Figure 3.

Reduced Stroke Volume and Cerebrovascular Pulsatility Drive Postural Ventilation

(A) Middle cerebral artery velocity (MCAv) pulsatility was continuously measured during 60° head-up tilt using beat-to-beat transcranial Doppler ultrasound. (B) Postural reductions in stroke volume were greater in patients with POTS. (C) Changes in stroke volume correlated with changes in MCAv pulsatility. (D) Postural reductions in MCAv pulsatility were also greater in patients with POTS and were strongly predictive of postural changes in ventilation (E) and MSNA burst amplitude (F). Data are presented as mean ± SD. Hemodynamic response to head-up tilt was compared between patients with POTS and control subjects using an independent-samples, 2-tailed Student’s t-test. Linear regressions were used to investigate the relationship of changes in ventilation and sympathetic nerve activity and hemodynamic status. PI = pulsatility index; other abbreviations as in Figure 1.