Cooling and dopamine
Abstract: There is little knowledge about the circulatory effects of dopamine in hypothermia. Induced hypothermia has been shown to improve outcome in various settings. Hypothermia is also used for preservation of organs that are harvested for transplantation. We evaluated lungs that were topically cooled for 6 hours in non-heart-beating donor pigs by transplanting them into recipient pigs and observing these for 24 hours. Furthermore, we studied the effects of hypothermia and dopamine on myocardial action potentials and contractions in porcine myocardial muscle strips. In addition, the circulatory effects of dopamine were studied in different settings in normo- and hypothermia in anesthetized pigs. We found that lungs that were topically cooled for 6 hours in non-heart-beating donor pigs were suitable for transplantation. Cooling to 32ºC prolonged the porcine myocardial action potential and contraction duration and increased the contractile force. Dopamine prolonged the porcine myocardial action potential and increased contractile force both in normo- and hypothermia. The heart rate was increased by dopamine at both temperature levels. Dopamine either increased (studyI) or did not change the arterial pressure in normothermia, whereas it reduced or caused no change (study V) in arterial pressure in hypothermia. Dopamine increased cardiac output and oxygen delivery in normothermia as well as in hypothermia, apart from in tachcyardic hypothermic piglets, in which dopamine caused aggravation of tachycardia and presumably a too short diastolic filling time. A high dosage of dopamine increased pulmonary vascular resistance at 32ºC. It is concluded that dopamine excerts principally much the same effects at 32ºC as in normothermia. However, dopamine may compromize ventricular filling in hypothermia due to it`s chronotropic effect combined with a hypothermia-induced shortening of diastolic filling time. Dopamine may also decrease the blood pressure substantially in cases where the sympathetic nervous tonus is high, e.g. after surface cooling during light anesthesia. Pulmonary vascular resistance may also be increased by dopamine at high dosages.
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