Longitudinal distribution of chlorine absorption in human airways: a comparison to ozone absorption.

The bolus inhalation method was used to measure the fraction of inhaled chlorine (Cl(2)) and ozone (O(3)) absorbed during a single breath as a function of longitudinal position in the respiratory system of 10 healthy nonsmokers during oral and nasal breathing at respired flows of 150, 250, and 1,000 ml/s. At all experimental conditions, <5% of inspired Cl(2) penetrated beyond the upper airways and none reached the respiratory air spaces. On the other hand, larger penetrations of O(3) beyond the upper airways occurred as flow increased and during nasal than during oral breathing. In the extreme case of oral breathing at 1,000 ml/s, 35% of inhaled O(3) penetrated beyond the upper airways and approximately 10% reached the respiratory air spaces. Mass transfer theory indicated that the diffusion resistance of the tissue phase was negligible for Cl(2) but important for O(3). The gas phase resistances were the same for Cl(2) and O(3) and were directly correlated with the volume of the nose and mouth during nasal and oral breathing, respectively.

Longitudinal distribution of chlorine absorption in human airways: comparison of nasal and oral quiet breathing.

The fraction of an inspired chlorine (Cl2) bolus absorbed during a single breath (Lambda) was measured as a function of bolus penetration (VP) into the respiratory system of five male and five female nonsmokers during both nasal and oral breathing at a quiet respiratory flow of 250 ml/s. The correspondence between VP and specific anatomic landmarks was found for each subject by a combination of acoustic reflection and nitrogen washout measurements. For both nasal and oral breathing, Lambda reached approximately 0. 95 at the distal end of the upper airways and reached 1.00 within the lower conducting airways. The values of a regional mass transfer parameter computed from the Lambda-VP data indicated that the resistance to Cl2 diffusion in the airway mucosa was negligible compared with the diffusion resistance in the respired gas. Changing the peak inhaled Cl2 concentration from 0.5 to 3.0 parts/million did not significantly affect the distribution of Cl2 absorption, suggesting that the underlying mass transport and chemical reaction processes were linear with respect to Cl2 concentration.

Enhancement of O2 and CO2 transfer through microporous hollow fibers by pressure cycling.

An intravascular gas exchange device for the treatment of respiratory failure consisted of a multitude of blind-ended hollow fibers glued in a pine-needle arrangement to a central gas supply catheter. It has previously been shown that gas desorption rates can be significantly enhanced by cycling gas pressure between a hypobaric level of 130 and an ambient level of 775 Torr. In this study, influences of the cycling frequency (f) and the cycle fraction during which hypobaric pressure is applied (theta) were investigated. Rates of O2 desorption from O2-saturated water and CO2 desorption from CO2-saturated water into a manifold containing 198 fibers, 380 microm in diameter, were measured over a range of f from 0.2 to 1.0 Hz. theta from 0.1 to 0.8, and fiber lengths from 4 to 16 cm. Relative to operation at ambient pressure, pressure cycling increased O2 transfer 3-4 times and CO2 transfer 4-6 times when the water flowed over the fiber manifold at 2.3 l/min. Transfer rates were relatively insensitive tof and theta with 80%-90% of maximum enhancement obtained when theta was as low as 0.2. Transfer rates increased continuously with fiber length, implying that pressure cycling reduced the intra-fiber resistance to gas diffusion. A mathematical diffusion model which utilized only two adjustable parameters, a mass transfer coefficient for O2 and for CO2, simulated the trends exhibited by desorption data.

Small intrapulmonary artery lung prototypes. Mathematical modeling of gas transfer.

Two diffusion models have been developed to analyze gas transfer data previously measured in an intravascular artificial lung consisting of a central gas supply catheter from which are tethered a large number of blind-ended microporous fibers of equal length. A convective-diffusion model (CD) describes the countercurrent transfer of a binary gas pair when gas is supplied at constant pressure conditions, and a well mixed (WM) cycled pressure model predicts transfer when the gas supply pressure is time cycled between compression and vacuum conditions. Regression of gas to gas and liquid to gas excretion data with the CD model resulted in estimates of the liquid phase mass transfer coefficient kAI. Because these values were intermediate between the kAI expected for flow parallel to a cylinder and for flow normal to a cylinder, gas transfer was influenced by both the tethered region of the fiber that was nearly perpendicular to the axis of the test section and the free end of the fiber that rested along the wall of the test section. With a time cycled gas supply pressure, the enhanced carbon dioxide and oxygen excretion predicted by the WM model was similar to the data, but a loss in transfer efficiency with fiber length was not accounted for by the theory.