Atelectasis from the outside (tumor, lymph node, tubercle). Another cause is poor surfactant spreading during inspiration, causing the surface tension to be at its highest which tends to collapse smaller alveoli. Atelectasis may also occur during suction, as along with sputum, air is withdrawn from the lungs. There are several types of atelectasis according to their underlying mechanisms or the distribution of alveolar collapse; resorption, compression, microatelectasis and contraction atelectasis. Relaxation atelectasis (also called passive atelectasis) is when a pleural effusion or a pneumothorax disrupts the contact between the parietal and visceral pleurae. Risk factors associated with increased likelihood of the
Effects of high altitude on humans Effects of high altitude on humans The effects of high altitude on humans are considerable. The percentage oxygen saturation of hemoglobin determines the content of oxygen in blood. After the human body reaches around 2,100 m (7,000 feet) above sea level, the saturation of oxyhemoglobin begins to decrease rapidly. However, the human body has both short-term and long-term adaptations to altitude that allow it to partially compensate for the lack of oxygen. There is a limit to the level of adaptation; mountaineers refer to the altitudes above as the "death zone", where it is generally believed that no human body