Physiological changes in respiratory function associated with ageing.

We read with interest the review of JANSSENS et al. [1] entitled "Physiological changes in respiratory function associated with ageing", more specifically the subheading devoted to changes in arterial oxygenation and ventilation-perfusion (V ©/Q ©) relationships. Although the seminal study of WAGNER et al. [2] was addressed in full, it was a shame that they did not discuss the more recent comprehensive work of our group in this field [3]. We extensively investigated the distributions of V ©/Q © ratios in 64 healthy individuals aged 18±71 yrs. The principal findings of that study were: 1) that V ©/Q © imbalance, but not increased intrapulmonary shunting, did increase with age as previously expected; 2) that the increase over the span of ~50 yrs was physiologically very small; 3) that most of the variance in V ©/Q © mismatch in this cohort of subjects was not due to ageing and remained unsettled; and 4) that the fall in arterial partial pressure of oxygen (PO2) with age was also quite small but was internally consistent with the V ©/Q © changes measured independently. V ©/Q © relationships were characterized in most of these healthy individuals by narrow distributions that widened slightly with age together with a trivial shunt of <1% of the cardiac output in 90% of cases. Both the second moments (dispersions) of pulmonary blood flow (Log SDQ) and of alveolar ventilation (Log SDV) increased by ~0.1 between 20±70 yrs. Accordingly, the dispersion of pulmonary perfusion (Log SDQ) increased from 0.36±0.47, akin to a decrease of oxygen tension in arterial blood (Pa,O2) of only ~6 mmHg. Only 10% of the total variance was attributed to age. A similar amount was due to intrasubject variability, but none was due to variations in other factors, such as forced expiratory volume in one second (FEV1), FEV1/forced vital capacity (FVC) ratio, weight or height. We did not measure closing volume and it is therefore likely that age could disturb V ©/Q © matching as a result of increases in closing volume. However, since the latter mechanism is highly unlikely to influence V ©/ Q © relationships in young healthy individuals [4], and since the variance of the dispersion of pulmonary blood flow was as large amongst the subset of young as that of old individuals, we would postulate that increased closing volume is not a determinant factor of the variance in V ©/Q © homogeneity.