Pulmonary Hypertension in Dogs and Cats

What does the cardiopulmonary system do?

The cardiopulmonary system is an intricate set of tissues and organs responsible for circulating blood, oxygen, and nutrients over the animal’s entire body. It also facilitates the removal of toxins derived from various metabolic processes in the body. It is mainly composed of the heart, the lungs, blood vessels, and the blood itself.

This system distributes blood rich in oxygen and nutrients throughout the entire body by relying on varying pressure in blood vessels produced by the heart to control and direct blood flow. The heart and blood vessels work to make sure the unidirectional flow of blood is kept for optimal blood circulation, oxygen, and nutrient distribution.

Parts of the Cardiopulmonary System

The main components of the cardiopulmonary system are the heart, the lungs, blood vessels, and the blood. All of these work together to help distribute oxygen and nutrients to different parts of the body.

The heart is the core organ of the system, responsible for circulating the blood around the animal’s body. It is divided into 2 sides, each containing 2 chambers, the atrium and ventricle. The right side receives used and oxygenated blood from the body and the left side receives newly oxygenated blood from the lungs. The chambers are divided and separated by valves, that open and close in a rhythmic pattern to ensure unidirectional flow of blood.

The lungs are responsible for blood-gas exchange. They oxygenate the blood they receive from the right side of the heart and bring it back to the left side for distribution to different tissues.

Blood vessels are mainly categorized into three types:

• Arteries - carry oxygenated blood away from the heart and into tissues and organs
• Veins - carry unoxygenated blood from organs and tissues back to the heart
• Capillaries - small vessels in tissues and organs where nutrient and gas exchange occur

How does blood circulate?

Blood circulation is a continuous, unidirectional process that facilitates the distribution of oxygen and nutrients to different tissues and organs in the animal’s body. The main organ responsible for circulating the blood is the heart. The contractions of its muscles produce pressure and propel the blood to flow into the surrounding blood vessels.

The left side of the heart, specifically the ventricle, contracts and pushes the blood from the heart to the aorta and into different surrounding arteries. It will then flow into the capillaries in various tissues and organs where nutrient and oxygen exchange will happen, then will flow back into the heart and will be received by the right atrium and ventricle. From there, it will be pushed to the lungs for blood-gas exchange and reoxygenation, then will flow back into the left side of the heart.

This circulation process is highly influenced by the pressure in the blood vessels, which ensures efficient flow of the blood throughout the system and the body. Any diseases that affect blood vessel pressure can disrupt the flow and compromise blood circulation.

What is pulmonary hypertension?

The pressure of the systems associated with each side of the heart is different, mainly because of the scope as to which it needs to transport blood. The left system has a higher pressure to help circulate blood into the different tissues and organs in the body, while the right system has a lower pressure because it only needs to transport blood from the heart to the lungs and back.

Normally, the systolic pressure of the pulmonary arteries is around 25 mmHg (millimeters of mercury). Pulmonary hypertension is described as a condition where the systolic pressure of the pulmonary arteries shoots up to more than 30 mmHg. There are many causes of pulmonary hypertension in dogs and cats, but the condition is generally classified into 5 types:

• Pulmonary arterial hypertension
• Pulmonary hypertension with left heart disease
• Pulmonary hypertension of pulmonary disease
• Pulmonary hypertension due to thrombolic disease
• Pulmonary hypertension due to other compressive mass lesions

Most reported cases of pulmonary hypertension in dogs and cats are due to left-sided heart disease. In dogs, the most common cause is mitral valve disease, where the valves separating the left atrium and left ventricle become defective and thick. In cats, thickening of the left ventricular wall, called hypertrophic cardiomyopathy, is the most common form of left heart disease. Both conditions result in pressure build-up from the left atrium leading to the lungs and pulmonary arteries.

Another common cause of pulmonary hypertension in animals is primary respiratory disease. Conditions that affect and compromise lung function result in increased resistance of pulmonary vessels and decreased ability to dilate appropriately. This increased resistance leads to increased pulmonary pressure, causing the blood to flow back from the pulmonary arteries into the right atrium. In response, the right side will then contract harder which further increases pressure and can lead to right-sided heart failure.

Other health conditions affecting heart function like heartworm infection and thromboembolism can lead to pulmonary hypertension.

Symptoms of Pulmonary Hypertension in Dogs and Cats

Since pulmonary hypertension can be caused by different disease processes and affects the core organs of the cardiopulmonary system, clinical signs associated with the condition are often generalized and related to poor heart and lung function.

Dogs and cats with pulmonary hypertension can exhibit lethargy, exercise intolerance, and excessive coughing. In some cases, affected animals will experience fainting episodes called syncope. If the condition progresses into right-sided heart failure, fluid will eventually accumulate into the animal’s abdomen and cause ascites.

Pulmonary Hypertension Treatment for Dogs and Cats

Treatment for pulmonary hypertension in dogs and cats is focused on addressing the underlying cause. Heartworm disease that causes pulmonary hypertension can be treated with heartworm medications. Thromboembolism that causes vascular resistance and hypertension can be addressed with anticoagulant medications.

Medications that help dilate pulmonary blood vessels, like sildenafil, can help reduce vascular resistance and control pulmonary hypertension. Along with medical treatment, nutrition and supplements appropriate for cardiopulmonary health can manage the clinical signs associated with the disease.

If your pet is exhibiting signs of possible cardiopulmonary disease, it’s best to visit your vet for a thorough assessment.

Read more:

Congestive Heart Failure in Dogs

Can cats develop heart disease?

Heart Murmurs in Dogs

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