Respiratory therapy is an effective way to treat high blood pressure and heart disease. Both hypertension and hypotension are circulatory disorders, and as the breathing or respiratory centre in the brain is quite close to the circulatory centre it should now occasion no surprise for readers to learn that breathing has an enormous influence upon the circulation and hence upon the regulation of the blood pressure.
The diaphragm is the most important breathing muscle and separates the chest from the abdominal cavity. On inhalation the diaphragm descends, flattens itself out and thus increases the size of the chest cavity. The most powerful movement of the diaphragm takes place in the supine position, stronger than when standing or sitting. For all that, many persons are unable to breathe so well in the supine position and to satisfy their air hunger, because the pressure conditions in the thoracic and abdominal cavities are different on lying than on standing or sitting.
Furthermore, on lying, the viscera press the diaphragm upwards more towards the head so that the lungs must contract more strongly. This is the real reason why with many heart sufferers the supine position is impossible. They suffer from orthopnea, i.e., they can breathe only in the erect position. Their air-need increases on lying, for only on sitting or standing can the diaphragm descend into the abdominal cavity, because the organs (viscera) no longer press against it.