Exertional inspiratory capacity and operating lung volumes in health: a population-based study

Inspiratory capacity (IC) should increase during exercise to allow unrestrained tidal volume expansion, mitigating uncomfortable respiratory sensations. However, preliminary evidence suggests that this is not universally seen in healthy individuals. Whether this negatively impacts on inspiratory reserves and dyspnoea remains unclear. To gain novel insights on the regulation of operating lung volumes in community-dwelling individuals, we determined the association of a lack of increase in IC during incremental cardiopulmonary exercise testing (dynamic inspiratory capacity (IC_dyn)) with demographic, anthropometric and respiratory functional data in a large population-based study.

We reviewed general characteristics, pulmonary function and cycle ergometer data from 1065 healthy individuals (51.5% women, aged 20-86 years) with normal lung function.

IC_dyn remained unchanged or decreased from rest to peak exercise (Δ (peak-rest) IC_dyn ≤0 L) in 245/1065 individuals (23.0%). Tidal volume increased to a lower extent after the ventilatory threshold compared to earlier exercise in these subjects; thus, peak end-inspiratory lung volume (EILV) and EILV/total lung capacity were similar to subjects showing IC_dyn >0 L despite higher EILVs. Albeit statistically significant, between-group differences in peak dyspnoea scores were modest (p=0.049). Multivariable regression revealed that age (particularly in women), higher body mass index and higher resting airway resistance were independently associated with ΔIC_dyn ≤0 L (p<0.001).

Elderly women and overweight/obese individuals may fail to increase IC_dyn during incremental exercise due to dynamic hyperinflation. Careful regulation of tidal volume, however, avoids critically high inspiratory constraints and limiting exertional dyspnoea.