Reliability of reference models for vital capacity in young Mexican males

The reliability of 33 prediction models for vital capacity was assessed in university students living in Mexico City (altitude = 2,240 m). Forced vital capacity (FVC) was predicted and measured in 83 healthy male students, 18 to 30 years old and non-smokers. Spirometric tests were performed with a 9 liter bell spirometer, according to ATS guidelines. Mean measured FVC was 5,094 +/- 555 mL (BTPS) while mean predicted FVC by the models ranged from 3,700 mL to 5,350 mL (BTPS) with a small but significative correlation between actual and reference values (r = 0.398 to 0.474, p < 0.05). The residual standard deviation showed values from 503 to 577 mL which were similar to those seen in the original population. Although 11 of the 33 models were able to predict mean observed FVC by Dunnett's test (p < 0.05), all of them showed significant bias on the regression between measured values and residuals of predicted values, i.e. intercepts (2,435 to 4,127 mL), slopes (-0.61 to -0.87) and correlations (-0.59 to -0.95) were statistically different from zero (p < 0.01). Our data remark the need to obtain appropriate reference FVC values in young Mexican males due to the questionable predictability of the models tested.