Comparison of unrestrained plethysmography and forced oscillation for identifying genetic variability of airway responsiveness in inbred mice

Abstract

Lung function detection in mice is currently most accurately measured by invasive techniques, which are costly, labor intensive, and terminal. This limits their use for large-scale or longitudinal studies. Noninvasive assays are often used instead, but their accuracy for measuring lung function parameters such as resistance and elastance has been questioned in studies involving small numbers of mouse strains. Here we compared parameters detected by two different methods using 29 inbred mouse strains: enhanced pause (Penh), detected by unrestrained plethysmography, and central airway resistance and lung elastance, detected by a forced oscillation technique. We further tested whether the phenotypic variations were determined by the same genomic location in genome-wide association studies using a linear mixed model algorithm. Penh, resistance, and elastance were measured in nonexposed mice or mice exposed to saline and increasing doses of aerosolized methacholine. Because Penh differed from airway resistance in several strains and because the peak genetic associations found for Penh, resistance, or elastance were located at different genomic regions, we conclude that using Penh as an indicator for lung function changes in high-throughput genetic studies (i.e., genome-wide association studies or quantitative trait locus studies) measures something fundamentally different than airway resistance and lung elastance.

Fig. 1.

Distribution of Penh_slope among 29 mouse strains for female and male mice. Strains are sorted by increasing average strain values in female mice. Penh, enhance pause.

Fig. 2.

Distribution of Rn_slope among 29 mouse strains for female and male mice. Strains are sorted by increasing average strain values in female mice. Rn, airway resistance.

Fig. 3.

Distribution of H_slope among 29 mouse strains for female and male mice. Strains are sorted by increasing average strain values in female mice. H, elastance.

Fig. 4.

Comparison of the median standardized ranks for Penh_slope and Rn_slope among 29 strains. There is no significant correlation between strain ranks of Penh_slope and Rn_slope for female (A, Rho = 0.12, P = 0.54) and male (B, Rho = −0.35, P = 0.07) mice. In A and B, the line indicates the line of best fit. P-value distributions of the differences in the strain ranks between Penh_slope and Rn_slope are shown for female (C) and male (D) mice. In C and D, the horizontal line indicates the threshold at P = 0.05. Strains below the line showed significant differences between the 2 parameters.

Fig. 5.

Comparison of the median standardized ranks for Penh_slope and H_slope among 29 strains. There is no significant correlation between strain ranks of Penh_slope and H_slope for female (A, Rho = 0.02, P = 0.94) and male (B, Rho = 0.31, P = 0.1) mice. In A and B, the line indicates the line of best fit. P-value distributions of the differences in the strain ranks between Penh_slope and H_slope are shown for female (C) and male (D) mice. In C and D, the horizontal line indicates the threshold at P = 0.05. Strains below the line showed significant differences between the 2 parameters.

Fig. 6.

Genome-wide associations for Penh_slope in female (A) and male (B) mice, Rn_slope in female (C) mice and H_slope in female (D) mice. The x-axis shows the chromosomal location in million base pairs (Mb), and the y-axis shows the strength of the association as score [score = −log10(P value)].