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

Abstract

Background The relationship of non-invasive CW Doppler cardiac output (CO USCOM) and stroke volume (SV USCOM) and calculated CO STRINGER and SV STRINGER 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 SV USCOM and CO USCOM. Stringer formula a-vDO 2 = 5.721 + (0.1047 ⁎ %VO 2max) and CO = VO 2/C(a-vDO 2) (direct Fick method) were applied. Results Total values of CO STRINGER vs. CO USCOM and SV STRINGER vs. SV USCOM showed high correlation ( r = 0.879 and r = 0.813, p < 0.01). Mean differences between total measures of CO STRINGER vs. CO USCOM were 0.4 ± 4.1 l/min and SV STRINGER vs. SV USCOM − 9.9 ± 19.9 cm 3. Mean % errors were CO STRINGER vs. CO USCOM − 31 ± 66% and SV STRINGER vs. SV USCOM − 39 ± 58% respectively. Regression modelling determined CO STRINGER = 1.58CO–4.02 l/min, and SV STRINGER = 1.45SV–35.60 cm 3. SV STRINGER vs. SV USCOM correlated best at peak exercise ( r = 0.997), followed by r = 0.668 at recovery 3min and 0.585 at recovery 1min. CO STRINGER vs. CO USCOM correlated best at recovery 3min ( r = 0.611), followed by recovery 1min ( r = 0.556) and moderately at peak exercise ( r = 0.447). At rest, both CO STRINGER and SV STRINGER were not correlated with CO USCOM and SV USCOM ( r = 0.276 and r = 0.130, respectively). Conclusion Calculated SV STRINGER and CO STRINGER are applicable at peak exercise and during recovery compared to CW Doppler SV USCOM and CO USCOM. However certain limitations are evident regarding calculated CO STRINGER at peak exercise and at rest in comparison to CW Doppler measurements.