Using heart rate to estimate the minute ventilation and inhaled load of air pollutants

The health effects of air pollution are associated with the concentration of pollutants and ventilation (VE). VE is difficult to measure directly and has been predicted by heart rate (HR). However, it is unclear whether equations between HR and VE obtained from a laboratory cardiopulmonary exercise test (CPET) can be extended to external groups and there is still a gap in their relationship for a Chinese population.

To establish an association between HR and VE in young Chinese individuals and verify the external validity of the model.

Eighty non-smoking participants aged 16-21 years underwent incremental tests using a bicycle ergometer, where the HR and minute VE were measured simultaneously. Linear mixed models were constructed with data obtained from a CPET. Ten individuals were chosen randomly as the external validation group. The predictive performance was assessed using an eight-fold cross-validation procedure. Air pollution concentration was monitored during the CPET and the inhaled load was calculated.

The overall estimation of the intercept and slope for all participants was 0.585 ± 0.013 and 0.007 ± 0.00002, respectively. The overall fitted R squared (R²) was 0.84. The median difference between the measured VE and the predicted VE was 0.3 L/min, and the difference between the inhaled load based on the fitted VE and the measured VE was 0.0-0.3 μg across all the participants. The eight folds cross-validation R² value was 0.78, suggesting high predictive accuracy.

This is the first study to derive a novel equation for the relationship between HR and VE in a young Chinese population and verify its external validity. This will be important in the assessment of the inhaled load in future epidemiology studies. However, inter-individual variations should also be considered when VE is estimated at an individual level.