Atelectasis as a collapse of lung tissue, atelectasis is not synonymous with a pneumothorax, which is a more specific condition that features atelectasis. Acute atelectasis may occur as a post-operative complication or as a result of surfactant deficiency. In premature neonates, this leads to infant respiratory distress syndrome. The term uses combining forms of "atel-" + "ectasis", from , "incomplete" + ἔκτασις, "extension". May have no signs and symptoms or they may include: It is a common misconception that atelectasis causes fever. A study of 100 post-op patients followed with serial chest X-rays and temperature measurements showed that the incidence of
High-altitude adaptation in humans Tibetans, Andeans and Ethiopians is indeed an observable instance of the process of natural selection in acting on favourable characters such as enhanced respiratory mechanisms in humans. Humans are naturally adapted to lowland environment where oxygen is abundant. When people from the general lowlands go to altitudes above , with atmospheric pressure 74% of normal they experience mountain sickness, which is a type of hypoxia, a clinical syndrome of severe lack of oxygen. Complications include fatigue, dizziness, breathlessness, headaches, insomnia, malaise, nausea, vomiting, body pain, loss of appetite, ear-ringing, blistering and purpling of the hands and feet, and dilated veins.