Evaluation of diaphragmatic contractility in patients with chronic obstructive lung diseases.

The indices of diaphragmatic contractility and respiratory ventilation were studied in 31 males with chronic obstructive bronchitis distributed into 2 groups: with hypercapnia (PaCO2 56.3 +/- 0.4 mm Hg) and normocapnia (PaCO2 42.7 +/- 1.4 mm Hg), with reduction of FEV1/VC to 42% and 52% of the due value, Pdimax to 63.4 +/- 5.3 cm H2O and 73.4 +/- 6.1 cm H2O. The plasmatic theophylline concentration 21.19 +/- 1.06 mkg/ml was maintained in five patients with hypercapnia for 10 days by intravenous administration of aminophylline. FEV1 and VC increased by 5% and 8% respectively, Pdimax by 59%, TTdi decreased from 0.10 +/- 0.02 to 0.06 +/- 0.01, and PaCO2--to 44.7 +/- 1.8 mmHg. Vt/Ti did not change significantly. Thus, in patients with irreversible bronchial obstruction the decrease of diaphragmatic contractility leads to the development of arterial hypercapnia. The maintenance of therapeutical concentration of theophylline in blood plasma permits to improve the ventilation function of respiratory muscles and normalize the PaCO2 level.