Events of pulmonary ventilation can be subdividing amount of air in lungs into -
4 volume
4 capacities
Spirometry
It is the process of measuring volumes of air that moves into and out of the respiratory system.
Spirometer
Spirometer is device used to measure volume of air exchanged in breathing.
Volumes
1. Tidal volume
Amount of air which passes into and out of lungs during each cycle of ordinary breathing (500ml).
Only 350 ml actually reach alveoli.
2. Respiratory reserve volume
Amount of air that can be inspired forcefully after inspiration of tidal volume.
3100ml
Deepest possible breath is taken.
3. Expiratory reserve volume
Amount of air that can be forcefully expired after expiration of the tidal volume.
(1000ml-1200ml)
Lungs can pushed out 1200ml of air in addition to 500ml tidal volume.
4. Residual volume
Volume of air remaining the lungs after the most forceful expiration.
1200ml
5. Minute volume of respiration
Total air taken in during one minute.
In 1 minutes about 6 liters of air is moved.into and out of lungs while at rest
Tidal volume X respiration rate
500x 12
6000ml/min
Capacities
1. Inspiratory capacity
It is the amount of air that can inspired with maximum effort.
Inspiratory capacity = tidal volume+ Inspiratory reserve volume
500+ 3100 = 3600ml
2. Functional residual capacity
This is the amount of air that remains in the lungs at the end of normal expiration.
Functional residual capacity = expiratory reserve volume + residual volume
1200+1200= 2400ml
3. Vital capacity
Vital capacity = inspiratory reserve volume+ tidal volume+ expiratory reserve volume
3100+ 500+ 1200 = 4800ml
4. Total lung capacity
Total lung capacity = Vital capacity + residual volume
4800+ 1200 = 6000ml
Alveolar Ventilation and Anatomical Dead Space
1. Alveolar ventilation
Volume of inspired air that actually reaches and ventilates the alveoli.
Only this volume of air takes part in exchange of gases between air and the blood.
Alveolar ventilation volume= tidal volume- dead space volume X respiratory rate
500ml- 150ml X 12
350ml x 12
4200ml/ min
2. Anatomical dead space
Lungs and air passage are never empty and excchange of gases take place across only the walls of alveolar ducts and alveoli.
Remaining capacity of Respiratory passage is called "dead space" (150ml)
Dead space volume = 150ml x 12
1800 ml/ min
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