Pressure volume curve and alveolar recruitment/ de-recruitment. A morphometric model of the respiratory cycle

Summary. H y p o t h e s i s : The changes in pulmonary volume taking place during respiration are accompanied by the opening and closing of the alveoli, with the number of alveoli open, at the same transpulmonary pressure (TPP) differing, depending on whether the lung is insufflated or deflated. Material and methods: Seventy 344 Fischer rats divided into five groups. Group 1 lungs were fixed by instilling 10% formalin through the trachea to a pressure of 25 cm H 2 O. The lungs of the next four groups were air- fi l l e d and fixed via the pulmonary artery: group 2 lungs were fixed in inflation at 10 cm H 2 O TPP; group 3 lungs were fixed in inflation at 20 cm. H 2 O TPP; the lungs of groups 4 and 5 were fi xed in deflation and, therefore, were inflated with air up to 27 cm. H 2 O to drop to 20 cm in group 4 and to 10 cm in group 5. The lungs were processed for light microscopy, carrying out a morphometric study. The results were statistically processed. Results: The lungs insufflated with liquid fixati ve at 25 cm of TPP reached higher values in the va r i a b l e s Pulmonary Volume, Internal Alveolar Surface (IAS) and Number of Alveoli, being statistically signif i c a n t (p<0.05) in comparison with the other four groups. In the lungs fixed in deflation, the pulmonary volume, IAS and number of alveoli were greater than in those fixed in inflation. The lungs fixed to 20 cm in deflation displayed s i g n i ficant statistical differences compared with those fi xed to 20 cm in inflation. The IAS and number of a l veoli gave good rates in relation with the pulmonary volume (r≥ 0.65). Three variables were used to measure the size of the alveoli, alveolar cord, alveolar surface and Lm, but none showed significant modifications. Conclusion: This study supports the hypothesis that changes in lung volume are related to the increase/decrease in the number of alveoli that are open/closed and not to the modification in the size of the a l v eoli. Alveolar recruitment is the microscopic expression of pulmonary hysteresis, since the number of alveoli open in deflation is greater than the number open during inflation.