Cardiovascular and Regional Blood Flow Changes during Halothane Anesthesia in the Aged Rat

The authors investigated the cardiovascular and regional hemodynamic changes that occur in the aged rat under unanesthetized control conditions and during the induction of halothane anesthesia. Regional blood flow changes were measured in young (4-month-old) and aged (27-29-month-old) F-344 rats using radioactive microspheres under unanesthetized conditions and during three levels of halothane anesthesia. Blood halothane levels were measured at each anesthetic level. The inspired concentrations of halothane were adjusted in young vs. aged rats so that each group was tested at the same depth of anesthesia. Results indicate that aged rats had significantly lower blood pressures than young rats in an unanesthetized state and at all levels of halothane anesthesia. Tissue blood flow was similar between young and aged rats in skeletal muscle and skin, while blood flow to renal and small intestinal tissues was consistently higher in young rats. Heart blood flow was initially 100 per cent higher in young rats but decreased to similar levels as aged at the highest levels of halothane anesthesia used. Cerebral blood flow was similar initially in young vs. aged, but increased in young rats with deeper levels of halothane anesthesia while decreasing in aged rats. These results indicate significant regional hemodynamic differences in young compared to aged rats under unanesthetized conditions as well as in response to halothane anesthesia.