Elasticity of the Pulmonary Alveolar Sheet

An analysis of experimental data on the pulmonary alveolar sheet of the cat shows: (1) As far as elasticity in the plane of the sheet is concerned, the alveolar sheet may be regarded as uniform; the compliance of the posts is the same as that of the membranes. (2) Within a physiological range of positive transmural pressure, the mean thickness of the sheet varies linearly with the pressure. Also, the stress distribution in the alveolar-capillary membrane is nonuniform and nonisotropic. A theoretical sheet thickness-pressure relation-ship is derived in which the effect of stress resultants (sum of elastic stress and surface tension) is explicitly linked to the compliance of the sheet thickness. The sheet-flow theory then shows that average flow is very sensitive to the arteriole pressure. The flow per alveolar sheet is (1/C) (ha * —hv4). Here ha and hv are equal to alveolar sheet thickness at the arteriole and venule, respectively. When par t> palv, ha = h0 + a(pBrt-paiv)> where p a r t is the blood pressure in the sheet at the arteriole, palv is the gas pressure in th