The effect of hydralazine dose on blood perfusion changes during hyperthermia

Experiments were performed to determine the dose-related effects of the intravenous administration of a vasodilator (hydralazine) on normal muscle blood perfusion during localized hyperthermia. Fourteen anaesthetized outbred canines were investigated, seven receiving the recommended dose level of 0.5 mg/kg and seven receiving one-quarter of that level. The changes in blood perfusion were estimated using two methods: calculation of an effective blood perfusion magnitude and the use of state and parameter estimation techniques. Both methods showed that the changes in blood perfusion induced by the hydralazine were significant, and that the differences between the results for the two drug doses were not significantly different. This suggests that low doses may be useful in humans, giving the same resultant blood perfusion increase but with a decreased patient risk relative to standard therapeutic doses of hydralazine. While the trends in the blood perfusion changes were the same for both calculation methods the effective perfusion method frequently yielded blood perfusion magnitudes significantly different from those obtained using the state and parameter estimation technique. The differences are postulated to be due to the fact that the effective perfusion values include conduction effects, thus overpredicting the amount of perfusion present. Thus, while the effective blood perfusion can be used as a qualitative indication of blood perfusion changes under certain conditions, we do not recommend its use as a quantitative measure of perfusion.