Figure 1.

Neurocardiorespiratory Responses to Head-Up Tilt

(A) Orthostatic challenges were performed in patients with postural orthostatic tachycardia syndrome (POTS) and control subjects using a 60° head-up tilt test with continuous measurements of ventilation, heart rate, and muscle sympathetic nerve activity (MSNA). (B) Neurocardiovascular responses to head-up tilt. Line plots illustrate representative patient traces of heart rate (top), ventilation (middle), and MSNA (bottom). (C) Bar charts show changes in heart rate (top), ventilation (middle), and MSNA (bottom). Data are presented as mean ± SD. Cardiorespiratory responses were compared between patients with POTS and control subjects using independent-samples 2-tailed Student’s t-tests. a.u. = arbitrary units.