Differences in overshoot of blood pressure after head-up tilt in two groups with chronic autonomic failure: pure autonomic failure and multiple system atrophy.

On head down tilt to the supine horizontal position ( tilt reversal) after head up tilt ( HUT), patients with orthostatic hypotension may show an increase in blood pressure ( BP) relative to baseline readings. We assessed this BP overshoot in 8 patients with pure autonomic failure (PAF, 64 +/- 13 years) and 8 patients with multiple system atrophy (MSA, 66 +/- 10 years). BP was intermittently measured during pre-tilt supine, HUT (60degrees, 10 min), and post-tilt supine periods. In addition, beat-to-beat BP was measured continuously using the Portapres model 2 device to calculate stroke volume (SV), cardiac output (CO) and total peripheral resistance (TPR). There was systolic BP overshoot of greater than or equal to 15mmHg after tilt reversal in 5 out of 8 PAF, but in only one of 8 MSA. A mean increase of systolic BP in PAF was significantly higher than that in MSA (p< 0.01). TPR increased over baseline level after tilt reversal, although there was no significant difference. SV and CO levels during the post-tilt supine period were similar to baseline levels. In conclusion, BP overshoot was prominent in the PAF group but not in the MSA group. The phenomenon of BP overshoot while supine, especially in PAF, may have implications for long term cardiac and vascular damage in such patients.