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

Abstract

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.

WISE-2005: effect of aerobic and resistive exercises on orthostatic tolerance during 60 days bed rest in women

“…) until presyncope. This test allows a precise and reproducible assessment of orthostatic tolerance (el-Bedawi and Hainsworth 1994). The test was ended if one of the following signs occurred: rapidly increasing symptoms (nausea, clammy skin, excessive sweating, pallor, vertigo), a sudden drop in blood pressure (SBP fall > 25 mmHg/min or DBP fall > 15 mmHg/min), a SBP < 70 mmHg, a sudden drop in HR (HR fall > 15 beats/ min), cardiac dysrhythmias.…”

Orthostatic hypotension following spinal cord injury: understanding clinical pathophysiology

“…This increase in the level of NA is due to tonic activation of autonomic circuits responsible for orthostatic stability in controls. However, in SCI individuals this descending control is markedly disrupted is supported either by a foot plate 65 or a harness 66 and is not tilted fully upright so that leg movements are avoided. During normal standing, on the other hand, postural muscles are continually reciprocally activated.…”

Water Drinking Acutely Improves Orthostatic Tolerance in Healthy Subjects

“…Afterward, increasing steps of lower body negative pressure (Ϫ20, Ϫ40, and Ϫ60 mm Hg) were applied for 10 minutes each while the subjects remained in the upright position. 4 The test protocol was stopped at the subjects' request, or when the systolic blood pressure fell to Ͻ80 mm Hg (or was Ͻ90 mm Hg and rapidly decreasing), or if heart rate was Ͼ150 bpm. Orthostatic tolerance was determined as the time to presyncope (minutes).…”

“…3 This response can be induced in most otherwise healthy subjects exposed to a sufficiently severe orthostatic stress. 4 Most patients have syncope infrequently and do not require aggressive treatment; however, some patients with frequent syncopal episodes do require therapeutic measures. Unfortunately, most pharmacological treatments do not result in sufficient symptomatic improvement.…”

“…We used a combination of head-up tilt testing and lower body negative pressure to induce neurally mediated presyncope in healthy subjects because this has been shown to provide a quantitative and reproducible measure of orthostatic tolerance. 4 Regular tilt testing is less useful as a method to induce neurally mediated syncope in healthy subjects because it exerts a weaker orthostatic stimulus.…”