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Pressure volume curve and alveolar recruitment/de-recruitment.
A morphometric model of the respiratory cycle
J.D. Escolar1, M.A. Escolar1, J. Guzmán2 and M. Roqués3
1Morphological Science Department, Faculty of Medicine, University
of Zaragoza, Zaragoza, Spain, 2Anatomy Institute of Biomedical
Science, Autonomous University of Ciudad Juarez, Mexico and 3Pediatrics
Department, La Fe Hospital, Valencia, Spain
Offprint requests to: Juan de
Dios Escolar, Department of Morphological Science, Faculty of
Medicine, University of Zaragoza. Domingo Miral s/n 50009. Spain.
Fax: 976 761 754. e-mail: jescolar@posta.unizar.es
Summary. Hypothesis: 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 H2O. The lungs of the next
four groups were air-filled and fixed via the pulmonary artery:
group 2 lungs were fixed in inflation at 10 cm H2O TPP; group
3 lungs were fixed in inflation at 20 cm. H2O TPP; the lungs of
groups 4 and 5 were fixed in deflation and, therefore, were inflated
with air up to 27 cm. H2O 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 fixative at 25 cm of
TPP reached higher values in the variables Pulmonary Volume, Internal
Alveolar Surface (IAS) and Number of Alveoli, being statistically
significant (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 significant statistical
differences compared with those fixed to 20 cm in inflation. The
IAS and number of alveoli 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 alveoli. 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.
Histol. Histopathol. 17, 383-392 (2002)
Key words: Morphometry, alveolar recruitment, hysteresis,
TLC, transpulmonary pressure
DOI: 10.14670/HH-17.383
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