Following large hemorrhages the blood pressure is reduced. In venesection the withdrawal of blood may not affect the blood pressure. The procedure is done to relieve overdistension of the heart.
In pleurisy with effusion and in pericarditis with effusion there is hypotension.
Collapse, whether from poisoning by drugs or as the result of dysentery, cholera, or profuse vomiting from whatever cause, reduces the blood pressure.
In cachectic states, such as cancer, the blood pressure is low. General wasting of the whole musculature includes that of the heart and the heart muscle shows the condition known as "brown atrophy."
A most interesting and important condition in which hypotension occurs is pulmonary tuberculosis. Haven Emerson has recently gone over the whole subject in a careful piece of work and his summary is as follows:
"Hypotension or subnormal blood pressure is universally found in advanced pulmonary tuberculosis, in which condition emaciation may play a part in its causation. Hypotension is found in almost all cases of moderately advanced tuberculosis, or in early cases in which the toxemia is marked except when arteriosclerosis, the so-called arthritic or gouty diathesis, chronic nephritis, or diabetes complicate the tuberculosis and bring about a normal pressure or a hypertension. Occasionally the period just preceding a hemoptysis or during a hemoptysis may show hypertension in a patient whose usual condition is that of hypotension.
"Hypotension has been found by so many observers in early, doubtful or suspected cases with or before physical signs of the disease in the lungs, and is considered by competent clinicians so useful a differential sign between various conditions and tuberculosis, that it should be sought for as carefully as it is the custom at present to search for pulmonary signs.
"Hypotension when found persistently in individuals or families or classes living under certain unhygienic conditions should put us on our guard against at least a predisposition to tuberculosis. Most unhygienic conditions, overwork, undernourishment and insufficient air, are of themselves causes of a diminished resistance, and it seems likely that a failure of normal cardiovascular response to exercise or change of position may be found to indicate this stage of susceptibility, especially to tuberculous infection.
"... Hypotension, when it is present in tuberculosis, increases with an extension of the process. Recovery from hypotension accompanies arrest or improvement. Return to normal pressure is commonly found in those who are cured. Continuation of hypotension seems never to accompany improvement. Prognosis can as safely be based on the alteration in the blood pressure as on changes in the pulse or temperature...."
There are a few drugs which lower the blood pressure, but, as a rule, their effects are more or less transitory. We know of no drug, unless it be iodide of potassium, which has the property of causing changes in the blood (decrease in viscosity?), which tends to reduce the blood pressure when it is excessive. This drug fails us many times.