title: Reduced stroke volume during exercise in postural tachycardia syndrome.
abstract: Postural tachycardia syndrome (POTS) is characterized by excessive tachycardia without hypotension during orthostasis. Most POTS patients also report exercise intolerance. To assess cardiovascular regulation during exercise in POTS, patients (n = 13) and healthy controls (n = 10) performed graded cycle exercise at 25, 50, and 75 W in both supine and upright positions while arterial pressure (arterial catheter), heart rate (HR; measured by ECG), and cardiac output (open-circuit acetylene breathing) were measured. In both positions, mean arterial pressure, cardiac output, and total peripheral resistance at rest and during exercise were similar in patients and controls (P > 0.05). However, supine stroke volume (SV) tended to be lower in the patients than controls at rest (99 +/- 5 vs. 110 +/- 9 ml) and during 75-W exercise (97 +/- 5 vs. 111 +/- 7 ml) (P = 0.07), and HR was higher in the patients than controls at rest (76 +/- 3 vs. 62 +/- 4 beats/min) and during 75-W exercise (127 +/- 3 vs. 114 +/- 5 beats/min) (both P < 0.01). Upright SV was significantly lower in the patients than controls at rest (57 +/- 3 vs. 81 +/- 6 ml) and during 75-W exercise (70 +/- 4 vs. 94 +/- 6 ml) (both P < 0.01), and HR was much higher in the patients than controls at rest (103 +/- 3 vs. 81 +/- 4 beats/min) and during 75-W exercise (164 +/- 3 vs. 131 +/- 7 beats/min) (both P < 0.001). The change (upright - supine) in SV was inversely correlated with the change in HR for all participants at rest (R(2) = 0.32), at 25 W (R(2) = 0.49), 50 W (R(2) = 0.60), and 75 W (R(2) = 0.32) (P < 0.01). These results suggest that greater elevation in HR in POTS patients during exercise, especially while upright, was secondary to reduced SV and associated with exercise intolerance.
authors.affiliation: Department of Anesthesiology, Mayo Clinic Foundation, Rochester, MN 55905, USA.
authors.forename: Shizue
authors.initials: S
authors.lastname: Masuki
authors.forename: John H
authors.initials: JH
authors.lastname: Eisenach
authors.forename: William G
authors.initials: WG
authors.lastname: Schrage
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Johnson
authors.forename: Niki M
authors.initials: NM
authors.lastname: Dietz
authors.forename: Brad W
authors.initials: BW
authors.lastname: Wilkins
authors.forename: Paola
authors.initials: P
authors.lastname: Sandroni
authors.forename: Phillip A
authors.initials: PA
authors.lastname: Low
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Joyner
mesh_terms: D000328:Adult; D002303:Cardiac Output, Low / Q000503:physiopathology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D007024:Hypotension, Orthostatic / Q000503:physiopathology; D008297:Male; D011187:Posture / Q000502:physiology*; D013318:Stroke Volume / Q000502:physiology*; D013610:Tachycardia / Q000503:physiopathology*