MAXIMAL INSPIRATORY PRESSURES AND DIMENSIONS OF THE DIAPHRAGM

We postulated that the variation of maximal voluntary inspiratory pres sures (P-I,P-max and P-di,P-max) among individuals largely reflects th e variation of the structural attributes of the inspiratory muscles, i n particular the muscular cross-sectional area of the diaphragm (CSA(d i)) and its axially projected area (A(thor)) To test this postulate, w e measured P-I,P-max in 36 healthy subjects, including 3 children and 15 weightlifters, and P-di,P-max in 11 subjects. Structural measuremen ts by ultrasonography and anthropometric calipers were available as re ported in the companion manuscript. We found a high degree of correlat ion of P-di,P-max with diaphragm thickness (t(di)), CSA(di), and CSA(d i)/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, an d 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 r espiratory muscles; (2) that the variation of maximal transdiaphragmat ic pressures is largely attributable to the normal variation of diaphr agm structure; (3) weight lifting increases diaphragm structure and pr essures.