Introduction: Normal values are of utmost importance in assessing lung function. While several projects, such as recently the Global Lung Function Initiative (GLI) have collected normal values for various human populations, the use of such reference values is practically non-existent for common translational animal models. Therefore, in our ongoing study we aimed at establishing normal values of end-expiratory lung volume (EELV) in rats.
Methods: 48 healthy male Sprague-Dawley rats (98-750g) were anaesthetized using iv. propofol-fentanyl and mechanically ventilated through a tracheostomy. EELV was measured by whole body plethysmography at increasing PEEP levels of 0, 1, 2, 3, 4, and 6 cmH2O. After correcting for instrumental dead space, reference equation for EELV was determined by multiple regression using candidate predictors PEEP, square root (SQRT) of body mass, body mass, and square of body mass. A forward likelihood ratio model selection method was used and changes in R2 were taken into account.
Results: The model containing SQRT(mass) and PEEP fitted the best (R2=0.86). The multiple regression analysis resulted in the following equation, working best for animals above 200g: EELV[ml]=0.79130*SQRT(mass[g])+1.12195*PEEP[cmH2O]?9.04022.
Conclusions: The current research proposes a reference equation for EELV in anesthetized male Sprague-Dawley rats. While further studies are still needed to describe reference equations in rats with other sex and strains, this work can serve as a starting point for the paradigm shift where reference values would also be considered for animal studies in respiratory research.
Funding: OTKA-NKFIH FK134274