(Circulation. 2000;102:3086.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
Abnormal Baroreflex Responses in Patients With Idiopathic Orthostatic Intolerance
From the Center for Autonomic and Peripheral Nerve Disorders (W.B.F., S.E.D., K.P.C., R.F.), Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Mass, and HRCA Research and Training Institute and Harvard Medical School Division on Aging (W.B.F., J.A.T.), Boston, Mass.
Correspondence to Roy Freeman, MD, Beth Israel Deaconess Medical Center, Boston, MA 02215. E-mail rfreeman{at}caregroup.harvard.edu
Background—Patients diagnosed with idiopathic orthostatic intolerance report symptoms of lightheadedness, fatigue, and nausea accompanied by an exaggerated tachycardia when assuming the upright posture. Often, these symptoms are present in the absence of any decrease in arterial pressure. We hypothesized that patients with idiopathic orthostatic intolerance would have impaired cardiac vagal and integrated baroreflex function, lower blood volume, and increased venous compliance.
Methods and
Results—Sixteen patients and 14 healthy
control subjects underwent the modified Oxford technique to assess
cardiac vagal baroreflex sensitivity. Progressive lower-body negative
pressure (to –50 mm Hg; LBNP) was used to examine the integrated
baroreflex response to progressive hypovolemic stimuli. Blood volume
and venous compliance were also assessed. Patients with idiopathic
orthostatic intolerance had lower cardiac vagal baroreflex sensitivity
(12±1 versus 25±4 ms/mm Hg; P
0.01). The
integrated baroreflex response to low levels of LBNP was characterized
by shorter R-R intervals and more symptoms such as lightheadedness,
despite similar levels of blood pressure. There was a trend toward
lower blood volume in the patient group (56±2 versus 63±3 mL/kg;
P=0.054).
Conclusions—Patients with idiopathic orthostatic intolerance have lower cardiac vagal baroreflex sensitivity and marginally lower blood volume and respond with faster heart rates despite similar levels of arterial pressure during LBNP. These findings may contribute to the exaggerated postural tachycardia and symptoms observed in patients with this disorder.
Key Words: baroreceptors • blood pressure • tachycardia • nervous system, autonomic
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