Biomedical subjects

G A Pincomb

Publications and source records attributed to G A Pincomb.

At least 19 recordsLinked to original sources

PubMed2000

Hypertension risk status and effect of caffeine on blood pressure.

We compared the acute effects of caffeine on arterial blood pressure (BP) in 5 hypertension risk groups composed of a total of 182 men. We identified 73 men with optimal BP, 28 with normal BP, 36 with high-normal BP, and 27 with stage 1 hypertension on the basis of resting BP; in addition, we included 18 men with diagnosed hypertension from a hypertension clinic. During caffeine testing, BP was measured after 20 minutes of rest and again at 45 to 60 minutes after the oral administration of caffeine (3.3 mg/kg or a fixed dose of 250 mg for an average dose of 260 mg). Caffeine raised both systolic and diastolic BP (SBP and DBP, respectively; P<0.0001 for both) in all groups. However, an ANCOVA revealed that the strongest response to caffeine was observed among diagnosed men, followed by the stage 1 and high-normal groups and then by the normal and optimal groups (SBP F(4),(175)=5.06, P<0.0001; DBP F(4,175)=3.02, P<0.02). Indeed, diagnosed hypertensive men had a pre-to-postdrug change in BP that was >1.5 times greater than the optimal group. The potential clinical relevance of caffeine-induced BP changes is seen in the BPs that reached the hypertensive range (SBP >/=140 mm Hg or DBP >/=90 mm Hg) after caffeine. During the predrug baseline, 78% of diagnosed hypertensive men and 4% of stage 1 men were hypertensive, whereas no others were hypertensive. After caffeine ingestion, 19% of the high-normal, 15% of the stage 1, and 89% of the diagnosed hypertensive groups fell into the hypertensive range. All subjects from the optimal and normal groups remained normotensive. We conclude that hypertension risk status should take priority in future research regarding pressor effects of dietary intake of caffeine.

Adult↗

PubMed1997

Men at risk for hypertension show elevated vascular resistance at rest and during mental stress.

Men at risk for development of hypertension may show elevated blood pressure at rest and during work on mental stressors. We examined which component of blood pressure, vascular resistance or cardiac output, accounted for raised blood pressures seen in a high-risk, normotensive sample. Parental history of hypertension and resting systolic blood pressures were used to categorize subjects into high (n = 19) and low (n = 14) risk groups. Blood pressure, heart rate, cardiac output, stroke volume, and vascular resistance were measured during rest, mental arithmetic, and reaction time. Compared to low risk subjects, the high risk men had significantly higher blood pressures accompanied by higher vascular resistances at rest and during mental stress. The groups had negligible differences in heart rate, stroke volume, and cardiac output. This pattern of results implicates vascular resistance as the dominant element in altered blood pressure control in these young men at high risk for hypertension.

Adult↗

PubMed1997

Cardiovascular and neuroendocrine adjustment to public speaking and mental arithmetic stressors.

In this study, we evaluated cardiovascular, neuroendocrine, and psychological adjustment to repeated presentations of a public speaking and a mental arithmetic task. Brief versions of mental arithmetic tasks have been used widely in previous reactivity studies, and growing attention to more socially salient tasks has led to the increased use of public speaking tasks. However, psychophysiological adjustment during extended and repeated exposure to these tasks has not been delineated. In the present study, 52 healthy men worked on three 8-min presentations of public speaking and of mental arithmetic in a repeated measure design. Both tasks produced substantial cardiovascular, adrenocorticotropic hormone, and cortisol responses; public speaking produced greater changes. Repeated presentations of public speaking produced a stable pattern of cardiac activation, whereas repetitions of the mental arithmetic initially produced large cardiac responses that changed to a more vascular tonus across task periods. Both tasks increased negative moods. However, correlations between the endocrine, cardiovascular, and negative moods were significant only during the public speaking stressor. The public speaking task is a socially relevant experimental protocol for studying reactivity in the laboratory setting and elicits relatively high, stable, and homogeneous responses.

Adrenocorticotropic Hormone↗

PubMed1996

Acute blood pressure elevations with caffeine in men with borderline systemic hypertension.

Whether the vasoconstrictive actions of caffeine are enhanced in hypertensive persons has not been demonstrated. Thus, caffeine (3.3 mg/kg) versus placebo was tested in 48 healthy men (aged 20 to 35 years) selected after screening on 2 separate occasions. Borderline hypertensive men (n = 24) were selected with screening systolic blood pressure (BP) of 140 to 160 mm Hg and/or diastolic BP 90 to 99 mm Hg. Low-risk controls (n = 24) reported no parental history of hypertension and had screening BP < 130/85 mm Hg. Participants were then tested on 2 occasions after 12-hour abstinence from caffeine in each of 2 protocols; this required a total of 4 laboratory visits. Caffeine-induced changes in diastolic BP were 2 to 3 times larger in borderline subjects than in controls (+8.4 vs +3.8 mm Hg, p < 0.0001), and were attributable to larger changes in impedance-derived measures of systemic vascular resistance (+135 vs +45 dynes.s.cm-5, p < 0.004). These findings were consistent and reached significance in both protocols. The percentage of borderline subjects in whom diastolic BP changes exceeded the median control response was 96%. Consequently, whereas all participants exhibited normotensive levels during the resting predrug baseline, 33% of borderline subjects achieved hypertensive BP levels after caffeine ingestion. Thus, in borderline hypertensive men, exaggerated responses to caffeine were: selective for diastolic BP, consistent with greater vasoconstriction, replicated in 2 protocols, and representative of nearly all borderline hypertensives. We suspect that the potential for caffeine to stabilize high resistance states in susceptible persons suggests that its use may facilitate their disease progression, as well as hinder accurate diagnosis and treatment.

Adult↗

PubMed1996

Caffeine and behavioral stress effects on blood pressure in borderline hypertensive Caucasian men.

Caffeine in dietary amounts raises blood pressure (BP), and its use increases during work stress; however, caffeine combined with behavioral stress has not been tested in borderline hypertensive (BH) men. Accordingly, this study tested a psychomotor stressor plus caffeine (3.3 mg/kg, equivalent to 2-3 cups of coffee) using a double-blind, crossover design in 24 BH men (140/90 mmHg < or = BP < or = 160/95 mmHg) and 24 controls (BP < or = 135/85 mmHg). BH men had modestly larger BP increases to the task and showed a greater combined effect of caffeine plus the task (+15/+11 mmHg) than controls (+10/+6 mmHg). BH men maintained response to the stressor in the face of an exaggerated BP response to caffeine, suggesting that use of caffeine during behavioral stress may elevate BP in BH individuals to a clinically meaningful degree.

Adult↗

PubMed1995

Adrenocortical effects of caffeine at rest and during mental stress in borderline hypertensive men.

We examined the effect or dietary doses of caffeine (3.3 mg/kg, equivalent to 2 to 3 cups of coffee) on adrenocortical responses to behavioral stress in borderline hypertensive (BH) men using a randomized, double-blind, caffeine-placebo crossover design. Cortisol levels were assessed in BH men and matched normotensive (NT) controls at rest and in response to 35 min of continuous work on a psychomotor task alternating with mental arithmetic. Caffeine at rest elevated cortisol among BHs hut not among NTs. Both groups showed significant cortisol responses to caffeine combined with the tasks. These findings may have implications for the dietary use of caffeine in persons at risk for hypertension when faced with stressful situations.

Journal Article↗

PubMed1994

Prolonged increase in blood pressure by a single oral dose of caffeine in mildly hypertensive men.

Caffeine is known to raise blood pressure (BP). We examined a single oral dose of caffeine (3.3 mg/kg, equivalent to 2 to 3 cups of coffee) on BP in 18 hypertensive (HTN) and 12 age-matched, normotensive (NT) men for 3 h. Systolic BPs were significantly higher after caffeine for both groups (P < .001) for the entire 3 h. The HTN group showed persistent elevation in diastolic BP for 3 h, whereas the increment of diastolic BP became smaller in the NT group 90 min after caffeine ingestion. Our results suggest that caffeine consumption may affect both diagnosis and treatment of hypertension and abstinence from caffeine may be beneficial, especially for hypertensive individuals.

Administration, Oral↗

PubMed1993

Cardiac adaptation to increased systemic blood pressure in borderline hypertensive men.

The present study examined cardiac characteristics of borderline hypertensive men with a positive parental history of hypertension. Hemodynamics in relation to left ventricular function and structure were evaluated in 15 borderline hypertensive men with a parental history of hypertension and in 20 normotensive control subjects with a negative parental history. Groups were matched in age, height, weight and percent body fat. Left ventricular mass and dimensions were measured by M-mode echocardiography, and left ventricular function was assessed by radionuclide ventriculography. Both groups had similar left ventricular mass, dimensions and wall thicknesses. In relation to control subjects, borderline hypertensive men had a significantly higher heart rate and blood pressure (BP) (p < 0.001), but a similar cardiac index. Borderline hypertensive men had a higher peripheral resistance index (p < 0.02), longer time to peak filling rate, and reduced cardiac efficiency, whereas they had higher contractility, minute and stroke work indexes than did control subjects (all p < 0.05); they also had higher diastolic BP (p < 0.03) during exercise, and sustained higher BP during recovery than did controls. Although this group of borderline hypertensive men did not have an altered cardiac anatomy, they had an increased vascular resistance, an altered diastolic function and a reduced cardiac efficiency while undergoing a greater work load. These cardiodynamic profiles are consistent with functional vascular changes and a parallel compensation by the heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗

PubMed1993

Impedance cardiography used to assess patterns of cardiovascular response to behavioral stressors.

This paper presents two examples of how impedance cardiography may be used to interpret the hemodynamic influences on blood pressures measured during behavioral stress. In Study 1, blood pressure changes which were similar during two tasks were shown to have important differences in their cardiac output and vascular resistance components. During work on a reaction time task having aversive incentives compared with a neutral task, the blood pressure changes were seen to be associated with lowered vascular resistance and raised cardiac activity, a "fight-flight" pattern. In Study 2, blood pressure response differences between two subject groups working on an identical task were found to have blood pressure changes differing in their underlying cardiac and vascular components as measured by impedance. Such uses impedance cardiography have widespread potential application in psychophysiological research with humans.

Adult↗

PubMed1993

Consistency of cardiovascular response pattern to caffeine across multiple studies using impedance and nuclear cardiography.

This paper illustrates the use of impedance cardiography in an applied research setting to examine some of the pharmacological effects of caffeine on cardiovascular function. A primary advantage of the technique was in providing a noninvasive approach for studying cardiac versus vascular mechanisms underlying blood pressure responses to acute caffeine challenge. Impedance cardiography allowed the quantification of stroke volumes and cardiac output, and the change in these variables over time in a within-subjects design. Systemic vascular resistances were then calculated when impedance data were combined with simultaneously measured blood pressures. Results from four studies are summarized in which caffeine significantly elevated systolic and diastolic blood pressures. Impedance-derived measures indicate that caffeine's pressor response can be attributed to increased systemic vascular resistance rather than to elevated cardiac output. Our findings were consistent across all four studies, and across all protocols within those studies. Furthermore, these response patterns were confirmed by obtaining similar results using nuclear ventriculography. Thus, with respect to the outcome of testing an applied question, impedance-derived findings were found to be reliable and valid when compared with another technique used more commonly in clinical settings.

Administration, Oral↗

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

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↗

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↗

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↗