The method for estimating the distributions of continuous Va/Q ratios was described by Wagner et al. Six inert gases (sulfur hexafluoride, ethane, cyclopropane, enflurane, diethyl ether, and acetone) were dissolved in lactated Ringer’s solution and infused into a peripheral vein at a constant rate set at 0.05 percent of Ve for at least 40 min. Arterial and mixed venous blood and expired gas samples were collected during stable conditions confirmed by constancy (±5 percent) of Ve, FE02, FECO2, and CO. Expired gas samples were collected with an appropriate time delay from a heated mixing chamber. canadian neighbor pharmacy viagra
Concentrations of the inert gases were measured with a gas chromatograph (HP 5890, Hewlett-Packard, Waltham, Mass) and blood-gas partition coefficients were determined.
Arterial to mixed venous (retention) and mixed expired to mixed venous (excretion) concentration ratios of the inert gases were used to obtain retention-solubility and excretion-solubility relationships. By formal mathematical analysis with enforced smoothing, these relationships were transformed into a 50-com-partmental distribution plot of blood flow and ventilation against Va/Q.’ Intrapulmonary shunt defined as fraction of Qt perfusing essentially nonventilated alveoli (Va/Q <0.005), low Va/Q as fraction of the pulmonary blood flow (Qt) perfusing poorly ventilated lung areas (0.005<Va/Q <0.1), high Va/Q as fraction of Ve ventilating poorly perfused lung areas (10<Va/Q <100), dead space as fraction of Ve ventilating nonperfused lung areas (Va/Q >100), mean Va/Q ratio of perfusion (Q) and ventilation (V), and logarithmic standard deviations of perfusion (logSDQ) and ventilation (logSDv) were derived from the 50-compartment model. Predicted values for РаОг were calculated from the recovered Va/Q distributions as described. The index DISPr-e* was calculated as the root mean square difference of measured retentions and excretions corrected for dead space. It is an overall index of Va/Q heterogeneity with a minimum value of zero (homogeneous lung) and a maximum value of 100 (100 percent shunt, 100 percent dead space).