LUNG VOLUMES: DEFINITIONS
Spirometer = Instrument used to measure lung volumes.
Peak flow meter = Instrument used to measure air flow through the respiratory system.
Tidal volume = Volume of air entering or leaving
the lungs in a single breath.
Normal TV = 500 ml.
Respiratory rate = Number of breaths per minute. Normal RR = 12 - 20 breaths/min.
Minute ventilation = Total volume of air breathed per minute. MV = TV x RR.
Dead space = Volume of air in each breath which does
not reach the alveoli. This is
approximately the volume of the conducting system. Normal dead space = 150 ml.
Alveolar ventilation = Volume of air which reaches the alveoli per minute.
Vital capacity = Maximum volume that can be exhaled
after a maximal inspiration.
This is measured using a spirometer.
Residual volume = Volume of air which is left in
the lungs after a maximal expiration.
Approximately 25% of vital capacity.
Total lung capacity = Volume of the lungs when completely
TLC = vital capacity + residual volume.
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