Oxygen Transport System in Children Living in the Russian Far North

We studied 654 healthy ten- to twelve-year-old children living in the Russian Far North (Taimyr peninsula) and in Siberia (town of Krasnoyarsk). The state of the body oxygenation and the systems responsible for oxygen delivery were studied according to the length of time living in the Russian Far North and season of the year. An examination of newcomer children revealed the following changes during the first year of living in the Russian Far North: an increased respiration rate and changes in its circadian rhythm; an increase in the heart rate, cardiac output, and cardiac index; an increase in the mean corpuscular volume in the red blood system; the activation of lipid peroxidation, and the changes in electrolyte balance of cells. The control mechanisms of oxygen transport system gradually stabilized during the ages of two to five years. In children living more than five years in the Russian Far North, the increased oxygen demand was met by the activation of cardiovascular and red blood systems aimed at more effective and adequate oxygen delivery to tissues.     

Autonomic regulation of the heart rate in humans under conditions of acute experimental hypoxia

Autonomic regulation of the heart rate (HR) was studied in young healthy volunteers under conditions of experimental acute normobaric hypoxia. Spectral analysis of the HR variability (HRV) was performed with differential sphygmography. The total spectral power (TP) of the HRV and its low and high frequency components (LF and HF, respectively) were assessed, and the sympathovagal balance (LFn/HFn) was calculated. Acute hypoxia increased the sympathetic and decreased the parasympathetic effects on the heart and was accompanied in the majority of subjects by a significant increase in HR and a decrease in HRV. The change in the autonomic regulation of the cardiac rhythm was assumed to be a mechanism of heart activity adaptation to acute hypoxia.Translated from Fiziologiya Cheloveka, Vol. 31, No. 1, 2005, pp. 82–87.Original Russian Text Copyright © 2005 by Nesterov.     

Cardiac electric field at the period of depolarization and repolarization of the frog heart ventricle

Multichannel mapping of electrical field on heart ventricle epicardium and the body surface in frogs Rana esculenta and Rana temporaria was performed at periods of the ventricular myocardium depolarization and repolarization. The zone of the epicardium early depolarization is located on epicardium of the ventricle base posterior wall, while the late depolarization zone--on its apex and on the base anterior wall. The total vector of sequence of the ventricle epicardium depolarization is directed from the base to the apex. The zone of the early repolarization is located in the apical area, while that of the late one--in the area of the base. On the frog body surface the cardioelectric field with the cranial zone of negative and the caudal zone of positive potentials is formed before the appearance of the QRS complex on ECG. At the period of the heart ventricle repolarization the zone of the cardioelectric field negative potentials is located in the cranial, while that of the positive ones--in the body surface caudal parts. The cardioelectric field on the frog body surface at the periods of depolarization and repolarization of the ventricle myocardium reflects adequately the projection of sequence of involvement with excitation and of distribution of potentials on epicardium.     

Formation of Cardioelectric Field on the Body Surface at a Period of Activation of Ventricular Myocardium in the Chicken Gallus domesticus

Spatial and temporal non-uniform and polyfocal depolarization of the subendocardial, intramural, and subepicardial layers of the ventricle myocardium in the chicken have been established experimentally. Different depth and time of formation of activation centers in the ventricular myocardium provide the appearance of groups of multiple depolarization foci on the epicardial surface of the ventricles. During the initial ventricular activity the cardioelectric field (CEF) on the chicken body surface is characterized by three periods of the dynamics of distribution of potentials: (1) the period of their gradual changes reflecting the electrical activity of excitation foci in the subendocardial, intramural, and subepicardial ventricular layers of myocardium on CEF; (2) the period of inversion consisting of an alteration of the mutual arrangement of the positive and negative CEF areas, this alteration corresponding in time to polyfocal depolarization of the epicardial surface of the ventricles; (3) the period of stability, during which the arrangement of the positive and negative CEF regions does not change, which is due to depolarization of multiple myocardium zones at the final phase of the heart ventricle activation.     

Effects of season and temperature acclimation on electrocardiogram and heart rate of toads

Electrocardiogram (ECG) was recorded from unrestrained toads of two species, one resistant (Bufo viridis) and the other sensitive (B. regularis) to low temperatures. Although the temperature-sensitive species could not survive at temperatures below 7-8 degrees C, heart rate is linearly and similarly related to ambient temperature in the two species. In B. viridis, the cold resistant species, heart rate in winter was 25% lower than in summer, and the dependency of heart rate on temperature was reduced by 50% in toads acclimated to 10 degrees C in winter. It was not possible to disclose any effect of acclimation on heart rate in summer, due to the large variation in the recorded values. The QRS amplitude in the ECG was considerably reduced at low temperature only in B. viridis. It is concluded that differences in cardiac activity cannot account for the distinct difference in thermal relations of the two species, and that it should reside at other regulatory levels.     

Age-Related Features of Morphological and Functional Development of Myocardium in Children of Five to Nine Years

Age-related features of the morphological and functional development of the myocardium were studied by echo- (EchoCG) and electrocardiography (ECG) in 200 children five to nine years of age. The most intensive anatomical development of myocardium was observed at the age of five to seven years, and a significant increase in cardiac output was observed at the age of eight to nine years both in boys and girls. The ECG amplitude and time parameters significantly changed from of five to nine years of age and were most pronounced at the age of seven to eight years. Different changes in cardiac rhythm and excitation conduction as well as repolarization and metabolic disturbances in the myocardium were often observed at this age. Static physical exercise caused marked changes in bioelectric activity of the myocardium. Two types of central circulatory responses to static exercise were found: an increase and a decrease in cardiac output. The mechanisms of cardiac rhythm regulation, which caused an increase in the stroke volume as a response to exercise, were different in children from five to nine years old. At the age of five to six years the homeometric mechanism was a crucial factor in the increase in stroke volume as a response to exercise, and at the age of seven to nine years both homeo- and heterometric mechanisms of cardiac rhythm regulation were very important.     

A view of the cardiac rhythm control: Intrinsic regulation

Regulation of the cardiac rhythm is intricate and occurs at least at two major levels, intrinsic and extrinsic. In turn, each of these levels can be divided into several sublevels. The factors regulating the cardiac activity eventually affect the duration of spontaneous diastolic depolarization of pacemaker myocytes of the sinoatrial node and, to a far lesser extent, the conduction velocity in the conduction system of the heart. Intrinsic regulation of the heart rate (HR) includes the myogenic sublevel and the sublevels of cell-to-cell communication, the cardiac nervous system, and humoral factors produced within the heart. Myogenic regulation is considered to be the first sublevel in control of the cardiac function. The available data suggest myogenic regulation only for the contractility of the myocardium. The cell-to-cell regulation sublevel involves two principal mechanisms. One depends on the heterogeneous structure of the sinoatrial node and within-node shifts of the dominant pacemaker, which is a group of cells that determine the HR and govern all other cells of the sinoatrial node. The other mechanism is based on the effects of peptides produced by cardiomyocytes and endothelial cells on pacemaker cells of the sinoatrial node. Regulatory peptides are also produced by the cardiac nervous system, which includes sensory and effector autonomic fibers, represents the cardiac part of the metasympathetic system, and forms intramural ganglia. In addition to modulating the HR, these peptides affect the contractility, microcirculation, coronary blood flow, preload, and afterload. Currently available data demonstrate that the autonomic nervous system is far more intricate than believed earlier. Using various neuropeptides, this system provides for fine adjustment of the cell functions, subject to its immediate control.Translated from Fiziologiya Cheloveka, Vol. 31, No. 2, 2005, pp. 116–129.Original Russian Text Copyright © 2005 by Nozdrachev, Kotelnikov, Mazhara, Naumov.Deceased.     

Cardiac electric field at the period of depolarization and repolarization of the frog heart ventricle

Multichannel mapping of electrical field on heart ventricle epicardium and the body surface in frogs Rana esculenta and Rana temporaria was performed at periods of the ventricular myocardium depolarization and repolarization. The zone of the epicardium early depolarization is located on epicardium of the ventricle base posterior wall, while the late depolarization zone—on its apex and on the base anterior wall. The total vector of sequence of the ventricle epicardium depolarization is directed from the base to the apex. The zone of the early repolarization is located in the apical area, while that of the late one—in the area of the base. On the frog body surface the cardioelectric field with the cranial zone of negative and the caudal zone of positive potentials is formed before the appearance of the QRS complex on ECG. At the period of the heart ventricle repolarization the zone of the cardioelectric field negative potentials is located in the cranial, while that of the positive ones—in the body surface caudal parts. The cardioelectric field on the frog body surface at the periods of depolarization and repolarization of the ventricle myocardium reflects adequately the projection of sequence of involvement with excitation and of distribution of potentials on epicardium.     

Topography and morphology of heart action-related EEG potentials

Joint ECG and EEG measurements were performed in 22 healthy subjects under standardized laboratory conditions. Averaged EEG potentials were computed using the R-peaks in the ECG as reference events. Spatio-temporal potential patterns of heart action-related EEG activity were obtained from 26 scalp channels. A heart action-related positive potential was found, peaking over the parietal scalp regions. Its independence from the cardiac electrical field, the source of an EEG artifact that may be confounded with heart action-related brain potentials, is demonstrated. The potential reaches its maximum amplitude of about 0.5 μV at a latency of about 500 ms after the R-peak. Its topography, with peak amplitudes at the parietal electrode locations, is different from the topography of potentials observed in the few comparable experimental studies published so far. This suggests the presence of somatosensory-evoked components in heart action-related potentials and indicates that a renewed discussion of the underlying neuronal processes is necessary.     

Spread of excitation through the heart upon electrical stimulation of the atrioventricular valves]

Experiments were conducted on the isolated hearts of rabbits and dogs. Synchronous recording of the electrical activity of the right auricle, the right ventricle, and tricuspid valve demonstrated the existence of definite functional associations between the auricular, ventricular and valvular depolarization. The spread of excitation in the heart in electrical stimulation of the atrio-ventricular valves was investigated. The impulses from the heterotopic excitation focus localized in these valves could be conducted to the other parts of the heart and thus lead to cardiac arrhythmias.     

温度对荒漠沙蜥心脏活动影响的实验研究

本文通过描记不同温度下荒漠沙晰(Phrynocephalus przewalskii)的心电图(ECG),对其心脏活动进行了分析研究。结果表明:随实验温度的升高,其心电图中各间期的持续时间相应地缩短;温度和各间期值呈显著负相关(P<0.01)。在一个心动周期中,温度的变化,对房室传导时间和静息期的影响最大,而对心室去极化与复极化的时程影响较小。随实验温度的升高,心率随之加快,其因素在于心动周期中静息期和房室传导时间相对值的缩短。     

Realization of biophysical models of cardiac electrical activity

Considered are the principles of realization of biophysical models of heart ventricle electrical activity in the form of a double electric layer on the surface of the electrically active myocardium (epicardium and endocardium) and the boundary surfaces dividing the model compartments with different electrophysiological characteristics. The model parameters are the electrophysiological and anatomical characteristics of the heart such as the geometry of the ventricles and the specialized His-Purkinje conduction system, the velocity of depolarization spread over myocardium, the ratio of the velocities of excitation transmission through the Myocardium / His / Purkinje elements of the model, the shape of transmembrane action potentials on the boundary surfaces, the orientation of the intrinsic anatomical axes of the heart relative to the initial set of coordinates, and some other biophysical characteristics of the myocardium. This model is the main unit of a computer simulation system, which includes databases of real and simulated electrocardiosignals.     

Plasma levels of dosulepine and heart electric field

Antidepressants, particularly tricyclic (TCA) antidepressants, may have cardiotoxic effects, such as cardiac arrhythmias, especially in patients with cardiovascular diseases. For most of TCA, no exact correlation between dosage, plasma levels and changes of ECG parameters of standard ECG has been found. So far, no relationship between dosulepine plasma levels and heart electric field parameters has been studied. We selected 18 female outpatient subjects diagnosed with recurrent depressive disorders, currently in the remission phase (HAMD < 10), without any cardiovascular disease. Patients were treated with daily dosulepine doses of 25-125 mg for 4-8 weeks. 30 heart electric field parameters were analyzed by Cardiag 128.1 diagnostic system as part of BSPM (Body Surface Potential Mapping). Acquired data were correlated with dosulepine plasma levels by means of Spearman's rank order correlation test. Four ECG parameters showed a significant correlation with dosulepine plasma levels: QRS axis deviation in frontal plane (p=0.01), DIAM 40 max (p<0.05), QRS-STT angle in transversal and left sagittal plane (p<0.05). The demonstrated changes confirmed dosulepine influence on the early myocardium depolarization phase and the correlation of this effect with dosulepine dose (its plasma concentration). The higher the dosulepine level, the more marked are the changes of the QRS-STT angle in transversal and sagittal planes and the changes in the QRS axis deviation in frontal plane. Repeatedly recorded changes in the heart electric field were dosulepine-specific and dependent on its plasma levels.     

Mechanoelectrical feedback in the healthy heart and in the heart with pathologies

The article discusses the issues of possible connection between mechanical phenomena in myocardium and the electrical processes. Not only cardiomyocytes, but also cardiac fibroplastic are considered as substratum for the mechanisms of mechano-electrical feedbacks. Cardiomyocytes and fibroplastic of healthy animals demonstrate the mechano-electrical feedbacks, which essentially mean that stretching of the cardiac tissue within the physiological limits to 2 mN changes the electrophysiological cell processes. Close to 90% repolarization potential of cardiomyocytes action the mechano-induced depolarization develops; over the background of depolarization, when it reaches the threshold values, extra potentials of action are generated. In fibroplastic, membrane mechano-induced hyperpolarization develops; as result of cellular interaction it may develop hyperpolarization of pacemaking cells of the right auricle and slow the cardiac rythm down. In case of a pathology, for instance, infarct of the left heart ventricle modification of electric cell activity was detected at quite low values of tissue stretching up to 0.2. mN. Mechano-induced depolarization of cardiomyocytes of animals affected by infarct develops at 50% level of repolarization phase of action potential, or at 90% of repolarization phase. In the former case development of mechano-induced depolarization coincides with the period of absolute cell refractering. Extra action potential develops immediately after the refractering phase when the mechano-induced depolarization shifts the membrane potential towards threshold values. In the latter case the mechano-induced depolarization transforms into extra action potential. With further stretching fibrillation develops. In fibroplastic the values of mechano-induced membrane hyperpolarization grow with greater scope of infarct damage. Magnitude of mechano-induced hyperpolarization of auricle fibroplastic taken from the animals with infarcts shows dependence on the period of remodelling if stretching is tissue is a standard parameter. With prolongation of the remodelling period the value of mechano-induced fibroplastic hyperpolarization diminishes. The problem of developing the combinations eliminating mechano-induced cardiac arrhythmia is raised.     

Mapping of ventricular tachycardia induced by thoracic neural stimulation in dogs

To investigate ventricular tachycardias produced in healthy canine myocardium by stimulation of sympathetic ganglia or cardiac nerves, we simultaneously recorded a surface ECG and 63 ventricular electrograms in anesthetized open-chest dogs. Isochronal and isopotential maps were generated off-line by computer. Ventricular tachycardia with uniform beat-to-beat morphology was induced in 13 or 22 dogs by electrical stimulation of the left stellate ganglion (five experiments), the left middle cervical ganglion (four experiments), the left caudal pole cardiopulmonary nerve (two experiments), or the ventrolateral cardiac nerve (eight experiments). It was not inducible by stimulation of the right-sided major cardiopulmonary nerves or ganglia. In most instances the earliest measured electrical excitation occurred on the posterior aspect of the ventricles. Isochronal maps demonstrated a radial spread of the impulse away from the area of earliest excitation. Changes in the region of earliest excitation and (or) activation pattern were accompanied by changes in QRS morphology. The potential gradients measured between areas displaying positive and negative T waves on the anterior and left lateral aspects of the ventricles were significantly increased by ventrolateral cardiac nerve stimulation. However, the ventricular regions where these potential gradients existed differed from the regions of earliest excitation during ventricular tachycardia. These results demonstrate that the thoracic autonomic nervous system can induce repetitive ventricular excitation originating from consistent loci.     

Correlation in the of the process of cardiac ventricle intramural depolarization and distribution of cardioelectric field potentials of the dog Canis familiaris

Based on a multichannel synchronous mapping of heart electric potentials, the sequence in time of the ventricle myocardium depolarization was compared with dynamics of distribution of cardioelectric potentials on the body surface in a dog. The cardioelectric field on the dog body surface at the period of the initial ventricular activity has been shown to be characterized by the presence of two inversions of the mutual disposition of areas of positive and negative potentials. Contribution to formation of distribution of the cardioelectric potentials on the body surface at each moment of the period of initial ventricular activity was made by all myocardial layers involved by excitation.     

Preliminary reference values for electrocardiography,echocardiography and myocardial morphometry in the European brown hare (Lepus europaeus)

The study aimed at defining reference values for electrocardiographic (ECG) and echocardiographic parameters as well as macroscopic dimensions of the heart and microscopic dimensions of cardiomyocytes in the European brown hare. The studies were conducted on 30 adult, clinically healthy hares of either sex caught in Poland. ECG and echocardiography were performed supravitally on anaesthetized hares. After euthanasia, gross and microscopic myocardial and cardiomyocyte dimensions were determined. Heart rate amounted to 140 ± 37.5 beats/min, the leading rhythm involved the sinus rhythm. P wave time was 26 ± 5 ms, PQ time was 80 ms, QRS time was 29 ± 3.5 ms, and ST was 97.5 ± 7 ms. Echocardiography determined a left ventricular wall end-diastolic diameter of 8.6 ± 2.0 mm and an intraventricular septum end-diastolic diameter of 5.75 ± 1.0 mm. The thickness of the interventricular septum corresponded to that of the free wall of the left ventricle, a finding consistent with physiological hypertrophy. Preliminary reference values were established for echocardiography. The findings were similar to those obtained at necropsy. The ECG and echocardiographic studies represent the first supravital examination of cardiac function in the hare. The obtained results illustrate adaptation of hare's myocardium to its mode of life. The cardiac findings resemble the athlete's heart syndrome described in humans. The findings may prove useful in further studies on the physiology of the cardio-vascular system in the hare.     

Effect of the form and anisotropy of the left ventricle on the drift of spiral waves

Three-dimensional spiral waves of electrical excitation in the myocardium are sources of dangerous cardiac arrhythmias. In this work, the dynamics of spiral waves of electrical excitation were studied in a symmetric anatomical model of the human heart left ventricle and a realistic ionic cell model of the human ventricular myocardium. Three factors that affect the drift waves in the heart were compared for the first time: the geometry of the heart wall, myocardial anisotropy, and wave chirality. Cardiac anisotropy was identified as a main factor in determining the drift of spiral waves. In the isotropic case, the dynamics were determined by the wall thickness, but did not depend on the wave chirality. In the anisotropic case, chirality was found to play a crucial role.

     

Central A1-receptor activation associated with onset of torpor protects the heart against low temperature in the Syrian hamster

Body temperature drops dramatically during hibernation, but the heart retains the ability to contract and is resistant to induction of arrhythmia. Although adaptive changes in the heart prior to hibernation may be involved in the cold-resistant property, it remains unclear whether these changes are sufficient for maintaining cardiac pulsatility under an extreme hypothermic condition. We forcibly induced hypothermia in Syrian hamsters by pentobarbital anesthesia combined with cooling of the animals. This allows reproduction of a hypothermic condition in the absence of possible hibernation-specific reactions. Unlike hypothermia in natural hibernation, the forced induction of hypothermia caused atrioventricular block. Furthermore, J-waves, which are typically observed during hypothermia in nonhibernators, were recorded on an ECG. The origin of the J-wave seemed to be related to irreversible injury of the myocardium, because J-waves remained after recovery of body temperature. An abnormal ECG was also found when hypothermia was induced in hamsters that were well adapted to a cold and darkened environment or hamsters that had already experienced hibernation. These results suggest that acclimatization prior to hibernation does not have a crucial effect at least on acquisition of cardiac resistance to low temperature. In contrast, an abnormal ECG was not observed in the case of hypothermia induced by central administration of an adenosine A1-receptor agonist and subsequent cooling, confirming the importance of the adenosine system for inducing hibernation. Our results suggest that some specific mechanisms, which may be driven by a central adenosine system, operate for maintaining the proper cardiac pulsatility under extreme hypothermia.     

圈养阿拉伯狒狒日活动时间格局及季节差异

动物个体行为的生态效应主要反映在它们的活动节律和时间分配上.2012年11月至2013年10月,在杭州野生动物园,用瞬时扫描取样法对1群圈养阿拉伯狒狒的日活动节律和活动时间分配进行了调查研究.结果表明: 1)在活动时间分配中,主要活动(频次百分率≥5%)包括休息(42.5%)、游动(16.2%)、玩耍(10.0%)、摄食(9.8%)、理毛(9.4%)和观望(7.3%);频次百分率低于5%的称为次要活动,共4.8%.2)阿拉伯狒狒的活动时间分配具有明显的季节性变化,冬季摄食和观望时间增加,玩耍和理毛时间减少,但休息和游动行为没有显著季节差异.3)阿拉伯狒狒通常在上午和下午分别出现摄食高峰,并随着气温逐渐转冷,摄食活动逐渐增加,出现3个摄食高峰;这可能是动物在寒冷季节为抵御寒冷而采取的补充能量的一种策略.4)在温暖季节,阿拉伯狒狒只有中午一个休息高峰和一个理毛高峰,更多时间用于游动和玩耍,表现为多峰特征;在寒冷的冬季,休息行为也体现了多峰特征,但其游动、玩耍和张望时间节律并不与温暖季节有明显差异.因此,杭州地区圈养阿拉伯狒狒的冬季日活动节律与许多灵长类(如黑冠长臂猿、维氏冕狐猴和绒毛猴等)不一样,采取摄食增加能量,而非休息减少能量消耗的策略.总之,阿拉伯狒狒的行为体现出明显的节律性,且其活动节律具有季节性差异,这些可能是阿拉伯狒狒适应于圈养环境特有的食物资源和温度变化的影响而形成的.