We studied the effects of digoxin, a compound that has an inotropic effect on the myocardium, on diaphragmatic function in 8 patients with chronic obstructive pulmonary disease. All the patients were in acute respiratory failure and were artificially ventilated. Diaphragmatic strength was assessed by measuring the transdiaphragmatic pressure generated at functional residual capacity during bilateral supramaximal electrical stimulation of the phrenic nerves. The latter were stimulated before and at 45 and 90 min after administration of digoxin (0.02 mg/kg infused for 10 min). In all the patients, cardiac output was measured by the thermodilution technique using a Swan-Ganz catheter placed in the pulmonary artery. Arterial blood gases and pH were maintained within normal range by mechanical ventilation. In all the patients, digoxin plasma levels reached the therapeutic range (mean values, 2.82 +/- 0.17 and 2.90 +/- 0.20 nmol/L at 45 and 90 min, respectively) after digoxin administration. Diaphragmatic strength improves significantly after digoxin administration, the transdiaphragmatic pressure for an identical phrenic stimulation increasing by 19.5% (p less than 0.001) on the average. This increase was noted 45 and 90 min after digoxin administration. We conclude that digoxin has a potent effect on diaphragmatic strength generation that may be beneficial in patients with chronic obstructive pulmonary disease during acute respiratory failure. Furthermore, this inotropic positive effect of digoxin on the diaphragm, as previously observed for the myocardium, emphasizes the similarities between these 2 contractile tissues.