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This Article Full Text Full Text (PDF) All Versions of this Article: 293/3/H1908    most recent 00439.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Stewart, J. M. Articles by Medow, M. S. Search for Related Content PubMed PubMed Citation Articles by Stewart, J. M. Articles by Medow, M. S.

Reduced central blood volume and cardiac output and increased vascular resistance during static handgrip exercise in postural tachycardia syndrome

Departments of ¹Pediatrics, ²Physiology, and ³Medicine, New York Medical College, Valhalla, New York

Submitted 10 April 2007 ; accepted in final form 29 June 2007

Postural tachycardia syndrome (POTS) is characterized by exercise intolerance and sympathoactivation. To examine whether abnormal cardiac output and central blood volume changes occur during exercise in POTS, we studied 29 patients with POTS (17–29 yr) and 12 healthy subjects (18–27 yr) using impedance and venous occlusion plethysmography to assess regional blood volumes and flows during supine static handgrip to evoke the exercise pressor reflex. POTS was subgrouped into normal and low-flow groups based on calf blood flow. We examined autonomic effects with variability techniques. During handgrip, systolic blood pressure increased from 112 ± 4 to 139 ± 9 mmHg in control, from 119 ± 6 to 143 ± 9 in normal-flow POTS, but only from 117 ± 4 to 128 ± 6 in low-flow POTS. Heart rate increased from 63 ± 6 to 82 ± 4 beats/min in control, 76 ± 3 to 92 ± 6 beats/min in normal-flow POTS, and 88 ± 4 to 100 ± 6 beats/min in low-flow POTS. Heart rate variability and coherence markedly decreased in low-flow POTS, indicating uncoupling of baroreflex heart rate regulation. The increase in central blood volume with handgrip was absent in low-flow POTS and blunted in normal-flow POTS associated with abnormal splanchnic emptying. Cardiac output increased in control, was unchanged in low-flow POTS, and was attenuated in normal-flow POTS. Total peripheral resistance was increased compared with control in all POTS. The exercise pressor reflex was attenuated in low-flow POTS. While increased cardiac output and central blood volume characterizes controls, increased peripheral resistance with blunted or eliminated in central blood volume increments characterizes POTS and may contribute to exercise intolerance.

orthostatic intolerance; mechanoreflex; metaboreflex; regional blood volume; exercise intolerance