title: Flow and volume dependence of rat airway resistance during constant flow inflation and deflation.
abstract: OBJECTIVE
  The aim of this study was to measure the flow and volume dependence of both the ohmic and the viscoelastic pressure dissipations of the normal rat respiratory system separately during inflation and deflation.
  
  
  METHODS
  The study was conducted in the Respiratory Physiology Laboratory in our institution. Measurements were obtained for Seven albino Wistar rats of both sexes by using the flow interruption method during constant flow inflations and deflations. Measurements included anesthesia induction, tracheostomy and positioning of a tracheal cannula, positive pressure ventilation, constant flow respiratory system inflations and deflations at two different volumes and flows.
  
  
  RESULTS
  The ohmic resistance exhibited volume and flow dependence, decreasing with lung volume and increasing with flow rate, during both inflation and deflation. The stress relaxation-related viscoelastic resistance also exhibited volume and flow dependence. It decreased with the flow rate at a constant lung volume during both inflation and deflation, but exhibited a different behavior with the lung volume at a constant flow rate (i.e., increased during inflations and decreased during deflations). Thus, stress relaxation in the rat lungs exhibited a hysteretic behavior.
  
  
  CONCLUSIONS
  The observed flow and volume dependence of respiratory system resistance may be predicted by an equation derived from a model of the respiratory system that consists of two distinct compartments. The equation agrees well with the experimental data and indicates that the loading time is the critical parameter on which stress relaxation depends, during both lung inflation and deflation.
authors.affiliation: Department of Human Anatomy and Physiology, Physiology Section, University of Padova, Via Marzolo, 3, 35100, Padova, Italy. alessandro.rubini@unipd.it
authors.forename: Alessandro
authors.initials: A
authors.lastname: Rubini
authors.forename: Emanuele Luigi
authors.initials: EL
authors.lastname: Carniel
authors.forename: Andrea
authors.initials: A
authors.lastname: Parmagnani
authors.forename: Arturo Nicola
authors.initials: AN
authors.lastname: Natali
mesh_terms: D000403:Airway Resistance / Q000502:physiology*; D000818:Animals; D004548:Elasticity / Q000502:physiology; D005260:Female; D008176:Lung Volume Measurements; D008297:Male; D023421:Models, Animal; D008954:Models, Biological; D012123:Pulmonary Ventilation; D051381:Rats; D017208:Rats, Wistar; D015656:Respiratory Mechanics / Q000502:physiology*; D014783:Viscosity