THERMAL METHOD FOR CONTINUOUS MEASUREMENT OF CEREBRAL PERFUSION

A new thermal system using constant heating power for continuous measu rement of cerebral perfusion is presented. It is designed and implemen ted for optimal perfusion sensitivity and dynamic response based on he at-transfer analysis of perfused brain tissue with thermistors on the cortical surface. Two matched thermistors are used, one to serve as a perfusion sensor and the other to compensate for the base-line tempera ture changes. To improve the signal-to-noise ratio of the measurement system, lock-in amplifiers are used to minimise long-term drift and lo w-frequency noise. Errors in the measurement caused by electrical and thermal fluctuations are tested and analysed. In vitro tests show that the measurement accuracy of temperature change is better than 10(-3)d egrees C, and the temperature resolution is even greater. In vivo eval uation confirms that the system is responsive to cerebral perfusion ch anges associated with sudden changes in mean arterial blood pressure c aused by bolus injection of norepinephrine, blood withdrawal and blood infusion. The dynamic response of the system is sufficient to detect the autoregulatory perfusion changes in response to arterial blood pre ssure alteration and the oscillations of cerebral blood flow.