DETERMINANTS OF MAXIMAL TRANSDIAPHRAGMATIC PRESSURE IN ADULTS WITH CYSTIC-FIBROSIS

To investigate whether diaphragmatic strength could be reduced in cyst ic fibrosis (CF), and to examine possible mechanisms leading to diaphr agmatic weakness, we measured transdiaphragmatic pressure (Pdi), toget her with lung mechanics, including dynamic ''intrinsic'' positive end- expiratory pressure (PEEPi,dyn), ventilation, lung volumes, and nutrit ional status in 15 adult patients with CF in stable clinical condition . Diaphragmatic strength was assessed as the maximum Pdi (Pdi(max)). N utritional assessment included the calculation of weight as a percenta ge of ideal weight for height (Wt/Ht). On average, our 15 CF patients had airway obstruction (FEV(1) = 59 +/- 28% predicted) and a small PEE Pi,dyn (1 +/- 0.7 cm H2O). Functional residual capacity averaged 52 +/ - 9% of the predicted total lung capacity. The Wt/Ht was normal on ave rage (95%), but with a large range from malnutrition to a good nutriti onal status (76 to 109%). We found that Pdi(max) decreased with increa sing FRC/TLC percent predicted (r = 0.55, p < 0.05), but more signific antly with decreasing Wt/HT (r = 0.76, p < 0.001). The multiple linear regression analysis for these factors was significant(R(2) = 0.70, p < 0.05); however, the partial regression coefficient was significant o nly for Wt/Ht (p < 0.01). These results suggest that in CF patients, d iaphragmatic strength decreases with the progression of the disease, i ncreasing lung volume and worsening nutritional status, and that malnu trition is the strongest determinant of diaphragmatic weakness.