Assessment of cardiovascular autonomic dysfunction in multiple system atrophy

Because heart rate is controlled mainly by the autonomic nervous system, ca rdiovascular autonomic dysfunction may contribute to the prognosis of patie nts with multiple system atrophy (MSA). To clarify cardiovascular autonomic dysfunctions in MSA, the authors investigated the relation between blood p ressure (BP) and pulse rate (PR), and assessed a power spectral analysis of heart rate variability (HRV) during the clinical course using ambulatory B P and a heart rate monitor for 24 hours. The authors studied seven patients with MSA (five men and two women, aged 61.0 +/- 5.8 years) and seven healt hy volunteers (four men and three women, aged 58.0 +/- 6.6 years) without h ypertension, heart disease, or intracranial lesions. The MSA group showed a bnormal circadian variations of BP and PR and a significantly decreased cor relation coefficient between BP and PR. A significant decrease and altered circadian variation also existed in the number of changes in successive R-R intervals greater than 50 msec (RR50) and in the power of the high- and lo w-frequency component of HRV. The authors observed a significant negative c orrelation between the duration of illness and the number of changes in suc cessive R-R intervals greater than 50 msec. The characteristic dysautonomia in MSA was a decrease in sympathetic and parasympathetic activity, with an abnormal circadian rhythm of BP and HRV. The balance between sympathetic a nd parasympathetic activity was also impaired. The parasympathetic modulati on represented by RR50 worsened according to the development of the illness . Those autonomic dysfunctions may have affected the cardiovascular systems , which may indicate a poor prognosis in patients with MSA. An analysis of HRV and the circadian rhythm of BP and HRV are useful in evaluating cardiac autonomic dysfunctions in MSA.