The heart and circulatory system

To understand what PH is, it first helps to understand a bit about the circulatory systemThe system of blood vessels and the heart that together moves blood throughout the body.. As shown in the figure, the heart pumps oxygen-poor bloodBlood that is returning to the heart and has had most of the oxygen removed. Oxygen is removed by other organs and muscles throughout the body to be used to make to the lungs so the blood can take up oxygen. Blood that is oxygen-poor is normally shown on diagrams as blue, whereas oxygen-rich bloodBlood that has a lot of oxygen dissolved in it. This is normally blood returning from the lungs and being pumped to the rest of the body by the heart. returning from the lungs is normally shown in red.

The heart and circulatory system

During periods of exercise, the heart beats more quickly to get more oxygen to the muscles. At the same time, the blood vessels carrying blood to the lungs (the pulmonary arteries) expand to allow more blood through. The pulmonary arteries do this by stretching slightly. In a person with PH, the walls of the pulmonary arteries are thicker, so are less able to stretch.

The pulmonary artery in a healthy person

 

The pulmonary artery in a person with PH

In a person with PH, because the pulmonary arteries are less able to stretch, the heart has to work harder to pump blood to the lungs. If the heart has to work harder than usual over a long period of time (months or years), it begins to work less effectively.