Long-term Blood Pressure Monitoring Research Articles

Design of small size and high sensitive less‐invasive wireless blood pressure sensor using MEMS technology

This study presents an implantable passive wireless blood pressure sensor using an inductive coupling wireless sensing technique that is designed for long-term monitoring of blood pressure in hypertension patients. This sensor includes a gold tapered square spiral inductor and a circular capacitor with a polyimide diaphragm. The purpose of this study is to minimise the dimension of the sensor due to the limitation of space around the vessel; therefore, a microelectromechanical systems (MEMS) inductor and a capacitor with small dimension and high sensitivity are used. In this structure, the diaphragm is deflected by applied pressure which capacitance and then resonance frequency are changed. These changes are sensed remotely with inductive coupling, which eliminates the need of wires connection for monitoring. In this method, a blood pressure signal can be obtained by measuring the impedance phase dip from the external coil. The distance between two coils is 8 mm. The sensor is designed to provide a resonance frequency range of 282-381 MHz for a pressure range of 0-250 mmHg. Simulation has been done using COMSOL Multiphysics and ADS software. The dimension of the sensor is 2.2 mm × 2.2 mm and the sensitivity of the sensor is 1550. This sensor has a small size and high sensitivity rather than previous works.

Wireless Blood Pressure Monitoring with a Novel Implantable Device: Long-Term In Vivo Results

Devices constantly tracking the blood pressure (BP) of hypertensive patients are highly desired to facilitate effective patient management and to reduce hospitalization. We report on experiences gathered in a pilot study that was designed to evaluate the prototype of a newly developed, minimally invasive implantable sensor system for long-term BP monitoring. The device was implanted in the femoral artery (FA) of 12 sheep via standard FA catheterization under fluoroscopic control. Accuracy of the recorded blood pressure was determined by comparison with a reference catheter, which was positioned in the contralateral FA immediately after implantation. Regular follow-up included angiography, computed tomography (CT), and control of functionality and position of the BP sensor. Animals were euthanized after 6 months. FA segments with in situ pressure sensor underwent macroscopic and histopathologic examinations. All implantations of the novel sensor device in the FA were successful and uneventful. High-quality BP recordings were documented. Bland-Altman plots indicate very good agreement. Comparison with measurements taken from the reference sensor revealed mean differences and standard deviations of -0.56 ± 0.85, 0.29 ± 1.44, and 0.85 ± 2.27 mmHg (diastolic, systolic, and pulse pressure, respectively) after exclusion of one outlier. CT uncovered deficiencies in cable stability that were addressed in a redesign. No thrombus formation, necrosis, or apoptosis were detected. The pilot study proved the technical feasibility of wireless BP measurement in the FA via a novel miniature sensor device.

Subcutaneous blood pressure monitoring with an implantable optical sensor

We introduce a minimally invasive, implantable system that uses pulse transit time to determine blood pressure. In contrast to previous approaches, the pulse wave is detected by a photoplethysmographic (PPG) signal, acquired with high quality directly on subcutaneous muscle tissue. Electrocardiograms (ECG) were measured with flexible, implantable electrodes on the same tissue. PPG detection is realized by a flat 20 mm x 6 mm optoelectronic pulse oximeter working in reflection mode. The optical sensor as well as the ECG electrodes can be implanted using minimally invasive techniques, with only a small incision into the skin, making long-term monitoring of blood pressure in day-to-day life for high-risk patients possible. The in vivo measurements presented here show that the deviation to intra-arterial reference measurements of the systolic blood pressure in a physiologically relevant range is only 5.5 mmHg, demonstrated for more than 12 000 pulses. This makes the presented sensor a grade B blood pressure monitor.

An implantable optical blood pressure sensor based on pulse transit time

An implantable sensor system for long-term monitoring of blood pressure is realized by taking advantage of the correlation between pulse transit time and blood pressure. The highly integrated implantable sensor module, fabricated using MEMS technologies, uses 8 light emitting diodes (LEDs) and a photodetector on chip level. The sensor is applied to large blood vessels, such as the carotid or femoral arteries, and allows extravascular measurement of highly-resolved photoplethysmograms. In addition, spectrophotometric approaches allow measurement of hemoglobin derivatives. For the calibration of blood pressure measurements, the sensor system has been successfully implemented in animal models.

Highly flexible capacitive strain gauge for continuous long-term blood pressure monitoring

An innovative procedure for measuring blood pressure, with none of the disadvantages of current procedures, is proposed. A highly-flexible capacitive strain gauge has been designed to measure changes in the diameter of a blood vessel; such changes are indicative of blood pressure. The sensor is implanted and wrapped around an arterial blood vessel during the normal course of a surgical procedure. In vivo tests, demonstrating the feasibility of this concept, are reported, along with in vitro tests and notes on sensor design and fabrication. These continuous blood pressure monitoring sensors may be used for a continuous long-term monitoring of blood pressure and pulse. They may also be combined with a real-time nerve stimulation technique or a course of medication to create a closed-loop system for blood-pressure control.

Estimating blood pressure using the pulse transit time of the two measuring from pressure pulse and PPG

Blood pressure (BP), one of the most important vital signs, is used to identify an emergency state and reflects the blood flow characteristics of the cardiovascular system. The conventional noninvasive method of measuring BP is inconvenient because patients must wear a cuff on their arm and the measurement process takes time. This paper proposes an algorithm for estimating the BP using the pulse transit time (PTT) of the photoplethysmography (PPG) and pressure pulse from finger at the same time as a more convenient way to measure the BP. After recording the electrocardiogram (ECG), measuring the pressure pulse, and performing PPG, we calculated the PTT from the acquired signals. Then, we used a multiple regression analysis to measure the systolic and diastolic BP indirectly. Comparing the BP measured indirectly using the proposed algorithm and the real BP measured with a sphygmomanometer, the systolic pressure had a mean error of <TEX>${\pm}3.240$</TEX> mmHg and a standard deviation of 2.530 mmHg, while the diastolic pressure had a satisfactory result, i.e., a mean error of <TEX>${\pm}1.807$</TEX> mmHg and a standard deviation of 1.396 mmHg. These results are more superior than existing method estimating blood pressure using the one PTT and satisfy the ANSI/AAMI regulations for certifying a sphygmomanometer i.e., the measurement error should be within a mean error of <TEX>${\pm}5$</TEX> mmHg and a standard deviation of 8 mmHg. These results suggest the possibility of applying our method to a portable, long-term BP monitoring system.

Development of A Nonintrusive Blood Pressure Estimation System for Computer Users

An individual's cardiovascular health is important. The measurement of blood pressure (BP) can be performed nonintrusively during normal daily activities. A study was designed to estimate systolic BP by measuring pulse arrival time (PAT) nonintrusively. PAT was obtained nonintrusively to estimate each individual's BP while he or she worked at a computer. Electrocardiogram (ECG) was measured with a capacitive-coupled electrocardiogram (CC-ECG) system and photoplethysmogram (PPG) was measured using specially installed circuits in a computer mouse. PAT was calculated from CC-ECG and PPG, and compared to PAT measured by the standard method. Three individuals participated in this study. Results correlated well. An equation to estimate BP from the measured PAT was derived for each of three individuals during a training period. Estimated BP was compared with measured BP in a series of experiments under varied BP conditions. For each individual, the estimated BP followed the measured BP within a tolerable error range. This method was also used for long-term BP monitoring. Results showed that this method could be useful for monitoring BP for telemedicine and e-health.

Direct Versus Guidewire-Assisted Pediatric Radial Artery Cannulation Technique

Radial artery cannulation is a more difficult procedure in pediatric patients. Direct technique commonly fails in these patients, and several techniques have been developed for successful arterial cannulation. The purpose of this study was to compare direct radial artery cannulation with guidewire-assisted cannulation in children undergoing cardiac or aortic surgery. The hypothesis was that the guidewire-assisted technique would lead to fewer attempts and provide better long-term blood pressure monitoring and blood sampling. One hundred pediatric patients with congenital heart defects undergoing major cardiovascular surgery, who required a radial artery catheter, were included in the study. Patients were divided into 2 groups: group 1 included 50 patients who had radial artery cannulation with the direct technique, and group 2 included 50 patients who had a guidewire-assisted radial artery cannulation. A radial artery was successfully cannulated in 48 patients in group 2 but only 38 patients in group 1. Mean elapsed time for radial artery cannulation was 22 +/- 4.6 minutes in group 1 and 7 +/- 4.2 minutes in group 2 (p = 0.001). The average number of attempts for cannulation was 4.5 in group 1 and 2.1 in group 2 (p = 0.022). The opposite radial or an alternative artery was used more commonly in the direct technique group. Satisfactory blood pressure monitoring and sampling of blood were obtained in 28 patients in group 1 and 46 patients in group 2 (p < 0.001). The authors recommend the use of a guidewire-assisted radial artery cannulation technique rather than a direct technique. The guidewire-assisted technique provided easy, safe, and quick cannulation and allowed for long-term satisfactory blood pressure monitoring and blood sampling because of the longer length of the Teflon catheter advanced into the artery over the guidewire, and a low rate of dissection of the radial artery.

Circadian hypo- and hyper-amplitude-tension (CHAT) associated with putative pheochromocytoma and 12-hourly phenoxybenzamine treatment

A 26-year-old white woman had an ablated sino-atrial node and ventricular pacemaker as an unusual feature of a pheochromocytoma-compatible history. Her status quo included, on three occasions, elevated 24-hour urinary epinephrine and metanephrine excretion. She monitored her blood pressure (BP) and heart rate (HR) at 15- to 60-minute intervals over several days, with interruptions, before and after the institution of 10 mg phenoxybenzamine per os every 12 hours (between 7:30 and 8:00 and between 19:30 and 20:00), with continued monitoring over several months. Her data were summarized for consecutive 3-day intervals by sphygmochron. Circadian parameters and original data are compared with gender- and age-specified reference values, yielding also non-parametric endpoints, such as the percentage time elevation, the extent of excess, and the timing of excess, that all can be acceptable for some days but unacceptable for other days. In her broader time structure, or chronome, cosinor analyses revealed a prominent and statistically significant circadian rhythm in BP and HR before and during the 12-hourly therapy. The 12-hour component of BP was more prominent during therapy than prior to it. A statistically significant decreasing trend occurred before therapy, and recurred during treatment. Chronomically interpreted monitoring revealed: 1) the persistence of a statistically significant circadian rhythm during 12-hourly phenoxybenzamine treatment; 2) days-long changes in BP MESOR, the duration of which could not be previously determined based on spotchecks; 3) changes in the circadian amplitude of BP, which can be either very small or very large, compatible with the diagnosis of intermittent circadian hyper-amplitude-tension (CHAT); and 4) a very wide range of BP and HR values, so that occasional (casual) measurements fail to convey the dynamics that may underlie this infrequently found clinical condition of an elevated catecholamine excretion compatible with a pheochromocytoma. All findings support the need for long-term monitoring of BP and HR that may account for controversy in earlier publications.

Blood pressure measurement in research and in clinical practice: recent evidence

For over a century the technique of blood pressure measurement developed by Riva-Rocci and Korotkoff has provided most of the data on hypertension diagnosis and treatment. Its limitations, however, are becoming increasingly evident and therefore alternative solutions are under investigation. This paper is intended to provide an overview of important recent progress in this field, and to highlight future perspectives. A major development in blood pressure measurement is the technical improvement of electronic manometers for use either in the clinic (with the auscultatory approach, as an alternative to use of mercury columns), or in automated oscillometric devices yielding blood pressure measurements devoid of observer-dependency, and allowing long-term blood pressure monitoring. In the latter case, blood pressure measurement is made possible in settings other than the physician's office, either through ambulatory blood pressure monitoring or through self blood pressure measurement at home. These methods are growing in clinical importance, but further studies are needed to define their indications more precisely in the clinical evaluation of hypertensive patients. Recently, important steps towards better standards of blood pressure measurement have been taken, as summarized in the guidelines jointly issued by the European Society of Hypertension (ESH) and the European Society of Cardiology (ESC), in the 7th Joint National Committee Report and (in even more detail) in the Blood Pressure Measurement Guidelines published by the ESH Working Group on Blood Pressure Monitoring. Blood pressure measurement is a rapidly developing field, the importance of which is increasingly acknowledged in the light of the growing awareness of the impact of hypertension on public health. Despite remarkable progress, many methodological issues still remain to be properly addressed.

Long-term blood-pressure monitoring in unrestrained animals.

Long-term blood-pressure monitoring in unrestrained animals.

Diastolic function parameters and atrial arrhythmias in patients with arterial hypertension

To investigate in patients with arterial hypertension (HT) the extent of left ventricular (LV) hypertrophy and diastolic function in relation to atrial arrhythmias. In 112 hypertensive patients (40 women, 72 men; mean age 50 +/- 6.6 years) with a mean systolic blood pressure for the cohort of 170 +/- 5 mmHg, their first invasive coronary angiography was performed between July 1995 and October 1997 because of angina pectoris and/or an abnormal stress electrocardiogram. After excluding coronary heart disease LV dimensions and diastolic function were measured by echocardiography; in 59 of the 112 patients LV hypertrophy was demonstrated. In addition, long-term blood pressure monitoring, exercise and long-term electrocardiography, late-potential analysis and measurement of heart rate variability were undertaken. The control group consisted of 51 patients without arterial hypertension after exclusion of coronary heart disease. Even in the hypertensive patients without LV hypertrophy diastolic LV function and ergometric exercise capacity were reduced. The risk of LV arrhythmias was significantly higher in patients with LV hypertrophy than those without and in the control group, as measured by the complexity of atrial arrhythmias (P < 0.001), the incidence of abnormal late potentials (P < 0.001) and reduction in heart rate variability (29.3 +/- 5.3 ms vs 47.8 +/- 12.1 ms vs 60.7 +/- 6.6 ms; P < 0.001). There were similar results regarding severe complex atrial arrhythmias (38.5 vs 15.0 vs 0%; P < 0.001). The incidence of atrial arrhythmias correlated with the LV diameter (r = 0.68, P < 0.001), LV morphological dimensions and diastolic function (isovolumetric relaxation time r = 0.44, P < 0.001) and the ratio of early to late diastolic inflow (r = 0.46; P < 0.001). Hypertensive patients have a higher risk of atrial and ventricular arrhythmias, depending on the degree of LV hypertrophy. But atrial arrhythmias, in contrary to ventricular arrhythmias, are also closely related to abnormalities in LV diastolic function.

Data Analysis of Long-term Blood Pressure Monitoring

Long-term blood pressure monitoring provides a large quantity of data with a wide inter-individual or inter-group variability. The conventional "mean/standard deviation" approach to data analysis is a relatively insensitive instrument for detecting circadian differences in blood pressure profile, mainly because the mean and the variability around the mean are processed separately. The proposed Standardized Systolic and Diastolic Scoring (SSDS) method enhances the analytical possibilities. Preliminary evaluation of the SSDS method using data obtained in an anti-hypertensive drug trial suggests clinical relevance.