Central and peripheral contributions to control of heart rate during heat acclimation

The contributions of the autonomic nervous system and the cardiac pacing cells in the development of heat-acclimation-induced bradycardia were analyzed, and the effect of heat acclimation on the chronotropic response of the heart to heat stress (40° C) was studied. Rats were acclimated at 34° C for 0, 5, 14, 30 and 60 days. Heart rate (HR) was measured in conscious animals, using chronic subcutaneous electrodes. Sympathetic and parasympathetic influences were studied by IP administration of 0.1 and 1 mg/100 g body weight atropine and propranolol respectively, while intrinsic HR (HR_i) was measured following administration of both drugs simultaneously. The effects of carbamylcholine and norepinephrine on the beating rate of isolated rat atria were investigated to study pacemaker responsiveness to neutrotransmitters. Up to day 14 of heat acclimation, bradycardia was attained by tonic parasympathetic acceleration (18%) and temporal sympathetic withdrawal (0.8% on day 14), to compensate for the gradually augmented HR_i (2.5% and 8% on days 5 and 14, respectively). Following long-term acclimation HR_i declined below pre-acclimation rate. This was associated with resumed sympathetic activity (16% and 10% on days 30 and 60 respectively) while parasympathetic activity continued to be high (18%). Tachycardia, known to occur with severe uncontrolled body hyperthermia, was attenuated following heat acclimation by 42%. It was concluded that during the initial phase of heat acclimation bradycardia is achieved primarily by changes in autonomic influences, while following long-term acclimation, changes in the intrinsic properties of the pacing cells (HR_i) and the autonomic system both play a role.     

心脑疾病对同步十二导联心电图多重分形谱的影响

对心脑疾病人群的同步十二导联ECG(心电图)进行多重分形特性分析,发现不同导联的多重分形曲线互不重叠。计算其十二导联平均的多重分形奇异强度分布范围以及分布范围的十二个导联间的离散特性,发现不同人群中存在互为交叉而有明显不同的结果。用十二导联多重分形Δα的平均值Δα及其离散度δα(取Δα的标准差)两个参量来描述其多重分形谱特征。发现健康人与心脏病人Δα接近,但δα相差较大;健康人与脑损伤患者δα接近,但Δα相差较大。预示着多重分形特性受到神经自律和心脏组织结构的自谐特性的双重控制,特征参数Δα与神经控制相对应,δΔ与心脏组织结构自谐特性的各向异性相对应。     

Free cytosolic calcium during spontaneous contractions in smooth muscle of the guinea-pig mesotubarium

The free intracellular calcium ion concentration ([Ca²⁺]_i) was measured simultaneously with isometric force in strips of guinea-pig mesotubarium using the Fura-2 technique. During the relaxed period (5–15 min) between spontaneous contractions [Ca²⁺]_i continues to decrease after full mechanical relaxation to reach a minimal level of 86±8 nM (n=9) just before the start of the next contraction. During the spontaneous contractions (5–15 min) [Ca²⁺]_i reached a maximum of 211±19 nM and then oscillated between 155±16 nM and 194±9 nM. Increased extracellular Ca²⁺ concentration to 10 mM from the standard concentration of 1.5 mM caused a decreased frequency of spontaneous contractions and an increase in [Ca²⁺]_i both in the relaxed and contracted states. In 10 mM extracellular Ca²⁺, addition of AlF₄ ^–, as 1 mM NaF + 10 M AlCl₃, caused a sustained increase in [Ca²⁺]_i and maintained force. Addition of verapamil (10 M) in this situation decreased [Ca²⁺]_i to the resting level. The results suggest that the cyclic appearance of trains of action potentials is related to variation in [Ca²⁺]_i, possibly via inactivation of Ca²⁺-dependent K⁺ channels.     

Evaluation of telephone transmission for computer electrocardiographic interpretation in Japan

The reliability of the Japanese public telephone facilities to transmit electrocardiograms (e.c.g.) for computer interpretation was assessed. The International Business Machine's (IBM) e.c.g. computer program by Bonner was used. No appreciable distortion of e.c.g. was observed following repeated transmission from hospitals separated by 1000 km. Thirty-four normal and 66 abnormal e.c.g.s. were transmitted twice. Identical results were observed in 97% of normals and 92% of abnormals. Following these fundamental experiments, 1236 patients' e.c.g.s. were transmitted for computer intepretation. The study showed that 98·6% (1219 cases) were technically satisfactory and 1·4% (17 cases) were not. The 17 unsatisfactory cases were classified into ten unreceivable data formats, six inconsistent measurements and one unacceptable noise level. The authors concluded that the Japanese public telephone facilities were acceptable for the transmission of e.c.g.s. for computer interpretation.     

Effects of acetylcholine on time-dependent currents in sheep cardiac Purkinje fibers

Voltage clamp experiments were carried out on sheep Purkinje fibers to determine the effect of Ach on the time-dependent currents.On the pacemaker current (i _{K 2}) Ach 10^–6 mol·l^–1 had the following effects: shift of the activation curve by a few mV in the depolarizing direction, without change in the rectifier ratio. The potential dependence of the time constants for activation and deactivation was influenced in a similar way as the activation curve.Ach had no effect on the positive dynamic current (i _qr ) or the late plateau outward current (i _x ).The slow inward current (i _si ) as well as the transient inward current (T.I.) were reduced in amplitude and slowed in time course by Ach.The changes in pacemaker current are important in explaining the increased rate of diastolic depolarization in the presence of Ach. The decrease of slow inward current by Ach cannot be made responsible for the plateau shift or the prolongation of the action potential.Supported by F.G.W.O. Belgium 3.0087.74     

病窦综合征患者脑电图改变与动态心电图指标的相关性研究

目的 :探讨病窦综合征 (SSS)患者的脑电图 (EEG)改变及其与动态心电图 (AECG)指标的关系。方法 :10 2例SSS患者分别记录EEG和AECG ,其中 4 8例接受起搏治疗的患者在安装起搏器后复查EEG。 30例正常人在同期做EEG检查作比较。结果 :10 2例SSS患者EEG异常率为 37.2 % ,显著高于正常人 (χ2 =12 .814 4 ,P <0 .0 0 1)。晕厥组EEG异常率为 4 4 .4 % ,显著高于非晕厥组 (χ2 =5 .8778,P <0 .0 5 )。 4 8例接受起搏治疗的患者在起搏治疗后 ,EEG异常率显著下降 (χ2 =18.0 0 ,P <0 .0 0 1)。EEG异常程度与AECG最低心率呈明显的负相关 (r =- 0 .70 99,P <0 .0 0 1) ,与长间歇时间呈正相关(r=0 .5 4 0 1,P <0 .0 0 1)。结论 :SSS患者EEG异常程度与AECG最低心率及长间歇时间存在密切相关性。EEG检查对SSS患者病情及脑功能评估具有重要价值     

Tyrosine kinase inhibition reduces i f in rabbit sinoatrial node myocytes

 We studied pacemaker current (i _f), the inward current activated by hyperpolarization in rabbit sinoatrial (SA) node myocytes, with the permeabilized-patch-clamp technique. The tyrosine kinase inhibitors genistein (50 μM) or herbimycin A (35 μM) reduced the amplitude of i _f in response to step hyperpolarizations in the diastolic range of potentials. A two-step voltage-clamp protocol revealed that the reduction in i _f is due to a decrease in maximal i _f conductance. The observed effects are due to tyrosine kinase inhibition since an inactive analog of genistein did not reduce i _f. To further examine the mechanism of action, we added 2 mM chlorophenylthio cAMP (CPTcAMP, a membrane-permeant cAMP analog) to the bathing Tyrode, which increased i _f. Genistein still reduced i _f in the presence of CPTcAMP. This suggests that the pathway mediating the actions of tyrosine kinase inhibition on i _f is independent of cAMP- or protein-kinase-A-mediated phosphorylation. Received: 28 January 1997 / Received after revision: 21 April 1997 / Accepted: 22 April 1997     

基于多分辨率分析的心室晚电位神经网络检测

采用多分辨率分析和人工神经网络相结合的方法实现对心室晚电位的检测。首先利用多分辨率分解技术提取高分辨率心电信号不同频带的能量构成一组特征值 ,再利用这些特征值训练BP神经网络 ,并完成对心室晚电位的识别。经过对 2 8例 3导高分辨率心电图实验数据的处理 ,取得了较高的识别准确率     

永久起搏电极植入途径及起搏类型的探讨

目的评价起搏电极的植入途径及永久起搏器的类型.方法选择1987～1999年安置的80例永久起搏器患者.结果经颈外静脉植入电极6例,手术时间为256±75分;经头静脉植入电极48例,手术时间为247±65分(P＞0.05);经锁骨下静脉途径植入电极26例,手术时间为118±35分(P均＜0.01).其中,AAI型3例(4%),DDD型5例(6%),VVI型72例(90%).结论经锁骨下静脉植入起搏电极,方法简单,组织损伤小,手术时间短,优于其它途径.VVI型起搏器在我国仍然是主要使用的起搏器.