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Biomedical subjects

H M Graitzer

Publications and source records attributed to H M Graitzer.

6 recordsLinked to original sources
PubMed1989

Exercise training bradycardia: the role of autonomic balance.

We used an algebraic model of resting heart rate (HRr), HRr-mn (HRo), to compare resting parasympathetic (n) and sympathetic (m) influence, intrinsic heart rate (HRo), and resting autonomic balance (Abal) in ten endurance-trained (ET) and ten nontrained (NT) men. The values of m, n, and Abal were determined by selective pharmacological blockade with atropine and metoprolol. HRo was obtained during double blockade with atropine and metoprolol. HRo and HRr were significantly lower (P less than or equal to 0.04 and P less than or equal to 0.01, respectively) in the ET subjects (79.5 +/- 2.8 beats.min-1 and 54.7 +/- 3.0 beats.min-1, respectively) when compared to the NT subjects (86.6 +/- 2.5 beats.min1 and 70.2 +/- 3.1 beats.min-1, respectively). Parasympathetic influence (n) was greater in the ET subjects (P less than or equal to 0.04), while sympathetic influence (m) was slightly (P less than or equal to 0.05) less in the ET subjects. Consequently, the value of Abal was significantly less in the ET subjects (P less than or equal to 0.02), indicating that resting parasympathetic predominance was significantly greater in the ET subjects. We concluded that the exercise training bradycardia, observed in this group of subjects, was due to both a lower HRo and an Abal with an augmented parasympathetic dominance.

Adult↗
PubMed1988

Effect of changes in cardiac autonomic balance on blood pressure regulation in man.

The role of cardiac autonomic balance in fitness-related differences in blood pressure regulation was evaluated by comparing the cardiovascular responses to lower body negative pressure (LBNP) in 10 trained and 10 untrained men. Cardiac autonomic balance was quantified as the ratio of resting heart rate to intrinsic heart rate, and was significantly lower in the trained subjects (0.68 +/- 0.03) than the untrained subjects (0.81 +/- 0.03) indicating a greater parasympathetic dominance at rest in the trained subjects. Arterial pressure decreased significantly more during LBNP in the trained subjects and was due to lower chronotropic and vasoconstrictor responses in these trained subjects. 'Cardiac autonomic balance' was equilibrated between the groups by partial parasympathetic blockade with atropine sulfate in the trained subjects and partial sympathetic blockade with metoprolol tartrate in the untrained subjects. Equilibration of cardiac autonomic balance eliminated the group differences in blood pressure maintenance, and chronotropic and vasoconstrictor responsiveness during LBNP. It was hypothesized that the elevated tone of parasympathetic control of the heart rate of the trained subjects resulted in an attenuation of blood pressure regulation.

Adult↗
PubMed1988

Baroreflex function in endurance- and static exercise-trained men.

The effect of exercise training mode on reflex cardiovascular control was studied in a cross-sectional design. We examined the cardiovascular responses to progressive incremental phenylephrine (PE) infusion to maximal rates of 120 micrograms/min and the delta heart rate/delta blood pressure responses to lower body negative pressure (LBNP) to -50 Torr in 30 men who were either endurance exercise trained (ET), untrained (UT), or weight trained (WT). During PE infusion, measures of blood pressures, forearm blood flow, heart rate and cardiac output, and calculations of forearm vascular resistance, stroke volume, and peripheral vascular resistance were made at each infusion rate when steady-state blood pressure was attained. No significant differences (P less than 0.05) in forearm blood flow or resistance were observed between the groups at any dose of PE, suggesting that the vasoconstrictor response was similar among the groups. Regression analyses of heart rate against mean blood pressure during the PE infusion were performed to evaluate baroreflex function. A linear model was used and correlation coefficients ranging from 0.82 to 0.96 were obtained (P less than 0.05). The slope of the line of best fit for the ET subjects (-0.57) was significantly less (P less than 0.05) than the slopes obtained for either the UT (-0.91) or WT (-0.88) subjects. In addition, the delta heart rate/delta blood pressure measurements obtained during LBNP reflected a similarly significant attenuation of reflex chronotropic control in the ET subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Blood pressure regulation during cardiac autonomic blockade: effect of fitness.

The purpose of this study was to determine the role of the autonomic nervous system's control of the heart in fitness-related differences in blood pressure regulation. The cardiovascular responses to progressive lower-body negative pressure (LBNP) were studied during unblocked (control) and full blockade (experimental) conditions in 10 endurance-trained (T) and 10 untrained (UT) men, aged 20-31 yr. The experimental conditions included beta 1-adrenergic blockade (metoprolol tartrate), parasympathetic blockade (atropine sulfate), or complete blockade (metoprolol and atropine). Heart rate, blood pressure, forearm blood flow, and cardiac output were measured at rest and -16 and -40 Torr LBNP. Forearm vascular resistance, peripheral vascular resistance, and stroke volume were calculated from these measurements at each stage of LBNP. Blood pressure was maintained, primarily by augmented vasoconstriction, equally in T and UT subjects during complete and atropine blockade. The fall in systolic and mean pressure from 0 to -40 Torr was greater (P less than 0.05) in the T subjects during the unblocked and metoprolol blockade conditions. This reduced blood pressure control during unblocked condition was attributable to attenuated vaso-constrictor and chronotropic responses in the T subjects. We hypothesize that an autonomic imbalance (elevated base-line parasympathetic activity) in highly trained subjects restricts reflex cardiac responses, which accompanied by an attenuated vasoconstrictor response, results in attenuated blood pressure control during a steady-state hypotensive stress.

Adult↗