Influence of captopril on the arterial baroreceptor reflex in patients with heart failure

In 16 male patients with heart failure (NYHA II-III), the influenceof a single dose of 25 mg captopril on the carotid sinus baroreceptorreflex was examined. Blood presure fell significantly by 11± 1.7 mm Hg (P < 0.001), whereas heart rate remainedunchanged (85 ± 3 vs. 83 ± 3 beats min^–1).Carotid sinus baroreceptors were stimulated by means of an airtightneck chamber. Two indices of baroreflex sensitivity were calculated.(1) The sensitivity to reflex heart rate slowing was increasedby captopril from –2.9 ± 0.7 to –5.0 ±1.3 ms mmHg^–1 (P <0.002). The higher the initial sensitivitythe more pronounced was the change after captopril with an increaseof sensitivity by 46% (y = 1.46x –0.17, P <0.01). Thisincrease in sensitivity cannot be explained by haemodynamicchanges induced by captopril. (2) In eight patients the sensitivityof the baroreflex to increased transmural pressure gradientsof the carotid sinus was evaluated by registration of the bloodpressure response to neck suction; this demonstrated an unchangedresponsiveness following captopril administration. From thesedata it can be concluded that captopril selectively augmentsa reflex bradycardia which is mediated by an increase in vagalefferent tone. The change in the reflex response depends onthe initial reflex sensitivity and cannot be explained by haemodynamicchanges caused by captopril.