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. Author manuscript; available in PMC: 2015 Jul 22.
Published in final edited form as: Am J Physiol Heart Circ Physiol. 2006 Mar 24;291(2):H904–H913. doi: 10.1152/ajpheart.01359.2005

Fig. 1.

Fig. 1

Spontaneous (left) and voluntary (right) hypocapnia brought about in a postural tachycardia syndrome (POTS) patient (left) and by voluntary hyperventilation (HV) in a healthy control subject (right), respectively. Voluntary hyperventilation was achieved by having the subject take a breath every 6 s and to breathe as deeply as possible. Such breathing was maintained for 3.5 min and stopped because of lightheadedness. End-tidal partial pressure of carbon dioxide (PetCO2), Respitrace volumes (Resp), and thoracic blood volumes (TBV) are shown from top to bottom. Upright tilt was associated with an increase in thoracic blood volume. Onset of hypocapnic hyperventilation was not related to an increase in thoracic blood volume.