MEDICAL BIOLOGY, ANATOMY, HUMAN PHYSIOLOGY AND PATHOLOGY - Ya.I.Fedonyuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

CHAPTER 6. THE RESPIRATORY PROCESS AND ITS PATHOLOGY

RESPIRATORY PHYSIOLOGY

PULMONARY VOLUMES AND CAPACITIES

External respiration is characterized by such parameters as tidal volume, inspiratory and expiratory reserve volumes, and vital capacity of the Lungs.

Tidal volume (TV) is The amount of air inhaled and exhaled during a normal, quiet breath. In adults, it averages about 500 mL.

Inspiratory reserve volume (IRV) is the maximum volume of air that can be additionally inhaled following a normal tidal inspiration. It is approximately 2500 mL.

Expiratory reserve volume (ERV) is the maximum volume of air that can be additionally exhaled following a normal tidal expiration. It averages about 1000 mL.

The sum of these three pulmonary volumes yields the vital capacity (VC). The VC is slightly higher in men, ranging from 4000 to 4500 mL, whereas in women it is 3000 to 3500 mL. In addition, VC depends on age, height, body weight, and physical conditioning.

Pulmonary volumes and vital capacity are measured by spirometry. Fig. 6.11 shows a spirogram.

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Fig. 6.11. Static parameters of external respiration

Not all the air present in the Respiratory system participates in gas exchange. Gas exchange between air and Blood takes place in the alveoli. The air located within the conducting airways (Nose, nasopharynx, Larynx, Trachea, Bronchi) does not take part in gas exchange. This volume is known as the anatomical dead space and amounts to 150 mL. Thus, if a person inhales 500 mL of air during quiet breathing, only 350 mL will actually participate in alveolar gas exchange. Nevertheless, the anatomical dead space plays an important role, as it is here that the air is warmed, filtered, and humidified.

Exhaled air contains more carbon dioxide and less oxygen than inhaled air. The lowest oxygen concentration and the highest carbon dioxide concentration are found in the alveolar air (Table 6.1).

TABLE 6.1

Composition of inspired, expired, and alveolar air