Upright hyperventilation occurs in ~25% of our patients with postural tachycardia syndrome (POTS). Poikilocapnic hyperventilation alone causes tachycardia. Here, we examined changes in respiration and hemodynamics comprising cardiac output (CO), systemic vascular resistance (SVR), and blood pressure (BP) measured during head-up tilt (HUT) in three groups: patients with POTS and hyperventilation (POTS-HV), patients with panic disorder who hyperventilate (Panic), and healthy controls performing voluntary upright hyperpnea (Voluntary-HV). Though all were comparably tachycardic during hyperventilation, POTS-HV manifested hyperpnea, decreased CO, increased SVR, and increased BP during HUT; Panic patients showed both hyperpnea and tachypnea, increased CO, and increased SVR as BP increased during HUT; and Voluntary-HV were hyperpneic by design and had increased CO, decreased SVR, and decreased BP during upright hyperventilation. Mechanisms of hyperventilation and hemodynamic changes differed among POTS-HV, Panic, and Voluntary-HV subjects. We hypothesize that the hyperventilation in POTS is caused by a mechanism involving peripheral chemoreflex sensitization by intermittent ischemic hypoxia. NEW & NOTEWORTHY Hyperventilation is common in postural tachycardia syndrome (POTS) and has distinctive cardiovascular characteristics when compared with hyperventilation in panic disorder or with voluntary hyperventilation. Hyperventilation in POTS is hyperpnea only, distinct from panic in which tachypnea also occurs. Cardiac output is decreased in POTS, whereas peripheral resistance and blood pressure (BP) are increased. This is distinct from voluntary hyperventilation where cardiac output is increased and resistance and BP are decreased and from panic where they are all increased.
Keywords: hyperventilation; postural tachycardia; systemic vascular resistance.