Figure 4.

Representative tracing from a patient with postural tachycardia syndrome (POTS)–hyperventilation. Beat‐to‐beat changes in arterial pressure (AP), heart rate (HR), cardiac output (CO), expiratory minute volume (V_E), end tidal carbon dioxide (ETCO ₂), and cerebral blood flow velocity (CBFv) are shown before and after administration of supplemental CO ₂. The figure suggests a small decrease in AP, a decrease in HR and V_E, and increases in CO, ETCO ₂, and CBFv after CO ₂ is administered. After CO ₂, the patient no longer fulfills HR criteria for POTS. Orthostatic symptoms improved, although V_E remained somewhat elevated.