measuring lung volume 3.1.1
reading spirometer traces
Spirometers
= a devise that can measure the movement of air into & out of the lungs
during inhalation, air is drawn from the air tight chamber causing the lid to move down, the pen attached to the lid therefore draws a downwards trace on the paper
during exhalation, air enters the air tight chamber, causing the lid to rise, the pen attached to the lid therefore draws an upwards trace on the paper
health & safety
individual is healthy (no asthmatics)
air tight chamber & tubes, so no air leaks
sterilise equipment especially mouth piece
soda lime should be fresh
ensure adequate supply of O2 (medical) in the air
ensure water doesn't enter air tubes
ensure temp of surroundings remains constant - gases expand as temp rises
when inhaling the trace will go down - when exhaling the trace will climb up
the volume of a single breath can therefore be calculated by measuring from the peak of an exhalation to the trough of an inhalation
the overall volume of gas decreases over time because the spirometer contains soda lime which absorbs CO2
when breathing the subject is using up the O2 from the tank, while CO2 breathed out is absorbed by the soda lime - as a result the gas volume decreases over the course of the experiment
lung volumes
interpreting spirometry traces
check y-axis - volume of air in spirometer or volume of air in lungs
breathing rate (breath per minute)
= num of peaks & troughs in 60 secs
tidal volume
= use 3 measurements of tidal volume & divide by 3 to find average
oxygen uptake
assume the volume of CO2 absorbed by soda lime equals the volume of O2 absorbed from alveoli into blood, therefore measuring the gradient of the spirometry trace enables us to calculate the rate of O2 uptake
check units asked for in exam
dm^3sec^-1
dm^3min^-1
factors it depends on
vital capcity
breathing rate
age/gender/height
fitness level
smoking
asthma/respiratory conditions/general health
uses
diagnosing respiratory conditions
sport physiologists - monitoring athletes fitness
mountaineering/deep sea diving