Physiological changes in respiratory function associated with ageing

Abstract

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 (PO 2 ) 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,O 2 ) 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.

Tissue elasticity and the ageing elastic fibre

“…In the aged lung, the loss of elasticity simulates emphysema (Knudson et al 1977;Turner et al 1968), and both forced expiratory volume and forced vital capacity are reduced (Meyer et al 1998). This reduction in tissue elasticity (both compliance and recoil), which has been well characterised in both human (Lai-Fook and Hyatt 2000;Turner et al 1968) and rodent lungs (Janssens et al 1999;Nagase et al 1994), plays an important role in increasing the risk of mortality in the ageing population as a result of acute pulmonary diseases (Janssens et al 1999;Meyer et al 1998). The mechanical properties of the lung are highly complex and depend on: the relative mechanical properties of the constituent ECM components (Fredberg and Kamm 2006), the arrangement of these molecules within the alveolar wall, and the geometrical construction of the alveolus itself (Kitaoka et al 2007;Wilson and Bachofen 1982).…”

Maximal respiratory pressure in healthy 20 to 89 year-old sedentary individuals of central São Paulo State

“…Dysfunction in this musculature can lead to hyperventilation, reduction in exercise tolerance and even respiratory insufficiency 3 . The evaluation of RMS is of great clinical importance 4 and can be measured by static and dynamic maneuvers.…”

Pressões respiratórias máximas: valores encontrados e preditos em indivíduos saudáveis

“…MIP and MEP can be used to quantify respiratory muscle strength in healthy individuals of all ages, in patients with several types of disorders, as well as to evaluate the response to respiratory muscular training [5][6][7][8][9][10] .…”