In an acute context,<unk>  can cause symptoms such as those in respiratory distress. These include breathlessness, an increased rate of breathing, use of the chest and abdominal muscles to breathe, and lip pursing. Chronic<unk>  may be compensated or uncompensated. The compensation may cause symptoms to be overlooked initially, however, further disease or a stress such as any increase in oxygen demand may finally unmask the existing<unk> . In a compensated state, blood vessels supplying less-ventilated areas of the lung may selectively contract, to redirect the blood to areas of the lungs which are better ventilated. However, in a chronic context, and if the lungs are not well ventilated generally, this mechanism can result in pulmonary hypertension, overloading the right ventricle of the heart and causing cor pulmonale and right sided heart failure. Polycythemia can also occur. In children, chronic<unk>  may manifest as delayed growth, neurological development and motor development and decreased sleep quality with frequent sleep arousals. Other symptoms of<unk>  may include cyanosis, digital clubbing, and symptoms that may relate to the cause of the<unk> , including cough and hemoptysis. Serious<unk>  typically occurs when the partial pressure of oxygen in blood is less than , the beginning of the steep portion of the oxygen–hemoglobin dissociation curve, where a small decrease in the partial pressure of oxygen results in a large decrease in the oxygen content of the blood. Severe hypoxia can lead to respiratory failure
Hypoxemia
Hypercapnia
Hypocapnia
Hyperaemia
Hypoventilation
Acidosis
Hypothermia
Hyperoxia