INFLUENCE OF AGE ON THE CARDIOVASCULAR-RESPONSE DURING GRADED HEMORRHAGE IN ANESTHETIZED RATS

The present study was designed to follow the cardiovascular response t o graded haemorrhage in two groups of adult rats of different ages. Gr oup A (n = 10) had a mean body weight (bwt) of 655 g (50 weeks old) an d group B (n = 10) had a mean bwt of 250 g (12 weeks old). After induc tion of anaesthesia, the carotid artery was cannulated for continuous intra-arterial blood pressure monitoring and for controlled haemorrhag e. Five per cent of the total blood volume (TBV) was removed every 15 min until a maximum of 50% was reached. Mean arterial pressure (MAP) f ell by 4-9 mm Hg each time 5% TBV was removed in both groups, and at t he end of the study the MAP was comparable in the two groups (34 +/- 1 0 mm Hg in group A and 28 +/- 8 mm Hg in group B). There were no signi ficant changes in heart rate (HR) in the young animals during haemorrh age, while there was a significant drop in heart rate in the older ani mals when blood loss exceeded 15% of TBV (P < 0.05). A significant dif ference was also observed in HR between the two groups of animals with blood loss in excess of 20% TBV (P < 0.05). It was concluded that alt hough the hypotension induced by graded haemorrhage was similar in you ng and old rats, the older animals were less able to maintain their HR , probably as a consequence of age- and anaesthetic-related changes in sympathetic activity.