Pressure Measurement Error Research Articles

Numerical evaluation of systematic errors of a non-invasive intracranial pressure measurement

Intracranial pressure (ICP) monitoring procedure can be applied to aid in secondary brain damage prevention. A high invasiveness of commonly used ICP measuring methods poses a risk of complications, and therefore new non-invasive methods are currently being developed. A promising non-invasive ICP measurement method is based on the existence of pressure balance state, which is driven by the unique morphological property of ophthalmic artery (OA). The value of ICP can be obtained by evaluating blood flow or artery characteristics in different OA segments, intracranial OA segment (IOA) and extracranial OA segment (EOA). In order to increase measurement accuracy, the systematic errors must be evaluated, which requires an implementation of a numerical model encompassing various physical phenomena. In this paper, a developed numerical model is presented, which was used to solve a transient fluid–structure interaction (FSI) problem of the pulsatile blood flow in a straight, physically meaningful anisotropic, hyperelastic OA, with ICP and external pressure (Pe) loads. It was found that the systematic error based on mean cross-sectional area difference between IOA and EOA segments was {–1.48, –1.37, –1.17} mmHg with ICP = {10, 20, 30} mmHg, respectively. The systematic error based on mean blood flow velocity difference between IOA and EOA segments was {–1.84, –1.76, –1.625} mmHg with ICP = {10, 20, 30} mmHg, respectively. The presented numerical model examined the worst-case scenario in terms of boundary conditions, which were immovable, while lengths of OA segments were physiologically relevant statistical means; however, the obtained systematic errors still met the clinical standards of ANSI/AAMI, where it is stated that the error should not exceed the ± 2 mmHg in the range of 0–20 mmHg of ICP. Boundary conditions and compliance affects the systematic error in both ways (reduce or increase it); this may explain the low systematic errors obtained in experimental studies by other authors.

Method of deflection corrected tonometry with phantom vessel experiments

BackgroundThe Continuous Non-Invasive measurement of arterial Blood Pressure [CNIBP] is possible via the method of arterial tonometry and the arterial volume clamp methods. Arterial tonometry successfully measures continuous arterial pressure but requires large vessel deformation and a highly miniaturized pressure sensor to obtain a direct calibration of pressure. A properly designed tonometer is capable of achieving pressure accuracy of less than 5% error at the radial artery. The volume clamp method achieves comparable errors but is generally restricted to the very peripheral arteries. Since the brachial or radial arteries are preferable sites to record blood pressure, tonometry is generally preferred. However, due to its strict operating requirements, tonometry requires a highly skilled operator. The greatest source of measurement error results from slight deviation from the artery wall applanation position. In this study, a method for correcting tonometry deflection error is introduced and evaluated using preliminary experiments. Methods-modelingIn prior analysis it has been shown that arterial wall flattening causes contact stress to become uniform and equal to the arterial pressure. In this article, we derive the contact stress for deflections other than the ideal applanation position and to allow variable vessel deflection. This analysis permits the contact stress to be corrected for tonometer positions that are not exact so that pressure accuracy is maintained in spite of less than ideal positioning. This will alleviate the necessity for highly skilled users and allow rapid determination of the pulse pressure. Methods-experimentalExperiments were performed to evaluate applied model corrections for tonometer accuracy versus vessel deflection. Two experiments were performed to evaluate tonometer accuracy when deflection is varied. The first experiment used no deflection correction and the second experiment applied model derived deflection correction. A force sensor was used to deflect a phantom latex vessel of known internal pressure. The corrected contact pressure was then compared with known pressures to evaluate the pressure accuracy. Results-modelinga geometric model was derived for vessel contact area versus deflection. This resulted in a formula that provides contact area continuously for any amount of deflection. Once the contact area is known the average tonometer contact pressure was obtained that corresponds with the vessel internal pressure. Results – experimentalA latex tubing phantom vessel was pressurized to a known amount and was deflected in increments over its full diameter while measuring contact force at each position. The model-derived formula was then used to calculate pressure at each position. The calculated pressure was then compared with known internal pressure to evaluate pressure accuracy for all the phantom pressure and deflection points. ConclusionsA modeling method for tonometer deflection correction was derived and evaluated using a phantom vessel. Average error was significantly reduced over the non-corrected data. The variability of error was also reduced for all data points collected. The experiments reveal that blood pressure measurement error can be reduced to levels obtained in near ideal tonometry conditions without the need for precise position control. The relaxed user precision is anticipated to simplify the use and design requirements for arterial tonometry in practice.

Abstract P352: The Quality of Blood Pressure Measurement in the Hemodialysis Unit

Objectives: The association of intradialytic blood pressure with interdialytic blood pressure and clinic outcomes is inconsistent. Poor technique of routine blood pressure measurement in the hemodialysis unit may contribute to this inconsistency. We aim to assess adherence to current blood pressure measurement standards in the hemodialysis unit. Methods: We assessed a convenience sample of 79 hemodialysis unit patient visits for adherence to five blood pressure measurements standards, per Hypertension Canada guidelines. The frequency of errors in blood pressure measurement was assessed by descriptive statistics. Results: In 79 blood pressure measurements only 6% had no errors in measurement technique across the five standards we assessed. The most common errors were cuff position (29% correct) and patient position (29% correct), while the upper arm was appropriately chosen in 94% of patients. Conclusion: Errors in blood pressure measurement technique were common and may contribute to inaccuracy in blood pressure measurement.

The role of the measurement uncertainty and error in the blood pressure measurement

The blood pressure measurement is a routinely procedure conducted in primary cares, health cares, pharmacies or even at home, by physicians in order to diagnosis hypertension, as well as by the users in order to administer medication. The sphygmomanometer is the instrument used to the procedure, however the indication of the blood pressure displayed is not always the true value of the measurement. Deviations due to measurement errors and uncertainties, an intrinsic component of all measuring devices, affect the indication, and consequently might affect the patient diagnosis. For example, a health patient can be diagnosed as hypertensive, demanding an unnecessary treatment. Then, the present study aims to investigate the impact of the measurement error and the uncertainty in misdiagnosis for hypertension. We applied a sphygmomanometer with well-known measurement error and uncertainty to a sample of patients with well-known blood pressure in order to identify how these parameters affect the result according to the instrument indication. The results show a misdiagnosis of 3.98%, for the diastolic and 4.29% for the systolic pressure, to the sphygmomanometer used in the simulations. The results show the importance of considering the metrological parameters for the diagnosis.

AUTOMATED BLOOD PRESSURE MEASUREMENT IN PATIENTS WITH HYPERTENSION AND ATRIAL FIBRILLATION. DATA FROM THE ESH RESEARCH PROJECT “MANAGEMENT OF ARTERIAL HYPERTENSION IN PATIENTS WITH HIGH BLOOD PRESSURE AND ATRIAL FIBRILLATION”

Objective: Atrial fibrillation (AF) is a frequent complication of long lasting hypertension, and carries a high risk of morbidity and mortality as well as of cardiovascular events. AF is also responsible for possible errors in blood pressure (BP) measurement. Limited information is available on the accuracy of blood pressure measurements when automated oscillometric (OSC) devices are used instead of the standard auscultatory approach (AUSC). The aim of this analysis was to compare blood pressure values measured using either a mercury sphygmomanometer or an automated electronic device in patients with AF. The analysis was limited to 353 patients (mean CHA2DSVA2SC score 3.9), enrolled in the international multicenter ESH Research Project on arterial hypertension and atrial fibrillation, in whom BP was measured 4 times with the standard AUSC approach (according to Guidelines) and 4 times with an OSC device. Results mean age was 72 ± 11 (range 20–94), BMI 28 ± 5, mean CHA2S2VASC 3.9. Mean BP values were 130.3 ± 19.5 for AUSC-SBP and 131.5 ± 20.1 for OSC-SBP and 75.8 ± 11.4 for AUSC-DBP and 76.5 ± 12.3 for OSC-DBP. Correlation coefficients between automated and manual blood pressure measurements were: r = 0.917 for SBP and r = 0.856 for DBP (p < 0.0001). The difference between the oscillometric and manual measurement was on average of 1.2 mmHg for systolic BP (SBP) and of 0.7 mmHg for diastolic BP (DBP). The standard deviations (SD) of the differences were, respectively, 8.07 and 6.39, and progressively increased wen 4, 3, 2 or 1 measurements were used. At Bland-Altman analysis the limits of agreement were −17 to 14.7 mmHg for SBP and -13.3 to 11.8 for DBP. Conclusions: In patients with hypertension and AF measurement of BP values with oscillometric devices provides similar BP values, with SD at the upper limit of AAMI criterion for the validation of devices, at least when 4 BP measurements are performed.

Usage of Connected Structure to Eliminate Blind Area of Piezoresistive Sensor Array

The existing piezoresistive sensor array adopts the classical configuration called “unconnected structure”, in which the piezoresistive materials in the subelements are separated with each other. Consequently, the sensor array cannot detect the pressure applied on the region among the sub elements (i.e., blind area). To eliminate the blind area, the traditional method is to use more subelements, leading to the increase of the number of the electrodes which complicates the sensor probe. To overcome the limitation, a connected structure, in which a whole piezoresistive sheet is used in all subelements, is designed. The pressure applied on any region of the connected structure can cause the changes in the resistances of the subelements. Therefore, the region bearing pressure can be located and the pressure value can be obtained without adding electrodes. The piezoresistive sensor array made of conductive polymer composite is used as an example. The experiments show that the pressure position can be evaluated, and the pressure measurement error is less than 30 kPa within the range from 0 to 0.4 MPa. The results indicate that the usage of the connected structure can eliminate the blind area by using less electrodes than the traditional method.

Experimental Study of the Polytropic Coefficient for an Air-Cooled, High-Compression-Ratio, Spark-Ignition Engine Fueled with Natural Gas, Biogas, and a Propane–Syngas Blend

The polytropic coefficient is an important variable for determining errors in pressure and volume measurements and for apparent heat release calculation in engine combustion analysis. For commercial gasoline-fueled spark ignition engines and diesel-fueled compression ignition engines exist a wide understanding about the thermodynamic models and values of polytropic coefficient, however, in other technologies, in which gaseous fuels are used, the pressure treatment strategies and heat transfer models should be adjusted to allow a better calculation of polytropic coefficient. This paper presents a study on the effects of fuel composition, spark timing, and engine load on polytropic coefficient determination in an air cooled spark ignition engine with high compression ratio (15.5:1), which it was fueled with natural gas, biogas, and propane-syngas blend. The experimental results suggests that during compression an appropriate crank angle interval for polytropic coefficient estimation is between 50 and 30 cra...

Barriers to Accurate Blood Pressure Measurement in the Medical Office.

Background: Despite the high prevalence of blood pressure (BP) measurement errors in the outpatient setting, little is known about why primary care clinics struggle to achieve consistently accurate BP measurements in routine practice. We investigated barriers affecting measurement of BP for adult patients in primary care. Methods: We conducted a qualitative evaluation in 6 adult primary care clinics. BP measurement was observed during 54 routine patient encounters. Six managers completed semistructured interviews and 18 clinical staff members participated in focus group discussions. We used an inductive, data-driven approach to identify and organize findings into cohesive, overarching themes describing factors affecting BP measurement. Results: Observed errors in BP measurement spanned the entire spectrum of steps required to obtain BP properly. Barriers to proper BP measurement were related to staff knowledge and behavior (inadequate knowledge, training, and feedback); workflow constraints (need to multitask, inadequate time); and equipment issues (BP monitors, seating). Patient characteristics and behavior also affected BP measurement. Conclusions: Correct measurement of BP is affected by a wide range of factors and is challenging to accomplish consistently in primary care. These findings may inform the design of performance improvement programs to maximize the quality of BP measurement in the outpatient setting.

Algoritma Interpolasi Nearest-Neighbor untuk Pendeteksian Sampul Pulsa Oscilometri Menggunakan Mikrokontroler Berbiaya Rendah

Non-invasive blood pressure measurement devices are widely available in the marketplace. Most of these devices use the oscillometric principle that store and analyze oscillometric waveforms during cuff deflation to obtain mean arterial pressure, systolic blood pressure and diastolic blood pressure. Those pressure values are determined from the oscillometric waveform envelope. Several methods to detect the envelope of oscillometric pulses utilize a complex algorithm that requires a large capacity memory and certainly difficult to process by a low memory capacity embedded system. A simple nearest-neighbor interpolation method is applied for oscillometric pulse envelope detection in non-invasive blood pressure measurement using microcontroller such ATmega328. The experiment yields 59 seconds average time to process the computation with 3.6% average percent error in blood pressure measurement.

Biomechanical Simulation of Stress Concentration and Intraocular Pressure in Corneas Subjected to Myopic Refractive Surgical Procedures

Recent advances in the analysis of corneal biomechanical properties remain difficult to predict the structural stability before and after refractive surgery. In this regard, we applied the finite element method (FEM) to determine the roles of the Bowman’s membrane, stroma, and Descemet’s membrane in the hoop stresses of cornea, under tension (physiological) and bending (nonphysiological), for patients who undergo radial keratotomy (RK), photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), or small incision lenticule extraction (SMILE). The stress concentration maps, potential creak zones, and potential errors in intraocular pressure (IOP) measurements were further determined. Our results confirmed that the Bowman’s membrane and Descemet’s membrane accounted for 20% of the bending rigidity of the cornea, and became the force pair dominating the bending behaviour of the cornea, the high stress in the distribution map, and a stretch to avoid structural failure. In addition, PRK broke the central linking of hoop stresses and concentrated stress on the edge of the Bowman’s membrane around ablation, which posed considerable risk of potential creaks. Compared with SMILE, LASIK had a higher risk of developing creaks around the ablation in the stroma layer. Our FEM models also predicted the postoperative IOPs precisely in a conditional manner.

Goldmann tonometer error correcting prism: clinical evaluation.

PurposeClinically evaluate a modified applanating surface Goldmann tonometer prism designed to substantially negate errors due to patient variability in biomechanics.MethodsA modified Goldmann prism with a correcting applanation tonometry surface (CATS) was mathematically optimized to minimize the intraocular pressure (IOP) measurement error due to patient variability in corneal thickness, stiffness, curvature, and tear film adhesion force. A comparative clinical study of 109 eyes measured IOP with CATS and Goldmann prisms. The IOP measurement differences between the CATS and Goldmann prisms were correlated to corneal thickness, hysteresis, and curvature.ResultsThe CATS tonometer prism in correcting for Goldmann central corneal thickness (CCT) error demonstrated a reduction to <±2 mmHg in 97% of a standard CCT population. This compares to only 54% with CCT error <±2 mmHg using the Goldmann prism. Equal reductions of ~50% in errors due to corneal rigidity and curvature were also demonstrated.ConclusionThe results validate the CATS prism’s improved accuracy and expected reduced sensitivity to Goldmann errors without IOP bias as predicted by mathematical modeling. The CATS replacement for the Goldmann prism does not change Goldmann measurement technique or interpretation.

IMPACT OF CORNEAL CHANGES IN PSEUDOEXFOLIATIVE SYNDROME ON THE COORDINATION DEGREE BETWEEN THE MAKLAKOV TONOMETER AND THE PASCAL DYNAMIC CONTOUR TONOMETER

Introduction. Pseudoexfoliative syndrome (PEX) changes the morphological structureof corneathat can affects its biomechanical properties. These properties affect the results of the intraocular pressure (IOP) measurement. Purpose of the study isto estimate the effect of PEХ on the error in intraocular pressure measurement (IOP) with Maklakov tonometer in relation to properties of the cornea. Materials and methods . The main group – 126 patients with PEХ, reference group – 104 patients without PEX. The main estimated indicator is the difference between the levels of IOP measured by the Maklakov tonometer and Pascaltonometer and coordination between two methods. Pascal tonometer was used as a reference one. Results and conclusions. The difference between the levels of IOP in the groups was unreliable. When measurements are made with Maklakov tonometer, PEX does not causethe significant tonometry error associated with properties of the cornea.

Flush air data sensing system design for air breathing air-to-air missile

The key technical difficulties and design flow of flush air data sensing (FADS) system design for air breathing air-to-air missile are analyzed. The aspirated air-to-air missile large slenderness than layout, high maneuverability, high angle of attack and low cost control characteristics proposed a high precision, multi-points of fault diagnosis and fault-tolerant and anti overload of fads system design method. Mainly includes the algorithm design based on strategy of pressure model, hierarchical diagnosis and multi-models of re-configurable fault-tolerant, the error source of the system control model design, high precision and anti overload pressure measurement module design and solution machine module design. According to the shape of a typical air breathing air-to-air missile, the FADS system principle prototype is designed, which is based on 9 pressure measuring points layout and flight Mach number 1.5–4.0. Prototype real-time solution test is done in 1.2 m×1.2 m supersonic wind tunnel. Test results show that: relative error of static pressure measurement is no more than 6.9%, measurement error of Mach number is no more than 0.10, the measurement errors of the angle of attack and side slip angle are no more than 1°. The measurement error of the reconstructed model is close to the baseline model error; algorithm fault diagnosis points is less than or equal to 3, the scope of fault diagnosis of P1 deviation is less than or equal to −20% or greater than or equal to 40%, P2–P9 deviation is less than or equal to −30% or greater than or equal to 30%. The algorithm has less than or equal to 2 fault tolerant ability. The measurement error level, fault diagnosis and tolerance ability of the system can meet the engineering requirements.

The analysis of the influence of temperature and atmospheric pressure measurement errors on the flight altitude determination error

The flight altitude may be determined in a variety of ways. This paper analyzes the method based on the measurement of pressure and temperature. The authors particularly draw attention to the influence of the temperature and pressure measurement errors on the accuracy of the determination of flight altitude. It also depends on the method of approximation. The discussed issues have been described with real data.

スロートタップフローノズルにおける静圧計測誤差に関する研究

The static pressure measurement error at a wall tap of a flow nozzle is examined for a wide range of Reynolds number. The static pressure measurement error is obtained using the measured discharge coefficient for the flow nozzle. The static pressure measurement error is influenced by the diameter of the wall tap and the viscosity of the working fluid. This paper presents several relations between the static pressure measurement error normalized by the wall shear stress and the tap Reynolds number, which is based on the diameter of the wall tap and the friction velocity. The best relation to reasonably explain the static pressure measurement error is proposed in this paper.

Determination of the VT-relaxation time of molecules from the compression pulse width of a photoacoustic signal: the effect of gas pressure measurement errors

Determination of the VT-relaxation time of molecules from the compression pulse width of a photoacoustic signal: the effect of gas pressure measurement errors

Static pressure measurement error at a wall tap of a flow nozzle for a wide range of Reynolds number

The static pressure measurement error at a wall tap of a flow nozzle is examined for a wide range of Reynolds number. The static pressure measurement error is obtained using the measured discharge coefficient for the flow nozzle. The static pressure measurement error is influenced by the diameter of the wall tap and the viscosity of the working fluid. This paper presents several relations between the static pressure measurement error normalized by the wall shear stress and the tap Reynolds number, which is based on the diameter of the wall tap and the friction velocity. The best relation to reasonably explain the static pressure measurement error is proposed in this paper.

Application of the Hartmann–Tran profile to precise experimental data sets of 12C2H2

Self- and nitrogen-broadened line shape data for the Pe(11) line of the ν1+ν3 band of acetylene, recorded using a frequency comb-stabilized laser spectrometer, have been analyzed using the Hartmann–Tran profile (HTP) line shape model in a multispectrum fitting. In total, the data included measurements recorded at temperatures between 125K and 296K and at pressures between 4 and 760Torr. New, sub-Doppler, frequency comb-referenced measurements of the positions of multiple underlying hot band lines have also been made. These underlying lines significantly affect the Pe(11) line profile at temperatures above 240K and poorly known frequencies previously introduced errors into the line shape analyses. The behavior of the HTP model was compared to the quadratic speed dependent Voigt profile (QSDVP) expressed in the frequency and time domains. A parameter uncertainty analysis was carried out using a Monte Carlo method based on the estimated pressure, transmittance and frequency measurement errors. From the analyses, the Pe(11) line strength was estimated to be 1.2014(50)×10−20 in cmmolecule−1 units at 296K with the standard deviation in parenthesis. For analyzing these data, we found that a reduced form of the HTP, equivalent to the QSDVP, was most appropriate because the additional parameters included in the full HTP were not well determined. As a supplement to this work, expressions for analytic derivatives and a lineshape fitting code written in Matlab for the HTP are available.

Temperature-insensitivity gas pressure sensor based on inflated long period fiber grating inscribed in photonic crystal fiber.

We demonstrated an inflated long period fiber grating (I-LPFG) inscribed in a pure-silica photonic crystal fiber (PCF) for high-sensitivity gas pressure sensing applications. The I-LPFG was inscribed by use of the pressure-assisted CO2 laser beam-scanning technique to inflate periodically air holes of a PCF along the fiber axis. Such an I-LPFG with periodic inflations exhibits a very high gas pressure sensitivity of 1.68nm/MPa, which is one order of magnitude higher than that, i.e., 0.12nm/Mpa, of the LPFG without periodic inflations. Moreover, the I-LPFG has a very low temperature sensitivity of 3.1 pm/°C due to the pure silica material in the PCF so that the pressure measurement error, resulting from the cross-sensitivity between temperature and gas pressure, is less than 1.8 Kpa/°C in the case of no temperature compensation. So the I-LPFG could be used to develop a promising gas pressure sensor, and the achieved pressure measurement range is up to 10MPa.

Challenges in standardization of blood pressure measurement at the population level.

BackgroundAccurate blood pressure measurements are needed in clinical practice, intervention studies and health examination surveys. Blood pressure measurements are sensitive: their accuracy can be affected by measurement environment, behaviour of the subject, measurement procedures, devices used for the measurement and the observer. To minimize errors in blood pressure measurement, a standardized measurement protocol is needed.MethodsThe European Health Examination Survey (EHES) Pilot project was conducted in 2009–2012. A pilot health examination survey was conducted in 12 countries using a standardized protocol. The measurement protocols used in each survey, training provided for the measurers, measurement data, and observations during site visits were collected and evaluated to assess the level of standardization.ResultsThe EHES measurement protocol for blood pressure was followed accurately in all 12 pilot surveys. Most of the surveys succeeded in organizing a quiet and comfortable measurement environment, and staff instructed survey participants appropriately before examination visits. In all surveys, blood pressure was measured three times, from the right arm in a sitting posture. The biggest variation was in the device used for the blood pressure measurement.ConclusionsIt is possible to reach a high level of standardization for blood pressure measurements across countries and over time. A detailed, standardized measurement protocol, and adequate training and monitoring during the fieldwork and centrally organized quality assessment of the data are needed. The recent EU regulation banning the sale of mercury sphygmomanometer in European Union Member States has set new challenges for the standardization of measurement devices since the validity of oscillometric measurements is device-specific and performance of aneroid devices depends very much on calibration.