Abstract
BackgroundLung diffusing capacity for carbon monoxide (DLCO) gives an overall assessment of functional lung surface area for gas exchange and can be assessed using various methods. DLCO is an important factor in exercise intolerance in patients with chronic obstructive pulmonary disease (COPD). We investigated if the intra-breath (IBDLCO) method may give a more sensitive measure of available gas exchange surface area than the more typical single breath (SBDLCO) method and if COPD subjects with the largest resting DLCO relative to pulmonary blood flow (Qc) would have a more preserved exercise capacity.MethodsInformed consent, hemoglobin, spirometry, SBDLCO, IBDLCO, and Qc during IBDLCO were performed in moderate to severe COPD patients, followed by progressive cycle ergometry to exhaustion with measures of oxygen saturation (SaO2) and expired gases.ResultsThirty two subjects (47% female, age 66 ± 9 yrs., BMI 30.4 ± 6.3 kg/m2, smoking hx 35 ± 29 pkyrs, 2.3 ± 0.8 on the 0-4 GOLD classification scale) participated. The majority used multiple inhaled medications and 20% were on oral steroids. Averages were: FEV1/FVC 58 ± 10%Pred, peak VO2 11.4 ± 3.1 ml/kg/min, and IBDLCO 72% of the SBDLCO (r = 0.88, SB vs IB methods). Using univariate regression, both the SB and IBDLCO (% predicted but not absolute) were predictive of VO2peak in ml/kg/min; SBDLCO/Qc (r = 0.63, p < 0.001) was the best predictor of VO2peak; maximal expiratory flows over the mid to lower lung volumes were the most significantly predictive spirometric measure (r = 0.49, p < 0.01). However, in multivariate models only BMI added additional predictive value to the SBDLCO/Qc for predicting aerobic capacity (r = 0.73). Adjusting for current smoking status and gender did not significantly change the primary results.ConclusionIn patients with moderate to severe COPD, preservation of lung gas exchange surface area as assessed using the resting SBDLCO/Qc appears to be a better predictor of exercise capacity than more classic measures of lung mechanics.
Highlights
Lung diffusing capacity for carbon monoxide (DLCO) gives an overall assessment of functional lung surface area for gas exchange and can be assessed using various methods
While a number of studies have examined predictors of exercise capacity in the chronic obstructive pulmonary disease (COPD) population, the majority of these have focused on measures of lung mechanics and while relationships are found between measures of maximal expiratory flows and volumes, measures of hyperinflation appear to be the most predictive [3, 8, 9, 26, 27]
While the reality is that these collective contributors to exercise limitation in COPD are all integrated and codependent, our work suggests that maintenance of a functional alveolar-capillary bed is an important determinant of patients ability to exercise and likely to carry on normal daily activities
Summary
Lung diffusing capacity for carbon monoxide (DLCO) gives an overall assessment of functional lung surface area for gas exchange and can be assessed using various methods. We investigated if the intra-breath (IBDLCO) method may give a more sensitive measure of available gas exchange surface area than the more typical single breath (SBDLCO) method and if COPD subjects with the largest resting DLCO relative to pulmonary blood flow (Qc) would have a more preserved exercise capacity. There are different ways to quantify DLCO, from the typical single breath method (SBDLCO), to various rebreathe, steady state, open-circuit and intra-breath techniques [14]. While the latter methods may represent in some sense more physiological quantification of functional lung surface area for gas transfer or exchange, the single breath method has been standardized with wellestablished predictive norms for clinical use [15]
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