Fig. 1. The effect of hyperventilation on a healthy subject (A ) and a pure autonomic failure patient (B ). In response to hyperventilation, the compensatory heart rate (upper trace ) increase is blunted despite the greater fall of blood pressure (middle trace ) in the autonomic failure patient compared to a control subject. The E^TCO²(bottom trace ) is decreased with hyperventilation. Signals from top to bottom, upper trace = heart rate (HR; beats/minute), middle trace = blood pressure (BP; mmHg), and bottom trace = end tidal carbon dioxide (E^TCO²; mmHg).