DYNAMIC CHANGES IN THE ZONE OF APPOSITION AND DIAPHRAGM LENGTH DURINGMAXIMAL RESPIRATORY EFFORTS

Background - Clinical tests of diaphragmatic strength are limited by t he wide normal variation in maximal pressure which result, in part, fr om changes in diaphragmatic length. During relaxation at different lun g volumes diaphragmatic length (LDI) can be estimated from the length of the zone of apposition (Lzapp) and the transverse diameter of the r ib cage (DRC). A study was carried out in two subjects using sequentia l digital radiography at six frames/second to determine whether these relations apply during maximal respiratory efforts which distort the r ib cage and diaphragm. Methods - The length of the anteroposterior con tour of the diaphragm and DRC were determined by curve fitting, Lzapp was measured with a millimetre rule. Results - A significant correlati on was found between LDI and Lzapp during both maximal inspiratory and expulsive manoeuvres (R(2) = 0.88 and 0.52). LDI was estimated from t he measurements of Lzapp and DRC using a multiple regression equation derived from measurements during static relaxation. Despite the comple x dynamic events at the onset Of these ''static'' manoeuvres, actual L DI correlated strongly with derived LDI using all data for the two man oeuvres in each subject (R(2) = 0.95 and 0.84). Measurements with ultr asonography (12 cm linear probe) and magnetometers confirmed the chang es in Lzapp and DRC during inspiratory and expulsive efforts. Conclusi ons - Non-invasive measurements of Lzapp and DRC can be used to derive an accurate estimate of diaphragmatic length under dynamic conditions .