Pulmonary Hypertension is a condition in which there is an increased blood pressure (greater than 25 mmHg) within the pulmonary vessels. This can be caused by an increase in blood flow within the lungs, constriction of pulmonary vessels, or obstruction of pulmonary vessels.
Mitral valve disease is one condition that can cause an increase in pulmonary blood pressure. The back flow of blood increases the volume of blood within the lungs, and this increased volume causes an increase in the pulmonary blood pressure.
Another cause of pulmonary hypertension is obstructive disease such as heartworm disease or pulmonary thromboembolism (a blood clot within a pulmonary vessel).
A third cause of pulmonary hypertension is pulmonary vasoconstriction. This condition can result when there is not enough oxygen being delivered to the lungs (i.e. in high altitudes, or with a primary bronchial disease such as a collapsed trachea). Constriction of the pulmonary vessels causes the right side of the heart to work harder, which can eventually lead to right-sided hypertrophy and congestive heart failure.
Signs of pulmonary hypertension include respiratory distress, coughing, exercise intolerance, and fainting. Thoracic radiographs and echocardiograms often reveal an enlarged pulmonary artery and right ventricle. This occurs because the right side of the heart needs to work harder in order to pump the blood through the hypertensive pulmonary vessels.
Treatments for pulmonary hypertension include:
- A low sodium diet
- Restricted exercise
- Short term oxygen therapy
- A vasodilator such as Enalapril, Hydralazine or Nifedipine.
Treatment with a vasodilator can be problematic because the drugs do not always work on the pulmonary vessels. These drugs may be more effective at decreasing systemic blood pressure, which can cause the heart to beat faster. This increase in heart rate may ultimately cause the right side of the heart to work harder, which may worsen the right-sided heart disease. However, Sildenafil (Viagra™) has shown promise with relatively pulmonary specific vessel dilation. Sildenafil has actually just been licensed under a different name for pulmonary hypertension and veterinary clinical pulmonary hypertension veterinary trials have shown a positive effect. Pimobendan (Vetmedin™) has also shown promise in similar fashion. Endothelin inhibitors are sometimes used in humans, but this can be very toxic and extremely expensive.
The prognosis of pulmonary hypertension is dependent upon the underlying cause. Your pet should be monitored regularly with thoracic radiographs and echocardiograms in order to adequately assess the disease.