[Effects of experimental ascites on diaphragm strength]

We studied the strength developed by the diaphragm during progressive ascitis induction (40 up to 280 ml/kg wt) and the changes in the radium of curvature in relation with its strength in 6 anesthetized dogs. Force generation of the diaphragm was assessed with the Pdi obtained with bilateral phrenic nerve stimulation at 60 Hz. In relation to increases in the abdominal liquid, the thoraco-pulmonary compliance decreases (p < 0.05) from 10.1 to 6.8 ml/kg/cm H2O. The radius of curvature increases 158% from the basal values; the calculated basal tension was 347 +/- 43, final 448 +/- 32 cm H2O/cm. The diaphragmatic length in percent of the basal value was 138%. The X-rays findings showed cephalic displacement, diaphragmatic flattening and stretching. The Pdi obtained should be the result of a complex interaction between the diaphragmatic geometry, the length, the degree of stretching during the contraction and preload. We can describe the changes in Pdi in 2 steps: initial increase and final decrease, associated to high Pga at the beginning and a low one later. First the Pdi increases by the Pga without significant changes in the Pes. The fact is that an increase in Pga can be related with cephalic displacement of the diaphragm with stretching and shortening of the radius of curvature and decreases in the abdominal compliance. The final decreases in the Pdi could be related with overstretching and decreases of the radius of curvature.