Contribution of Arterial Compliance and Vascular Resistance to Effective Arterial Elastance Changes During Exercise: 1375: Board #14 10:30 AM - 11:30 AM

Effective arterial elastance (Ea), an index of arterial load, increases with elevations in left ventricular elastance to maximize the efficiency of left ventricular stroke work during exercise. The arterial load is comprised of both systemic arterial compliance (C) and systemic vascular resistance (R)-to-cardiac cycle length (T) ratio (R/T) and is regulated by a reciprocal combination between C and R. Under resting condition, the relative contribution of 1/C to Ea is less than R/T (approximately one-third that of R/T). However, the contributions of C and R to Ea during exercise remain unclear. R markedly decreases during exercise, but Ea increases. We hypothesized that C during exercise (conditions of increased arterial load) becomes the predominant factor determining Ea.

PURPOSE: This study was aimed to clarify whether the contribution of C to Ea increases during exercise to maintain a balance with left ventricular elastance, and this phenomenon is altered by different exercise intensity.

METHODS: Ea (0.9 × systolic blood pressure/stroke volume), C (stroke volume/pulse pressure), R (mean blood pressure/cardiac output), and T were measured at rest and during exercise of 40, 60, and 80% maximal oxygen uptake (VO₂max) using Doppler echocardiography and sphygmomanometry in 45 healthy young men.

RESULTS: Ea did not differ between rest and 40%VO₂max, but it was significantly greater at 60% and 80%VO max. 1/C significantly increased during exercise in an exercise intensity-dependent manner, whereas R/T significantly decreased at 40%VO₂max and gradually increased at 60% and 80%VO₂max. These results suggest that, under conditions of increased exertion, 1/C contributes to changes in Ea than R/T. Additionally, we performed multiple linear regression analysis to confirm relative contributions of C and R to Ea. Ea was highly related to 1 /C and R/T at all conditions (all r²=1.00). The contribution (the standardized regression coefficient) of 1/C to Ea at rest was lower than R/T, but this contribution elevated with increasing exercise intensity (Ratio of 1/C to R/T: rest, 0.45 vs. 40%VO₂max, 0.64; 60%VO₂max, 0.96; 80%VO₂max, 0.89).

CONCLUSION: This study demonstrated that the contribution of systemic arterial compliance to effective arterial elastance increases during exercise, and the peak contribution was observed at moderate exercise intensity (60%VO max). Therefore, we propose that the increased contribution of systemic arterial compliance to effective arterial elastance may participate in the regulation of the arterial load during exercise. Supported by grants from the Ministry of Education, Culture, Sports, Science and Technology of Japan (17700486).