Forced vital capacity (FVC) of the lung is the volume of air that can be
forcibly expelled from the lung from the maximum inspiration to the maximum
expiration.
Forced expiratory volume in 1 second (FEV1) is the volume of air that can be
expelled from maximum inspiration in the first second.
FEV1/FVC ration is the FEV1 expressed as a percentage of the FVC (or VC
if that is greater) ie the proportion of the vital capacity inhaled in the first
second. It distinguishes between reduced FEV1 due to restricted lung volume and
that due to obstruction. Obstruction is defined as an FEV1/FVC ratio of <70%
Vital Capacity (VC): Is the change in volume of gas in the lungs from complete inspiration to complete expiration.
Peak Expiratory Flow Rate (PEFR): Is
the greatest flow that can be sustained for 10 milliseconds on forced expiration starting from full inflation of the lungs. It
is measured in Litres per minute with a peak flow meter.
Forced Expiratory Flow Rate (FEFR 25% - 75%): This
is the average forced expiratory flow rate at the middle part of the FVC manoeuvre. Expressed in Litres per second it gives an indication of what is happening in the lower airways. It is a more sensitive parameter and not as reproducible as the others. It is a useful serial measurement because it will be affected before FEV, so can act as an early warning sign of disease
Expiratory Vital Capacity (EVC): The maximum volume of gas
which can be expired from the lungs during a relaxed
expiration from a position of full inspiration.
Inspiratory Vital Capacity (IVC): The maximum volume of
gas which can be inspired into the lungs during a relaxed
inspiration from a position of full expiration. The
expiratory phase is the one more commonly used to measure
obstruction and restriction within the lungs.
IVC can be obtained in two ways -
1. Static test - performed without regard to time
e.g. Vital Capacity (VC)
2. Dynamic test - performed at forcible and maximum
effort against time. e.g. FEV, (Forced expiratory volume
in the first second from a maximum inspiration)
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