ULTRASOUND EVALUATION OF THE PARALYZED DIAPHRAGM

Ultrasound has been used to evaluate diaphragm thickness in the zone o f apposition of the diaphragm to the rib cage. The purpose of this stu dy was to determine if ultrasonography could distinguish between a par alyzed and normally functioning diaphragm, We predicted that a paralyz ed diaphragm would be atrophic and not shorten, therefore it would be thin and not thicken during inspiration. Thirty subjects (five with bi lateral diaphragm paralysis, seven with unilateral diaphragm paralysis , three with inspiratory weakness but normally functioning diaphragms, and 15 healthy control subjects) had diaphragm ultrasound performed w ith a 7.5 to 10.0 MHz transducer placed over the lower rib cage in the mid-axillary line, The thickness of the diaphragm (t(di)) was measure d to the nearest 0.1 mm at FRC (t(di)FRC) and TLC (t(di)TLC). Diaphrag m thickening during inspiration (Delta t(di)) was calculated as (t(di) TLC - t(di)FRC)/t(di)FRC. In patients with unilateral paralysis, t(di) and Delta t(di) for the paralyzed hemidiaphragm were significantly le ss than those values for the normally functioning hemidiaphragm (1.7 /- 0.2 mm versus 2.7 +/- 0.5 mm [mean + SD] p < 0.01 for t(di), and -8 .5 +/- 13% versus 65 +/- 26% [p < 0.001] for Delta t(di)). The t(di) a nd Delta t(di) for patients with bilateral diaphragm paralysis were si gnificantly less than those values for the healthy volunteers (1.8 +/- 0.2 versus 2.8 +/- 0.4 and -1 +/- 15% versus 37 +/- 9% for t(di) and Delta t(di), respectively) (p < 0.001). We conclude that ultrasound me asurements of t(di) and Delta t(di) can be used to determine if a diap hragm is paralyzed and confirm our predictions that a chronically para lyzed diaphragm is atrophic and does not thicken during inspiration.