Combined head-up tilt and lower body suction: a test of orthostatic tolerance

A combined tilt-table and lower body suction chamber to provide a progressive test of orthostatic tolerance which avoided the use of drugs and had a defined end point even in most asymptomatic subjects has been constructed and evaluated. An air-tight cover, sealed to a tilt-table and to the subject at the level of the iliac crest, was used to study the responses to: head-up tilting for 20 min, then tilting plus lower body suction at -20 and -40 mmHg for 10 min at each. Blood pressure, heart rate and cardiac output were measured noninvasively and orthostatic tolerance was assessed as the time to imminent onset of syncope. All subjects tolerated tilt alone but 84% developed signs and symptoms of presyncope during the suction. Younger women had a lower orthostatic tolerance than other groups. Values of the variables measured during tilting alone did not correlate with the measured orthostatic tolerance, but during the suction subjects who developed early syncope showed larger decreases in cardiac output and smaller maximal heart rates than the more resistant subjects. The test is repeatable and is likely to be of value in the assessment of orthostatic tolerance in patients and for evaluating the effects of various interventions.