The Effect of Pendelluft and Dead Space on Nitrogen Clearance: Mathematical and Experimental Models and their Application to the Study of the Distribution of Ventilation*

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Abstract
Reinspired mixed dead space gas and Pendelluft may be considered to be part of a single process of interalveolar gas transfer. The effect of interalveolar gas transfer on nitrogen clearance from a two chamber lung model can be described by a single set of equations which hold for synchronous, and series ventilation. Interalveolar gas transfer may theoretically be either bidirectional or unidirectional. Bidirectional transfer results in an underestimation of the effective ventilation and volume of the well-ventilated compartment when nitrogen washout is analyzed by available methods. The volume of the poorly ventilated compartment is overestimated and its effective ventilation is usually overestimated but may be correctly or underestimated as distribution becomes more uneven. Unidirectional transfer has the same qualitative effect except that the ventilation of the poorly ventilated space is always overestimated. The distortions produced by both types of gas transfer become less marked as ventilation becomes more uneven. Nitrogen washout data from a model consisting of two rubber balloons connected with a Y tube agree well with the mathematical predictions. Application of the theory to data obtained from patients with advanced chronic obstructive lung disease suggests that estimates of the functional residual capacity and of the volume and ventilation of the poorly ventilated spaces are not greatly affected by interalveolar gas transfer when nitrogen washout is analyzed by usual methods.