Girculation model for monitoring arterial systolic blood pressure

The theoretical basis of a new technique for monitoring systolic blood pressure is explained. This method permits continuous beat-by-beat monitoring of systolic pressure. The circulatory system is considered as a simple elastic reservoir emptying through a resistance. If certain assumptions and conditions hold, the time rate of blood-volume change in a peripheral vascular region, during diastole or systole, can be related to the arterial systolic pressure. A critical element of the technique is the maintenance of the measured peripheral vascular region at near maximal vasodilatation. If the peripheral vascular bed is well dilated, and the subject is resting or doing light exercise, the technique should permit following of blood-pressure changes with a good approximation after calibration against a standard method of measuring blood pressure (sphygmomanometer).     

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.     

Analysis for the non-invasive determination of arterial properties and for the transcutaneous continuous monitoring of arterial blood pressure

Analyses are developed for the procedures of (i) the noninvasive determination of the arterial elastic properties and (ii) the transcutaneous continuous monitoring of arterial blood pressure. Expressions for the pulse wave velocity and arterial pressure are derived, separately, in terms of (1) the nonlinear arterial elastic properties (the coefficients of the strain energy density function), the internal and external diameters of the deformed pressurised artery and the ratio of the unpressurised arterial internal and external diameters, and (2) the nonlinear arterial elastic properties, unpressurised tube diameters and the external diameter of the pressurised artery. It is then shown that if the values of the pulse velocities at an arterial section and of the corresponding arterial diameters are obtained (say, by transcutaneous ultrasonic monitoring) at three instants, then adequate equations are obtained (from the above pulse velocity expressions) which can be solved to yield the values of the arterial properties and the undeformed arterial internal and external diameters. These values are substituted in the expression for arterial pressure, to yield an expression for the arterial pressure, solely in terms of the external arterial diameters. Hence, by continuously transcutaneously ultrasonically monitoring the external arterial diameter, the arterial pressure can be monitored continuously and noninvasively. The feasibility and the required accuracy of making these measurements are currently under investigation.     

Long-term ambulatory monitoring of indirect arterial blood pressure using a volume-oscillometric method

A new portable instrument equipped with a microprocessor was designed for the long-term ambulatory monitoring of indirect arterial pressure in the human finger at desired intervals using a volume-oscillometric technique. All the necessary procedures such as (1) programmed control of cuff pressure, (2) detection of the systolic end-point and the point of maximum amplitude of arterial volume pulsations, (3) reading of the cuff pressures corresponding to these two points, (4) its processing and (5) recording of the systolic and mean pressure together with heart rate on a digital memory integrated circuit were performed automatically. After the monitoring, the data were reproduced and analysed by a conventional personal computer. Simultaneous comparison of the data with direct measurement, operation and evaluation of this instrument, and ambulatory monitoring were carried out. With this instrument noninvasive and accurate monitoring of arterial pressure could be made in unrestricted subjects during daily activities.     

Noninvasive automatic monitoring of instantaneous arterial blood pressure using the vascular unloading technique

For the noninvasive monitoring of the beat-to-beat systolic and diastolic pressure and pressure waveform in the human finger, a new automated instrument was designed. This measurement is based on a principle called the vascular unloading technique. Using a hydraulic servocontrol system, the vascular volume change caused by intra-arterial pressure change can be compensated by applying counter pressure to maintain a constant vascular volume in the unloaded state. In this state the controlled counterpressure instantaneously follows the intra-arterial pressure. In this instrument all the necessary procedures, such as the setting of the reference value for the servocontrol, control of the servogain, processing and displaying of the data on a recorder, were carried out automatically. The simultaneous comparison of data with direct measurements and a few examples of the indirect pressure recordings by this instrument are shown and the principles, operation and evaluation of this method are described. This instrument was shown to permit the nonivasive and accurate tracking of instantaneous arterial pressure and to perform acceptably over a wide range of arterial pressure.     

Noninvasive monitoring of arterial blood oxyhemoglobin

Scientific-Industrial Association “Krasnogvardeets”, St. Petersburg. Translated from Meditsinskaya Tekhnika, No. 5, pp. 12–14, September–October, 1992.     

Soft wearable contact lens sensor for continuous intraocular pressure monitoring

Intraocular pressure (IOP) is a primary indicator of glaucoma, but measurements from a single visit to the clinic miss the peak IOP that may occur at night during sleep. A soft chipless contact lens sensor that allows the IOP to be monitored throughout the day and at night is developed in this study. A resonance circuit composed of a thin film capacitor coupled with a sensing coil that can sense corneal curvature deformation is designed, fabricated and embedded into a soft contact lens. The resonance frequency of the sensor is designed to vary with the lens curvature as it changes with the IOP. The frequency responses and the ability of the sensor to track IOP cycles were tested using a silicone rubber model eye. The results showed that the sensor has excellent linearity with a frequency response of ∼8 kHz/mmHg, and the sensor can accurately track fluctuating IOP. These results showed that the chipless contact lens sensor can potentially be used to monitor IOP to improve diagnosis accuracy and treatment of glaucoma.     

Reduction of false arterial blood pressure alarms using signal quality assessement and relationships between the electrocardiogram and arterial blood pressure

The paper presents an algorithm for reducing false alarms related to changes in arterial blood pressure (ABP) in intensive care unit (ICU) monitoring. The algorithm assesses the ABP signal quality, analyses the relationship between the electrocardiogram and ABP using a fuzzy logic approach and post-processes (accepts or rejects) ABP alarms produced by a commerical monitor. The algorithm was developed and evaluated using unrelated sets of data from the MIMIC database. By rejecting 98.2% (159 of 162) of the false ABP alarms produced by the monitor using the test set of data, the algorithm was able to reduce the false ABP alarm rate from 26.8% to 0.5% of ABP alarms, while accepting 99.8% (441 of 442) of true ABP alarms. The results show that the algorithm is effective and practical, and its use in future patient monitoring systems is feasible.     

Integrated circuit system for digitizing arterial blood pressure and heart rate

The measurement of arterial blood pressure during physiological, pharmacological or behavioral manipulations generates a vast amount of data which must be reduced. Hand scoring is both time consuming and inaccurate, while on-line computer analysis may be prohibitively expensive. As an alternative, an inexpensive circuit is described which digitizes, stores, and prints out mean systolic and diastolic blood pressure, as well as heart rate, from up to four analog channels. Channels are sequentially digitized, each for an interval dialed on the front panel (1–999 sec). For each beat, a peak and trough detector enables the systolic and diastolic accumulators, respectively, thus storing two ten bit words from the analog to digital converter. For each systolic occurrence, a count of one is added to the heart rate counter. At the end of the recording interval, an output routine prints the interval number, mean systolic pressure, mean diastolic pressure, and total heart beats. Offset and gain controls allow precise calibration of various transducer and polygraph amplifiers.     

Long-term control of arterial blood pressure.

Two concepts for the long-term regulation of arterial pressure were considered in this review, the neural control hypothesis and the volume regulation hypothesis. The role of the nervous system and fluid volume regulation are intertwined in a way that has made it difficult to experimentally evaluate their separate contributions in the long-term regulation of arterial pressure. Nevertheless, from a substantial body of work related to the neural control of cardiovascular function, it appears that the ability of the nervous system to control arterial pressure is limited to the detection and correction of rapid short-term changes of arterial pressure. A long and exhaustive search has yet yielded no new neural mechanisms beyond the classic sinoaortic baroreceptors that can detect changes of arterial pressure. The baroreceptor mechanisms are of great importance for the moment-to-moment stabilization of arterial pressure, but because they do not possess sufficient strength and because they reset in time to the prevailing level of arterial pressure, they cannot provide a sustained negative feedback signal to provide long-term regulation of arterial pressure in face of sustained stimuli. This is not to say that the nervous system cannot affect the long-term level of arterial pressure. A distinction is made here between the many factors that can influence the long-term level of pressure and those that actually serve to detect changes of pressure and serve to maintain the level of pressure within a narrow range over the period of our adult lifetime. In this sense, there is evidence that in genetically susceptible individuals, environmental stresses can influence the long-term level of arterial pressure via the central and peripheral neural autonomic pathways. It is inappropriate, however, to view the nervous system as a long-term controller of arterial pressure because there is yet no evidence that the CNS can detect changes of arterial pressure nor changes in total body sodium and water content over sustained periods whereby it could provide an adequate long-term normalization of such error signals. In contrast, evidence has grown in support of the renal pressure-diuresis volume regulation hypothesis for the long-term control of arterial pressure over the past decade. An enhanced understanding of the mechanisms of pressure diuresis-natriuresis coupled with studies exploring how changes of vascular volume can influence vascular smooth muscle tone provide a compelling basis for this hypothesis of long-term arterial pressure regulation. This overall concept is represented and summarized in Figure 12.(ABSTRACT TRUNCATED AT 400 WORDS)     

A minicomputer system for long-term automatic blood pressure monitoring

An automated system for the indirect measurement of blood pressure on seacted factory workers has been developed and has been in continuous daily operation for nine months. Six industrial workers on a conveyor assembly line are monitored serially. Because of completely automatic operation of this system, blood-pressure data can be collected over a long time period without any experimenter intervention. This system was developed as part of a larger study titled “Effects of Paced Performance on Industrial Productivity, Job Satisfaction and Physiological Stress,” NSF Grant #7718695     

Verylow frequency variability in arterial blood pressure and blood volume pulse

Several parameters of the cardiovascular system fluctuate spontaenously owing to the activity of the autonomic nervous system. In the study, the simultaneous very low frequency (VLF) fluctuations of the arterial blood pressure, the tissue blood content and the tissue blood volume pulse are investigated. The latter two parameters are derived from the baseline BL and the amplitude AM of the photoplethysmographic (PPG) signal, measured on the fingertips of 20 healthy male subjects: the changes in the PPG parameters AM and BV, defined by BV=const.-BL, are related to the change in the tissue blood volume pulse and the total tissue blood volume, respectively. The VLF fluctuations in BV and AM are directly correlated, those of AM preceding those of BV by 4–13 heart-beats. The VLF fluctuations in the systolic (SBP) and the diastolic (DBP) blood pressure are inversely correlated to those of AM and BV, those of AM preceding those of SBP and lagging behing those of DBP by about one heart-beat. For most subjects, the period P of the PPG pulse, which is equal to the cardiac cycle period, directly correlates with AM and BV and inversely correlates with DBP and SBP. On average, the fluctuations fluctuations in tissue blood volume, systolic blood volume pulse, diastolic and systolic blood pressure, and heart period, together with their interrelationship, can provide a better understanding of the autonomic nervous control of the peripheral circulation and a potential tool for the evaluation of its function.