Author(s): MARINA, F., DAISUKE, H., KEISEI, K., TAKEAKI, M., SHIGEKI, S., TOMOKO, I., MICHINARI, H., TAKASHI, T., Institution: NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND TECHNOLOGY, Country: JAPAN, Abstract-ID: 1266

INTRODUCTION:
During dynamic large-muscle exercise, increased blood demand is met through coordinated interaction between the left ventricle (LV) and the vascular system. Vascular load consists of pulsatile and steady components determined primarily by central elastic arteries and systemic vascular resistance (SVR), respectively. However, it remains unclear which component predominantly modulates LV contraction work during dynamic exercise. This study used cardiac magnetic resonance (CMR) to examine the associations of aortic characteristic impedance (Zc), representing pulsatile load, and SVR, representing steady load, with LV systolic work during supine cycling exercise.
METHODS:
Twenty-eight healthy young adults (14 men and 14 women, 24 ± 4 years) were studied at rest and during supine cycling exercise (15 W for men or 10 W for women). Aortic blood velocity, blood pressure, and LV volumes were measured using CMR. The aortic impedance modulus was obtained by frequency-domain analysis, and Zc was calculated as the mean modulus above the first zero-phase crossing. LV pressure–volume (PV) loop was constructed using LV pressure noninvasively estimated from the aortic pressure waveform. Stroke work (SW) and potential energy (PE) were derived from the PV loop. SVR was calculated as mean arterial pressure divided by cardiac output.
RESULTS:
Exercise heart rate corresponded to 49.8 ± 10.7% of maximal heart rate measured during cardiopulmonary test. SVR significantly decreased during exercise (rest: 1904 dyne·s/cm^5 [1802-2007] vs. cycling: 1152 dyne·s/cm^5 [1035-1269], p < 0.001), whereas Zc showed no significant change from rest. SW (6593 mmHg·mL [6046-7139] vs. 8339 mmHg·mL [7760-8919], p < 0.001) and PE (4886 mmHg·mL [4220-5551] vs. 6068 mmHg·mL [5359-6776], p = 0.001) significantly increased with exercise only in men but not women. Within-subject correlation analysis revealed significant negative correlations between SVR and SW (rrm = -0643, p = 0.002) and PE (rrm = -0.575, p = 0.008) across all participants, whereas no association between Zc and either SW or PE was observed.
CONCLUSION:
These findings indicate that during dynamic exercise performed in the supine posture, reductions in steady, rather than changes in pulsatile vascular load, are associated with attenuation of LV contraction work. Furthermore, this ventricular–vascular interaction may be sex-dependent, with a stronger association between vascular load and LV contraction work in men than in women.