Reliability of a new device to assess the oxygen consumption of human respiratory muscles. Med. Sci. Sports Exerc., Vol. 31, No. 7, pp. 1076-1082, 1999.
Purpose: This study tests the reliability of a new device for assessing the oxygen consumption of the respiratory muscles (V̇O2 resp.).
Methods: Fourteen healthy male volunteers participated in the study. The device consists of an expandable external ventilatory dead space created with pieces of plastic tubing and a spirometer filled with 100% oxygen. It also incorporates a carbon dioxide absorber. Total V̇O2 (V̇O2 tot.) was recorded from the spirometric closed circuit and ventilation (V̇E), from the spirometer tracing. For 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 V̇O2 tot. and V̇E increased progressively. Because log V̇O2 tot. was linearly related to V̇E, we calculated the slope value (log V̇O2-V̇E) and the Y-intercept (V̇E = 0) of the semilog regression representing, respectively, V̇O2 resp. and metabolic V̇O2 (V̇O2 met.).
Results: When compared with values in the literature, these values did not differ from those recorded in subjects of a similar age group. The V̇O2 resp. and V̇O2 met. calculated in T1 and T2 were not different (V̇O2 resp. = 0.0066 ± 0.0005 for T1 vs 0.0067 ± 0.0005 log mL·min−1/L·min−1 for T2 and V̇O2 met. = 269.3 ± 28.6 for T1 vs 281.9 ± 24.1 mL·min−1 for T2). The coefficients of variation were: 25% at T1 and 23% at T2 for V̇O2 resp. and 34% at T1 and 29% at T2 for V̇O2 met. Moreover, significant correlations (r = 0.96, P < 0.001 for V̇O2 resp., r = 0.95, P < 0.001 for V̇O2 met.), high coefficients of determination (r2 = 0.92 for V̇O2 resp., r2 = 0.90 for V̇O2 met.) and negligible SEE (0.0005 for V̇O2 resp., 0.2 mL·min−1 for V̇O2 met.) were found between the two tests. When we plotted the mean values of V̇O2 resp. and V̇O2 met. measured at T1 and T2 against their respective differences, more than 95% of the slight differences ranged between the limits defined by mean value ± 2 SD, reflecting the small discrepancy between duplicate measurements.
Conclusion: The results confirm that the test performed with this device is useful and reliable for assessing the V̇O2 resp. in healthy subjects.