Effects of Dopamine on Diaphragm Fatigue

Thousands of people every year require mechanical ventilation for various illnesses. In the process of "weaning" from mechanical ventilation, respiratory muscles particularly the diaphragm can become fatigued. In addition, frequently these patients are also on low dose dopamine to improve diuresis and renal function. Using a rat model, we hypothesized that intravenous low doe dopamine could prevent and treat diaphragm fatigue by increasing diaphragm blood flow (DBF). There were three groups of rats: (1) normal saline group, (2) dopamine at fatigue group and (3) dopamine before inspiratory resistance loading (IRL). Adult male Sprague-Dawley rats were cannulated for infusion and withdrawal of blood and measurement of intrathoracic pressure (ITP). Diaphragm shortening (DS) was measured with an ultrasonic sensor attached to the inferior diaphragm surface. Aortic blood flow and DBR were measured using fluorescent microspheres. Diaphragm fatigue was induced or attempted to be induced using IRL. When diaphragm fatigue was attained, Group I was given saline for 30 min while maintaining IRL. At the time of diaphragm fatigue, Group II was given low dose dopamine (2 ug/kg/min) for 30 min while maintaining IRL. In Group III dopamine administration was started before and continued throughout the period of IRL. Administering dopamine after the development of diaphragm fatigue (Group II) increased diaphragm performance as measured by increased diaphragm shortening and was accompanied by an increased diaphragm blood flow. Administering dopamine prior to and throughout IRL (Group III) prevented diaphragm fatigue. We concluded that low dose dopamine can prevent and/or reverse diaphragm fatigue in rats without a significant change in aortic blood flow. This effect of dopamine may be due to increased oxygen delivery associated with the increased diaphragm blood flow resulting in less free radical formation and thus less muscle damage.

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