The Modelflow method significantly underestimated the increase in cardiac output during heat stress (2.3 l/min via cannulation vs 4.5 l/min via thermodilution, P<0.01).
Does the Modelflow method accurately estimate cardiac output compared to thermodilution during whole body heat stress in healthy subjects?
The Modelflow method significantly underestimates cardiac output during whole body heat stress and subsequent lower-body negative pressure compared to the thermodilution gold standard.
Absolute Event Rate: 2.3% vs 4.5%
p-value: p=<0.01
An estimation of cardiac output can be obtained from arterial pressure waveforms using the Modelflow method. However, whether the assumptions associated with Modelflow calculations are accurate during whole body heating is unknown. This project tested the hypothesis that cardiac output obtained via Modelflow accurately tracks thermodilution-derived cardiac outputs during whole body heat stress. Acute changes of cardiac output were accomplished via lower-body negative pressure (LBNP) during normothermic and heat-stressed conditions. In nine healthy normotensive subjects, arterial pressure was measured via brachial artery cannulation and the volume-clamp method of the Finometer. Cardiac output was estimated from both pressure waveforms using the Modeflow method. In normothermic conditions, cardiac outputs estimated via Modelflow (arterial cannulation: 6.1 ± 1.0 l/min; Finometer 6.3 ± 1.3 l/min) were similar with cardiac outputs measured by thermodilution (6.4 ± 0.8 l/min). The subsequent reduction in cardiac output during LBNP was also similar among these methods. Whole body heat stress elevated internal temperature from 36.6 ± 0.3 to 37.8 ± 0.4°C and increased cardiac output from 6.4 ± 0.8 to 10.9 ± 2.0 l/min when evaluated with thermodilution (P < 0.001). However, the increase in cardiac output estimated from the Modelflow method for both arterial cannulation (2.3 ± 1.1 l/min) and Finometer (1.5 ± 1.2 l/min) was attenuated compared with thermodilution (4.5 ± 1.4 l/min, both P < 0.01). Finally, the reduction in cardiac output during LBNP while heat stressed was significantly attenuated for both Modelflow methods (cannulation: -1.8 ± 1.2 l/min, Finometer: -1.5 ± 0.9 l/min) compared with thermodilution (-3.8 ± 1.19 l/min). These results demonstrate that the Modelflow method, regardless of Finometer or direct arterial waveforms, underestimates cardiac output during heat stress and during subsequent reductions in cardiac output via LBNP.
Shibasaki et al. (Thu,) conducted a other in Healthy normotensive subjects (n=9). Modelflow method vs. Thermodilution method was evaluated on Increase in cardiac output during whole body heat stress (p=<0.01). The Modelflow method significantly underestimated the increase in cardiac output during heat stress (2.3 l/min via cannulation vs 4.5 l/min via thermodilution, P<0.01).