Pressure Measurement Technology Research Articles

Development of Non-Invasive Continuous Blood Pressure Measurement System Based on Multiple Feature Parameters

To address the issue of the difficulty in implementing non-invasive continuous blood pressure measurement technology in China, this study developed a high-performance synchronous electrocardiogram (ECG) and photoplethysmography (PPG) signal acquisition system. A PC-based human-computer interaction software platform was constructed, and continuous blood pressure measurement-related algorithms were integrated. Multiple feature parameters such as pulse wave transit time based on synchronous ECG and PPG signals were extracted, enabling non-invasive continuous blood pressure measurement. To verify the measurement accuracy of the system, tests and comparative verifications were carried out. The results demonstrated that the system could meet the requirements of relevant standards and have good application value.

Discussion on the upper limit of HIFU sound pressure measurement based on laser interferometry

Abstract High intensity focused ultrasound (HIFU) technology is a non-invasive treatment technique that can achieve non-invasive treatment of tumors and other diseases. The accuracy of HIFU sound pressure is crucial for the clinical efficacy and safety of HIFU treatment. The sound pressure measurement technology based on laser interferometry is the recommended method for ICE TC87, which has the advantages of high measurement accuracy and good traceability, and is therefore widely adopted as the new generation of sound pressure standards. However, the upper limit of the laser interferometric HIFU sound pressure measurement currently reported is about 10 MPa, which is far lower than the actual sound pressure of HIFU technology. In response to this issue, the upper limit of HIFU sound pressure measurement was discussed from the perspective of laser interference systems. The mathematical relationship between the HIFU sound pressure and the optical and electrical signals of the laser interference system under the condition of nonlinear sound field is established. The mathematical analysis of HIFU sound pressure requirements for the bandwidth of laser interference systems is discussed. Using experimental and numerical simulation methods, the effect of HIFU sound pressure on the bandwidth of a laser interference system under nonlinear acoustic field conditions was studied.

In-shoe plantar pressure measurement technologies for the diabetic foot: A systematic review

IntroductionLoss of cutaneous protective sensation and high plantar pressures increase the risk for diabetic foot patients. Trauma and ulceration are imminent threats, making assessment and monitoring essential. This systematic review aims to identify systems and technologies for measuring in-shoe plantar pressures, focusing on the at-risk diabetic foot population. MethodsA systematic search was conducted across four electronic databases (Scopus, Web of Science, PubMed, Oxford Journals) using PRISMA methodology, covering articles published in English from 1979 to 2024. Only studies addressing systems or sensors exclusively measuring plantar pressures inside the shoe were included. ResultsA total of 87 studies using commercially available devices and 45 articles proposing new systems or sensors were reviewed. The prevailing market offerings consist mainly of instrumented insoles. Emerging technologies under development often feature configurations with four, six or eight resistive sensors strategically placed within removable insoles. Despite some variability due to the inherent heterogeneity of human gait, these devices assess plantar pressure, although they present significant differences between them in measurement results. Individuals with diabetic foot conditions appears exhibit elevated plantar pressures, with reported peak pressures reaching approximately 1000 kPa. The results also showed significant differences between the diabetic and non-diabetic groups. ConclusionInstrumented insoles, particularly those incorporating resistive sensor technology, dominate the field. Systems employing eight sensors at critical locations represent a pragmatic approach, although market options extend to systems with up to 960 sensors. Differences between devices can be a critical factor in measurement and highlights the importance of individualized patient assessment using consistent measurement devices.

A Survey on Blood Pressure Measurement Technologies: Addressing Potential Sources of Bias.

Regular blood pressure (BP) monitoring in clinical and ambulatory settings plays a crucial role in the prevention, diagnosis, treatment, and management of cardiovascular diseases. Recently, the widespread adoption of ambulatory BP measurement devices has been predominantly driven by the increased prevalence of hypertension and its associated risks and clinical conditions. Recent guidelines advocate for regular BP monitoring as part of regular clinical visits or even at home. This increased utilization of BP measurement technologies has raised significant concerns regarding the accuracy of reported BP values across settings. In this survey, which focuses mainly on cuff-based BP monitoring technologies, we highlight how BP measurements can demonstrate substantial biases and variances due to factors such as measurement and device errors, demographics, and body habitus. With these inherent biases, the development of a new generation of cuff-based BP devices that use artificial intelligence (AI) has significant potential. We present future avenues where AI-assisted technologies can leverage the extensive clinical literature on BP-related studies together with the large collections of BP records available in electronic health records. These resources can be combined with machine learning approaches, including deep learning and Bayesian inference, to remove BP measurement biases and provide individualized BP-related cardiovascular risk indexes.

Normative Values of Static-dynamic Plantar Pressure and its Cutoff Values

Pressure measurement technology is being increasingly used by physical therapists, podiatric physicians, and surgeons in both clinical practice and research. Plantar pressure was recently proposed as a strong predictor of adverse outcomes. Few reviews have been conducted to identify a standard for the plantar pressure in healthy participants, older people, and children. The aims of this study were to explore currently available normative values of static-dynamic plantar pressure and its cutoff values. The SCOPUS, Rehabilitation, MEDLINE, EBSCO, PEDro, and PubMed electronic databases were systematically searched from January 2000 to December 2022. All articles were analyzed using a standardized template to extract various data, such as the first author's details, publication year, country of origin, participant age and gender, sample size, population characteristics, instrument used for measurement, plantar pressure distribution (PPD) type, normative data, and cutoff values. In literature review, the researchers selected nine studies, and in all studies, they selected different areas of foot for normative values. Areas selected for PPD were forefoot, hallux, big toe, second toe, third through fifth toes, toes 2–5, metatarsal 1–5, lateral forefoot, middle forefoot, medial forefoot, midfoot, lateral midfoot, medial forefoot, lateral area of the heel, medial area of the heel, heel, right foot total, left foot total, and right + left total. Age, gender, and body mass index (BMI) affect the results of the plantar pressure. It is necessary to take age, gender, and BMI into consideration when conducting stratified physical evaluations for the evaluation of older people individuals’ screening and outcome.

Measurement of interfacial shear stress in gas–liquid two-phase stratified flow

Gas–liquid two-phase stratified flow exists in many industrial processes. Although the flow pattern is simple, the interfacial shear prediction of stratified flow is still the focus of the study. The calculation of the shear stress at the gas–liquid interface is closely related to the measurement of the void fraction and pressure drop of the stratified flow. In this study, a new method for the calculation of interfacial shear stress of gas–liquid two-phase stratified flow is proposed. Differential pressure measurement and planar laser-induced fluorescence technology are combined to obtain important parameters for stratified flow under low-speed flow conditions (Ql = 0.10–0.25 m3/h, Qg = 0.35–1.00 m3/h). The interfacial shear stress is successfully calculated using macroparameters. The uncertainty associated with the calculated parameters using the proposed method is 2.67%, and this study verifies the accuracy of the linear relationship. The method provides a new way to obtain the interfacial shear stress of gas–liquid stratified flow.

Development and clinical validation of a miniaturized finger probe for bedside hemodynamic monitoring

Our aim is to develop a blood pressure (BP) measurement technology that could be integrated into a finger-worn pulse oximeter, eliminating the need for a brachial cuff. We present a miniature cuffless tonometric finger probe system that uses the oscillometric method to measure BP. Our approach uses a motorized press that is used to apply pressure to the fingertip to measure BP. We verified the functionality of the device in a clinical trial (n= 43) resulting in systolic and diastolic pressures ((mean± SD) mmHg) of (-3.5± 8.4) mmHg and (-4.0± 4.4) mmHg, respectively. Comparison was made with manual auscultation (n= 26) and automated cuff oscillometry (n= 18). In addition to BP, we demonstrated the ability of the device to assess arterial stiffness (n= 18) and detect atrial fibrillation (n= 6). We were able to introduce a sufficiently small device that could be used for convenient ambulatory measurements with minimal discomfort.

Experimental study of methane explosion containing coal dust in flame instability and pressure variation process

It is important to understand the evolution process of an explosion flow field for accident prevention. This study investigated the effects of low coal dust concentrations on gas explosion characteristics by incorporating coal dust into air-methane gas mixtures (the volume fraction of methane is 12.5%, 9.5% and 6.5%, respectively) in a cylindrical combustion chamber for conducting explosion experiments. Pressure measurement and laser schlieren technology were used to record explosion pressure variations and to capture flame schlieren images. The results revealed that the flame radius shrank with elevated coal dust concentration at the initial stage of explosion. At a methane concentration of 6.5%, the flame appeared to float up, and the explosion reaction intensity increased with higher coal dust content. The flame spread out in a spherical morphology was observed at 9.5% and 12.5% methane concentrations. With elevated coal dust concentration, increased the maximum explosion pressure and pressure rise rate first, then decreased it. The dynamic coupling of flame instability propagation and pressure had a limited effect on the rising explosion pressure. In addition to providing experimental data for validating and enhancing the kinetic mechanism of gas-dust chemical reactions, these findings provide in-depth insight into prevention and management of coal-mine catastrophes.

Experimental study on transition of dynamic airfoil in pitching oscillation

The transition characteristics of dynamic airfoil have significant effects on the aerodynamic performance of wind turbines, helicopter rotor blades, jet engine compressor blades, etc. The time domain and time-frequency domain characteristics of transition on a NACA0012 airfoil during its pitching oscillation were experimentally studied using wall pressure measurement technology with high time accuracy in this paper. The variable slip window technology was used to detect the transition position, and the proper orthogonal decomposition (POD) method and wavelet analysis were combined to perform the time-frequency analysis. In the gradual forward movement of the transition, the low-frequency instability is gradually enhanced by the main flow and the inverse pressure gradient, and significantly submerges the high-frequency fluctuated feature. The higher order moments of the wall pressure during dynamic airfoil transition deviate significantly from the Gaussian characteristics, which is caused by the low-frequency instability and high-frequency burst. The POD method is able to distinguish low-frequency instability from the high-frequency feature. The reduced frequency had significant effects on the transition. With the increase of the reduced frequency, the hysteresis effect of the transition became more and more significant, and the frequency component of transition was more concentrated and the energy was stronger.

Ultra-high-sensitivity gas pressure sensor based on a cascaded Fabry-Perot interferometer and the Vernier effect

Subject of study. An ultra-sensitive gas pressure sensor based on a cascaded Fabry-Perot interferometer is proposed. Purpose of the work. In the proposed sensor, we greatly improve the gas pressure sensitivity of the sensor by using the optical Vernier effect method. Method. During the fabrication of the sensor, one Fabry-Perot interferometer is used as the sensing interferometer, and the other Fabry-Perot interferometer is used as the reference interferometer. Both Fabry-Perot interferometers are fabricated by two sections of single-mode fiber spliced at both ends of a section of a quartz capillary. Then, a micro-hole is drilled in the capillary wall of the sensing Fabry-Perot interferometer by using femtosecond laser micro-processing technology for gas pressure measurement. When the free spectral ranges of two Fabry-Perot interferometers are similar, the optical Vernier effect will be generated by cascading them. By precisely controlling the cavity length difference between two Fabry-Perot interferometers, a very high sensitivity magnification factor can be obtained. Main results. The experimental results show that the sensitivity of the Vernier effect sensor is 133.2 nm/MPa in the pressure measurement range of 0–0.8 Mpa, which is 33.3 times higher than that of the single sensor Fabry-Perot interferometer. In addition, the temperature cross-sensitivity of the sensor is relatively small, only 0.93 kPa/°C. The sensor is flexible in design and easy to manufacture and operate. Practical significance. The proposed sensor has extremely high gas pressure sensitivity, and it can be used in the fields of chemical production, pharmaceuticals, oil and gas storage, and environmental protection for high-sensitivity gas pressure measurement.

JS-HR-5: APPROPRIATE BLOOD PRESSURE ASSESSMENT METHODS FOR THE PREVENTION OF HYPERTENSION COMPLICATIONS BY NEW TECHNOLOGIES

Blood pressure (BP) values can vary and fluctuate widely depending on the method and the environment of BP measurement. Appropriate measurement and interpretation of BP values enable us to make an accurate diagnosis and treatment of hypertension. The BP measuring approach is shifting from traditional methods (office BP, ambulatory and home BP monitoring) to wearable devices and technology. Self-measured BP as well as BP measured by wearable devices gives us frequent BP values, which allows us to detect high risk population and to reduce cardiovascular risks. In this session, we will introduce the latest papers on “Hypertension management and device” in the “Hypertension Research up-to-date 2021. ∼ Current topics of hypertension journals.∼” This session will also introduce the significance of blood pressure measurement and the latest blood pressure measurement technologies.

S-37-6: THE PROMISE OF CUFFLESS BLOOD PRESSURE MONITORING IN MANAGING HYPERTENSION

Although blood pressure measurement is perhaps the most common measurement done in clinical practice, many have started to challenge this procedure and calling for transformation in blood pressure monitoring. This is because blood pressure measurement in primary care has many problems, whether clinic, 24-hour ambulatory or home blood pressures are taken. Cuffless blood pressure measurement technologies have been knocking on the door for years, with the first patents already registered over 20 years ago. With advancements in data science, machine learning, artificial intelligence, and mobile phone technologies, many start-ups and major global tech giants are now presenting to the end-user an array of highly innovative technologies. Cuffless monitoring includes many devices from wrist-worn watch-type devices to mobile phone tech (transdermal optical facial video processing or oscillometric finger pressing), wearable ultrasound patches, temporary graphene electronic tattoos, glasses, and even from a toilet seat. These technologies has a major benefit, namely blood pressure being taken without any user awareness. But it also has the potential to harness long-term prognostic cardiovascular information over and beyond blood pressure that may become particularly useful. Continuous long-term cuffless monitoring will provide for the first time the opportunity to move from averaging snapshot readings to capturing the continuous dynamic fluctuations of blood pressure in a high-definition video recording. There are, however, still several hurdles that need to be overcome before cuffless technologies can be implemented in clinical care. While biomedical engineers may exert their energy on ensuring that a cuffless innovation can accurately reflect brachial blood pressure, this is not the only aspect to consider. Manufacturers of conventional cuff-based devices have to painstakingly follow the ISO 81060–2:2018 Universal Standard to validate the device for accuracy. The rules are different for cuffless devices. Novel cuffless technologies vary substantially and use many techniques such as pulse transit time, pulse wave analyses, and ultrasound. The key question is whether these devices can accurately track the dynamic changes in blood pressure over time. Currently, an ISO 81060–3 standard is being developed to validate cuffless devices but due to the heterogenous technologies used by cuffless manufacturers there are major challenges. For this and other reasons, the European Society of Hypertension has released a consensus statement that due to fundamental questions regarding the accuracy, performance and implementation of cuffless devices in practice, these devices cannot be recommended for clinical use, while recognising the considering potential.

In Situ Volume Recovery Method for Non-Seal Gas Pressure Measurement Technology: A Comparative Study.

Coal seam gas pressure is one of the basic parameters for coalbed methane resource exploitation and coal mine gas disaster prevention. However, the present coal seam gas pressure measurement technology requires harsh field measurement conditions and a long testing period. In this study, a novel non-seal gas pressure measurement technology is proposed, and this technology is mainly aimed at three different changes before and after the collection of coal samples and realizes the real gas pressure measurement through the compensation of gas leakage, in situ volume recovery of the coal core, and reservoir temperature simulation. The technique not only can measure the original gas pressure of coal seam quickly and accurately but also does not need to seal the measuring hole. This paper focuses on the study of a key factor that affects the accuracy of non-seal gas pressure measurement: the restoration of in situ volume. Based on this, the influence of four different in situ volume recovery methods on the measurement accuracy is compared with the self-developed non-sealing gas pressure measuring system. Experimental results show that the in situ volume of the coal core cannot be completely restored by stress loading. Although the contact injection method can restore the original volume of the coal core, the pressure recovery error is large due to the replacement and displacement of the gas effect of water and the inclusion of the coal body effect of oil. Interestingly, the combination of stress loading and contact oil injection can not only restore the original volume of the coal core but also minimize the pressure recovery error, which is only less than 10%. Finally, based on the abovementioned experimental results, the in situ volume recovery method of non-seal gas pressure measurement technology is improved. Therefore, the research results of this paper provide a scientific basis for the field application of non-seal gas pressure measurement technology.

Noninvasive blood oxygen, heartbeat rate, and blood pressure parameter monitoring by photoplethysmography signals

The popularization of long-term invasive tools for continuously monitoring blood pressure remains challenging. However, with the rising popularity of wearable personal health management devices, non-cuff blood pressure measurement technology that applies electrocardiography (ECG) and photoplethysmography (PPG) has gradually received increasing attention. In particular, whether blood pressure can be measured continuously by the PPG signal alone is of great interest. In this study, we aim to develop a device that includes systolic and diastolic blood pressure calculation formulas derived from characteristic waveform points in the PPG time domain and that can measure blood oxygenation and heart rate. This device applies empirical formulas developed by PPG waveforms in the PhysioNet MIMIC-II database to calculate blood pressure. The systolic and diastolic pressures are then compared with the actual blood pressures obtained from invasive blood pressure waveforms to verify the effectiveness and feasibility of the complete developed system. Overall, 263 waveforms with double peaks and 261 waveforms with only a single peak totaling 524 sets of data are used to derive the empirical formulas. The systolic blood pressure estimation result using single peak analysis has an excessively large error exceeding ±40 mmHg, providing no reference value. However, systolic blood pressure estimation is notably better in double peak analysis, with error values reducing to approximately 23 mmHg. Diastolic pressure estimation errors are low with both single (±7 mmHg) and double peak (±4 mmHg) analyses. The error is lower in double-peak analysis than in single-peak analysis for obtaining systolic pressure from PPG waves. We plan to use PPG to detect additional physiological parameters in the future, e.g., respiratory rate, heart rate variability, or irregular heartbeat, to further enhance the functionality of PPG-based wearable devices.

Blood pressure monitoring techniques in the natural state of multi-scenes: A review.

Blood pressure is one of the basic physiological parameters of human physiology. Frequent and repeated measurement of blood pressure along with recording of environmental or other physiological parameters when measuring blood pressure may reveal important cardiovascular risk factors that can predict occurrence of cardiovascular events. Currently, wearable non-invasive blood pressure measurement technology has attracted much research attention. Several different technical routes have been proposed to solve the challenge between portability or continuity of measurement methods and medical level accuracy of measurement results. The accuracy of blood pressure measurement technology based on auscultation and oscillography has been clinically verified, while majority of other technical routes are being explored at laboratory or multi-center clinical demonstration stage. Normally, Blood pressure measurement based on oscillographic method outside the hospital can only be measured at intervals. There is a need to develop techniques for frequent and high-precision blood pressure measurement under natural conditions outside the hospital. In this paper, we discussed the current status of blood pressure measurement technology and development trends of blood pressure measurement technology in different scenarios. We focuses on the key technical challenges and the latest advances in the study of miniaturization devices based on oscillographic method at wrist and PTT related method at finger positions as well as technology processes. This study is of great significance to the application of high frequency blood pressure measurement technology.

Cuffless Blood Pressure Monitoring: Academic Insights and Perspectives Analysis.

In recent decades, cuffless blood pressure monitoring technology has been a point of research in the field of health monitoring and public media. Based on the web of science database, this paper evaluated the publications in the field from 1990 to 2020 using bibliometric analysis, described the developments in recent years, and presented future research prospects in the field. Through the comparative analysis of keywords, citations, H-index, journals, research institutions, national authors and reviews, this paper identified research hotspots and future research trends in the field of cuffless blood pressure monitoring. From the results of the bibliometric analysis, innovative methods such as machine learning technologies related to pulse transmit time and pulse wave analysis have been widely applied in blood pressure monitoring. The 2091 articles related to cuffless blood pressure monitoring technology were published in 1131 journals. In the future, improving the accuracy of monitoring to meet the international medical blood pressure standards, and achieving portability and miniaturization will remain the development goals of cuffless blood pressure measurement technology. The application of flexible electronics and machine learning strategy in the field will be two major development directions to guide the practical applications of cuffless blood pressure monitoring technology.

Real-Time Monitoring of Intraocular Pressure in Glaucoma Patients Using Wearable Mobile Medicine Devices.

Glaucoma is caused by excessive aqueous humor in the eye, resulting in a continuous or intermittent increase of intraocular pressure, which exceeds the tolerance of the eyeball and damages the optic nerve. Existing treatments for glaucoma do not work well or have significant side effects. Intraocular pressure signal is a very important physiological signal that needs real-time and accurate monitoring in glaucoma patients, especially in severe glaucoma patients. Therefore, long-term, real-time, and accurate monitoring of intraocular pressure is of great significance for the diagnosis and treatment of glaucoma patients. The use of wearable devices for real-time ocular diagnosis and treatment of glaucoma patients is an effective approach. However, the current commonly used intraocular pressure measurement and monitoring technology is difficult to meet the diagnosis and monitoring needs of glaucoma patients in terms of size, measurement accuracy, power consumption, and intelligence. Therefore, facing the needs of glaucoma disease treatment, this topic studies an implantable flexible intraocular pressure sensor for long-term continuous monitoring of intraocular pressure in glaucoma patients and mainly focuses on the working principle, structural design, process fabrication, measurement and control system, characterization, and performance test of the intraocular pressure sensor. It is of great significance for personalized and accurate treatment of glaucoma patients.

Estimation of Beat-by-Beat Blood Pressure and Heart Rate From ECG and PPG Using a Fine-Tuned Deep CNN Model

Given that current cuffless blood pressure (BP) measurement technologies feature acceptable overall accuracy, this paper proposed a sufficiently accurate cuffless BP estimation method based on photoplethysmography (PPG) and electrocardiography (ECG) signals. This study used single-channel PPG and ECG signals to estimate heart rate (HR), diastolic BP (DBP), and systolic BP (SBP). A modified long-term recurrent convolutional network comprising a multi-scale convolution network and a long short-term memory (LSTM) network was used to develop a deep learning model for accurately estimating BP and HR. The PPG and ECG signal data of 1551 patients were obtained from the Data Sets-UCI Machine Learning Repository of the University of California, Irvine. The study dataset comprised ECG, PPG, and arterial BP (ABP) signals from the PhysioNet MIMIC II dataset. The original signals were processed by removing noise and artifacts. The aforementioned dataset contains 12,000 records in a hierarchical data format, with each record containing three signals, namely 125-Hz ECG signals from channel II (ECG lead II), 125-Hz PPG signals from the fingertip, and 125-Hz invasive ABP signals. To validate the stability and performance of the developed model, ten-fold cross-validation was conducted. The mean absolute error (MAE) (standard deviation (SD)) values of the developed model for predicting SBP, DBP, and HR were 2.24 mmHg (3.59 mmHg), 1.40 mmHg (2.56 mmHg), and 0.84 bpm (2.23 bpm), respectively. In addition, the estimated SBP and DBP values satisfied the standards of the British Hypertension Society and the Association for the Advancement of Medical Instrumentation. Compared with the methods proposed in other studies, the deep learning model developed in this study required a lower number of layers to provide accurate SBP, DBP, and HR estimations. The results of this study confirmed the effectiveness of the proposed deep learning architecture.

CO<sub>2</sub> positive pressure measurement technology based on absorption spectroscopy

为了研究可调谐半导体激光吸收光谱(TDLAS)技术在气体检测过程中，正压条件下的相邻谱线影响问题，建立基于积分吸光度的压力测量模型。以CO₂为研究对象，在室温、高纯度条件下进行了范围为（1～2）atm的压力测量仿真和实验。实验结果显示：随着压力的增大，相邻吸收谱线相互影响程度加剧，吸光度曲线偏离零基线的程度加大；实验测量结果在1.25 atm处最大相对偏差为4.94%，在2.00 atm处最小相对偏差为0.73%，平均相对偏差为3%。

Highly sensitive resistance-type flexible pressure sensor for cuffless blood-pressure monitoring by using neural network techniques

Blood pressure is an important parameter of a heart-pumping function, vascular peripheral resistance, and blood volume in human body. The non-invasive blood pressure measurement method has attracted tremendous attention due to its advantages of simple operation and comfort. In this paper, graft-modified MWCNTs and water-based polyurethane are used as filler and matrix, which are combined with simple dipping process to produce a resistance-type flexible pressure sensor with crack structure. The sensor with crack structure exhibits a high gauge factor (∼1582.7), fast response time (∼58 ms) and good repeatability (>2000 cycles) under 0–5% strain. By attaching the sensor to the radial artery of human wrist, the pulse waveform is accurately captured. By adopting the time-domain analysis method, in addition to the fast Fourier transform and threshold method which is employed to position and extract the characteristic value of pulse signal, a three-layer back propagation neural network is constructed to regress blood pressure value. The correlation coefficients of systolic blood pressure, diastolic blood pressure and mean blood pressure were 0.950, 0.875 and 0.947, respectively, which could meet the A-level standards of British Hypertension Society and Association for the Advancement of Medical Instrumentation. This study provides a good real-time and portable technology for home blood pressure measurement.