MANUAL PHYSIOLOGY PRACTICAL - Repository:The Medical ...

FM/UOJ
INSTRUMENS USED IN RESPIRATORY EXPERIMENTS
Stethograph
The stethograph is a corrugated rubber tube, closed at both ends. The cavity of the
tube is connected to a tambour by a noncompressible tube. Stretch on the corrugated
rubber tube increases the volume which reduces the pressure in the system which pulls
the drum of the tambour down. A pen on the tip of the pointer, connected to the tambour,
writes on a moving drum which gives the pattern of the changes in the volume in the
system. When the stethograph applied to the chest of a person, the chest movements can
be recorded.
Spirometer:
The spirometer contains two concentric cylinders. The space between the two
cylinders is filled with water in which an inverted cylinder (breathing chamber) moves up
and down. There are two passages in the inner cylinder communication on the top with
the breathing chamber and at the bottom with the inhalation and exhalation corrugated
tubes; the breathing chamber can either be connected to the tubes (to the subject) or
closed while the tubes open to atmosphere by rotating the union by a lever. The subject
breathes from the breathing chamber when the union is at ‘spirometer’ and breathes from
air when the union is turned to ‘atmosphere’. The inverted cylinder is connected to a
counter-weight, a piece of lead, by a string running over a system of pulleys. A pen,
attached to the counter-weight, records movements of the inverted cylinder (changes in
the volume of the breathing chamber) on a moving drum.
Douglas Bag:
This is a rubber or plastic bag used to collect expired air over a specific period.
Wet gas meter:
This is an instrument used to measure the volume of a gas at atmospheric
pressure. The air pushed through the inlet rotates a wheel which is sealed by water. The
wheel is connected to a system of dial which indicates the volume of the gas passed.
Since the gas passes over water, the measured volume includes saturated water vapor.
Dry gas meter
This instrument is used to measure the volume of gas at atmospheric pressure and
ambient water vapour pressure. It consists of chambers formed by movable diaphragm.
When the gas is allowed to go through the inlet, it changes the relative pressure in the
chambers & they alternatively get filled. So the diaphragm moves like bellow. Levers
connected to diaphragm rotate a crank shaft, which drives a counter mechanism to
transform the volume of gas pass through in cubic meter on the outside dial.
Respiration
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