Stethography is the process of recording of respiratory movements in man. The instrument used is called stethograph and the recording obtained is called stethogram
To record the normal respiratory movements of the given subject and to study the changes seen with voluntary hyperventilation,deg lutition and exercise.
1. Kymograph, recording drum.
2. Stethograph: It consists of a corrugated canvas rubber tube with side clips.One end of the tube is closed and the other end can be connected to the Marey’s tambour. There is a metallic chain with a hook at its tip
attached to the closed end of the stethograph for tying the instument around the chest.
3. Marey’s tam bour: This consists of a writing lever, metal tube to which the stethograph is connected and a diaphragm which is attached to the end of the metal tube. The diaphragm consists of a metallic cup with a thin rubber membrane tied tautly around its mouth. The writing lever is placed in contact with the rubber membrane by means of a metal disc.
Normal respiratory movements: Seat the subject comfortably facing away from the recording drum.Tie the stethograph around the chest at the nipple level where movements are maxim um.Allow him to relax and breathe quietly without any affort.Connect the stethograph to the Marey’s tambour so that pressure changes, in the stethograph are transmitted to it. The writing lever is seen to move with movements of the chest.The kymograph is set at slow speed. Bring the writing lever in contact with the recording surface at a tangent.Keep the stethograph sufficiently taut so that the recordings are about an inch in height. Record the normal respiratory movements over a length of 3 inches.
Voluntary hyperventilation: Ask the subject to breathe as deeply and rapidly as he can. Record the movements continuously till normal respiration is resumed.
Effect of swallowing: While normal respiratory movements are being recorded, ask the subject to drink water from a cup and record the effect.
Effect of exercise: Disconnect the stethograph from the tam bour and ask the subject to do moderate exercise, for 2-3 minutes. Immediately connect the stethograph to the tambour and record the respiratory movements, till the normal pattern is resumed.
Write the title of the experiment and label the various events recorded.
During inspiration the chest expands and the stethograph is stretched. The pressure inside the stethograph decreases, this fall in pressure being transmitted to the Marey’s tambour. The rubber diaphragm is therefore pulled down causing a downward movement of the writing lever. During expiration recoil of the stethograph causes the reverse changes and therefore an upward movement of the writing lever. Thus downstroke in the tracing represents inspiration and upstroke, expiration. During voluntary hyperventilation, there is an increase in the rate and depth of respiration. This is followed by a temporary cessation of breathing (apnoea), after which breathing returns to normal.
During deglutition there is a temporary stoppage of breathing. This is called deglutition apnoea and is followed by normal breathing.
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