The lungs, which are situated in the chest with the heart sitting between the right and the left lung lobe, usually get their blood supply from 2 different sources.
Most of the blood (95%) comes from the low-pressure pulmonary arteries and ends up in the pulmonary capillary bed, where gas is exchanged. A small portion (about 5%) of the blood supply circulates via high-pressure bronchial arteries, which come from the aorta and supply the structures of the major airways with blood.
In most cases of haemoptysis the blood originates from the pulmonary capillary bed (low pressure) and only in more rare cases (e.g. due to trauma or injury) from the high-pressure bronchial arteries.
If large volumes of blood enter the airway there is a risk of drowning and massive haemoptysis may result in severe anaemia, both of which are life threatening.
The reasons for haemoptysis can vary widely, common causes of haemoptysis include:
a. Infection: An infection of the main airways (called bronchitis) and the lung tissue (called pneumonia) are perhaps the most common (approximately 70%) causes of mild episodes of haemoptysis. Often other symptoms such as fatigue, fever or even shortness of breath are present as well. Usually with treating the underlying infection, the haemoptysis will disappear as well. Another typical cause of haemoptysis is still tuberculosis, which can present with night sweats and loss of weight.
b. Cancer: Cancer of the lung can develop from the cells lining the bronchi (airways). One of the earliest symptoms of lung cancer can be the coughing of blood; in fact, it can be the first symptom before others develop. Usually lung cancer develops in people above the age of 50 and who are smokers or have had a history of smoking or passive smoking. There are also other types of lung cancer that can develop in younger, non-smoking patients.
c. Bronchiectasis: One or more airways are unusually widened. This can lead to an extra production of mucous that collects in these areas – which explains the main symptom of a recurrent cough with large amounts of phlegm. These widened airways have a preponderance of getting infected, which can result in blood being mixed in the phlegm.
d. Inhalation of foreign bodies: The inhalation of small objects such as peanuts or small toy parts can cause injury and bleeding from the airways. This can frequently happen in children and when suspected, should be addressed by a pediatrician (doctor specialising in children care).
e. Pulmonary embolism: A pulmonary embolism is a blood clot blocking the main blood vessels of the lung. This is a potentially life-threatening condition that can present with (severe) breathlessness, chest pain and haemoptysis.
f. Heart failure: Severe heart failure can lead to a build-up of fluids in the lungs and which, besides breathlessness, can also lead to blood stains in the sputum – which often is frothy.
g. Inflammation and abnormal tissue deposits: Usually these are much more rare conditions, which may not only affect the lung tissue but can lead to abnormal tissue deposits in a variety of organs. Sometimes these inflammatory lesions and tissue deposits can lead to bleeding which then causes hemoptysis. Some conditions that would fall under this category would be Wegener’s granulomatosis, Goodpasture’s syndrome, lupus pneumonitis or endometriosis.
h. No cause identified: Some patients (about 5%) may fall under this category, where no clear cause can be established even when all necessary investigations have been performed.