Effect of body weight and muscularity on human diaphragm muscle mass, thickness, and area.

To assess the consequences to the human diaphragm of alterations in body weight and muscularity, we measured the mass, thickness, area, and length of diaphragm muscle at necropsy. Of 33 subjects who were clinically well until sudden death, 27 had sedentary occupations and normal weight (group N), while 6 were nonobese laborers whose average weight was 40% greater than normal (group M). Among 37 patients dying of more prolonged illness, 23 were of normal weight (group W), while 14 weighed 71% of normal (group U). Subjects with obesity, chronic pulmonary disease, or edema were excluded. Disease per se did not significantly affect diaphragm dimensions. However, in group M diaphragm muscle mass, thickness, area, and length were 165, 129, 125, and 117% of normal (P less than 0.005), whereas in group U the corresponding values were 57, 73, 77, and 83% (P less than 0.001). Thus alterations in body weight and muscularity profoundly affect diaphragm muscle mass, causing a nearly threefold variation between muscular normal subjects and underweight patients.