Diagnostic characteristics of 11 formulae for calculating corrected flow time as measured by a wearable Doppler patch

Simultaneous Venous-Arterial Doppler Ultrasound During Early Fluid Resuscitation to Characterize a Novel Doppler Starling Curve: A Prospective Observational Pilot Study

Background: The likelihood of a patient being preload responsive-a state where the cardiac output or stroke volume (SV) increases significantly in response to preload-depends on both cardiac filling and function. This relationship is described by the canonical Frank-Starling curve. Research Question: We hypothesize that a novel method for phenotyping hypoperfused patients (ie, the "Doppler Starling curve") using synchronously measured jugular venous Doppler as a marker of central venous pressure (CVP) and corrected flow time of the carotid artery (ccFT) as a surrogate for SV will refine the pretest probability of preload responsiveness/unresponsiveness. Study Design and Methods: We retrospectively analyzed a prospectively collected convenience sample of hypoperfused adult emergency department (ED) patients. Doppler measurements were obtained before and during a preload challenge using a wireless, wearable Doppler ultrasound system. Based on internal jugular and carotid artery Doppler surrogates of CVP and SV, respectively, we placed hemodynamic assessments into quadrants (Qx) prior to preload augmentation: low CVP with normal SV (Q1), high CVP and normal SV (Q2), low CVP and low SV (Q3) and high CVP and low SV (Q4). The proportion of preload responsive and unresponsive assessments in each quadrant was calculated based on the maximal change in ccFT (ccFTΔ) during either a passive leg raise or rapid fluid challenge. Results: We analyzed 41 patients (68 hemodynamic assessments) between February and April 2021. The prevalence of each phenotype was: 15 (22%) in Q1, 8 (12%) in Q2, 39 (57%) in Q3, and 6 (9%) in Q4. Preload unresponsiveness rates were: Q1, 20%; Q2, 50%; Q3, 33%, and Q4, 67%. Interpretation: Even fluid naïve ED patients with sonographic estimates of low CVP have high rates of fluid unresponsiveness, making dynamic testing valuable to prevent ineffective IVF administration.

Is the Corrected Carotid Flow Time a Clinically Acceptable Surrogate Hemodynamic Parameter for the Left Ventricular Ejection Time?

OBJECTIVE

The corrected left ventricular ejection time (cLVET) comprises the phase from aortic valve opening to aortic valve closure corrected for heart rate. As a surrogate measure for cLVET, the corrected carotid flow time (ccFT) has been proposed in previous research. The aim of this study was to assess the clinical agreement between cLVET and ccFT in a dynamic clinical setting.

METHODS

Twenty-five patients with severe aortic valve stenosis (AS) were selected for transcatheter aortic valve replacement (TAVR). The cLVET and ccFT were derived from the left ventricular outflow tract (LVOT) and the common carotid artery (CCA), respectively, using pulsed wave Doppler ultrasound. Bazett's (B) and Wodey's (W) equations were used to calculate cLVET and ccFT. Measurements were performed directly before (T1) and after (T2) TAVR. Correlation, Bland-Altman and concordance analyses were performed.

RESULTS

Corrected LVET decreased from T1 to T2 (p < 0.001), with relative reductions of 11% (B) and 9% (W). Corrected carotid flow time decreased (p < 0.001), with relative reductions of 12% (B) and 10% (W). The correlation between cLVET and ccFT was strong for B (ρ = 0.74, p < 0.001) and W (ρ = 0.81, p < 0.001). The bias was -39 ms (B) and -37 ms (W), and the upper and lower levels of agreement were 19 and -98 ms (B) and 5 and -78 ms (W), respectively. Trending ability between cLVET and ccFT was good (concordance 96%) for both B and W.

CONCLUSION

In TAVR patients, the clinical agreement between cLVET and ccFT was acceptable, indicating that ccFT could serve as a surrogate measure for cLVET.

Evaluation of hemorrhagic shock and fluid resuscitation in pigs using handless Doppler carotid artery ultrasound

OBJECTIVE

This study aimed to utilize a hemorrhagic shock pig model to compare two hemodynamic monitoring methods, pulse index continuous cardiac output (PiCCO) and spectral carotid artery Doppler ultrasound (CDU). Additionally, we sought to explore the feasibility of employing CDU as a non-invasive hemodynamic monitoring tool in the context of hemorrhagic shock and fluid resuscitation.

DESIGN

Animal experiments.

SETTING AND SUBJECTS

Female pigs were selected, and hemorrhagic shock was induced by rapid bleeding through an arterial sheath.

INTERVENTIONS

Hemodynamic monitoring was conducted using both PiCCO and CDU during episodes of hemorrhagic shock and fluid resuscitation.

MEASUREMENTS AND MAIN RESULTS

Among the 10 female pigs studied, CDU measurements revealed a significant decrease in carotid velocity time integral (cVTI) compared to baseline values under shock conditions. During the resuscitation phase, after the mean arterial pressure (MAP) returned to its baseline level, there was no significant difference between cVTI and baseline values. A similar trend was observed for carotid peak velocity (cPV). The corrected flow time (FTc) exhibited a significant difference only at the time of shock compared to baseline values. In comparison to PiCCO, there was a significant correlation between cVTI and MAP (r = 0.616, P < 0.001), stroke volume (SV) (r = 0.821, P < 0.001), and cardiac index (CI) (r = 0.698, P < 0.001). The carotid Doppler shock index (cDSI) displayed negative correlations with MAP (r =  - 0.593, P < 0.001), SV (r =  - 0.761, P < 0.001), and CI (r =  - 0.548, P < 0.001), while showing a positive correlation with the shock index (SI) (r = 0.647, P < 0.001).

CONCLUSIONS

Compared to PiCCO, CDU monitoring can reliably reflect the volume status of hemorrhagic shock and fluid resuscitation. CDU offers the advantages of being non-invasive, providing real-time data, and being operationally straightforward. These characteristics make it a valuable tool for assessing and managing hemorrhagic shock, especially in resource-limited settings.

A new method to evaluate carotid blood flow by continuous Doppler monitoring during cardiopulmonary resuscitation in a porcine model of cardiac arrest

AIM

We used a wearable carotid Doppler patch to study carotid blood flow patterns in a porcine model of cardiac arrest to identify return of spontaneous circulation (ROSC) and hemodynamics associated with different arrhythmias and the quality of compressions.

METHODS

Twenty Landrace pigs were used as models of cardiac arrest following a standard protocol. Carotid blood flow was monitored continuously using noninvasive ultrasound. Carotid spectral waveforms were captured during various arrhythmias and CPR. Typical carotid blood flow waveforms were recorded at the time of ROSC, and hemodynamic changes were compared with carotid blood flow parameters.

RESULTS

The results showed that the carotid blood flow waveforms varied with ventricular arrhythmia type. During CPR, compression depth correlated significantly with carotid maximal velocity (Vmax) (Spearman correlation coefficient (r) = 0.682, P < 0.001) and velocity-time integral (VTI) (r = 0.794, P < 0.001). Vmax and VTI demonstrated moderate predictive value for survival. The regular carotid blood flow pattern towards the brain was observed during ROSC, concurrent with compression waveforms. After ROSC, VTI and carotid pulse volume (cPV) showed similar trends as stroke volume (SV). The carotid minute volume (cMV) exhibited a similar trend as cardiac output (CO).

CONCLUSIONS

Carotid blood flow monitoring could provide valuable information about different arrhythmias as well as the quality of CPR. Carotid flow monitoring allows for timely and effective identification of ROSC. In addition, it may provide valuable hemodynamic information after ROSC.

The Correlation between Carotid Artery Corrected Flow Time and Velocity Time Integral during Central Blood Volume Loss and Resuscitation

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 (R1 cycle = 0.70, R2 cycles = 0.74, and R10 cycles = 0.81).

Conclusions

These results positively support future clinical investigations employing common carotid artery Doppler as a surrogate for central hemodynamics.

Simultaneous venous-arterial Doppler during preload augmentation: illustrating the Doppler Starling curve

Providing intravenous (IV) fluids to a patient with signs or symptoms of hypoperfusion is common. However, evaluating the IV fluid 'dose-response' curve of the heart is elusive. Two patients were studied in the emergency department with a wireless, wearable Doppler ultrasound system. Change in the common carotid arterial and internal jugular Doppler spectrograms were simultaneously obtained as surrogates of left ventricular stroke volume (SV) and central venous pressure (CVP), respectively. Both patients initially had low CVP jugular venous Doppler spectrograms. With preload augmentation, only one patient had arterial Doppler measures indicative of significant SV augmentation (i.e., 'fluid responsive'). The other patient manifested diminishing arterial response, suggesting depressed SV (i.e., 'fluid unresponsive') with evidence of ventricular asynchrony. In this short communication, we describe how a wireless, wearable Doppler ultrasound simultaneously tracks surrogates of cardiac preload and output within a 'Doppler Starling curve' framework; implications for IV fluid dosing are discussed.

A Wireless, Wearable Carotid Doppler Ultrasound Aids Diagnosis and Monitoring of Pericardial Tamponade: A Case Report

Pericardial tamponade can often be diagnosed through clinical findings and echocardiography; however, the diagnosis can be aided by demonstrating the hemodynamic consequences of the effusion. We describe the use of a wearable carotid Doppler device to help diagnose and monitor pericardial tamponade.

CASE SUMMARY

A 54-year-old man developed hypotension after an endobronchial biopsy for a lung mass. Echocardiography showed a pericardial effusion with sonographic evidence of tamponade. A wearable carotid Doppler device demonstrated low corrected carotid flow time (CFT) (a surrogate for stroke volume) with significant respiratory variation, supporting the diagnosis of tamponade. The patient underwent pericardiocentesis which revealed purulent pericardial fluid from a mediastinal abscess. After drainage there was increased CFT and reduced respiratory variability in Doppler, surrogates of improved stroke volume.

CONCLUSION

A wearable carotid Doppler device is a noninvasive tool that can help determine the hemodynamic impact of a pericardial effusion, and potentially aid in the diagnosis of pericardial tamponade.

A Novel Spectral Index for Tracking Preload Change from a Wireless, Wearable Doppler Ultrasound

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/A_POWER) would be a surrogate for the ratio of the vascular areas of these two vessels and (2) the V/A_POWER would track the anticipated CVP change during simulated hemorrhage and resuscitation. To illustrate this proof-of-principle, we compared the change in V/A_POWER 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/A_POWER during simulated hemorrhage and transfusion via lower body negative pressure (LBNP) and release. With these Interesting Images, we show that the Doppler V/A_POWER ratio qualitatively tracks anticipated changes in CVP (e.g., cardiac preload) which is promising for both diagnosis and management of hemodynamic unrest.

The effect of gravity-induced preload change on the venous excess ultrasound (VExUS) score and internal jugular vein Doppler in healthy volunteers

BACKGROUND

The venous excess ultrasound (VExUS) score is a multi-organ Doppler approach to assess venous congestion. Despite growing use of VExUS in research and clinical practice, other veins can be visualized to assess for venous hypertension, which may overcome acquisition barriers of the VExUS exam. In this pilot, observational study, we used a wearable Doppler ultrasound to assess the relationship between jugular venous Doppler and the VExUS score under different preload conditions. We hypothesized that jugular Doppler morphology would accurately distinguish preload conditions, that it would most closely relate to the hepatic venous Doppler morphology in the fully supine position and that the VExUS score would be influenced by preload condition.

RESULTS

We recruited 15 healthy volunteers with no cardiovascular history. Preload change was achieved using a tilt-table with three positions: supine, fully upright, and 30-degree head-down tilt. In each position, a VExUS score was performed; furthermore, inferior vena collapsibility and sphericity index were calculated. At the same time, jugular venous Doppler was captured by a novel, wireless, wearable ultrasound system. A continuous jugular venous Doppler morphology was 96% accurate for detecting the low preload condition. The jugular venous Doppler morphology was highly correlated with the hepatic vein, but only in the supine position. Gravitational position did not significantly affect the sphericity index or the VExUS score.

CONCLUSIONS

The jugular vein Doppler morphology was able to accurately distinguish low from high preload conditions in healthy volunteers. Comparisons between VExUS Doppler morphologies and other veins should occur in the supine position when gravitational pressure gradients are minimized; finally, different preload conditions in healthy subjects did not affect the VExUS score.

Evaluating corrected carotid flow time as a non-invasive parameter for trending cardiac output and stroke volume in cardiac surgery patients

PURPOSE

The corrected carotid flow time (ccFT) is derived from a pulsed-wave Doppler signal at the common carotid artery. Several equations are currently used to calculate ccFT. Its ability to assess the intravascular volume status non-invasively has recently been investigated. The purpose of this study was to evaluate the correlation and trending ability of ccFT with invasive cardiac output (CO) and stroke volume (SV) measurements.

METHODS

Eighteen cardiac surgery patients were included in this prospective observational study. ccFT measurements were obtained at three time points: after induction of anesthesia (T1), after a passive leg raise (T2), and post-bypass (T3). Simultaneously, CO and SV were measured by calibrated pulse contour analysis. Three different equations (Bazett, Chambers, and Wodey) were used to calculate ccFT. The correlation and percentage change in time (concordance) between ccFT and CO and between ccFT and SV were evaluated.

RESULTS

Mean ccFT values differed significantly for the three equations (p < 0.001). The correlation between ccFT and CO and between ccFT and SV was highest for Bazett's (ρ = 0.43, p < 0.0001) and Wodey's (ρ = 0.33, p < 0.0001) equations, respectively. Concordance between ΔccFT and ΔCO and between ΔccFT and ΔSV was highest for Bazett's (100%) and Wodey's (82%) equations, respectively. Subgroup analysis demonstrated that correlation and concordance between SV and ccFT improved when assessed within limited heart rate (HR) ranges.

CONCLUSION

The use of different ccFT equations leads to variable correlation and concordance rates between ccFT and CO/SV measurements. Bazett's equation acceptably tracked CO changes in time, while the trending capability of SV was poor.

Carotid Doppler ultrasound for non-invasive haemodynamic monitoring: a narrative review

Objective.Accurate haemodynamic monitoring is the cornerstone in the management of critically ill patients. It guides the optimization of tissue and organ perfusion in order to prevent multiple organ failure. In the past decades, carotid Doppler ultrasound (CDU) has been explored as a non-invasive alternative for long-established invasive haemodynamic monitoring techniques. Considering the large heterogeneity in reported studies, we conducted a review of the literature to clarify the current status of CDU as a haemodynamic monitoring tool.Approach.In this article, firstly an overview is given of the equipment and workflow required to perform a CDU exam in clinical practice, the limitations and technical challenges potentially faced by the CDU sonographer, and the cerebrovascular mechanisms that may influence CDU measurement outcomes. The following chapter describes alternative techniques for non-invasive haemodynamic monitoring, detailing advantages and limitations compared to CDU. Next, a comprehensive review of the literature regarding the use of CDU for haemodynamic monitoring is presented. Furthermore, feasibility aspects, training requirements and technical developments of CDU are addressed.Main results.Based on the outcomes of these studies, we assess the applicability of CDU-derived parameters within three clinical domains (cardiac output, volume status, and fluid responsiveness), and amongst different patient groups. Finally, recommendations are provided to improve the quality and standardization of future research and clinical practice in this field.Significance.Although CDU is not yet interchangeable with invasive 'gold standard' cardiac output monitoring, the present work shows that certain CDU-derived parameters prove promising in the context of functional haemodynamic monitoring.

The time cost of physiologically ineffective intravenous fluids in the emergency department: an observational pilot study employing wearable Doppler ultrasound

BACKGROUND

Little data exist on the time spent by emergency department (ED) personnel providing intravenous (IV) fluid to 'responsive' versus 'unresponsive' patients.

METHODS

A prospective, convenience sample of adult ED patients was studied; patients were enrolled if preload expansion was indicated for any reason. Using a novel, wireless, wearable ultrasound, carotid artery Doppler was obtained before and throughout a preload challenge (PC) prior to each bag of ordered IV fluid. The treating clinician was blinded to the results of the ultrasound. IV fluid was deemed 'effective' or 'ineffective' based on the greatest change in carotid artery corrected flow time (ccFT_∆) during the PC. The duration, in minutes, of each bag of IV fluid administered was recorded.

RESULTS

53 patients were recruited and 2 excluded for Doppler artifact. There were 86 total PCs included in the investigation comprising 81.7 L of administered IV fluid. 19,667 carotid Doppler cardiac cycles were analyzed. Using ccFT_∆ ≥  + 7 ms to discriminate 'physiologically effective' from 'ineffective' IV fluid, we observed that 54 PCs (63%) were 'effective', comprising 51.7 L of IV fluid, whereas, 32 (37%) were 'ineffective' comprising 30 L of IV fluid. 29.75 total hours across all 51 patients were spent in the ED providing IV fluids categorized as 'ineffective.'

CONCLUSIONS

We report the largest-known carotid artery Doppler analysis (i.e., roughly 20,000 cardiac cycles) in ED patients requiring IV fluid expansion. A clinically significant amount of time was spent providing physiologically ineffective IV fluid. This may represent an avenue to improve ED care efficiency.

Inferring the Frank-Starling Curve From Simultaneous Venous and Arterial Doppler: Measurements From a Wireless, Wearable Ultrasound Patch

The Frank–Starling relationship is a fundamental concept in cardiovascular physiology, relating change in cardiac filling to its output. Historically, this relationship has been measured by physiologists and clinicians using invasive monitoring tools, relating right atrial pressure (P_ra) to stroke volume (SV) because the P_ra-SV slope has therapeutic implications. For example, a critically ill patient with a flattened P_ra-SV slope may have low P_ra yet fail to increase SV following additional cardiac filling (e.g., intravenous fluids). Provocative maneuvers such as the passive leg raise (PLR) have been proposed to identify these “fluid non-responders”; however, simultaneously measuring cardiac filling and output via non-invasive methods like ultrasound is cumbersome during a PLR. In this Hypothesis and Theory submission, we suggest that a wearable Doppler ultrasound can infer the P_ra-SV relationship by simultaneously capturing jugular venous and carotid arterial Doppler in real time. We propose that this method would confirm that low cardiac filling may associate with poor response to additional volume. Additionally, simultaneous assessment of venous filling and arterial output could help interpret and compare provocative maneuvers like the PLR because change in cardiac filling can be confirmed. If our hypothesis is confirmed with future investigation, wearable monitors capable of monitoring both variables of the Frank–Starling relation could be helpful in the ICU and other less acute patient settings.

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

Objective

Doppler ultrasonography of the common carotid artery is used to infer stroke volume change and a wearable Doppler ultrasound has been designed to improve this workflow. Previously, in a human model of hemorrhage and resuscitation comprising approximately 50,000 cardiac cycles, we found a strong, linear correlation between changing stroke volume, and measures from the carotid Doppler signal, however, optimal Doppler thresholds for detecting a 10% stroke volume change were not reported. In this Research Note, we present these thresholds, their sensitivities, specificities and areas under their receiver operator curves (AUROC).

Results

Augmentation of carotid artery maximum velocity time integral and corrected flowtime by 18% and 4%, respectively, accurately captured 10% stroke volume rise. The sensitivity and specificity for these thresholds were identical at 89% and 100%. These data are similar to previous investigations in healthy volunteers monitored by the wearable ultrasound.

A wireless optoelectronic skin patch for light delivery and thermal monitoring

Wearable optoelectronic devices can interface with the skin for applications in continuous health monitoring and light-based therapy. Measurement of the thermal effect of light on skin is often critical to track physiological parameters and control light delivery. However, accurate measurement of light-induced thermal effects is challenging because conventional sensors cannot be placed on the skin without obstructing light delivery. Here, we report a wearable optoelectronic patch integrated with a transparent nanowire sensor that provides light delivery and thermal monitoring at the same location. We achieve fabrication of a transparent silver nanowire network with >92% optical transmission that provides thermoresistive sensing of skin temperature. By integrating the sensor in a wireless optoelectronic patch, we demonstrate closed-loop regulation of light delivery as well as thermal characterization of blood flow. This light delivery and thermal monitoring approach may open opportunities for wearable devices in light-based diagnostics and therapies.

The Doppler shock index measured by a wearable ultrasound patch accurately detects moderate-to-severe central hypovolemia during lower body negative pressure

OBJECTIVE

Moderate-to-severe hemorrhage is a life-threatening condition, which is challenging to detect in a timely fashion using traditional vital signs because of the human body's robust physiologic compensatory mechanisms. Measuring and trending blood flow could improve diagnosis of clinically significant exsanguination. A lightweight, wireless, wearable Doppler ultrasound patch that captures and trends blood flow velocity could enhance hemorrhage detection.

METHODS

In 11 healthy volunteers undergoing simulated hemorrhage and resuscitation during graded lower body negative pressure (LBNP) and release, we studied the relationship between stroke volume (SV) and common carotid artery velocity time integral (VTI) and corrected flow time (FTc). We assessed the diagnostic accuracy of 2 variations of a novel metric, the Doppler shock index (ie, the DSIVTI and DSIFTc), at capturing moderate-to-severe central hypovolemia defined as a 30% reduction in SV. The DSIVTI and DSIFTc are calculated as the heart rate divided by either the VTI or FTc, respectively.

RESULTS

A total of 17,822 cardiac cycles were analyzed across 22 LBNP protocols. The average SV reduction to the lowest tolerated LBNP stage was 40%; there was no clinically significant fall in the mean arterial pressure. Correlations between changing SV and the common carotid artery VTI and FTc were strong (R 2 of 0.87, respectively) and concordant. The DSIVTI and DSIFTc accurately detected moderate-to-severe central hypovolemia with values for the area under the receiver operator curves of 0.96 and 0.97, respectively.

CONCLUSION

In a human model of hemorrhage and resuscitation, measures from a wearable Doppler ultrasound patch correlated strongly with SV and identified moderate-to-severe central hypovolemia with excellent diagnostic accuracy.

Ability of Carotid Corrected Flow Time to Predict Fluid Responsiveness in Patients Mechanically Ventilated Using Low Tidal Volume after Surgery

Predicting fluid responsiveness in patients under mechanical ventilation with low tidal volume (VT) is challenging. This study evaluated the ability of carotid corrected flow time (FTc) assessed by ultrasound for predicting the fluid responsiveness during low VT ventilation. Patients under postoperative mechanical ventilation and clinically diagnosed with hypovolemia were enrolled. Carotid FTc and pulse pressure variation (PPV) were measured at VT of 6 and 10 mL/kg predicted body weight (PBW). FTc was calculated using both Bazett’s (FTcB) and Wodey’s (FTcW) formulas. Fluid responsiveness was defined as a ≥15% increase in the stroke volume index assessed by FloTrac/Vigileo monitor after administration of 8 mL/kg of balanced crystalloid. Among 36 patients, 16 (44.4%) were fluid responders. The areas under the receiver operating characteristic curves (AUROCs) for the FTcB at VT of 6 and 10 mL/kg PBW were 0.897 (95% confidence interval [95% CI]: 0.750–0.973) and 0.895 (95% CI: 0.748–0.972), respectively. The AUROCs for the FTcW at VT of 6 and 10 mL/kg PBW were 0.875 (95% CI: 0.722–0.961) and 0.891 (95% CI: 0.744–0.970), respectively. However, PPV at VT of 6 mL/kg PBW (AUROC: 0.714, 95% CI: 0.539–0.852) showed significantly lower accuracy than that of PPV at VT of 10 mL/kg PBW (AUROC: 0.867, 95% CI: 0.712–0.957; p = 0.034). Carotid FTc can predict fluid responsiveness better than PPV during low VT ventilation. However, further studies using automated continuous monitoring system are needed before its clinical use.

Carotid Doppler Measurement Variability in Functional Hemodynamic Monitoring: An Analysis of 17,822 Cardiac Cycles

Carotid Doppler ultrasound is used as a measure of fluid responsiveness, however, assessing change with statistical confidence requires an adequate beat sample size. The coefficient of variation helps quantify the number of cardiac cycles needed to adequately detect change during functional hemodynamic monitoring.

DESIGN

Prospective, observational, human model of hemorrhage and resuscitation.

SETTING

Human physiology laboratory at Mayo Clinic.

SUBJECTS

Healthy volunteers.

INTERVENTIONS

Lower body negative pressure.

MEASUREMENTS AND MAIN RESULTS

We measured the coefficient of variation of the carotid artery velocity time integral and corrected flow time during significant cardiac preload changes. Seventeen-thousand eight-hundred twenty-two cardiac cycles were analyzed. The median coefficient of variation of the carotid velocity time integral was 8.7% at baseline and 11.9% during lowest-tolerated lower body negative pressure stage. These values were 3.6% and 4.6%, respectively, for the corrected flow time.

CONCLUSIONS

The median coefficient of variation values measured in this large dataset indicates that at least 6 cardiac cycles should be averaged before and after an intervention when using the carotid artery as a functional hemodynamic measure.

A novel, hands-free ultrasound patch for continuous monitoring of quantitative Doppler in the carotid artery

Quantitative Doppler ultrasound of the carotid artery has been proposed as an instantaneous surrogate for monitoring rapid changes in left ventricular output. Tracking immediate changes in the arterial Doppler spectrogram has value in acute care settings such as the emergency department, operating room and critical care units. We report a novel, hands-free, continuous-wave Doppler ultrasound patch that adheres to the neck and tracks Doppler blood flow metrics in the common carotid artery using an automated algorithm. String and blood-mimicking test objects demonstrated that changes in velocity were accurately measured using both manually and automatically traced Doppler velocity waveforms. In a small usability study with 22 volunteer users (17 clinical, 5 lay), all users were able to locate the carotid Doppler signal on a volunteer subject, and, in a subsequent survey, agreed that the device was easy to use. To illustrate potential clinical applications of the device, the Doppler ultrasound patch was used on a healthy volunteer undergoing a passive leg raise (PLR) as well as on a congestive heart failure patient at resting baseline. The wearable carotid Doppler patch holds promise because of its ease-of-use, velocity measurement accuracy, and ability to continuously record Doppler spectrograms over many cardiac and respiratory cycles.

Functional Hemodynamic Monitoring With a Wireless Ultrasound Patch

In this Emerging Technology Review, a novel, wireless, wearable Doppler ultrasound patch is described as a tool for resuscitation. The device is designed, foremost, as a functional hemodynamic monitor-a simple, fast, and consistent method for measuring hemodynamic change with preload variation. More generally, functional hemodynamic monitoring is a paradigm that helps predict stroke volume response to additional intravenous volume. Because Doppler ultrasound of the left ventricular outflow tract noninvasively measures stroke volume in realtime, it increasingly is deployed for this purpose. Nevertheless, Doppler ultrasound in this manner is cumbersome, especially when repeat assessments are needed. Accordingly, peripheral arteries have been studied and various measures from the common carotid artery Doppler signal act as windows to the left ventricle. Yet, handheld Doppler ultrasound of a peripheral artery is susceptible to human measurement error and statistical limitations from inadequate beat sample size. Therefore, a wearable Doppler ultrasound capable of continuous assessment minimizes measurement inconsistencies and smooths inherent physiologic variation by sampling many more cardiac cycles. Reaffirming clinical studies, the ultrasound patch tracks immediate SV change with excellent accuracy in healthy volunteers when cardiac preload is altered by various maneuvers. The wearable ultrasound also follows jugular venous Doppler, which qualitatively trends right atrial pressure. With further clinical research and the application of artificial intelligence, the monitoring modalities with this new technology are manifold.