Techniques for Non-Invasive Monitoring of Arterial Blood Pressure

Comparing Intra-Arterial, Auscultatory, and Oscillometric Measurement Methods for Arterial Blood Pressure

AIM

This study aimed to compare the measurement results of arterial blood pressure obtained through intra-arterial, auscultatory, and oscillometric methods.

METHOD

This prospective and descriptive study was conducted with 180 patients hospitalized in the intensive care units of cardiovascular surgery and anesthesia. Arterial blood pressures of the patients in the study were measured with 3 methods, and the mean arterial pressure values obtained by each method were analyzed to find out whether they were different or consistent.

RESULTS

The average systolic blood pressure value using the intra-arterial method was found to be 125.47 ± 21.39 mm Hg, and the average of diastolic blood pressure measurement obtained using the oscillometric method was the highest (73.91 ± 10.62 mm Hg). The highest correlation was seen between the arterial BP measurements of the intra-arterial and auscultatory methods (systolic [0.96] and diastolic [0.90]). According to the British and Irish Hypertension Society protocol, a very good agreement between the diastolic blood pressure values and a good agreement between the systolic blood pressure values were obtained.

CONCLUSION

The measurement results obtained through the auscultatory method more consistent with the results obtained through the intra-arterial method compared with those obtained using the oscillometric method.

How well do we understand pulsatility in the context of modern ventricular assist devices?

BACKGROUND

Modern ventricular assist devices (VADs) use a continuous flow design. It has been suggested that a lack of pulsatility contributes to a range of adverse outcomes including pump thrombus, gastrointestinal bleeding and stroke. To better assess the role of pulsatility in these adverse events, we first require a clear definition of 'pulsatility' in the setting of a severely impaired ventricle and a modern continuous flow VAD.

METHODS

A literature review was conducted to elucidate the understanding of pulsatility in modern VAD literature. Search engines used included PUBMED, EMBASE and the Cochrane library. Articles were appraised on three aspects: Whether they mentioned pulsatility; whether they mentioned which pulsatility measure was used and finally which methodology was used to obtain the value.

RESULTS

Of 354 articles reviewed, only 13 met our broad inclusion criteria. Of these articles, the most cited measure was pulsatility index (PI) - used by 11 of the publications. The methodology used to obtain the value was not uniform and five articles did not clearly state it. Other measures included pulse pressure and surplus haemodynamic energy. The majority of articles did not directly discuss pulsatility in the setting of patient-pump interaction.

CONCLUSION

Most publications did not provide a definition for pulsatility. In those that did, the most common measure was PI. Measuring PI was not standardised. Few papers addressed the impact of intrinsic ventricular function and arterial compliance on pulsatility. We suggest that future publications adopt a uniform definition which encompasses both patient and pump characteristics.

Initial orthostatic hypotension and orthostatic intolerance symptom prevalence in older adults: A systematic review

Background

Initial orthostatic hypotension is a clinically relevant syndrome in older adults which has been associated with symptoms of orthostatic intolerance. The aim of this systematic review was to determine the prevalence of orthostatic intolerance symptoms in older adults with initial orthostatic hypotension.

Methods

MEDLINE (from 1946), EMBASE (from 1974) and Cochrane were searched to December 6th^, 2019 using the terms "initial orthostatic hypotension", "postural hypotension" and "older adults". Study selection involved the following criteria: published in English; mean or median age ≥ 65 years and diagnosis of initial orthostatic hypotension encompassed a decrease in systolic blood pressure by ≥ 40  mmHg and/or diastolic blood pressure by ≥ 20  mmHg within a maximum of 1 min following a postural change.

Results

Of 8311 articles, 12 articles reporting initial orthostatic hypotension prevalence in 3446 participants with a mean age of 75 (6 SD) years (56.5% female) were included. Five initial orthostatic hypotension definition variations were utilised and symptoms were reported in six articles (968 participants, mean age 73.4 (6.1 SD) years, 56% female). The prevalence of symptoms in older adults with initial orthostatic hypotension ranged from 24 to 100% and was dependent on variations in timing or the inclusion of symptoms in the initial orthostatic hypotension definition.

Conclusions

Where orthostatic intolerance symptoms were reported, a large proportion of older adults with a diagnosis of initial orthostatic hypotension were symptomatic. However, the literature on initial orthostatic hypotension and orthostatic intolerance symptoms is scarce and a variety of definitions of initial orthostatic hypotension are utilised.

A Continuous Cuffless Blood Pressure Estimation Using Tree-Based Pipeline Optimization Tool

High blood pressure (BP) may lead to further health complications if not monitored and controlled, especially for critically ill patients. Particularly, there are two types of blood pressure monitoring, invasive measurement, whereby a central line is inserted into the patient’s body, which is associated with infection risks. The second measurement is cuff-based that monitors BP by detecting the blood volume change at the skin surface using a pulse oximeter or wearable devices such as a smartwatch. This paper aims to estimate the blood pressure using machine learning from photoplethysmogram (PPG) signals, which is obtained from cuff-based monitoring. To avoid the issues associated with machine learning such as improperly choosing the classifiers and/or not selecting the best features, this paper utilized the tree-based pipeline optimization tool (TPOT) to automate the machine learning pipeline to select the best regression models for estimating both systolic BP (SBP) and diastolic BP (DBP) separately. As a pre-processing stage, notch filter, band-pass filter, and zero phase filtering were applied by TPOT to eliminate any potential noise inherent in the signal. Then, the automated feature selection was performed to select the best features to estimate the BP, including SBP and DBP features, which are extracted using random forest (RF) and k-nearest neighbors (KNN), respectively. To train and test the model, the PhysioNet global dataset was used, which contains 32.061 million samples for 1000 subjects. Finally, the proposed approach was evaluated and validated using the mean absolute error (MAE). The results obtained were 6.52 mmHg for SBS and 4.19 mmHg for DBP, which show the superiority of the proposed model over the related works.

Non-invasive measurement of pulse pressure variation using a finger-cuff method (CNAP system): a validation study in patients having neurosurgery

The finger-cuff system CNAP (CNSystems Medizintechnik, Graz, Austria) allows non-invasive automated measurement of pulse pressure variation (PPV_CNAP). We sought to validate the PPV_CNAP-algorithm and investigate the agreement between PPV_CNAP and arterial catheter-derived manually calculated pulse pressure variation (PPV_INV). This was a prospective method comparison study in patients having neurosurgery. PPV_INV was the reference method. We applied the PPV_CNAP-algorithm to arterial catheter-derived blood pressure waveforms (PPV_INV−CNAP) and to CNAP finger-cuff-derived blood pressure waveforms (PPV_CNAP). To validate the PPV_CNAP-algorithm, we compared PPV_INV−CNAP to PPV_INV. To investigate the clinical performance of PPV_CNAP, we compared PPV_CNAP to PPV_INV. We used Bland–Altman analysis (absolute agreement), Deming regression, concordance, and Cohen's kappa (predictive agreement for three pulse pressure variation categories). We analyzed 360 measurements from 36 patients. The mean of the differences between PPV_INV−CNAP and PPV_INV was −0.1% (95% limits of agreement (95%-LoA) −2.5 to 2.3%). Deming regression showed a slope of 0.99 (95% confidence interval (95%-CI) 0.91 to 1.06) and intercept of −0.02 (95%-CI −0.52 to 0.47). The predictive agreement between PPV_INV−CNAP and PPV_INV was 92% and Cohen’s kappa was 0.79. The mean of the differences between PPV_CNAP and PPV_INV was −1.0% (95%-LoA−6.3 to 4.3%). Deming regression showed a slope of 0.85 (95%-CI 0.78 to 0.91) and intercept of 0.10 (95%-CI −0.34 to 0.55). The predictive agreement between PPV_CNAP and PPV_INV was 82% and Cohen’s kappa was 0.48. The PPV_CNAP-algorithm reliably calculates pulse pressure variation compared to manual offline pulse pressure variation calculation when applied on the same arterial blood pressure waveform. The absolute and predictive agreement between PPV_CNAP and PPV_INV are moderate.

Use of pulse contour technology for continuous blood pressure monitoring in pediatric patients

OBJECTIVES

This study evaluates the accuracy of continuous blood pressure monitoring using pulse contour technology with the ClearSight monitoring device, a noninvasive alternative to placing an invasive arterial line, in pediatric patients.

METHODS

Children younger than 18 years admitted to a pediatric ICU, who required an arterial line, and fit into the ClearSight finger cuff were included. Blood pressure measurement for systolic, diastolic, and mean arterial pressures (MAP) obtained by the ClearSight device were compared with those obtained with the intra-arterial catheter as well as automated cuff measurements using the mixed-effects model. Analysis was conducted for entire cohort, and measurements obtained with and without vasopressor use.

RESULTS

There were 213 measurements from 10 patients. There was a statistically significant difference in systolic blood pressure when comparing arterial line and ClearSight systolic and diastolic measurements between the two methods (P < 0.001). There was no statistical difference between arterial MAP and ClearSight MAP (P = 0.957). Results were similar when ClearSight measurements were compared with automated cuff measurements. Both the vasopressor use and nonvasopressor use groups showed a statistically significant difference between arterial and ClearSight measurements for systolic and diastolic pressures, but not for the MAP.

CONCLUSIONS

Measurements of MAP obtained by the ClearSight device were almost identical to those obtained by the intra-arterial catheter. Although there was a difference in systolic blood pressures between the two methods, in those patients receiving inotropic support, the difference was within the range of what is considered acceptable in validating blood pressure devices.

Continuous noninvasive monitoring of arterial pressure using the vascular unloading technique in comparison to the invasive gold standard in elderly comorbid patients: A prospective observational study

BACKGROUND AND AIMS

Elderly patients aged ≥65 years represent a growing population in the perioperative field, particularly orthopedic and vascular surgery. The higher degree of age-related or comorbid-dependent vascular alterations renders these patients at risk for hemodynamic complications and likely denote a possible limitation for modern, non-invasive arterial pressure monitoring devices. The aim was to compare vascular unloading technique-derived to invasive measurements of systolic (SAP), diastolic (DAP), and mean arterial pressure (MAP) in elderly perioperative patients.

METHODS

This prospective observational study included patients aged ≥65 years scheduled for orthopedic and patients ≥50 years with peripheral artery disease Fontaine stage ≥ II scheduled for vascular surgery, respectively. Invasive radial artery and non-invasive finger-cuff (Nexfin system) arterial pressures were recorded before and after induction of general anesthesia and during surgery. Correlation, Bland-Altman, and concordance analyses were performed. Measurements of arterial pressure were also compared during intraoperative hypotension (MAP <70 mm Hg) and hypertension (MAP >105 mm Hg).

RESULTS

Sixty patients with orthopedic (N = 25, mean (SD) age 77 (5) years) and vascular surgery (N = 35, age 69 [10] years) were enrolled. Seven hundred data pairs of all patients were analysed and pooled bias and percentage error were: SAP: 14.43 mm Hg, 43.79%; DAP: -2.40 mm Hg, 53.78% and MAP: 1.73 mm Hg, 45.05%. Concordance rates were 84.01% for SAP, 77.87% for DAP, and 86.47% for MAP. Predefined criteria for interchangeability of absolute and trending values could neither be reached in the overall nor in the subgroup analyses orthopedic vs vascular surgery. During hypertension, percentage error was found to be lowest for all pressure values, still not reaching predefined criteria.

CONCLUSION

Arterial pressure monitoring with the vascular unloading technique did not reach criteria of interchangeability for absolute and trending values. Nevertheless, the putatively beneficial use of noninvasive arterial pressure measurements should be further evaluated in the elderly perioperative patient.

Predicting hypotension in the ICU using noninvasive physiological signals

Hypotension frequently occurs in Intensive Care Units (ICU), and its early prediction can improve the outcome of patient care. Trends observed in signals related to blood pressure (BP) are critical in predicting future events. Unfortunately, the invasive measurement of BP signals is neither comfortable nor feasible in all bed settings. In this study, we investigate the performance of machine-learning techniques in predicting hypotensive events in ICU settings using physiological signals that can be obtained noninvasively. We show that noninvasive mean arterial pressure (NIMAP) can be simulated by down-sampling the invasively measured MAP. This enables us to investigate the effect of BP measurement frequency on the algorithm's performance by training and testing the algorithm on a large dataset provided by the MIMIC III database. This study shows that having NIMAP information is essential for adequate predictive performance. The proposed predictive algorithm can flag hypotension with a sensitivity of 84%, positive predictive value (PPV) of 73%, and F1-score of 78%. Furthermore, the predictive performance of the algorithm improves by increasing the frequency of BP sampling.

Non-invasive measurement of pulse pressure variation using a finger-cuff method in obese patients having laparoscopic bariatric surgery

Pulse pressure variation (PPV) is a dynamic cardiac preload variable used to predict fluid responsiveness. PPV can be measured non-invasively using innovative finger-cuff systems allowing for continuous arterial pressure waveform recording, e.g., the Nexfin system [BMEYE B.V., Amsterdam, The Netherlands; now Clearsight (Edwards Lifesciences, Irvine, CA, USA)] (PPV_Finger). However, the agreement between PPV_Finger and PPV derived from an arterial catheter (PPV_ART) in obese patients having laparoscopic bariatric surgery is unknown. We compared PPV_Finger and PPV_ART at 6 time points in 60 obese patients having laparoscopic bariatric surgery in a secondary analysis of a prospective method comparison study. We used Bland–Altman analysis to assess absolute agreement between PPV_Finger and PPV_ART. The predictive agreement for fluid responsiveness between PPV_Finger and PPV_ART was evaluated across three PPV categories (PPV < 9%, PPV 9–13%, PPV > 13%) as concordance rate of paired measurements and Cohen’s kappa. The overall mean of the differences between PPV_Finger and PPV_ART was 0.5 ± 4.6% (95%-LoA − 8.6 to 9.6%) and the overall predictive agreement was 72.4% with a Cohen’s kappa of 0.53. The mean of the differences was − 0.7 ± 3.8% (95%-LoA − 8.1 to 6.7%) without pneumoperitoneum in horizontal position and 1.1 ± 4.8% (95%-LoA − 8.4 to 10.5%) during pneumoperitoneum in reverse-Trendelenburg position. The absolute agreement and predictive agreement between PPV_Finger and PPV_ART are moderate in obese patients having laparoscopic bariatric surgery.

A Feasibility Study of Non-Invasive Continuous Estimation of Brachial Pressure Derived From Arterial and Venous Lines During Dialysis

Objective: Intradialytic haemodynamic instability is a significant clinical problem, leading to end-organ ischaemia and contributing to morbidity and mortality in haemodialysis patients. Non-invasive continuous blood pressure monitoring is not currently part of routine practice but may aid detection and prevention of significant falls in blood pressure during dialysis. Brachial blood pressure is currently recorded intermittently during haemodialysis via a sphygmomanometer. Current methods of continuous non-invasive blood pressure monitoring tend to restrict movement, can be sensitive to external disturbances and patient movement, and can be uncomfortable for the wearer. Additionally, poor patient blood circulation can lead to unreliable measurements. In this feasibility study we performed an initial validation of a novel method and associated technology to continuously estimate blood pressure using pressure sensors in the extra-corporeal dialysis circuit, which does not require any direct contact with the person receiving dialysis treatment. Method: The paper describes the development of the measurement system and subsequent in vivo patient feasibility study with concurrent measurement validation by Finapres Nova physiological measurement device. Real-time physiological data is collected over the entire period of (typically 4-hour) dialysis treatment. Results: We identify a quasi-linear mathematical function to describe the relationship between arterial line pressure and brachial artery BP, which is confirmed in a patient study. The results from this observational study suggest that it is feasible to derive a continuous measurement of brachial pressure from continuous measurements of arterial and venous line pressures via an empirically based and updated mathematical model. Conclusion: The methodology presented requires no interfacing to proprietary dialysis machine systems, no sensors to be attached to the patient directly, and is robust to patient movement during treatment and also to the effects of the cyclical pressure waveforms induced by the hemodialysis peristaltic blood pump. This represents a key enabling factor to the development of a practical continuous blood pressure monitoring device for dialysis patients.

[Principles and pitfalls of arterial blood pressure measurement]

The determination of arterial blood pressure is a fundamental part of basic cardiovascular monitoring in perioperative, intensive care and emergency medicine. Blood pressure can be measured directly via an arterial catheter, which is the most accurate method. Blood pressure is most commonly monitored using noninvasive intermittent methods with an occluding upper arm cuff. Noninvasive intermittent blood pressure measurements can also be performed either manually using palpation and auscultation or automatically based on an oscillometric algorithm. Furthermore, methods such as the vascular unloading technique with a finger plethysmographic sensor are available for continuous and noninvasive blood pressure monitoring. This article explains the principles of the individual methods, the sources of errors, advantages and disadvantages and discusses the fields of application in the clinical routine.

Noninvasive measurement of arterial blood pressure in patients with continuous-flow left ventricular assist devices: a systematic review

Accurate mean blood pressure determination is essential to prevent adverse events in patients with continuous-flow left ventricular assist devices (CFLVAD). We sought to evaluate the accuracy of noninvasive methods of blood pressure measurement compared with invasive intra-arterial recordings in patients with CFLVAD. Systematic electronic search was performed on four online databases (PubMed, Scopus, Embase, and Web of Knowledge) for the terms "Blood Pressure" AND ("Heart-Assist Devices" OR "Left ventricular Assist Devices"). Only studies that compared an intra-arterial and noninvasive blood pressure measurement were included. Electronic search of scientific literature identified 5968 articles. After deduplication, screening of titles and abstracts, full-text review, and excluding incorrect populations and comparator, a total of 12 studies with 502 participants were included, of those 402 participants who had intra-arterial blood pressure measurement. Doppler mean arterial blood pressure showed a very high correlation with mean intra-arterial blood pressure (r = 0.97, r = 0.87) in low pulsatility situations. When the pulsatility was not evaluated, the correlation was high moderate (r = 0.63, r = 0.741). In low pulsatility situations, the correlation was moderate to high moderate (r = 0.42 to r = 0.65). Oscillometer automatic blood pressure cuff showed a moderate to very high correlation with intra-arterial mean arterial blood pressure (r = 0.42, r = 0.86) but also could be low in the context of low pulsatility associated with inconsistent success in noninvasive measurement (r = 0.25). Studies correlating intra-arterial with noninvasive techniques were performed in the context of routine clinical care using fluid-filled catheters. The degree of correlation between both methods is at least moderate.

Accuracy and Reliability of a Disposable Vascular Pressure Device for Arterial Pressure Monitoring in Critical Care Transport

OBJECTIVE

Arterial catheterization is a commonly performed procedure in intensive care units to guide the management of critically ill patients who require precise hemodynamic monitoring; however, this technology is not always available in the transport setting because of cumbersome and expensive equipment requirements. We compared the accuracy and reliability of a disposable vascular pressure device (DVPD) with the gold standard (ie, the transducer pressure bag invasive arterial monitoring system) used in intensive care units to determine if the DVPD can be reliably used in place of the traditional pressure transducer setup.

METHODS

This study was a single-center, prospective, observational study performed in the adult intensive care unit of a large academic university hospital. A convenience cohort of hemodynamically stable, adult critically ill patients with femoral, brachial, or radial arterial catheters was recruited for this study. The Compass pressure device (Centurion Medical Products, Williamston, MI) is a disposable vascular pressure-sensing device used to assure venous access versus inadvertent arterial access during central line placement. The DVPD was attached to an in situ arterial catheter and measures the mean intravascular pressure via an embedded sensor and displays the pressure via the integrated LCD screen. Using a 3-way stopcock, the DVPD was compared with the standard arterial setup. We compared the mean arterial pressure (MAP) in the standard setup with the DVPD using Bland-Altman plots and methods that accounted for repeated measures in the same subject.

RESULTS

Data were collected on 14 of the 15 subjects enrolled. Five measurements were obtained on each patient comparing the DVPD with the standard arterial setup at 1-minute intervals over the course of 5 minutes. A total of 70 observations were made. Among the 15 subjects, most (10 [67%]) were radial or brachial sites. The average MAP scores and standard deviation values obtained by the standard setup were 83.5 mm Hg (14.8) and 81.1 mm Hg (19.3) using the DVPD. Just over half (51.4%) of the measurements were within a ± 5-mm Hg difference. Using Bland-Altman plotting methods, standard arterial measurements were 2.4 mm Hg higher (95% confidence interval, 0.60-4.1) than with the DVPD. Differences between the 2 devices varied significantly across MAP values. The standard arterial line measurements were significantly higher than the DVPD at low MAP values, whereas the DVPD measurements were significantly higher than the standard arterial line at high MAP values.

CONCLUSION

The DVPD provides a reasonable estimate of MAP and may be suitable for arterial pressure monitoring in settings where standard monitoring setups are not available. The DVPD appears to provide "worst-case" values because it underestimates low arterial blood pressure and overestimates high arterial blood pressure. Future trials should investigate the DVPD under different physiological conditions (eg, hypotensive patients, patients with ventricular assist devices, and patients on extracorporeal membrane oxygenation), different patient populations (such as pediatric patients), and in different environments (prehospital, air medical transport, and austere locations).

Cardiovascular dynamics during peroral endoscopic myotomy for esophageal achalasia: a prospective observational study using non-invasive finger cuff-derived pulse wave analysis

Peroral endoscopic myotomy (POEM) is natural orifice transluminal endoscopic surgery to treat esophageal achalasia. During POEM, cardiovascular dynamics can be impaired by capnoperitoneum, capnomediastinum, and systemic carbon dioxide accumulation. We systematically investigated changes in cardiovascular dynamics during POEM. We included 31 patients having POEM in this single-center prospective observational study. Before and every 5 min during POEM we measured mean arterial pressure (MAP), heart rate (HR), cardiac index (CI), stroke volume index (SVI), and systemic vascular resistance index (SVRI) using non-invasive finger cuff-derived pulse wave analysis. During POEM, the median MAP was higher than the median baseline MAP of 77 (67;86) mmHg. HR (median at baseline: 67 (60;72) bpm), CI (2.8 (2.5;3.2) L/min/m²), SVI (42 (34;51) mL/m²), and SVRI (1994 (1652; 2559) dyn × s × cm^-5 × m^-2) remained stable during POEM. Mixed model-derived 95% confidence limits of hemodynamic variables during POEM were 72 to 106 mmHg for MAP, 65 to 79 bpm for HR, 2.7 to 3.3 L/min/m² for CI, 37 and 46 mL/m² for SVI, and 1856 and 2954 dyn × s × cm^-5 × m^-2 for SVRI. POEM is a safe procedure with regard to cardiovascular dynamics as it does not markedly impair MAP, HR, CI, SVI, or SVRI.

Human Vital Signs Detection Methods and Potential Using Radars: A Review

Continuous monitoring of vital signs, such as respiration and heartbeat, plays a crucial role in early detection and even prediction of conditions that may affect the wellbeing of the patient. Sensing vital signs can be categorized into: contact-based techniques and contactless based techniques. Conventional clinical methods of detecting these vital signs require the use of contact sensors, which may not be practical for long duration monitoring and less convenient for repeatable measurements. On the other hand, wireless vital signs detection using radars has the distinct advantage of not requiring the attachment of electrodes to the subject's body and hence not constraining the movement of the person and eliminating the possibility of skin irritation. In addition, it removes the need for wires and limitation of access to patients, especially for children and the elderly. This paper presents a thorough review on the traditional methods of monitoring cardio-pulmonary rates as well as the potential of replacing these systems with radar-based techniques. The paper also highlights the challenges that radar-based vital signs monitoring methods need to overcome to gain acceptance in the healthcare field. A proof-of-concept of a radar-based vital sign detection system is presented together with promising measurement results.

Can we rely on the pulse transit time - pressure relationship - models comparison

An unobtrusive, noninvasive and continuous pressure measurement is invaluable however, still being under research and development. There are many attempts proposing an appropriate relationship between pulse pressure velocity and pressure. Fifteen different formulas, both theoretical and experimental, describing relation between blood pressure and cross-sectional area of the vessel were examined. Using these formulas the relation between blood pressure and pulse transit time were derived. The results obtained show variety of dependences. For some of them an explicit derivation was not possible due to non-linear characteristics of the models. It follows from the study performed that depending on the assumptions accepted, even using the same approach, one can obtain contradictory results.

Blood Pressure Estimation Based on Pulse Arrival Time and Heart Rate : A Correlation Analysis for Critically Ill Patients

Arterial blood pressure (ABP) is a vital hemodynamic signal to be monitored in general population- especially in critically ill patients. Pulse arrival time (PAT) has been widely used for the noninvasive measurement of systolic blood pressure (SBP) and diastolic blood pressure (DBP) and has shown excellent results for a healthy person as compared to the existing gold standard methods. In this study, we have used correlation analysis to study the feasibility of using PAT and heart rate (HR) for noninvasive BP (SBP and DBP) measurement for critically ill subjects. Physiological signals used for this study were collected from the MIMIC-II database of Physionet. Initially, we conducted a correlation analysis and then tried to estimate BP using linear regression. We found that the BP correlation with HR is more as compared with PAT. However, these correlations are not consistent. We have also found that PAT and HR can track the BP change as long as the correlation coefficient lies between ±0.7 and ±1. When the correlation falls below, this noninvasive BP estimation using PAT and HR needs to be revisited and improved for clinical applicability.

Effect of preoperative fluid therapy on hemodynamic stability during anesthesia induction, a randomized study

BACKGROUND

Preserving perfusion pressure during anesthesia induction is crucial. Standardized anesthesia methods, alert fluid therapy and vasoactive drugs may help maintain adequate hemodynamic conditions throughout the induction procedure. In this randomized study, we hypothesized that a pre-operative volume bolus based on lean body weight would decrease the incidence of significant blood pressure drops (BPD) after induction with target-controlled infusion (TCI) or rapid sequence induction (RSI).

METHODS

Eighty individuals scheduled for non-cardiac surgery were randomized to either a pre-operative colloid fluid bolus of 6 ml kg^-1 lean body weight or no bolus, and then anesthetized by means of TCI or RSI. The main outcome measure was blood pressure drops below the mean arterial pressure 65 mm Hg during the first 20 minutes after anesthesia induction. ClinicalTrials.com Identifier: NCT03394833.

RESULTS

Pre-operative fluid therapy decreased the incidence of BPDs fivefold, from 23 of 40 (57.5%) individuals without fluids to 5 of 40 (12.5%) with fluid management, P < .001. The mean BPD was greater in the groups without pre-operative fluids compared to the groups with fluid management; 53 ± 18 mm Hg vs 43 ± 14 mm Hg, P = .007. The overall mean volume of pre-operative fluid bolus infused was 387 ± 52 ml. There was no difference in hemodynamic stability between TCI and RSI. No correlation was shown between incidence of BPDs and increasing age, medication, hypertension, diabetes, renal failure, or low physical capacity.

CONCLUSIONS

Pre-operative fluid bolus decreased the incidence of significant blood pressure drops during TCI and RSI induction of general anesthesia.

Accuracy of non-invasive and minimally invasive hemodynamic monitoring: where do we stand?

One of the most important variables in assessing hemodynamic status in the intensive care unit (ICU) is the cardiac function and blood pressure. Invasive methods such as pulmonary artery catheter and arterial line allow monitoring of blood pressure and cardiac function accurately and reliably. However, their use is not without drawbacks, especially when the invasive nature of these procedures and complications associated with them are considered. There are several newer methods of noninvasive and minimally invasive hemodynamic monitoring available. In this manuscript, we will review these different methods of minimally invasive and non-invasive hemodynamic monitoring and will discuss their advantages, drawbacks and limitations.

Soft Wearable Pressure Sensors for Beat-to-Beat Blood Pressure Monitoring

Wrinkled gold thin films on elastomeric substrates are used as robust parallel plate electrodes for soft capacitive pressure sensors. The wrinkled structures create a robust integration with the polymer, allowing repeated normal force to deform the thin film without failure. By incorporating microridged structures that support the counter electrodes to create air cavities within the elastomeric dielectric layer, pressure sensitivity is further increased to 0.148 kPa^-1 over a wide dynamic range of up to 10 kPa. The wide dynamic range and pressure sensitivity of the pressure sensor allow for consistent measurements of the pressure exerted by the radial artery located on the wrist. The soft capacitive pressure sensor displays comparable results when tested against an FDA approved device (Clearsight, Edwards Lifesciences, Irvine, CA) measuring beat-to-beat blood pressure. These soft pressure sensors using wrinkled thin films, therefore, illustrate considerable potential to continuously monitor beat-to-beat blood pressure.

Development and clinical validation of a non-invasive, beat-to-beat blood pressure monitoring device, compared to invasive blood pressure monitoring during coronary angiography

Objective

To develop and test a beat-to-beat blood pressure monitoring device during coronary angiography, and compare it with invasive blood pressure monitoring.

Methods

Twenty-eight patients with an indication for hemodynamic study were selected for this investigation, and kept in supine position. Before starting the coronary angiography, they were instructed about the use of the left radial bracelet for beat-to-beat blood pressure monitoring.

Results

There was a significant difference between the time required for the catheterization laboratory team to acquire the first invasive blood pressure reading and the time to obtain the first beat-to-beat reading (11.1±5.1 and 1.5±1.8, respectively; p<0.0001). The intraclass correlation coefficients (95%CI) of systolic and diastolic blood pressures were 0.897 (0.780-0.952) and 0.876 (0.734-0.942), indicating good reproducibility.

Conclusion

This study showed the process to develop a beat-to-beat blood pressure monitoring device. When compared to invasive blood pressure monitoring, there were no significant differences between the two methods. This technique may play a promising coadjuvant role when combined with invasive monitoring during coronary angiography procedures.

Continuous non-invasive determination of nocturnal blood pressure variation using photoplethysmographic pulse wave signals: comparison of pulse propagation time, pulse transit time and RR-interval

OBJECTIVE

Cardiovascular diseases are the leading cause of death, whereas nocturnal ambulatory blood pressure (BP) is the most potent predictor for cardiovascular risk. The volume clamp and pulse transit time (PTT) are common methods for continuous non-invasive BP measurement, but have drawbacks during unsupervised ambulatory use and undisturbed sleep. The pulse propagation time (PPT), defined as the time between pulse wave systolic peak and diastolic peak, provides valid information about the pressure pulse waveform. However, the use of PPT for nocturnal BP variation determination and whether such variation is affected by BP or heart rate (i.e. RR-interval or RRI) has not been investigated.

APPROACH

To assess whether the PPT method is suitable for ubiquitous nocturnal BP monitoring, we compared systolic blood pressure (SBP) estimates derived from PPT, PTT, and RRI signals with parallel recorded BP measurements. The RRI-derived SBP signals were used as a baseline for testing a potential heart rate dependency. This work provides an overview of BP measurements, presents the developed real-time signal analysis, and describes the performance assessment. The signal analysis was validated with data records from 42 subjects acquired from an ergometry and sleep laboratory in equal parts.

MAIN RESULTS

The algorithms applied to the ergometry laboratory database achieved a correlation coefficient between reference SBP and estimated SBP_PPT of 0.89 (p  <  0.001) with bias 0.1 mmHg and limits of agreement (LoA)  -29.8 to 30.0 mmHg, SBP_PTT of 0.97 (p  <  0.001) with bias 0.0 mmHg and LoA  -15.2 to 15.3 mmHg, and SBP_RRI of 0.96 (p  <  0.001) with bias 0.0 mmHg and LoA  -19.5 to 19.5 mmHg. For the sleep laboratory database, the correlation coefficient was 0.95 (p  <  0.001) with bias 0.2 mmHg and LoA  -18.3 to 18.8 mmHg for SBP_PPT, 0.88 (p  <  0.001) with bias 0.0 mmHg and LoA  -25.0 to 24.9 mmHg for SBP_PTT, and 0.88 (p  <  0.001) with bias of 0.1 mmHg and LoA  -23.6 to 23.7 mmHg for SBP_RRI. A heart rate dependency of PPT or PTT could not be found. The analysis of variance shows no significant differences between the reference SBP values and the estimated values for either the ergometry (F(3, 627)  =  2.27, p  =  0.08) or the sleep laboratory (F(3, 327)  =  2.28, p  =  0.08).

SIGNIFICANCE

In conclusion, the PPT method seems to be an interesting alternative for continuous determination of SBP during simplified cardiovascular monitoring and sleep screening compared to more expensive devices based on volume clamp or PTT methods.

Discrepancy between invasive and non-invasive blood pressure readings in extremely preterm infants in the first four weeks of life

Background

The agreement between invasive and non-invasive blood pressure (BP) readings in the first days of life of preterm infants is contentiously debated.

Objective

To compare mean, systolic and diastolic invasive (IBP) and non-invasive BP (NBP) readings obtained during routine care in the first four weeks of life of extremely preterm infants.

Methods

We extracted pairs of IBP and NBP readings obtained from preterm infants born below 28 weeks of gestation from the local database. After exclusion of erroneous measurements, we investigated the repeated measures correlation and analyzed the agreement (bias) and precision adjusted for multiple measurements per individual.

Results

Among 335 pairs of IBP and NBP readings obtained from 128 patients, we found correlation coefficients >0.65 for mean, systolic and diastolic BP values. The bias for mean BP readings was -0.4 mmHg (SD 6.1), for systolic BP readings 6.2 mmHg (SD 8.1), and for diastolic BP readings -4.3 mmHg (SD 6.5). Overestimation of systolic IBP and underestimation of diastolic IBP by the non-invasive measurement were found both in the group with gestational age from 23 to 25.9 weeks and in the group with gestational age from 26 to 27.9 weeks. Systolic NBP readings tended to exceed invasive readings in the range <50 mmHg (bias 9.9 mmHg) whereas diastolic NBP readings were lower than invasive values particularly in the range >30 mmHg (bias -5.5 mmHg).

Conclusion

The disagreement between invasive and non-invasive BP readings in infants extends to the first four weeks of life. Biases differ for mean, systolic and diastolic BP values. Our observation implies that they may depend on the range of the blood pressure. Awareness of these biases and preemptive concomitant use of IBP and NPB readings may contribute to reducing over- or under-treatment.

Validation of the mobile wireless digital automatic blood pressure monitor using the cuff pressure oscillometric method, for clinical use and self-management, according to international protocols

The purpose of this study was to evaluate the accuracy of a mobile wireless digital automatic blood pressure monitor for clinical use and mobile health (mHealth). In this study, a manual sphygmomanometer and a digital blood pressure monitor were tested in 100 participants in a repetitive and sequential manner to measure blood pressure. The guidelines for measurement used the Korea Food & Drug Administration protocol, which reflects international standards, such as the American National Standard Institution/Association for the Advancement of Medical Instrumentation SP 10: 1992 and the British Hypertension Society protocol. Measurements were generally consistent across observers according to the measured mean ± SD, which ranged in 0.1 ± 2.6 mmHg for systolic blood pressure (SBP) and 0.5 ± 2.2 mmHg for diastolic blood pressure (DBP). For the device and the observer, the difference in average blood pressure (mean ± SD) was 2.3 ± 4.7 mmHg for SBP and 2.0 ± 4.2 mmHg for DBP. The SBP and DBP measured in this study showed accurate measurements that satisfied all criteria, including an average difference that did not exceed 5 mmHg and a standard deviation that did not exceed 8 mmHg. The mobile wireless digital blood pressure monitor has the potential for clinical use and managing one's own health.

Verification of exercise-induced transient postural tachycardia phenotype in Gulf War Illness

One third of Gulf War Illness (GWI) subjects in a recent study were found to develop transient postural tachycardia after submaximal exercise stress tests. Post-exercise postural tachycardia is a previously undescribed physiological finding. A new GWI cohort was studied to verify this novel finding and characterize this cardiovascular phenomenon. Subjects followed the same protocol as before. The change in heart rate between recumbent and standing postures (ΔHR) was measured before exercise, and after submaximal bicycle exercise. About one-fourth of the verification cohort (14/57) developed transient postural tachycardia after submaximal exercise. These subjects were the Stress Test Activated Reversible Tachycardia (START) phenotype. The largest change was observed between pre-exercise and time points 2 ± 1 (mean ± SD) hours post exercise (1^st Peak Effect). Eleven subjects had Postural Tachycardia Syndrome (POTS) before and after exercise. The remaining subjects had normal ΔHR (12 ± 5 bpm) and no 1^st Peak Effect, and were the Stress Test Originated Phantom Perception phenotype (STOPP). These findings indicate that about one-fourth of all Gulf War Illness study participants (24/90) developed transient postural tachycardia after the submaximal exercise stress test. The START phenotype was defined as being distinctly different from POTS. Additional studies are required to examine this phenomenon in other illnesses and to determine pathological mechanisms.