ABSTRACT
BACKGROUND: This study was aimed to elucidate the effect of propofol anesthesia on circulatory response to hemorrhage in rats by power spectral analysis of heart rate and blood pressure variability. METHODS: Nineteen male Sprague-Dawley rats weighing 350-580 g were divided into propofol (2 mg/kg, iv)-anesthetized (P, n=10) and saline control (C, n=9) groups. Blood pressure signal was digitized at 500 Hz for 5 min at basal, during hemorrhage and after hemorrhage. The signal was analyzed with fast Fourier transform algorithm to yield power spectra of systolic (SPV) and diastolic (DPV) blood pressure and cycle length variability (HRV). Very low frequency (VLF, 0.02-0.26 Hz), low frequency (LF, 0.26-0.75 Hz), high frequency (HF, 0.75-5.00 Hz) powers, LF/HF ratio and total power were obtained. Powers of each band were expressed as percent of total power. RESULTS: Blood pressure was decreased during hemorrhage in C and with a greater magnitude in P. Heart rate tended to increase during hemorrhage in C, but was not changed in P. LF powers of SPV in P was decreased after propofol injection. Hemorrhage decreased LF and increased HF. LF powers of DPV in P was decreased after propofol injection. Hemorrhage caused a further decrease in LF. LF powers of HRV in P was decreased after propofol injection. Hemorrhage caused a further decrease in LF. Powers of SPV, DPV and HRV in C were not changed by hemorrhage. LF/HF of SPV, DPV and HRV were decreased during hemorrhage in P, but not in C. CONCLUSIONS: These results suggest that propofol depressed sympathetic activity to diminish peripheral vascular tone and hemorrhage under propofol anesthesia resulted in a greater blood pressure fall due to impaired sympathetic compensation including attenuated baroreflex mechanism.