Lung Volumes, Capacities and Dead Space- Definitions and Normal values . Knowledge of these values are quite important to understand respiratory physiology, pathological basis of various respiratory illnesses and for anesthesia.
Tidal Volume (TV)- Volume of gas inspired or expired in each breath during normal quiet respiration. It is 400-500 ml ie 10ml/kg
Inspiratory Reserve Volume ( IRV)- It is the maximum volume of gas which a person can inhale from end inspiratory position. It is 2400 to 2600 ml.
Inspiratory Capacity ( IC)- It is the maximum volume which can be inhaled from end expiratory position ie, IRV + TV. It is 2500 + 500= 3000 ml or 3 L
Expiratory Reserve Volume- Maximum volume of gas that can be expired after normal expiration. It is 1200 to 1500 ml.
Vital Capacity- Maximum volume of gas that can be exhaled after maximum inhalation ie, it is IRV+TV+ ERV. Its value is 4200 to 4500 ml ( 75-80 ml/kg).
Functional Expiratory Volume ( FEV)– It is vital capacity per time. FEV1 is VC in 1st sec.
Residual Volume- It is the volume of gas still present in lungs after maximal expiration. It is 1200-1500 ml.
Maximum breathing capacity- Maximum volume of air that can be breathed/minute. It is 120-170 litre/min ( normally it can be measured for 15 sec and expressed as litre/min)
Minute Volume- It is tidal volume X Respiratory rate. It is 500 X 12= 6000 ml/min
Total Lung volume- IRV+TV+ERV+RV = 5500 to 6000ml
Functional Residual Capacity( FRC)- It is the volume of gas in lungs after end expiration. It is ERV + RV. It is 2400-2600 ml. During anaesthesia FRC decreases by 15-20%.
DEAD SPACE: It is the volume of the respiratory tract that does not participate in gas exchange. It is approximately 300 ml in normal lungs.
a.ANATOMIC DEAD SPACE: Volume of the conducting airways, approximately 150 ml
b.PHYSIOLOGIC DEAD SPACE: The volume of the lung that does not participate in gas exchange.In normal lungs, is equal to the anatomic dead space (150 ml). May increase in several lung diseases.
Reference- Short Text book of Anesthesia- A. Yadav, Web.