Share this book Facebook. Last edited by ImportBot. An edition of Encyclopedia of Medical Devices and Instrumentation This edition was published in Apr 07, by Wiley-Interscience — pages. Not in Library.
Libraries near you: WorldCat. Download for print-disabled. Encyclopedia of Medical Devices and Instrumentation First published in Bracke et al. The circuit uses a special clocking scheme, in which the analog sensor circuit block is clocked at a low 8 kHz frequency, while the sigmadelta modulator is clocked at kHz. The technique ultimately reduces power consumption to 90 mW on the ON-state. In such cases, power can only be found via a battery implanted together with the sensing system or through passive telemetry.
In passive telemetry, energy may be harvested from a remote electromagnetic eld transmitted outside the body. The same eld may also be used to receive control data and transmit sensor data to a data logger.
In both cases, minimizing power consumption is essential. A simple low power interface for biomedical applications could be realized by using a simple relaxation oscillator 46, A capacitance-to-frequency modulated output was rst proposed by Hanneborg et al. This circuit delivers a digital pulse trail with frequency dependent on the sensor. Figure 9. Simple electrical model of a capacitive sensor. Parasitic capacitances is designated by Cp1,2, conductances by Gp and the sensing capacitance by Cs.
Figure Circuit blocks of the capacitive electronic interface as described by W. The circuit consists of two current sources: a switch and a Schmitt trigger. The unknown capacitance is periodically charged and discharged by ipping the switch between current I and I Fig.
An implementation of this type of capacitance-to-frequency converter is presented in Fig. The circuit converts capacitance at its input into a frequency signal that can be readily fed to a digital microcontroller for processing. Either a capacitive sensor or a reference may be. Block diagram of the capacitive to frequency converter proposed by Hanneborg et al. The circuit consists of two current sources, a switch and a Schmitt trigger.
The parameter Vc is a control signal that allows for switching between the unknown sensor capacitance Cx and a reference capacitor Cref. The response of a pressure measuring system based on this circuit realized in 1. It operates at 4 V and draws 20 mA of average current.
A photograph of this system is shown in Fig. In medical science, however, there is often the need for long-term monitoring of vital life parameters. A good example is abdominal aortic aneurysm AAA , which is a ballooning of the abdominal aorta. Patients who suffer from this condition need to undergo a procedure during which a stent graft is inserted.
After the operation, however, it is possible that the aneurysmal sac is not completely isolated, leading to recurrent pressurization of the sac, a complication that, if left undetected, may lead to rupture of the sac and patient death.
Long-term, postoperation monitoring of the patients is therefore necessary. Early efforts for systems for the monitoring of blood pressure 54 used miniature active transmitters to transfer measured data and were battery powered, which limited.
Schematic of Schmitt-trigger based oscillator used as a capacitive interface. An alternative approach to power these modules is through induction coupling, while the same radio frequency RF eld can be used to transfer data out of the implanted module The implanted circuit should be virtually immune to supply uctuations arising from random misalignment of the implanted and the external coil.
A new circuit was developed based on the previous architecture, but in which each circuit block was redesigned. The block diagram of the passive telemetry system is depicted in Fig. It consists of an external control unit the base unit and an implantable transponder. Wireless communication can then be established between the two units, based on an absorption modulation mechanism.
The transponder receives power and external control data. Frequency response of a pressure measuring system consisting of the simple circuit of Fig.
A photograph of a hybrid pressure measuring system consisting of a capacitive sensor and associated signal conditioning electronic circuit. The base unit, on the other hand, demodulates the transmitted data and processes it though a microcontroller to convert the signal into an eight bit unsigned byte array. The resulting byte can then be sent to a PC through a serial output.
The block diagram of the transponder electronics is shown in Fig. The improved capacitance-to-frequency circuit is used to interface a capacitive pressure sensor.
The circuit consists of two basic blocks: a bandgap reference voltage generator and an oscillator. In order to achieve independence of the output frequency from the received power, this time the oscillator operates on an internally stabilized voltage generated from a bandgap reference. In addition, to further immune the system from supply uctuations a current mode comparator is used in the oscillator. The bandgap reference voltage circuit is capable of operating at a low power supply as it operates on an internally regulated voltage VREG This same node is also used for the supply of the oscillator circuit after the contributions of the extra branches of the oscillator are accounted for.
The oscillator itself is designed around a current mode comparator that results in an output frequency independent of power supply uctuations and with small temperature drift.
Triggering levels of this oscillator are dened by two currents: Ih and Il. Equation 5 implies that the output frequency is independent of the supply voltage and is dependent on temperature through the mobility term in k and the threshold voltage Vt. Note also that the bias voltage Vbias is chosen to be equal to the bandgap reference voltage produced from the previous stage, and is thus considered independent of voltage and temperature variations.
The system remains operational for a supply voltage down to 2. Simulated pressure pulses as those present in the aorta were measured using passive telemetry Fig. Silicon is the material of choice for these devices, which are nding applications for measuring pressure and. By taking the inverse of eq. Simulated pressure pulses as those present in the aorta measured using passive telemetry.
Actually, although most of the existing devices are not integrated together with signal conditioning electronic circuits on the same chip, in the future it is expected that there will be an increasing integration scheme driven by the need of higher level miniaturization.
Because of their low power consumption advantage, capacitive microsensors are of interest as implantable monitoring devices. An attractive application appears to be a miniaturized telemetry system that combines techniques for wireless power and data transfer to a capacitive sensor integrated with signal conditioning electronics. Silicon Diffused-Element Piezoresistive Diaphragm. J Appl Phys ; Smith CS. Piezoresistance Effect in Germanium and Silicon.
Phys Rev ; Development of a miniature Pressure Transducer for Biomedical Application. Data Science Int. Konigberg Instruments Inc. Pasadena, California. Pressure sensitivity in anisotropically etched thindiaphragm pressure sensors. Passive Silicon Transensor Sens Actuators ;A21 13 A capacitive pressure sensor with low impedance output and active.
Sens Actuators ;A21 Goosen JFL. Design considerations for silicon sensors for use in catheters and guide wires. Smart Mater Struct ; A miniature self-aligned pressure sensing element. J Micromech Microeng ; Miniature ber optic pressure sensor. A free-hangMelva ing strain-gauge for ultraminiaturized pressure sensors.
Sens Actuators A ;97 8 J MicroElectroMech S ;9 1 Naja N, Ludominky A. Biomed Microdevices ;6 1 A readout circuit for an intra-ocular pressure sensor, Sens. Actuators A ; Hierold C, et al. Low power integrated pressure sensor for medical application. Sens Actuators A ;73 12 Polliack AA, et al. Laboratory and clinical tests of a prototype pressure sensor for clinical assessment of prosthetic socket t. Prosth Ortho Inter ;26 1 Threedimensional measurements of the pressure distribution in articail joits with a capacitive sensor array.
J Biomech ; Inclination measurement of human movement using a 30D accelerometer with autocalibration. Puers R, Reyntjen S. Design and processing experiments of a new miniaturized capacitive triaxial accelerometer. Sens Actuators A ;68 Design, realiLo zation and characterization of a symmetrical triaxial capacitive accelerometer for medical application. Sens Actuators A ;61 Huang Y, et al.
Fabricating capacitive micromachined ultrasonic transducers with wafer-bonding technology. J Microelectromech S ;12 2 Cianci E, et al. One-dimensional capacitative micromachined ultrasonic transducer arrays for echographic probes. Microelect Eng ; The rst low voltage, low noise differential silicon microphone, technology development and measurement results. Sens Actuators A ; J MicroElectroMech S ;7 4 : Hydrogel-actuated capacitive transducer for wireless biosensors.
Biomed Microdevices ;4 2 Petersen KE. Silicon as a mechanical material. Proc IEEE ;70 5 Guidelines for etching silicon MEMS structures using uorine high-density plasmas at cryogenic temperatures. J MicroElectroMech S ;11 4 Madou M.
Fundamentals of Microfabrication: The Science of Miniaturization. Wallis G, Pomerantz DI. Field assisted glass-metal sealing. An implantable pressure sensor for use in cardiology. Tong QY, Gosele U. Semiconductor Wafer Bonding. New York: Wiley-Interscience; Mechanically induced Si layer tranfer in hydrogen-implanted Si wafers.
Appl Phys Lett ; Goustouridis D, et al. Low temperature wafer bonding for thin silicon lm transfer. Sens Actuators A ; Tsuchiya T, Funabashi H. A z-axis differential capacitive SOI accelerometer with vertical comb electrodes. Comparative evaluation of drying techniques for surface micromachining. Jin X, et al. Fabrication and characterization of surface micromachined capacitive ultrasonic immersion transducers. J Microelectromech S ; A CMOS-compatible high aspect ratio silicon-on-glass in-plane micro-accelerometer.
Semiconductor pressure sensor based on FET structure. Ko WH, Wang Q. Touch mode capacitive pressure sensors. Hanneborg A, et al. An integrated capacitive pressure sensor with frequency-modulated output. Sens Actuators ; 9 4 Senturia S. Microsystem Design. Boston: Kluwer Academic Publishers; Matsumoto Y, Esashi M. Integrated silicon capacitive accelerometer with PLL servo technique. A universal transducer interface for capacitive and resistive sensor elements. Analog Integr Circuits Signal Process ; A generic interface chip for capacitive sensors in low-power multi-parameter Microsystems.
A novel low-cost capacitivesensor interface. Trans Instr Meas ;45 2 On the optimization of ultra low power front-end interfaces for capacitive sensors. Sens Actuators A ; 2 A solid-state pressure-sensing microsystem for biomedical applications. Implantable Blood Pressure Telemetry System.
Neukomm PA, Kuendig H. Passive wireless actuator control and sensor signal transmission. Sens Actuators ;A21A Tham KM, Nagaraj K. It is the amount of blood pumped by the ventricles of the heart and can be dened as the product of stroke volume SV and heart rate HR , where stroke volume is the amount of blood expelled by the ventricle with each contraction and the HR is the number of contractions per minute: CO SV HR Cardiac output gives an indication of ventricular function and is also used in the calculation of a number of owdependent parameters, such as cardiac index, systemic vascular resistance, pulmonary vascular resistance, valve areas, and intracardiac shunt ratios.
The Fick technique is the gold standard in CO measurement. It relies on direct measurement of oxygen consumption and expenditure to derive the rate of blood ow throughout the individual.
This came after almost 30 years of work by Fick and numerous others, who reasoned that diffusion was one of the most essential events within the living organism. In , Fick had published his ndings relating to diffusion of gas across a uid membrane. These became known as Ficks law of diffusion and stated that the rate of diffusion of a gas is proportional to the partial pressures of the gas on either side of the membrane, the area across which diffusion is taking place and the distance over which diffusion must take place.
As an aside, Fick also invented contact lenses in The publication by Adolf Fick stated: It is astonishing that no one has arrived at the following obvious method by which [the amount of blood ejected by the ventricle of the heart with each systole] may be determined directly, at least in animals.
One measures how much oxygen an animal absorbs from the air in a given time, and how much carbon dioxide it gives off. During the experiment one obtains a sample of arterial and venous blood; in both the oxygen and carbon dioxide content are measured.
As one knows the total quantity of oxygen absorbed in a given time one can calculate how many cubic centimeters of blood passed through the lungs in this time. Or if one divides by the number of heart beats during this time one can calculate how many cubic centimeters of blood are ejected with each beat of heart.
The corresponding calculation with the quantities of carbon dioxide gives a determination of the same value, which controls the rst 1. In simplest terms, cardiac output can be calculated as a ratio of the amount of oxygen consumed through breathing and the rate in which oxygen is taken up by the tissues.
An alternative to the Douglas bag method is the use of a metabolic rate meter with a hood or facemask, a variablespeed blower and a servocontrol loop with an oxygen sensor. This method employs essentially the same principle as the Douglas bag method, but gives a real-time measurement of VO2.
The variable-speed blower maintains a flow of room air through the hood or facemask past the patient into a polarographic oxygen sensor gold and silversilver chloride electrode , varying the flow in order to keep the oxygen concentration at the measuring electrode constant. By keeping the oxygen concentration at the measuring electrode constant, the only variable is the flow rate through the system. Under steady-state conditions, this is the only variable determining the oxygen consumption VO2.
Although this method provides a real-time measurement of VO2, thus excluding the need for collection of a Douglas bag, it is still rather time and labor intensive. In addition, it has been suggested that it is difcult to obtain reproducible results and the method gives consistently lower results then the Douglas bag technique. Arteriovenous Difference As with oxygen consumption, measurement of oxygen uptake by the body involves measuring blood oxygen content before and after entering the lungs.
The arteriovenous oxygen difference AVdiff is the difference between the content of oxygen ctO2 in the oxygenated arterial blood leaving the lungs and the deoxygenated venous blood returning to the lungs mL O2 per mL of blood. The AVdiff represents the volume of oxygen delivered to meet the bodys metabolic demands. Again, this gure is multiplied by 10 to give the AVdiff in units of mL O2 per liter of blood.
Cardiac Output The rate at which oxygen is taken up by the lungs and the rate at which it is taken up by the body is now known from the above calculations. The ratio of these two gures gives the cardiac output. The examples above show that the lungs take up mL of oxygen each minute and that the blood takes up 63 mL of oxygen for each liter that passes through the lungs.
How many lots of 63 mL 1 L aliquots of blood must pass through the lungs to take up mL of oxygen each minute?
The answer is 5. This is best done in the resting state so that there is constant oxygen consumption over the collection period. Then, from the volume of expired gas, the oxygen content of the expired gas and the oxygen content of the inspired room air, it is possible to calculate the amount of oxygen taken up by the individual. Applying a factor of 10 gives this gure as milliliters of O2 per liter of expired gas, which are the units used later in the calculation. Dividing the total volume of expired gas by the collection time gives the minute ventilatory rate, expressed in liters per minute L min1.
The product of the O2 difference mL L1 and the minute volume L min1 is the oxygen consumption VO2 expressed in milliliters of oxygen absorbed per minute. Obviously, these will vary from day to day, leading to a potential source of variation in the calculation of oxygen consumption, and ultimately, cardiac output. The combined gas law a combination of Boyles and Charles law describes the relationship of pressure, temperature, and volume in a gas.
This law can be used to correct measured gas volumes to standard temperature and pressure STP. This means that the measured volume of gas is standardised to K and mmHg As well as correcting for variations in atmospheric pressure, it is also necessary to correct for water vapor pressure.
Daltons law tells us that the pressure of a gas mixture is equal to the partial pressures of all of the components of the mixture. Water vapor is present in the atmosphere and in exhaled gas and its partial pressure contributes to the total atmospheric pressure. Water vapor exerts a constant pressure at a given temperature, regardless of the atmospheric pressure.
Water vapor pressure is 47 mmHg 6. Before correcting for STP it is necessary to subtract the water vapor pressure from the total atmospheric pressure to obtain the dry gas pressure at the ambient temperature. This is known as standard temperature and pressure, dry STPD , which is used for the correction. Arteriovenous Oxygen Difference Although many current generation analyzers can calculate oxygen content ctO2 , earlier models did not.
It may be necessary to manually calculate oxygen content from the hemoglobin level Hb and oxygen saturation of a sample. Hemoglobin is able to carry 1. Therefore, by multiplying the hemoglobin. Simply stated, this is the maximum amount of oxygen that can be carried by mL of the individuals blood and is dependent on the hemoglobin level.
Some textbooks have quoted the constant as 1. Oxygen carrying capacity Hgb mL dL1 If the total amount of oxygen that the blood is capable of carrying and the saturation of the sample is known, it is possible to calculate the oxygen content of that sample.
Figure 1 shows a complete example of CO measurement using the Fick technique. We then assume that the amount of blood pumped by the right ventricle through the lungs is equal to the amount pumped by the left ventricle through the systemic vessels since the cardiovascular system is a closed system. This assumption does not always hold true and it is sometimes necessary to alter the calculation.
The term shunt describes the condition where a communication exists between the left- and right-sided chambers of the heart. If this condition results in shunting of blood between the venous and arterial circulation, the assumption becomes invalid because some blood is being recirculated through part of the circuit and the two ventricles are pumping unequal volumes.
If an intracardiac shunt is known or suspected, it is necessary to collect blood samples at different points than the standard arterial and pulmonary artery sites. Calculation of cardiac output and. Includes an accompanying website with the design of thecertified ECG product www. Download PDF. You may also like. This technique is insensitive to background noise, but arm movement may cause an errant reading. It may overestimate. Volumetric oscillometry is a technique based on detection of nger volume pulsations under a cuff.
The pressures are estimated as the cuff pressures at which nger volume oscillations begin systolic pressure and become maximal mean pressure. Diastolic pressure is then derived from the known systolic and mean pressures. One problem with this technique is that this nger pressure may have a variable relationship to the brachial pressure. Another problem is that the technique cannot directly assess diastolic pressure. Despite some problems associated with the mentioned techniques, their accuracy has been conrmed by validation testing using mercury sphygmomanometry and intraarterial measurement.
Patients are advised to wear the monitor for a period of 24 h, preferably during a normal working day. The monitor is preprogrammed to measure and record blood pressure at certain time intervals, preferably every min during daytime hours and every min during nighttime hours. Patients are also advised to document their activity during the testing period for assessment of any stressrelated blood pressure.
The monitoring device consists of a small central unit and an attached cuff. The central unit contains a pump for cuff ination and deation, and the memory device, such as tape or digital chip, for recording. The time intervals between the measurements, maximal and minimal ination pressures, and deation rate are programmable according to the physicians order.
The recording pressures can be retrieved from the tape or memory chip for analysis. Due to recent applications of digital technology and advanced software programs, a large amount of data can be stored in a small chip, and analysis can also be done automatically to generate a patients report for the physicians use.
A complete patients report normally contains all blood pressure readings over a 24 h period, heart rates, mean arterial pressures, and statistic summaries for daytime, nighttime, and 24 h periods. New Clinical Concepts Related to Ambulatory Blood Pressure Monitoring A few new considerations related to ambulatory blood pressure monitoring have emerged.
These include blood pressure load, pressure dipping, pressure variability, and white-coat hypertension. Health professionals need to understand these concepts in order to properly interpret or use data collected from monitoring. Blood Pressure Load. This is dened as the proportion of the 24 h pressure recordings above the thresholds for waking and sleep blood pressure.
Blood pressure load is helpful in the diagnosis of hypertension and in the prediction of end-organ damage. It has been considered closely correlated with left ventricle. Dipping and Circadian Blood Pressure Variability. Dipping is a term used to describe the circadian blood pressure variation during 24 h ambulatory blood pressure monitoring.
In normotensive patients there is circadian blood pressure variability. Typically, the peak blood pressures occur around 6 a. In comparison to dippers, nondippers have been reported associated with higher prevalence of left ventricular hypertrophy, albuminuria, peripheral arterial changes, and cerebral lacunae. Nondippers have also been reported to have increased cardiovascular mortality rates 8. White-Coat Hypertension. This is a condition in which blood pressure is persistently elevated in the presence of a doctor, but falls to normal levels when the patient leaves the medical facilities.
Measurement by a nurse or trained nonmedical staff may reduce this effect. Because decisions regarding treating hypertension are usually made on the basis of isolated ofce blood pressure reading, a doctor may incorrectly diagnose this group of patients as sustained hypertension and prematurely start the therapy. However, white-coat hypertension can be easily detected by either ambulatory blood pressure monitoring or self-monitoring at home.
It may or may not be benign, requiring denitive outcome studies to rule out any end-organ damages. It also requires continued surveillance by self-monitoring at home and repeat ambulatory blood pressure monitoring every 12 years 9, The ambulatory blood pressure prole should also be inspected in relation to diary data and time of drug therapy.
Indications of Ambulatory Blood Pressure Monitoring Although ambulatory blood pressure monitoring was originally developed as a research tool, it has widely been applied in clinical practice to help diagnose and manage hypertensive patients. It is indicated to rule out white-coat hypertension, to evaluate drug-resistant hypertension, to assess symptomatic hypertension or hypotension, to diagnose hypertension in pregnancy, and to assess adequacy of.
Ofce-based blood pressure measurement cannot differentiate sustained hypertension from white-coat hypertension. Historical appraisal and review of self-recorded blood pressures may aid in identication of patients with white-coat hypertension. However, ambulatory blood pressure monitoring is more effective in this clinical scenario to rule out white-coat hypertension. Recognition and proper management of patients with white-coat hypertension may result in a reduction in medication use and eliminate related cost and side effects.
Drug-Resistant Hypertension. Ambulatory blood pressure monitoring helps evaluate whether additional therapy is needed. The causes include true drugresistant hypertension as well as other conditions such as superimposition of white-coat hypertension on existing hypertension, patients noncompliance, pseudohypertension secondary to brachial artery calcication, and sleep apnea and other sleep disorders.
Ambulatory blood pressure monitoring can help differentiate the true drug resistant hypertension from the above-mentioned conditions Episodic Hypertention. A single ofce-based measurement of blood pressure may or may not detect episodic hypertension as in pheochromocytoma. In this clinical scenario the 24 h ambulatory blood pressure monitoring is a useful diagnostic tool.
It is indicated if a patients symptoms or signs are suggestive of episodic hypertension Borderline or Labile Hypertension. Patients with borderline hypertension often demonstrate only some but not all elevated blood pressure readings in ofce-based measurement, 24 h ambulatory blood pressure monitoring can benet these patients and provide a useful diagnostic information for physicians use Hypertension with End-Organ Damage.
Patients who exhibit worsening of end-organ damage may suggest inadequate 24 h blood pressure control. Occasionally, those patients may demonstrate adequate blood pressure control based on the ofce-based measurements. In this condition, a 24 h blood pressure monitoring is needed to rule out inadequate blood pressure control, which is associated with worsening of end-organ damage Some hypertensive patients are at particularly high. Those patients require rigorous blood pressure control over 24 h.
Ambulatory blood pressure monitoring can be applied to assess the 24 h control Suspected Syncope or Orthostatic Hypotension. Transient hypotensive episodes and syncope are difcult to assess with the ofce-based blood pressure measurements, but are readily recorded with ambulatory blood pressure monitoring.
Therefore, if symptoms and signs are suggestive of syncope or orthostatic hypertension, patients can benet from 24 h blood pressure monitoring, especially in conjuction with Holter monitoring Hypertension in Pregnancy. It is important to differentiate true hypertension in pregnancy from white-coat hypertension, to avoid unwarranted hospitalizations or medication use. In this clinical scenario, ambulatory blood pressure monitoring would help to rule out white-coat hypertension and identify pregnancy-induced hypertension Clinical Research.
Since ambulatory blood pressure monitoring can provide more samples of blood pressure measurements, data from this device is therefore much more statistically signicant than a single isolated ofcebased reading. Therefore, statistical signicance of clinical studies can possibly be achieved with smaller numbers of patients.
This is very important for the efcient study of new therapeutic agents Limitations of Ambulatory Blood Pressure Monitoring Although ambulatory blood pressure monitoring has been proved useful in the diagnosis and management of hypertension, the technology remains underused secondary to lack of experience in interpretation of results, unfamiliarity with devices, and some economic issues.
Adequate staff training, regular calibration of devices, and good quality control are required. The patients diary of daily activities and time of drug treatment are also needed for proper data analysis and interpretation. Future Development Like any other ambulatory device, an ideal noninvasive ambulatory blood pressure monitoring device should be user-friendly, light-weight, compact in size, digitalized for automated data management, and low in cost.
Application of newer technologies will make such devices available, hopefully, in the near future. Figure 3. Ambulatory glucose monitoring with guardian real time system Medtronic MiniMed. Development of minimally invasive or noninvasive ambulatory glucose monitoring devices that provide accurate, near-continuous measurements of blood glucose level have the potential to improve diabetes care signicantly.
Such devices will provide information on blood glucose levels, as well as rate and direction of change, which can be displayed to patients in real-time and be stored for later analysis by physicians. It provides continuous real-time glucose readings around the clock.
Due to the huge market potential, many biomedical and medical instrument companies are developing similar devices for ambulatory glucose monitoring. Several innovative devices have recently been unveiled; many more are still in development. It is expected that some of them will be eventually U.
Food and Drug Administration FDA approved as a replacement for standard blood glucose monitors, providing patients with a new option for long-term, daily monitors in the near future. The FDA is concerned about the accuracy of ambulatory continuous glucose monitoring devices when compared to the accuracy of standard monitoring devices. This issue will be eventually eliminated as related technologies become more and more mature. Technically, a typical ambulatory glucose monitoring device consists of a glucose sensor to measure glucose levels and a memory chip to record data information.
Glucose Sensors The glucose sensors for ambulatory glucose monitoring devices are either minimally invasive or completely noninvasive. A variety of technologies have emerged over the past decade aiming at development of ideal glucose sensors suitable for ambulatory monitoring. A typical minimally invasive ambulatory continuous glucose sensor is a subcutaneous device developed by Minimed, Inc. The sensor is designed to be inserted into a patients abdominal subcutaneous tissue.
The technology involves measurement of glucose levels of. It is essential to monitor blood glucose to ensure overall adequate blood glucose control. Traditional standard blood glucose. The blood glucose levels are then derived from the measured interstitial uid glucose levels. The detection mechanism involves use of a low uorescence molecule. Electrons are transferred from one part of the molecule to another when excited by light.
This prevents bright uorescence from occurring When bound to glucose, the molecule prevents the electrons from interfering with uorescence, and the molecule becomes a bright uorescent emitter. Therefore, the glucose levels can be determined based on the brightness of uorescence. The glucose information will be transmitted from the sensor to a watch-like device worn on the wrist. Using this type of sensor, two devices have been developed by the company.
One is a device that can be worn by the patient for a few days to record the glucose levels for the physicians analysis. The other is a device that can alert patients of impending hyperglycemia or hypoglycemia if the glucose levels go beyond the physicians predetermined upper and lower limits. The sensor can also work in conjunction with an implanted insulin pump, creating a biomechanical or articial pancreas in response to the change at the glucose levels It is predictable that such a biomechanical pancreas will eventually benet millions of diabetic patients whose glucose control is dependant on insulin.
Complete noninvasive sensors for ambulatory glucose monitoring are even more attractive since they do not need any blood or interstitial samples to determine glucose levels. Several such sensors have recently been developed based on different technologies. For example, a glucose sensor that can be worn like a wristwatch has been developed by Pendragon Medical AG Zurich, Switzerland.
This sensor can continuously monitor blood glucose level without the need for a blood sample. It is based on impedance spectroscopy technology The principle of this technology relates to the fact that blood glucose changes produce signicant conductivity changes, causing electric polarization of cell membranes. At the same time, the sensor generates an electronic eld that uctuates according to the electrical conductivity of the body.
A micro antenna in the sensor then detects these changes and correlates them with changes in serum glucose. With this technology, blood glucose levels can be monitored noninvasively in real time. Another promising noninvasive sensor is based on the possibility of measuring glucose by detecting small changes in the retinal capillaries. By scanning the retinal microvasculature, the sensor can directly measure glucose levels in aqueous humor using a reectometer.
Recently, a plastic thin sensor, which can be worn like a contact lens, has been innovated 22, The sensor changes its color based on the concentration of glucose, from red, which indicates dangerously low glucose levels, to violet, which indicates dangerously high glucose concentrations.
When glucose concentration is normal, the sensor is green. Integration of the sensor material into commercial contact lenses may also be possible with this technology.
Memory Chips Memory chips are used to record glucose data information for later use by the physician. The digital chips have many advantages, such as compact size, large memory, easy data transmission via wire or wireless, and possible. Patients can also upload their glucose data from digital memory chips to web-based data management systems, allowing diabetic patients and their health care providers to analyze and communicate glucose information using the internet.
Signicances of Ambulatory Glucose Monitoring Ambulatory glucose monitoring can provide continuous data on blood glucose levels. Such data can improve diabetic care by enabling patients to adjust insulin delivery according to the rate and direction of blood glucose change, and by warning of impending hypoglycemia and hyperglycemia.
Doctors can use ambulatory glucose monitoring to help diagnose problematic cases, ne-tune medications, and get tighter control of blood glucose levels for high risk patients. Obviously, the monitoring will improve overall blood glucose control, reducing short-term adverse complications and delaying onset of long-term serious complications, such as end-stage renal disease, heart attack, blindness, stroke, neuropathy, and lower extremity amputation.
In addition, continuous ambulatory glucose monitoring is a key step toward the development of articial pancreas, which could deliver insulin automatically in response to blood glucose levels. It is expected that such an articial pancreas would greatly benet many diabetic patients and provide them new hope for better quality of life. Future Development Although many continuous ambulatory glucose monitoring devices are still in the stage of clinical trials, there is little doubt as to the value of the devices in management of diabetic patients.
It is expected that millions of diabetic patients will be beneted once such devices are widely available. At the same time, introduction of more and more new devices highlights the need for careful evaluation to ensure accuracy and reliability. Cooperation between the manufacturers and physicians to ne-tune the technology will eventually lead to approval of the devices by the FDA to replace traditional invasive standard glucose monitoring.
Technology for continuous ambulatory glucose monitoring is also required to make an articial pancreas, which would offer great hope for millions of patients with diabetes. Continuous advancement in a variety of technologies provides more and more innovative ambulatory devices to serve the patients need. Applications of information technology and specialized software tools make autotransmission and autoanalysis of ambulatory monitoring data possible.
Clinicians will be able to monitor their ambulatory patients distantly without a hospital or ofce visits. In addition, integration of the technology of continuous ambulatory monitoring with an implantable automatic therapeutic pump may create a biomechanical system in response to specic abnormal changes. The articial pancreas currently in development is a typical example for.
Caduff A, et al. First human experiments with a novel noninvasive, non-optical continuous glucose monitoring system. Biosens Bioelecs ; Ophthalmic glucose sensing: a novel monosaccharide sensing disposable and colorless contact lens. Analyst England ; Ophthalmic glucose monitoring using disposable contact lensesa review. J Fluoresc ; Holter NJ. New method for heart studies: Continuous electrocardiography of active subjects over long periods is now practical.
Science ; Heilbron EL. Advances in modern electrocardiographic equipment for long-term ambulatory monitoring. Card Electrophysiol Rev ;6 3 Kadish AH, et al. Circulation ; Kinlay S, et al. Event recorders yield more diagnoses and are more cost-effective than 48 hour Holter monitoring in patients with palpitations. Ann Intern Med ; Portable blood pressure recorder accuracy and preliminary use in evaluation intradaily variations in pressure. Am Heart J ; Zachariah PK, et al.
Blood pressure load: A better determinant of hypertension. Mayo Clin Proc ; Assessment of the daily blood pressure load as a determinant of cardiac function in patients with mild-to-moderate hypertension.
Pickering TG. The clinical signicance of diurnal blood pressure variations: dippers and nondippers. Verdecchia P, et al. White-coat hypertension: not guilty when correctly dened. Blood Press Monit ; Pickering TG, et al.
How common is white coat hypertension. Hypertension ; Palatini P, et al. Is resistant hypertension really resistant?
Am J Hypertens ; Canadian hypertension society quidelines for ambulatory blood pressure monitoring. Pickering T. Recommendations for the use of home self and ambulatory blood pressure monitoring.
OBrien E, et al. Use and interpretation of ambulatory blood pressure monitoring: recommendations of the British Hypertension Society. BMJ ; Halligan A, et al. Twenty-four-hour ambulatory blood pressure measurement in a primigravid population. J Hypertens ; Conway J, et al. The use of ambulatory blood pressure monitoring to improve the accuracy and reduce the numbers of subjects in the clinical trials of antihypertensive agents.
J Clin Exper Hypertension ; Cross TM, et al. Performance evaluation of the MinMed continuous glucose monitoring system during patient home use. Diab Technol Ther ; In vivo molecular sensing in diabetes mellitus: an implantable glucose sensor with direct electron transfer.
Diabetes ; Jaremko J, Rorstad O. Advances toward the implantable articial pancreas for treatment of diabetes. Diabs Care ; The presence, concentration, and activity of chemical constituents are indicators of various organ functions. Concentrations higher or lower than expected sometimes require immediate attention. Some of the reasons to analyze body uids: 1. Screening of an apparently healthy population for unsuspected abnormalities.
Conrming or ruling out a diagnosis. Monitoring changes during treatment, improvement of condition or lack of improvement. Detecting or monitoring drug levels for diagnosis or maintenance of optimal therapeutic levels. By the s, demands of clinicians for laboratory tests increased rapidly. Classical methods of manual laboratory techniques could not keep up with these demands. The cost of performing large numbers of laboratory tests by manual methods became staggering and the response time was unacceptable.
The article in the rst edition of this Encyclopedia published in describes the history of laboratory instrumentation during the previous three decades 1. Reviewing that long list of automated instruments, with the exception of a few, all became museum pieces.
During the last 15 years the laboratory landscape changed drastically. In addition, new group of automated instruments were introduced during this period. They were developed to perform bedside or near patient testing, collectively called Point of Care Testing instruments.
In this period in addition to new testing instruments, perianalytical instrumentation for specimen handling became available. Their combined result is increased productivity and reduction of manpower requirements, which became imperative due to increased cost of healthcare and dwindling resources. This article will present some nancial justication of these investments. Blood specimens yield the most information about the clinical status of the patient though in many cases urine is the preferred sample.
For specialized tests, other body uids that include sweat and spinal uid are used. When some tests, such as glucose and lipids, require fasting specimens, patients are prepared accordingly. Common errors affecting all specimens include the following: Inaccurate and incomplete patient instructions prior to collection. Failure to label a specimen correctly.
Insufcient amount of specimen to perform the test. Specimen leakage in transit due to failure to tighten specimen container lids. Interference by cellular elements of blood. Phlebotomy techniques for blood collection have considerably improved with better gauge needles and vacuum tubes for collection. The collection tubes are color coded with different preservatives so that the proper container can be used for a particular analyte.
The cells should be separated from the serum by centrifugation within 2 h of collection. Grossly or moderately hemolyzed specimens may be unsuitable for certain tests. The effect is much greater in neonates 2. If there is a delay in separating the cells from the serum, the blood should be collected in a gray top tube containing sodium uoride as a preservative that inhibits glycolysis.
Urine collection is prone to errors as well, some of which include 3 : Failure to obtain a clean catch specimen. No preservative added if needed prior to the collection.
Once specimens are properly collected and received in the clinical laboratory, processing may include bar coding, centrifugation, aliquoting, testing and reporting of results. Clinical chemistry analyzers can be grouped according to throughput of tests and diversity of tests performed and by function, such as immunoassay analyzers, critical care blood gas analyzers, and urinalysis testing systems.
Point of Care analyzers vary in terms of accuracy, diversity and menu selection. Some of the features to consider while evaluating low or high volume analyzers are listed below: Test menu available on instrument: Number of different measured assays onboard simultaneously.
Number of user-dened open channels. Reagents: Preparation of reagents if any. Storage of reagents. On board stability. Bar-coding for inventory control. Specimen volume: Minimum sample volume. Dead volume. Instrument supplies: Use of disposable cuvettes. Clot detection features along with quantitation of hemolysis and turbidity detection. Auto dilution capabilities of analyzer. Frequency of calibration. Quality control requirements. Stat capability.
LIS interface. Maintenance procedures on instrument; anticipated downtime. Analyzer costs expressed in cost per reportable test.
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