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Extracellular volume expansion and delayed resolution of hypertension after canine aortic coarctectomy
Insights
Surgical correction of aortic coarctation in dogs led to transient hypertension and volume expansion, driven by sympathetic activation and baroreceptor changes. These hemodynamic shifts normalized over weeks post-surgery.
Area of Science:
- Cardiovascular Surgery
- Pediatric Cardiology
- Physiology
Background:
- Aortic coarctation is a congenital heart defect requiring surgical intervention.
- Understanding post-surgical hemodynamic changes is crucial for patient recovery.
- Neonatal coarctation models provide insights into surgical outcomes.
Purpose of the Study:
- To investigate hemodynamic alterations following surgical correction of thoracic aortic coarctation.
- To compare physiological responses in coarcted dogs versus control subjects.
- To elucidate the mechanisms underlying post-coarctectomy hypertension and volume expansion.
Main Methods:
- Surgical correction of induced aortic coarctation in neonatal dogs.
- Hemodynamic monitoring including systemic and femoral pressures.
- Assessment of extracellular volume (ECV) and plasma renin activity (PRA).
- Comparison with sham-operated littermate controls.
Main Results:
- Surgical repair abolished pressure gradients, followed by a transient rise in systemic pressure.
- Significant increases in femoral systolic pressure (47-57 mmHg) and ECV (7.1-7.6%) were observed in coarcted dogs.
- Post-coarctectomy tachycardia was noted, with comparable fluid administration, blood loss, and PRA across groups.
- ECV expansion peaked concurrently with elevated blood pressure.
Conclusions:
- Post-coarctectomy baroreceptor stimulation likely induces sympathetic-mediated renal sodium retention and volume expansion.
- Sustained hypertension may result from sympathetic activation and volume expansion until baroreceptor readjustment.
- These findings highlight the complex physiological adaptations following aortic coarctation repair.
Abstract:
The hemodynamic changes occurring after surgical correction of thoracic aortic coarctation were studied in two neonatally coarcted dogs at six months of age and compared to sham surgery in two littermate controls. Excision of the tight iatrogenic aortic band with direct aortic reanastomosis abolished pressure gradients. Post-coarctectomy systemic pressure rose, after an early transient fall, to pre-operative proximal levels and was sustained for two to four weeks before decreasing to control normotensive values. Femoral systolic pressure (and renal perfusion pressure) rose by 47-57 mmHg in coarcted dogs (p less than .001). Extracellular volume (ECV) increased in both coarcted animals, peaking 28-32 cc/kg (7.1-7.6% increase) above precoarctectomy levels. Peak ECV expansion coincided with the peak post-coarctectomy blood pressure. Fluid administration, blood losses and plasma renin activity (PRA) were comparable in all animals. Post-coarctectomy tachycardia was also noted in coarcted dogs (p less than .001), whereas neither ECV nor heart rate changes occurred in control animals. We postulate that post-coarctectomy baroreceptor stimulation results in sympathetically-mediated renal sodium retention, not only preventing a pressure diuresis, but resulting in overt volume expansion. Failure of PRA suppression despite increased distal pressure and volume excess may also reflect sympathetic activation. Data are compatible with the view that sympathetic activation and consequent volume expansion transiently sustain hypertension in the post-coarctectomy setting until baroreceptor re-adjustments permit normalization of blood pressure.