Abstract
NEW FINDINGS: What is the central question in this study? How reliable is the combined measurement of the pulmonary diffusing capacity to carbon monoxide and nitric oxide (D(LCO/NO) ) during exercise and in the resting supine position, respectively? What is the main finding and its importance? The D(LCO/NO) technique is reliable with a very low day-to-day variability both during exercise and in the resting supine position, and may thus provide a useful physiological outcome that reflects the alveolar-capillary reserve in humans. ABSTRACT: D(LCO/NO) , the combined single-breath measurement of the diffusing capacity to carbon monoxide (D(LCO) ) and nitric oxide (D(LNO) ) measured either during exercise or in the resting supine position may be a useful physiological measure of alveolar-capillary reserve. In the present study, we investigated the between-day test-retest reliability of D(LCO/NO) -based metrics. Twenty healthy volunteers (10 males, 10 females; mean age 25 (SD 2) years) were randomized to repeated D(LCO/NO) measurements during upright rest followed by either exercise (n = 11) or resting in the supine position (n = 9). The measurements were repeated within 7 days. The smallest real difference (SRD), defined as the 95% confidence limit of the standard error of measurement (SEM), the coefficient of variance (CV), and intraclass correlation coefficients were used to assess test-retest reliability. SRD for D(LNO) was higher during upright rest (5.4 (95% CI: 4.1, 7.5) mmol/(min kPa)) than during exercise (2.7 (95% CI: 2.0, 3.9) mmol/(min kPa)) and in the supine position (3.0 (95% CI: 2.1, 4.8) mmol/(min kPa)). SRD for D(LCOc) was similar between conditions. CV values for D(LNO) were slightly lower than for D(LCOc) both during exercise (1.5 (95% CI: 1.2, 1.7) vs. 3.8 (95% CI: 3.2, 4.3)%) and in the supine position (2.2 (95% CI: 1.8, 2.5) vs. 4.8 (95% CI: 3.8, 5.4)%). D(LNO) increased by 12.3 (95% CI: 11.1, 13.4) and D(LCOc) by 3.3 (95% CI: 2.9, 3.7) mmol/(min kPa) from upright rest to exercise. The D(LCO/NO) technique provides reliable indices of alveolar-capillary reserve, both during exercise and in the supine position.