IN-VIVO ASSESSMENT OF DIAPHRAGM CONTRACTION BY ULTRASOUND IN NORMAL SUBJECTS

Background - Ultrasound allows observation of the thickness of the dia phragm in the zone of apposition in vivo during relaxation and maximum inspiratory efforts. Methods - Changes of diaphragm thickness were st udied by B mode (two dimensional) ultrasound in 13 healthy men aged 29 -54 years in the seated position. A high resolution 7.5 MHz ultrasound transducer was held perpendicular to the chest wall in the line of a right intercostal space between the anteroaxillary and mid-axillary li nes to observe the diaphragm in the zone of apposition 0.5-2 cm below the costophrenic angle. The changes of thickness were observed while b reath holding at total lung capacity (TLC), functional residual capaci ty (FRC), and residual volume (RV). At FRC the thickness while relaxin g against a closed mouthpiece and during a maximum inspiratory mouth p ressure (PImax) manoeuvre was recorded. The thickening ratio (TR) was calculated as TR = thickness during PImax manoeuvre/thickness while re laxing. Results - Mean (SD) thickness was 4.5 (0.9) mm at TLC, 1.7 (0. 2) mm at FRC, and 1.6 (0.2) mm at RV. During the PImax manoeuvre at FR C mean thickness increased from 1.7 (0.2) mm during relaxation to 4.4 (1.4) mm, while mean PImax and TR were -104 (33) cm H2O and 2.6 (0.7), respectively. There was a high degree of correlation between TR and t he pressure achieved during the maximum inspiratory manoeuvre (r = -0. 82). Conclusions - Ultrasound provides a noninvasive assessment of dia phragm thickness with change of lung volume and during the PImax manoe uvre which should prove useful in assessing diaphragm mass and contrac tion in respiratory and muscle disease.