Hypocapnia and cerebral hypoperfusion in orthostatic intolerance

Vera Novak, Judith M. Spies, Peter Novak, Benjamin R. McPhee, Teresa A. Rummans, Phillip Anson Low

Research output: Contribution to journalArticle

139 Citations (Scopus)

Abstract

Background and Purpose - Orthostatic and other stresses trigger tachycardia associated with symptoms of tremulousness, shortness of breath, dizziness, blurred vision, and, often, syncope. It has been suggested that paradoxical cerebral vasoconstriction during head-up tilt might be present in patients with orthostatic intolerance. We chose to study middle cerebral artery (MCA) blood flow velocity (BFV) and cerebral vasoregulation during tilt in patients with orthostatic intolerance (OI). Methods - Beat-to-beat BFV from the MCA, heart rate, CO2, blood pressure (BP), and respiration were measured in 30 patients with OI (25 women and 5 men; age range, 21 to 44 years; mean age, 31.3±1.2 years) and 17 control subjects (13 women and 4 men; age range, 20 to 41 years; mean age, 30±1.6 years); ages were not statistically different. These indices were monitored during supine rest and head-up tilt (HUT). We compared spontaneous breathing and hyperventilation and evaluated the effect of CO2 rebreathing in these 2 positions. Results - The OI group had higher supine heart rates (P < 0.001) and cardiac outputs (P < 0.01) than the control group. In response to HUT, OI patients underwent a greater heart rate increment (P < 0.001) and greater reductions in pulse pressure (P < 0.01) and CO2 (P < 0.001), but total systemic resistance failed to show an increment. Among the cerebrovascular indices, all BFVs (systolic, diastolic, and mean) decreased significantly more, and cerebrovascular resistance (CVR) was increased in OI patients (P < 0.01) compared with control subjects. In both groups, hyperventilation induced mild tachycardia (P < 0.001), a significant reduction of BFV, and a significant increase of CVR associated with a fall in CO2. Hyperventilation during HUT reproduced hypocapnia, BFV reduction, and tachycardia and worsened symptoms of OI; these symptoms and indices were improved within 2 minutes of CO2 rebreathing. The relationships between CO2 and BFV and heart rate were well described by linear regressions, and the slope was not different between control subjects and patients with OI. Conclusions - Cerebral vasoconstriction occurs in OI during orthostasis, which is primarily due to hyperventilation, causing significant hypocapnia. Hypocapnia and symptoms of orthostatic hypertension are reversible by CO2 rebreathing.

Original languageEnglish (US)
Pages (from-to)1876-1881
Number of pages6
JournalStroke
Volume29
Issue number9
StatePublished - Sep 1998

Fingerprint

Orthostatic Intolerance
Hypocapnia
Blood Flow Velocity
Hyperventilation
Heart Rate
Head
Tachycardia
Cardiac Output
Middle Cerebral Artery
Dizziness
Vasoconstriction
Cerebrovascular Circulation
Respiration
Blood Pressure
Syncope
Dyspnea
Linear Models

Keywords

  • Hypocapnia
  • Hypoperfusion
  • Hypotension, orthostatic
  • Orthostatic intolerance
  • Ultrasonography, Doppler, duplex

ASJC Scopus subject areas

  • Cardiology and Cardiovascular Medicine
  • Neuroscience(all)

Cite this

Novak, V., Spies, J. M., Novak, P., McPhee, B. R., Rummans, T. A., & Low, P. A. (1998). Hypocapnia and cerebral hypoperfusion in orthostatic intolerance. Stroke, 29(9), 1876-1881.

Hypocapnia and cerebral hypoperfusion in orthostatic intolerance. / Novak, Vera; Spies, Judith M.; Novak, Peter; McPhee, Benjamin R.; Rummans, Teresa A.; Low, Phillip Anson.

In: Stroke, Vol. 29, No. 9, 09.1998, p. 1876-1881.

Research output: Contribution to journalArticle

Novak, V, Spies, JM, Novak, P, McPhee, BR, Rummans, TA & Low, PA 1998, 'Hypocapnia and cerebral hypoperfusion in orthostatic intolerance', Stroke, vol. 29, no. 9, pp. 1876-1881.
Novak V, Spies JM, Novak P, McPhee BR, Rummans TA, Low PA. Hypocapnia and cerebral hypoperfusion in orthostatic intolerance. Stroke. 1998 Sep;29(9):1876-1881.
Novak, Vera ; Spies, Judith M. ; Novak, Peter ; McPhee, Benjamin R. ; Rummans, Teresa A. ; Low, Phillip Anson. / Hypocapnia and cerebral hypoperfusion in orthostatic intolerance. In: Stroke. 1998 ; Vol. 29, No. 9. pp. 1876-1881.
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