Influence of Changes in Blood Pressure on Cerebral Perfusion and Oxygenation

Abstract

Abstract-Cerebral autoregulation (CA) is a critical process for the maintenance of cerebral blood flow and oxygenation.Assessment of CA is frequently used for experimental research and in the diagnosis, monitoring, or prognosis of cerebrovascular disease; however, despite the extensive use and reference to static CA, a valid quantification of "normal" CA has not been clearly identified. While controlling for the influence of arterial PCO 2 , we provide the first clear examination of static CA in healthy humans over a wide range of blood pressure. In 11 healthy humans, beat-to-beat blood pressure (radial arterial), middle cerebral artery blood velocity (MCAv; transcranial Doppler ultrasound), end-tidal PCO 2 , and cerebral oxygenation (near infrared spectroscopy) were recorded continuously during pharmacological-induced changes in mean blood pressure. In a randomized order, steady-state decreases and increases in mean blood pressure (8 to 14 levels; range: Ϸ40 to Ϸ125 mm Hg) were achieved using intravenous infusions of sodium nitroprusside or phenylephrine, respectively. MCAv mean was altered by 0.82Ϯ0.35% per millimeter of mercury change in mean blood pressure (R 2 ϭ0.82). Changes in cortical oxygenation index were inversely related to changes in mean blood pressure (slopeϭϪ0.18%/mm Hg; R 2 ϭ0.60) and MCAv mean (slopeϭϪ0.26%/cm ⅐ s Ϫ1; R 2 ϭ0.54). There was a progressive increase in MCAv pulsatility with hypotension. These findings indicate that cerebral blood flow closely follows pharmacological-induced changes in blood pressure in otherwise healthy humans. Thus, a finite slope of the plateau region does not necessarily imply a defective CA. Moreover, with progressive hypotension and hypertension there are differential changes in cerebral oxygenation and MCAv mean . (Hypertension. 2010;55:698-705.)

Assessment of cerebral autoregulation: the quandary of quantification

“…Third, there is a need for better standardization of terminology. Although the term "cerebral autoregulation" is commonly used, it is not always clear whether the reference is used to describe the same physiological construct (25). Our findings indicate that it may not be possible to reduce CA, a nonlinear and complex process, into a single all-encompassing index.…”

Dynamic cerebral autoregulation during and following acute hypoxia: role of carbon dioxide

“…The mechanisms of CA are complex and incompletely understood, but likely rely on a combination and interaction of myogenic, neural, endothelial, and metabolic factors (1,32). Although recently challenged in both healthy humans (18) and patients (13), the conventional model of static CA proposes that cerebral blood flow (CBF) is independent of steady-state changes in mean arterial pressure (MAP) between ϳ50 and 160 mmHg (17). In contrast, dCA responds to sudden changes in blood pressure and is frequently active throughout a typical day, such as during rapid adjustments in posture.…”

Measuring cerebrovascular autoregulation in preterm infants using near-infrared spectroscopy: an overview of the literature

“…This concept is largely adapted from insights from adult studies [8]; CBF is suggested to be stable (plateau) over a wide ABP range, reflecting 'intact' static cerebrovascular autoregulation (lower panel in Figure 1). Noteworthy, in adult studies, it has been suggested that this plateau might not be completely horizontal [9,10]. Absent autoregulation is often represented by a strong linear relationship between CBF and ABP (upper panel in Figure 1).…”