Biomedical Engineering BE513: Biomedical Instrumentation I

Projects

These are some basic ideas, which you can either follow completely, or modify in order to build one of your own designs.

If you need an instrumentation amplifier, you can use a pre-packaged one, such as the AD620. This has a gain up to 1000, CMMR 100dB and works on a power supply of 2.3-18V.

The Report should be about 10 pages.

The Presentation will be 15 mins, with 5 mins for questions.

Electronic Stethoscope

The stethoscope was invented by Laennec in 1750. The original was simply a horn which the physician applied to the chest of the patient. Later versions allowed the clinician to remain at a respectable distance, by the use of flexible tubes, and this design is still the most popular today. The main uses for a stethoscope are: Most of these sounds are very low frequency, and this is a challenge for the design of an electronic stethoscope. Once recorded, the sounds could be stored, analysed and sent via a phone or modem link to a specialist.

Galvanic Skin Response (GSR)


The GSR, or Electrodermal Response (EDR), is a simple way to measure the state of relaxation or excitement of a subject. Since sweat gland activity is controlled by sympathetic nerve activity (part of the autonomic nervous system), the skin impedance varies with the level of psychological stress. The GSR is one of the principal parts of a lie detector, or polygraph, test. Electrodes are usually placed on the skin of the palms. The circuit can be very simple or a bit more complicated.

Electroencephalogram (EEG)

EEG, electroencephalography, is the recording of voltages from the brain via scalp electrodes, first done by Berger in the late 1920s. The amplitude of EEG waves is very small, typically in the range of tens of microvolts. They are thought to be caused by synchronized activity in very large numbers of synapses in the cerebral cortex. The EEG curves are classed according to "rhythm". There are five recognized rhythms:
 

Delta 0.1-4 Hz deep sleep, lucid dreaming, increased immune functions, hypnosis
Theta 4-8 Hz deep relaxation, meditation, increased memory, focus, creativity, lucid dreaming, hypnagogic state, small children, various pathological conditions. 
Alpha 8-12 Hz light relaxation, "super learning", positive thinking
Low Beta 12-15 Hz relaxed focus, improved attentive abilities
Midrange Beta 15-18 Hz increase mental ability, focus, alertness, IQ
High Beta above 18 Hz fully awake, normal state of alertness, stress and anxiety
Gamma 40 Hz associated with information-rich task processing and high-level information processing

Applications of EEG include epilepsy diagnosis, brain tumor localiation, lie-detection (the police polygraph uses EEG), biofeedback and emotion analysis. Some recent products even allow people to play music, move computer screen cursors, interact with games, turn on appliances, and even guide wheelchairs - all by controlling their brain-wave patterns. Biofeedback is perhaps the most interesting to try as a project.

Phonocardiogram (PCG)

Recording of the sound produced by the beating heart. It's particularly useful for investigating murmurs caused by valve problems. The PCG can be hard to hear in noisy surroundings and, in any case, the heart generates 'noise' (note this is auditory, not electrical, noise) of its own, compounded by noisy signals from imperfect measuring instruments (microphones). There are sounds generated by breathing, by the contact of stethoscope on skin. To the ear, this noise can be a hissing or scratchy sound, masking the real sounds of normal or abnormal heart function. When a phonocardiogram is displayed as a trace on a screen, the noise shows as random spikes, interfering with the true record of the heart's activity.

Sphygmomanometer

Blood pressure is a combination of the force initiated by the heart as it pumps blood into the arteries and through the circulatory system, and that of the arteries as they resist blood flow. tThe American Heart Association (AHA) considers a measurement of 130/85 normal for adults. The higher number is the systolic reading, which refers to the pressure while the heart is beating. The lower or diastolic number signifies the pressure when the heart is resting between beats. The AHA recommends that patients whose blood pressure ranges from 130-139/85-89 be closely monitored for high blood pressure (hypertension).

Blood pressure can be taken via invasive or noninvasive means. Invasive techniques employ needles or catheters with intravascular transducers. These methods are
considered the most accurate, but are clearly not appropriate for routine measurement in the doctor's office. The first non-invasive test was developed in 1905 by Dr. Korotkoff of Russia, using a stethoscope during cuff deflation to listen to arterial blood flow. Sounds occur at systolic pressure, which later disappear when diastolic pressure is reached. These Korotkoff sounds still form the basis of all noninvasive sphygmomanometers. Korotkoff's sounds occur in five phases:

                           • Faint, clear tapping (systolic pressure).
                           • Murmurs or swishing sounds.
                           • Crisper, louder sounds.
                           • Distinct, abrupt muffle of sound.
                           • Lack of sound (diastolic pressure in adults).

The point at which repetitive, clear tapping sounds first appear (Korotkoff Phase I) gives the systolic blood pressure (SBP). This technique is important because Phase I sounds sometimes disappear as pressure is reduced and reappear at a lower level (the auscultatory gap), resulting in underestimation of the SBP. The disappearance of sound (Korotkoff Phase V) should be taken as the diastolic reading. In some patients (e.g. pregnant, elderly, anemic) muffling of the Korotkoff sounds (Phase IV) is taken as the diastolic pressure.

Eye motion-controlled mouse

When the eyes move, biopotentials are generated. These corneo-retinal potentials (from the back of the eye to the front of the eye) biopotentials are generated by the retinal dipole, and variously called the EOG (Electro-oculogram), ERG (Retinogram) or ENG (Nystagmogram). The potentials vary with a number of factors, e.g. light level, blinking, and tends to drift.EOG electrodes EOG circuit

Wireless Heart Rate meter (cardiotachograph)

A Heart Rate Monitor uses ECG electrodes to monitor heart rate and rhythm. It is extremely useful in anesthesia, surgery, medicine, exercise testing, sports medicine and research. Heart Rate (HR) is usually measured as the interval between successive heart beats (inter-beat interval, IBI). Each time a heart beat occurs, a self-adjusting circuit in the Interval Timer converts the electrical shape of the heart wave into a discrete 'trigger'. This trigger is used first to take the reading of the clock (which is transferred to a temporary electronic memory or buffer) and then it re-starts the clock at zero. Most commercial devices use a chest strap and wireless link to a wristwatch, which does the prcessing and display.

Beltless Heart Rate Watch

HEALTH PRODUCTS - Strapless Heart Watch

Putting on a chest strap can be a bit inconvenient - what about picking up the ECG from the wrist? These watch are now becoming very popular and cheap. You'll need a very sensitive amplifier, capable of working with dry electrodes (back of the watch + tip of a finger of the other hand).
 

Photoplethysmograph

rheoscreen PPG finger sensor and pressure cuff. Click to see a larger image.


Photoplethysmography (PPG)  is based on the determination of the optical properties of a selected skin area. For this purpose non-visible infrared light is emitted into the skin. More or less light is absorbed, depending on the blood volume in the skin. Consequently, the backscattered light corresponds with the variation of the blood volume. Blood volume changes can then be determined by measuring the reflected light and using the optical properties of tissue and blood. You can see this effect with your own eyes: skin with less blood looks white, while skin with more blood looks darker. The photoplethysmograph does nearly the same thing but with much higher sensitivity and resolution.

The is a noninvasive method for measuring volume changes in parts of the body cause by blood being pumped in and out. In Volume Displacement plethysmography, the scattering or reflection of light (wavelength 650nm) is detected with a photodiode and transimpedance amplifier. (Beer-Lambert law).diagram of the infrared sensor and its interaction with the skin anatomy
 
 

Pulse Transit Time blood pressure monitor

The Pulse Transit Time (R-P Interval), the time delay between the R wave in the EKG (or more proximal, e.g. brachial PPG) and the peripheral pulse felt at the wrist has a degree of correlation with Diastolic Blood Pressure (DBP).

Pulse Wave Analysis by impedance plethysmography

The impedance of extremeeties such as fingers, arms and legs changes with the blood flow in and out, so this provides another method for plethysmography.
The arterial pulse wave has a very low amplitude and is superimposed on the venous blood volume changes. Pulse wave measurements are possible in many locations including the head (this measurement is called rheoencephalography). Pulse waves can also be measured in the fingers and toes with photoplethysmography.

The shape of the pulse wave is determined, in part, by the elasticity of the blood vessels. A trained technician can analyze the shape of the curve to get early information about a developing arterial vascular disease. The pulse wave analysis can often detect changes very early, and is noninasive, very easy to use, and one of the most economical techniques available today. The pulse wave is changed by different diseases:


 

EMG-Timer

Repetitive stress disorder (RSI) is common problem in certian occupations, such as computer operators, due to over or prolonged use of certain muscles. This project aims at designing an EMG controlled timer that will measure the accumulated time that a muscle has been active, and trigger an alarm when it is over-used.

Breathing Sensor

Breathing, or respiration, is usually measured by a

Plant Biodynamic Response Detector

Living plant tissues or leaves are capable of simultaneously sensing temperature change, gravitational variation, electromagnetic fields, and a host of other environmental effects. So maybe plants could be used as sensors?

Wheelchair pressure monitor

 Review the physiology of skin vascularization Use an integrator, NE555 timer and a force-sensitive resistor (FSR) to create an alarm that depends on Note that the response of an FSR is non-linear (logarithmic) so you will need to linearize it with an exponential amplifier


This page last updated 2 Sept 2002 by Chris Kirtley