We analyzed the respiratory air flow by the three-dimensional asymmetric human bronchial tree model using the finite element method (ANSYS, PA). It was difficult to model all of the human bronchial air way so that we devised three simplified models such as asymmetric Y-bifurcation model, symmetric Y-bifurcation model and T-bifurcation model. Human bronchi were made up by these three models. The asymmetric Y-bifurcation model was used for the first bronchus that consisted of right lung at 30° and left lung at 45° connected to the mother bronchus based on anatomical data. We used the T-bifurcation model for the second and third bronchi in the right lung. The RUL was located perpendicularly to the second bronchus. The RML was located perpendicularly to the third bronchus and further the RLL was located axially to the third bronchus.
Maximum average air flow velocity was calculated to be 1140 mm/s in RUL, 1490 mm/s in RML, 2650 mm/s in RLL, 1330 mm/s in LUL, 1200 mm/s in LLL. When we assumed all pressure drops to be 100%, the pressure drop until the seventh bronchus was 80 % in RUL, 85 % in RML, 84 % in RLL, 79 % in LUL, 81 % in LLL respectively.