Maximal inspiratory pressures and dimensions of the diaphragm

We postulated that the variation of maximal voluntary inspiratory pressures (P-I,P-max and P-di,P-max) among individuals largely reflects the variation of the structural attributes of the inspiratory muscles, in particular the muscular cross-sectional area of the diaphragm (CSA(di)) and its axially projected area (A(thor)) To test this postulate, we measured P-I,P-max in 36 healthy subjects, including 3 children and 15 weightlifters, and P-di,P-max in 11 subjects. Structural measurements by ultrasonography and anthropometric calipers were available as reported in the companion manuscript. We found a high degree of correlation of P-di,P-max with diaphragm thickness (t(di)), CSA(di), and CSA(di)/A(thor) (r(2) = 0.89, 0.89, and 0.77, respectively). P-I,P-max was also correlated with diaphragm structural measurements, although less well. The weight-lifters had greater pressures, thicker diaphragms, and greater diaphragm maximal stress (sigma(max)) than adults of similar stature who had not trained with weights. We conclude (1) that both P-di,P-max and P-I,P-max reflect in part structural attributes of the respiratory muscles; (2) that the variation of maximal transdiaphragmatic pressures is largely attributable to the normal variation of diaphragm structure; (3) weight lifting increases diaphragm structure and pressures.