Arterial waveform analysis

Ophthalmic artery Doppler in women with hypertensive disorders of pregnancy: relationship to blood pressure control and renal dysfunction at 6-9 weeks postnatally

OBJECTIVES

To examine the postnatal course of ophthalmic artery (OA) Doppler in women with hypertensive disorders of pregnancy (HDP) and to evaluate the correlation between OA Doppler parameters and poor postnatal blood pressure control and renal dysfunction at 2-3 weeks and 6-9 weeks postnatally.

METHODS

This was a prospective cohort study of women with a singleton pregnancy and HDP seen at a tertiary pregnancy hypertension clinic between 2019 and 2021. Three visits were included: Visit 1, the last visit to the antenatal hypertension clinic within 2 weeks prior to delivery; Visit 2, at 2-3 weeks postnatally; and Visit 3, at 6-9 weeks postnatally. At each visit, maternal demographic characteristics, medical history, blood pressure and OA Doppler were obtained. In addition, fetal growth and fetal Dopplers were examined antenatally and, at 6-9 weeks postnatally, estimated glomerular filtration rate and proteinuria were quantified. Study participants were divided into four hypertension groups, according to longitudinal changes in blood pressure at the three visits. For the postnatal visits, hypertension was defined as systolic blood pressure (SBP) ≥ 140 mmHg and/or diastolic blood pressure (DBP) ≥ 90 mmHg in the absence of antihypertensive medication, and SBP ≥ 130 mmHg and/or DBP ≥ 80 mmHg whilst taking antihypertensives. Group 1 was hypertensive at all three visits; Group 2 was hypertensive at Visits 1 and 2 but normotensive at Visit 3; Group 3 was hypertensive at Visits 1 and 3 but normotensive at Visit 2; and Group 4 was hypertensive at Visit 1 but normotensive at Visits 2 and 3. The longitudinal changes in mean arterial pressure (MAP), peak systolic velocity (PSV) 1, PSV2 and the ratio of PSV2/PSV1 over the three timepoints were examined by a repeated-measures, multilevel, linear mixed-effects analysis, controlling for maternal age, weight at presentation and use of antihypertensive medication. In addition, we examined the longitudinal change in OA Doppler parameters in women with different degrees of postnatal blood pressure control and in those with and those without renal dysfunction at 6-9 weeks postnatally.

RESULTS

A total of 108 women were recruited to the study, of whom 86 had new-onset hypertension and 22 had chronic hypertension. When controlling for maternal age, weight at presentation and use of antihypertensive medication, a significant decline in log10 MAP (P < 0.001), log10 PSV1 (P < 0.001) and log10 PSV2 (P = 0.01) was seen between Visits 1 and 3. Log10 PSVR did not change with time. When assessing OA Doppler against hypertension group, log10 PSV1 and log10 PSV2 did not differ between the hypertension groups, whilst Group 4 had a lower log10 PSVR compared with Group 1 (P < 0.01), Group 2 (P = 0.03) and Group 3 (P < 0.01). At 6-9 weeks postnatally, log10 PSVR was lower in those without compared to those with renal dysfunction (-0.021, P = 0.01), whilst log10 MAP, log10 PSV1 and log10 PSV2 values did not differ. Log10 PSVR did not change with time and remained at -0.12 (95% CI, -0.13 to -0.11) across the three visits.

CONCLUSIONS

In women with HDP, the OA-PSVR was significantly higher in those with labile or persistently raised blood pressure postnatally compared to women whose blood pressure normalized. Similarly, the OA-PSVR at 6-9 weeks postnatally was significantly higher in women with renal dysfunction vs those without dysfunction. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

Comparison of Central and Peripheral Arterial Blood Pressure Gradients in Critically Ill Patients: A Systematic Review and Meta-Analysis

OBJECTIVES

Measurement of blood pressure taken from different anatomical sites, are often perceived as interchangeable, despite them representing different parts of the systemic circulation. We aimed to perform a systematic review and meta-analysis on blood pressure differences between central and peripheral arterial cannulation in critically ill patients.

DATA SOURCES

We searched MEDLINE, Cochrane Central Register of Controlled Trials, and Embase from inception to December 26, 2023, using Medical Subject Headings (MeSH) terms and keywords.

STUDY SELECTION

Observation study of adult patients in ICUs and operating rooms who underwent simultaneous central (femoral, axillary, or subclavian artery) and peripheral (radial, brachial, or dorsalis pedis artery) arterial catheter placement in ICUs and operating rooms.

DATA EXTRACTION

We screened and extracted studies independently and in duplicate. We assessed risk of bias using the revised Quality Assessment for Studies of Diagnostic Accuracy tool.

DATA SYNTHESIS

Twenty-four studies that enrolled 1598 patients in total were included. Central pressures (mean arterial pressure [MAP] and systolic blood pressure [SBP]) were found to be significantly higher than their peripheral counterparts, with mean gradients of 3.5 and 8.0 mm Hg, respectively. However, there was no statistically significant difference in central or peripheral diastolic blood pressure (DBP). Subgroup analysis further highlighted a higher MAP gradient during the on-cardiopulmonary bypass stage of cardiac surgery, reperfusion stage of liver transplant, and in nonsurgical critically ill patients. SBP or DBP gradient did not demonstrate any subgroup specific changes.

CONCLUSIONS

SBP and MAP obtained by central arterial cannulation were higher than peripheral arterial cannulation; however, clinical implication of a difference of 8.0 mm Hg in SBP and 3.5 mm Hg in MAP remains unclear. Our current clinical practices preferring peripheral arterial lines need not change.

Use of an Artificial Intelligence Device for Evaluating Blood Loss in Complex Major Orthopaedic Surgery Procedures

BACKGROUND

An artificial intelligence algorithm that analyzes the pulse oximeter waveform in the fingertip can be used to determine the compensatory reserve index (CRI) in trauma patients. This measurement shows the remaining cardiovascular capacity and is known to be more specific and sensitive in detecting blood loss than are routine vital signs. We hypothesized that the CRI measurement could predict loss of reserve cardiovascular capacity in patients undergoing major orthopaedic surgery, and therefore could help in their management.

METHODS

A total of 304 patients undergoing lower extremity arthroplasty consented to participate in waveform monitoring. Pulse oximeter waveforms were sensed with a fingertip probe and processed with a tablet computer that remained with the patient during surgery and recovery in the hospital. The CRI, systolic blood pressure, and heart rate were evaluated throughout the postoperative period.

RESULTS

The CRI measurement identified a group of patients who were significantly more likely to require transfusions and emergency medical care (P = .000021). Patients who had morbid obesity were especially likely to have low CRI results and a high percentage of clinical events. A CRI of 0.40 or more was evaluated retrospectively as the criterion for withholding transfusion in 54 patients, but that group had a significantly higher incidence of transfusion later in treatment than did the cohort as a whole. The systolic blood pressure and heart rate were not useful in predicting the need for transfusion until late in treatment.

CONCLUSIONS

This study suggests that the CRI measurement can identify patients at risk for transfusion and the need for urgent medical care and may aid in the management of blood loss and transfusion in major orthopedic surgery.

The association of arterial blood pressure waveform-derived area duty cycle with intra-arrest hemodynamics and cardiac arrest outcomes

AIM

Develop a novel, physiology-based measurement of duty cycle (Arterial Blood Pressure-Area Duty Cycle [ABP-ADC]) and evaluate the association of ABP-ADC with intra-arrest hemodynamics and patient outcomes.

METHODS

This was a secondary retrospective study of prospectively collected data from the ICU-RESUS trial (NCT02837497). Invasive arterial waveform data were used to derive ABP-ADC. The primary exposure was ABP-ADC group (<30%; 30-35%; >35%). The primary outcome was systolic blood pressure (sBP). Secondary outcomes included intra-arrest physiologic goals, CPR quality targets, and patient outcomes. In an exploratory analysis, adjusted splines and receiver operating characteristic (ROC) curves were used to determine an optimal ABP-ADC associated with improved hemodynamics and outcomes using a multivariable model.

RESULTS

Of 1129 CPR events, 273 had evaluable arterial waveform data. Mean age is 2.9 years + 4.9 months. Mean ABP-ADC was 32.5% + 5.0%. In univariable analysis, higher ABP-ADC was associated with lower sBP (p < 0.01) and failing to achieve sBP targets (p < 0.01). Other intra-arrest physiologic parameters, quality metrics, and patient outcomes were similar across ABP-ADC groups. Using spline/ROC analysis and clinical judgement, the optimal ABP-ADC cut point was set at 33%. On multivariable analysis, sBP was significantly higher (point estimate 13.18 mmHg, CI95 5.30-21.07, p < 0.01) among patients with ABP-ADC < 33%. Other intra-arrest physiologic and patient outcomes were similar.

CONCLUSIONS

In this multicenter cohort, a lower ABP-ADC was associated with higher sBPs during CPR. Although ABP-ADC was not associated with outcomes, further studies are needed to define the interactions between CPR mechanics and intra arrest patient physiology.

Estimation of Physiologic Pressures: Invasive and Non-Invasive Techniques, AI Models, and Future Perspectives

The measurement of physiologic pressure helps diagnose and prevent associated health complications. From typical conventional methods to more complicated modalities, such as the estimation of intracranial pressures, numerous invasive and noninvasive tools that provide us with insight into daily physiology and aid in understanding pathology are within our grasp. Currently, our standards for estimating vital pressures, including continuous BP measurements, pulmonary capillary wedge pressures, and hepatic portal gradients, involve the use of invasive modalities. As an emerging field in medical technology, artificial intelligence (AI) has been incorporated into analyzing and predicting patterns of physiologic pressures. AI has been used to construct models that have clinical applicability both in hospital settings and at-home settings for ease of use for patients. Studies applying AI to each of these compartmental pressures were searched and shortlisted for thorough assessment and review. There are several AI-based innovations in noninvasive blood pressure estimation based on imaging, auscultation, oscillometry and wearable technology employing biosignals. The purpose of this review is to provide an in-depth assessment of the involved physiologies, prevailing methodologies and emerging technologies incorporating AI in clinical practice for each type of compartmental pressure measurement. We also bring to the forefront AI-based noninvasive estimation techniques for physiologic pressure based on microwave systems that have promising potential for clinical practice.

Emerging sensing and modeling technologies for wearable and cuffless blood pressure monitoring

Cardiovascular diseases (CVDs) are a leading cause of death worldwide. For early diagnosis, intervention and management of CVDs, it is highly desirable to frequently monitor blood pressure (BP), a vital sign closely related to CVDs, during people's daily life, including sleep time. Towards this end, wearable and cuffless BP extraction methods have been extensively researched in recent years as part of the mobile healthcare initiative. This review focuses on the enabling technologies for wearable and cuffless BP monitoring platforms, covering both the emerging flexible sensor designs and BP extraction algorithms. Based on the signal type, the sensing devices are classified into electrical, optical, and mechanical sensors, and the state-of-the-art material choices, fabrication methods, and performances of each type of sensor are briefly reviewed. In the model part of the review, contemporary algorithmic BP estimation methods for beat-to-beat BP measurements and continuous BP waveform extraction are introduced. Mainstream approaches, such as pulse transit time-based analytical models and machine learning methods, are compared in terms of their input modalities, features, implementation algorithms, and performances. The review sheds light on the interdisciplinary research opportunities to combine the latest innovations in the sensor and signal processing research fields to achieve a new generation of cuffless BP measurement devices with improved wearability, reliability, and accuracy.

Machine learning predicts blood lactate levels in children after cardiac surgery in paediatric ICU

BACKGROUND

Although serum lactate levels are widely accepted markers of haemodynamic instability, an alternative method to evaluate haemodynamic stability/instability continuously and non-invasively may assist in improving the standard of patient care. We hypothesise that blood lactate in paediatric ICU patients can be predicted using machine learning applied to arterial waveforms and perioperative characteristics.

METHODS

Forty-eight post-operative children, median age 4 months (2.9-11.8 interquartile range), mean baseline heart rate of 131 beats per minute (range 33-197), mean lactate level at admission of 22.3 mg/dL (range 6.3-71.1), were included. Morphological arterial waveform characteristics were acquired and analysed. Predicting lactate levels was accomplished using regression-based supervised learning algorithms, evaluated with hold-out cross-validation, including, basing prediction on the currently acquired physiological measurements along with those acquired at admission, as well as adding the most recent lactate measurement and the time since that measurement as prediction parameters. Algorithms were assessed with mean absolute error, the average of the absolute differences between actual and predicted lactate concentrations. Low values represent superior model performance.

RESULTS

The best performing algorithm was the tuned random forest, which yielded a mean absolute error of 3.38 mg/dL when predicting blood lactate with updated ground truth from the most recent blood draw.

CONCLUSIONS

The random forest is capable of predicting serum lactate levels by analysing perioperative variables, including the arterial pressure waveform. Thus, machine learning can predict patient blood lactate levels, a proxy for haemodynamic instability, non-invasively, continuously and with accuracy that may demonstrate clinical utility.

Critical Information from High Fidelity Arterial and Venous Pressure Waveforms During Anesthesia and Hemorrhage

PURPOSE

Peripheral venous pressure (PVP) waveform analysis is a novel, minimally invasive, and inexpensive method of measuring intravascular volume changes. A porcine cohort was studied to determine how venous and arterial pressure waveforms change due to inhaled and infused anesthetics and acute hemorrhage.

METHODS

Venous and arterial pressure waveforms were continuously collected, while each pig was under general anesthesia, by inserting Millar catheters into a neighboring peripheral artery and vein. The anesthetic was varied from inhaled to infused, then the pig underwent a controlled hemorrhage. Pearson correlation coefficients between the power of the venous and arterial pressure waveforms at each pig's heart rate frequency were calculated for each variation in the anesthetic, as well as before and after hemorrhage. An analysis of variance (ANOVA) test was computed to determine the significance in changes of the venous pressure waveform means caused by each variation.

RESULTS

The Pearson correlation coefficients between venous and arterial waveforms decreased as anesthetic dosage increased. In an opposing fashion, the correlation coefficients increased as hemorrhage occurred.

CONCLUSION

Anesthetics and hemorrhage alter venous pressure waveforms in distinctly different ways, making it critical for researchers and clinicians to consider these confounding variables when utilizing pressure waveforms. Further work needs to be done to determine how best to integrate PVP waveforms into clinical decision-making.

Timing errors and temporal uncertainty in clinical databases-A narrative review

A firm concept of time is essential for establishing causality in a clinical setting. Review of critical incidents and generation of study hypotheses require a robust understanding of the sequence of events but conducting such work can be problematic when timestamps are recorded by independent and unsynchronized clocks. Most clinical models implicitly assume that timestamps have been measured accurately and precisely, but this custom will need to be re-evaluated if our algorithms and models are to make meaningful use of higher frequency physiological data sources. In this narrative review we explore factors that can result in timestamps being erroneously recorded in a clinical setting, with particular focus on systems that may be present in a critical care unit. We discuss how clocks, medical devices, data storage systems, algorithmic effects, human factors, and other external systems may affect the accuracy and precision of recorded timestamps. The concept of temporal uncertainty is introduced, and a holistic approach to timing accuracy, precision, and uncertainty is proposed. This quantitative approach to modeling temporal uncertainty provides a basis to achieve enhanced model generalizability and improved analytical outcomes.

Waveform Morphology Comparison in Wearable Blood Pressure Sensors

Wearable devices for continuous non-invasive blood pressure monitoring must be capable of providing a continuous waveform representative of arterial blood pressure. This paper establishes the distinctions in waveform morphology between wearable sensor modalities, specifically millimeter-wave radar and photoplethysmography, when compared to a reference continuous non-invasive blood pressure monitor. An analysis of a 115-subject dataset was conducted to assess waveform suitability. Millimeter-wave radar waveform morphology was found to more closely resemble continuous non-invasive blood pressure than photoplethysmography. Clinical Relevance- This paper compares the waveform morphology and content of signals from wearable sensors in the context of continuous non-invasive blood pressure monitoring.

A Review of Noninvasive Methodologies to Estimate the Blood Pressure Waveform

Accurate estimation of blood pressure (BP) waveforms is critical for ensuring the safety and proper care of patients in intensive care units (ICUs) and for intraoperative hemodynamic monitoring. Normal cuff-based BP measurements can only provide systolic blood pressure (SBP) and diastolic blood pressure (DBP). Alternatively, the BP waveform can be used to estimate a variety of other physiological parameters and provides additional information about the patient's health. As a result, various techniques are being proposed for accurately estimating the BP waveforms. The purpose of this review is to summarize the current state of knowledge regarding the BP waveform, three methodologies (pressure-based, ultrasound-based, and deep-learning-based) used in noninvasive BP waveform estimation research and the feasibility of employing these strategies at home as well as in ICUs. Additionally, this article will discuss the physical concepts underlying both invasive and noninvasive BP waveform measurements. We will review historical BP waveform measurements, standard clinical procedures, and more recent innovations in noninvasive BP waveform monitoring. Although the technique has not been validated, it is expected that precise, noninvasive BP waveform estimation will be available in the near future due to its enormous potential.

Distinct morphologies of arterial waveforms reveal preload-, contractility-, and afterload-deficient hemodynamic instability: An in silico simulation study

Hemodynamic instability is frequently present in critically ill patients, primarily caused by a decreased preload, contractility, and/or afterload. We hypothesized that peripheral arterial blood pressure waveforms allow to differentiate between these underlying causes. In this in-silico experimental study, a computational cardiovascular model was used to simulate hemodynamic instability by decreasing blood volume, left ventricular contractility or systemic vascular resistance, and additionally adaptive and compensatory mechanisms. From the arterial pressure waveforms, 45 features describing the morphology were discerned and a sensitivity analysis and principal component analysis were performed, to quantitatively investigate their discriminative power. During hemodynamic instability, the arterial waveform morphology changed distinctively, for example, the slope of the systolic upstroke having a sensitivity of 2.02 for reduced preload, 0.80 for reduced contractility, and -0.02 for reduced afterload. It was possible to differentiate between the three underlying causes based on the derived features, as demonstrated by the first two principal components explaining 99% of the variance in waveforms. The features with a high correlation coefficient (>0.25) to these principal components are describing the systolic up- and downstroke, and the anacrotic and dicrotic notches of the waveforms. In this study, characteristic peripheral arterial waveform morphologies were identified that allow differentiation between deficits in preload, contractility, and afterload causing hemodynamic instability. These findings are confined to an in silico simulation and warrant further experimental and clinical research in order to prove clinical usability in daily practice.

Changes in ophthalmic artery Doppler during acute blood-pressure control in hypertensive pregnant women

OBJECTIVE

To examine the changes in ophthalmic artery Doppler indices and their association with changes in mean arterial blood pressure (MAP) and systolic (SBP) and diastolic (DBP) blood pressure, following acute antihypertensive treatment in women with hypertensive disorders of pregnancy presenting with high blood pressure.

METHODS

This was a prospective cohort study of 31 pregnant women presenting at 30 + 0 to 39 + 6 weeks' gestation for management of their hypertension. Paired maternal blood-pressure and ophthalmic-artery-Doppler measurements were performed prior to and at 30 min and 60 min after starting antihypertensive medication. In patients who did not achieve blood-pressure control (i.e. when blood pressure was < 140/90 mmHg) by 60 min, paired readings were continued up to 120 min. If blood-pressure control was still not achieved at that point, patients were admitted to hospital. Univariate linear regression was performed to determine the association of ophthalmic artery peak systolic velocity (PSV) ratio with SBP, DBP and MAP before treatment and after blood-pressure control. The longitudinal changes in MAP, SBP, DBP and PSV ratio from pretreatment to 30 min and 60 min after commencement of antihypertensives were examined by repeated measure, multilevel, linear mixed-effects analysis.

RESULTS

Antihypertensive treatment was associated with a decrease in SBP, DBP, MAP and PSV ratio. At 60 min following antihypertensive treatment, the decrease in SBP, DBP, MAP and PSV ratio was 12.1 mmHg (95% CI, 9.0-15.1 mmHg; P < 0.0001), 9.1 mmHg (95% CI, 6.5-11.5 mmHg; P < 0.0001), 10.0 mmHg (95% CI, 7.6-12.4 mmHg; P < 0.0001) and 0.07 (95% CI, 0.03-0.11 mmHg; P < 0.001), respectively. From the total cohort, 20 (64.5%) women had achieved blood-pressure control at 60 min and another seven (22.6%) by 120 min from commencement of antihypertensive treatment. Four (12.9%) women did not achieve blood-pressure control during this period and were admitted to hospital. The relationship between PSV ratio and SBP, DBP and MAP was assessed before treatment (n = 31) and at the point of blood-pressure control in women in whom this was achieved by 120 min (n = 27). Prior to treatment, there was a significant association between PSV ratio and MAP (P < 0.0001, R²  = 0.39). This was primarily due to the association of PSV ratio with DBP (P < 0.0001, R²  = 0.39) and less so due to its association with SBP (P = 0.02, R²  = 0.16). At the point of achieving blood-pressure control, there was no significant association between PSV ratio and MAP (P = 0.7), DBP (P = 0.5) or SBP (P = 0.7).

CONCLUSIONS

Acute blood-pressure control in pregnancy is associated with a concomitant reduction in blood pressure and ophthalmic artery PSV ratio. In hypertensive pregnant women, there is a significant association of PSV ratio with MAP, SBP and DBP, which disappears after blood pressure is reduced to < 140/90 mmHg following antihypertensive treatment. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Ophthalmic artery peak systolic velocity ratio distinguishes preeclampsia from chronic and gestational hypertension: A prospective cohort study

OBJECTIVE

To examine whether the ophthalmic artery peak systolic velocity ratio (OA PSV-ratio) is higher in women with preeclampsia (PE), compared to gestational hypertension (GH) and chronic hypertension (CH), after controlling for confounding variables.

DESIGN

Prospective cohort.

SETTING

Specialist hypertension clinic in a tertiary referral centre.

POPULATION

Singleton pregnancies presenting between 32+0 to 36+6 weeks' gestation with PE (n=50), GH (n=54) and CH (n=56).

METHODS

Paired measurements of maternal mean arterial pressure (MAP) and OA PSV-ratio were performed by trained sonographers. Multiple linear regression was fitted to the OA PSV-ratio, including maternal characteristics and medical history, GH, PE and MAP and use of antihypertensive medication.

MAIN OUTCOME MEASURE

Whether PE is independently associated with higher OA PSV-ratio.

RESULTS

MAP was significantly higher in both GH (p=0.0015) and PE (p=0.008) than in CH pregnancies. There was no significant difference between PE and GH (0.670). The OA PSV-ratio was significantly higher in PE than CH (p=0.0008) and GH (p=0.015). There was no significant difference between the OA PSV-ratio in CH and GH (p=0.352). Multiple linear regression modelling showed that the OA PSV-ratio was influenced by maternal weight (p=0.005), maternal age (p=0.014), antihypertensive medications (p=0.007) and MAP (p<0.0001). After controlling for these variables, the OA PSV-ratio was still significantly higher in those with PE (p=0.0002).

CONCLUSIONS

The OA PSV-ratio is influenced by maternal weight, age, antihypertensive medications and MAP. PE is an independent predictor of OA PSV-ratio, which therefore may be a useful point-of-care test when assessing women presenting with hypertension.

Non-Invasive Assessment of Damping of Blood Flow Velocity Pulsatility in Cerebral Arteries With MRI

Background

Damping of heartbeat‐induced pressure pulsations occurs in large arteries such as the aorta and extends to the small arteries and microcirculation. Since recently, 7 T MRI enables investigation of damping in the small cerebral arteries.

Purpose

To investigate flow pulsatility damping between the first segment of the middle cerebral artery (M1) and the small perforating arteries using magnetic resonance imaging.

Study Type

Retrospective.

Subjects

Thirty‐eight participants (45% female) aged above 50 without history of heart failure, carotid occlusive disease, or cognitive impairment.

Field Strength/Sequence

3 T gradient echo (GE) T1‐weighted images, spin‐echo fluid‐attenuated inversion recovery images, GE two‐dimensional (2D) phase‐contrast, and GE cine steady‐state free precession images were acquired. At 7 T, T1‐weighted images, GE quantitative‐flow, and GE 2D phase‐contrast images were acquired.

Assessment

Velocity pulsatilities of the M1 and perforating arteries in the basal ganglia (BG) and semi‐oval center (CSO) were measured. We used the damping index between the M1 and perforating arteries as a damping indicator (velocity pulsatility_M1/velocity pulsatility_CSO/BG). Left ventricular stroke volume (LVSV), mean arterial pressure (MAP), pulse pressure (PP), and aortic pulse wave velocity (PWV) were correlated with velocity pulsatility in the M1 and in perforating arteries, and with the damping index of the CSO and BG.

Statistical Tests

Correlations of LVSV, MAP, PP, and PWV with velocity pulsatility in the M1 and small perforating arteries, and correlations with the damping indices were evaluated with linear regression analyses.

Results

PP and PWV were significantly positively correlated to M1 velocity pulsatility. PWV was significantly negatively correlated to CSO velocity pulsatility, and PP was unrelated to CSO velocity pulsatility (P = 0.28). PP and PWV were uncorrelated to BG velocity pulsatility (P = 0.25; P = 0.68). PWV and PP were significantly positively correlated with the CSO damping index.

Data Conclusion

Our study demonstrated a dynamic damping of velocity pulsatility between the M1 and small cerebral perforating arteries in relation to proximal stress.

Level of Evidence

4

Technical Efficacy

Stage 1

Pulse taking by a piezoelectric film sensor via mode energy ratio analysis helps identify pregnancy status

In order to solve the problem of non-invasive diagnosis and monitoring of women during pregnancy, a piezoelectric film pulse sensing system combined with the mode energy ratio (MER) analysis is utilized to detect human pulses to reveal pregnant conditions. Inspired by traditional Chinese medicine (TCM), pulse diagnosis has a history of more than 2,500 years. The life energy of the human body helps the diagnosis of the disease through the circulation of blood vessels connected to the organs. A PVDF piezoelectric film sensor is used to emulate the pulse taking process in TCM to record the pulse signals. And the algorithm of MER is proposed based on empirical mode decomposition (EMD). Through the MER analysis of 83 female volunteers with different pregnancy statuses, the identification and warning of pregnancy status and physical health indicators are realized.

Clinical Validation of a Soft Wireless Continuous Blood Pressure Sensor During Surgery

We test a new wireless soft capacitance sensor (CAP) based on applanation tonometry at the radial and dorsalis pedis arteries against the gold standard, invasive arterial line (A-Line), for continuous beat to beat blood pressure (BP) measurements in the Operating Room during surgical procedures under anesthesia in 17 subjects with the mean age and body mass index (BMI) of 57. 35 ± 18.72 years and 27.36 ± 4.20 kg/m², respectively. We have identified several parameters to monitor in order to compare how well the CAP sensor tracks the entire hemodynamic waveform as compared to the A-Line. This includes waveform similarity, heart rate (HR), absolute systolic BP (SBP), diastolic BP (DBP), and temporal response to a vasopressor. Overall, the CAP sensor shows good correlations with A-Line with respect to hemodynamic shape (r > 0.89), HR (mean bias = 0.0006; SD = 0.17), absolute SBP, and DBP in a line of best fit (slope = 0.98 in SBP; 1.08 in DBP) and the mean bias derived from Bland-Altman method to be 1.92 (SD = 12.55) in SBP and 2.38 (SD = 12.19) in DBP across body habitus and age in OR patients under general anesthesia. While we do observe drifts in the system, we still obtain decent correlations with respect to the A-Line as evidenced by excellent linear fit and low mean bias across patients. When we post-process using a different calibration method to account for the drift, the mean bias and SD improve dramatically to −1.85 and 7.19 DBP as well as 1.43 and 7.43 SBP, respectively, indicating a promising potential for improvement when we integrate strategies to account for movement identified by our integrated accelerometer data.

Intraoperative Invasive Blood Pressure Monitoring and the Potential Pitfalls of Invasively Measured Systolic Blood Pressure

Invasive intraarterial blood pressure measurement is currently the gold standard for intraoperative hemodynamic monitoring but accurate systolic blood pressure (SBP) measurement is difficult in everyday clinical practice, mostly because of problems with hyper-resonance or damping within the measurement system, which can lead to erroneous treatment decisions if these phenomena are not recognized. A hyper-resonant blood pressure trace significantly overestimates true systolic blood pressure while underestimating the diastolic pressure. Invasively measured systolic blood pressure is also significantly more affected than mean blood pressure by the site of measurement within the arterial system. Patients in the intraoperative period should be treated based on the invasively measured mean blood pressure rather than the systolic blood pressure. In this review, we discuss the pros/cons, mechanisms of invasive blood pressure measurements, and the interpretation of the invasively measured systolic blood pressure value.

Perioperative Hemodynamic Monitoring: An Overview of Current Methods

Perioperative hemodynamic monitoring is an essential part of anesthetic care. In this review, we aim to give an overview of methods currently used in the clinical routine and experimental methods under development. The technical aspects of the mentioned methods are discussed briefly. This review includes methods to monitor blood pressures, for example, arterial pressure, mean systemic filling pressure and central venous pressure, and volumes, for example, global end-diastolic volume (GEDV) and extravascular lung water. In addition, monitoring blood flow (cardiac output) and fluid responsiveness (preload) will be discussed.

Hemodynamic Patterns Before Inhospital Cardiac Arrest in Critically Ill Children: An Exploratory Study

Supplemental Digital Content is available in the text.

OBJECTIVES:

To characterize prearrest hemodynamic trajectories of children suffering inhospital cardiac arrest.

DESIGN:

Exploratory retrospective analysis of arterial blood pressure and electrocardiogram waveforms.

SETTING:

PICU and cardiac critical care unit in a tertiary-care children’s hospital.

PATIENTS:

Twenty-seven children with invasive blood pressure monitoring who suffered a total of 31 inhospital cardiac arrest events between June 2017 and June 2019.

INTERVENTIONS:

None.

MEASUREMENTS AND MAIN RESULTS:

We assessed changes in cardiac output, systemic vascular resistance, stroke volume, and heart rate derived from arterial blood pressure waveforms using three previously described estimation methods. We observed substantial prearrest drops in cardiac output (population median declines of 65–84% depending on estimation method) in all patients in the 10 minutes preceding inhospital cardiac arrest. Most patients’ mean arterial blood pressure also decreased, but this was not universal. We identified three hemodynamic patterns preceding inhospital cardiac arrest: subacute pulseless arrest (n = 18), acute pulseless arrest (n = 7), and bradycardic arrest (n = 6). Acute pulseless arrest events decompensated within seconds, whereas bradycardic and subacute pulseless arrest events deteriorated over several minutes. In the subacute and acute pulseless arrest groups, decreases in cardiac output were primarily due to declines in stroke volume, whereas in the bradycardic group, the decreases were primarily due to declines in heart rate.

CONCLUSIONS:

Critically ill children exhibit distinct physiologic behaviors prior to inhospital cardiac arrest. All events showed substantial declines in cardiac output shortly before inhospital cardiac arrest. We describe three distinct prearrest patterns with varying rates of decline and varying contributions of heart rate and stroke volume changes to the fall in cardiac output. Our findings suggest that monitoring changes in arterial blood pressure waveform-derived heart rate, pulse pressure, cardiac output, and systemic vascular resistance estimates could improve early detection of inhospital cardiac arrest by up to several minutes. Further study is necessary to verify the patterns witnessed in our cohort as a step toward patient rather than provider-centered definitions of inhospital cardiac arrest.

Bioreactance and fourth-generation pulse contour methods in monitoring cardiac index during off-pump coronary artery bypass surgery

The pulmonary artery catheter (PAC) is considered the gold standard for cardiac index monitoring. Recently new and less invasive methods to assess cardiac performance have been developed. The aim of our study was to assess the reliability of a non-invasive monitor utilizing bioreactance (Starling SV) and a non-calibrated mini-invasive pulse contour device (FloTrac/EV1000, fourth-generation software) compared to bolus thermodilution technique with PAC (TDCO) during off-pump coronary artery bypass surgery (OPCAB). In this prospective study, 579 simultaneous intra- and postoperative cardiac index measurements obtained with Starling SV, FloTrac/EV1000 and TDCO were compared in 20 patients undergoing OPCAB. The agreement of data was investigated by Bland-Altman plots, while trending ability was assessed by four-quadrant plots with error grids. In comparison with TDCO, Starling SV was associated with a bias of 0.13 L min^-1 m^-2 (95% confidence interval, 95% CI, 0.07 to 0.18), wide limits of agreement (LOA, - 1.23 to 1.51 L min^-1 m^-2), a percentage error (PE) of 60.7%, and poor trending ability. In comparison with TDCO, FloTrac was associated with a bias of 0.01 L min^-1 m^-2 (95% CI - 0.05 to 0.06), wide LOA (- 1.27 to 1.29 L min^-1 m^-2), a PE of 56.8% and poor trending ability. Both Starling SV and fourth-generation FloTrac showed acceptable mean bias but imprecision due to wide LOA and high PE, and poor trending ability. These findings indicate limited reliability in monitoring cardiac index in patients undergoing OPCAB.

Evaluation of the agreement of two oscillometric blood pressure devices with invasive blood pressure in anaesthetized chimpanzees (Pan troglodytes)

OBJECTIVE

To evaluate the agreement of two noninvasive blood pressure devices: a human device with the cuff placed on the wrist (Omron R1) and a veterinary device with the cuff placed on the upper brachium (Surgivet Advisor Vital Signs Monitor) with invasive blood pressure (IBP) measurement in anaesthetized chimpanzees.

STUDY DESIGN

Prospective clinical study.

ANIMALS

A convenience sample of 11 adult chimpanzees undergoing anaesthesia for translocation and routine health checks.

METHODS

Systolic (SAP) and diastolic arterial pressures (DAP) were continuously recorded via a transducer connected to a femoral artery cannula, and at 5 minute intervals from the two oscillometric devices. Agreement was explored using Bland-Altman analysis and bias defined as the mean difference between the two measurement methods. Spearman correlation coefficients were calculated. Significance was set at p < 0.05.

RESULTS

Bias and standard deviation for the Surgivet compared with IBP were 8.6 ± 18 for SAP and 8.4 ± 9.9 for DAP, showing a significant underestimation of both variables. Limits of agreement (LOA) were from -27 to 44 for SAP and from -11 to 28 for DAP. Correlation coefficients between the Surgivet and IBP values were 0.86 for SAP and 0.85 for DAP (p < 0.0001). Bias and standard deviation for the Omron compared with the IBP were -21 ± 25 for SAP and -18 ± 15 for DAP, showing a significant overestimation of both variables. LOA were from -70 to -28 for SAP and from -47 to 11 for DAP. Spearman correlation coefficients between the Omron and IBP values were 0.64 for SAP and 0.72 for DAP (p < 0.0001).

CONCLUSIONS AND CLINICAL RELEVANCE

Although neither device met all the criteria for device validation, the Surgivet presented better agreement with IBP values than the Omron in adult anaesthetized chimpanzees.

The slope of cerebral oxyhemoglobin oscillation is associated with vascular reserve capacity in large artery steno-occlusion

Inadequate cerebral perfusion is a risk factor for cerebral ischemia in patients with large artery steno-occlusion. We investigated whether prefrontal oxyhemoglobin oscillation (ΔHbO₂, 0.6-2 Hz) was associated with decreased vascular reserve in patients with steno-occlusion in the large anterior circulation arteries. Thirty-six patients with steno-occlusion in the anterior circulation arteries (anterior cerebral artery, middle cerebral artery, and internal carotid artery) were included and compared to thirty-six control subjects. Patients were categorized into two groups (deteriorated vascular reserve vs. preserved vascular reserve) based on the results of Diamox single- photon emission computed tomography imaging. HbO₂ data were collected using functional near-infrared spectroscopy. The slope of ΔHbO₂ and the ipsilateral/contralateral slope ratio of ΔHbO₂ were analyzed. Among the included patients (n = 36), 25 (69.4%) had deteriorated vascular reserve. Patients with deteriorated vascular reserve had a significantly higher average slope of ΔHbO₂ on the ipsilateral side (5.01 ± 2.14) and a higher ipsilateral/contralateral ratio (1.44 ± 0.62) compared to those with preserved vascular reserve (3.17 ± 1.36, P = 0.014; 0.93 ± 0.33, P = 0.016, respectively) or the controls (3.82 ± 1.69, P = 0.019; 0.94 ± 0.29, P = 0.001). The ipsilateral/contralateral ΔHbO₂ ratio could be used as a surrogate for vascular reserve in patients with severe steno-occlusion in the anterior circulation arteries.

Lessons Learned From the First Pilot Study of the Compensatory Reserve Index After Congenital Heart Surgery Requiring Cardiopulmonary Bypass

BACKGROUND

Early warning systems that utilize dense physiologic data and machine learning may aid prediction of decompensation after congenital heart surgery (CHS). The Compensatory Reserve Index (CRI) analyzes changing features of the pulse waveform to predict hemodynamic decompensation in adults, but it has never been studied after CHS. This study sought to understand the feasibility, safety, and potential utility of CRI monitoring after CHS with cardiopulmonary bypass (CPB).

METHODS

A single-center prospective pilot cohort of patients undergoing pulmonary valve replacement was studied. Compensatory Reserve Index was continuously measured from preoperative baseline through the first 24 postoperative hours. Average CRI values during selected procedural phases were compared between patients with an intensive care unit (ICU) length of stay (LOS) <3 days versus LOS ≥3 days.

RESULTS

Twenty-three patients were enrolled. On average, 17,445 (±3,152) CRI data points were collected and 0.33% (±0.40) of data were missing per patient. There were no adverse events related to monitoring. Five (21.7%) patients had an ICU LOS ≥3 days. Compared to the ICU LOS <3 days group, the ICU LOS ≥3 days group had a greater decrease in CRI from baseline to immediately after CPB (-0.3 ± 0.1 vs -0.1 ± 0.2, P = .003) and were less likely to recover to baseline CRI during the monitoring period (20% vs 83%, P = .017).

CONCLUSIONS

Compensatory Reserve Index monitoring after CHS with CPB seems feasible and safe. Early changes in CRI may precede meaningful clinical outcomes, but this requires further study.

Safety of arterial catheterization using the distal radial approach in intensive care unit management: A pilot study

BACKGROUND

Arterial catheter (A-line) is essential for managing severely ill patients, and the radial artery is the most common insertion site in the intensive care unit (ICU). However, many accidental removals occur because the insertion site of A-line in the traditional radial approach (TRA) overlaps with the joint flexion. Recent reports have shown no significant difference in the complication rates between coronarography using the distal radial approach (DRA) and that using TRA. However, to date, no report has examined accidental removals of DRA in the ICU. This study aimed to retrospectively evaluate the safety of the DRA A-line in ICU management.

METHODS

This retrospective, descriptive, and observational study enrolled patients who underwent A-line insertion using the DRA at the authors' facility, which is a university hospital with approximately 1100 beds, from January 1, 2019 to August 31, 2019. The participants' clinical data were extracted from their medical records. The primary outcome was the number of accidental removals.

RESULTS

The study included 20 patients with a median age of 70 (interquartile range (IQR): 58.5-77) years: 10 patients with traumas, 6 with cerebral hemorrhages, 2 with gastrointestinal perforations, and 2 with other diagnoses. The number of punctures was 1 in 15 patients, 2 in 4 patients, and 3 in 1 patient. Only 1 patient required ultrasound guidance, whereas 12 patients required the use of guidewires. The median duration after insertion was 3 (IQR 2.5-5.5) days. Accidental removal was noted in only one patient. No other complications were observed during the period from insertion to removal.

CONCLUSIONS

DRA may be a safe option for insertion of a new A-line in the ICU.

Physiology of Human Hemorrhage and Compensation

Hemorrhage is a leading cause of death following traumatic injuries in the United States. Much of the previous work in assessing the physiology and pathophysiology underlying blood loss has focused on descriptive measures of hemodynamic responses such as blood pressure, cardiac output, stroke volume, heart rate, and vascular resistance as indicators of changes in organ perfusion. More recent work has shifted the focus toward understanding mechanisms of compensation for reduced systemic delivery and cellular utilization of oxygen as a more comprehensive approach to understanding the complex physiologic changes that occur following and during blood loss. In this article, we begin with applying dimensional analysis for comparison of animal models, and progress to descriptions of various physiological consequences of hemorrhage. We then introduce the complementary side of compensation by detailing the complexity and integration of various compensatory mechanisms that are activated from the initiation of hemorrhage and serve to maintain adequate vital organ perfusion and hemodynamic stability in the scenario of reduced systemic delivery of oxygen until the onset of hemodynamic decompensation. New data are introduced that challenge legacy concepts related to mechanisms that underlie baroreflex functions and provide novel insights into the measurement of the integrated response of compensation to central hypovolemia known as the compensatory reserve. The impact of demographic and environmental factors on tolerance to hemorrhage is also reviewed. Finally, we describe how understanding the physiology of compensation can be translated to applications for early assessment of the clinical status and accurate triage of hypovolemic and hypotensive patients. © 2021 American Physiological Society. Compr Physiol 11:1531-1574, 2021.

Wearable Sensors Incorporating Compensatory Reserve Measurement for Advancing Physiological Monitoring in Critically Injured Trauma Patients

Vital signs historically served as the primary method to triage patients and resources for trauma and emergency care, but have failed to provide clinically-meaningful predictive information about patient clinical status. In this review, a framework is presented that focuses on potential wearable sensor technologies that can harness necessary electronic physiological signal integration with a current state-of-the-art predictive machine-learning algorithm that provides early clinical assessment of hypovolemia status to impact patient outcome. The ability to study the physiology of hemorrhage using a human model of progressive central hypovolemia led to the development of a novel machine-learning algorithm known as the compensatory reserve measurement (CRM). Greater sensitivity, specificity, and diagnostic accuracy to detect hemorrhage and onset of decompensated shock has been demonstrated by the CRM when compared to all standard vital signs and hemodynamic variables. The development of CRM revealed that continuous measurements of changes in arterial waveform features represented the most integrated signal of physiological compensation for conditions of reduced systemic oxygen delivery. In this review, detailed analysis of sensor technologies that include photoplethysmography, tonometry, ultrasound-based blood pressure, and cardiogenic vibration are identified as potential candidates for harnessing arterial waveform analog features required for real-time calculation of CRM. The integration of wearable sensors with the CRM algorithm provides a potentially powerful medical monitoring advancement to save civilian and military lives in emergency medical settings.

Physiology and clinical utility of the peripheral venous waveform

The peripheral venous system serves as a volume reservoir due to its high compliance and can yield information on intravascular volume status. Peripheral venous waveforms can be captured by direct transduction through a peripheral catheter, non-invasive piezoelectric transduction, or gleaned from other waveforms such as the plethysmograph. Older analysis techniques relied upon pressure waveforms such as peripheral venous pressure and central venous pressure as a means of evaluating fluid responsiveness. Newer peripheral venous waveform analysis techniques exist in both the time and frequency domains, and have been applied to various clinical scenarios including hypovolemia (i.e. hemorrhage, dehydration) and volume overload.

Arterial insertion method: A new method for systematic evaluation of ultrasound-guided radial arterial catheterization

Introduction:

Peripheral arterial catheter insertion is a common procedure for critically ill patients requiring frequent blood gas sampling and continuous blood pressure monitoring. There are clear advantages of ultrasound-guided arterial cannulation, which have shown to be more effective in reducing complications, time to successful cannulation, number of attempts, and overall first-time success rates. Evidence suggests that using palpation alone has a first-time success rate of less than 70% yet is still a widely performed technique. A systematic evaluation may be required to reduce variations in arterial catheterization practices.

Design:

The arterial insertion method is a systematic evaluation to aid in arterial catheter insertion with ultrasound guidance, intended to improve the procedural approach. The process of arterial insertion method ensures appropriate choice of zone selection to optimize catheter longevity and performance in patients requiring arterial access. Moving the insertion site proximally 4 cm from the red zone into the green zone may reduce mechanical complications and preserve catheter performance and dwell time.

Conclusion:

The standardization of ultrasound guidance in arterial catheterization promotes vessel health and patient safety through device and site optimization. The arterial insertion method systematic evaluation may be utilized to reduce variation in practice and promote the use of ultrasound as a standard for the insertion of radial arterial catheters.

Radial artery cannulation in intensive care unit patients: Does distance from wrist joint increase catheter durability and functionality?

INTRODUCTION

Radial artery cannulation (RAC) is a common procedure in Intensive Care Units (ICU); radial catheters for ICU patients require increased durability to collect blood samples and to guarantee continuous hemodynamic monitoring. Failure in catheter functionality needs catheter replacement, impacting on staff workload, costs, and patient safety and discomfort.

METHODS

prospective non-randomised cohort study on adult ICU patients describing intensivists and critical care nurses' approach in radial artery catheterization.

RESULTS

A sample of 103 radial artery cannulations was observed. Catheterization was performed blind in 71 patients (68.9%) and with ultrasound guidance (USG) in 32 (31.1%); majority of blind inserted RAC were at a distance between 0 and 3.9 cm from wrist joint (77.5%) while catheters inserted from 4 to 10 cm were mainly positioned with USG (84.4%). Radial catheters inserted with USG at a distance of 4 to 10 cm from wrist joint had an in-situ time double than those inserted blind (8.2 ± 7.5 vs 4.8 ± 7.3, p < 0.038).

CONCLUSIONS

As recommended by current evidence and guidelines, USG represents a valuable support during arterial catheterization and is recommended in adult patients with clinical signs of shock, obese, swelling, and in the paediatric population. RAC in the forearm proximally, at a distance of at least 4 cm from wrist, could increase catheter durability and functionality for ICU patients. USG for cannulation in this forearm area is mandatory because of the deeper course of the radial artery.

The Compensatory Reserve Index Responds to Acute Hemodynamic Changes in Patients with Congenital Heart Disease: A Proof of Concept Study

Patients with congenital heart disease (CHD) who undergo cardiac procedures may become hemodynamically unstable. Predictive algorithms that utilize dense physiologic data may be useful. The compensatory reserve index (CRI) trends beat-to-beat progression from normovolemia (CRI = 1) to decompensation (CRI = 0) in hemorrhagic shock by continuously analyzing unique sets of features in the changing pulse photoplethysmogram (PPG) waveform. We sought to understand if the CRI accurately reflects changing hemodynamics during and after a cardiac procedure for patients with CHD. A transcatheter pulmonary valve replacement (TcPVR) model was used because left ventricular stroke volume decreases upon sizing balloon occlusion of the right ventricular outflow tract (RVOT) and increases after successful valve placement. A single-center, prospective cohort study was performed. The CRI was continuously measured to determine the change in CRI before and after RVOT occlusion and successful TcPVR. Twenty-six subjects were enrolled with a median age of 19 (interquartile range (IQR) 13-29) years. The mean (± standard deviation) CRI decreased from 0.66 ± 0.15 1-min before balloon inflation to 0.53 ± 0.16 (p = 0.03) 1-min after balloon deflation. The mean CRI increased from a pre-valve mean CRI of 0.63 [95% confidence interval (CI) 0.56-0.70] to 0.77 (95% CI 0.71-0.83) after successful TcPVR. In this study, the CRI accurately reflected acute hemodynamic changes associated with TcPVR. Further research is justified to determine if the CRI can be useful as an early warning tool in patients with CHD at risk for decompensation during and after cardiac procedures.

Heparinized Saline Solution vs. Saline Solution (0.9% Sodium Chloride) for the Maintenance of Dorsal Pedal Arterial Catheter Patency in Dogs Undergoing General Anesthesia: A Pilot Study

Heparin is widely used as an anticoagulant solution for maintaining arterial catheter patency. In humans, increasing evidence suggests that heparinized saline solution (HS) has no advantages over a saline (0.9% sodium chloride) solution (SS) in maintaining arterial catheter patency. To date, no studies have been conducted on the effectiveness of these solutions at maintaining arterial catheter patency in veterinary medicine. The objective of this pilot study was to determine the feasibility of a study and to report the treatment efficacy comparing HS and SS for the maintenance of the dorsal pedal arterial catheter patency during direct arterial blood pressure measurements in anesthetized dogs. Client-owned dogs undergoing abdominal surgery were allocated to two groups to receive either a continuous infusion of HS or SS through the dorsal pedal artery, and the arterial pressure waveform was monitored during general anesthesia. Our feasibility outcomes included the proportion of the screened veterinary patients that completed the study and the success rate of arterial catheter placement. The clinical outcomes were assessed by the number of catheter-flushing procedures, occlusion rate, the duration of the initial catheter-flushing procedures, and the duration of catheter occlusion. Of the 51 dogs screened, 41 (80.4%) completed the study. The success rate of arterial catheter placement in the HS and SS groups were 87.5 and 80.0%, respectively. There were no differences in the number of catheter-flushing procedures and occlusion rate between groups (28.6 vs. 20.0%, relative risk [RR]: 1.429, 95% confidence interval [CI]: 0.472–4.323, P = 0.719 and 14.3 vs. 15.0%, RR: 0.952, 95% CI: 0.217–4.179, P = 1.000, respectively). No differences were found in the probability of time to the initial catheter-flushing procedure and occlusion between groups assessed by the Kaplan-Meier method (P = 0.546 and P = 0.867, respectively). This study revealed the feasibility of a study comparing HS and SS for dorsal pedal arterial catheter patency during direct arterial blood pressure measurements in anesthetized dogs. Clinical outcome analyses were underpowered and thus, could not determine the meaningful differences in treatment efficacy between the groups. However, the information gained from this study provides insight for future study designs.

Cardiopulmonary Activity Monitoring Using Millimeter Wave Radars

Current cardiopulmonary activity monitoring is based on contact devices which cannot be used in extreme cases such as premature infants, burnt victims or rescue operations. In order to overcome these limitations, the use of radar technologies emerges as an alternative. This paper aims to enhance the comprehension that non-contact technologies, in particular radar techniques, offer as a monitoring tool. For this purpose, a modified low cost commercial 122 GHz frequency-modulated continuous-wave (FMCW) radar is used to better fit the current application domain. The radar signals obtained are processed using a classic linear filtering algorithm aiming to separate the breathing from the heartbeat component while preserving signals integrity. In a standoff configuration and with different subject orientations, results show that the signal obtained with the radar can be used to extract not only the respiratory and heartbeat rates, but also the heart rate variability (HRV) sequence. Moreover, results evidence the coupling between breathing and heartbeat, also showing that the HRV sequence obtained can identify the respiratory sinus arrhythmia (RSA) effect. Finally, the radar is tested in a simultaneous multi-target scenario, demonstrating its monitoring capabilities in more complex situations. Nevertheless, there are some challenges left to use the system in a real-life monitoring environments, such as the removal of random body movements.

Correlation Between Doppler Derived Carotid Artery Corrected Flow Time and Pressure Transducer Derived Radial Artery Corrected Flow Time: A Prospective Observational Study

PURPOSE

Carotid artery corrected flow time (cFT) derived from Doppler USG is a known predictor of volume responsiveness. However, it can't be obtained continuously, and is operator dependent. In this prospective study, correlation between Doppler derived carotid artery cFT and pressure transducer derived radial artery cFT was evaluated in adult patients undergoing surgery under general anaesthesia.

METHODS

Doppler derived carotid artery cFT were obtained from n = 51 adult patients at n = 125 time points. Simultaneously, pressure transducer waveforms were saved at the time of measurement of carotid artery cFT. Later, images were analyzed by an image processing computer software; both pulse pressure variation and cFT were estimated from pressure transducer waveform.

RESULTS

Radial artery flow times measured by two independent observers, were significantly correlated (r² = 0.99, p < 0.00001). Bland-Altman analysis found limits of agreement - 8.3 to 6.3 ms [mean difference (95% CI) - 0.98 (- 1.63, - 0.32)]. Doppler derived carotid artery cFT & pressure transducer derived radial artery cFT were also significantly correlated [r² = 0.78, p < 0.0001]. However, radial artery cFT was significantly higher than carotid artery cFT [p < 0.0001, paired sample t test]. Radial artery cFT > 404.4 ms had an sensitivity and specificity of 87.34% and 85% respectively with a grey zone was between 393.7 and 417 ms to predict PPV ≥ 12%.

CONCLUSION

Pressure transducer derived radial artery cFT correlated with Doppler derived carotid artery cFT and may be a reasonable predictor of volume responsiveness. Further studies are required to confirm its role in various clinical scenario for prediction of volume responsiveness.

Non-Invasive Venous waveform Analysis (NIVA) for monitoring blood loss in human blood donors and validation in a porcine hemorrhage model

STUDY OBJECTIVE

There is an unmet need for a non-invasive approach to diagnose hemorrhage early, before changes in vital signs occur. Non-Invasive Venous waveform Analysis (NIVA) uses a unique physiological signal (the peripheral venous waveform) to assess intravascular volume. We hypothesized changes in the venous waveform would be observed with blood loss in healthy adult blood donors and characterized hemorrhage using invasive monitoring in a porcine model.

DESIGN

Prospective observational study.

SETTING

American Red Cross donation center.

PATIENTS

50 human blood donors and 12 non-donating controls; 7 Yorkshire pigs.

INTERVENTIONS

A venous waveform capturing prototype (NIVA device) was secured to the volar aspect of the wrist in human subjects. A central venous catheter was used to obtain hemodynamic indices and venous waveforms were obtained using the prototype NIVA device over the saphenous vein during 400 mL of graded hemorrhage in a porcine model.

MEASUREMENTS

Venous waveforms were transformed from the time to the frequency domain. The ratiometric power contributions of the cardiac frequencies were used to calculate a NIVA value representative of volume status.

MAIN RESULTS

A significant decrease in NIVA value was observed after 500 mL of whole blood donation (p < .05). A ROC curve for the ability of the NIVA to detect 500 mL of blood loss demonstrated an area under the curve (AUC) of 0.94. In the porcine model, change in NIVA value correlated linearly with blood loss and with changes in hemodynamic indices.

CONCLUSIONS

This study provides proof-of-concept for a potential application of NIVA in detection of blood loss. NIVA represents a novel physiologic signal for detection of early blood loss that may be useful in early triage and perioperative management.

Blood Pressure Estimation Using On-body Continuous Wave Radar and Photoplethysmogram in Various Posture and Exercise Conditions

The pulse arrival time (PAT), pre-ejection period (PEP) and pulse transit time (PTT) are calculated using on-body continuous wave radar (CWR), Photoplethysmogram (PPG) and Electrocardiogram (ECG) sensors for wearable continuous systolic blood pressure (SBP) measurements. The CWR and PPG sensors are placed on the sternum and left earlobe respectively. This paper presents a signal processing method based on wavelet transform and adaptive filtering to remove noise from CWR signals. Experimental data are collected from 43 subjects in various static postures and 26 subjects doing 6 different exercise tasks. Two mathematical models are used to calculate SBPs from PTTs/PATs. For 38 subjects participating in posture tasks, the best cumulative error percentage (CEP) is 92.28% and for 21 subjects participating in exercise tasks, the best CEP is 82.61%. The results show the proposed method is promising in estimating SBP using PTT. Additionally, removing PEP from PAT leads to improving results by around 9%. The CWR sensors present a low-power, continuous and potentially wearable system with minimal body contact to monitor aortic valve mechanical activities directly. Results of this study, of wearable radar sensors, demonstrate the potential superiority of CWR-based PEP extraction for various medical monitoring applications, including BP measurement.

Cardiac output estimation by multi-beat analysis of the radial arterial blood pressure waveform versus intermittent pulmonary artery thermodilution: a method comparison study in patients treated in the intensive care unit after off-pump coronary artery bypass surgery

Cardiac output (CO) is a key hemodynamic variable that can be minimally invasively estimated by pulse wave analysis. Multi-beat analysis is a novel pulse wave analysis method. In this prospective observational clinical method comparison study, we compared CO estimations by multi-beat analysis with CO measured by intermittent pulmonary artery thermodilution (PATD) in adult patients treated in the intensive care unit (ICU) after off-pump coronary artery bypass surgery (OPCAB). We included patients after planned admission to the ICU after elective OPCAB who were monitored with a radial arterial catheter and a pulmonary artery catheter. At seven time points, we determined CO using intermittent PATD (PATD-CO; reference method) and simultaneously recorded the radial arterial blood pressure waveform that we later used to estimate CO using multi-beat analysis (MBA-CO; test method) with the Argos monitor (Retia Medical; Valhalla, NY, USA). Blood pressure waveforms impaired by inappropriate damping properties or artifacts were excluded. We compared PATD-CO and MBA-CO using Bland-Altman analysis accounting for repeated measurements, the percentage error, and the concordance rate derived from four-quadrant plot analysis (15% exclusion zone). We analyzed 167 CO values of 31 patients. Mean PATD-CO was 5.30 ± 1.22 L/min and mean MBA-CO was 5.55 ± 1.82 L/min. The mean of the differences between PATD-CO and MBA-CO was 0.08 ± 1.10 L/min (95% limits of agreement: - 2.13 L/min to + 2.29 L/min). The percentage error was 40.7%. The four-quadrant plot-derived concordance rate was 88%. CO estimation by multi-beat analysis of the radial arterial blood pressure waveform (Argos monitor) shows reasonable agreement compared with CO measured by intermittent PATD in adult patients treated in the ICU after OPCAB.

Cardiac output estimation using multi-beat analysis of the radial arterial blood pressure waveform: a method comparison study in patients having off-pump coronary artery bypass surgery using intermittent pulmonary artery thermodilution as the reference method

Pulse wave analysis enables stroke volume to be estimated from an arterial blood pressure waveform. Multi-beat analysis is a novel pulse wave analysis method. We aimed to investigate cardiac output (CO) estimations using multi-beat analysis of the radial arterial blood pressure waveform in patients undergoing off-pump coronary artery bypass surgery (OPCAB) using intermittent pulmonary artery thermodilution (PATD) as the reference method. This was a prospective clinical method comparison study. In 58 patients, we measured CO using PATD (PATD-CO; reference method) and simultaneously recorded the radial arterial blood pressure waveform that we used for off-line estimation of CO based on multi-beat analysis (MBA-CO; test method) using the Argos CO monitor (Retia Medical; Valhalla, NY, USA). The final analysis was performed using 572 paired CO measurements. We performed Bland-Altman analysis accounting for multiple observations per patient. To describe the ability of the test method to track changes in CO over time we computed four-quadrant plots using a central exclusion zone of 15% and calculated the concordance rate. Mean PATD-CO was 4.13 ± 1.26 L/min and mean MBA-CO was 4.31 ± 1.25 L/min. The mean of the differences between PATD-CO and MBA-CO was - 0.20 L/min with a standard deviation of ± 1.14 L/min and 95% limits of agreement of - 2.48 to + 2.08 L/min. The concordance rate for CO changes between PATD-CO and MBA-CO was 89%. CO estimations using multi-beat analysis (Argos monitor) show reasonable agreement and trending ability compared with PATD-CO as the reference method in adult patients during OPCAB.

Clinical assessment of a non-invasive wearable MEMS pressure sensor array for monitoring of arterial pulse waveform, heart rate and detection of atrial fibrillation

There is an unmet clinical need for a low cost and easy to use wearable devices for continuous cardiovascular health monitoring. A flexible and wearable wristband, based on microelectromechanical sensor (MEMS) elements array was developed to support this need. The performance of the device in cardiovascular monitoring was investigated by (i) comparing the arterial pressure waveform recordings to the gold standard, invasive catheter recording (n = 18), (ii) analyzing the ability to detect irregularities of the rhythm (n = 7), and (iii) measuring the heartrate monitoring accuracy (n = 31). Arterial waveforms carry important physiological information and the comparison study revealed that the recordings made with the wearable device and with the gold standard device resulted in almost identical (r = 0.9–0.99) pulse waveforms. The device can measure the heart rhythm and possible irregularities in it. A clustering analysis demonstrates a perfect classification accuracy between atrial fibrillation (AF) and sinus rhythm. The heartrate monitoring study showed near perfect beat-to-beat accuracy (sensitivity = 99.1%, precision = 100%) on healthy subjects. In contrast, beat-to-beat detection from coronary artery disease patients was challenging, but the averaged heartrate was extracted successfully (95% CI: −1.2 to 1.1 bpm). In conclusion, the results indicate that the device could be useful in remote monitoring of cardiovascular diseases and personalized medicine.

A novel method to quantify arterial pulse waveform morphology: attractor reconstruction for physiologists and clinicians

Current arterial pulse monitoring systems capture data at high frequencies (100-1000 Hz). However, they typically report averaged or low frequency summary data such as heart rate and systolic, mean and diastolic blood pressure. In doing so, a potential wealth of information contained in the high-fidelity waveform data is discarded, data which has long been known to contain useful information on cardiovascular performance. Here we summarise a new mathematical method, attractor reconstruction, which enables the quantification of arterial waveform shape and variability in real-time. The method can handle long streams of non-stationary data and does not require preprocessing of the raw physiological data by the end user. Whilst the detailed mathematical proofs have been described elsewhere (Aston et al 2008 Physiol. Meas. 39), the authors were motivated to write a summary of the method and its potential utility for biomedical researchers, physiologists and clinician readers. Here we illustrate how this new method may supplement and potentially enhance the sensitivity of detecting cardiovascular disturbances, to aid with biomedical research and clinical decision making.

Study of continuous blood pressure estimation based on pulse transit time, heart rate and photoplethysmography-derived hemodynamic covariates

It is widely recognized that pulse transit time (PTT) can track blood pressure (BP) over short periods of time, and hemodynamic covariates such as heart rate, stiffness index may also contribute to BP monitoring. In this paper, we derived a proportional relationship between BP and PPT^-2 and proposed an improved method adopting hemodynamic covariates in addition to PTT for continuous BP estimation. We divided 28 subjects from the Multi-parameter Intelligent Monitoring for Intensive Care database into two groups (with/without cardiovascular diseases) and utilized a machine learning strategy based on regularized linear regression (RLR) to construct BP models with different covariates for corresponding groups. RLR was performed for individuals as the initial calibration, while recursive least square algorithm was employed for the re-calibration. The results showed that errors of BP estimation by our method stayed within the Association of Advancement of Medical Instrumentation limits (- 0.98 ± 6.00 mmHg @ SBP, 0.02 ± 4.98 mmHg @ DBP) when the calibration interval extended to 1200-beat cardiac cycles. In comparison with other two representative studies, Chen's method kept accurate (0.32 ± 6.74 mmHg @ SBP, 0.94 ± 5.37 mmHg @ DBP) using a 400-beat calibration interval, while Poon's failed (- 1.97 ± 10.59 mmHg @ SBP, 0.70 ± 4.10 mmHg @ DBP) when using a 200-beat calibration interval. With additional hemodynamic covariates utilized, our method improved the accuracy of PTT-based BP estimation, decreased the calibration frequency and had the potential for better continuous BP estimation.

Perioperative Goal-Directed Therapy Using Invasive Uncalibrated Pulse Contour Analysis

“Perioperative goal-directed therapy” (PGDT) aims at an optimization of basic and advanced global hemodynamic variables to maintain adequate oxygen delivery to the end-organs. PGDT protocols help to titrate fluids, vasopressors, or inotropes to hemodynamic target values. There is considerable evidence that PGDT can improve patient outcome in high-risk patients if both fluids and inotropes are administered to target hemodynamic variables reflecting blood flow. Despite this evidence, PGDT strategies aiming at an optimization of blood flow seem to be not well implemented in routine clinical care. The analysis of the arterial blood pressure waveform using invasive uncalibrated pulse contour analysis can be used to assess hemodynamic variables used in PGDT protocols. Pulse contour analysis allows the assessment of stroke volume (SV)/cardiac output (CO) and pulse pressure variation (PPV)/stroke volume variation (SVV) and thus helps to titrate fluids and vasoactive agents based on principles of “functional hemodynamic monitoring.” Pulse contour analysis-based PGDT treatment algorithms can be classified according to the hemodynamic variables they use as targets: PPV/SVV, SV/CO, or a combination of these variables. From a physiologic point of view, algorithms using both dynamic cardiac preload and blood flow variables as hemodynamic targets might be most effective in improving patient outcome. Future research should focus on the improvement of hemodynamic treatment algorithms and on the identification of patient subgroups in which PGDT based on uncalibrated pulse contour analysis can improve patient outcome.

Accuracy, Precision, and Trending of 4 Pulse Wave Analysis Techniques in the Postoperative Period

OBJECTIVE

The aim of this study was to analyze the accuracy, precision, and trending ability of the following 4 pulse wave analysis devices to measure continuous cardiac output: PiCCO₂ ([PCCO]; Pulsion Medical System, Munich, Germany); LiDCO_Rapid ([LCCO]; LiDCO Ltd, London, UK); FloTrac/Vigileo ([FCCO]; Edwards Lifesciences, Irvine, CA); and Nexfin ([NCCO]; BMEYE, Amsterdam, The Netherlands).

DESIGN

Prospective, observational clinical study.

SETTING

Intensive care unit of a single-center, teaching hospital.

PARTICIPANTS

The study comprised 22 adult patients after elective coronary artery bypass surgery.

INTERVENTIONS

Three measurement cycles were performed in all patient durings their immediate postoperative intensive care stay before and after fluid loading. Hemodynamic measurements were performed 5 minutes before and immediately after the administration of 500 mL colloidal fluid over 20 minutes.

MEASUREMENTS AND MAIN RESULTS

PCCO, LCCO, FCCO, and NCCO were assessed and compared with cardiac output derived from intermittent transpulmonary thermodilution (ICO). One hundred thirty-two matched sets of data were available for analysis. Bland-Altman analysis using linear mixed effects models with random effects for patient and trial revealed a mean bias ±2 standard deviation (%error) of -0.86 ± 1.41 L/min (34.9%) for PCCO-ICO, -0.26 ± 2.81 L/min (46.3%) for LCCO-ICO, -0.28 ± 2.39 L/min (43.7%) for FCCO-ICO, and -0.93 ± 2.25 L/min (34.6%) for NCCO-ICO. Bland-Altman plots without adjustment for repeated measurements and replicates yielded considerably larger limits of agreement. Trend analysis for all techniques did not meet criteria for acceptable performance.

CONCLUSIONS

All 4 tested devices using pulse wave analysis for measuring cardiac output failed to meet current criteria for meaningful and adequate accuracy, precision, and trending ability in cardiac output monitoring.