One of the important factors affecting the mechanics of respiration is the extensibility of the lung tissue, or lung compliance. There are 2 types of lung compliance: static and dynamic.
Static compliance is determined at the end of exhalation in conditions of a complete absence of flow in the airways:
Cstat = Vt / (Pplat – PDKV).
Dynamic compliance is measured in the presence of airflow in the airways:
Cdyn = Vt / (Ppeak – PDKV).
The value of Cdyn depends on the resistance of the airways and, compared with Cstat, to a lesser extent reflects the extensibility of the lung tissue.
The normal values of Cstat are 50 ml / mm water. Art. and more. The lower the compliance, the worse the condition of the lung tissue. The development of pneumonia and acute respiratory distress syndrome most often leads to a decrease in Cstat.
Resistance of the airways (Raw), affecting the advancement of the gas flow, is calculated as the ratio of the difference between the peak pressure in the airways (Ppeak) and Pplat to the air velocity in the airways:
Raw = (Ppeak – Pplat) / V.
Normal values of airway resistance are 3-10 cm of water. Art./l in 1 s.
Raw can increase with bronchospasm, bronchial obstruction, emphysema, excessive moistening of the respiratory filter.