Cardiac output during exercise: A comparison of four methods

Abstract

Several techniques assessing cardiac output (Q) during exercise are available. The extent to which the measurements obtained from each respective technique compares to one another, however, is unclear. We quantified Q simultaneously using four methods: the Fick method with blood obtained from the right atrium (Q(Fick-M)), Innocor (inert gas rebreathing; Q(Inn)), Physioflow (impedance cardiography; Q(Phys)), and Nexfin (pulse contour analysis; Q(Pulse)) in 12 male subjects during incremental cycling exercise to exhaustion in normoxia and hypoxia (FiO2 = 12%). While all four methods reported a progressive increase in Q with exercise intensity, the slopes of the Q/oxygen uptake (VO2) relationship differed by up to 50% between methods in both normoxia [4.9 ± 0.3, 3.9 ± 0.2, 6.0 ± 0.4, 4.8 ± 0.2 L/min per L/min (mean ± SE) for Q(Fick-M), Q(Inn), QP hys and Q(Pulse), respectively; P = 0.001] and hypoxia (7.2 ± 0.7, 4.9 ± 0.5, 6.4 ± 0.8 and 5.1 ± 0.4 L/min per L/min; P = 0.04). In hypoxia, the increase in the Q/VO2 slope was not detected by Nexfin. In normoxia, Q increases by 5-6 L/min per L/min increase in VO2, which is within the 95% confidence interval of the Q/VO2 slopes determined by the modified Fick method, Physioflow, and Nexfin apparatus while Innocor provided a lower value, potentially reflecting recirculation of the test gas into the pulmonary circulation. Thus, determination of Q during exercise depends significantly on the applied method.

Comparison of cardiac output estimates by bioreactance and inert gas rebreathing methods during cardiopulmonary exercise testing

“…The data presented here are consistent with previous studies that have reported lower cardiac output from the inert gas rebreathing when compared with other non‐invasive cardiac output measuring devices, that is pulse contour analysis, (Bartels, ; Siebenmann, ). This is probably due to recirculation of N 2 O, which reduces alveolar‐arterial diffusion gradient for N 2 O and further attenuate N 2 O uptake (Bartels, ).…”

Phlebotomy eliminates the maximal cardiac output response to six weeks of exercise training

“…The method has previously been validated showing a day-to-day reproducibility of 4.3% (18) and that the measured Q values are accurate compared with the direct Fick method (7). In our experience the Innocor tends to underestimate Q and that this is most likely due to an overlap in recirculation of the inert gas if multiple measurements are performed (55). In the current study the rebreathings were separated by several minutes with the intent to eliminate potential effects of recirculating inert gas.…”

The effects of menstrual cycle phase on the incidence of plateau at and associated cardiorespiratory dynamics

“…Given that there is no effect for menstrual cycle phase or indeed OCP use on SV, alternate explanations are sought. A possibility for the rising and highly variable results reported by Wang and colleagues (Wang et al ., ) could be the approach used to estimate SV, single breath (SB) breathing procedure, a physically challenging procedure requiring the participant to perform a series of maximal expirations followed by maximal inspiration where the breath in a gas mixture of 0·3% of CO, CH 4 , C 2 H 2 , 21% O 2 in balanced nitrogen, and has been associated with increased variability when compared to less demanding methods (Siebenmann et al ., ). In the present study, the non‐invasive Physioflow ® thoracic impedance device was used, which has been shown to provide both valid and reliable results in the determination of SV and HR under both submaximal and maximal exercise conditions (Siebenmann et al ., ).…”