Physiological void

The physiologically ineffective cavity (Vd / Vt) is the gas inhaled each time, and a part of it stays in the respiratory tract from the upper respiratory tract to the respiratory bronchioles. This part of the gas does not participate in the gas exchange between the alveoli and blood. Or dead space. Its volume is about 150ml. The gas that enters the alveoli can also be partially exchanged with the blood due to the uneven distribution of blood flow in the lungs. This part of the alveolar volume is called the alveolar ineffective cavity. The alveolar ineffective cavity and the anatomical ineffective cavity are collectively called a physiological ineffective cavity. The physiologically ineffective cavity of a healthy person when lying down is equal to or close to the anatomic ineffective cavity.