Cardiovascular responses to tilting in tetraplegic man.

1. A study has been made of the effect of head-up tilt on blood pressure, heart rate, forearm blood flow and occluded vein pressure in the hand and foot in non-bedridden patients with chronic, closed, complete, localized traumatic transection of the cervical spinal cord.2. In typical responses the blood pressure fell and the heart rate rose progressively for about 2 min, tending to plateau thereafter. The average falls in mean blood pressure for tilts of +30, +45 and +60 degrees were from 68 to 44, 74 to 36 and 70 to 44 mm Hg respectively, and the corresponding heart rate increases were from 67 to 85, 62 to 97 and 62 to 103 beats/min respectively. One patient lost consciousness when his blood pressure was 29/19 mm Hg and one other patient experienced symptoms suggesting cerebral ischaemia.3. Following the return to horizontal, the blood pressure and heart rate usually returned to their previous values within 1 min and the blood pressure tended to overshoot slightly in the following few minutes. No immediate blood pressure overshoot occurred after the tilt except in association with a spasm of skeletal muscles.4. There was consistently a decrease in forearm blood flow, sometimes to unrecordably low levels and a venoconstriction with postural change and it is argued that these changes are the result of spinal cardiovascular reflexes to peripheral vessels. Following the return to the horizontal position, there was occasionally a large immediate increase in forearm blood flow.5. Following the intravenous administration of 3 mg atropine on two occasions, head-up tilting produced further small heart rate increases.6. Spasms of skeletal muscle occur frequently in these patients and greatly modify the effects of postural stimuli. Bladder percussion also modifies the normal response.