Intra-arterial Blood Pressure Research Articles

Flexible adaptive sensing tonometry for medical-grade multi-parametric hemodynamic monitoring

Continuous hemodynamic monitoring in a wearable means can play a crucial role in managing hypertension and preventing catastrophic cardiovascular events. In this study, we have described the fully wearable tonometric device, referred to as flexible adaptive sensing tonometry (FAST), which is capable of continuous and accurate monitoring of hemodynamic parameters within the medical-grade precision. In particular, the FAST system integrates a 1 × 8 unit array of highly sensitive and highly flexible iontronic sensing (FITS) with 1 mm spatial resolution and a closed-loop motion system. The flexible tonometric architecture has been used to determine the radial arterial position with high sensitivity and high conformability, which simplifies the biaxial searching process of the traditional applanation tonometry into a highly efficient uniaxial applanation while keeping the medical-precision assessments. Importantly, a self-calibration algorithm can be automatically implemented during the applanation process, from which the intra-arterial blood pressure wave can be continuously predicted within the medical-grade precision, and subsequently, multi-parametric hemodynamic analysis can be performed in real-time. Experimental validations on health volunteers have demonstrated that the FAST measurements are all within the required accuracy of the clinical standards for continuous pulse wave assessments, blood pressure monitoring as well as other key hemodynamic parameter evaluations. Therefore, the FAST system, by integrating the flexible iontronic sensing array, provides a real-time, medical-grade hemodynamic monitoring solution in a continuously wearable manner, from which remote patient-centered monitoring can be delivered with both medical precision and convenience.

Comparison of forearm and intra-arterial blood pressure measurements according to body and arm positions in obese patients.

Noninvasive blood pressure (BP) monitoring is very important also difficult for accurate diagnosis and monitor of obese patients. The study aimed to assess the agreement between forearm arm BP and intra-arterial BP values in a different body and arm positions in obese patients. The descriptive study was carried out on 60 intensive care patients with a body mass index above 30 kg/m2 who were monitored with invasive radial BP in the general and surgical intensive care units. BP values obtained from the upper arm and forearm with different arm and body positions were compared with intra-arterial BP results. Bland-Altman analysis and correlation coefficient were used for the accuracy of upper and forearm noninvasive BP reading in different positions. The best agreement was found between the forearm systolic BP in the supine and half-sitting position with the arm down and intra-arterial BP values. Also, the best agreement in diastolic BP was found between the half-sitting and half-sitting position with the arm down and intra-arterial BP. Forearm systolic BP measurement, especially in the supine and half-sitting position with the arm below the heart level position, was best agreement with intra-arterial measurement, regarded as the gold standard. For this reason, it is more appropriate to use forearm BP measurement in obese patients monitored in intensive care to obtain accurate results.

Agreement between noninvasive oscillometric and invasive intra-arterial blood pressure in children with ruptured brain arteriovenous malformations

BackgroundDivergence between intra-arterial catheters blood pressure (ABP) and noninvasive oscillometry (NIBP) may affect the care of children with brain arteriovenous malformations (bAVMs). We described the agreement between ABP and NIBP in these children. MethodsWe conducted a retrospective review of patients admitted to the pediatric intensive care unit between 2017 and 2023 with bAVM rupture. Paired ABP and NIBP measurements were collected. Bland-Altman analyses were used to assess agreement. Correlation analysis was conducted between higher ABP and divergence between systolic BP (SBP) measurements. Hypertension was defined as mean arterial pressure (MAP) exceeding age-based 95th percentile. ResultsThirty-four patients with 1901 BP pairs were observed. Bias overall was acceptable, but standard deviation (SD) was high. The best agreement of MAP was in non-hypertensive (bias 1.23 mmHg, SD 8.03 mmHg) and radial arterial catheters (bias 1.83 mmHg, SD 9.08 mmHg) subgroups. Bias for SBP was higher in hypertension (10.98 mmHg) and in infratentorial bAVMs (7.42 mmHg), suggesting poorer agreement in these subgroups. There were significant correlations between intra-arterial MAP and SBP divergence (R = +0.346, p<.001) and between intra-arterial SBP and SBP divergence (R = +0.677, p<.001), suggesting divergence widens with higher BP. Around 25 % of measurement pairs diverged to where one measurement crossed the clinical threshold for treatment, while the other did not, with ABP being more frequently higher than NIBP. ConclusionsThere is good agreement between ABP and NIBP, particularly in non-hypertensive ranges and with radial arterial catheters. Measurements, however, diverge in hypertension. Further research must define age-based thresholds, validate methods of BP measurement, and determine the effect of BP reduction on outcomes in these children.

Validation of oscillometric ratio and maximum gradient methods for non-invasive blood pressure measurement with intra-arterial blood pressure measurements as reference.

Most non-invasive blood pressure (BP) measurements are carried out using instruments which implement either the Ratio or the Maximum Gradient oscillometric method, mostly during cuff deflation, but more rarely during cuff inflation. Yet, there is little published literature on the relative advantages and accuracy of these two methods. In this study of 40 lightly sedated individuals aged 64.1 ± 9.6 years, we evaluate and compare the performance of the oscillometric ratio (K) and gradient (Grad) methods for the non-invasive estimation of mean pressure, SBP and DBP with reference to invasive intra-arterial values. There was no significant difference between intra-arterial estimates of mean pressure made via Korotkoff sounds (MP-OWE) or the gradient method (MP-Grad). However, 17.7% of MP-OWE and 15% of MP-Grad were in error by more than 10 mmHg. SBP-K and SBP-Grad underestimated SBP by 14 and 18 mmHg, whilst accurately estimating DBP with mean errors of 0.4 ± 5.0 and 1.7 ± 6.1 mmHg, respectively. Relative to the reference standard SBP-K, SBP-Grad and DBP-Grad were estimated with a mean error of -4.5 ± 6.6 and 1.4 ± 5.6 mmHg, respectively, noting that using the full range of recommended ratios introduces errors of 12 and 7 mmHg in SBP and DBP, respectively. We also show that it is possible to find ratios which minimize the root mean square error (RMSE) and the mean error for any particular individual cohort. We developed linear models for estimating SBP and SBP-K from a range of demographic and non-invasive OWE variables with resulting mean errors of 0.15 ± 5.6 and 0.3 ± 5.7 mmHg, acceptable according to the Universal standard.

Measuring blood pressure from Korotkoff sounds as the brachial cuff inflates on average provides higher values than when the cuff deflates

Objectives. In this study, we test the hypothesis that if, as demonstrated in a previous study, brachial arteries exhibit hysteresis as the occluding cuff is deflated and fail to open until cuff pressure (CP) is well below true intra-arterial blood pressure (IAPB), estimating systolic (SBP) and diastolic blood pressure (DBP) from the presence of Korotkoff sounds (KS) as CP increases may eliminate these errors and give more accurate estimates of SBP and DBP relative to IABP readings. Approach. In 62 subjects of varying ages (45.1 ± 19.8, range 20.6–75.8 years), including 44 men (45.3 ± 19.4, range 20.6–75.8 years) and 18 women (44.4 ± 21.4, range 20.9–75.3 years), we sequentially recorded SBP and DBP both during cuff inflation and cuff deflation using KS. Results. There was a significant (p < 0.0001) increase in SBP from 122.8 ± 13.2 to 127.6 ± 13.0 mmHg and a significant (p = 0.0001) increase in DBP from 70.0 ± 9.0 to 77.5 ± 9.7 mmHg. Of the 62 subjects, 51 showed a positive increase in SBP (0–14 mmHg) and 11 subjects showed a reduction (−0.3 to −7 mmHg). The average differences for SBP and DBP estimates derived as the cuff inflates and those derived as the cuff deflates were 4.8 ± 4.6 mmHg and 2.5 ± 4.6 mmHg, not dissimilar to the differences reported between IABP and non-invasive blood pressure measurements. Although we could not develop multiparameter linear or non-linear models to explain this phenomenon we have clearly demonstrated through ANOVA tests that both body mass index (BMI) and pulse wave velocity are implicated, supporting the hypothesis that the phenomenon is associated with age, higher BMI and stiffer arteries. Significance. The implications of this study are that brachial sphygmomanometry carried out during cuff inflation could be more accurate than measurements carried out as the cuff deflates. Further research is required to validate these results with IAPB measurements.

Functional Outcomes Associated With Blood Pressure Decrease After Endovascular Thrombectomy

The associations between blood pressure (BP) decreases induced by medication and functional outcomes in patients with successful endovascular thrombectomy remain uncertain. To evaluate whether BP reductions induced by intravenous BP medications are associated with poor functional outcomes at 3 months. This cohort study was a post hoc analysis of the Outcome in Patients Treated With Intra-Arterial Thrombectomy-Optimal Blood Pressure Control trial, a comparison of intensive and conventional BP management during the 24 hours after successful recanalization from June 18, 2020, to November 28, 2022. This study included 302 patients who underwent endovascular thrombectomy, achieved successful recanalization, and exhibited elevated BP within 2 hours of successful recanalization at 19 stroke centers in South Korea. A BP decrease was defined as at least 1 event of systolic BP less than 100 mm Hg. Patients were divided into medication-induced BP decrease (MIBD), spontaneous BP decrease (SpBD), and no BP decrease (NoBD) groups. The primary outcome was a modified Rankin scale score of 0 to 2 at 3 months, indicating functional independence. Primary safety outcomes were symptomatic intracerebral hemorrhage within 36 hours and mortality due to index stroke within 3 months. Of the 302 patients (median [IQR] age, 75 [66-82] years; 180 [59.6%] men), 47 (15.6%)were in the MIBD group, 39 (12.9%) were in the SpBD group, and 216 (71.5%) were in the NoBD group. After adjustment for confounders, the MIBD group exhibited a significantly smaller proportion of patients with functional independence at 3 months compared with the NoBD group (adjusted odds ratio [AOR], 0.45; 95% CI, 0.20-0.98). There was no significant difference in functional independence between the SpBD and NoBD groups (AOR, 1.41; 95% CI, 0.58-3.49). Compared with the NoBD group, the MIBD group demonstrated higher odds of mortality within 3 months (AOR, 5.15; 95% CI, 1.42-19.4). The incidence of symptomatic intracerebral hemorrhage was not significantly different among the groups (MIBD vs NoBD: AOR, 1.89; 95% CI, 0.54-5.88; SpBD vs NoBD: AOR, 2.75; 95% CI, 0.76-9.46). In this cohort study of patients with successful endovascular thrombectomy after stroke, MIBD within 24 hours after successful recanalization was associated with poor outcomes at 3 months. These findings suggested lowering systolic BP to below 100 mm Hg using BP medication might be harmful.

Evaluation of the oscillometric method for noninvasive blood pressure measurement during cuff deflation and cuff inflation with reference to intra-arterial blood pressure.

There is little quantitative clinical data available to support blood pressure measurement accuracy during cuff inflation. In this study of 35 male and 5 female lightly anaesthetized subjects aged 64.1 ± 9.6 years, we evaluate and compare the performance of both the oscillometric ratio and gradient methods during cuff deflation and cuff inflation with reference to intra-arterial measurements. We show that the oscillometric waveform envelopes (OWE), which are key to both methods, exhibit significant variability in both shape and smoothness leading to at least 15% error in the determination of mean pressure (MP). We confirm the observation from our previous studies that K1 Korotkoff sounds underestimate systolic blood pressure (SBP) and note that this underestimation is increased during cuff inflation. The estimation of diastolic blood pressure (DBP) is generally accurate for both the ratio and the gradient method, with the latter showing a significant increase during inflation. Since the gradient method estimates SBP and DBP from points of maximum gradient on each OWE recorded, it may offer significant benefits over the ratio method. However, we have shown that the ratio method can be optimized for any data set to achieve either a minimum mean error (ME) of close to 0 mmHg or minimum root mean square error (RMSE) with standard deviation (SD) of <5.0 mmHg. We conclude that whilst cuff inflation may offer some advantages, these are neither significant nor substantial, leaving as the only benefit, the potential for more rapid measurement and less patient discomfort.

Comparison of cuff inflation and cuff deflation brachial sphygmomanometry with intra-arterial blood pressure as reference.

Conventional sphygmomanometry with cuff deflation is used to calibrate all noninvasive BP (NIBP) instruments and the International Standard makes no mention of calibrating methods specifically for NIBP instruments, which estimate systolic and diastolic pressure during cuff inflation rather than cuff deflation. There is however increasing interest in inflation-based NIBP (iNIBP) instruments on the basis of shorter measurement time, reduction in maximal inflation pressure and improvement in patient comfort and outcomes. However, we have previously demonstrated that SBP estimates based on the occurrence of the first K1 Korotkoff sounds during cuff deflation can underestimate intra-arterial SBP (IA-SBP) by an average of 14 ± 10 mmHg. In this study, we compare the dynamics of intra-arterial blood pressure (IABP) measurements with sequential measurement of Korotkoff sounds during both cuff inflation and cuff deflation in the same individual. In 40 individuals aged 64.1 ± 9.6 years (range 36-86 years), the overall dynamic responses below the cuff were similar, but the underestimation error was significantly larger during inflation than deflation, increasing from 14 ± 10 to 19 ± 12 mmHg ( P < 0.0001). No statistical models were found which could compensate for this error as were found for cuff deflation. The statistically significant BP differences between inflation and deflation protocols reported in this study suggest different behaviour of the arterial and venous vasculature between arterial opening and closing which warrant further investigation, particularly for iNIBP devices reporting estimates during cuff inflation. In addition, measuring Korotkoff sounds during cuff inflation represents significant technical difficulties because of increasing pump motor noise.

The accuracy of radial artery applanation tonometry and intra-arterial blood pressure monitoring in critically ill patients: An evidence-based review.

The invasive intra-arterial approach is the gold standard for measuring blood pressure in intensive care units where accuracy is crucial. However, invasive procedures increase the risk of infections and mortality. This evidence-based review aimed to determine whether continuous non-invasive blood pressure (CNIBP) monitoring, using Radial Artery Applanation Tonometry (RAAT) devices, is as accurate as invasive methods. Six papers were included: three prospective cohort studies and three comparative studies. Most studies showed that mean arterial pressure is accurately recorded through RAAT monitoring; however, more research is needed to assess the accuracy of non-invasive readings of systolic and diastolic blood pressures, as data are not always concordant.

Cochlear Implantation with Fontan Circulation: A Rare Case of Non-Cardiac Pediatric Surgery

Background: Fontan circulation is a cardiac circulation following the Fontan procedure in patients with a single ventricle congenital heart defect. This circulation depends on the difference in pressure between pulmonary capillaries and central venous pressure to achieve optimal cardiac output. This case report aims to discuss intraoperative anesthesia management in a patient with Fontan circulation undergoing a non-cardiac surgical operation.&#x0D; Case presentation: The patient is a 7-year-old male with a history of congenital heart disease who has undergone the Fontan circulation procedure and is now undergoing Cochlear implantation surgery. The patient was managed with general anesthesia - endotracheal intubation and controlled ventilation during the operation, following the principle of minimizing intrathoracic positive pressure, low PEEP, and low tidal volume with a target peripheral saturation &gt; 95%. Cardiac output monitoring during the intraoperative period is done using intra-arterial blood pressure. After 5 hours of surgery, the patient was extubated with stable hemodynamics. &#x0D; Conclusion: The primary goal of intraoperative anesthesia management in patients with Fontan circulation is to maintain an optimal transpulmonary gradient by ensuring optimal transpulmonary blood flow, thus preserving cardiac output.

Abstract 16382: Inaccuracy of Non-Invasive Brachial Cuff-Measured Blood Pressure During Surgery

Introduction: Blood pressure (BP) is an essential vital sign to be monitored during surgery. BP is measured only by Non-Invasive brachial Cuff-measured Blood Pressure (NICBP) devices in 90% of surgeries in US. However, previous studies demonstrated possible inaccuracy of NICBP. The inaccuracy of BP during surgery is a significant public concern because it can result in missing therapeutic potentials and consequently increasing cardiovascular risks during and after surgery. However, there is no large study to evaluate the accuracy of NICBP measured during surgery. Method: It has been known that invasive intra-arterial blood pressure (IABP) measured by an arterial line catheter is an optimal reference for validation of NICBP accuracy given its highest level of accuracy. Our study collected 2,814,154 pairs of BP measurements between NICBP and IABP which were measured at the same time during surgery from 38,706 patients who received surgeries at University of California, Los Angeles from 2016 through 2023. Result: We evaluated the accuracy of NICBP compared to IABP using Confusion matrix analysis (Fig 1). We defined predicted BP classification when BP is classified by NICBP. We also defined actual BP classification when BP is classified by IABP. We categorized BP according to Mean Arterial Pressure (MAP; mmHg) into 5 groups; MAP&lt;65, 65≤MAP&lt;75, 75≤MAP&lt;95, 95≤MAP&lt;105, and 105≤MAP. True Positive rates of each classification ranged from 36.7% to 66.7% (Fig 1). It was surprising that 49.9% in actual MAP (aMAP)&lt;65, 56.9% in 65≤aMAP&lt;75, 33.9% in 75≤aMAP&lt;95, 63.4% in 95≤aMAP&lt;105, and 50.6% in 105≤ aMAP was misclassified into the incorrect BP classifications by NICBP. Conclusion: Our study demonstrated noticeable inaccuracy of BP by NICBP compared to IABP during surgery. Given high reliability solely on NICBP in measuring BP during the majority of surgery cases, the inaccuracy of NICBP may cause significant public health concerns due to unoptimized BP management during surgery.

Cerebral Blood Flow Assessed with Phase-contrast Magnetic Resonance Imaging during Blood Pressure Changes with Noradrenaline and Labetalol: A Trial in Healthy Volunteers.

Adequate cerebral perfusion is central during general anesthesia. However, perfusion is not readily measured bedside. Clinicians currently rely mainly on mean arterial pressure (MAP) as a surrogate, even though the relationship between blood pressure and cerebral blood flow is not well understood. The aim of this study was to apply phase-contrast magnetic resonance imaging to characterize blood flow responses in healthy volunteers to commonly used pharmacologic agents that increase or decrease arterial blood pressure. Eighteen healthy volunteers aged 30 to 50 yr were investigated with phase-contrast magnetic resonance imaging. Intra-arterial blood pressure monitoring was used. First, intravenous noradrenaline was administered to a target MAP of 20% above baseline. After a wash-out period, intravenous labetalol was given to a target MAP of 15% below baseline. Cerebral blood flow was measured using phase-contrast magnetic resonance imaging and defined as the sum of flow in the internal carotid arteries and vertebral arteries. Cardiac output (CO) was defined as the flow in the ascending aorta. Baseline median cerebral blood flow was 772 ml/min (interquartile range, 674 to 871), and CO was 5,874 ml/min (5,199 to 6,355). The median dose of noradrenaline was 0.17 µg · kg-1 · h-1 (0.14 to 0.22). During noradrenaline infusion, cerebral blood flow decreased to 705 ml/min (606 to 748; P = 0.001), and CO decreased to 4,995 ml/min (4,705 to 5,635; P = 0.01). A median dose of labetalol was 120 mg (118 to 150). After labetalol boluses, cerebral blood flow was unchanged at 769 ml/min (734 to 900; P = 0.68). CO increased to 6,413 ml/min (6,056 to 7,464; P = 0.03). In healthy, awake subjects, increasing MAP using intravenous noradrenaline decreased cerebral blood flow and CO. These data do not support inducing hypertension with noradrenaline to increase cerebral blood flow. Cerebral blood flow was unchanged when decreasing MAP using labetalol.

Blood pressure variability from intra-arterial pressure recordings in humans

Objectives: The study presents the magnitude of variation of systolic and diastolic pressures over a few minutes from intra-arterial pressure recordings in 51 hemodynamically stable patients in an intensive care unit. Materials and Methods: Conscious surgical ICU patients, with arterial pressure cannulae placed as the standard of care, were recruited after obtaining informed consent. A validated data acquisition system was used to record intra-arterial blood pressure for a period of 10 minutes following a Fast-Flush test. Only those recordings with acceptable dynamic characteristics as per Gardner’s criteria were included in the analysis. Results: Three categories of systolic and diastolic pressure variability namely “beat-to-beat” variability, “Respiratory” variability, and “Total magnitude of variation” during the duration of recording, were reported for each of the 51 patients. The mean (± SD) of the total magnitude of variation for systolic and diastolic pressures in the study sample were 21 ± 9 mmHg and 14 ± 5 mmHg respectively. Conclusion: Given the magnitude of systolic and diastolic pressure variations over a few minutes, the validity of reporting single- point values for these pressures and using single-point cut-offs for diagnosis and treatment of hypertension must be re-evaluated.

Experimental renal transplantation in rats improves cardiac dysfunction caused by chronic kidney disease while LVH persists.

Chronic kidney disease (CKD) causes congestive heart failure (CHF) with systolic dysfunction and left ventricular hypertrophy (LVH), which is a major contributor to increased mortality in CKD patients. It remains unclear whether cardiovascular changes that occur during the course of CKD can be reversed when renal function is restored by transplantation. To investigate this, chronic kidney disease was established in F344 rats by subtotal nephrectomy (SNx) for 8 weeks, followed by transplantation of a functional kidney from an isogenic F344 donor. SNx rats without transplantation and sham-operated animals served as controls. Renal function was assessed before and throughout the experiment. In addition, cardiac ultrasound was performed at weeks 0, 8, 12 and 16. At the end of the experiment, intra-arterial blood pressure was measured and kidneys and hearts were histologically and molecularly examined. Eight weeks after SNx, rats developed marked renal dysfunction associated with significant glomerulosclerosis and tubulointerstitial fibrosis, but also an increase in left ventricular mass. After transplantation, renal function normalized but relative heart weight and ventricular mass as assessed by ultrasound scans showed no reduction compared with SNx controls. However, left ventricular wall thickness, fractional shortening and ejection fraction was normalized by renal transplantation. At 8 weeks after kidney transplantation, cardiac expression of BNP and FGF23 was also at levels comparable to healthy controls, whereas these factors were significantly increased in SNx rats. Cardiac fibrosis, as measured by fibronectin mRNA expression, was completely normalized, whereas cardiac fibronectin protein was still slightly but not significantly increased in transplanted animals compared to controls. In addition, the myofibroblast marker collagen 1, as assessed by immunohistochemistry, was significantly increased in SNx rats and also normalized by renal transplantation. Interestingly, CD68+ macrophages were significantly reduced in the hearts of SNx rats and in transplanted animals at slightly higher levels compared to controls. Restoration of renal function by kidney transplantation normalized early cardiac changes at most functional and molecular levels, but did not completely reverse LVH. However, further studies are needed to determine whether restoration of renal function can also reverse LVH at a later time point.

CAN RECORDING KOROTKOFF SOUNDS DURING BRACHIAL CUFF INFLATION PROVIDE MORE ACCURATE NON-INVASIVE ESTIMATES OF INTRA-ARTERIAL BLOOD PRESSURE?

Objective: We have previously demonstrated that recording onset and termination of Korotkoff sounds as markers of systolic (SBP) and diastolic (DBP) during brachial cuff deflation results in underestimation of true SBP. In this study we explore whether recording Korotkoff sounds during cuff inflation provides more accurate non-invasive estimates of intra-arterial blood pressure (IABP). Design and method: Experiments were carried out on 15 participants, (14 males, 64.3 ± 10.4 years; one female, 86 yo), undergoing coronary angiography. A conventional (oscillometric) BP cuff, with a microphone for Korotkoff sounds, was placed on the upper arm. The cuff was inflated at rate of approximately 2.5mm Hg/sec and deflated at the same rate. Inflation and deflation cycles were randomised and separated by 2 - 3 minutes. IABP was measured below the cuff with a fluid-filled catheter inserted via the radial artery and an external transducer. Korotkoff sounds were processed electronically, and custom algorithms identified the cuff pressure (CP) at which the first and last Korotkoff sounds were heard. Results: Systolic (SBP), and diastolic (DBP) pressure were 147.7.6 ± 12.7 and 70.7 ± 9.7mmHg. The CP at which the brachial artery closes during rapid (∼20mmHg/sec) cuff inflation (132.0 ± 17.1) was similar to that of slow (2.5mmHg/sec) inflation (132.0 ± 16.3 mmHg). However, peak Korotkoff sound energy was significantly reduced (P = 0.003) from 0.19 ± 0.1 to 0.15 ± 0.09 RMS volts and the Korotkoff sounds were often observed to disappear prematurely before brachial artery closure. Difference between intra-arterial SBP and CP at the last recorded Korotkoff sound (27.5 ± 9.3 mmHg) during cuff inflation was significantly higher (P = 0.0025) than during slow cuff deflation (18.9 ± 8.3 mmHg). In contrast, DBP recorded at first onset of the Korotkoff sounds (70.5 ± 11.1 mmHg) was consistently similar to intra-arterial DBP (70.7 ± 9.7 mmHg). Conclusions: SBP estimates derived from the last Korotkoff sound recorded as the cuff inflates generates greater errors than when Korotkoff sounds are first recorded as the cuff deflates. In contrast, the estimate of DBP derived from the first onset of the Korotkoff sound as the cuff inflates, appears to reflect accurately the true intra-arterial DBP.

KOROTKOFF SOUNDS DO NOT PROVIDE AN ACCURATE ESTIMATE OF SYSTOLIC AND DIASTOLIC PRESSURE IN SPHYGMOMANOMETRY AND CANNOT BE USED AS A CALIBRATION STANDARD FOR NIBP DEVICES

Objective: Noninvasive blood pressure (NIBP) devices are calibrated against validated auscultation sphygmomanometers using Korotkoff sounds. This study aimed to investigate the timing of Korotkoff sounds in relation to pulse appearance in the brachial artery and values of intra-arterial blood pressure. Design and method: Experiments were carried out on 15 participants, (14 males, 64.3 ±10.4 years; one female, 86 yo), undergoing coronary angiography. A conventional (oscillometric) BP cuff, with a microphone for Korotkoff sounds, was placed on the upper arm. Intra-arterial brachial artery pressure (IABP) was measured below the cuff with a fluid-filled catheter inserted via the radial artery and an external transducer. Finger photoplethysmography was used to measure brachial pulse wave velocity (PWV). Korotkoff sounds were processed electronically and custom algorithms identified the cuff pressure (CP) at which the first and last Korotkoff sounds were heard. PWV and max slope of the IABP pressure pulse were recorded to estimate arterial stiffness. Results: The brachial artery closed at a CP of 132.0±17.1 mmHg. Systolic (SBP), and diastolic (DBP) pressure were 147.6±14.3 and 72.7±10.1mmHg; mean pressure (MP, 100.1±10.4 mmHg) was similar to MP derived from the peak of the oscillogram (98.5±13.6 mmHg). Difference between IABP and CP recorded at first and last occurrence of Korotkoff sounds were, SBP: 18.9±8.3 (range 2-29) mmHg, DBP: 4.0±4.3 (range -1.6 -12.4) mmHg. Multiple linear regression showed that differences increase with arterial stiffness and can be compensated for using a prediction equation for calculation of true SBP (tSBP) using heart rate (HR) and Korotkoff derived systolic (SBPk) and diastolic (DBPk), at least over the limited age range for this study cohort. Conclusions: SBP and DBP derived from the onset and termination of Korotkoff sounds can underestimate IABP by up to 29 mmHg. Since Korotkoff sounds are the recommended method mandated by the universal standard for the validation of blood pressure measuring devices, these errors are propagated through to all NIBP measurement devices irrespective of whether they use auscultatory or oscillometric methods thus explaining the well known differences recorded between NIBP measurements and intra-arterial BP measurements.

Optimizing the input feature sets and machine learning algorithms for reliable and accurate estimation of continuous, cuffless blood pressure

The advent of mobile devices, wearables and digital healthcare has unleashed a demand for accurate, reliable, and non-interventional ways to measure continuous blood pressure (BP). Many consumer products claim to measure BP with a cuffless device, but their lack of accuracy and reliability limit clinical adoption. Here, we demonstrate how multimodal feature datasets, comprising: (i) pulse arrival time (PAT); (ii) pulse wave morphology (PWM), and (iii) demographic data, can be combined with optimized Machine Learning (ML) algorithms to estimate Systolic BP (SBP), Diastolic BP (DBP) and Mean Arterial Pressure (MAP) within a 5 mmHg bias of the gold standard Intra-Arterial BP, well within the acceptable limits of the IEC/ANSI 80601-2-30 (2018) standard. Furthermore, DBP’s calculated using 126 datasets collected from 31 hemodynamically compromised patients had a standard deviation within 8 mmHg, while SBP’s and MAP’s exceeded these limits. Using ANOVA and Levene’s test for error means and standard deviations, we found significant differences in the various ML algorithms but found no significant differences amongst the multimodal feature datasets. Optimized ML algorithms and key multimodal features obtained from larger real-world data (RWD) sets could enable more reliable and accurate estimation of continuous BP in cuffless devices, accelerating wider clinical adoption.

Hemoglobin and cerebral hypoxic vasodilation in humans: Evidence for nitric oxide-dependent and S-nitrosothiol mediated signal transduction.

Cerebral hypoxic vasodilation is poorly understood in humans, which undermines the development of therapeutics to optimize cerebral oxygen delivery. Across four investigations (total n = 195) we investigated the role of nitric oxide (NO) and hemoglobin-based S-nitrosothiol (RSNO) and nitrite () signaling in the regulation of cerebral hypoxic vasodilation. We conducted hemodilution (n = 10) and NO synthase inhibition experiments (n = 11) as well as hemoglobin oxygen desaturation protocols, wherein we measured cerebral blood flow (CBF), intra-arterial blood pressure, and in subsets of participants trans-cerebral release/uptake of RSNO and . Higher CBF during hypoxia was associated with greater trans-cerebral RSNO release but not , while NO synthase inhibition reduced cerebral hypoxic vasodilation. Hemodilution increased the magnitude of cerebral hypoxic vasodilation following acute hemodilution, while in 134 participants tested under normal conditions, hypoxic cerebral vasodilation was inversely correlated to arterial hemoglobin concentration. These studies were replicated in a sample of polycythemic high-altitude native Andeans suffering from excessive erythrocytosis (n = 40), where cerebral hypoxic vasodilation was inversely correlated to hemoglobin concentration, and improved with hemodilution (n = 6). Collectively, our data indicate that cerebral hypoxic vasodilation is partially NO-dependent, associated with trans-cerebral RSNO release, and place hemoglobin-based NO signaling as a central mechanism of cerebral hypoxic vasodilation in humans.

Impact of atrial fibrillation on the accuracy of oscillometric blood pressure monitoring in ICU patients from a large real-world database.

Oscillometric blood pressure (BP) measurement in atrial fibrillation patients is controversial due to stroke volume variation. Here, we performed a cross-sectional study to investigate the impact of atrial fibrillation on the accuracy of oscillometric BP in the ICU setting. Adult patients with atrial fibrillation or sinus rhythm records were enrolled from Medical Information Mart for Intensive Care-III database. Concurrently recorded noninvasive oscillometric BPs (NIBPs) and intra-arterial BPs (IBPs) were classified as atrial fibrillation or sinus rhythm group according to heart rhythm. Bland-Altmann plots assessed bias and limits of agreement of NIBP to IBP. Pairwise comparison was performed on NIBP/IBP bias between atrial fibrillation and sinus rhythm. Linear mixed-effect model was used to assess the impact of heart rhythm on NIBP/IBP bias after adjusting confounders. Two thousand, three hundred and thirty-five patients (71.95 ± 11.23 years old, 60.90% were men) were included. Systolic, diastolic, and mean NIBP/IBP biases were not clinically different between atrial fibrillation and sinus rhythm circumstances (SBP bias: 0.66 vs. 1.21 mmHg, P = 0.002; DBP: -5.29 vs. -5.17, P = 0.1; mean BP: -4.45 vs. -4.19, P = 0.01). After adjusting for age, sex, heart rate, arterial BP, and vasopressor usage, the effect of heart rhythm on NIBP/IBP bias was within ±5 mmHg for SBP and DBP [effect on SBP bias: 3.32 mmHg (95% confidence interval (CI) 2.89-3.74), P < 0.001; DBP: -0.89 (-1.17 to -0.60), P < 0.001], while the effect on mean BP bias was not significant [0.18 mmHg (-0.10 to 0.46), P = 0.2]. Atrial fibrillation would not influence the agreement of oscillometric BP to IBP in ICU patients compared with sinus rhythm.

Variations of Blood Pressures in Lean Zucker Rats Fed Low or High Fat Diets

The purpose of this study was to determine whether lean (Fa/?) Zucker rats which exhibit greater metabolic efficiency in response to a high (48%) fat diet also exhibit hypertension. Twenty-nine lean (Fa/?) and eleven obese (fa/fa) Zucker rats were fed low (12% energy) and high (48% energy) fat diets. Food intake and weight change were recorded weekly to obtain an index of energy efficiency. After 6 wk, direct intra-arterial blood pressure was measured in conscious, unrestrained animals. Arterial blood was collected for analyses of plasma insulin and glucose. The high fat diet had no effect on blood pressure in obese rats, although obese animals fed both diets had significantly higher blood pressure than lean siblings. High fat feeding in lean rats unmasked a heterogeneity in blood pressure. Blood pressure in this group was significantly correlated with weight change, energy efficiency ratio and plasma glucose concentration. Lean rats fed the high fat diet with blood pressures above the group median exhibited significantly greater plasma insulin (P < 0.02) and glucose (P < 0.01) concentration and energy efficiency ratios (P < 0.01) than those with lower blood pressures. Thus, it appears that there were two groups of lean animals present, one of which was more phenotypically sensitive to high fat feeding than the other. This suggests a possible gene dosage effect of the fa allele in the Zucker rat model.