Impact of propofol general anesthesia on cardiovascular and cerebrovascular closed loop variability interactions

The aim of the study is to assess the impact of general propofol-based anesthesia on both cardiovascular and cerebrovascular regulations. The strength and latency of cardiovascular and cerebrovascular controls were monitored by computing cross-correlation function (CCF) between heart period (HP) and systolic arterial pressure (SAP) and between mean arterial pressure (MAP) and mean cerebral blood flow (MCBF) velocity. HP, SAP, MAP and MCBF velocity were recorded in 25 patients (63.4 +/- 8.7 yrs, 2 females) undergoing coronary artery bypass grafting before (PRE) and after (POST) induction of propofol general anesthesia. Subjects breathed spontaneously during PRE, while they were mechanically ventilated during POST. CCFs were sampled at the first peak, or valley, with both negative and positive lags closest to zero according to a priori physiological notions about the CCF sign and latency of the presumed dynamic interactions. The null hypothesis of uncoupling was tested by associating pairs of signals from different subjects. Bidirectional interactions were detected, thus indicating the action of closed loop regulatory mechanisms along baroreflex and mechanical feedforward pathway in the case of HP-SAP control and along pressure-to-flow link and Cushing reflex in the case of MCBF-MAP control. Propofol anesthesia did not alter the coupling strength along baroreflex, feedforward mechanical pathway and pressure-to-flow link, while significantly decreased the strength of the Cushing reflex. Moreover, propofol anesthesia significantly shortened the baroreflex and pressureto-flow link latencies. The proposed analysis suggests profound modifications of cardiovascular and cerebrovascular controls during general anesthesia as a likely result of autonomic function modifications induced by propofol.