Evaluation of alveolar amplitude response technique for determination of lung perfusion in exercise

We investigated the influence of tracer gas venous return on the determination of pulmonary perfusion (Qp) using the alveolar amplitude response technique (AART) to evaluate the applicability of this technique at rest and during exercise. The venous return influence was calculated by a computer simulation applied to a simplified body compartment model. Using the AART method, which neglects the influence of venous return, a simulation based on acetylene as a tracer gas predicted an overestimation of the actual value of Qp ranging from 0 to 10% for all work loads investigated. These theoretical results were compared with experimental results. Experiments with human subjects with acetylene as the tracer gas yielded an underestimation of Qp of about 20% at rest and an overestimation of about 7% under different exercise conditions. Experiments with anesthetized dogs showed an underestimation of Qp of about 12% for acetylene and about 6% for halothane. The theoretical and experimental results related to exercise conditions are thus in good quantitative agreement. The experimental data obtained for acetylene with human subjects at rest and with anesthetized dogs are also in good quantitative agreement. However, they deviate considerably from theoretical predictions. This discrepancy may be due to the simplified body compartment model used in the calculations, which can considerably influence the calculated results, especially for conditions at rest. The main conclusion of this paper is that recirculating tracer gas does not unduly influence results for Qp obtained with the AART method when halothane is used as the tracer gas.