Download Physiology of Respiration - International Fire Training Centre

INTERNATIONAL FIRE TRAINING CENTRE
FIREFIGHTER INITIAL
PHYSIOLOGY OF RESPIRATION
Throughout this note he means he/she and his means his/hers.
INTRODUCTION
It is important that as Breathing Apparatus wearers we have a good understanding of how the body
functions with regard to the mechanism of breathing.
We are required to wear Breathing Apparatus on the instructions of the Officer in Charge whenever
there is a risk of personnel suffering respiratory injury or discomfort. Breathing Apparatus will provide
protection against atmospheres which will not support life.
AIM
To make the student understand the Physiology of Respiration.
OBJECTIVE
At the end of the Instructional Session dealing with this subject and after detailed study of this note
you will be able to:
♦ Define the purpose of Oxygen and Carbon Dioxide
♦ Define the mechanism of breathing
♦ Explain inhalation and exhalation
♦ State the respiratory drive
♦ Define degrees of work
CONTENTS
•
•
•
•
•
•
•
•
•
•
Introduction
Aims and Objectives
General
Oxygen and Carbon Dioxide
Composition of Air
The Respiratory Cycle
Respiratory Drive
Degrees of Work
Rates of Breathing
Summary
GENERAL
In order to understand fully the principles which govern the use of breathing apparatus, it is first
necessary to know something of the composition of the atmosphere and of the process of respiration.
The human body needs a constant supply of oxygen in order to survive. Oxygen is a constituent of
air, and the body normally obtains this from the atmosphere. When at rest its requirements are
comparatively low, and air is sucked into and out of the lungs by breathing movements at a rate of
about 12 to 20 times per minute. When more energy is exerted, either through work or nervous
excitement, the breathing rate is increased and may be as much as 30 times a minute, or even more.
At rest about ½ litre of air is normally inhaled at each breath and about the same quantity is exhaled;
this amount is known as tidal air. By taking a very deep breath, a further 3 litres may be taken in, and
on subsequent very deep exhalation, this may be increased by a further 1½ litres. The total amount
thus exhaled, i.e. about 4½ litres on average, is known as the vital capacity and varies with different
people. This variation in lung capacity is the reason for the varying demands on breathing apparatus
by different wearers doing the same work.
OXYGEN
Oxygen supports combustion. When the oxygen enters the cells of the tissues it allows combustion to
take place within the cell, burning glucose to provide the heat energy force needed by the cell to
perform its function.
CARBON DIOXIDE
The waste product of this combustion is Carbon Dioxide. This passes from the cells into the
bloodstream which transports it back to the lungs so that we can breathe it out of our bodies.
COMPOSITION OF AIR
The air which is drawn into the lungs consists of three principal gases.
Nitrogen
Oxygen
Carbon Dioxide
79%
21%
Traces
It also contains small percentages of five other gases which include: Argon, Hydrogen, Neon, Helium
and Krypton. As these gases comprise of less than 1% of the atmosphere, they are included in the
percentage of Nitrogen for our practical purposes.
Oxygen as previously stated, is the vital ingredient. Nitrogen takes no active part in respiration at
ordinary pressures, being an inert gas which passes in and out of the body practically unchanged.
THE RESPIRATORY CYCLE
The body must draw air into the lungs, hold it for a sufficient time for the oxygen required to be
absorbed, and then expel it. This process is known as respiration, and consists of two spontaneous
actions, inhalation (breathing in) and exhalation (breathing out). Inhalation is effected by a muscular
effort which raises the ribs and lowers the diaphragm, thus enlarging the chest cavity and creating a
partial vacuum which causes air to enter. Exhalation normally requires no effort, as, when the breath
is released, the ribs fall and the diaphragm rises automatically, thus contracting the chest cavity and
forcing the air out.
The transfer of the inhaled oxygen from the lungs to the rest of the body is effected by the blood,
which in its circuit of the body passes through the lungs, where it absorbs a certain quantity of oxygen.
This travels with the blood through the main arteries to the lesser arteries, and finally into a vast
network of blood vessels known as capillaries. These vessels have very thin walls through which a
continual discharge of oxygen takes place. At the same time, carbon dioxide, which the body
generates as a waste product, is transferred to the blood. Having now changed from a bright to a
dark red, the blood is then driven back by the action of the heart through the veins to the lungs where
the carbon dioxide is given off and exhaled, and a further supply of oxygen is taken up. In this
process the composition of the air changes to approximately:
Nitrogen
79%
Oxygen
17%
Carbon Dioxide 4%
Nitrogen
Oxygen
Carbon Dioxide
That is to say, about 4% of oxygen is absorbed and an equal amount of carbon dioxide given off,
therefore exhaled air consists of:
Nitrogen
Oxygen
Carbon Dioxide
79%
16%
5%
RESPIRATORY DRIVE
The monitoring parts at the back of the brain constantly check the levels of oxygen and carbon dioxide
in the blood. The brain will react to any changes in these levels by altering the rate and depth of
breathing until the levels of oxygen and carbon dioxide are normal again.
High carbon dioxide acts as a trigger increasing exhalation depth and rate of breathing.
Low oxygen allows carbon dioxide levels to increase. This stimulates breathing.
Heavy work requires more fuel hence more oxygen - this lowers the oxygen levels and increases
carbon dioxide - so breathing rate increases.
DEGREES OF WORK
The air consumption rate of open circuit BA can vary over a wide range. This variation depends on a
number of factors including the work rate of the wearer, their physique and the environmental
conditions in which they are working, to enable the duration of open circuit BA to be estimated,
however, a notional consumption rate of 40 litres is used. This approximates to a wearer walking at a
speed of 6 kph.
AIR CONSUMPTION.
Degree of Work Carried Out
Rest
Light Work
Moderate Work
Heavy Work
Air Consumption
8 - 12 litres/minute
12 - 20 litres/minute
20 - 40 litres/minute
40 - 60 litres/minute
SUMMARY
As Breathing Apparatus Wearers we should understand that the body will support, through increased
inhalation, any physical exertions that we carry out and that failure to monitor the respiratory drive can
lead to durations of SCBA to be drastically reduced.