Biomedical Instrumentation

Archive for the ‘Biomedical Basics’ Category

Dear all! A device capable of generating artificial pacing impulses and delivering them to heart is known as a pacemaker system or pace maker. Generally a pacemaker consists of pulse generator and electrodes. Pacemakers are used to extend the life of the cardiac patient having total bundle block. Generally, Sino Atrial node is responsible for the starting of heart beat; hence it is termed as natural pacemaker. The pacemaker can be fixed either externally or internally in the body. Based on the placement, it is classified as internal or external. Internal pacemaker is one which the entire unit is placed inside the body. It may be permanently implanted on the patients whose SA nodes are failed to function or those who suffered from permanent heart block. Internal Pacemaker systems are implanted with the pulse generator placed in a surgically pocket below the right or left clavicle, in left sub costal region. In case of women, it is placed beneath the left or right major pectoralis muscle. Internal leads are connected to the electrodes that directly contact the surface of the myocardium shows the pulse generator fixed in abdomen. The internal pacemaker system is implanted internally. There is no external connection for applying power. So, the pulse generator should be completely self-contained with a battery, which is capable of operating continuously for a specified period.

The heart is the centre of the circulatory system. The circulatory system helps in supplying the oxygen and digested food to different parts of the body and removing carbon dioxide from our body. The heart will act as the pump. The heart pumps the blood by a movement called as the “heart beat”. The normal heart beat rate is 72 beats per minute. The heart pumps the blood through the pulmonary circulation to the lungs and through systematic circulation to other organs of the body. Generally the heart is divided into four chambers such as right atrium, left atrium, right ventricle, left ventricle. The filling action is done by atrium and pumping action is done by ventricle. Get more details about personal loans for people with bad credit.The blood vessel that carries pure blood from heart to various organs is known as arteries. Similarly the blood vessel through which the impure blood returns to the heart is known as veins. The types of blood circulation can be divided in to three types which include pulmonary circulation, systematic circulation, and coronary circulation. There are four valves present in the heart such as mitral valve, semi lunar valve, tricuspid valve and aortic valve. The two types of blood pressure can be measured namely systole and diastole. The contraction of the heart muscle is termed as the systole. The relaxation of the heart muscle is termed as the diastole. The systolic pressure is 120 mm of Hg, the diastolic pressure is 80 mm of Hg for normal human being.

Dear friends! As a bio medical engineer I hereby bring to your kind attention about cells and its structure which is most important for our body structure. Cell is the basic living unit of the human body, each organ in our human body consists of different cells and each type of cells is responsible for one particular function. Entire body contains 100 trillion cells. All cells have the ability to reproduce new cells whenever the cells of a particular type are destroyed, until the appropriate number is filled. For example, 25 trillion red blood cells will transport oxygen from lungs to the tissues i.e. the oxygen combines with carbohydrates, fat or protein in order to release the energy required for cell function. You know that, generally the structure of cell cannot be seen by naked eye, it can be viewed only be biological scope. So don’t try to see the structure of cell with naked eye. Each cell consists of a centrally located nucleus. The cell core is surrounded by cytoplasm. The cytoplasm is separated from the surrounding fluid by the cell membrane.

Dear friends! You must know about the need of ventilators. These are used to provide artificial respiration. Artificial respiration should be applied to the patient whenever respiration is suspended due to reasons like gas poisoning, electric shock, accidents etc. the cerebral cortex is not able to survive for more than 3 to 5 minutes without oxygen. So, resuscitation should be started be started without any delay before the heart muscle fails. The artificial respiration is used to ventilate the alveoli with air and it is also used to simulate the respiratory centers to renew the activities. Ventilators are classified in to time cycled ventilators, volume cycled ventilators, and pressure cycled ventilators.

If we consider the human body as a building, the skeleton is the frame work. It proves the mechanical stability. It protects the delicate organ. The skeletal also contains bone marrows [normally the blood cells are formed in the bone marrows]. The skeletal system will act as the reservoir for calcium and phosphorus. The skeletal bones are enclosed by a membrane called periosteum, from which new bones are formed in the healing of fractures. The skeletal is divided in to cranium skull, pelvis, and foot bones. The friction in the joints is reduced by the smooth articular cartilage present in the skeletal system.

The sounds and murmurs from the heart can be picked up from the chest using a stethoscope. The conversion of heart sounds into electrical signals can be done by condenser microphone. The sounds from the heart are termed as phonogram or phonocardiogram and the instrument used to measure the heart sounds is called as phonocardiograph. The technique of listening to sounds produced by the organs and vessels of the body is called as Auscultation.

Applications of digital computer in medicine and related fields are so numerous. Most of these applications, however, utilize a few basic capabilities of the computer which provide an insight to ways in which computer can be used in conjunction with modern medical electronics and instrumentation.

• Data acquisition and storage: The reading of instruments and transcribing of data can be done automatically under control of computer. This not only results in a substantial saving of time and effort, but also reduces the possibilities of number of errors in the data. When data are expected at irregular intervals, the computer can continuously scan all input sources and accept data whenever they are actually produced. The ability of the digital computer to store and retrieve large quantities of data is well known. The biomedical field provides ample opportunities to make use of this capability. In a modern hospital large amounts of data are accumulated from many sources.
  
• Data reduction and transformation: The sequence of numbers resulting from digitizing an analog physiological signal such as ECG or EEG would be quite useless if retrieved from the computer in raw form. To obtain meaningful information from such data some form of data reduction or transformation is necessary to represent the data as a set of specific parameters. These parameters can be analyzed, compared with other parameters, or otherwise manipulated.
  
• Mathematical operation and pattern recognition: Many important physiological variables cannot be measured directly, but must be calculated from other variables that are accessible. If a digital computer is connected on-line with the measuring instruments, the calculated results can often be obtained while the patient is still connected to the instruments. To reduce certain types of physiological data into useful parameters, it is often necessary that important features of a physiological waveform or an image be identified. Digital computer programs are available to search the data representing the ECG signal for certain predetermined characteristics that identify each of the important peaks.
  
• Limit detection and control function: In application involving monitoring and screening, it is often necessary to determine when a measured variable exceeds certain limits. By comparison of measured parameter with each limit of the range, the computer can indicate which parameters exceed the limit and the amount by which they deviate from normal. Digital computers are capable of providing output signals that can be used to control other devices. The computer can also be used to provide feedback to the source of its data.

Information obtained from a sensor or transducer is often in terms of current intensity, voltage level, frequency or signal phase relative to a standard. Voltage measurements are the easiest to make, as the signal from the transducer can be directly applied to an amplifier having high input impedance. However, most of the transducers produce signal in terms of current, which can be conveniently converted into voltage by using operational amplifiers with appropriate feedback. To make an accurate measurement of voltage, it is necessary to arrange that the input impedance of the measuring device must be large compared with the output impedance of the signal source.

This is to minimize the error that would occur, if an appreciable fraction of the signal source. This is to minimize the error that would occur, if an appreciable fraction of the signal source were dropped across the source impedance. Conversely, accurate measurement of current source signals necessitates that the source output impedance be large compared with the receiver input impedance. Ideally, a receiver that exhibits zero input impedance would not cause any perturbation of the current source. Therefore, high-impedance would not cause any perturbation of the current source. Therefore, high-impedance current sources are more easily handled than low-impedance current sources.

In general, the frequency response of the system should be compatible with the operating range of the signal being measured. To process the signal waveform without distortion, the bandpass of the system must encompass all of the frequency components of the signal that contribute significantly to signal strength. The range can be determined quantitatively by obtaining a Fourier analysis of the signal. The bandpass of an electronic instrument is usually defined as the range between the upper and lower half-power frequencies. The results of a measurement in medical instruments are usually displayed either on analog meters or digital displays.

The primary purpose of medical instrumentation is to measure or determine the presence of some physical quantity that may some way assist the medical personnel to make better diagnosis and treatment. Accordingly, many types of instrumentation systems are presently used in hospitals and other medical facilities. The majority of the instruments are electrical or electronic systems, although mechanical systems such as ventilators or Spiro meters are also employed. Certain characteristic features, which are common to most instrumentation systems, are also applicable to medical instrumentation systems. In the broadest sense, any medical instrument would comprise of the following four basic function components.

Measurand and Display system: The physical quantity or condition that the instrumentation system measures are called the measurand. The source for the measurand is the human body which generates a variety of signals. The measurand may be on the surface of the body or it may be blood pressure in the chambers of the heart. Display Systems Provides a visible representation of the quantity as a displacement on a scale, or on the chart of a recorder, or on the screen of a cathode ray tube or in the numerical form.

Transducer or sensor: A transducer is a device that converts one form of energy to another. Because of the familiar advantages of electric and electronic methods of measurement, it is usual practice to convert into electrical quantities all non –electrical phenomenons associated with the measurand with the help of a transducer. Another term sensor is also used in medical instrumentation systems. Basically, a sensor converts a physical measurand to an electrical signal. The sensor should be minimally invasive and interface with the living system with minimum extraction of energy.

Signal conditioner: Converts the output of the transducer into an electrical quantity suitable for operation of the display or recording system. Signal conditioners may vary in complexity from a simple resistance network or impedance matching device to multi-stage amplifiers and other complex electronic circuitry. Signal conditioning usually include functions such as amplification, filtering analog-to-digital and digital-to-analog conversion or signal transmission circuitry. They help in increasing the sensitivity of the instruments by amplification of the original signal or its transduced form.

Biomedical signals are those signals which are used primarily for extracting information on a biological system under investigation. The process of extracting information could be simple as feeling the pulse of a person on the wrist or as complex as analyzing the structure of internal soft tissues by an ultrasound scanner. Biomedical signals originate from a variety of sources such as:

Bioelectric signals: These are unique to the biomedical systems. They are generated by nerve cells and muscle cells. Their basic source is the cell membrane potential which under certain conditions may be excited to generate an action potential. The electric field generated by the action of many cells constitutes the bio-electric signal. The most common examples of bioelectric signals are the ECG and EEG.

Bio-acoustic signals and Biomechanical signals: The measurement of acoustic signals created by many biomedical phenomena provides information about the underlying phenomena. The examples of such signals are: flow of blood in the heart, through the heat’s valves and flow of air through the upper and lower airways and in the lungs which generate typical acoustic signal. These signals originate from some mechanical function of the biological system. They include all types of motion and displacement signals, pressure and flow signals etc. The movement of the chest wall in accordance with the reparatory activity is an example of this type of signal.

Biochemical signals and Bio-magnetic signals: The signals which are obtained as a result of chemical measurements from the living tissue or from samples analyzed in the laboratory. The examples are measurement of partial pressure of carbon-di-oxide, partial pressure of oxygen and concentration of various ions in the blood. Extremely weak magnetic fields are produced by various organs such as the brain, heart and lungs. The measurement of these signals provides information which is not available in other types of bio-signals. Magneto-encephalograph signal is the example for it.