Diagnostic characteristics of 11 formulae for calculating corrected flow time as measured by a wearable Doppler patch.
Intensive Care Med Exp
Ultrasonography, Doppler, Wearable Electronic Devices, Blood Flow Velocity
BACKGROUND: Change of the corrected flow time (Ftc) is a surrogate for tracking stroke volume (SV) in the intensive care unit. Multiple Ftc equations have been proposed; many have not had their diagnostic characteristics for detecting SV change reported. Further, little is known about the inherent Ftc variability induced by the respiratory cycle.
MATERIALS AND METHODS: Using a wearable Doppler ultrasound patch, we studied the clinical performance of 11 Ftc equations to detect a 10% change in SV measured by non-invasive pulse contour analysis; 26 healthy volunteers performed a standardized cardiac preload modifying maneuver.
RESULTS: One hundred changes in cardiac preload and 3890 carotid beats were analyzed. Most of the 11 Ftc equations studied had similar diagnostic attributes. Wodeys' and Chambers' formulae had identical results; a 2% change in Ftc detected a 10% change in SV with a sensitivity and specificity of 96% and 93%, respectively. Similarly, a 3% change in Ftc calculated by Bazett's formula displayed a sensitivity and specificity of 91% and 93%. Ftc
CONCLUSIONS: Most of the 11 different equations used to calculate carotid artery Ftc from a wearable Doppler ultrasound patch had similar thresholds and abilities to detect SV change in healthy volunteers. Variation in Ftc induced by the respiratory cycle is important; measuring a clinically significant change in Ftc with statistical confidence requires a large sample of beats.
Kenny, Jon-Émile S; Barjaktarevic, Igor; Mackenzie, David C; Eibl, Andrew M; Parrotta, Matthew; Long, Bradley F; and Eibl, Joseph K, "Diagnostic characteristics of 11 formulae for calculating corrected flow time as measured by a wearable Doppler patch." (2020). Maine Medical Center. 1919.