Age dependent effects of haemorrhage on the arterial baroreflex control of heart rate in conscious lambs

Abstract

Previously, we showed that arterial pressure decreased after moderate haemorrhage in conscious lambs, whereas a compensatory increase in heart rate occurred only in newborns. These findings provided evidence to suggest an age‐dependent effect of haemorrhage on the arterial baroreflex control of heart rate. Therefore, in the present study, the arterial baroreflex was assessed in conscious lambs aged 14±1 days (G I, N=4) and 43±7 days (G II, N=6) before (control, C) and at 30 and 60 min after haemorrhage (30% of calculated blood volume). The following parameters governing the arterial baroreflex were evaluated: Heart rate range (P1), slope coefficient (P2), systolic arterial pressure at midpoint (P3), minimum HR (P4), and maximum gain (Gmax). Values are mean±SEM; *p<0.05 compared with C; †p<0.05 compared with G I.Predominant effects of haemorrhage were: a decrease in P1 which was greater in G I than G II, and a decrease in Gmax which was greater in G II than G I. Therefore, severe haemorrhage alters several parameters governing the arterial baroreflex control of heart rate, these effects being developmentally regulated.This research was supported by the Canadian Institutes of Health Research (CIHR).