Haemodynamic response to haemorrhage: distinct contributions of midbrain and forebrain structures.
The 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.
Troy
B P
BP
Department of Anatomy and Histology, The University of Sydney, NSW 2006, Australia.
Heslop
D J
DJ
Bandler
R
R
Keay
K A
KA
D000818:Animals; D001794:Blood Pressure / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology; D006470:Hemorrhage / Q000503:physiopathology*; D008297:Male; D008636:Mesencephalon / Q000502:physiology*; D016548:Prosencephalon / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley