Diaphragm Motion Heterogeneity as a Result of Gravity-Induced Pleural Pressure Variation During Free Breathing
G Li1*, M Rosu2, J Wei3, R Kincard4, J Mechalakos5, (1) Memorial Sloan-Kettering Cancer Center, New York, NY, (2) Virginia Commonwealth University, Richmond, VA, (3) City College of New York, New York, NY, (4) Memorial Sloan-Kettering Cancer Center, New York, NY, (5) Memorial Sloan-Kettering Cancer Center, New York, NYSU-E-J-127 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: To investigate the physical relationship between diaphragm motion heterogeneity and gravity direction for lung motion modeling. It is hypothesized that diaphragm motion overcomes gravity-induced pressure (GIP) to provide even common pleural pressure (CPP) around the chest wall during free breathing.
Methods: A respiratory motion model was developed to account for GIP over CPP at posterior (P) and anterior (A) chest wall. The movement of the diaphragm to compensate for GIP was assumed proportional to GIP, given GIP<|CPP|max. Thus, the P/A ratio of diaphragm motion (M-PA) should equal the P/A ratio of pleural pressure (P-PA). To estimate GIP, lung density and AP separation were measured on full-inhalation phase CT, assuming the lung as viscous fluid. At anterior side(supine), both S-I and P-A motions produced CPP with an assumed equal contribution. Software was developed to quantify and visualize lung density gradient. 4DCT images from 12 supine patients and 5 patients in both supine and prone positions were analyzed. Local lung densities were monitored at 4 regions: A, P, I and S, and the density ratios (D-PA and D-SI) were calculated for all supine and prone scans.
Results: For the 12 supine patients, it was found that diaphragm motion was location dependent: A=0.7(σ=0.3)cm, I=1.4(σ=0.5)cm, and P=2.4(σ=1.0)cm. A lung gradient aligned with gravity: D-PA=1.6(σ=0.5) while D-SI=1.0(σ=0.2). Calculated GIP=3.7(σ=0.9)cmH2O [=2.7(σ=0.7)mmHg] was similar to |CPP|max (-3mmHg at inhalation). The estimated M-PA=4 [=P-PA=(2xCPP)/(0.5xCPP)] was consistent with the measured M-PA=3.9(σ=1.6). In the 5 patients with both supine and prone scans, 4 reversed the motion ratio from supine [M-PA=3.7(σ=1.6)] to prone [M-PA=1.1(σ=0.8)].
Conclusion: This study demonstrated a population-based physical relationship of local motion of the diaphragm and the direction of gravity. Posterior diaphragm (supine) was predicted and confirmed to move about 4 times more than anterior diaphragm. Further study on individual-based physical relationships is currently under investigation.