Abstract
Alveolar‐capillary surface area for pulmonary gas exchange falls with aging, causing a reduction in lung diffusing capacity for carbon monoxide (DLCO). However, during exercise additional factors may influence DLCO, including pulmonary blood flow and pulmonary vascular pressures. First, we sought to determine the age‐dependent effect of incremental exercise on pulmonary vascular pressures and DLCO. We also aimed to investigate the dependence of DLCO on pulmonary vascular pressures during exercise via sildenafil administration to reduce pulmonary smooth muscle tone. Nine younger (27 ± 4 years) and nine older (70 ± 3 years) healthy subjects performed seven 5‐min exercise stages at rest, 0 (unloaded), 10, 15, 30, 50, and 70% of peak workload before and after sildenafil. DLCO, cardiac output (Q), and pulmonary artery and wedge pressure (mPAP and mPCWP; subset of participants) were collected at each stage. mPAP was higher (P = 0.029) and DLCO was lower (P = 0.009) throughout exercise in older adults; however, the rate of rise in mPAP and DLCO with increasing Q was not different. A reduction in pulmonary smooth muscle tone via sildenafil administration reduced mPAP, mPCWP, and the transpulmonary gradient (TPG = mPAP–mPCWP) in younger and older subjects (P < 0.001). DLCO was reduced following the reduction in mPAP and TPG, regardless of age (P < 0.001). In conclusion, older adults successfully adapt to age‐dependent alterations in mPAP and DLCO. Furthermore, DLCO is dependent on pulmonary vascular pressures, likely to maintain adequate pulmonary capillary recruitment. The rise in pulmonary artery pressure with aging may be required to combat pulmonary vascular remodeling and maintain lung diffusing capacity, particularly during exercise.
Highlights
Healthy aging is associated with alterations in both lung diffusing capacity and pulmonary hemodynamics, but the interplay between these variables remains unclear
The catalyst for investigating the relationship between pulmonary hemodynamics and lung diffusing capacity came from a previous study in our laboratory in which we found that, during incremental exercise, the rate of increase in lung diffusing capacity was remarkably similar in older adults compared to their younger counterparts
We found that healthy older individuals had a greater pulmonary artery pressure and lower lung diffusing capacity for a given cardiac output throughout exercise versus younger individuals
Summary
Healthy aging is associated with alterations in both lung diffusing capacity and pulmonary hemodynamics, but the interplay between these variables remains unclear. The ability to transfer gases from the alveoli to blood, is reduced with aging, both at rest and during exercise (Chang et al 1992; Stam et al 1994; Guenard and Marthan 1996; Coffman et al 2017) This is likely in part due to remodeling of the pulmonary alveoli and capillaries (Butler and Kleinerman 1970; Thurlbeck and Angus 1975; Verbeken et al 1992; Gillooly and Lamb 1993) which acts to reduce surface area available for gas exchange. It is feasible that age-dependent increases in pulmonary vascular pressures may alter the increase in lung surface area available for gas exchange, during exercise
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