Aging is associated with deterioration in the structure and function of the pulmonary circulation. We characterized the lung diffusing capacity for carbon monoxide (DL), alveolar-capillary membrane conductance (Dm), and pulmonary-capillary blood volume (Vc) response to discontinuous incremental exercise at 25, 50, 75, and 90% of peak work (W) in four groups: ) Young [27 ± 3 yr, maximal oxygen consumption (V̇o): 110 ± 18% age predicted]; 2) Young Highly Fit (27 ± 3 yr, V̇o: 147 ± 8% age predicted); ) Old (69 ± 5 yr, V̇o: 116 ± 13% age predicted); and ) Old Highly Fit (65 ± 5 yr, V̇o: 162 ± 18% age predicted). At rest and at 90% W, DL, Dm, and Vc were decreased with age. At 90% W, DL, Dm, and Vc were greater in Old Highly Fit vs. Old adults. The slope of the DL-cardiac output (Q̇) relationship from rest to end exercise at 90% W was not different between Young, Young Highly Fit, Old, and Old Highly Fit (1.35 vs. 1.44 vs. 1.10 vs. 1.35 ml·mmHg·liter blood, = 0.388), with no evidence of a plateau in this relationship during exercise; this was also true for Dm-Q̇ and Vc-Q̇. V̇o was positively correlated with ) DL, Dm, and Vc at rest; and ) the rest to end exercise change in DL, Dm, and Vc. In conclusion, these data suggest that despite the age-associated deterioration in the structure and function of the pulmonary circulation, expansion of the pulmonary capillary network does not become limited during exercise in healthy individuals regardless of age or cardiorespiratory fitness level. Healthy aging is a crucial area of research. This article details how differences in age and cardiorespiratory fitness level affect lung diffusing capacity, particularly during high-intensity exercise. We conclude that highly fit older adults do not experience a limit in lung diffusing capacity during high-intensity exercise. Interestingly, however, we found that highly fit older individuals demonstrate greater values of lung diffusing capacity during high-intensity exercise than their less fit age-matched counterparts.

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We asked whether aged adults are more susceptible to exercise-induced pulmonary edema relative to younger individuals. Lung diffusing capacity for carbon monoxide (DLCO), alveolar-capillary membrane conductance (Dm) and pulmonary-capillary blood volume (Vc) were measured before and after exhaustive discontinuous incremental exercise in 10 young (YNG; 27±3 yr) and 10 old (OLD; 69±5 yr) males. In YNG subjects, Dm increased (11±7%, P=0.031), Vc decreased (−10±9%, P=0.01) and DLCO was unchanged (30.5±4.1 vs. 29.7±2.9 ml/min/mmHg, P=0.44) pre- to post-exercise. In OLD subjects, DLCO and Dm increased (11±14%, P=0.042; 16±14%, P=0.025) but Vc was unchanged (58±23 vs. 56±23 ml, P=0.570) pre- to post-exercise. Group-mean Dm/Vc was greater after vs. before exercise in the YNG and OLD subjects. However, Dm/Vc was lower post-exercise in 2 of the 10 YNG (−7±4%) and 2 of the 10 OLD subjects (−10±5%). These data suggest that exercise decreases interstitial lung fluid in most YNG and OLD subjects, with a small number exhibiting evidence for exercise-induced pulmonary edema.

Alveolar-capillary membrane conductance (DM,CO) and pulmonary-capillary blood volume (VC) are calculated via lung diffusing capacity for carbon monoxide (DLCO) and nitric oxide (DLNO) using the single breath, single oxygen tension (single-FiO2) method. However, two calculation parameters, the reaction rate of carbon monoxide with blood (θCO) and the DM,NO/DM,CO ratio (α-ratio), are controversial. This study systematically determined optimal θCO and α-ratio values to be used in the single-FiO2 method that yielded the most similar DM,CO and VC values compared to the ‘gold-standard’ multiple-FiO2 method. Eleven healthy subjects performed single breath DLCO/DLNO maneuvers at rest and during exercise. DM,CO and VC were calculated via the single-FiO2 and multiple-FiO2 methods by implementing seven θCO equations and a range of previously reported α-ratios. The RP θCO equation (Reeves and Park, Respiration physiology 88:1–21, 1992.) and an α-ratio of 4.0–4.4 yielded DM,CO and VC values that were most similar between methods. The RP θCO equation and an experimental α-ratio should be used in future studies.