measuring lung volumes Flashcards
what is breathing rate
the number of breaths per minute
what is oxygen uptake
the volume of oxygen absorbed by the lungs in one minute
what is tidal volume
the volume of air inhaled or exhaled in one breath, usually measured at rest
what is a spirometer
a device that can measure the movement of air into and out of the lungs
what is vital capacity
the greatest volume of air that can be expelled from the lungs after taking the deepest possible breath
what are the three ways to measure the capacity of the lungs
- peak flow meters
- vitalographs
- spirometer
what is a peak flow meter
measures the rate at which air can be expelled from the lungs. people with asthma often use these to monitor how well their lungs are working
what is a vitalograph
the patient breathes out as quickly as possible through a mouthpiece. the instrument produces a graph of the amount of air they breathe out and how quickly its breathed back in
how do we use a spirometer
a float chamber spirometer consists of a chamber of air or medical grade oxygen floating on a tank of water. during inspiration, air is drawn from the chamber so the lid moves down. during expiration, the air returns to the chamber raising the lid
how is the movement of air recorded
on a datalogger
what happens to the carbon dioxide rich air that is exhaled
it is passed through a chamber of soda lime which absorbs the carbon dioxide
what does the soda lime allow to be measured
oxygen consumption
what can many spirometers not measure
the rate of oxygen consumption
what are the precautions that must be taken when using a spirometer
- the subject should be healthy and in particular free from asthma
- the soda lime should be fresh and functioning
- there should be no air leaks in the apparatus as this would give invalid or inaccurate results
- the mouthpiece should be sterilised
- the water chamber must not be overfilled (or water will enter the air tubes)
what is tidal volume
the volume of air inhaled or exhaled during relaxed breathing
when is tidal volume usually measured
at rest
what is tidal volume sufficient for
supplying all the oxygen in the body at rest
what is the tidal volume in an average adult
0.5dm3 or 500cm3
what is tidal volume 15% of
vital capacity
what is inspiratory capacity
maximum possible volume inhaled after a relaxed exhalation
what is expiratory capacity
maximum possible volume exhaled after a relaxed inhalation
what is inspiratory reserve volume
the maximum volume of air you can breathe in, over and above normal inhalation
- the extra air that is breathed in deeply (forcefully) is your IRV
what is the average inspiratory reserve volume in an adult
2.4dm3 or 2400cm3
what is expiratory reserve volume
maximum volume of air you can force out of your lungs over and above the normal tidal volume of air you breathe out
- when you breathe out deeply (forcefully) the extra air breathed out is the ERV
what is the average expiratory reserve volume for an adult
0.3dm3
what is vital capacity
maximum volume of air that can be exhaled after a maximal inhalation
how is vital capacity measured
by taking a deep breath and expiring all the air as possible from the lungs
what does vital capacity of a person depend on
size of a person (height), age, gender, level of regular exercise
what is the average vital capacity of an adult
5000cm3 or 5dm3
vital capacity =
tidal volume + expiratory reserve volume + inspiratory reserve volume
what is the total lung capacity
the total volume of air the lungs can hold after a maximal inhalation
total lung capacity = ..
.. = vital capacity + residual volume
what is functional residual capacity
volume remaining in the lungs after the end of a normal expiration
what is residual volume
amount of air left in the lungs after a maximal exhalation. its the capacity of the airways and alveoli when deflated
why does there need to be some air left in the lungs
to prevent the alveoli from collapsing
what is the average residual volume
1.2dm3
what can’t be directly measured
residual volume
what does breathing do
supplies oxygen for respiration and removes carbon dioxide produced in respiration
what happens as a person breathes through the spirometer
oxygen is absorbed by the blood and replaced by carbon dioxide. this carbon dioxide is absorbed by the soda lime in the spirometer so that the volume of the air in the chamber decreases. this decrease is observed and measured on the spirometer trace
how can we work out the oxygen uptake from measuring the decrease in volume
if we assume the volume of carbon dioxide released and absorbed by the soda lime is equal to the volume of oxygen absorbed by the blood then measuring the gradient of the decrease in volume enables us to work out the rate of oxygen uptake
what happens as the person breathes in
the chamber lid falls
what happens as the person breathes out
the chamber lid rises
what happens to the spirometer trace as the person breathes out
it rises
what happens to the spirometer trace as person breathes in
it falls
what happens as the demands of the body change
the pattern and volume of breathing changes
what is the difference between breathing rate and ventilation rate
the breathing rate is the number of breaths taken per minute and the ventilation rate is the total volume of air inhaled in one minute
how to work out the ventilation rate
ventilation rate = tidal volume x breathing rate (per minute)
what is the breathing rate at rest
usually about 12-14 breaths per minute
what happens when the oxygen demands of the body increases
the tidal volume of air moved in and out of the lungs with each breath can increase from 15% to as much as 50% of the vital capacity, the breathing rate also increases. in this way, the ventilation rate of the lungs and the oxygen uptake during gaseous exchange can be increased to meet the demands of the tissues
how does a spirometer work
- a person breathes in and out of an enclosed air chamber. the air is trapped between the spirometer float and the water.
- as the person breathes in, the volume of air inside the chamber decreases and float drops down
- as the person breathes out, the volume of air inside the chamber increases and the float is pushed up
- the float is attached to a pen which writes on paper attached to a revolving drum
what is used to fill the air chamber
either atmospheric air or medical grade oxygen
what is the function of the counterbalance
it reduces the resistance for the subject who is breathing as without it he would have to breathe forcefully
why does the apparatus contain water
air is trapped between the water and the float
what is the purpose of the water
provides an airtight seal so that pressure variation does not lead to incorrect readings
why does the apparatus have soda lime
ensures carbon dioxide is absorbed by the soda lime so the subject is not breathing in more carbon dioixde as this would affect blood pH and denature enxymes. the valves ensure that air passes in a one way direction so that CO2 is removed
how is oxygen consumption measured
if the chamber of the spirometer is filled with oxygen you can use it to measure how much oxygen you use over a period of time. there must be soda lime in the container.
why does the volume of oxyge n in the spirometer get less and less with each breath
each time you breathe in, you take oxygen from the chamber and the float drops. when you breathe out, the unused oxygen in your expired air goes back into the air chamber, but the carbon dioxide in your expired air is absorbed by the soda lime. so the total volume of gas going back into the chamber is less than you took from it
how do you work out the mean tidal volume
measure the tidal volume for each of the breaths using the spirometer trace
add these together
divide by the number of breaths
how to calculate the mean breathing rate
measure the total time taken on the trace
then count the number of breaths taken in that time
divide the number of breaths by the time in seconds to find the number of breaths per second
how to work out ventilation rate
breathing rate x mean tidal volume
how to work out vital capacity
breathing out every bit of air that you can from your lungs and then taking your very largest breath in
how to calculate oxygen consumption
work out the difference in the volume of air at the start and the end of the session to work out the volume of oxygen the subject used
work out the time taken in seconds
volume of oxygen/time taken then multiply it by 60
units for oxygen consumption
dm3m-1
