• B P Troy, D J Heslop, R Bandler, and K A Keay.
• Department of Anatomy and Histology, The University of Sydney, NSW 2006, Australia.
• Auton Neurosci. 2003 Oct 31;108(1-2):1-11.

AbstractThe haemodynamic response to a fixed volume haemorrhage passes through three distinct phases: a normotensive, compensatory phase; a hypotensive, decompensatory phase; and a post-haemorrhage, recompensatory phase. The role of the forebrain and midbrain in regulating the triphasic response to a 'fast' (1.5%/min) or 'slow' (0.75%/min) rate of blood withdrawal (30% haemorrhage) was evaluated by comparing, in unanaesthetised rats, the effects of pre-collicular (PCD) vs. pre-trigeminal decerebrations (PTD). It was found that pre-trigeminal decerebration attenuated the decompensatory (hypotensive) phase to either a fast or slow haemorrhage. In contrast, pre-collicular decerebration attenuated the compensatory and recompensatory phases of the response to a 'fast' (but not a slow) haemorrhage. These results suggest that the integrity of (i) forebrain structure(s) are critical for compensatory and recompensatory responses to 'rapid' blood loss; and (ii) midbrain structure(s) are critical for the decompensatory response to progressive blood loss irrespective of rate.

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