Lepicovska V, Novak P, Nadeau R
Research Center, Hôpital du Sacré-Coeur de Montréal, Canada.
Clin Auton Res. 1992 Oct;2(5):317-26. doi: 10.1007/BF01824302.
In this study, the responses during syncope were determined by noninvasive beat-to-beat analysis during passive orthostasis. Twenty patients with recurrent unexplained syncope (13 men and seven women) and ten healthy aged-matched control subjects were studied during 80 degrees head-up tilt for 25 min. Time-frequency mapping of R-R intervals, systolic and diastolic pressures and respiration was used to determine the responses to tilt. The spectral estimation was based on a modified Wigner distribution and the frequency content was evaluated on a beat-to-beat basis. Ten patients developed syncope (tilt-positive group) during tilt, while the remaining ten were asymptomatic (tilt-negative group). Control subjects reacted to tilt by the immediate shortening of R-R intervals to a plateau with an accompanying moderate increase in diastolic pressure. In the tilt-negative group the responses to tilt were similar, but of greater amplitude. In contrast, in the tilt-positive group, R-R intervals gradually and continuously decreased with tilt while systolic and diastolic pressures increased until shortly before syncope, when an abrupt fall in blood pressure followed by R-R intervals lengthening occurred. Furthermore, the R-R intervals fluctuations at both respiratory and nonrespiratory frequencies were the highest at rest as well as during tilt in the tilt-positive group. Nonrespiratory fluctuations in blood pressure increased more during tilt in both tilt-positive and negative groups compared to the control group. The nonrespiratory fluctuations in R-R intervals and blood pressure reached a maximum at syncope, simultaneously with hypotension and bradycardia. Time-frequency mapping has demonstrated that an elevated parasympathetic tone at rest which persists during orthostasis identifies patients prone to vasodepressor syncope. The counteracting sympathetic activation is not sustained and results in hypotension followed by cardioinhibition and loss of consciousness.
在本研究中，通过被动直立位期间的无创逐搏分析来确定晕厥期间的反应。对20例不明原因复发性晕厥患者（13例男性和7例女性）和10例年龄匹配的健康对照者进行了研究，让他们在80度头高位倾斜25分钟。利用R-R间期、收缩压和舒张压以及呼吸的时频映射来确定对倾斜的反应。频谱估计基于修正的维格纳分布，并且在逐搏基础上评估频率成分。10例患者在倾斜期间发生晕厥（倾斜阳性组），而其余10例无症状（倾斜阴性组）。对照者对倾斜的反应是R-R间期立即缩短至平台期，同时舒张压适度升高。在倾斜阴性组中，对倾斜的反应相似，但幅度更大。相比之下，在倾斜阳性组中，R-R间期随着倾斜逐渐持续下降，而收缩压和舒张压升高，直到晕厥前不久，此时血压突然下降，随后R-R间期延长。此外，在倾斜阳性组中，呼吸频率和非呼吸频率下的R-R间期波动在静息时以及倾斜期间都是最高的。与对照组相比，倾斜阳性组和阴性组在倾斜期间血压的非呼吸波动增加更多。R-R间期和血压的非呼吸波动在晕厥时达到最大值，同时伴有低血压和心动过缓。时频映射表明，静息时升高且在直立位时持续存在的副交感神经张力可识别易发生血管减压性晕厥的患者。交感神经的代偿性激活不能持续，导致低血压，随后是心脏抑制和意识丧失。
