Dynamic modulation of cerebrovascular resistance as an index of autoregulation under tilt and controlled PETCO2

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 52; no. 3; pp. R653 - R662
• Main Authors: EDWARDS, Michael R, SHOEMAKER, J. Kevin, HUGHSON, Richard L
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Physiological Society 01.09.2002
• Subjects: Biological and medical sciences; Blood pressure; Brain; Circulatory system; Fundamental and applied biological sciences. Psychology; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Vertebrates: nervous system and sense organs; Doppler ultrasound study; Human; Regional blood flow; Cardiovascular control; Head; Central nervous system; Carbon dioxide; Partial pressure; Vascular resistance; Self regulation; Tilt; Blood pressure; Hemodynamics; Transfer function; Brain (vertebrata)
• ISSN: 0363-6119; 1522-1490

Transfer function analysis of the arterial blood pressure (BP)-mean flow velocity (MFV) relationship describes an aspect of cerebrovascular autoregulation. We hypothesized that the transfer function relating BP to cerebrovascular resistance (CVRi) would be sensitive to low-frequency changes in autoregulation induced by head-up tilt (HUT) and altered arterial PCO2. Nine subjects were studied in supine and HUT positions with end-tidal PCO2 (PETCO2) kept constant at normal levels: +5 and 5 mmHg. The BP-MFV relationship had low coherence at low frequencies, and there were significant effects of HUT on gain only at high frequencies and of PCO2 on phase only at low frequencies. BP CVRi had coherence >0.5 from very low to low frequencies. There was a significant reduction of gain with increased PCO2 in the very low and low frequencies and with HUT at the low frequency. Phase was affected by PCO2 in the very low frequencies. Transfer function analysis of BP CVRi provides direct evidence of altered cerebrovascular autoregulation under HUT and higher levels of PCO2.