Microvascular pulsatility of the ageing brain and confounding effects of anaesthesia

Microvascular pulsatility in the brain is crucial for sustaining the delicate balance between the brains metabolic demands and blood supply, as it affects nutrient exchange, waste removal and blood-brain barrier permeability. Abnormal pulsatility, associated with ageing or vascular risk factors, may impair the clearance of metabolic waste or contribute to conditions such as cerebral small vessel disease, ultimately leading to dementia and increasing the risk of stroke. In the present study, we introduce a new approach for robust full-field characterization of microvascular pulsatility and apply it to study cerebral perfusion and pulsatility across nearly the entire lifespan of awake and anaesthetized C57BL/6 mice. Our findings in awake animals reveal remarkably stable perfusion and pulsatility from 18 to 81 weeks, with pulsatility starting to change only in the final weeks of observation. In contrast, measurements taken under anaesthesia display a range of age-dependent and age-independent changes. We show that isoflurane affects the perfusion in an age-dependent manner, and both isoflurane and ketamine-xylazine, despite their distinct mechanisms, double the perfusion pulsatility and affect vascular diameter pulsatility in a complex manner, highlighting a previously overlooked detrimental effect of anaesthesia on assessing brain function.