The Effect of Isometric Exercise on the Left Ventricular Volume in Normal Man

Abstract

The effect of isometric handgrip exercise (IHG) on left ventricular (LV) size and performance was studied noninvasively on 15 normal subjects at rest and at the end of 3 min of IHG at 50% of maximum contraction. Left ventricular internal diameter was measured at end-diastole and end-systole on LV echograms, the indirect carotid pulse was recorded, and blood pressure measured by sphygmomanometry. Using the cube formula, LV end-diastolic (EDVI) and end-systolic (ESVI) volume indices were computed, and stroke (SI) and cardiac (CI) indices were derived. Mean blood pressure (BPm) and systemic vascular resistance (SVR) were calculated from these data by a technique previously described. In comparison to values at rest, IHG resulted in a significant ( P < 0.01) rise in CI (3.5 ± 0.2 to 4.4 ± 0.3 L/min/m 2 ), BPm (87 ± 2 to 120 ± 4 mm Hg) and heart rate (79 ± 3 to 97 ± 4 beats/min). The product (SI x BPm), used as an index of LV stroke work, increased substantially (52 ± 3 to 74 ± 4 gm-m/m 2 ). No significant change was noted in EDVI (60 ± 4 to 62 ± 3 ml/m 2 ), SI (44 ± 2 to 46 ± 2 ml/m 2 ), and SVR (1209 ± 69 to 1275 ± 63 dynes/sec/cm –5 ). Thus normal hearts responded to IHG by increasing CI through tachycardia and pumping the same SI against increased afterload, without utilizing diastolic volume reserves. These data support the hypothesis that isometric muscular exercise leads to an augmentation of LV myocardial contractility in normal man.

Autonomic Adjustments to Exercise in Humans

“…The reasons for these discrepant findings are unclear, but are suggested to relate in part to the level of LBNP, and thus cardiopulmonary unloading, utilized (12). While isometric handgrip has a limited effect on either preload (central venous pressure) or left-ventricular enddiastolic volume in young healthy individuals (319), dynamic exercise with a relatively large muscle mass evokes a much greater increase in left ventricle preload, stroke volume, and contractility (367). Thus, it would be reasonable to expect cardiopulmonary vagal afferents to provide a marked inhibition of SNA during dynamic exercise.…”

Blood pressure and heart rate responses during a fatiguing isometric exercise in paraplegic men with hypertension

“…These aerents in turn cause, in healthy men and women, a change in out¯ow in sympathetic nerves. The sympathetic out¯ow has been shown to cause a small increase in cardiac output due to an increase in left ventricular contractility (Krayenbuehl et al 1972;Quinones et al 1974;Stefadouros et al 1974a, b) in the face of an increased after load on the heart (Lind et al 1964;Helfant et al 1971) with a small increase in systemic vascular resistance (Stefadouros et al 1974b;Petrofsky 1982Petrofsky , 1987. The result is that there is an increase in both the systolic and diastolic blood pressure throughout the duration of the exercise.…”

The effects of cold and exercise on the cardiovascular system

“…The SBP rise26 55 84 is driven largely by an increase in CO;85 86 SVR remains unchanged87 or increases 88. End diastolic volume does not change84 and SV remains constant89 or decreases 88.…”