Blood coming from the lungs is usually bright red and frothy whereas that from the stomach may be dark red, brown or black and mixed with scraps of food. Vomiting is usually preceded by retching and nausea, but a hemorrhage from the lung may come quietly and without warning. Blood in the lung may be associated with severe coughing and occasionally severe coughing may tear tissue so as to produce bleeding.
In the early stages of pneumonia a severe cough may bring up blood, because the lungs are at that time heavily congested. Such blood has a rusty or prune juice color, but may be bright red.
Among the commonest causes of blood from the lungs, in the absence of tuberculosis, is the passing of a clot elsewhere in the body into the pulmonary artery, the large blood vessel that supplies the lung with blood. The small blood vessels around the area become congested and the irritation causes a cough which may bring up blood.
In chronic bronchiectasis the surface tissue of the bronchial tubes may be torn with severe coughing so that blood appears in the sputum.
The hemorrhage from the lungs in tuberculosis is due to actual erosion or destruction of blood vessels by the disease. Cavities form in the lung in tuberculosis due to destructive action by the germs. The blood vessels in the walls of these cavities may be eroded. One of the dangers is spread of the infection by inhaling and by forcible expulsion of germs in severe coughing.
Among young people with hearts that have been damaged by disease, especially with narrowing of the mitral valve of the heart, the backing up of blood into the lungs causes swelling of the large and small blood vessels with occasional breaking and therefore a hemorrhage from the lungs.
Any time blood comes from the lungs the symptom should be taken as a warning that something serious has occurred.