Non‐Invasive Measurement of Cerebral Vascular Compliance During Post Exercise Ischemia

Abstract

Increases in blood pressure and sympathetic nerve activity (SNA) decrease cerebrovascular compliance. However, in humans it is unclear where in the cerebrovascular tree this decrease in compliance occurs; at the level of the major cerebral arteries or at the distal cerebral arterioles. The aim of this study was to use a novel MRI based method to measure arterial compliance (AC) of cerebral arteries during post exercise ischemia (PEI) induced after isometric forearm contraction. In 8 men aged 25-42 years, arterial blood volumes were assessed in diastole and systole with short inversion time arterial spin labelling. AC was calculated by dividing the percentage change in arterial blood volume from diastole to systole by the brachial pulse pressure. AC was assessed in the internal carotid and basilar arteries (ICA, BA) feeding the Circle of Willis (CoW), and in the middle cerebral arteries (MCA) at the level of and branching from the CoW. During PEI there were significant increases (paired t-tests, p < 0.05) in systemic mean arterial pressure (+9.2 ± 10.6 mmHg) and SNA (+10.5 ± 7.8 burst/100 heartbeats). Figure 1 illustrates that during PEI the arteries below and at the level of the CoW show a decrease in AC, while the MCA flow territories distal from the CoW show no change in AC. These results indicate that during PEI AC decreases only in the major brain feeding arteries. Figure 1. Compliance plotted against slice location. Note that the data is averaged over the major brain feeding arteries below the CoW (ICA and BA) and both the right and left MCA at the level of and above the CoW. Error bars indicate standard error of the mean.