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Chapter: 11th Zoology : Chapter 12 : Basic Medical Instruments and Techniques

Diagnostic and Monitoring Instruments

Basic Medical Instruments and Techniques

Diagnostic and Monitoring Instruments


Stethoscope is a medical device used to hear the internal sounds of the human body such  as  heart  beat,  sounds  due  to  inhalation  and  exhalation  of  air  in  the  lungs, stomach, intestinal movements and also foetal movements. The modern electronic stethoscope is a high precision instrument used to hear with clarity the internal sounds of the human body even in a noisy environment or through the heavy clothing of the patient. A typical stethoscope consists of a disc shaped resonator that is placed against chest with two rubber tubes connected to earpieces. This is simply known as binaural stethoscope. It is a simple but an effective diagnostic tool to localize problems and to diagnose diseases (Figure12.1).


Clinical significance of stethoscope


1.              Stethoscope helps to find the normal and abnormal heart beat sounds and also to diagnose valve functions.


2.              It helps to diagnose lung diseases such as pneumonia, pulmonary edema, bronchitis and pleuritis.


3.              Stethoscopes along with sphygmomanometer are used to read the blood pressure.


4.              It outlines the status of cardiac, respiratory and intestinal disorders.




Sphygmomanometer is a device that measures the blood pressure hence known as blood pressure meter, blood pressure monitor or blood pressure gauge. It consists of a rubber cuff which is wrapped around the upper arm and the other end is connected to a mercury manometer which directly measures the pressure in a uniformly graduated scale ((Figure12.2).


By gradually increasing and reducing the pressure in the cuff, the systolic and diastolic blood pressure is clearly monitored by the sounds of arterial blood flow. The cuff is smoothly wrapped around the upper arm 3 cm above the elbow. The resonator of the stethoscope is placed on the brachial artery at the elbow to hear the blood flow sounds. The cuff is then rapidly inflated to 180 mm Hg and is then slowly deflated. As the pressure in the cuff falls a “whooshing” sound is heard then the blood flow starts again in the artery. This indicates the patient’s systolic pressure. Then the pressure is slowly released until no sound is heard. This is measured as the diastolic blood pressure. For better clinical understanding readings may be taken in both arms.


Types of sphygmomanometer


1.Manual sphygmomanometer


a. Mercury sphygmomanometer: It shows blood pressure by affecting the height of a column of mercury which does not require calibration.


b. Aneuroid sphygmomanometer: It is a mechanical type with a dial and it requires calibration checks unlike mercury manometer.


2.Digital sphygmomanometer: 

It detects systolic and diastolic pressures by an oscillometric detector. It is easy to use even without training.


The maximum pressure exerted during the ventricular contraction is called systolic pressure and the minimum pressure exerted during the ventricular relaxation is called diastolic pressure.


Normal Blood Pressure = 120/80 mmHg

Systolic pressure = 120 mm Hg

Diastolic pressure = 80 mm Hg


Clinical Significance


1.     To diagnose pathological conditions such as hypertension and hypotension


2.     Helps to assess the state of blood circulation.


3.     Provides the functional details of heart.




Glucometer is a simple and portable medical device used to record the approximate levels of blood glucose. It is a battery operated digital meter. A drop of blood is taken from the tip of the finger and placed on the disposable test strip. The meter reads the blood sample and displays the glucose level in the units of mg/dL. Most glucometers are based on the electrochemical technology or colour reflectance principle (Figure12.3).




1.              Handy and portable


2.              Immediate results, the results are displayed in approximately 40 seconds.


3.              Requires no calculation


4.              No training is required for operating the instrument


Normal Glucose Values in blood


Normal glucose value: 70 – 100 mg/dL

Random blood sugar: 80 – 120 mg/dL

Fasting blood sugar: 70 – 110 mg/dL

Post – prandial blood sugar: 70 – 140mg/dL




Autoanalyser is a computer controlled device. It is used for quick estimation of several bio -chemical parameters like glucose, urea, cholesterol, enzymes and other proteins present in body fluids. The analyser is fully integrated with all the necessary controls such as temperature of reaction, volumes of sample, reagents and transfer of fluids. More sophisticated multichannel autoanalysers with capabilities of selecting any type of analysis for any one set of samples are available now (Figure12.4).


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11th Zoology : Chapter 12 : Basic Medical Instruments and Techniques : Diagnostic and Monitoring Instruments |

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