Assessment of breath holding index during orthostasis.

The aim of the study was to assess differences in cerebrovascular reactivity in healthy subjects during orthostasis. Twenty healthy volunteers (11 men and 9 women) with no atherosclerotic risk factors were evaluated by use of transcranial Doppler. The breath holding index (BHI) was obtained in supine and upright posture using standardized procedure. Student's t-test was used on comparison of the mean blood flow velocities (MBFV) and BHI between supine and upright posture and between the left and right side of the body. The middle cerebral artery MBFV in supine posture was 66.6 cm/s on the right side and 68.5 cm/s on the left side and in upright posture 60.6 cm/s on the right side and 62.3 cm/s on the left side. There was no significant MBFV difference either between supine and upright posture or between male and female subjects. The mean BHI in supine posture was 1.59 on the right side, 1.65 on the left side, and in upright posture 1.63 on the right side and 1.7 on the left side, without significant sex difference. There was no statistically significant differences in BHI between supine and upright posture (P = 0.81 and P = 0.68 for the right and left side, respectively) or between the two sides of the body in supine (P = 0.71) and upright posture (P = 0.8). In conclusion, evaluation of cerebrovascular reactivity yielded no significant difference in BHI values during orthostatic stress.