A comparison of real-time CW Doppler and calculated cardiac output according to the Stringer formula for non-invasive hemodynamics in exercise testing.

BACKGROUND

The relationship of non-invasive CW Doppler cardiac output (COUSCOM) and stroke volume (SVUSCOM) and calculated COSTRINGER and SVSTRINGER based on the Stringer calculations in healthy athletes is unknown.

METHODS

20 athletes (19.9+/-11 years) underwent a standardized stepwise treadmill test including breath-by-breath spirometry, and non-invasive SVUSCOM and COUSCOM. Stringer formula a-vDO2=5.721+(0.1047%VO2max) and CO=VO2/C(a-vDO2) (direct Fick method) were applied.

RESULTS

Total values of COSTRINGER vs. COUSCOM and SVSTRINGER vs. SVUSCOM showed high correlation (r=0.879 and r=0.813, p<0.01). Mean differences between total measures of COSTRINGER vs. COUSCOM were 0.4+/-4.1 l/min and SVSTRINGER vs. SVUSCOM -9.9+/-19.9 cm3. Mean % errors were COSTRINGER vs. COUSCOM -31+/-66% and SVSTRINGER vs. SVUSCOM -39+/-58% respectively. Regression modelling determined COSTRINGER=1.58CO-4.02 l/min, and SVSTRINGER=1.45SV-35.60 cm3. SVSTRINGER vs. SVUSCOM correlated best at peak exercise (r=0.997), followed by r=0.668 at recovery3 min and 0.585 at recovery1 min. COSTRINGER vs. COUSCOM correlated best at recovery3 min (r=0.611), followed by recovery1 min (r=0.556) and moderately at peak exercise (r=0.447). At rest, both COSTRINGER and SVSTRINGER were not correlated with COUSCOM and SVUSCOM (r=0.276 and r=0.130, respectively).

CONCLUSION

Calculated SVSTRINGER and COSTRINGER are applicable at peak exercise and during recovery compared to CW Doppler SVUSCOM and COUSCOM. However certain limitations are evident regarding calculated COSTRINGER at peak exercise and at rest in comparison to CW Doppler measurements.