STRUCTURE AND FUNCTION RELATIONSHIPS OF THE RESPIRATORY MUSCLES

Potential relationships between the structure of the diaphragm and ext ernal intercostals and several indices of respiratory muscle function, lung function and nutrition in 27 patients (61+/-10 yrs of age) subje cted to thoracotomy as a result of a lung neoplasm have been investiga ted, Prior to surgery the nutritional status of the patients was asses sed and lung function (spirometry, lung volumes, transfer factor of th e lungs for carbon monoxide, arterial blood gases) and respiratory mus cle function (maximal inspiratory pressure (MIP) and diaphragmatic fun ction were measured). Biopsies of the diaphragm land external intercos tals) mere obtained during surgery. On average, patients showed mild a irflow-limitation (forced expiratory volume in one second (FEV1), 70+/ -14% of predicted value, FEV1/forced vital capacity (FVC), 70+/-9%) wi th some air trapping (residual volume (RV), 139+/-50% pred) and normal gas exchange (arterial oxygen tension (P-a,P-O2) 11.3+/-1.33 kPa (85/-10 mmHg)) and arterial carbon dioxide tension (P-a,P-CO2) 5.4+/-0.5 kPa (40.6+/-4 mmHg), MIP was 77+/-25% pred; maximal transdiaphragmatic pressure was 90+/-27 cmH(2)O. Most morphometric measurements of the d iaphragm and external intercostals were within the range of values rep orted previously in other skeletal muscles. The size of the fibres of these two respiratory muscles was positively related (p<0.05) to MIP ( % pred), There were no significant relationships between the structure of both muscles and nutritional status or any index of lung function. In conclusion, in the population studied, the fibre size of the diaph ragm and external intercostals appears to relate to their ability to g enerate force.