Issue Description

At birth, mammals must adapt from living in a fluid environment (the amniotic fluid) and acquiring oxygen through the mother's blood, to breathing air and acquiring oxygen through their own lungs. The ductus arteriosus is very important in the adaptation process. This is a small communicating blood vessel between the pulmonary artery (which carries blood to the lungs), and the aorta (which carries blood to the rest of the body). Before birth, most of the blood from the fetal heart bypasses the fetal lungs via the ductus arteriosus. The lungs gradually become functional fairly late in fetal development. At birth, the blood supply from the mother is of course cut off, the dog (or other mammal) begins breathing on its own, and blood flow through the ductus arteriosus decreases dramatically. Within a few days, the ductus closes off completely.

Where the ductus does not close, the dog is left with a patent ductus arteriosus.

The extent to which this affects the dog depends on the degree of patency, or opening, of the ductus.

Symptoms

The degree to which your dog is affected depends on the magnitude of the defect. This can range anywhere from a small blind pocket off the aorta which doesn't cause any problems, to varying degrees of abnormal blood flow through the ductus between the aorta and the pulmonary artery. Most commonly there is a shunt from the left to the right side of the heart , with blood from the higher pressure aorta continuously shunted to the main pulmonary artery. This means an increased volume of blood to the lungs which results in fluid build-up (pulmonary edema) and volume overload to the left heart. You may see coughing, reduced tolerance of exercise, loss of weight, and eventually, congestive heart failure. Without surgery, premature death is likely.

Less commonly, there is a right-to-left shunt. This may be the case from birth or, it may develop because the PDA is so large that the pressure in the lungs, and resultant resistance to this pressure, markedly increase. In effect, the circulation is the same as when the dog was a fetus - that is, some of the blood leaving the right side of the heart bypasses the lungs entirely. This results in circulation of poorly oxygenated blood. Your dog may have shortness of breath and weakness or collapse in the hind limbs.