Changes in the T-wave vector loop of the three-dimensional vectorcardiogram during exposure to cold pressor stress

Three-dimensional vectorcardiography was used to characterize changes in the T-wave vector loop during exposure to cold pressor stress. Data were collected from 8 subjects during baseline, cold pressor, and recovery periods. Maximum vector length, polar angle of the longest vector, azimuth angle of the longest vector, sum of all vectors, polar angle of the vector sum, azimuth angle of the vector sum, surface area of the loop, and maximum distance between adjacent vectors were computed from the T-wave vector loop. The amplitude of the one-dimensional T-wave (TWA) was also computed. Interbeat interval and TWA decreased during hand immersion and increased during recovery. Of the vectorcardiographic measures, only maximum vector length and vector sum showed statistically significant change; both decreased during the task and returned to baseline during recovery. TWA accounted for 46% of the task related variance compared to 53% and 47% respectively, for vector sum and maximum vector length. Changes in TWA probably reflect a true change in cardiac electrical potential rather than a change in T-wave vector loop shape or orientation.     

Differential β- and α-adrenergic activation during psychological stress

The responsivity of several cardiovascular indices to a computerized mental arithmetic stress and a cold pressor stress were investigated in 22 healthy adult subjects. The major findings were that the largely β-adrenergically driven T-wave amplitude, pre-ejection period, R-wave to pulse interval, and left ventricular ejection time values responded only to mental arithmetic; a significant decrease in cardiac output and increase in peripheral resistance were elicited during the cold pressor test; inter-beat-interval and subjective stress ratings responded significantly to both stresses compared to baseline levels, but more intensely to mental arithmetic than the cold pressor test; blood pressure, stroke volume and the maximum of the first derivative of the raw impedance signal responded unspecifically to both stresses. These findings support the idea that cardiovascular responses to psychological challenge depend on the level of cognitive processing required for the task. In addition, the superfluity of multiple variable measurements to study cardiovascular reactivity in such situations is discussed. Accepted: 3 September 1996     

Tracking cardiac electrical instability by computing interlead heterogeneity of T-wave morphology.

Oscillations in T-wave morphology, particularly T-wave alternans (TWA), have been fundamentally linked to increased susceptibility to ventricular fibrillation (VF). We investigated whether the escalation in complexity of T-wave oscillations before VF is attributable to increased spatial heterogeneity of repolarization. Peak interlead T-wave heterogeneity (TWH) was measured by second central moment analysis of T-wave morphology in epicardial electrograms in dogs during left anterior descending coronary artery occlusion. TWH differentiated cases in which myocardial ischemia provoked VF from those without VF (563 +/- 56 vs. 139 +/- 36 microV, P < 0.01). In the former group, progressive, significant increases in TWH above preocclusion baseline (70 +/- 8 microV) began at 2.25 min after the start of occlusion and were associated successively with TWA (at 155 +/- 19 microV), T-wave multupling (at 386 +/- 100 microV), complex oscillatory T-wave forms (at 560 +/- 76 microV), discordant TWA (at 572 +/- 98 microV), and VF at 4.36 +/- 0.14 min. TWH in precordial ECGs in 12 pigs during angioplasty-balloon-induced myocardial ischemia also discriminated animals that experienced VF (from 90 +/- 14 at baseline to 382 +/- 39 microV, P < 0.05) from those without VF (from 96 +/- 17 at baseline to 199 +/- 61 microV, NS). Ischemia-induced changes in ST segment and T-wave amplitude did not predict VF. Heightened spatial heterogeneity of repolarization, as assessed by second central moment analysis of TWH, underlies TWA and increased risk for ischemia-induced VF. Monitoring spatial TWH from precordial leads could prove useful in stratifying risk for life-threatening arrhythmias.     

Effect of cold pressor stimulation on plasma norepinephrine, dopamine-beta-hydroxylase, and renin activity

Changes in plasma levels of norepinephrine, dopamine-β-hydroxylase (DβH), and renin activity were observed in nine healthy volunteers during cold pressor stimulation. Increases in mean arterial blood pressure and heart rate during cold stimulation were accompanied by a sharp rise in plasma norepinephrine, while plasma DβH and renin activity showed little or no change. The results indicate that plasma norepinephrine accurately reflects acute activation of the sympathetic nervous system in contrast to plasma DβH and renin activity.     

利用Poincare 散点图法检测t 波交替的指标研究

目的:利用Poincare散点图进行t波交替检测,不仅从形态上找到检测标准,进一步研究散点中有效的定量指标。方法:以European ST-T Database标准心电数据库和MIT-BIH心律失常数据库的心电信号作为检测对象,以128个连续心拍的t波中的7个点为检测数据,相邻心拍t波差分后组成新序列,并由差分序列作出散点图,观察散点形态。根据形态区别和t波交替的幅值变化特点,利用个散点到x+y=0直线的距离均值作为定量检测指标D0,为避免不同心电信号幅值影响,D0除以RQ峰值差为最终指标D,找出合适阈值判定是否存在t波交替,并与谱分析法的检测结果比较分析。结果:①从Poincare散点图形态上,存在t波交替的散点图与正常t波存在明显区别,存在t波交替则散点集中在以x+y=0为轴线的附近,形成类似椭圆的狭长形状;而正常t波形成的散点会以原点为中心均匀分布,散点形态为圆形。②由t波交替的特点和散点图形态可知,定量检测指标D越小,就越有可能存在t波交替。经过大量仿真测试和谱分析法的比较,规定检测标准为,当D<=35uv时,存在t波交替;指标D与谱分析法的结论相吻合,并且两种方法的判定结果由kappa一致性检验,一致性程度好,进一步说明D指标具有优越的敏感性,是t波交替检测的有效指标。结论:Poincare散点图的散点分布形态和散点到x+y=0轴线的距离均值分别是是t波交替有效的定性和定量检测指标。     

The need for studies to evaluate the reproducibility of the T-wave alternans (TWA), and the rationale for a correction index of the TWA

Sudden cardiac death (SCD) due to various cardiomyopathies is currently prevented by the implantation of an automated cardioverter/defibrillator (ICD). ICD impalntation in patients who are not survivors of SCD, or have not suffered potentially lethal ventricular arrhythmias, are based on the presence of cardiomyopathy with a reduced left ventricular ejection fraction. The bulk of patients who are considered suitable for an ICD implantation and receive such devices, do not experience device therapy shocks at follow-up ("false positives"), thus creating a climate of uncertainty among patients and physicians about the soundness of our current eligibility criteria for ICDs. In addition the cost of inappropriate ICDs is staggering, and the undue exposure of "false positive" patients to complications, and hardships is disconcerting. T-wave alternans (TWA) has emerged as a possible "risk detection of SCD" technology, but its reproducibility has not been tested. Peripheral edema (extracardiac) or other cardiac mechanisms, unrelated to the degree of SCD risk, alter the amplitude, and other attributes, of the T-waves. Since TWA may be T-wave amplitude-, or other T-wave attributes-dependent (this is still a speculation), a need may be emerging for its correction by the T-wave amplitude (TWA index); such an index may enhance the reproducibility, and evaluate the true sensitivity, specificity and predictive accuracy of the TWA in detecting future victims of SCD.     

Postural kinematics of trumpet playing

This paper examines the effects of anthropometry on body posture of trumpeters playing in standing position. Sixteen virtuosi trumpeters were photographed while hitting three notes (low C, high F and high F sustained) during performance of musical tasks. Initial standing posture and anthropometric data were recorded. Six body segment angles were computed and a vectorial sum was obtained to describe whole body posture in neutral and playing conditions. Horn angle and dental overbite were also computed. Earlier results showed that the musical task has no effect on playing posture. One-way ANOVA showed notable differences between the neutral posture and the note-related playing postures. A multiple regression model showed that in addition to the note effect, anthropometric variables, mainly neck length, explain the changes in playing posture. Horn angle is determined by the dental overbite. The importance of the anthropometric variables in playing the more demanding notes indicate that anthropometry may act to constrain trumpeters' performance.     

Comparative effects of single- and linear triple-site rapid bipolar pacing on atrial activation in canine models

Nonuniform conduction may cause block and/or delay, thereby providing a substrate for the onset and maintenance of reentrant atrial arrhythmias. We tested the hypothesis that linear triple-site, bipolar, rapid pacing (LTSBRP) of the right atrium generates more uniform wave-front propagation compared with single-site, bipolar, rapid pacing (SSBRP), thereby reducing and/or eliminating conduction block and delay that is otherwise present. Five dogs with pericarditis and three normal dogs were studied. Three plunge-wire electrode pairs were placed 5-7 mm apart in both perpendicular and parallel configurations at the superior aspect of the crista terminalis and were used to pace at 200- and 300-ms cycle lengths for < or =6 s. During pacing, 380 electrograms were recorded simultaneously from electrode arrays placed epicardially on the atria, which produced activation sequence maps for each pacing episode. Local conduction-velocity vectors were computed for each site during each episode. Histograms of absolute velocity vector angles from the x-axis (of the crista terminalis) were plotted to assess uniformity of wave-front propagation, and the magnitude of each vector was computed to assess the local speed. LTSBRP showed 1) more uniform linear activation wave fronts compared with SSBRP, 2) velocity vectors with a more uniform magnitude and direction compared with SSBRP, 3) a predominant absolute velocity vector angle vs. a scattered angle distribution with SSBRP, and 4) shorter right atrial activation time and faster mean epicardial speed than SSBRP for each pacing cycle length. LTSBRP created a more uniform wave-front propagation with less or no conduction block and/or delay compared with SSBRP.     

Baroreflex modulation of muscle sympathetic nerve activity during cold pressor test in humans

The purpose of this project was to test the hypothesis that baroreceptor modulation of muscle sympathetic nerve activity (MSNA) and heart rate is altered during the cold pressor test. Ten subjects were exposed to a cold pressor test by immersing a hand in ice water for 3 min while arterial blood pressure, heart rate, and MSNA were recorded. During the second and third minute of the cold pressor test, blood pressure was lowered and then raised by intravenous bolus infusions of sodium nitroprusside and phenylephrine HCl, respectively. The slope of the relationship between MSNA and diastolic blood pressure was more negative (P < 0.005) during the cold pressor test (-244.9 +/- 26.3 units x beat(-1) x mmHg(-1)) when compared with control conditions (-138.8 +/- 18.6 units x beat(-1) x mmHg(-1)), whereas no significant change in the slope of the relationship between heart rate and systolic blood pressure was observed. These data suggest that baroreceptors remain capable of modulating MSNA and heart rate during a cold pressor test; however, the sensitivity of baroreflex modulation of MSNA is elevated without altering the sensitivity of baroreflex control of heart rate.     

Does Anthropomorphism of Dogs Affect Pain Perception in Animal-Assisted Interventions? An Exploratory Study

The purpose of this exploratory study was to determine the effects of anthropomorphism of a therapy dog on pain perception during an animal-assisted intervention. Participants were 32 college women who were randomly assigned to the anthropomorphism condition or the control condition. All participants engaged in a pretest cold pressor task to measure base-line individual differences in pain tolerance and perceptions of pain intensity and pain unpleasantness. After completing this task, participants in the anthropomorphism group engaged in a task intended to prime them to view a therapy dog anthropomorphically. Specifically, they rated photos of dogs on a series of humanlike traits (e.g., “this dog would be a good listener”). Participants in the control condition rated photos of dogs on a series of canine traits (e.g., “this dog would make a good watchdog”). After this experimental manipulation, participants engaged in a second cold pressor task in the presence of a therapy dog and the therapy dog handler. We hypothesized that participants in the anthropomorphism group would demonstrate greater pain tolerance and report lower levels of pain intensity and pain unpleasantness during the second cold pressor task than participants in the control group. Results provide partial support for these hypotheses. Participants in the anthropomorphism group reported lower posttest pain intensity than participants in the control group. In addition, they demonstrated greater posttest pain tolerance than participants in the control group—but only under conditions of medium or high pretest pain tolerance. The two groups did not differ with respect to posttest pain unpleasantness. The results of this exploratory study provide preliminary evidence that prompting individuals to view a therapy dog anthropomorphically may augment their experience of pain relief from a therapy dog visit.     

Quantitative evaluation of cell orientation in culture.

A quantitative method to assess mutual orientation of cells in cultures on a substrate includes the following operations: (1) the cellular groups to be evaluated are chosen; (2) position of the long axis for each nucleus of the group is determined; (3) the axis OX is arbitrary chosen for every group and the angles alphai between the long axis of every nucleus i and the axis OX are measured. Every nucleus i corresponds to a vector of unit length ei with the angles 2alpha. D, the mean of the vectors ei for every cell group is calculated. This value of D is compared with a set of values of D computed according to a model of mutual orientation studies in a simulation experiment. In this model the group of n vectors consists of a fraction of Kn parallel vectors (o less than or equal to K less than or equal to I) and of (I minus K)n randomly oriented vectors. K corresponding to the computed D which is equal to the experimental value of D is considered as an index of orientation for the group. Contact orientation with respect to the relief of the substrate may be evaluated as a root mean square deviation sigma0 to the angles between the long axes of cell nuclei and the direction of relief. Examples of the measurements of K and sigma0 in cell cultures are given.     

Is T-wave alternans T-wave amplitude dependent?

The possible dependence of T-wave alternans (TWA) on T-wave amplitude was investigated in 3 orthogonal leads (X, Y, Z) 20-min resting ECG recordings and in the derived vector magnitude (VM) from 176 healthy (H) subjects and 200 coronary-artery-disease (CAD) patients. After application of our adaptive-match-filter based method for parameterization of TWA in terms of its amplitude (TWA_A) and product-magnitude (TWA_PM, defined as the product of TWA_A times TWA duration), and once a TW_A parameter was defined for T-wave amplitude quantification, the existence of intra- and inter-subjects relationships of TWA_A and TWA_PM vs. TW_A was tested. Compared to the H-population, the CAD-population showed a significant (P < 0.05) increase of TWA_A (62 ± 38 μV vs. 54 ± 25 μV) and TWA_PM (4029 ± 2974 beat μV vs. 3107 ± 1976 beat μV) and a significant decrease of TW_A (298 ± 194 μV vs. 467 ± 246 μV). These repolarization changes, however, occurred with no significant intra- or inter-subjects relationships of TWA_A and TWA_PM vs. TW_A. Thus, in our CAD and H populations there was no evidence of TWA dependence on T-wave amplitude.     

Acute volume overload elevates T-wave alternans magnitude.

The objective of this study was to determine whether acute volume loading elevates T-wave alternans (TWA) in dogs with structurally normal hearts. TWA predicts sudden cardiac arrest in patients with left ventricular dysfunction and congestive heart failure. However, volume load and ventricular stretch may themselves precipitate arrhythmias. It is unclear to what extent volume load causes TWA. In six male mongrel dogs [25.8 kg (SD 4.2)] under general anesthesia, we measured TWA during progressive atrial pacing to 160 beats/min. Pacing was performed at baseline, at the midpoint and peak of a saline infusion designed to induce acute CHF, and then during diuresis. Dog 1 was hypothermic throughout the protocol and excluded from analysis. For dogs 2-6, 102 ml/kg (SD 30) were infused over 315 min (SD 50), causing pulmonary capillary wedge pressure to rise from 9.6 (SD 3.5) to 21.2 mmHg (SD 1.6) (P < 0.01), and heart rate variability to fall (P < 0.01). TWA magnitude (Valt) rose in all dogs with volume load (P < 0.001). Compared with baseline, TWA at peak infusion had higher magnitude [Valt 3.4 (SD 1.95) vs. 0.5 muV (SD 0.35); P = 0.011] and occurred at lower heart rates [128 (SD 6) vs. 151 beats/min (SD 12); P = 0.008]. Net volume load was linearly related to Valt (P < 0.01), with each 10 ml/kg net volume load increasing Valt by 0.23 muV. Acute volume overload elevates TWA in normal canine hearts. Although dramatic, however, this effect may contribute clinically to abnormal TWA only in patients with marked volume overload. Future studies should examine the interaction of fluid overload, myocardial disease, and arrhythmia susceptibility.     

A novel measure characterized by a polar energy surface approximation for recognition and classification of transmembrane protein structures

A new theoretical method has been developed for recognition and classification of membrane proteins. The method is based on computation of a polar energy surface that can reveal characteristic interaction patterns for individual helices even if crystal or NMR structure coordinates are not available. A protein with N transmembrane helices is described as a set of N vectors that are derived from a Fourier analysis of this polar energy surface computed for each helix. We then derive a polarity difference score (PDS) for any two proteins computed as the root mean square deviation between the respective vector coordinate sets. The score was found to correlate with the degree of structural similarity between the following three protein families for which tertiary structures have been determined: bacteriorhodopsin, rhodopsin, and the cytochrome c oxidase III subunit.     

A mapping of an ensemble of mitochondrial sequences for various organisms into 3D space based on the word composition

To visualize a bird's-eye view of an ensemble of mitochondrial genome sequences for various species, we recently developed a novel method of mapping a biological sequence ensemble into Three-Dimensional (3D) vector space. First, we represented a biological sequence of a species s by a word-composition vector x(s), where its length ∣x(s)∣represents the sequence length, and its unit vector x(s)/∣x(s)∣represents the relative composition of the K-tuple words through the sequence and the size of the dimension, N=4(K), is the number of all possible words with the length of K. Second, we mapped the vector x(s) to the 3D position vector y(s), based on the two following simple principles: (1) ∣y(s)∣=∣x(s)∣and (2) the angle between y(s) and y(t) maximally correlates with the angle between x(s) and x(t). The mitochondrial genome sequences for 311 species, including 177 Animalia, 85 Fungi and 49 Green plants, were mapped into 3D space by using K=7. The mapping was successful because the angles between vectors before and after the mapping highly correlated with each other (correlation coefficients were 0.92-0.97). Interestingly, the Animalia kingdom is distributed along a single arc belt (just like the Milky Way on a Celestial Globe), and the Fungi and Green plant kingdoms are distributed in a similar arc belt. These two arc belts intersect at their respective middle regions and form a cross structure just like a jet aircraft fuselage and its wings. This new mapping method will allow researchers to intuitively interpret the visual information presented in the maps in a highly effective manner.     

琼脂糖凝胶的合适浓度对于回收酶切后质粒载体的重要性

目的：探讨琼脂糖凝胶的不同浓度对回收不同大小的酶切后质粒载体纯度的影响。方法：将2种质粒载体酶切,并经不同浓度的琼脂糖凝胶电泳分析,通过比较酶切前和酶切后载体的相对位置,研究胶浓度对回收酶切后载体纯度的影响。结果：不同浓度的琼脂糖凝胶中,酶切前和酶切后载体的相对位置会发生变化,对能否成功回收到纯度高的酶切后DNA片段有重要影响;质粒大小不同,胶浓度的影响也不同。结论：合适的胶浓度对于回收酶切后质粒载体具有重要意义,应选择合适的胶浓度回收酶切后质粒载体。     

基于相关分析方法的非稳态心电T波交替检测研究

目的：研究T波段幅度、形态逐拍交替变化的心电变异现象检测。方法：本研究首先使用Mexican．hat小波检测R峰并对心电信号进行预处理;在提取T波矩阵方面为减少心拍间内差,采用点乘最大法,最大程度地对齐T波;最后基于时域相关分析方法检测T波交替幅度、交替心拍,追踪非稳态心电信号中短暂的交替数据段。结果：利用相关分析法对样本数据所测交替幅度与谱分析法相比更加显著,并且可以检测出谱分析方法无法检测的交替心拍。结论：时域相关分析方法能够更精确地追踪T波交替随时间变化的现象,但其对输入数据要求较高,因此在检测中可以先通过谱分析方法检测为阳性TWA的基础上,再对心电信号进行相关分析,从而确定非稳态交替时间段和更加准确的交替幅度。     

Catecholamines are key modulators of ventricular repolarization patterns in the ball python (Python regius)

Ectothermic vertebrates experience daily changes in body temperature, and anecdotal observations suggest these changes affect ventricular repolarization such that the T-wave in the ECG changes polarity. Mammals, in contrast, can maintain stable body temperatures, and their ventricular repolarization is strongly modulated by changes in heart rate and by sympathetic nervous system activity. The aim of this study was to assess the role of body temperature, heart rate, and circulating catecholamines on local repolarization gradients in the ectothermic ball python (Python regius). We recorded body-surface electrocardiograms and performed open-chest high-resolution epicardial mapping while increasing body temperature in five pythons, in all of which there was a change in T-wave polarity. However, the vector of repolarization differed between individuals, and only a subset of leads revealed T-wave polarity change. RNA sequencing revealed regional differences related to adrenergic signaling. In one denervated and Ringer’s solution–perfused heart, heating and elevated heart rates did not induce change in T-wave polarity, whereas noradrenaline did. Accordingly, electrocardiograms in eight awake pythons receiving intra-arterial infusion of the β-adrenergic receptor agonists adrenaline and isoproterenol revealed T-wave inversion in most individuals. Conversely, blocking the β-adrenergic receptors using propranolol prevented T-wave change during heating. Our findings indicate that changes in ventricular repolarization in ball pythons are caused by increased tone of the sympathetic nervous system, not by changes in temperature. Therefore, ventricular repolarization in both pythons and mammals is modulated by evolutionary conserved mechanisms involving catecholaminergic stimulation.     

The combined effect of the cold pressor test and isometric exercise on heart rate and blood pressure

The purpose of this study was to determine if the cold pressor test during isometric knee extension [15% of maximal voluntary contraction (MVC)] could have an additive effect on cardiovascular responses. Systolic and diastolic blood pressures, heart rate and pressure rate product were measured in eight healthy male subjects. The subjects performed the cold pressor tests and isometric leg extensions singly and in combination. The increases of systolic and diastolic blood pressure during isometric exercise were of almost the same magnitude as those during the cold pressor test. The responses of arterial blood pressure, and heart rate to a combination of the cold pressor test and isometric knee extension were greater than for each test separately. It is suggested that this additional effect of cold immersion of one hand during isometric exercise may have been due to vasoconstriction effects in the contralateral unstressed limb. In summary, the circulatory effects of the local application of cold during static exercise at 15% MVC were additive.