Published in:
01-01-2019 | Original Article
Cardiac output with modified cardio-impedance against inert gas rebreathing during sub-maximal and maximal cycling exercise in healthy and fit subjects
Published in: European Journal of Applied Physiology | Issue 1/2019
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Purpose
We measured cardiac output (\(\dot {Q}\)) during sub-maximal and supra-maximal exercise with inert gas rebreathing (\({\dot {Q}_{{\text{IN}}}}\)) and modified cardio-impedance (\({\dot {Q}_{{\text{PF}}}}\)) and we evaluated the repeatability of the two methods.
Methods
\(\dot {V}\)O2 and \(\dot {Q}\) were measured twice in parallel with the two methods at sub-maximal (50–250 W) and supra-maximal exercise in 7 young subjects (25 ± 1 years; 74.4 ± 5.2 kg; 1.84 ± 0.07 m).
Results
\({\dot {Q}_{{\text{IN}}}}\) and \({\dot {Q}_{{\text{PF}}}}\) increased by 3.4 L·min−1 and by 5.1 L·min−1 per 1 L·min−1 of increase in \(\dot {V}{{\text{O}}_{\text{2}}}\), respectively. Mean \({\dot {Q}_{{\text{PF}}}}\) (23.3 ± 2.5 L·min−1) was 9% lower than \({\dot {Q}_{{\text{IN}}}}\) (25.8 ± 2.2 L·min−1) during supra-maximal exercise. Bland–Altman analysis showed that: (i) bias (\({\dot {Q}_{{\text{PF}}}}\)–\({\dot {Q}_{{\text{IN}}}}\)) was significantly different from zero (− 0.65 ± 2.61 L·min−1) and; (ii) the ratios \({\dot {Q}_{{\text{PF}}}}\) ÷ \({\dot {Q}_{{\text{IN}}}}\) were linearly related with \(\dot {Q}\), indicating that \({\dot {Q}_{{\text{IN}}}}\) tended to overestimate \(\dot {Q}\) in comparison with \({\dot {Q}_{{\text{PF}}}}\) for values ranging from 10.0 to 15.0 L·min−1 and to underestimate it for larger values. The coefficient of variation was similar for sub-maximal values (8.6% vs. 7.7%; 95% CL: ×/÷1.31), but lower for \({\dot {Q}_{{\text{PF}}}}\) (7.6%; 95% CL: ×/÷ 2.05) than for \({\dot {Q}_{{\text{IN}}}}\) (27.7%; 95% CL: ×/÷2.54) at supra-maximal intensity.
Conclusions
\({\dot {Q}_{{\text{PF}}}}\) seems to represent a valuable alternative to invasive methods for assessing \(\dot {Q}\) during sub-maximal exercise. The \({\dot {Q}_{{\text{PF}}}}\) underestimation with respect to \({\dot {Q}_{{\text{IN}}}}\) during supra-maximal exercise suggests that \({\dot {Q}_{{\text{PF}}}}\) might be less optimal for supra-maximal intensities.