The effect of acute exercise on pulsatile load in healthy aging

Abstract

Pulsatile load is a complex, time-varying afterload imposed on the heart that the left ventricle must work against to promote forward blood flow. Pulsatile load is determined by multiple factors, of which wave reflection magnitude (RM) and reflected wave transit time (RWTT) are the focus of this dissertation. A larger RM and shortened RWTT amplify mid-to-late systolic load, thereby wasting left ventricular effort and preceding the development of cardiovascular disease, like heart failure. Older adults (OA) display an elevated RM and earlier RWTT at rest compared to young adults (YA) due to age-related changes in arterial structure (increased arterial stiffness) and function. Acute exercise modulates wave reflection, however, is highly dependent on exercise modality and intensity. In YA, acute lower body aerobic exercise decreases RM and RWTT while handgrip exercise increases RM and decreases RWTT. However, it is unknown how age-related changes in arterial structure and function may influence RM and RWTT during supine cycle and handgrip exercise, and whether OA respond differently than YA. Purpose: To determine the effects of acute dynamic supine cycle exercise and isometric handgrip exercise on RM and RWTT in healthy YA and OA. Hypotheses: Compared to YA, 1) OA would have an attenuated reduction in RM but an augmented reduction in RWTT during supine cycle exercise; and 2) OA would have an augmented increase in RM and an augmented reduction in RWTT during handgrip exercise. Methods: Radial artery pressure waveforms and aortic blood flow velocities were acquired via applanation tonometry and echocardiography, respectively, at baseline and during supine cycle and handgrip exercise in 20 YA (25±5 yrs) and 20 OA (66±4 yrs). Central pressure waveforms were synthesized from radial waves using a generalized transfer function. Pressure-flow relations were analyzed offline to perform wave separation analysis. This provided a comprehensive assessment of ventricular-arterial interactions for the determination of the relative amplitude and timing of forward (Pf) and backward (Pb) pressure waves, yielding RM (Pb/Pf) and RWTT. Results: As expected, baseline RM was greater in OA (YA: 40±6 vs. OA: 49±6%, p<0.05) and RWTT was shorter in OA compared to YA (YA: 191±20 vs. OA: 140±18 ms, p<0.05). Light-to-moderate supine cycle exercise decreased RM to a greater extent in OA compared to YA; however, the reduction in RWTT was attenuated in OA. Handgrip exercise increased RM in YA, but not OA. Lastly, RWTT decreased in YA during HG exercise, but not in OA. Conclusion: Compared to YA, OA had a greater reduction in wave reflection during supine cycle exercise but had no response during handgrip exercise. These data indicate an enhanced beneficial effect during acute aerobic exercise for OA and attenuated deleterious wave reflection responses during handgrip exercise.