Non-invasive continuous blood pressure measurement based on mean impact value method, BP neural network, and genetic algorithm

As an essential physiological indicator within the human body, noninvasive continuous blood pressure (BP) measurement is critical in the prevention and treatment of cardiovascular disease. However, traditional methods of blood pressure prediction using a single-wavelength Photoplethysmographic (PPG) have bottlenecks in further improving BP prediction accuracy, which limits their development in clinical application and dissemination. To this end, this study proposed a method to fuse a four-wavelength PPG and a BP prediction model based on the attention mechanism of a convolutional neural network and bidirectional long- and short-term memory (ACNN-BiLSTM). The effectiveness of a multi-wavelength PPG fusion method for blood pressure prediction was evaluated by processing PPG signals from 162 volunteers. The study compared the performance of the PPG signals with different individual wavelengths and using a multi-wavelength PPG fusion method in blood pressure prediction, assessed using mean absolute error (MAE), root mean squared error (RMSE) and AAMI-related criteria. The experimental results showed that the ACNN-BiLSTM model achieved a better MAE ± RMSE for a systolic BP and diastolic BP of 1.67 ± 5.28 and 1.15 ± 2.53 mmHg, respectively, when using the multi-wavelength PPG fusion method. As a result, the ACNN-BiLSTM blood pressure model based on multi-wavelength PPG fusion could be considered a promising method for noninvasive continuous BP measurement.

IntroductionThe intra-arterial catheter (invasive method) is the clinical and reference standard for continuous blood pressure (BP) monitoring. Continuous noninvasive blood pressure (CNBP) monitoring methods, for example applanation tonometry, volume clamp, and cuffless BP monitoring devices are gaining popularity. This review clarified the evidence on the accuracy of CNBP monitoring devices, which could potentially replace invasive monitoring in clinical care.MethodsA systematic search was carried out to look for systematic reviews with the following elements:Population: patients needing continuous BP monitoring;Intervention: CNBP monitoring devices;Comparator: intra-arterial BP monitoring; andOutcomes: accuracy of BP monitoring.The databases searched included PubMed (MEDLINE), Epistemonikos, and the Cochrane Database of Systematic Reviews. Two reviewers independently reviewed the search results and shortlisted relevant articles for retrieval of full texts. Included reviews were critically appraised with the AMSTAR 2 instrument and the findings were summarized in a narrative synthesis.ResultsThree systematic reviews with meta-analyses of fairly good quality were included. The included primary studies were conducted in perioperative or critical care settings. Subgroup analyses by CNBP monitoring method were included in each meta-analysis. The findings from the systematic reviews were consistent. On average, CNBP devices consistently measured lower systolic BPs than the invasive method (mean difference <0) and measured higher diastolic BPs and mean arterial pressures than the invasive method (mean difference >0), with wide ranging 95 percent limits of agreement. It was evident from subgroup analyses that the measurements obtained from different CNBP methods varied significantly.ConclusionsThis rapid review found the accuracy of CNBP monitoring devices to be suboptimal in comparison with invasive monitoring. CNBP devices should not be routinely used but may be considered when there is difficult arterial access, or in patients who do not require arterial puncture for other purposes.

BackgroundArterial catheters are often used for blood pressure monitoring in the intensive care unit (ICU), but they can cause complications. Non-invasive continuous finger blood pressure monitors could serve as an alternative. However, failure to obtain finger blood pressure signals is reported in up to 12% of ICU patients. ObjectivesOur primary objective was to identify the success rate of finger blood pressure monitoring in ICU patients. Secondary objectives were to assess whether patient admission characteristics could be used to identify patients unsuitable for non-invasive blood pressure monitoring and to determine the quality of non-invasive blood pressure waveforms. MethodsRetrospective observational study conducted in a cohort of 499 ICU patients. When available, the signal quality of the first hour of finger measurement was determined using an open-source waveform algorithm. ResultsFinger blood pressure signals were obtained in 94% of patients. These patients had a high quality blood pressure waveform for 84% of the measurement time. Patients without a finger blood pressure signal significantly more frequently had a history of kidney and vascular disease, were more often treated with inotropic agents, had lower hemoglobin levels, and had higher arterial lactate levels. ConclusionsFinger blood pressure signals were obtained in nearly all ICU patients. Significant differences in baseline characteristics between patients with and without finger blood pressure signals were found, but they were not clinically relevant. The characteristics studied could therefore not be used to identify patients unsuitable for finger blood pressure monitoring.

Objective: To explore the effect of continuous non-invasive blood pressure monitoring on intraoperative hemodynamics and postoperative myocardial injury in craniotomy. Methods: 120 cases of elective craniotomy were divided into the self-control group (continuous non-invasive blood pressure monitoring and intermittent cuff non-invasive blood pressure monitoring, CNAP group) and propensity score matching group (only intermittent cuff non-invasive blood pressure measurement in previous craniotomy, PSM group); Goal-directed hemodynamic management in CNAP group included heart rate (HR), blood pressure (BP), stroke volume (SV), stroke variability (SVV), and systemic vascular resistance index (SVRI). The main index is to compare the troponin level within 72 hours after operation between the CNAP group and the PSM group; The secondary indicators are the comparison of the hemodynamic conditions between the CNAP group and the PSM at 10 specific time points. Results: The incidence of postoperative myocardial injury in the CNAP group was significantly lower than that in the PSM group (12% vs. 30%, P = 0.01); in the CNAP group hypotensive episodes (6 vs. 3, P = 0.01), positive balance of fluid therapy (700 vs. 500 mL, P &lt; 0.001), more use of vasoactive drugs (29 vs. 18, P = 0.04), more stable hemodynamics medical status (P = 0.03) were recorded. Conclusion: The hemodynamic management strategy based on continuous non-invasive blood pressure monitoring can reduce the incidence of myocardial injury after elective craniotomy and maintain a more stable hemodynamic state.

In patients undergoing general anaesthesia, intraoperative hypotension occurs frequently and is associated with adverse outcomes such as postoperative acute kidney failure, myocardial infarction or stroke. A history of chronic hypertension renders patients more susceptible to a decrease in blood pressure (BP) after induction of general anaesthesia. As a patient's BP is generally monitored intermittently via an upper arm cuff, there may be a delay in the detection of hypotension by the anaesthetist. The current study investigates whether the presence of continuous BP monitoring leads to improved BP stability. Randomised, controlled and single-centre study. A total of 160 orthopaedic patients undergoing general anaesthesia with a history of chronic hypertension. The patients were randomised to either a study group (n = 77) that received continuous non-invasive BP monitoring in addition to oscillometric intermittent monitoring, or a control group (n = 83) whose BP was monitored intermittently only. The interval for oscillometric measurements in both groups was set to 3 min. After induction of general anaesthesia, oscillometric BP values of the two groups were compared for the first hour of the procedure. Anaesthetists were blinded to the purpose of the study. BP stability and hypotensive events. There was no difference in baseline BP between the groups. After adjustment for multiple testing, mean arterial BP in the study group was significantly higher than in the control group at 12 and 15 min. Mean ± SD for study and control group, respectively were: 12 min, 102 ± 24 vs. 90 ± 26 mmHg (P = 0.039) and 15 min, 102 ± 21 vs. 90 ± 23 mmHg (P = 0.023). Hypotensive readings below a mean pressure of 55 mmHg occurred more often in the control group (25 vs. 7, P = 0.047). Continuous monitoring contributes to BP stability in the studied population. NCT02519101.

The T-Line TL-200 (Tensys Medical, San Diego, CA, USA) is a non-invasive arterial blood pressure (BP) monitoring system allowing continuous "beat-to-beat" monitoring of systolic arterial pressure (SAP), mean arterial pressure (MAP), and diastolic arterial pressure (DAP). It provides a real-time BP waveform like that obtained using an arterial catheter. The aim of this study was to compare BP measurements obtained using the T-Line TL-200 with simultaneous invasive BP measurements using a femoral arterial catheter in unselected critically ill medical patients. In 28 patients treated in a medical intensive care unit (ICU), BP values were simultaneously obtained using a femoral arterial catheter and the T-Line TL-200. All recorded data were included in the final analysis. For comparison of BP measurements, Bland-Altman analysis accounting for repeated measurements was performed (primary endpoint). A total of 76,826 pairs of BP measurements (each consisting of SAP, MAP, and DAP) were analyzed. For MAP, Bland-Altman analysis revealed a mean difference of +0.47 mmHg (95 % limits of agreement -16.53 to +17.46 mmHg). For SAP and DAP, the bias and 95 % limits of agreement were -9.01 mmHg (-37.47 to +19.45 mmHg) and +5.22 mmHg (-13.50 to +23.94 mmHg), respectively. Non-invasive, continuous, radial BP measurement with the T-Line TL-200 is basically feasible in medical ICU patients (with a low bias for MAP compared to MAP assessed using a femoral arterial catheter). High limits of agreement (particularly of SAP and DAP) preclude the use of the device as a single source of BP information in unstable critically ill patients.

The innovative vascular unloading technology (VUT) allows continuous noninvasive arterial blood pressure (AP) monitoring. We aimed to investigate whether the VUT enables AP changes to be detected earlier compared with intermittent AP monitoring in patients undergoing gastrointestinal endoscopy. In this prospective observational study, we recorded continuous AP measurements with the VUT (CNAP system; CNSystems Medizintechnik AG, Graz, Austria) and intermittent AP measurements with upper arm cuff oscillometry in 90 patients undergoing complex gastrointestinal endoscopy (Department of Interventional Endoscopy at the University Medical Center Hamburg-Eppendorf, Hamburg, Germany). A "hypotensive phase" was defined as a time period of at least 30s during which ≥ 50% of the VUT-AP values were in a predefined range of hypotension, i.e., AP value a) ≥ 10% below the last oscillometric value and b) ≤ 65mmHg for mean AP or ≤ 90mmHg for systolic AP. In the 5-min-interval between two oscillometric measurements, one or more hypotensive phases were detected in 26 patients (29%) for mean AP and in 27 patients (30%) for systolic AP. Hypotensive phases had a mean duration of 195 ± 99s for mean AP and 197 ± 97s for systolic AP with a mean procedure duration of 36 (± 21) min. Continuous noninvasive AP monitoring using the VUT enables hypotensive phases to be detected earlier compared with intermittent AP monitoring during complex gastrointestinal endoscopy. These hypotensive phases may be missed or only belatedly recognized with intermittent AP monitoring. Continuous noninvasive AP measurement facilitates detecting hemodynamic instability more rapidly and therefore may improve patient safety.

Article CNAP – Evolution of Continuous Non-Invasive Arterial Blood Pressure Monitoring was published on September 7, 2013 in the journal Biomedical Engineering / Biomedizinische Technik (volume 58, issue SI-1-Track-G).

The Finapres is a noninvasive monitor that continuously displays the arterial waveform, pulse rate, and systolic, mean, and diastolic blood pressure. We determined its bias (mean prediction error) and precision (mean absolute error), relative to directly measured radial arterial blood pressure, in 16 otherwise healthy patients undergoing spinal fusion surgery under hypotensive anesthetic techniques. Data were recorded during three contiguous epochs: 20 min of normotension; 30 min following the initiation of hypotension; 20 min of hypotension. The Finapres demonstrated a systolic, mean, and diastolic bias (+/- standard deviation) of 3.6 +/- 12.3, 5.2 +/- 10.8, and 8.3 +/- 9.4 mmHg, respectively. There were no significant differences in systolic bias among the epochs, whereas mean and diastolic bias were both greater during the hypotensive epoch, compared to the normotensive epoch. In 2 of the 16 patients, systolic and mean arterial pressure bias exceeded 20 mmHg. Finapres precisions of systolic, mean, and diastolic blood pressures were 9.8 +/- 9.0, 8.7 +/- 7.6, and 10.4 +/- 8.2 mmHg, respectively. Precisions among the epochs were not significantly different. When Finapres pressures were "corrected" by subtracting the baseline difference between Finapres and oscillometrically determined mean pressure, bias decreased significantly. The correction process did not improve precision. The Finapres closely tracked changes in blood pressure, even in the presence of a large bias. In most patients, the Finapres is a useful continuous noninvasive blood pressure monitor. Periodic calibration of the Finapres by the difference between Finapres and oscillometrically determined mean arterial pressure is recommended.

In this paper, we propose a compact, wearable biosensor for the noninvasive measurement of human radial artery pulse waveform curve (PWC) and blood pressure (BP). In this system, self-mixing interferometry (SMI) technology is employed to measure the weak arterial vascular deformation, enabling accurate PWC retrieval. Based on the reconstructed PWC features, BP values are precisely estimated by means of deep learning method. Here continuous wavelet transform (CWT), enabling visualization of the relationship between the SMI signal temporal frequency components and the PWC characteristics, is highlighted for PWC flipping points seeking and convolutional neural network (CNN) input parameter acquisition. For the first time, a novel deep learning network preprocessing method is proposed that allows direct feature extraction from the CWT scalogram of SMI signal without the complicated PWC reconstruction algorithm. The robustness and accuracy of our device are validated by a series of clinical measurements, mean absolute error (MAE) and standard deviation (STD) values are calculated and compared with the existing models. We approach minimal BP estimation results (MAE ± STD) of 1.41 ± 1.89 mmHg for systolic blood pressure (SBP) and 1.78 ± 2.01 mmHg for diastolic blood pressure (DBP), respectively. The luxuriant novelties and remarkable performance clearly demonstrate our wearable sensor’s great potential in BP monitoring, and other clinical applications.

Blood pressure (BP) measurement is regarded as one of the most important parameters in the clinical evaluation of patients. It is helpful in both acute and chronic cases. Most medical examinations include BP measurement as it is the best indicator of cardiovascular health. In some cases, it is very important to examine the status of pressure valves continuously for long time periods. To prevent premature death, it can be used for daily health-care monitoring. The main problem with BP measurement is that all existing techniques use an inflatable cuff which is a discrete technique and may cause discomfort for the patients. Recently, few alternative techniques have been developed for non-invasive continuous measurement of BP. This review focuses on brief discussion of some of the methods for BP measurement both invasive and non-invasive and due to fewer side-effects and convenience of attachment of sensors of photoplethysmogram (PPG), this review mainly focuses on the plethysmography technique using pulse transit time for BP measurement. At present, many researchers are working on this method, and it has the potential to be the most widely used technique for a long time non-invasive continuous observation of BP in the future. This review also briefly discussed some of the artifact removal techniques in the PPG waveform and inaccuracies related to sensors due to the external factors such as noise and temperature.

Noninvasive continuous blood pressure (BP) monitoring is not yet practically available for daily use. Challenges include making the system easily wearable, reducing noise level and improving accuracy. Variations in each person's physical characteristics, as well as the possibility of different postures, increase the complexity of continuous BP monitoring, especially outside the hospital. This study attempts to provide an easily wearable solution and proposes training to specific posture and individual for further improving accuracy. The wrist watch-based system we developed can measure electrocardiogram and photoplethysmogram. From these two signals, we measure pulse transit time through which we can obtain systolic and diastolic blood pressure through regression techniques. In this study, we investigate various functions to perform the training to obtain blood pressure. We validate measurements on different postures and subjects, and show the value of training the device to each posture and each subject. We observed that the average RMSE between the measured actual systolic BP and calculated systolic BP is between 7.83 to 9.37 mmHg across 11 subjects. The corresponding range of error for diastolic BP is 5.77 to 6.90 mmHg. The system can also automatically detect the arm position of the user using an accelerometer with an average accuracy of 98%, to make sure that the sensor is kept at the proper height. This system, called BioWatch, can potentially be a unified solution for heart rate, SPO2 and continuous BP monitoring.

ObjectiveThis study aimed to investigate the accuracy and precision of continuous, non-invasive blood pressure obtained using the ClearSight system by comparing it with invasive arterial blood pressure, and to assess the hemodynamic changes using invasive methods and the ClearSight system in patients undergoing cesarean section.MethodsArterial pressure was measured invasively with an intra-arterial catheter and non-invasively using the ClearSight system during cesarean section in patients with placenta previa or placenta accreta. Blood pressure measurements obtained using these two means were then compared.ResultsTotal 1,277 blood pressure measurement pairs were collected from 21 patients. Under Bland-Altman analysis, the ClearSight system demonstrated an acceptable accuracy with a bias and standard deviation of 8.8±13.4 mmHg for systolic blood pressure, −6.3±7.1 mmHg for diastolic blood pressure, and −2.7±8.0 mmHg for median blood pressure. Cardiac index levels were significantly elevated during fetal delivery and 5 minutes after placental removal, and systemic vascular resistance index levels were significantly decreased during fetal delivery and 40 minutes after placental removal.ConclusionIn patients undergoing cesarean section, the ClearSight system showed excellent accuracy and precision compared to that of the currently used invasive monitoring system.

Noninvasive continuous or intermittent blood pressure and heart rate patient monitoring in the ED

Research on a feature selection method based on median impact value for modeling in thermal power plants