Static autoregulation in humans

Abstract

A recent publication in JCBFM, "Static autoregulation in humans" gives rise to critical comments. Autoregulation of cerebral blood flow implies that flow is rather constant within a certain blood pressure (BP) range with a lower and an upper pressure limit. The physiology at the two limits is very different, making comparison of the brain's vulnerability at the limits questionable. The recent publication in JCBFM claims a narrow autoregulatory range based on pooling of data from several studies. However, we argue that such pooling blurs the autoregulatory limits. We summarize the classical literature, therefrom we argue for a broad autoregulatory range.

Keywords: Autoregulation; cerebral autoregulation; cerebral blood flow regulation; cerebral hemodynamics; hemodynamics; meta-analysis.

Figure 1.

The slope of the CBF/blood pressure relation below the lower limit of autoregulation. (a) Low blood pressure, (b) normal blood pressure and (c) higher lower limit of CBF autoregulation. The low limit corresponds to a steeper CBF/blood pressure slope. Normalised to resting CBF 100%: A-slope: 2,50, B-slope: 1,67 and C-slope: 1,25%CBF/MABP. Data pooling. (a, b, c) Three schematic autoregulatory plots with different limits of the autoregulatory plateau and different levels of baseline cerebral blood flow. (d) The three curves from the top row are plotted on top of each other after adding random noise (adding an individual random value to CBF value between −10% and 10%). (e) The same data after normalising to both baseline blood pressure and CBF at baseline blood pressure. Not normalising yields a blurring of the autoregulatory limits, which becomes evident after normalization. CBF: cerebral blood flow; MABP: mean arterial blood pressure.