Dynamic vs. fixed bag filling: Impact on cardiac output rebreathing protocol

Abstract A main purpose of this study was to compare the repeatability (2.77 multiplied by the within-subject SD) between two different rebreathing protocols on cardiac output ( Q ˙ ) , pulmonary diffusing capacity for carbon monoxide (DLCO ) and nitric oxide (DLNO ), and pulmonary capillary blood volume (Vc). This study compared two bag volume conditions [Fixed Bag Volume (FBV) = BV fixed at 60% of forced vital capacity; Dynamic Bag Volume (DBV) = BV matched to tidal volume at each stage of exercise]. Ten females (age = 27 ± 8 years; V ˙ O 2 , peak = 2.5 ± 0.6 L/min ) had measurements at rest (12%), 50%, 88%, and 100% of V ˙ O 2 , peak on two study days in a balanced, crossover design. Neither the slope nor intercept of Q ˙ vs. V ˙ O 2 were different between FBV or DBV. The slope of DLCO vs. Q ˙ was the same but intercept was higher for FBV. The BV affected the slope and the intercept between DLNO vs. Q ˙ ( p < 0.05). The repeatability was similar between both protocols for Q ˙ (2.8–3.4 l/min) and DLNO (33–42 ml/min/mmHg) regardless of exercise intensity. However, the measurement error was lower for Vc when using the FBV protocol ( p < 0.05). This study shows that the pattern of BV used during rebreathing maneuvers affects DLNO vs. Q ˙ relation more than it affects DLCO and Vc vs. Q ˙ . In addition FBV protocol provides more repeatable Vc measurements at any exercise stage compared to the DBV protocol.