Effects of age on responses to isometric exercise: Isometric handgrip in noninvasive screening for cardiovascular disease

Abstract

Isometric handgrip (IHG) imposes an acutely increased afterload on the left ventricle. Utilizing systolic time intervals, we studied various responses to IHG, measured as changes from resting values with near-maximum IHG, in old normal (ON) subjects, young normal (YN) subjects, and old patients with hypertensive heart disease (HHD) and patients with coronary artery disease (CAD). There were no differences in responses to IHG between ON and patients with HHD or patients with CAD. However, there were clear differences between the responses of ON and YN subjects. Increase in heart rate (HR) was much more prominent in YN (ON vs. YN = +11.6 ± 2.6 vs. +51.6 ± 5.7 beats per minute p < 0.001). Pre-ejection period (PEP) end isovolumic contraction time (IVCT) increased in ON but decreased in YN (PEP + 6.2 ± 1.7 vs. −11.0 ± 3.7 msec., p < 0.001; IVCT +8.1 ± 2.2 vs. −13.8 ± 3.4 msec., p < 0.001. Shortening of LVET was much more marked in YN (−6.5 ± 4.1 vs. −63.3 ± 9.9 msec. p < 0.001), but this was entirely due to the HR differences since there was no difference in ejection time index (+ 5.1 ± 3.4 vs. −0.4 ± 7.3 msec. p > 0.5). IHG produced no significant differences between ON and YN in the timing of the “mitral” component of the first heart sound (q-Im), in the ratio PEP/LVET, or in pulse transmission time (PTT). By contrast, resting control PTT was markedly short in ON, especially those with CAD. Resting PTT in ON was 27.1 ± 2.6 msec.; in YN 43.7 ± 1.4 msec.; in CAD patients 20.7 ± 1.3 msec. We conclude that even near-maximal IHG does not seem to be an adequate noninvasive screening test for cardiovascular disease in that age alone seems to have the most significant influence on the responses.