Kenny, Jon‐Émile S.

Abstract Introduction Detecting and estimating blood volume loss are important for the diagnosis and management of life-threatening hemorrhage. There is a direct relationship between percent blood volume loss (BVL%) and falling in stroke volume (SV); furthermore, there is a direct relationship between diminishing SV and the corrected flow time of the carotid artery (ccFT). Therefore, we hypothesized that change in ccFT (ccFTΔ) would directly relate with BVL% in a phlebotomy paradigm. Materials and Methods A prospective, convenience sample of healthy volunteers was studied. Volunteers underwent blood donation protocol in a physiology lab. A wireless, wearable Doppler ultrasound system monitored ccFT during blood donation. Traditional vital signs were also measured throughout. The relationship between traditional vital signs as well as ccFTΔ were compared to BVL% using 2 mixed linear regression models. Results Data from 20 subjects and blood donations comprising 46,123 cardiac cycles are included. On average 413.5 ± 39 mL of blood were drawn representing 8.6 ± 1.6% BVL%. There was a significant and strong linear relationship between BVL% and ccFTΔ during blood draw with the regression slope demonstrating that for every 1 ms reduction in ccFT there was a 0.4% reduction in blood volume. Conclusions In healthy subjects and when blood loss is the sole mechanism for falling SV, we estimate that for every 1 ms reduction in ccFT, there is an approximate 0.4 BVL%. Validation of these results in patients with traumatic hemorrhage is underway.

Abstract Background: Doppler ultrasound of the common carotid artery is used to infer central hemodynamics. For example, change in the common carotid artery corrected flow time (ccFT) and velocity time integral (VTI) are proposed surrogates of changing stroke volume. However, conflicting data exist which may be due to inadequate beat sample size and measurement variability – both intrinsic to handheld systems. In this brief communication, we determined the correlation between changing ccFT and carotid VTI during progressively severe central blood volume loss and resuscitation. Methods: Measurements were obtained through a novel, wireless, wearable Doppler ultrasound system. Sixteen participants (ages of 18–40 years with no previous medical history) were studied across 25 lower body-negative pressure protocols. Relationships were assessed using repeated-measures correlation regression models. Results: In total, 33,110 cardiac cycles comprise this analysis; repeated-measures correlation showed a strong, linear relationship between ccFT and VTI. The strength of the ccFT-VTI relationship was dependent on the number of consecutively averaged cardiac cycles (R 1 cycle = 0.70, R 2 cycles = 0.74, and R 10 cycles = 0.81). Conclusions: These results positively support future clinical investigations employing common carotid artery Doppler as a surrogate for central hemodynamics.

A wireless, wearable Doppler ultrasound offers a new paradigm for linking physiology to resuscitation medicine. To this end, the image analysis of simultaneously-acquired venous and arterial Doppler spectrograms attained by wearable ultrasound represents a new source of hemodynamic data. Previous investigators have reported a direct relationship between the central venous pressure (CVP) and the ratio of the internal jugular-to-common carotid artery diameters. Because Doppler power is directly related to the number of red cell scatterers within a vessel, we hypothesized that (1) the ratio of internal jugular-to-carotid artery Doppler power (V/APOWER) would be a surrogate for the ratio of the vascular areas of these two vessels and (2) the V/APOWER would track the anticipated CVP change during simulated hemorrhage and resuscitation. To illustrate this proof-of-principle, we compared the change in V/APOWER obtained via a wireless, wearable Doppler ultrasound to B-mode ultrasound images during a head-down tilt. Additionally, we elucidated the change in the V/APOWER during simulated hemorrhage and transfusion via lower body negative pressure (LBNP) and release. With these Interesting Images, we show that the Doppler V/APOWER ratio qualitatively tracks anticipated changes in CVP (e.g., cardiac preload) which is promising for both diagnosis and management of hemodynamic unrest.