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Cardiac output with modified cardio-impedance against inert gas rebreathing during sub-maximal and maximal cycling exercise in healthy and fit subjects

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Abstract

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.

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Abbreviations

BW :

Body weight

CaO2 :

Arterial blood concentration of O2

(CaO2–C\(\bar {v}\)O2):

Artero-to-mixed venous blood difference in O2 concentrations

CV:

Coefficient of variation

ΔWL:

Net increment of workload during incremental test to exhaustion

ES:

Effect size

H :

Height

Hb :

Haemoglobin

HR:

Heart rate

HRmax :

Maximal heart rate

N2O:

Nitrous oxide

\(\dot {Q}\) :

Cardiac output

\({\dot {Q}_{{\text{IN}}}}\) :

Cardiac output assessed by using inert gas rebreathing

\({\dot {Q}_{{\text{max}}}}\) :

Maximal cardiac output

\({\dot {Q}_{{\text{PF}}}}\) :

Cardiac output assessed using cardio impedance (Physioflow™)

\(\dot {Q}\) aO2 :

Systemic oxygen delivery

\(\dot {Q}\) aO2max :

Maximal systemic oxygen delivery

RC:

Repeatability coefficient

SF6 :

Sulfur hexafluoride

TE:

Typical error

TTE:

Time to exhaustion

\(\dot {V}\)CO2 :

Carbon dioxide output

\(\dot {V}\) E :

Pulmonary ventilation

\(\dot {V}\)O2 :

Oxygen uptake

\(\dot {V}\)O2s :

Oxygen uptake at steady state

\(\dot {V}\)O2max :

Maximal oxygen uptake

\(\dot {V}\)O2peak :

Peak oxygen uptake

WL:

Workload

WLmax :

Maximal workload

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Acknowledgements

The authors heartily thank the volunteers who participated in the investigation, because without their collaboration this study would not have been possible. We would like also to thank the personnel and the Department of Physical Performances of the Norwegian School of Sport Sciences that hosted Alessio Del Torto during the investigation, and in particular Eng. Svein Leirstein for his technical assistance. A Grant of the University of Brescia, from the International Student Mobility Office for students’ stages abroad, funded the stay of Alessio Del Torto at the Norwegian School of Sport Sciences, Oslo, Norway.

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Authors and Affiliations

  1. Department of Molecular and Translational Medicine, University of Brescia, Viale Europa 11, 25123, Brescia, Italy

    Alessio del Torto

  2. Department of Physical Performance, Norwegian School of Sport Sciences, Sognsveien 220, 0806, Oslo, Norway

    Alessio del Torto, Øyvind Skattebo, Jostein Hallén & Carlo Capelli

  3. Department of Medical Area (DAME), University of Udine, Udine, Italy

    Alessio del Torto

Authors
  1. Alessio del Torto
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  2. Øyvind Skattebo
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  3. Jostein Hallén
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  4. Carlo Capelli
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Correspondence to Alessio del Torto.

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The authors declare no conflicts of interest.

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Communicated by Massimo Pagani.

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del Torto, A., Skattebo, Ø., Hallén, J. et al. Cardiac output with modified cardio-impedance against inert gas rebreathing during sub-maximal and maximal cycling exercise in healthy and fit subjects. Eur J Appl Physiol 119, 163–170 (2019). https://doi.org/10.1007/s00421-018-4011-z

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