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      Baroreceptor unloading in postural tachycardia syndrome augments peripheral chemoreceptor sensitivity and decreases central chemoreceptor sensitivity.

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          Abstract

          While orthostatic tachycardia is the hallmark of postural tachycardia syndrome (POTS), orthostasis also initiates increased minute ventilation (Ve) and decreased end-tidal CO(2) in many patients. We hypothesized that chemoreflex sensitivity would be increased in patients with POTS. We therefore measured chemoreceptor sensitivity in 20 POTS (16 women and 4 men) and 14 healthy controls (10 women and 4 men), 16-35 yr old by exposing them to eucapneic hyperoxia (30% O(2)), eucapneic hypoxia (10% O(2)), and hypercapnic hyperoxia (30% O(2) + 5% CO(2)) while supine and during 70° head-upright tilt. Heart rate, mean arterial pressure, O(2) saturation, end-tidal CO(2), and Ve were measured. Peripheral chemoreflex sensitivity was calculated as the difference in Ve during hypoxia compared with room air divided by the change in O(2) saturation. Central chemoreflex sensitivity was determined by the difference in Ve during hypercapnia divided by the change in CO(2). POTS subjects had an increased peripheral chemoreflex sensitivity (in l·min(-1)·%oxygen(-1)) in response to hypoxia (0.42 ± 0.38 vs. 0.19 ± 0.17) but a decreased central chemoreflex sensitivity (l·min(-1)·Torr(-1)) CO(2) response (0.49 ± 0.38 vs. 1.04 ± 0.18) compared with controls. CO(2) sensitivity was also reduced in POTS subjects when supine. POTS patients are markedly sensitized to hypoxia when upright but desensitized to CO(2) while upright or supine. The interactions between orthostatic baroreflex unloading and altered chemoreflex sensitivities may explain the hyperventilation in POTS patients.

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          Author and article information

          Journal
          Am. J. Physiol. Heart Circ. Physiol.
          American journal of physiology. Heart and circulatory physiology
          American Physiological Society
          1522-1539
          0363-6135
          Jul 2011
          : 301
          : 1
          Affiliations
          [1 ] The Center for Pediatric Hypotension, Ste. 1600S, 19 Bradhurst Ave., New York Medical College, Hawthorne, NY 10532, USA. indu_taneja@hotmail.com
          Article
          ajpheart.01211.2010
          10.1152/ajpheart.01211.2010
          3129924
          21536847
          6e0fdc86-5507-4bc9-b346-f14184a638c4
          History

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