Resetting of aortic baroreceptors in response to hypotension does not alter gain sensitivity.

1. In chronic hypertension, the baroreceptors reset to hypertensive levels with a decrease in gain sensitivity, but only a few studies have evaluated baroreceptor resetting during chronic hypotension and, under these conditions, no consistent information is available concerning changes in baroreceptor gain sensitivity. Therefore, in the present study, the aortic baroreceptor function curve and the baroreflex control of heart rate (HR) were evaluated in chronic hypotension produced by myocardial infarction (MI) with no heart failure. 2. Aortic baroreceptor function curves were studied in anaesthetized three groups of rats: (i) MI-7, six rats 7 days after MI; (ii) MI-30, nine rats 30 days after MI; and (iii) five control animals (SHAM). The pressure-nerve activity relationship was measured during rapid changes in blood pressure by integrating the whole-nerve activity of the baroreceptors in a computerized beat-to-beat analysis. 3. Both long-term periods (7 or 30 days) of hypotension were accompanied by complete resetting of the baroreceptor in rats (the leftward displacement of the baroreceptor curve matched the decrease in blood pressure). Moreover, the resetting of the baroreceptor function curve was not accompanied by changes in gain sensitivity (1.47, 1.64 and 1.67%/mmHg for SHAM, MI-7 and MI-30 groups, respectively) and the baroreflex control of HR was normal comparing SHAM and MI-30 groups (bradycardic 1.62 +/- 0.18 vs 1.99 +/- 0.52 b.p.m./mmHg, respectively; tachycardic 3.6 +/- 0.5 vs 4.1 +/- 0.4 b.p.m./mmHg for, respectively). 4. The data indicate that the resetting of baroreceptors in chronic hypotension is stable and is not accompanied by changes in gain sensitivity, as observed in hypertension. This may account for the normal baroreflex control of HR observed in non-anaesthetized rats.

Utilizaçäo dos raios laser na destruiçäo de placas ateromatosas "in vivo": estudo experimental / Use of laser beams in the removal of atheromatous plaques in vivo: experimental study

Treze cäes foram submetidas a enxerto de artéria humana com aterosclerose. Um segmento arterial foi interposto entre os cotos de uma carótida seccionada e, após uma semana, raios laser de argônio foram aplicados sobre as placas através de cateterismo cardiovascular. Conseguiu-se destruir porçöes das placas de ateroma, sem parada de circulaçäo sangüínea, em todos os casos reestudados, bem como demonstrar a inocuidade dos produtos voláteis resultantes. Em 30% dos casos, perfurou-se a artéria, em virtude do näo alinhamento correto entre as fibras ópticas e eixo arterial