Disrupted fluid balance and baroreflex sensitivity in acute aortic regurgitation

Acute aortic regurgitation (AR) causes abrupt volume overload to the heart. The implication of this acute volume overload concerning fluid balance and autonomic participation remains unknown. We studied fluid balance (sodium and water intake and excretion), autonomic modulation and heart rate variability (HRV) in acute AR rats. Male Wistar rats (260-280g) were submitted to sham or AR surgery by retrograde puncture of the aortic valves leaflets. The presence and severity of AR was confirmed by echocardiography exams one week after the surgeries. The left ventricule diastolic diameter and the left atrium area were bigger in acute AR than in sham rats. The fluid behavior was challenged by combining furosemide and captopril in low doses. This combined treatment induces water and sodium intake behavior within one hour. There was an increase in water intake and natriureses following a fluid depletion in acute AR rats. The daily intake and natriuresis were not altered. The diastolic arterial pressure was lower in AR than in sham and there were no changes in autonomic modulation. The study of HRV shows an increase in the high-frequency component in acute AR rats. However, there was a decrease in the spontaneous baroreflex sensitivity in these rats. In conclusion, the results show that an acute volume overload to the heart impairs since its onset not only the fluid balance but also baroreflex sensitivity.