Reliability of a new device to assess the oxygen consumption of human respiratory muscles

Purpose: This study tests the reliability of a new device for assessing the oxygen consumption of the respiratory muscles ((V) over dot O-2 resp.). Me thods: Fourteen healthy male volunteers participated in the study. The devi ce consists of an expandable external ventilatory dead space created with p ieces of plastic tubing and a spirometer filled with 100% oxygen. It also i ncorporates a carbon dioxide absorber. Total (V) over dot O-2 ((V) over dot O-2 tot.) was recorded from the spirometric closed circuit and ventilation ((V) over dot (E)), from the spirometer tracing. Fur each subject the test procedure was carried out in duplicate (T1 and T2) after an overnight fast . The dead space was increased at a constant rate of 260 mL every 90 s, and (V) over dot O-2 tot, and (V) over dot (E) increased progressively. Becaus e log (V) over dot O-2 tot, was linearly related to (V) over dot (E), we ca lculated the slope value (log (V) over dot O-2-(V) over dot (E)) and the Y- intercept ((V) over dot (E) = 0) of the semilog regression representing, re spectively, (V) over dot O-2 resp. and metabolic (V) over dot O-2 ((V) over dot O-2 met.). Results: When compared with values in the literature, these values did not differ from those recorded in subjects of a similar age gro up. The (V) over dot O-2 resp. and (V) over dot O-2 met. calculated in T1 a nd T2 were not different (90, resp. = 0.0066 +/- 0.0005 for T1 vs 0.0067 +/ - 0.0005 log ml . min(-1)/L . min(-1) for T2 and (V) over dot O-2 met. = 26 9.3 +/- 28.6 for T1 vs 281.9 +/- 24.1 mL . min(-1) for T2). The coefficient s of variation were: 25% at T1 and 23% at T2 for (V) over dot O-2 resp. and 34% at T1 and 29% at T2 for (V) over dot O-2 met. Moreover. significant co rrelations (r = 0.96, P < 0.001 for (V) over dot O-2 resp., r = 0.95, P < 0 .001 for (V) over dot O-2 met.), high coefficients of determination (r(2) = 0.92 for (V) over dot O-2 resp., r(2) = 0.90 for (V) over dot O-2 met.) an d negligible SEE (0.0005 for (V) over dot O-2 resp., 0.2 ml . min(-1) for ( V) over dot O-2 met.) were found between the two tests. When we plotted the mean values of (V) over dot O-2 resp. and (V) over dot O-2 met. measured a t T1 and T2 against their respective differences, more than 95% of the slig ht differences ranged between the limit:, defined by mean value +/- 2 SD, r eflecting the small discrepancy between duplicate measurements. Conclusion: The results confirm that the test performed with this device is useful and reliable for assessing the (V) over dot O-2 rasp. in healthy subjects.