Pulmonary to arterial circulatory transfer function: importance in respiratory control.

Abstract

The transfer function between alveolar or pulmonary capillary and the respiratory chemoreceptors is of theoretical importance in the respiratory control system. The effects of pulmonary artery or alveolus to systemic artery passage on the dispersion of diffusible and nondiffusible indicators were considered to approximate alveolar to chemoreceptor transit. Two methods were employed: A) preformed curves applying venous injection and pulmonary artery (PA) and femoral arterial (FA) recording or alveolar Po2 was altered and Pao2 was recorded; B) slug injection into the PA. with FA recording. In studies from normal subjects, humans with heart disease, and dogs, the transfer function from method B indicated a much greater dispersion of indicator than by method A and suggested that slug injection did not approach a unit impulse input. When controlled respiration was employed, similar results were obtained. These findings indicate that alveolar to arterial passage is characterized by rather small temporal distribution of transit times about the mean time, particularly in human studies. The distribution of transit times was expressed as a transfer function. When transfer function representative of various circulatory disorders was incorporated into a schema of the integrated respiratory control system, the transfer function led to stability except when the mean transit time was 3 to 4 times normal.