Tag Archives: Medical

How does blood pressure measuring apparatus (sphygmomanometer) work?

As a dynamic pump, the heart forces blood around an impressive network of arteries and veins which, if joined end to end, would circle the Earth two-and-a-half times. The pressure that is exerted during this process can most conveniently be measured in the brachial artery that passes through the upper arm. The greatest pressure occurs when the heart valve that pumps the blood (the ventricle) contracts and the lowest pressure occurs when this valve is relaxed. Determination of blood pressure therefore consists of two measurements, that of the greatest value and the lowest.

Blood pressures are recorded in millimeters of mercury (mmHg), about 120 millimeters being the normal high or systolic value, and around 80 millimeters the low diastolic value. Such average readings would be stated by a physician as ‘120’ over ‘80’. This means that the pressure exerted by the pumping action of the heart would physically suffice to raise a column of liquid mercury to these heights. Standard atmospheric pressure at sea level, by way of comparison, is 760 millimeters at 0° Celsius.

The apparatus used by physicians for measuring blood pressure is called sphygmomanometer (picture, above). It consists of (1) a pressure gauge housing a vertical glass column containing a reservoir of mercury; (2) a tube connected to a cuff, or wrapping sleeve that can be filled with air; and (3) a hollow rubber ball which pumps air into the cuff. To take blood pressure, the physician wraps the cuff around the patient’s arm. Air is first pumped into the cuff by squeezing the rubber ball. A stethoscope is placed over the artery of the arm just below the cuff. Forcing air into the cuff causes it to pass down on the artery, so the mercury in the tube rises. In other words, the pressure of the blood in the brachial artery is transmitted through the air contained in the cuff of the mercury. Moments later, as air is released from the cuff by means of a valve on the bulb, normal blood flow returns and the mercury starts to fall.

The first sound heard through the stethoscope is that of the systolic (upper) pressure, and the level of the mercury column measures that value. The next sound is the diastolic pressure, its valve being similarly observed from the calibrations on the pressure gauge.

Some physicians use another kind of apparatus which consists of a simple pressure gauge, which is calibrated in terms of millimeters of mercury. This handy instrument has eliminated the need for column containing liquid mercury which is considered an environmental hazard. Pressure is transmitted to a diaphragm at the back of such device, and pointer needle moves across a round dial to the appropriate value.

A person’s blood pressure never stays at a particular level, but varies according to his own level of physical activity and also his state of mind.

You might also like:

How can doctors tell our temperature by feeling our pulse?

The rate at which the pulse beats and the level of temperature in the body have distinct connection with each other, and go more or less together, so that when the doctor counts pulse rate and finds that it is just the rate it should be, he expects also to find the temperature quite usual. If however, he finds that the pulse is twice as rapid as usual, he will also probably find that the temperature is much higher than normal, because the thing that causes the one to become rapid causes the other to go up.

Thus, in all cases of fever where there is some poisonous substance in the body, this substance causes the heart to beat faster, and the pulse to become rapid, and it also causes a disturbance in that part of the brain controlling the temperature, so that both the pulse and the temperature are thrown out of gear.

More reading:
Pulse (Wikipedia)

Related posts:

How does the pain killer Aspirin work inside the body?

Aspirin has been in the market since 1899, relieving people’s pains, fevers and inflammation. Scientific research has shown that the drug works because it affects the body’s production of prostaglandins. These substances, produced in response to stress, are in a way, opposites of aspirin: they heighten pain and stimulate fever and inflammation. Ordinarily, prostaglandins have desirable effects. When a pin pricks you, for example, your skin takes particular notice, since prostaglandins sensitize nerves that carry pain impulses to the brain. And if you get an infection from the pin prick, these substances help to increase the body temperature to fight the invading micro-organisms. Further, prostaglandins dilate blood vessels in the infected area, allowing more blood to come in to aid healing. This often causes inflammation.

Aspirin or acetylsalicylic acid bonds with an enzyme that helps produce prostaglandins, preventing it from doing its work. With reduced prostaglandin production, pain, fever and inflammation ease. Research also shows that part of aspirin’s pain killing power comes simply from the placebo effect – the user’s belief that aspirin will in fact bring relief. Aspirin also reduces blood clotting, an additional property that could prevent cardiovascular diseases.

More reading:
Aspirin (Wikipedia)
History of aspirin (Wikipedia)
Prostaglandin (Wikipedia)

Related posts:

Who invented stethoscope? How does it work?

When conducting a medical examination a doctor frequently taps the chest and back with his fingers and listens to the sound. Even more often he uses his stethoscope, one of the first instruments that the medical student must acquire. This sort of examination may seem very simple and superficial but the trained ear can learn a great deal by listening to the sounds of the body organs.
The first person known to have used the method of tapping the chest (percussion method) was an Austrian called Leopold Auenbrugger. As a boy, he had often seen his father (an innkeeper) tapping barrels to find out how full they were and, later, in the middle of the 18th century, he applied this method to the detection of chest diseases.

The lungs lie in a cavity surrounded by the ribs and the diaphragm. When breathing in, the diaphragm is lowered and the rib-cage expanded. Air then flows into the lungs to take up the extra space. A number of chest diseases are caused by the accumulation of fluid. A fluid-filled cavity produces a dull thud. Percussion is thus a very quick way of detecting some chest disorders. The stethoscope is a very simple instrument but of great value to the doctor. It is merely a device for picking up sounds and vibrations (e.g. heartbeat) made by the body organs, and conveying these sounds to the ear. The modern instrument consists of a small funnel or a hollow drum attached to a forked rubber tube. Attached to the others ends of the fork are two ear-pieces through which the doctor listens when the cup is put on the surface of the body.

For many centuries ‘medical’ men had listened to the heart beating by direct application of the ear to the chest but this was unsatisfactory and certainly unhygienic. Rene Laennec is credited with inventing the stethoscope in 1816. The story is that the stoutness of his patient made it impossible for him to listen to the heart, and so, remembering some children playing with a hollow log, he rolled up some paper and used it as an ear trumpet. He was able to hear the heart more clearly than ever before. In 1819 Laennec published a book in which he described a wooden stethoscope he had constructed. The early stethoscopes were of this simple design, but soon the two-ear-piece models were developed. It is ironic that Laennec should have died of tuberculosis – one of the diseases that the stethoscope has done much to detect.

The stethoscope was first used in studying the heart and lungs, and this is still its commonest use. It is, however, frequently used for detecting the pulse in the arm, and also for investigating abnormalities in the elementary canal.

You might also like:

Why vaccination prevents us from having smallpox?

There are some diseases from which a person never suffers twice, because the first attack makes the sufferer immune, or proof against a second attack of the particular microbes that cause this illness. Small-pox is one of the diseases against which we can be so protected.

But many years ago an English scientist named Edward Jenner discovered that it was not necessary to have the actual disease in order to become protected, but that it was sufficient to produce a very slight illness by vaccination (see, picture). The effect of this was found to be such that people who were properly vaccinated were quite free from the infection of small-pox for some years, generally five years at least. After that the effect is apt to wear off, and so in some countries it is a custom to be vaccinated every five years.

More reading:
Vaccination (Wikipedia)
Edward Jenner (Wikipedia)

Related posts:

Why are some medicines in capsule form whereas others are in tablet form?

There are number of reasons. The manufacturers take into account the properties of medicines first. Chemical properties of some medicines change and efficacy reduce on their being exposed to humidity or oxygen in the air. Doses of such medicines have to be packed in capsules. A capsule also becomes necessary in case of bitter dose. If tablet form is essential then that tablet has to be coated with a tasteless material. Whether digestive system has to assimilate the dose immediately or gradually in the stomach is also an important matter to be considered. A dose meant to be assimilated gradually is best administered in the form of a hard tablet because capsule ordinarily made of gelatin is quickly dissolved by the acidic gastric juices of the stomach.

It is possible to give this kind of dose in capsule also provided that the dose is in granular form and not in powder form. In such a case overriding medical reason is assimilation of the dose in small quantities spread over a long period rather than assimilation of the entire dose in a few minutes.

Additional Reading:
Capsule (Wikipedia)

Related posts:

How is ‘expiry date’ of medicines determined?

Some decades ago there were no chemists’ shops. Instead of chemists druggists used to mix various compounds according to physicians’ prescriptions and sell them either in powder form or liquid form. Sometimes physician’s assistant used to prepare such mixture in the dispensary itself so he was known as compounder. These types of medicines did not require a cautionary notice of ‘expiry date’ to be written on the label because patients used to consume the medicine within a few days.

Over a period of time pharmaceuticals manufacturing companies started manufacturing and selling such compounds in the form of tablets and capsules. Chemists’ shops replaced druggists’ stores. Now there was no longer certainty that tablets and mixtures were consumed immediately after production. If medicines remain unused for a long time some changes may take place in the properties of the ingredients due to heat and moisture. This would reduce efficacy of medicines, so it became essential to write ‘expiry date’ on the packaging material of medicines.

The best method for determination of date of expiry is to store the tablets or capsules for a long period at the normal room temperature but pharmaceutical companies resort to sort cuts to avoid such time consuming method. They store four samples of medicine at four different temperatures for a fixed period of time and then analyze the effects on the ingredients of the medicine. They ascertain the extent of loss of efficacy of these samples and determine ‘expiry date’ based on the average loss of efficacy.

Why are X-rays named after a letter of alphabet? What makes the X-rays pass through solid objects?

When scientists are not able to understand some phenomenon thoroughly they use the symbol X to denote it. The German physicist Wilhelm Roentgen who discovered X-rays in 1895 had not properly understood the mysteries of his own discovery. So the newly discovered rays came to be denoted by the symbol X.

The X-rays are very penetrative rays having much shorter wavelength than that of the visible light. So they are able to penetrate some objects which are opaque for the visible light. E.g. when X-ray photograph of a patient is taken these rays fully penetrate the soft muscles, are somewhat absorbed in highly dense muscles and are absorbed to a great extent in hard boned. The image in X-ray photograph shows the skin and soft muscles as completely black portion through which X-rays have penetrated and as white portion those parts of the body in which X-rays have been absorbed.

Additional reading:
X-ray (Wikipedia)

Related post:

Which material is used for making capsules of medicine?

If it is not categorically stated on the label of medicine by the manufacturer one has to assume that gelatin is used for making capsule. Gelatin is an animal product (non-vegetarian). And it is manufactured from collagen, a fibrous substance that joins bones, cartilage and tendon (tissues that join muscles to bones) of cattle like cows and buffaloes. Some glycerin is added to make the capsule soft.
Another use of gelatin is in making jelly with which a scoop of ice-cream is sometimes ‘topped’, although many people are not aware of it. However, it is a different matter if the label states that jelly is made from vegetable products. This type of notice should be made compulsory by the government in case of bakery products also.

More Reading:
Capsule (pharmacy) (Wikipedia)

Related posts: