Carotid artery velocity time integral and corrected flow time measured by a wearable Doppler ultrasound detect stroke volume rise from simulated hemorrhage to transfusion

Fig. 1. Picture of wireless, wearable Doppler ultrasound device

Fig. 2. Hemodynamic data captured during lower body negative pressure (LBNP) and release. Measures from A–D are synchronously captured. Each faint line represents a single protocol, while the emboldened line represents the average of all protocols. A Stroke volume (SV) percent change during progressively severe LBNP (i.e., hemorrhage model) and release of LBNP (i.e., rapid transfusion model). B Mean arterial pressure (MAP) percent change. C velocity time integral (VTI) from the wearable Doppler percent change. D corrected flow time (ccFT) percent change. E The optimal carotid artery maximum VTI threshold for distinguishing ≥ + 10% SV∆. Each data point represents a 10-s average. Prior to subsampling, there were 3596 data points categorized as < + 10% SV∆ and 598 data points categorized as ≥ + 10% SV∆. The data categorized as < + 10% SV∆ were randomly subsampled, iteratively 1000 times, to 598 data points (see methods). The sensitivity of maximum VTI is 532/598 = 89% and specificity is 598/598 = 100%. F The optimal ccFT threshold for distinguishing + 10% SV∆. Each data point represents a 10-s average. The sensitivity is 532/598 = 89% and specificity is 598/598 = 100%