Guzmán C E, Sánchez G M, Márquez M F, Hermosillo A G, Cárdenas M
Departamento de Electrofisiología, Instituto Nacional de Cardiología Ignacio Chávez, México, D.F., Mexico.
Arch Med Res. 1999 May-Jun;30(3):203-11. doi: 10.1016/s0188-0128(99)00022-6.
Patients with syncope show different responses to head-up tilt (HUT) test, which may be due to different pathophysiological mechanisms.
HUT (70 degrees) was performed in 24 patients who experienced recurrent syncope. Nine patients had a cardioinhibitory (CI) response, 7 patients had a vasodepressor (VD) response, and 8 patients had a mixed (MX) response. Heart rate variability was analyzed at 60-sec periods during HUT.
Total spectrum (TS) was greater at rest and 1 min after syncope in the CI and MX groups as compared to the VD group. Low frequency spectrum (LF) was significantly greater during rest and the first minute after syncope in the CI groups as compared with the VD group. After the rest period, the CI and MX groups showed more elevated high frequency spectrum (HF) values than the VD group (p < 0.01). One minute after syncope, the HF increased in the CI and MX groups but not in the VD group (p < 0.01). The VD group showed higher LF/HF ratio from the beginning of rest (3.9 +/- 4.1) as compared to the CI and MX groups (p < 0.01). This difference was most significant 2 min before syncope occurred. The CI and MX groups showed greater pNN50 and rMSSD as compared to the VD group.
Our results suggest that vagal tone is higher in subjects showing cardioinhibitory and mixed responses to HUT. In contrast, patients with a vasodepressor response showed predominantly sympathetic activity. These findings suggest that there are different pathophysiological mechanisms underlying syncope.
晕厥患者对直立倾斜（HUT）试验表现出不同反应，这可能是由于不同的病理生理机制所致。
对24例复发性晕厥患者进行70度直立倾斜试验。9例患者有心脏抑制（CI）反应，7例患者有血管减压（VD）反应，8例患者有混合（MX）反应。在直立倾斜试验期间，以60秒为时间段分析心率变异性。
与血管减压组相比，心脏抑制组和混合组在静息时以及晕厥后1分钟的总频谱（TS）更大。与血管减压组相比，心脏抑制组在静息时和晕厥后第一分钟的低频频谱（LF）显著更大。静息期后，心脏抑制组和混合组的高频频谱（HF）值比血管减压组升高得更多（p<0.01）。晕厥后1分钟，心脏抑制组和混合组的HF增加，而血管减压组未增加（p<0.01）。与心脏抑制组和混合组相比，血管减压组从静息开始时的LF/HF比值更高（3.9±4.1）（p<0.01）。这种差异在晕厥发生前2分钟最为显著。与血管减压组相比，心脏抑制组和混合组的pNN50和rMSSD更大。
我们的结果表明，对直立倾斜试验表现出心脏抑制和混合反应的受试者迷走神经张力较高。相反，有血管减压反应的患者主要表现为交感神经活动。这些发现提示晕厥存在不同的病理生理机制。
