Airway mechanics and lung tissue viscoelasticity: effects of altered blood hematocrit in the pulmonary circulation

The contribution of the hematocrit (Hct) of the blood in the pulmonary vasculature to the overall lung mechanics has not been characterized. We therefore set out to establish how changes of the Hct level in the pulmonary circulation affect the airway and lung tissue viscoelastic properties. The Hct level of the blood in an isolated perfused rat lung model was randomly altered. Intermediate (26.5%), followed by low (6.6%) or normal Hct (43.7%) were set in 2 consecutive sequences. The pulmonary capillary pressure was maintained constant throughout the experiment and the pulmonary hemodynamic parameters were monitored continuously. The airway resistance (Raw), the viscous (G) and elastic (H) parameters and the hysteresivity (eta=G/H) of the lung tissues were obtained from measurements of forced oscillatory input impedance data. Raw was not affected by the alterations of the Hct levels. As concerns the lung tissues, the decrease of Hct to intermediate or low levels resulted in close to proportional decreases in the viscoelastic parameters G (16.5+/-7.7%, 12.1+/-9.5%, p<0.005) and H (13.2+/-8.6%, 10.8+/-4.7%, p