刺激颈迷走神经引起的心动过速及其对心脏功能的影响

刺激犬的颈迷走神经外周端时可引起心动过缓,而对心脏的抑制作用则逐渐减弱,表现为心率逐渐恢复(但比对照慢)。刺激后DBP立即下降,而SBP系逐渐下降,且下降程度没有DBP大。在刺激时及停止后均出现ES,其分别占刺激次数的47％和53％。在刺激停止后出现PVT(平均加速24.5次/min),PVT期间R波和BP波数不等,SV和BP轻度降低。LVET缩短和PEP/LVET比值升高,出现ES时,SV和BP较ES前显著降低。反映PVT时心脏功能降低。PVT的要理不太清楚,本研究表明反射性迷走撤退在PVT中不起作用。Q-T/Q-S_2比值增大是CA释放的间接证据。心得安可减弱PVT,阿托品可增强PVT,说明PVT由迷走静经释放CA所致。

Tachycardia Following Neck Yagal Stimulation and It's Effects on Cardiac Function

The present study was made on 16 mongrel dogs. The peripheral end of neck vagus was stimulated 51 times. Bradycardia was elicited at the beginning of stimulation, but the negative chronotropic effect was reduced gradually. This indicates that heart rate was slowly recovering during the period of vagal stimulation. The retoverd heart rate was still significantly slower than the pre-stimulation control waluss. There was a marked fall in diastolic pressure immediately after stimulation. The systolic pressure had a gradual fall and the decrcase was less than that of the diastolic pressure. Extrasystole (ES) incidence accounted for 47% and 53% of the total stimulation number during and after stimulation respectively.Postvagal tachycardia (PVT) developed immediately after the cessation of the vagal stimulation. The average increase of heart rate was 21.5 beats/mm. During PVT period numbers of R wave and BP wave were not equal. Stroke Volume (SV) and BP decreased moderately, LVET shortened and PEP/LVET ratio increased slightly. This shows that cardiac function was reduced at PVT. When ES appeared, SV and BP decreased more remarkably than before ES, it further indicates that cardiac pump function was obviously reduced.The mechanism of PVT is not quite clear. From this study it is considered that a reflexive vagus withdrawal do not play a role in the postvagal tachycardia. The increase of Q-T/Q-S2 ratio is an indirect evidence of catecholamine liberation. The blockage of beta receptors by propranolol markedly reduces the tachycardia. PVT is enhanced by atropine. These results show that PVT results from catechola-mine release by the vagus.