The haemodynamic consequences of a carotid-jugular fistula in the rat during hypocapnia

This study was undertaken to examine further the effects of hypocapnia and the contribution of hypotension to the haemodynamic consequences of cerebral arteriovenous fistula ablation in the rat chronic carotid-jugular fistula model. Regional cerebral blood flow (rCBF) was measured by the ¹⁴C-iodoantipyrine technique under halothane anaesthesia 12 weeks after the creation of the fistula. rCBFs in all groups were conducted at a similar PaCO₂ (22-26 mmHg). The rCBF in control animals ranged from a mean of 51-71 ml/100 g/min at a mean systemic arterial pressure of 136 mmHg, and 56-71 ml/100 g/min at a mean systemic arterial pressure of 89 mmHg after 2.5 ml blood loss. These values correspond to those expected for this degree of hypocapnia in rats without a carotid-jugular fistula. In animals with an open carotid-jugular fistula created 12 weeks prior to the study, mean rCBFs at comparable blood pressure ranged from 23-33 ml/100 g/min in normotensive animals and 29-44 ml/100 g/min in the hypotensive animals. These flows were not significantly different. The conclusion of this study is that the carotid-jugular fistula group is able to autoregulate and maintain a constant regional cerebral blood flow during the challenge of hypotension under hypocapnic conditions. This ability to autoregulate is preserved despite the chronic hypoperfusion due to the arteriovenous shunt and the added insult of low regional cerebral blood flows caused by hypocapnia at the time of the experiment.