Figure 2.

Data averaged over all groups for heart rate (HR), cardiac output (CO), mean arterial pressure (MAP), and systemic vascular resistance (SVR). Before the delivery of CO ₂, HR was significantly increased for all postural tachycardia syndrome (POTS) groups compared with controls. CO was decreased compared with controls and was significantly lower in patients with POTS‐↓CO (decreased CO without hyperventilation) compared with other patients with POTS. Upright CO decreased significantly and SVR increased significantly in all POTS groups compared with controls. MAP increased during tilt in the POTS‐hyperventilation (HV) group compared with control. After administration of supplemental CO ₂ to patients with POTS‐HV, HR, CO, MAP, and SVR were no longer different from control. NL indicates normal; **P<0.001, ***P<0.0001, ^‡ P<0.025.