Inspired Air Alveolar Air And Expired Air

Inspired Air, Alveolar Air, and Expired Air

Inspired Air Definition: Inspired air is the atmospheric air, which is inhaled during inspiration.

Inspired Air Composition: The composition of inspired air is given in Table 123-1

Read And Learn More: Medical Physiology Notes

Alveolar Air

Alveolar Air Definition:

1. Alveolar air is the air present in the alveoli of the lungs. It is different from the air. There are four reasons for the difference between alveolar air and inspired air:
2. The alveolar air is partially replaced by the atmospheric air during each breath
3. Oxygen diffuses from the alveolar air into pulmonary capillaries constantly
4. Carbon dioxide diffuses from pulmonary blood into alveolar air constantly
5. The dry atmospheric air is humidified while passing through a respiratory passage just before entering the alveoli.

Alveolar Air Composition: The composition of alveolar air is given in Table 123-1.

Alveolar Air Renewal: The alveolar air is constantly renewed. The rate of renewal is slow during normal breathing.

• During each breath, out of 500 mL of tidal volume only 350 mL of air enters the alveoli and the remaining quantity of 150 mL (30%) becomes dead space air.
• Hence, the amount of alveolar air replaced by new atmospheric air with each breath is only about 70% of the total alveolar air.

Thus,

This slow renewal of alveolar air is important in preventing sudden changes in the concentration of gases in the blood.

Alveolar Air Method Of Collection:

• Alveolar air is collected by using a Haldane-Priestly tube. This tube consists of a canvas rubber tube, which is 1 meter long and 2.5 cm in diameter. The tube is opened on both ends.
• A mouthpiece is fitted at one end of the tube. Near the mouthpiece, there is a side tube, which is fixed with a sampling tube.
• The mouthpiece and the side tube are interconnected by means of a three-way cock.
• By keeping the mouthpiece in the mouth, the subject makes a forceful expiration through the mouthpiece.
• The alveolar air is expired at the end of forced expiration. So, by using the three-way cock, the last portion of expired air (alveolar air) is collected in the sampling tube.

Expired Air

Expired Air Definition: Expired air is the amount of air that is exhaled during expiration. It is a combination of dead space air and alveolar air.

Expired Air Composition:

• The concentration of gases in expired air is somewhere between inspired air and alveolar air.
• The composition of expired air is given in Table 123-1 along with the composition of inspired air and alveolar air.

Expired Air Method of Collection:

Expired air is collected by using a Douglas bag.