Partitioning of pulmonary impedance in excised human and canine lungs

Partitioning of pulmonary resistance of 15 excised human and 5 canine lungs by means of a retrograde catheter demonstrated that the share of peripheral airways (with an ID of 2.4 mm or less) and of lung tissue in pulmonary resistance was markedly larger (44-96%) in humans than in dogs (41-59%). Similar percentages were found in patients with chronic obstructive pulmonary disease (COPD). The variations of resistance with volume during deflation and inflation of the lungs were due primarily to variations of peripheral resistance (Rp). The latter systematically increased at high and low lung volumes. Higher Rp values, with a more pronounced frequency dependence, were met in patients with COPD. A morphometrical study showed an inverse relationship between the value of Rp and the mean diameter of the terminal bronchioles, provided the airways density was taken into account.