Reliability of reference models for vital capacity in young Mexican females

To assess the reliability of 29 prediction models for vital capacity when these are applied as reference for young females, natives and residents in Mexico City (altitude = 2,240 m).

Transversal, prospective and comparative study.

Metropolitan Autonomous University, Mexico.

Sixty females clinically healthy, 17 to 29 years old, non-smokers.

Vital capacity was predicted from 29 models and measured with a bell spirometer (Collins 9 L) according to the American Thoracic Society guidelines. Statistical comparison was done between measured and predicted values by linear regression, analysis of variance and analysis of residuals.

Mean of measured vital capacity was 3,625 mL while mean values of predicted vital capacities varied from 2,644 mL to 3,962 mL. Actual and reference values showed a small but significative correlation (r = 0.40 to 0.49). By Dunnett's test, means from six of the 29 models showed non-significant differences (p > 0.05) with the mean of the measured vital capacity; however, all 29 models presented significative bias in the regression line between actual values and the residuals of predicted values (correlation coefficient, slope and intercept statistically different from zero, p < 0.05).

Due to the large bias found, models tested in the present study have limitations to predict accurate reference values for young mexican females.