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Archive for the ‘Stethoscopes’ Category

Stethoscopes.

STETHOSCOPES.

These require little maintenance apart from the replacement of lost parts such as ear pieces, the diaphragms or a split tube.
On the older types the tubing may perish and need replacing for which, ordinary tubing of a suitable size may be fitted, though proper stethoscope tubing can be purchased if you have the money to spend.
Most newer stethoscopes have a tubing fitted that does not perish, though it will go sticky and have to be thrown away if some chemicals come in to contact with it.
It is also pre-formed into a `Y’ shape so you do need to buy that shape tube if it does need replacing though of course you can use other tubing and ‘Y’ piece to connect the headset to the stethoscope chest piece.
If the complaint is that nothing can be heard then there are four main things to look for.

1. That the ear pieces are not blocked with wax, if they are, unscrew them and push the wax out and clean with a little spirit or soapy water.

2. That the diaphragm is missing or split, replacements can be purchased or you can make your own out of a piece of `X’ ray film or similar plastic sheet.

3. That the tube is split, the cure for this is obvious. If it is the type with the pre-formed `Y’ shaped tube and you can’t get any, you will have to make up the tubing using ordinary tube and a metal or plastic `Y’ connector.

4. That they are not using it properly, this may sound a bit silly, but on the newer type the head can be turned so that one of two sides can be used, if you try to use the side that has not been opened to the tube it follows that you won’t hear anything. It does happen.

Whilst on the subject of the two different sides of the chest piece, as it is called, they are used to listen for sounds of different types, higher and lower frequencies.
The bell side of the stethoscope is used for listening to the lower frequency sounds and the diaphragm is used to listen to the other frequencies including the high ones.
One firm that make stethoscopes called Littmann of America have now developed a new floating diaphragm stethoscope.
What they say is that in the old stethoscopes where the diaphragm is held in position by a ring that is screwed in place, that the diaphragm is stressed in an uneven manner by the ring, this means that the frequency response of the diaphragm is not even over the whole of its width, so what they have now done is to hold the diaphragm in place with a special plastic snap on ring that tensions the diaphragm evenly all round.
They say that this makes the frequency response much more even across the whole surface of the diaphragm. How much difference it makes to the sound quality of the instrument I couldn’t say.

Sometimes the screw on ring that holds the diaphragm in place will get really stuck and it seems that no amount of huffing and puffing will move them, try an old rubber inner off a BP machine cuff, this will help you to get a better grip, sometimes you can try too hard only to find that by doing it gently you will move it without any trouble. Don’t ask me why.

Early stethoscopes were simply round lengths of wooden tube. Once it was found how much more you could hear this way a more permanent wooden cylinder was made, in 1828 it was improved by the addition of an ear piece and a trumpet-shaped end, in 1850 two ear pieces were added to make it much like the stethoscope we know today.

For listening to babies in their mother’s womb there is a stethoscope called a foetal stethoscope that is just like the old ones, a metal or plastic tube with an ear piece and a trumpet-shaped end.

You can also get electronic stethoscopes, but the maintenance of these is outside the scope of this book.
The size of the ear piece is important, a leak only five times larger than a human hair has a marked effect, especially at low frequencies.

The stethoscope below has an external spring.

steth2

This one has an internal spring. Here you can clearly see the two sides, you can change sides by simply twisting it. Check you have the side you want by tapping the diaphragm, if you can hear it the diaphragm is in use, if not the bell side is in use.

steth1

This is an old Sprague Bowles stethoscope. As you can see it has two tubes, this type normally uses tubing that will perish, replacement tubes can be purchased by whatever length you want. However, when it comes to it you can use any smooth bore tube that will fit. With these, the two different sides are selected by operating the lever you can see in the middle.

sprague bowles

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