6. Medical and Biological Instruments

These instruments are commonly asked in General Science sections because of their everyday relevance to healthcare.

A helpful pattern when revising this section is to notice that most medical instruments fall into one of two broad families: those that record an electrical signal generated naturally by the body (such as the ECG, which records the heart's electrical activity, and the EEG, which records the brain's electrical activity), and those that provide a magnified or amplified view — visual or acoustic — of a body part that cannot otherwise be directly seen or heard clearly (such as the endoscope, ophthalmoscope, otoscope, and stethoscope). Keeping this two-family distinction in mind makes it much easier to avoid mixing up which instrument does what.

6.1 Stethoscope

Stethoscope. (See Section 5.3 above.) Used to listen to internal body sounds, especially the heart and lungs; invented by René Laennec.

6.2 Sphygmomanometer

Sphygmomanometer. An instrument used to measure arterial blood pressure, expressed as two readings — systolic pressure (when the heart contracts) over diastolic pressure (when the heart relaxes), in millimetres of mercury (mm Hg). The traditional mercury sphygmomanometer consists of an inflatable cuff wrapped around the upper arm, connected to a mercury manometer; the cuff is inflated to temporarily stop blood flow in the artery and then slowly deflated while a stethoscope is used to listen for the characteristic Korotkoff sounds that mark the systolic and diastolic pressures. Digital sphygmomanometers use oscillometric electronic sensors instead.

A normal resting blood pressure for a healthy adult is often cited as approximately 120/80 mm Hg (120 mm Hg systolic over 80 mm Hg diastolic); readings consistently higher than this are associated with hypertension (high blood pressure), while readings consistently lower are associated with hypotension (low blood pressure) — both of which a physician may investigate further.

6.3 Endoscope

Endoscope. An instrument used to visually examine the interior of hollow organs or body cavities (such as the stomach, intestines, or urinary bladder) without invasive surgery. It consists of a long, thin, flexible (or rigid) tube fitted with a light source and a camera or a system of lenses/optical fibres, which is inserted into the body and transmits real-time images to an external monitor; the procedure is called endoscopy. Variants include the gastroscope, colonoscope, laparoscope, and bronchoscope, named after the organ examined.

The flexible endoscope relies on bundles of thin optical fibres, each of which transmits light by total internal reflection along its length, allowing the tube to bend around the curves of the digestive tract while still carrying a clear image back to the observer — the same total-internal-reflection principle used in fibre-optic communication cables.

6.4 Electrocardiograph (ECG/EKG)

Electrocardiograph (ECG/EKG). An instrument used to record the electrical activity of the heart over a period of time, producing a graphical trace called an electrocardiogram. Electrodes placed on the skin (chest, arms, and legs) detect the tiny electrical impulses generated by the heart muscle with each heartbeat, which are amplified and recorded; the resulting waveform (with characteristic P, QRS, and T waves) helps diagnose heart rhythm abnormalities, heart attacks, and other cardiac conditions. The technique was pioneered by the Dutch physiologist Willem Einthoven, who received the Nobel Prize for this work.

6.5 Ophthalmoscope

Ophthalmoscope. An instrument used by doctors to examine the interior of the eye, particularly the retina, optic disc, and blood vessels at the back of the eye, through the pupil. It uses a system of mirrors or prisms and a controlled light source to illuminate the interior of the eye and allow the examiner to view it clearly, aiding diagnosis of conditions such as glaucoma, diabetic retinopathy, and retinal detachment.

6.6 Otoscope

Otoscope. An instrument used to examine the ear canal and the eardrum (tympanic membrane), consisting of a light source and a magnifying lens attached to a cone-shaped speculum that is gently inserted into the outer ear. It helps physicians diagnose ear infections, wax blockages, and eardrum perforations.

6.7 Electroencephalograph (EEG)

Electroencephalograph (EEG). An instrument used to record the electrical activity of the brain, in a manner analogous to how an ECG records the electrical activity of the heart. Small electrodes are placed on the scalp to detect the tiny electrical signals produced by neurons, and the resulting trace (electroencephalogram) shows characteristic brain-wave patterns; it is widely used to diagnose epilepsy, sleep disorders, and to assess brain activity/function.

6.8 Phonocardiograph

Phonocardiograph. An instrument used to graphically record the sounds and murmurs produced by the heart during its pumping cycle, providing an objective, permanent record compared to the subjective listening done with a plain stethoscope. It uses a sensitive microphone placed on the chest to pick up heart sounds, which are then amplified and plotted as a waveform (phonocardiogram) for detailed analysis, useful in diagnosing valve disorders.

Quick Revision Table — Medical/Biological Instruments