thinking (WIST).

Examined in detail the performance of 36 hospitalized male schizophrenics on the Whitaker Index of Schizophrenic Thinking (WIST). Results indicated two interesting phenomena. First, the performance of patients with the highest level of cognitive deficit approached a random level of responding with respect to both the type of error made and the propensity to improve after an error. Second, a subgroup of these highly impaired Ss, identified as "streakers," displayed periods of virtually error-free responding, interspersed with periods of extremely impaired performance. The streaking phenomenon, as well as the tendency toward randomness, was discussed in terms of attentional anomalies.

Adult↗