Pulmonary vascular resistance (PVR) is the resistance to flow of blood vessels in the pulmonary circulation. It is also called pulmonary vascular resistance and is used to regulate blood flow.
What is pulmonary vascular resistance?
Pulmonary vascular resistance (PVR) is the resistance to flow of blood vessels in the pulmonary circulation. Pulmonary vascular resistance is only about one-tenth as great as the total peripheral resistance of the large body circulation. Correspondingly, arterial blood pressure in the lungs reaches only a nominal value of 20/8 mmHg. The pulmonary circulation (small circulation) transports blood from the heart to the lungs and returns it from there. In the process, oxygen-depleted blood is enriched and the lungs are ventilated at the same time. From the right ventricle, this blood is drained through both pulmonary arteries. They divide into smaller and smaller vessels and eventually merge into the capillaries (hair vessels). The alveoli, which are enclosed by the hair vessels, then exchange the carbon dioxide in the blood for oxygen by diffusion. The enriched blood returns to the left atrium of the heart via the pulmonary veins. The bronchial arteries are also part of this circuit, as they supply oxygenated blood to the lungs. When the oxygen concentration of the blood in the pulmonary arteries decreases, they narrow (vasoconstriction), increasing pulmonary vascular resistance. In other areas of the lungs, it decreases accordingly. Ventilation of the lungs is organized by this reciprocal mechanism.
Function and Purpose
Vascular resistance in the lungs depends on the particular diameter of the vascular segment and the flow rate of the blood. The viscosity of the blood is equally important for PVR. The longer a vessel is, the greater the vascular resistance. If the radius of a vessel halves along its path, the resistance becomes sixteen times greater. If the vascular resistance increases, for example due to a narrowing (stenosis), the blood flow to the lungs deteriorates. If this affects only short sections of the respective vessel, it can usually be compensated. In the case of large stenoses, however, symptoms of disease soon become apparent. The best way to prevent possible hypertension in the lungs is through timely and effective treatment of the many chronic diseases that may precede it. Therefore, in these cases, the recommended preventive examinations are advisable. This is especially true if any of the known pre-existing conditions of pulmonary hypertension have occurred or there is an increased risk of them. Regular measurements of vascular resistance or pulmonary blood pressure are possible at any time without major technical requirements.
Diseases and complaints
If the vascular resistance rises continuously and brings an increase in blood pressure in the pulmonary circulation, pulmonary hypertension develops. It may be followed by what is called right heart failure, in which the atrium and ventricle of the right side of the heart are weakened, which are supposed to replenish blood from the pulmonary circulation. In hypertension, the mean blood pressure in the pulmonary artery (pulmonary artery) rises from its normal value between 12 and 16 mmHg to more than 25 mmHg at rest. In the patient’s mild stress state, the first symptoms become noticeable between 30 and 40 mmHg. From a pulmonary blood pressure of 50 to 70 mmHg, the cardiac load increases sharply and the affected person feels a considerable decline in physical performance. Circulatory problems and weakness may occur. Serious dangers arise when pulmonary arterial blood pressure exceeds 100 mmHg. In acute pulmonary hypertension, the pulmonary arteries become extremely constricted and their vascular muscles thicken at the same time. The vascular cross-section becomes alarmingly small. If the hypertension proceeds chronically, the vascular muscles also swell, but they are also gradually transformed into connective tissue. Thus, the efficiency of the arteries decreases, the lungs can only take up less oxygen and, as a consequence, the pulmonary vascular resistance increases again. People affected by this mostly notice symptoms such as sore throat, shortness of breath, weakness, circulatory problems and feelings of fainting.Also known are bluish skin discolorations in various parts of the body (cyanosis), water retention and temporary paling of the hands and feet due to lack of blood flow (Raynaud’s syndrome). In many cases, pulmonary hypertension arises from previous diseases of the lungs (embolism, fibrosis), calcifications in the respiratory tract, asthma, AIDS and congenital or acquired heart defects. In therapy, the primary disease must first be cured. If this is successful, there is a chance of successful treatment of pulmonary hypertension. However, very often only risky and medically controversial drug treatment steps are feasible here, or there are major obstacles to the approval of special drugs. It has also been suspected for some time that certain drugs used to suppress appetite may promote pulmonary hypertension. In special cases of pulmonary hypertension, long-term therapy with oxygen may lead to success. Heart/lung transplants have been tried and tested, but these must always be carefully tailored to the patient’s particular health condition. If primary heart disease is present, treatment options are very limited. Without therapy, life expectancy in hypertension of the lung is on average in the range of less than three years. A common cause of death is right cardiac decompensation (right heart failure), usually associated with very severe arrhythmias. For these reasons, early surgery is desirable in children with congenital heart defects to rule out the development of pulmonary hypertension with some certainty. In any case, those suffering from pulmonary hypertension should avoid major physical exertion and, if possible, avoid altitudes above 2000 meters.
