The large-scale developments of integrated health services present great challenges to the efficient and reliable implementation of information technology, especially in large, divisionalized organizations. There is a need to take a more sophisticated approach to understanding the complexities of organizational factors than has traditionally been the case.
Background -Clinical tests of diaphragmatic strength are limited by the wide normal variation in maximal pressure which result, in part, from changes in diaphragmatic length. During relaxation at different lung volumes diaphragmatic length (LDI) can be estimated from the length of the zone of apposition (Lzapp) and the transverse diameter of the rib cage (DRC). A study was carried out in two subjects using sequential digital radiography at six frames/second to determine whether these relations apply during maximal respiratory efforts which distort the rib cage and diaphragm. Methods -The length of the anteroposterior contour of the diaphragm and DRC were determined by curve fitting. Lzapp was measured with a millimetre rule. Results -A significant correlation was found between LDI and Lzapp during both maximal inspiratory and expulsive manoeuvres (R2 = 0-88 and 052). LDI was estimated from the measurements of Lzapp and DRC using a multiple regression equation derived from measurements during static relaxation. Despite the complex dynamic events at the onset of these "static" manoeuvres, actual LDI correlated strongly with derived LDI using all data for the two manoeuvres in each subject (R2 = 095 and 084 Maximal pressures developed by the diaphragm depend, not only on its neural drive and muscle strength, but also on its forcelength and force-velocity relations. Other factors, including the cross sectional area of the lower rib cage and diaphragmatic shape, may also be important. Using sequential digital radiography at six frames/second we observed progressive muscle shortening at the onset of maximal "static" inspiratory efforts which move the diaphragm to a less advantageous position on the force-length curve.3 By contrast, the "extra" pressure developed during expulsive manoeuvres with the glottis held open was associated with transient lengthening of the diaphragm-6 produced by the abdominal muscles.78 The changes in length and velocity of diaphragmatic muscle explained much of the difference in maximal voluntary transdiaphragmatic pressure between the manoeuvres.3 These observations suggest that measurements of the diaphragmatic muscle length and velocity might improve the predictive power of clinical tests of respiratory muscle strength.Because diaphragmatic length (LDI) is difficult to measure in vivo, interest has focused on the relation between LDI and the width of the zone of apposition between the diaphragm and chest wall (Lzapp). A linear relation exists between LDI and Lzapp (measured from radiographs) during relaxation at lung volumes between residual volume (RV) and total lung capacity (TLC).9 During an "isovolume manoeuvre", however, in which LDI is essentially constant, Lzapp decreases as the diameter of the rib cage (DRC) increases because the diaphragm "peels away" from the chest wall.'011 Rochester and coworkers'2 examined radiographs taken during relaxation at different lung volumes and found that 95%
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