MANUAL PHYSIOLOGY PRACTICAL - Repository:The Medical ...

FM/UOJ
Experiment M 1
MEASUREMENT OF METABOLIC RATE
Every living organism depends on energy change from one from to anothermetabolism
- for its survival. Generally, chemical energy stored in the nutrients is
converted into usable energy through ATP and finally the energy leaves the body as heat
or external work performed. The rate at which energy is utilized, the metabolic rate, gives
valuable information regarding the state of the body and the amount of food needed.
The metabolic rate can be measured either by measuring the heat output (direct
calorimetry) or by measuring the oxygen consumption which is responsible for energy
release (indirect calorimetry). Direct calorimetry requires enormous facilities to contain
the individual in an insulated room over long periods and it is not possible in this
laboratory. Two methods are available to measure metabolic rate by indirect calorimetry:
spirometer method and Weir’s method.
1. Spirometer Method
This is based on a subject breathing pure oxygen from a closed chamber and
directing the expired air with remaining oxygen through soda lime to absorb the carbon
dioxide and back to the chamber.
Instruments
Spirometer, oxygen analyzer, normogram for energy value of oxygen.
Method
Empty the breathing chamber of the spirometer and turn the exit to “atmosphere”
position. Fill the chamber with oxygen. Connect one tube leading from the exit the inlet
of the one way valve; the out let of the valve to the lower opening of the soda lime
canister; and the out let from the canister to the breathing chamber. Seat the subject
comfortably and apply mouth piece and nose clip. Wait for a few minutes to till the
subject familiarizes with the set up. Switch on the kymograph at low speed, turn the exit
to “spirometer” position and wait for five minutes. At the end of the time stop the
kymograph, disconnect the subject and remove the tracing.
Record the temperature in the breathing chamber, the atmospheric pressure at the
barometer and the saturated vapour pressure at the temperature of the chamber. Obtain the
energy value of the oxygen from the normogram.
Note that the normogram relates the energy value to the respiratory quotient which
is the ratio of carbon dioxide produced to the oxygen consumed. As the carbon dioxide
has been absorbed in the soda lime, actual respiratory quotient cannot be measured. The
respiratory quotient, therefore, has to be deducted from the type of metabolic fuel, which
depends mainly on the last meal. Assuming that the subject had a balanced meal, the
respiratory quotient is assumed to be 0.85.
Metabolism & Temperature
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