文档介绍：Chapter 5
Respiration is an important sign of life and it is the exchange of gas between the body and the environment. It includes three processes: external respiration (pulmonary ventilation and gas exchange in lungs), gas transport in the blood and internal respiration.
Pulmonary ventilation is the exchange of gas between the alveolus and the environment. The rhythmic contraction and relaxation of the respiratory muscles leads to the expansion or reduction of the chest cavity, which results in the expansion or reduction of the alveoli to change the alveolar pressure. During inspiration, alveolar pressure is lower than the atmospheric pressure so air flows into the lung (inhalation). During expiration, opposite changes occur because the alveolar pressure is greater than the atmospheric pressure and so air flows out of the lung (exhalation). Therefore the original impetus of pulmonary ventilation is respiratory movement and the direct impetus is the pressure difference between alveolar pressure and atmospheric pressure.
The intrapleural pressure (IP) is very important in the process of pulmonary ventilation. It means the pressure in the pleural space and is made of two factors: alveolar pressure (AP) acting on alveolar cell wall (namely visceral pleura) and recoil force (RF) of lung. They can be expressed as follows: IP=AP-RF. Hence, the intrapleural pressure is a slig