心音信号的分形研究

本文通过引入分形概念,首次为描述心音信号的复杂程度给出了一个定量的指标——分数维数。研究结果表明:心音信号确实存在着“无标度区”,具有典型的分形特性;心音信号的分维值能显著性地区分正常心音、二尖瓣病变心音(包括二尖瓣狭窄、二尖瓣关闭不全及二尖瓣狭窄加关闭不全)和主动脉瓣病变心音(主动脉瓣狭窄、主动脉瓣关闭不全及主动脉瓣狭窄加关闭不全)。     

慢性低氧大鼠肾上腺皮质球状带的变化

将Ｗｉｓｔａｒ大鼠喂养在逐渐降低的常压低氧条件下，用氮气和空气的混合气体调节氧含量。氧浓度由正常逐步降低为１５％、１２％、１０％、８％，最后降至７％，实验共进行１１２ｄ，结果显示低氧动物体重下降，肾上腺重量减少，肾上腺皮质球状带萎缩，脂质丢失，球状带细胞线粒体肿胀和空泡变性，溶酶体增多，表明在慢性常压低氧中，当吸入气氧含量降至７％时，可导致肾上腺皮质球状带细胞超微结构改变，从而影响醛固酮的合成与分     

Operant Conditioning of Heart Rate: Somatic Correlates

The relationships between heart rate (HR) and several parameters of somatic activity were evaluated in human subjects when shuck avoidance was made contingent on either increases or decreases in HR. In order to depict any influence of the contingency specific 10 HR, somatic activity was controlled to varying degrees by instructions and the use of non-contingent control groups. When increases in HR were reinforced, the contingency we found to influence somatic activity but an effect specific to HR was also observed. When decreases in HR were reinforced, there was no evidence that HR were influenced independently of somatic activity. The result are discussed with respect to several current issues.     

Adrenaline and the plateau phase of the cardiac action potential

Summary Conduction block in heart cells by K⁺ rich, or Na⁺ depleted solutions can be overcome by adrenaline. In order to explain this phenomenon, the effect of adrenaline on the membrane resting and action potentials of cow Purkinje fibers was measured at various extracellular concentrations of Na⁺, K⁺ and Ca⁺⁺, in the presence of tetrodotoxin, Mn⁺⁺ and beta-receptor antagonists.It was found that adrenaline specifically increases the amplitude and duration of the plateau phase of the cardiac action potential. Plateu-like action potentials, without preceding Na⁺-spike, can be generated and conducted in an all-or-nothing way. In K⁺ rich solutions and under the influence of adrenaline, the depolarization proceeds in two steps. The first step corresponds to the Na⁺-spike. The second step or secondary depolarization corresponds to the plateau; it was not modified by changes of the membrane potential between –85 and –55 mV, or by reduction of extracellular Na⁺ ions, but was specifically blocked by Mn⁺⁺ ions and beta-receptor antagonists. Its amplitude increased by 17 mV for a tenfold change in extracellular Ca⁺⁺. Tetrodotoxin preferentially blocked the Na⁺-spike, but also slowed the rate of potential change during the secondary depolarization.The simplest explanation for the observed phenomena can be found in an increase of Ca⁺⁺ inward current under the influence of adrenaline. The existence of an inward Na⁺⁺ current, different in characteristics from the Na⁺ conductance during the fast upstroke, cannot be ruled out. Some data are in accord with a decrease in K⁺ conductance.     

Mechanical heart valve prostheses:: identification and evaluation (erratum)

Mechanical heart value prostheses have been in use since the 1950s. Many prostheses have been used for a while and then discontinued. Today, there are a large number and variety of prostheses in use and an even larger variety that are in place in patients. These may be explanted at any time for a number of reasons. It is essential for the practicing pathologist to be able to identify the prosthesis and be aware of some of its reported complications and modes of failure. This article, and a second one on bioprosthetic heart valves, is designed as a ready reference guide to heart valve prostheses, their important identifying features, their common complications, and modes of failure. It should help in the accurate identification of explanted prosthetic valves and more definitive reports. This accuracy of identification as well as tracking of abnormalities noted will, we hope, permit the identification of new failure modes and the recording of causes of failure of new (or even modified) prosthetic heart valves.     

Wavelet transform analysis of heart rate variability during myocardial ischaemia

Analysis of heart rate variability (HRV) is a valuable, non-invasive method for quantifying autonomic cardiac control in humans. Frequency-domain analysis of HRV involving myocardial ischaemic episodes should take into account its non-stationary behaviour. The wavelet transform is an alternative tool for the analysis of non-stationary signals. Fourteen patients have been analysed, ranging from 40 to 64 years old and selected from the European Electrocardiographic ST-T Database (ESDB). These records contain 33 ST episodes, according to the notation of the ESDB, with durations of between 40s and 12min. A method for analysing HRV signals using the wavelet transform was applied to obtain a time-scale representation for very low-frequency (VLF), low-frequency (LF) and high-frequency (HF) bands using the orthogonal multiresolution pyramidal algorithm. The design and implementation using fast algorithms included a specially adapted decomposition quadrature mirror filter bank for the frequency bands of interest. Comparing a normality zone against the ischaemic episode in the same record, increases in LF (0.0112±0.0101 against 0.0175±0.0208s²Hz⁻¹; p<0.1) and HF (0.0011±0.0008 against 0.0017±0.0020s²Hz⁻¹; p<0.05) were obtained. The possibility of using these indexes to develop an ischaemic-episode classifier was also tested. Results suggest that wavelet analysis provides useful information for the assessment of dynamic changes and patterns of HRV during myocardial ischaemia.     

Effects of cytosolic Ca2+ on the Ca2+ content of the sarcoplasmic reticulum in saponin-permeabilized rat ventricular trabeculae

 Rat ventricular trabeculae were mounted for isometric tension recording, and then permeabilized with saponin. The Ca²⁺ concentration ([Ca²⁺]) within the permeabilized preparation (cytosolic [Ca²⁺]) was monitored continuously using Indo-1 and the integrals of Ca²⁺ transients resulting from brief caffeine application used as an index of the sarcoplasmic reticulum (SR) Ca²⁺ content. The relationship between SR Ca²⁺ content and cytosolic [Ca²⁺] was studied within the reported physiological range (i.e. 50–250 nmol · l^–1 Ca²⁺). Increasing cytosolic [Ca²⁺] from 50 nmol · l^–1 to 250 nmol · l^–1 increased the steady-state SR Ca²⁺ content about threefold. However, increasing [Ca²⁺] above 250 nmol · l^–1 typically resulted in spontaneous SR Ca²⁺ release, with no further increase in SR Ca²⁺ content. The SR Ca²⁺ content increased only slowly when cytosolic [Ca²⁺] was increased; it was unchanged 20 s after a rapid increase in cytosolic [Ca²⁺], but increased progressively to a new steady-state level during the following 1–2 min. In a parallel series of experiments using intact papillary muscles, increasing extracellular [Ca²⁺] (from 0.5 to 5 mmol · l^–1) significantly increased twitch tension within 20 s of the solution change. These results support previous suggestions that the SR Ca²⁺ content may increase when diastolic cytosolic [Ca²⁺] rises during inotropic interventions such as increased stimulus rate or extracellular [Ca²⁺]. However, the rate at which SR Ca²⁺ responds to changes in cytoplasmic [Ca²⁺] within the diastolic range does not appear rapid enough to explain the early potentiation of twitch tension in intact preparations after an increase in extracellular [Ca²⁺]. Received: 26 August 1997 / Accepted: 28 October 1997     

CONSISTENCY OF PERFORMANCE CHANGE AND AUTONOMIC RESPONSE AS A FUNCTION OF EXPRESSED ATTITUDE TOWARD A SPECIFIC STRESS SITUATION

A persistent problem in stress research has been that some individuals may show impairment, while others show improvement or no change in performance under stress. Attempts to relate this variance in performance to general anxiety or other personality variables have generally not been too successful. Based upon responses to a fear of shock item in an attitude questionnaire, Ss were classified as “high fear of shock” or “low fear of shock” types. Half of the Ss in each group were assigned a perceptual-motor task; the others were assigned a cognitive-interference task. After training, all Ss were informed that they would be required to maintain their training performance levels in a situation in which they would be shocked if performance declined. Performance and heart rate measures taken during training were compared with the same measures taken under the threat-of-shock conditions. Results indicate significant differences between groups in both performance and physiological activity with “high fear of shock”Ss exhibiting relatively greater performance impairment and increased heart rate.