Accurate Pressure Measurement Research Articles

Accuracy of Non-Invasive Blood Pressure Measurements at the Arm, Calf , and Finger

Accuracy of Non-Invasive Blood Pressure Measurements at the Arm, Calf , and Finger

Rancang Bangun Sistem Pengukuran Tekanan Udara Menggunakan DT-Sense Barometric Pressure Berbasis Internet of Things dengan Display Smartphone

Weather be a very important thing to observe. One of the weather paramaters is air pressure. The air pressure on a surface is the force given to a surface or area by the air column above the surface. This research designed an air pressure gauge using DT-Sense Barometric Pressure which used to measure the value of the air pressure based of Internet Of Things with measurement result displayed on a smartphone. For data retrieval techniques were done by directly and indirectly. The amount that carried out directly is air pressure, while the indirect amount is the precision and the accuracy of air pressure measurements. The result of this research was the system performance specifications consist of mechanical systems that were supported by electronic systems. The precision measurements were done by comparing the results from Digital Barometer with the air pressure gauge that has been made. The percentage of average erros that obtained was 0.02965%, the relative precision average on the system was 0.99955, and the precision percentage of the tool was very good at 99.995%. The accuracy measurements were done by measuring the air pressure under the same conditions. The measurements were done by 10 times with reading on a constant standard measuring tools. The average accuracy of the system was 0.99 with an average standard deviation of 0.7 and relative errors average 0.0098%.

Development of a Flexible Meniscus Sensor for Detection of Force Distribution in Knee Arthroplasty

With the increasing demand for total knee arthroplasty (TKA) surgery, more attention has been paid to the accurate measurement of pressure and adjustment of knee prosthesis. The tightness between artificial meniscus and articular head and the thickness of artificial meniscus will directly affect the matching between knee joint and human body. At present, the installation and adjustment of knee joint during operation largely depends on the personal experience of doctors. In this work, a flexible pressure sensing device with bendable and distortable sensor arrays for force detection in knee arthroplasty is fabricated and characterized to provide quantitative data guidance and reference for knee arthroplasty. The internal pressure of prosthesis knee joint can be effectively detected through real-time obtaining for output voltages of sensor array. The densely distributed measuring points feedback abundant pressure distribution information. The pressure device shows good repeatability, consistency and small hysteresis in large detection range and stability in dynamic response which indicates promising potential in applications of knee arthroplasty.

Interpretation of Volatility Tandem Differential Mobility Analyzer (V-TDMA) data for accurate vapor pressure and enthalpy measurement: Operational considerations, multiple charging, and introduction to a new analysis program (TAO)

Significant evaporation of pure aerosols in a Volatility Tandem Differential Mobility Analyzer (V-TDMA) creates two Condensation Particle Counter (CPC) response peaks. Two hypotheses for the observ...

The impact of atrial fibrillation on accuracy of oscillometric blood pressure measurement: effect of ventricular rate.

This study evaluated the impact of ventricular rate (VR) in atrial fibrillation (AF) patients with oscillometric BP measurements. This study included 138 patients with AF and 112 patients with sinus rhythm (SR) who underwent coronary angiography. Left arm BP was measured three times with an oscillometric device, and the average was recorded as the final oscillometric value. At the same time, the average of three intra-aortic BP readings was used as invasive values. Delta BP was the difference between intra-aortic and oscillometric BP. Meanwhile, the BP percentage difference (PD-BP) was calculated with the following formula: PD-BP = (delta BP/intra-aortic BP) × 100%. Based on the VR, four subgroups of AF and SR patients, <80, 80-99, 100-120, and >120 bpm, were created, and the mean PD-BP for both systolic blood pressure (SBP) and diastolic blood pressure (DBP) was significantly higher in the AF group than in the SR group. Moreover, the mean PD-SBP values gradually increased as VR increased in both groups. More importantly, the difference in PD-SBP between the AF and SR groups increased as VR increased: when VR was <80 bpm, the levels were similar (-2.0 ± 3.5 vs. -1.4 ± 2.7 mm Hg, NS), but these values in AF patients were significantly higher when VR was 80-99 bpm (-3.7 ± 5.0 vs. -1.8 ± 2.3 mm Hg, p < 0.05), 100-120 bpm (-6.1 ± 4.3 vs. -2.3 ± 1.9 mm Hg, p < 0.05) and >120 bpm (-7.8 ± 4.9 vs. -2.9 ± 1.7 mm Hg, p < 0.05). The accuracy of oscillometric BP measurements are dependent on the ventricular rate in AF patients even after three measurements, and a higher ventricular rate may result in larger underestimations of oscillometric BP.

Neurogenic bladder monitoring using the cystomanometer and cystoelastometer

Patients with neurogenic bladder (NGB) require periodic urodynamics (UDS) to evaluate bladder function, which in turn helps guide management. At times, bladder decompensation or hydronephrosis may develop in patients between urodynamic testing intervals. Increased surveillance has improved outcomes in other chronic conditions (e.g., diabetes). Two novel devices, the cystomanometer (CM) and cystoelastometer (CEM), have been developed at the authors' institution to allow for home bladder pressure monitoring. The handheld CM can be attached to the end of any catheter and records the opening bladder pressure along with a time stamp. In addition, the CEM actively evacuates urine via a pump and records the urine volume evacuated. For safety, the pump slows and stops as it detects increasing resistance. Data are stored and transmitted wirelessly from both devices to a smartphone. A novel phone application stores, displays, and transmits data to a secure hospital server. This aim of this study was to validate the function of the CM and CEM and their accuracy relative to UDS. Institutional review board approval was obtained. All patients with NGB managed with intermittent catheterization undergoing routine UDS were eligible for study inclusion. At the completion of UDS, the instillation port of the 6-French dual-lumen UDS catheter was connected to the CM or CEM. Bladder parameters were simultaneously recorded using the device and UDS during bladder emptying. Correlative statistics were calculated. A total of 36 patients (30 children/6 adults; age range from 1.2 to 38 years [median: 7.5 years]) underwent CM testing. Strong pressure correlation with UDS was identified (R2=0.89). A total of 42 patients (30 children/12 adults; age range of 2.9-85.2 years [median: 12.2 years]) underwent CEM testing. Again, strong pressure correlation was found (R2=0.77). Cystoelastometer volume measurements were highly correlated with measured volumes (Fig.4, R2=0.98). Both the CM and CEM functioned well and transmitted the data wirelessly to a smartphone. The data from these devices were strongly correlated with simultaneous data from the UDS. A limitation is that these devices were used by healthcare providers, and therefore, use by patients or their parents/caregivers at home has not been demonstrated. The CM and CEM devices provide accurate bladder pressure and volume measurements. The potential for improved patient monitoring and care is promising. Reliability testing and the effects of such monitoring on patient outcomes remain to be determined.

Design of Intelligent Monitoring System for Knee Joint

Combined with physical modelling, motion capture and microprocessor technology, a human knee joint intelligent monitoring system based on nine-axis attitude angle sensor WT901 is developed. The overall design of the system and its hardware and software design are completed. The system adopts STM32 to improve the practicability of the system, use App to enhance the human-computer interaction capability. The results of the system tests indicate that the system realized accurate measurement of knee-bending angle and pressure. In addition, the system can also warn of sports posture errors and knee fatigue, and it is wearable and has low energy consumption.

Rebound Tonometry over Soft Contact Lenses.

Introduction:Goldmann applanation tonometry (GAT) is named as a gold standard for intraocular pressure (IOP) measurement.Aim:To assess the accuracy of intraocular pressure (IOP) measurements using rebound tonometry over hydrogel and silicone hydrogel contact lenses (CLs) of different powers.Methods:This study included 117 eyes of 61 patients (12 male, 49 female), all habitual wearers of hydrogel and silicone hydrogel CLs, and none previously diagnosed with glaucoma, ocular hypertension or anterior surface disease. Five IOP measurements were taken over each eye using a rebound tonometer (Icare): with soft CLs in situ and then repeated without CLs. Lens power ranged from -9.50 to +10.00 spherical diopters and to a maximum of -0.75 cylinder diopters.Results:A significant positive correlation was found between IOP measurements with and without CLs. The difference between IOP measurements with (mean 20.74±5.19 mmHg) and without (mean 18.79±4.36 mmHg) CLs was found to be 1.95 mmHg (P <0.01). Statistical analysis was performed using the paired t-test and a correlation coefficient was calculated (r = 0.59; P <0.001). We have observed that increase in central corneal thickness (CCT) correlates positively with increase of measurement error of rebound tonometry (r = 0.43; P <0.001).Conclusion:We have shown good reliability of IOP measurements over CLs of different materials and thickness profiles while using rebound tonometer which makes it a feasible and accurate method for clinical purposes.

Continuous Blood Pressure Measurement Platform: A Wearable System Based on Multidimensional Perception Data

The mobile crowd sensing technology in the environment integrating human, machines and things is an emerging direction in social computing. In kinematics research, continuous blood pressure monitoring and calibration are the basis for revealing the correlation between athlete motor function and blood pressure. At the same time, in the field of medical research, hypertension can be more easily controlled, thus improving the effectiveness of hypertension treatment. This paper presents the design principle of a human-machine fusion system based on CrowdOS, a mobile crowd sensing platform. The system innovatively establishes the correlation between blood pressure and exercise, improves the accuracy of cuffless blood pressure measurement, and verifies the feasibility of calibrating continuous cuffless blood pressure measurement based on exercise information. Using our system and electronic cuff sphygmomanometer, we measured 65 groups of data in walking, running, sitting and climbing stairs, each group lasting about 10 minutes. Based on these data, we established a regression analysis model for blood pressure measurement calibration. The accuracy of blood pressure calibration was improved from the original systolic root mean square error of 13.43mmHg and diastolic root mean square error of 8.35mmHg to 9.76mmHg and 5.56mmHg. The design method proposed in this paper provides a feasible solution for continuous cuffless blood pressure measurement and calibration, and shows broad application prospects in the fields of athlete scientific training and medical care.

Vacuum metrology based on refractive index of gas

With the development of vacuum technology, subject to the influence of directional flow and uneven temperature, the thermodynamic equilibrium state is destroyed. In this case, the pressure reference is not suitable for characterizing the vacuum state. To ensure the long-term stability and reproducibility of the measurement system, vacuum metrology will be characterized by gas density. The precisive measurement of gas refractive index based on a Fabry-Perot cavity can be used to derive the gas density. This kind of an optical measurement of vacuum links macroscopic dielectric constants of gases with microscopic polarization parameters of atoms and molecules. It replaces the physical standard based on the mercury pressure gauge with the quantum standard. In this paper, we discuss the reverse process from refractive index to gas pressure, and use the laser-locked Fabry-Perot cavity method to measure the refractive index of argon gas. The contribution of related parameters to the uncertainty of determined gas pressure is analyzed. The influences of material parameters and experimental parameters such as gas molar susceptibility, molar susceptibility, dielectric second Virial coefficient and temperature on gas pressure accuracy are analyzed. The result shows that the uncertainty in our measurement of argon within 1 atm is &lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}$u = \sqrt {{{(6\;{\rm{mPa}})}^2} + {{(73 \times {{10}^{ - 6}}p)}^2}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200706_M2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200706_M2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. Currently, the uncertainty mainly comes from the measurement deviation of gas temperature inside the cavity. After repeating the measurement a few times, the results show that the statistical uncertainty of refractive index is within 100 ppm, which is limited by the accuracy of the pressure gauge used here. In addition, we compare the dipole calculated by the &lt;i&gt;ab initio&lt;/i&gt; method with that by the DOSD method. The results show that the dynamic polarizability obtained by the &lt;i&gt;ab initio&lt;/i&gt; method is consistent with our experimental results. In conclusion, these experimental results show that the measurement of gas pressure based on the gas refractive index has high repeatability and accuracy. If the temperature control and corresponding measurement accuracy of the gas are further improved, this method can also be used to obtain high-precision microscopic parameters such as the polarizabilities of atoms and molecules. In the future work, we will focus on improving the temperature control and the design of the cavity to reduce cavity leakage and deflation. It is possible that the measurement accuracy of the gas pressure will be increased to 10 ppm level, which is the same level as the current standard pressure gauge and will become a new standard for pressure measurement in the future.

Pediatric Hypertension: Parent Perspectives.

Clinical practice guidelines for diagnosis and management of pediatric hypertension have been available for decades. Yet, most cases of hypertension in children are undiagnosed. Provider and system-based factors, such as the complexity of diagnostic standards, and a failure among physicians to recognize the importance of hypertension in children, play a role in underdiagnosis. It is unclear, however, how patient and family behaviors impact the diagnosis and treatment of pediatric hypertension. We aimed to explore the perspectives of parents whose children have had multiple high blood pressure readings or have been diagnosed with hypertension to inform clinicians with areas for practice improvement. In a 2 site qualitative study, we interviewed parents of 15 children diagnosed with hypertension. Results from semi-structured interviews with parents revealed barriers to the diagnosis of pediatric hypertension, including uncertainty about the diagnosis and concerns around the accuracy of blood pressure measurements. Delay in diagnosis and lack of child engagement emerged as obstacles to the treatment of pediatric hypertension.

A new method for detecting the outer corneal contour in images from an ultra-fast Scheimpflug camera

BackgroundThe Corvis® ST tonometer is an innovative device which, by combining a classic non-contact tonometer with an ultra-fast Scheimpflug camera, provides a number of parameters allowing for the assessment of corneal biomechanics. The acquired biomechanical parameters improve medical diagnosis of selected eye diseases. One of the key elements in biomechanical measurements is the correct corneal contour detection, which is the basis for further calculations. The presented study deals with the problem of outer corneal edge detection based on a series of images from the afore-mentioned device. Corneal contour detection is the first and extremely important stage in the acquisition and analysis of corneal dynamic parameters.ResultA total of 15,400 images from the Corvis® ST tonometer acquired from 110 patients undergoing routine ophthalmologic examinations were analysed. A method of outer corneal edge detection on the basis of a series of images from the Corvis® ST was proposed. The method was compared with known and commonly used edge detectors: Sobel, Roberts, and Canny operators, as well as others, known from the literature. The analysis was carried out in MATLAB® version 9.0.0.341360 (R2016a) with the Image Processing Toolbox (version 9.4) and the Neural Network Toolbox (version 9.0). The method presented in this paper provided the smallest values of the mean error (0.16%), stability (standard deviation 0.19%) and resistance to noise, characteristic for Corvis® ST tonometry tests, compared to the methods known from the literature. The errors were 5.78 ± 9.19%, 3.43 ± 6.21%, and 1.26 ± 3.11% for the Roberts, Sobel, and Canny methods, respectively.ConclusionsThe proposed new method for detecting the outer corneal contour increases the accuracy of intraocular pressure measurements. It can be used to analyse dynamic parameters of the cornea.

Characterisation and optimisation of MEMS based pressure sensors for deep space missions

AbstractPressure sensors are extensively used in spacecraft propulsion system for health monitoring and determining the on‐orbit functional life of the spacecrafts. This is possible by employing PVT (Pressure‐Volume‐Temperature) method wherein pressure sensors and temperature sensors mounted in the propellant tank are used for accurate measurement of pressure and temperature. Pressure sensors are also employed for control &amp; other system health monitoring applications. For aerospace applications, they have to perform under harsh and volatile environments and demands utmost reliability and long‐term performance stability. Hence, it is essential to characterise and optimise these sensors by adopting adequate design methodologies test philosophies. A detailed study has been carried out and the performances were evaluated for establishing the usage of MEMS based pressure sensors.

Whether lowering intraocular pressure is needed for thyroid associated ophthalmopathy with intraocular hypertension

Patients with thyroid associated ophthalmopathy often have elevated intraocular pressure. Patients and doctors are often confused about whether intraocular hypertension in thyroid associated ophthalmopathy needs to be lowered. There are several theories on the possible causes of this kind of increased intraocular pressure: restriction and compression of the globe by fibrotic and enlarged rectus muscles, increased episcleral venous pressure resulting from orbital congestion and venous outflow obstruction, and increased resistance to trabecular outflow. In addition, the patient's eye position and the device for measuring intraocular pressure also have great impacts on the accuracy of intraocular pressure measurement. At the same time, there are very few patients with thyroid associated ophthalmopathy combined with primary glaucoma. Therefore, whether patients with elevated intraocular pressure need to be treated depends on the specific clinical manifestations of the thyroid associated ophthalmopathy. Intraocular pressure of most patients can be lowered by active treatment for thyroid associated ophthalmopathy; antiglaucoma medical therapy may be necessary for patients whose intraocular pressure cannot be lowered; only very few cases of glaucoma require antiglaucoma drugs or surgery. (Chin J Ophthalmol, 2019, 55:811-813).

About ecology around industrial areas of Mariupol

The oxygen content in the atmospheric air of cities, as well as in residential, office and industrial premises is the most important factor in the health and well-being of citizens. With high temperature and high absolute humidity of the surface air, the oxygen content in ambient air is minimal, and people may experience signs of hypoxia. In the industrial southern cities to which the city of Mariupol (Ukraine) belongs, there are additional factors that impede human breathing: higher (relative to the territory surrounding the city) air temperature and pollution of the atmosphere, including carbon monoxide and suspended particles. This results in conditions of abnormal heat and industrial emissions to an increase in the morbidity and mortality of the urban population. Accurate measurements of partial pressure and partial density of oxygen require special equipment and techniques, since the percentage of oxygen in ambient air is large enough, and its changes are relatively small. Most modern instruments used by urban atmospheric monitoring services are focused on measuring significant deviations of oxygen content from the norm. Air quality monitoring services do not usually measure the density of oxygen, apparently due to the implicit assumption of the negligible effect of changes in weather conditions on its content. In addition, the measurement of small changes in the oxygen content in the surface air is a rather complicated technical task. The paper presents an attempt to analytically determine the distribution of oxygen concentrations in the surface layers of the atmosphere around the places of oxygen runoff from the atmosphere at metallurgical enterprises of Mariupol, provides an analytical model based on the theory of "reverse flow" in a one-dimensional formulation of oxygen flow from the surface layer. The corresponding concentration contour lines were obtained at various distances from the oxygen sink sites. At the same time, the oxygen concentration decreases inversely with the distance from the drain, which makes it quite easy to estimate the distribution of concentrations in the surface layer of the atmosphere around the metallurgical enterprises at known coordinates of its drain points in calm weather. The spatial variability and episodes of anomalous oxygen content in the surface air are analyzed in the context of their possible effect on people's well-being.

On the ecological state of the atmosphere around the industrial areas of Mariupol

The oxygen content in the atmospheric air of cities, as well as in residential, office and industrial premises is the most important factor in the health and well-being of citizens. With high temperature and high absolute humidity of the surface air, the oxygen content in ambient air is minimal, and people may suffer hypoxia. In the industrial southern cities to which the city of Mariupol (Ukraine) belongs, there are additional factors that impede human breathing: higher (relative to the territory surrounding the city) air temperature and pollution of the atmosphere, including carbon monoxide and suspended particles. This results in an increase in the morbidity and mortality of the urban population under the conditions of abnormal heat and industrial emissions. Accurate measurements of partial pressure and partial density of oxygen require special equipment and techniques, since the percentage of oxygen in ambient air is large enough, and its changes are relatively small. Most modern instruments used by urban atmospheric monitoring services are focused on measuring significant deviations of oxygen content from the norm. Air quality monitoring services do not usually measure the density of oxygen, apparently due to the implicit assumption of the negligible effect of weather conditions changes on its content. In addition, the measurement of small changes in the oxygen content in the surface air is a rather complicated technical task. The paper presents an attempt to analytically determine the distribution of oxygen concentrations in the surface layers of the atmosphere around the places of oxygen runoff from the atmosphere at metallurgical enterprises of Mariupol, provides an analytical model based on the theory of «reverse flow» in a one-dimensional formulation of oxygen flow from the surface layer. The corresponding concentration contour lines were obtained at various distances from the oxygen sink sites. In doing so, the oxygen concentration decreases inversely with the distance from the drain, which makes it quite easy to estimate the distribution of concentrations in the surface layer of the atmosphere around the metallurgical enterprises at known coordinates of its drain points in calm weather. The spatial variability and episodes of anomalous oxygen content in the surface air have been analyzed from considerations of their possible effect on people’s well-being

Finite element simulation of Goldmann tonometry after refractive surgery

BackgroundThe problem of accuracy of intraocular pressure (IOP) measurement using Goldmann Applanation Tonometry (GAT) after a refractive surgery is still unresolved.In this study a numerical simulation of refractive surgery and GAT is proposed as a method to evaluate accuracy of the correction formula for GAT reading after changes in corneal curvature and thickness. MethodsIn the finite element analysis the effect of the corneal shell buckling was taken into account. This effect is responsible for the nonlinear relation of Goldmann applanation tonometer measurement and intraocular pressure. Goldmann applanation tonometry was simulated for different ablation depths and values of intraocular pressure levels. FindingsThe results of the simulation indicate a strong relation between the Goldmann applanation reading and the intraocular pressure level for values greater than nominal (about 16 mmHg). The estimation error of the intraocular pressure after changes in corneal geometry, is lower than 1 mmHg for IOP = 32 mmHg and lower than 3 mmHg for IOP = 48 mmHg. InterpretationThe proposed correction formula of Goldmann applanation tonometry occurred to be useful in the cases after the corneal refractive surgery regardless of the intraocular pressure values and ablation depth.

Printing pressure uniformization through adaptive feedforward control in roll-to-roll printing process

Roll-to-roll printed electronics is a fabrication technology for electrical devices using functional ink and flexible material films. When the printing pressure is not uniform between the two rolls in the roll-to-roll process, the printing quality degrades, which makes commercialization of printed electronics difficult. In this study, we constructed a system in which both ends of the impression roll are driven individually, unlike the conventional printing pressure control system, for accurate printing pressure measurement. However, in the actual process, since the printing pressure cannot be measured in real time in the nip, which is the contact surface between one roll and the other roll, a load cell is installed at both ends of the impression roll to measure the printing pressure. This measurement limit causes a measurement delay. To compensate for the measurement delay, we measure the printing pressure and perform a frequency analysis of the measured printing pressure to calculate the correct measurement delay value. Then we calculate the measurement delay using the frequency response function and use a time delay predictor to compensate for the calculated measurement delay. However, even if the measurement delay is compensated for, there is a printing pressure error due to repeatable run-out (RRO). To eliminate the residual error after compensating for the measurement delay, we perform a frequency analysis of the printing pressure after compensating for the measurement delay. We then apply adaptive feedforward control to uniformize the printing pressure additionally.

On the Accuracy of Quartz Pressure Sensor in the Seafloor Affected by Transport Condition

Improving the accuracy of pressure measurements on the seafloor can reveal small vertical crustal deformations, contributing to the knowledge of earthquake-generation processes. The pressure, temperature, and attitude dependencies of a high-accuracy quartz pressure sensor have been evaluated in a laboratory environment simulating an in situ seafloor measurement at 2000-m depth. This depth corresponds to that of a seismogenic zone in the Nankai Trough, Japan. To detect crustal deformations on a centimeter scale, pressure measurements with an accuracy of 1 hPa, corresponding to a depth change of 1 cm, are required. High-resolution pressure measurements-and thus evaluation of pressure sensor dependencies-are critical. Temperature dependencies were evaluated by placing a gauge incorporating the sensor in a temperature-controlled bath from 2 °C to 24 °C under a constant pressure of 20 MPa. Pressure dependence was evaluated by changing the applied pressure from 10 to 30 MPa at a constant temperature of 24 °C. Attitude dependence was evaluated by tilting the gauge from 0° to 14° under constant pressure and temperature conditions. These results were used to investigate the impact of gauge transportation from the laboratory to the seafloor. We calculated changes in each factor sufficient to cause a measurement bias of 1 hPa: 1) a sensor temperature change of 0.3 °C; 2) a pressure variation of ±3 MPa from 20 MPa; and 3) a tilt change of 2.3°. The temperature dependence has the greatest influence on the measurement accuracy, highlighting the particular importance of ambient temperature change throughout the measurement procedure.

Accurate vapor pressure measurements of supercooled water in the temperature range between 252 K and 273 K

The accurate knowledge of the saturation vapor pressure of liquid water and ice has a great importance in a host of applications where humidity measurements are involved since it enables the correct conversion among different physical quantities that quantify the water vapor amount of a humid gas mixture.More specifically, accurate saturation vapor pressure measurements of supercooled water are strongly required in meteorology and atmospheric sciences, especially in cloud microphysics studies.Considering the importance of this kind of measurements and the limited availability of experimental data in the literature, further measurements in the metastable region were carried out at the Istituto Nazionale di Ricerca Metrologica (INRIM).The sample cell used in the experiment is a U-shaped capillary tube made of borosilicate glass, whose temperature is kept constant by immersion in a thermostatic bath with a high temperature stability (about 1 mK). The cell is connected to a capacitive diaphragm pressure gauge measuring the equilibrium water vapor pressure, that varies between about 116 Pa at T = 252.25 K and 615 Pa at T = 273.25 K.In the present work, the measuring method and the experimental setup are described and the measurements results reported. The results obtained in the whole temperature range are compared with those available in the literature and with the commonly adopted saturation vapor pressure formulations. A complete uncertainty budget is also given, resulting in an expanded relative uncertainty ranging from 0.06% at 273.25 K to 0.20% at 252.25 K.