High Blood Pressure in the Lungs in Dogs

Canine pulmonary hypertension is a condition where there is an abnormally elevated systolic blood pressure. This is documented to be at about >70mmHg and is known to be the top number measuring pressure as the muscles of the heart contract. Diastolic pressure is the lower number and measures pressure when the heart is resting. In normal heart function, the right ventricle (the lower right pumping chamber of the heart) receives blood from the right atrium (that amasses blood from remote places of the body) and disperses it to the pulmonary arteries that are responsible for carrying the oxygenated blood to the lungs while ridding the body of CO2. When a dog suffers from pulmonary hypertension, vasoconstriction occurs, resulting in the narrowing of the blood vessels thus restricting blood flow. In addition, it produces an increasing amount of vascular resistance, where the resistance must be overpowered in order for the blood to circulate to the lungs and the other organs of the body. With the passage of time, the lungs, arteries, and heart become impaired. The lining walls inside of the arteries thicken and do not allow an adequate amount of blood to flow freely to other major areas and organs of the body. The minuscule capillaries in the lungs become restricted, forcing the heart to work harder to push blood through, leaving very low oxygen levels to circulate in between the heart and lungs. As the heart works to overcome vascular resistance, the right ventricle of the heart dilates and expands, and the left ventricle fills with blood abnormally. In all essence, your dog will suffer from low levels of oxygen that inhibit his health.

Canine pulmonary hypertension is a rare disorder that occurs as a result of a variety of diseases and ailments. With this condition, elevated blood pressure forces a greater resistance to oxygen-rich blood passing through to the pulmonary veins, arteries, and capillaries that lead to the bronchi, causing heart failure. Middle-aged to older small breed dogs are prone to this condition.

• Asymptomatic (no symptoms in primary hypertension) 
• Dyspnea
• Fainting (syncope)
• Exercise intolerance
• Lethargy
• Coughing
• Cyanosis (blue/purple shaded gums and tongue)
• Congestive heart failure
• Renal deterioration
• Lack of appetite
• Frequent thirst
• Frequent urination

Types

There are two types of canine pulmonary hypertension.

Primary Pulmonary Hypertension

• Also known as idiopathic or essential hypertension
• Asymptomatic
• No known or underlying cause
• Extremely rare

Secondary Pulmonary Hypertension

• Symptomatic
• Resulting from disease
• Kidney disease
• Tumors
• Diabetes
• Chronic left-lateral congestive heart failure
• Chronic lung diseases (bronchitis, pneumonia, vasoconstriction, tracheal collapse)
• Heartworm disease
• Pulmonary thromboembolism (large blood clotting)
• Cushing’s disease
• Hyperadrenocorticism

• Canine pulmonary hypertension is not a disease that manifests within itself, but results due to a wide variety of different illnesses 
• Most dogs suffer from this condition because of defects pertaining to degenerative heart valve diseases that include chronic left-sided congestive heart failure 
• In addition, heartworm infestation is widely known to severely limit the amount of blood flow as the worms infiltrate the pulmonary cavities and restrict blood circulation
• Chronic bronchial obstructions  that include tracheal collapse and laryngeal paralysis are a factor
• Chronic respiratory diseases like pulmonary fibrosis, bronchitis, and pneumonia may lead to this condition
• Other thromboembolic or neoplastic disorders that can occur such as thrombocythemia (too many platelets that cause blood clotting)
• There are medications such as Ephedrine and Doxapram that are used for hypotension disorder where the outcome of vasoconstriction (the narrowing flow of the blood vessels) is desired
• Diabetes mellitus and diets high in sodium (similar to humans) can elevate blood pressure in dogs
• Obesity and unhealthy eating habits can contribute to general hypertension similar as in humans
• High altitudes and exposure to nicotine, carbon monoxides  and marijuana can also contribute to pulmonary hypertension
• Consistent stress, anxiety, fear, and even excitement are uncommon factors but can add cause to the disorder as well

The most noninvasive way to perform blood pressure analysis on your dog is to use the standard oscillometric method that uses a sensor attached to a cuff that is wrapped around one of the limbs. The sensor has the ability to monitor pulse pressure readings within the blood vessels. Standard testing for your pet during this diagnostic visit will include complete blood count, serum biochemistry, and urinalysis. Chest x-rays may be able to shed light on other illnesses that could be present, and provide evidence of right-sided heart enlargement, neoplasia, or pneumonia. A test may be conducted to eliminate a diagnosis of heartworm invasion as well.

The use of ultrasonography or an echocardiogram (cardiac ultrasound of the heart) is most effective as a non-invasive procedure to help eliminate possible underlying causes for the pulmonary hypertension. Cardiac catheterization requires anesthesia and is extremely invasive, a catheter is inserted into the central pulmonary artery to assess measurement of blood pressure. However, it can be only performed by a surgeon who is both highly qualified and experienced, therefore it is uncommon because it is costly and intrusive.

If your dog is suffering from symptoms of severe oxygen limitation such as syncope or cyanosis, oxygen therapy must be immediately given in order to stabilize him for treatment.  Treatment for a known underlying disease process will be paramount. Diuretics (Spironolactone, Furosemide) can be used in relation to congestive heart failure. Heartworm disease medication can be given monthly or be given via intravenous injection. If your dog is suffering from a chronic lung disease such as pneumonia or bronchitis, bronchodilators (Theophylline) work well as a vasodilator to lower pulmonary artery pressure.  Antibiotics and corticosteroids may be prescribed to reduce inflammation.

If the hypertension is caused by thromboembolism, medications are used to inhibit coagulation and platelet numbers (thrombocythemia). Vasodilator therapy will likely be long term. A newer medication that is used is called Sildenafil Citrate (Viagra in humans) or Tadalafil (Cialis), which are medications that possess the ability to pacify the lungs, allowing blood to flow liberally and reduce the pressure of the heart. Studies have shown that the uses of these medications result in significant lowered pulmonary arterial pressure.

The outlook for recovery for canines with pulmonary hypertension can be average to poor. Medication is used to alleviate and treat the symptoms to prevent deterioration but do not provide a cure. With Sildenafil therapy for example, the survival rate has been reported to increase a pet’s lifespan by up to 2 years.  Prior to this new therapy, patients succumbed to fatality days after receiving the diagnosis. The best way to treat hypertension in your dog is to do all means to prevent it from worsening. In addition, be sure that your dog is not stressed or anxious, and try not to allow him to get too excited.