Assessment of strain effects of normal values of respiratory mechanics in rats

<bold>Introduction:</bold> Normal values are routinely used in interpreting lung function tests. While several studies have established reference values for human patients, such values have not been characterized in common animal models. Therefore, our aim was to establish normal values of respiratory mechanical parameters in the two most common rat strains used in respiratory research. <bold>Methods:</bold> Healthy male Sprague-Dawley (SPRD, n=53) and Wistar (WIST, n=30) rats were anesthetized and mechanically ventilated. Respiratory mechanics were measured by forced oscillations at increasing PEEP levels of 0, 1, 2, 3, 4, and 6 cmH₂O. The constant phase model was fitted to the impedance spectra, then airway resistance (Raw) and tissue elastance (H) were identified. Reference equations were determined for Raw and H by using mixed-effect multiple regression models for each strain with predictors PEEP, square root (SQRT) of body mass and their interaction. <bold>Results:</bold> The models for Raw and H fitted well for both strains with high R² values and normally distributed residuals. Multivariate mixed-model ANCOVA revealed a significant interaction between the predictor variables and strain (p=0.03) for Raw but not for H (p=0.56). <bold>Conclusions:</bold> In our ongoing study we have found significant differences in models predicting Raw values of male SPRD and WIST rats, suggesting that strain needs to be considered for reference equations for Raw, while prediction of H is not affected by strain. <bold>Funding:</bold> OTKA-NKFIH FK134274 <table-wrap><object-id>erj;64/suppl_68/PA2602/TB1</object-id><object-id>T1</object-id><object-id>TB1</object-id><table><colgroup><col></col></colgroup><tbody><tr><td>ln(X) = <bold>a</bold>*SQRT(mass[g]) + <bold>b</bold>*PEEP[cmH₂O] + <bold>c</bold>*PEEP[cmH₂O]*SQRT(mass[g]) + <bold>d</bold></td></tr><tr><td><bold>X</bold></td><td><bold>Strain</bold></td><td><bold>a</bold></td><td><bold>b</bold></td><td><bold>c</bold></td><td><bold>d</bold></td><td><bold>R²</bold></td></tr><tr><td><bold>Raw</bold> (cmH₂O.s/l)</td><td>SPRD</td><td>-0.064</td><td>-0.202</td><td>0.001</td><td>5.456</td><td>0.89</td></tr><tr><td>WIST</td><td>-0.067</td><td>-0.312</td><td>0.009</td><td>5.410</td><td>0.85</td></tr><tr><td><bold>H</bold> (cmH₂O/l)</td><td>BOTH</td><td>-0.087</td><td>-0.199</td><td>0.002</td><td>9.929</td><td>0.95</td></tr></tbody></table></table-wrap>