Pulmonary Hypertension in Dogs
Pulmonary hypertension occurs when pulmonary arteries/capillaries vasoconstrict (narrow), are obstructed, or receive excessive blood flow. The capillaries of the lungs are very tiny branches of blood vessels only one cell in thickness, connecting the smallest veins to the smallest arteries for the exchange of oxygen and carbon dioxide to the blood and tissues. Arteries carry oxygenated blood from the heart to the lungs, so high blood pressure in the left atrium of the heart can also cause elevated pressure in the capillaries of the lungs.
High pulmonary blood pressure is dangerous because it can alter the shape and performance of the heart. The right ventricle is enlarged, while the left ventricle fills abnormally. Less oxygenated blood reaches the body, leading to troubled breathing, exercise intolerance, and blue-purple tinged skin. Eventually, this increased blood pressure in the right heart can lead to the pooling of blood in the body. The tricuspid valve can also be affected. Located in the right side of the heart, separating the right atrium (upper chamber) from the right ventricle (lower chamber), the tricuspid valve consists of three flaps of tissue that prevent blood from flowing back into the atrium from the ventricle. High pulmonary blood pressure can bring about abnormal functioning of the tricuspid valves, causing a back-flow of blood from the right ventricle back into the right atrium, eventually leading to right-sided congestive heart failure.
Pulmonary hypertension in humans is typically due to an abnormal congenitally formed arrangement of the blood vessels in the lungs (pulmonary vasculature), but with dogs, the current medical findings show that they only develop secondary pulmonary hypertension, that is, hypertension in the lungs due to an underlying disease.
Symptoms and Types
- Exercise intolerance
- Trouble breathing
- Bluish-purplish tinged skin
- Coughing or vomiting up blood
- Enlarged abdomen
- Weight Loss
Pulmonary (lung) disease
- Vascular (blood vessel) blockage
- Adult respiratory distress syndrome
- Thrombosis (blood clot blocking the blood vessels in the lung)
Extrapulmonary causes of chronic hypoxia (inadequate levels of oxygen reaching the lung tissues)
- Overactive adrenal glands
- Protein-losing nephropathy (a kidney disease where proteins normally kept by the body are lost in the urine)
- Inflammation of the pancreas
- Heart disease
- Heartworm disease
- High altitude disease
- Not breathing enough (due to paralysis, etc.)
Your veterinarian will perform a thorough physical exam on your dog, taking into account the background history of symptoms and possible incidents that might have precipitated this condition. You will need to give a thorough history of your dog's health and onset of symptoms. In order to find the underlying cause for the pulmonary disorder, your veterinarian will order a blood chemical profile, a complete blood count, a urinalysis, and an arterial blood gas (ABG) test, to measure the levels of oxygen and carbon dioxide in the blood, as well as to measure the capability of the lungs to move oxygen into the blood. If there is any fluid that has escaped from the vessels into the lining of the lungs (pleura) or abdomen (referred to as effusion), your veterinarian will take a sample for laboratory analysis. If a blood clot in the lung is suspected (pulmonary thrombosis), your veterinarian may perform several more blood tests to confirm this.
A comprehensive examination of the thorax, the cavity where the lungs reside, is essential for diagnosis. Thoracic radiography, or x-ray imaging, is an essential diagnostic tool for your veterinarian to visualize pulmonary abnormalities and/or heart disease. Likewise, an echocardiogram (using Doppler) is a more sensitive tool for finding heart abnormalities, pulmonary blood clots, and measuring pressure gradients in blood vessels when the heart is contracting. Your veterinarian may also use an electrocardiogram (ECG, EKG) to evaluate the electrical functioning of the heart. Recordings from this test would allow your doctor to make a diagnosis based on any observed abnormalities, if they exist, indicating lack of oxygen to the heart muscle.