Blood pressure and cerebral oxygenation responses to skeletal muscle tension: a comparison of two physical maneuvers to prevent vasovagal reactions.

ABSTRACT

AIM: The present study compared blood pressure, heart rate, and cerebral oxygenation responses to two manipulations used to prevent vasovagal reaction -- skeletal muscle tensing alone and skeletal muscle tensing with leg crossing. METHODS AND RESULTS: Using a repeated measures within-subjects design, healthy young adults engaged in a brief laboratory protocol that included an initial 3 min resting baseline, 3 min of muscle tensing (or no-tensing control), and a 1 min orthostatic challenge. This sequence was repeated three times for each participant to allow for a direct comparison of physiological responses to two different muscle-tensing manipulations as compared to the no-tensing control condition. Results indicated that, relative to the no-tensing, both muscle tensing manipulations elicited significant increases in systolic blood pressure (8.7 +/- 1.1 mmHg), diastolic blood pressure (4.9 +/- 0.6 mmHg), and heart rate (10.9 +/- 0.9 bpm), while a significant increase in cerebral oxygenation was only observed in response to muscle tensing with legs crossed (0.8 +/- 0.2%). Blood pressure and heart rate responses to orthostatic challenge did not differ between the two tensing manipulations, although muscle tensing with legs crossed was followed by a more rapid recovery of cerebral oxygenation levels. CONCLUSION: These findings suggest that muscle tensing elicits physiological adaptations that may help reduce the risk of vasovagal reactions; however, the combination of lower body tension with the legs crossed is likely to be most effective as it was uniquely associated with significant increases in the flow of oxygenated blood to the brain.