PETCO2 is Correlated with Peak Cardiac Output during Exercise in Patients with Ischemic Heart Disease

Background: Although a value of end-tidal CO2 pressure (PETCO2) is reported to relate with cardiac index, it is still unclear whether PETCO2 also shows cardiac functions during exercise in patients with ischemic heart disease (IHD). We investigate the relationship between cardiac functions and PETCO2 in patients with IHD.
Design and methods: We enrolled consecutive 221 heart disease patients (65±14 y.o., 73% males) who had performed cardiopulmonary exercise testing and impedance cardiography simultaneously during 2016 in our hospital. We compared cardiac functions [peak stroke volume (SV), heart rate (HR) and cardiac output (CO)] with PETCO2 in patients with AMI (n=25), stable AP (SAP)(n=89), OMI (n=64) and normal coronary (0VD) (n=43).
Results: PETCO2 at respiratory compensation (RC) point was highest during a ramp exercise. Maximum PETCO2 was significantly correlated with peak CO (r = 0.437), peak SV (r = 0.260) and peak HR (r = 0.416) in all subjects. Peak CO is correlated with maximum PETCO2 in patients with AMI (r = 0.641), SAP (r = 0.323), OMI (r = 0.446) and 0VD (r = 0.491). Correlation coefficient between peak HR and PETCO2 were greater than that between peak SV and PETCO2 in each disease category. In patients with SAP, correlation between peak HR and PETCO2 was significant but weak (r=0.04). Peak HR was lower than that in other patients.
Conclusion: PETCO2 at RC point was correlated with peak CO during exercise in patients with IHD. However, in patients with SAP, correlation between peak CO and PETCO2 was lower than that of other IHD patients.This is assumed to be due to a lower peak HR. It seems that maximum PETCO2 is a new parameter of peak CO, and maximum PETCO2 is modulated by peak HR.