![]() ![]() Written and informed consent was obtained for all subjects, and the study was approved by the Research Ethics Board of Health Sciences North. The procedures followed were in accord with the ethical standards of the committee on human experimentation at our institution. Exclusion criteria were known cardiovascular history and/or taking regular cardiovascular medications. We recruited 26 healthy, adult volunteers. Using the ultrasound patch capable of recording carotid Doppler spectra continuously, we evaluated the dispersion of Ftc during quiet respiration calculated by 2 Ftc formulae, as an exploratory analysis. Given that mechanical systole has better correlation with SV than electrical systole, we hypothesized that mechanical Ftc formulae would better detect SV change than those derived to correct electrical systole. Five of the Ftc formulae were initially derived to correct mechanical systole, while the remaining 6 were proposed to correct electrical systole for heart rate. 1), we studied 11 Ftc formulae for their ability to detect a 10% change in SV in healthy volunteers. Using a wearable Doppler ultrasound patch (Fig. Furthermore, these formulae may be categorized by whether they correct for electrical systole (i.e., the duration from the onset of the Q wave to the end of the T wave) or mechanical systole (i.e., the duration from the upstroke of the pulse to the closure of the aortic valve). Numerous Ftc formulae have been proposed and fall generally into linear and non-linear varieties. Consequently, when using the change in systolic duration to predict change in SV, an underlying assumption is that afterload, contractility, and heart rate remain constant.Ĭonstant heart rate may be achieved mathematically by calculating the corrected flow time (Ftc). Yet, the length of systole is also mediated by afterload, contractility, and heart rate. Moreover, the direct relationship between systolic duration and SV was reaffirmed in humans using both indicator-dye dilution and pressure gradient techniques. Indeed, previous animal work employing isolated, supported heart preparations has shown that when heart rate and blood pressure are controlled, the duration of systole is directly related to SV. 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.Ĭhange in the duration of systole has been used as an accurate surrogate for stroke volume (SV) in the critically ill, chronically ill, and in healthy volunteers. 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. The coefficient of variation of Ftc during quiet breathing for these formulae were 0.06 and 0.07, respectively. As an exploratory analysis, we studied 3335 carotid beats for the dispersion of Ftc during quiet breathing using the equations of Wodey and Bazett. Ftc Wodey had 100% concordance and an R 2 of 0.75 with change in SV these values were 99%, 0.76 and 98%, 0.71 for Ftc Chambers and Ftc Bazetts, respectively. Similarly, a 3% change in Ftc calculated by Bazett’s formula displayed a sensitivity and specificity of 91% and 93%. 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. Most of the 11 Ftc equations studied had similar diagnostic attributes. One hundred changes in cardiac preload and 3890 carotid beats were analyzed. 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. Further, little is known about the inherent Ftc variability induced by the respiratory cycle. Multiple Ftc equations have been proposed many have not had their diagnostic characteristics for detecting SV change reported. Change of the corrected flow time (Ftc) is a surrogate for tracking stroke volume (SV) in the intensive care unit. ![]()
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