Difference in cardiovascular response during orthostatic stress in Parkinson's disease and multiple system atrophy.

Although orthostatic hypotension is more prominent in multiple system atrophy (MSA) than in Parkinson's disease (PD), there is no study comparing the degree of decrease in total peripheral resistance and cardiac response during orthostatic stress between both diseases. In this study, we examined whether there is a difference in cardiovascular response between MSA and PD. We examined the results of the head-up tilt test in 68 patients with MSA, 28 patients with cardiac non-denervated PD, and 70 patients with cardiac denervated PD whose total peripheral resistance after 60° tilting was lower than the value at 0°. Differences in cardiac output and blood pressure changes were compared against the decrease in total peripheral resistance. There was no difference in the degree of decrease in total peripheral resistance among the three groups. However, the slope of the regression line revealed that the increase in cardiac output against the change in total peripheral resistance was significantly lower in the MSA group than in the cardiac non-denervated and denervated PD groups, and that the decrease in systolic blood pressure against the change in total peripheral resistance was significantly greater in the MSA group than in the cardiac non-denervated and denervated PD groups. In MSA, the cardiac response during orthostatic stress is lower than that in PD, possibly underlying the fact that orthostatic hypotension is more prominent in MSA than in PD.