Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Four dogs with canine heartworm disease (CHD) and four control dogs were tested during a 21 minute submaximal, incremental, graded treadmill test, under normal conditions and after 2 mg/kg propranolol, i.v. Arterial and venous blood gas and pH, heart rate, systemic blood pressure, hematocrit, rectal temperature, lactate, glucose, and electrolytes were measured. CHD dogs had lower sodium and P(,a)O(,2) levels. All dogs displayed progressive increments in heart rate, hematocrit, and potassium and small gains in rectal temperature during exercise. Mean arterial blood pressure (MABP) and arterial pH increased and remained elevated throughout exercise. P(,v)O(,2) and P(,a)CO(,2) decreased, but P(,a)O(,2) did not change during exercise. At the onset of exercise, the responses of MABP, heart rate, hematocrit, potassium, arterial pH and P(,a)CO(,2) at the onset of exercise were greater in the CHD dogs. There was a slight increment in lactate during exercise, but no difference in lactate between the two groups. Control dogs exhibited a slight increment in sodium and chloride levels in exercise, while CHD dogs did not. At rest, propranolol increased glucose levels, which did not change during exercise. While propranolol increased P(,a)O(,2) in CHD dogs, their values were still significantly lower than those of control dogs. P(,a)O(,2) did not change during beta blocked exercise. MABP and heart rate were significantly lower at ech stage of work following propranolol. During beta-blocked exercise, changes in lactate, sodium, chloride and hematocrit were similar to those in non-blocked exercise. Potassium levels were greater in the beta-blocked exercise. During both exercise tests, CHD dogs had consistently, but insignificantly, higher potassium, heart rate, and MABP values than control dogs. Dogs with CHD exhibited greater respiratory alkalosis at the onset of exercise. The CHD dogs' responses at the onset of exercise in heart rate and MABP indicated an exaggerated pressor response. The greater increments in hematocrit and potassium at the beginning of work suggested an enhanced alpha receptor response in the CHD dogs.