TP Segment Research Articles

Исследование соотношений между показателями ритмической активности сердца человека

The purpose of this article was to determine the correlations between the electrical and mechanical parameters of the rhythmic activity of the heart (HRA) in humans taking into account age and the effect of functional loads. Materials and methods. The research involved 146 people of both sexes aged between two hours after birth and 92 years, who were examined using functional tests that differed depending on the age of the subjects. Electrocardiogram (ECG) and heart rate (HR) parameters were recorded in the standard lead II using the Poly-Spectrum ECG system (Neurosoft, Ivanovo). Results. Correlations between HRA parameters can be traced from the first hours of post-embryogenesis throughout the rest of a person’s life. The data obtained indicate a dependence of HRA on the age and on the effect of functional tests, as well as confirm the proposition that there is an inverse relationship between HR dynamics and the dynamics of myocardial electrical parameters. ECG recordings at birth indicate that the correlations between ECG and HR are formed as early as in the prenatal period. Their correlations in people aged between 70 and 92 years indicate a strain associated with the wear and tear of the body’s functional systems. HR and ECG parameters are based on the electrical properties of the myocardium, which are significantly affected by the autonomic nervous system (ANS). A linear range of correlations between HR and ECG intervals was compiled. The maximum values of the duration of the PP interval and TP segment correspond to the minimum HR values. With an increase in HR from 40 to 80 beats/min, the duration of the TP segment decreases twoto three-fold. With HR reaching 120 ± 5 beats/min, the duration of the TP segment drops to zero. Since the increase in HR continues further in response to functional tests, it is obvious that at this stage the process is provided only by the neurohumoral components of the ANS. Due to the maximum variability of the duration of the TP segment, its most important role in the organization of HRA is emphasized.

“Defining the Isoelectric Line in Electrocardiography”: A Comprehensive Review

Electrocardiography (ECG or EKG) is a fundamental tool in cardiovascular diagnosis, relying on the accurate identification of the isoelectric line as a reference point. However, the definition of the isoelectric line has encountered controversies and nuances, particularly regarding its association with the TP segment, the ST segment under specific conditions, and the PQ junction in select circumstances. This comprehensive review navigates through these complexities, addressing clinical implications, methodological challenges, and potential future directions. Understanding the isoelectric line’s intricacies is essential for precise EKG interpretation and informed clinical decision-making in cardiology.

Downsloping TP Segment in the Precordial Leads on a Standard 12-lead Electrocardiogram: Suspected Cardiac Impulse-tapping Artifact.

We herein report an 80-year-old man showing a downsloping TP segment together with an increase in the height of the T wave in the precordial leads on a standard 12-lead electrocardiogram (ECG). Separately, an 87-year-old woman showed only a downsloping TP segment in the precordial leads on a standard 12-lead ECG. Neither patient reported chest pain or dyspnea when ECGs was obtained. This downsloping TP segment in the precordial leads on the standard 12-lead ECG is thought to be due to a cardiac impulse-tapping artifact. Differential diagnoses are also discussed.

Unfamiliar waveforms spanning from the ST to TP segments only observed in certain limb leads of the standard 12-lead electrocardiogram due to Aslanger' s sign.

Unfamiliar waveforms spanning from the ST to TP segments only observed in certain limb leads of the standard 12-lead electrocardiogram due to Aslanger' s sign.

Соотношение ультразвуковых и электрокардиографических параметров внутрисердечной гемодинамики при физической нагрузке у человека

The purpose of this article was to study the mechanism of reduction in stroke volume after intense physical activity (the Astrand effect). Materials and methods. The research involved 23 apparently healthy male students of Syktyvkar State University named after Pitirim Sorokin (age: 19 ± 1 years, body weight: 75 ± 13 kg, height: 177 ± 7 cm, body mass index: 24 ± 4 kg/m2). The physical load consisted of the Stange test (voluntary inspiratory breath-holding) and the Martinet test (squats to failure) performed simultaneously. The parameters of intracardiac haemodynamics were assessed using electrocardiography and ultrasonography. Results. We established that at rest, about 80 cm3 of blood passes through the mitral valve and the aortic valve in a cardiac cycle lasting on average about 0.30 s. Under physical load, the total blood flow volume through the mitral valve is reduced by 8 %, while through the aortic valve, by 15 %. The decrease in stroke volume under physical load, accompanied by an increase in heart rate, is due to a reduction in the TP segment of the electrocardiogram (diastole). The free blood flow (during diastole) from the left atrium through the mitral valve stops and the forced flow (during systole) starts, coinciding in time with the PQ interval (left atrial systole) on the electrocardiogram. Changes in the subjects’ parameters associated with the flow dynamics through the mitral valve and further through the aortic valve, as well as the processes in the TP segment (diastole) indicate that it is the shortened diastole during exercise that serves as the main link in the mechanism of all subsequent rearrangements of intracardiac haemodynamics. This study contributes to the understanding of the mechanism of the Astrand effect. Moreover, it demonstrated the dependence of the diastolic function of the ventricles on the volume of free blood flow (during diastole) through the mitral valve during the contraction of the TP segment according to the electrocardiographic data.

Precise T-wave endpoint detection using polynomial fitting and natural geometric approach algorithm

QT interval (QT) is defined as the distance between the beginning of the QRS complex and the end of the T-wave, and it reflects the time course of the ventricular depolarization and repolarization on the surface electrocardiogram (ECG). QT and its variability over time are modulated by the autonomic nervous system and are related to arrhythmogenesis. A challenging task for appropriate QT assessment is the detection of the T-wave endpoint. This study proposes a novel automatic approach to correctly identify the T-wave endpoint. After the peak of the T-wave, it was assumed that the quasi-asymptotical hyperbolic waveform decay of the T-wave acutely bends to meet the ECG baseline and then smooths out onto the TP segment. The point showing the maximal baseline bending is usually assumed by the cardiologists as the T-wave endpoint. In this approach, the terminal portion of the T-wave was represented by a parsimonious-optimal order polynomial function, in which the Cartesian curvature was calculated. One hundred and one ECG records from Physionet QT Database were analyzed to investigate the performance of the method. A Cartesian Curvature-based method (CGM) was developed and applied for automated detection of the T-waves endpoints. Q-waves were also measured automatically. The QTs were calculated and compared with respective cardiologist manual marks provided by QT Database by Pearson's correlation and Bland-Altman charts. High correlation (Pearson's Correlation = 0.94; p < 0.001) between the novel approach and the reference marks, observed in all analyses, showed the method's suitability to identify T-wave endpoints. The CGM performs as the cognitive experience of the cardiologist and has a simple mathematical implementation, indicating to be a promising tool for QT interval assessment.

Is Electrocardiogram Helpful in Predicting a Rise in Troponin I as a Marker of Anthracycline Cardiotoxicity?

Screening patients on anthracycline-based chemotherapy regimens for the development of cardiotoxicity can be resource intensive. We therefore studied various traditional electrocardiogram (ECG) parameters to correlate and possibly predict the development of elevated Troponin I as a surrogate marker of anthracycline-induced cardiotoxicity. This was a single-centre prospective cohort study done between January 2014 to January 2016. Baseline ECG was compared with ECG performed after chemotherapy and different parameters were compared. Patients were divided into Troponin I positive and negative groups based on the test performed at the end of chemotherapy, using a cut-off of 0.06 ng/dL. Of the 160 patients studied, 131 (81.9%) were Troponin I negative (TnI-) and 29 (18.1%) were positive (TnI+). Breast cancer accounted for 79% of all cancers in this study. Many ECG parameters were compared between the TnI- and TnI+ groups. Of them, TP segment and TP/QT showed a significant decrease in the TnI+ group. The mean (95% confidence interval) TP in the TnI- group was 162.9 ms (145.4, 180.4) and in TnI+ groups was 117.9 ms (89, 146.8) (p = 0.03). Corresponding values for TP/QT were 0.47 (0.42, 0.51) and 0.35 (0.27, 0.42) (p = 0.02). These changes were not significant in multivariate analysis and likely reflected the different mean heart rates (HR) in both the groups, as suggested by partial correlation which was run with HR as a confounder. ECG parameters, such as QTcH, TP and TP/QT do not helpful predicting Troponin I elevations in patients on anthracycline-based chemotherapy. Further studies based on hard endpoints, for example, clinical systolic dysfunction occurring at one year, would give better information on their utility.

ECG segmentation algorithm based on bidirectional hidden semi-Markov model

Accurate segmentation of electrocardiogram (ECG) waves is crucial for cardiovascular diseases (CVDs). In this study, a bidirectional hidden semi-Markov model (BI-HSMM) based on the probability distributions of ECG waveform duration was proposed for ECG wave segmentation. Four feature-vectors of ECG signals were extracted as the observation sequence of the hidden Markov model (HMM), and the statistical probability distribution of each waveform duration was counted. Logistic regression (LR) was used to train model parameters. The starting and ending positions of the QRS wave were first detected, and thereafter, bidirectional prediction was employed for the other waves. Forwardly, ST segment, T wave, and TP segment were predicted. Backwardly, P wave and PQ segments were detected. The Viterbi algorithm was improved by integrating the recursive formula of the forward prediction and backward backtracking algorithms. In the QT database, the proposed method demonstrated excellent performance (Acc = 97.98%, F1 score of P wave = 98.37%, F1 score of QRS wave = 97.60%, F1 score of T wave = 97.79%). For the wearable dynamic electrocardiography (DCG) signals collected by the Shandong Provincial Hospital (SPH), the detection accuracy was 99.71% and the F1 of each waveform was above 99%. The experimental results and real DCG signal validation confirmed that the proposed new BI-HSMM method exhibits significant ability to segment the resting and DCG signals; this is conducive to the detection and monitoring of CVDs.

Вариабельность временных и амплитудных показателей ЭКГ у людей пожилого и старческого возраста

The purpose of this article was to determine the effect of the clinostatic test on the electrical properties of the myocardium in older adults leading an active lifestyle. Materials and methods. The study involved 38 people aged between 70 and 90 years living in a northern city (Syktyvkar, 61°N) and leading an active lifestyle. The indicators of the electrical properties of the cardiac muscle were determined before and after the clinostatic test. For this purpose, an ECG was recorded in the standard lead II in the standing and lying positions. Results. Using the method of paired comparisons, we showed a decrease in heart rate under the influence of the clinostatic test from 76 ± 10 beats/min to 64 ± 10 beats/min. The variability of ECG components according to pNN50 (the percentage of successive NN intervals differing from each other by more than 50 ms) in older adults in the standing position was, on average, two times lower than in the lying position. The PP interval increased from 0.81 ± 0.12 s (in the standing position) to 0.90 ± 0.10 s (in the lying position). The PT interval remained practically unchanged, staying at the level of (0.46 ± 0.07) – (0.49 ± 0.07) s. The TP segment grew from 0.35 to 0.42 ± 0.10 s. The RD amplitude was 1.04 ± 0.43 mV in the standing and 0.88 ± 0.30 mV in the lying position; the propagation rate of depolarization in the cardiac muscle was 245 ± 137 and 205 ± 106 mm/s, respectively. In addition, the paper discussed the mechanism of opposite reactions to the clinostatic test, i.e. increasing duration of cardiointervals and decreasing amplitude indicators. For citation: Irzhak L.I., Russkikh N.G., Parshukova A.N. Variability of Time and Amplitude ECG Indicators in Older Adults. Journal of Medical and Biological Research, 2021, vol. 9, no. 4, pp. 355–365. DOI: 10.37482/2687-1491-Z073

C87. Serial Cases of Cardiovascular Manifestation on Leptospirosis: A Tales of Unfortunate Events

Abstract Background Leptospirosis is a zoonosis disease caused by Leptospira species. It's endemic and has become a major public health issue, especially in tropical regions. Clinical manifestation varies from mild or asymptomatic to severe multiple organ failure. We report cases of severe leptospirosis which complicates supraventricular tachycardia and myoperdicarditis from Universitas Sebelas Maret Academic Hospital. Case Summary The first case was a 44-year-old man referred from Internal Medicine Department with Leptospira infection with Weil’s disease. On 5th daycare, the patient was reporting had an episode of tachyarrhythmia, the ECG show SVT-AVNRT, there was no history of arrhythmic events before admitted to the hospital, the echocardiography was normal. The second case was a 67-year-old man who was referred from emergency department with shortness of breath, the ECG reveals diffuse ST-segment elevation in all limb and precordial leads with reciprocal ST-depression at aVR and V1, there was also downsloping of the PR and TP segment on precordial leads (Spodick’s sign), with normal ejection fraction on echocardiographic examination with pericardial thickening. Both patients have hsTroponin levels rose above the normal limit and serological testing found positive leptospira IgM. Discussion Severe leptospirosis can cause multi-organ dysfunction including cardiac involvement. The patients, in this case, suffered from leptospirosis with SVT-AVNRT and myopericarditis. The exact pathophysiology is still unclear, but there are several hypotheses, such as cytokine storms and direct damage from leptospira endotoxins. Arrhythmias and cardiac disturbance in leptospirosis patients are associated with poor outcomes and higher mortality rates.

C87. Serial Cases of Cardiovascular Manifestation on Leptospirosis: A Tales of Unfortunate Events

Abstract Background Leptospirosis is a zoonosis disease caused by Leptospira species. It's endemic and has become a major public health issue, especially in tropical regions. Clinical manifestation varies from mild or asymptomatic to severe multiple organ failure. We report cases of severe leptospirosis which complicates supraventricular tachycardia and myoperdicarditis from Universitas Sebelas Maret Academic Hospital. Case Summary The first case was a 44-year-old man referred from Internal Medicine Department with Leptospira infection with Weil’s disease. On 5th daycare, the patient was reporting had an episode of tachyarrhythmia, the ECG show SVT-AVNRT, there was no history of arrhythmic events before admitted to the hospital, the echocardiography was normal. The second case was a 67-year-old man who was referred from emergency department with shortness of breath, the ECG reveals diffuse ST-segment elevation in all limb and precordial leads with reciprocal ST-depression at aVR and V1, there was also downsloping of the PR and TP segment on precordial leads (Spodick’s sign), with normal ejection fraction on echocardiographic examination with pericardial thickening. Both patients have hsTroponin levels rose above the normal limit and serological testing found positive leptospira IgM. Discussion Severe leptospirosis can cause multi-organ dysfunction including cardiac involvement. The patients, in this case, suffered from leptospirosis with SVT-AVNRT and myopericarditis. The exact pathophysiology is still unclear, but there are several hypotheses, such as cytokine storms and direct damage from leptospira endotoxins. Arrhythmias and cardiac disturbance in leptospirosis patients are associated with poor outcomes and higher mortality rates.

Electrocardiogram Findings Associated With Malignant Pericardial Effusion and Cardiac Tamponade.

Electrocardiogram Findings Associated With Malignant Pericardial Effusion and Cardiac Tamponade.

EKG eponimi

Eponyms are widely represented in technical, social and natural sciences. Electrocardiography terms, named after the researcher who first described them, have not been summarized in one place until now. Wellens syndrome (Henrick Joan Joost Wellens, Dutch cardiologist) refers to a subgroup of patients with unstable angina who are at risk of developing an anterior myocardial infarction. In 2008, the Dutch cardiologist Robert Jan de Winter described a unique electrocardiographic (ECG) finding for proximal left anterior descending artery occlusion, named de Winter's pattern.Smith-Sgarbossa criteria (Elena Sgarbossa, Stephen Smith) are used to recognize acute myocardial infarction in patients with left bundle branch block. Schamroth's sign (Abraham Leo Schamroth, South African cardiologist) is an indirect ECG finding that indicates chronic obstructive pulmonary disease. Wolff-Parkinson-White syndrome (WPW) was named after the doctors who in 1930. first described the syndrome of short PR interval and abnormal QRS complexes, associated with paroxysmal tachycardia (Louis Wolff, John Parkinson, Paul Dudley White). S1Q3T3 or McGinn-White sign (Sylvester McGinn and Paul White) was first described in 1935. as an ECG finding in support of acute pulmonary heart disease. Second degree AV blocks could be type Wenckebach (Karel Frederik Wenckebach, Dutch anatomist) or type Mobitz (Woldemar Mobitz, Russian-German physician). Ashman's phenomenon (Richard F. Ashman, American physiologist) is a simple ECG manifestation of conduction disturbances, caused by a change in frequency. Bix's rule (Harold Bix) is used to recognize supraventricular tachycardia. Brugada syndrome (Pedro and Josep Brugada) is a congenital channelopathy of sodium channels, with a high risk of sudden cardiac arrest. TP segment's down-sloping in the early stage of pericarditis is called Spodick's sign (David H. Spodick, American cardiologist).

Multi-Ethnic Genome-Wide Association Study of Decomposed Cardioelectric Phenotypes Illustrates Strategies to Identify and Characterize Evidence of Shared Genetic Effects for Complex Traits.

We examined how expanding electrocardiographic trait genome-wide association studies to include ancestrally diverse populations, prioritize more precise phenotypic measures, and evaluate evidence for shared genetic effects enabled the detection and characterization of loci. We decomposed 10 seconds, 12-lead electrocardiograms from 34 668 multi-ethnic participants (15% Black; 30% Hispanic/Latino) into 6 contiguous, physiologically distinct (P wave, PR segment, QRS interval, ST segment, T wave, and TP segment) and 2 composite, conventional (PR interval and QT interval) interval scale traits and conducted multivariable-adjusted, trait-specific univariate genome-wide association studies using 1000-G imputed single-nucleotide polymorphisms. Evidence of shared genetic effects was evaluated by aggregating meta-analyzed univariate results across the 6 continuous electrocardiographic traits using the combined phenotype adaptive sum of powered scores test. We identified 6 novels (CD36, PITX2, EMB, ZNF592, YPEL2, and BC043580) and 87 known loci (adaptive sum of powered score test P<5×10-9). Lead single-nucleotide polymorphism rs3211938 at CD36 was common in Blacks (minor allele frequency=10%), near monomorphic in European Americans, and had effects on the QT interval and TP segment that ranked among the largest reported to date for common variants. The other 5 novel loci were observed when evaluating the contiguous but not the composite electrocardiographic traits. Combined phenotype testing did not identify novel electrocardiographic loci unapparent using traditional univariate approaches, although this approach did assist with the characterization of known loci. Despite including one-third as many participants as published electrocardiographic trait genome-wide association studies, our study identified 6 novel loci, emphasizing the importance of ancestral diversity and phenotype resolution in this era of ever-growing genome-wide association studies.

Standardisation of electrocardiographic examination in corn snakes (Pantherophis guttatus).

Corn snakes are a very common pet reptile species, yet there is an absence of evidence-based literature standardising collection of ECG or detailing ECG deflection morphology in the normal animal. The authors describe a well-tolerated, reproducible technique and detail the cardiac cycle in terms of lead 2 equivalent waveforms and intervals. 29 adult corn snakes. This prospective study evaluated, under species-appropriate, standardised conditions, a technique for producing standard six-lead ECG tracings. Lead 2 equivalent cardiac cycles were described in detail and statistically analysed for sex, weight, length, heart rate and mean electrical axis. High-quality tracings demonstrated common ECG characteristics for this species, including no Q, S or SV waves, prolonged PR and RT intervals, rhythmic oscillation of the baseline, short TP segments, and a right displaced mean electrical axis. An influence of sex, weight or length on heart rate and mean electrical axis was not identified. To the authors' knowledge, this is the first study to describe a standardised technique for recording ECG in significant numbers of normal corn snakes. Ranges have been provided that may be of diagnostic value or form the basis for future development of reference intervals for this species.

A novel density-volume calcium score by non-contrast CT predicts coronary plaque burden on coronary CT angiography: Results from the MACS (Multicenter AIDS cohort study)

BackgroundThe purpose of this study is to determine if a new score calculated with coronary artery calcium (CAC) density and volume is associated with total coronary artery plaque burden and composition on coronary CT angiography (CCTA) compared to the Agatston score (AS). MethodsWe identified 347 men enrolled in the Multicenter AIDS cohort study who underwent contrast and non-contrast CCTs, and had CAC>0. CAC densities (mean Hounsfield Units [HU]) per plaque) and volumes on non-contrast CCT were measured. A Density-Volume Calcium score was calculated by multiplying the plaque volume by a factor based on the mean HU of the plaque (4, 3, 2 and 1 for 130–199, 200–299, 300–399, and ≥400HU). Total Density-Volume Calcium score was determined by the sum of these individual scores. The semi-quantitative partially calcified and total plaque scores (PCPS and TPS) on CCTA were calculated. The associations between Density-Volume Calcium score, PCPS and TPS were examined. ResultsOverall, 2879 CAC plaques were assessed. Multivariable linear regression models demonstrated a stronger association between the log Density-Volume Calcium score and both the PCPS (β 0.99, 95%CI 0.80–1.19) and TPS (β 2.15, 95%CI 1.88–2.42) compared to the log of AS (PCPS: β 0.77, 95%CI 0.61–0.94; TPS: β 1.70, 95%CI 1.48–1.94). Similar results were observed for numbers of PC or TP segments. ConclusionThe new CAC score weighted towards lower density demonstrated improved correlation with semi-quantitative PC and TP burden on CCTA compared to the traditional AS, which suggests it has utility as an alternative measure of atherosclerotic burden.

Effect of Modified Valsalva Maneuver on Heart Rate and ECG among Young Non –Athletes and Athletes

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Differential Watermarking of Multilead ECG Baseline.

Digital watermarking has been widely recognized as an effective tool for embedment of auxiliary data in the host record. This paper presents a new method of watermarking using lead-to-lead difference of values in the baseline of the host electrocardiogram. The method starts with delineation of the baseline and uses Kirchoff voltage law or interpolation to predict any selected lead from the remaining ones. Next, the difference between the predicted and actual value is considered as noise and subjects to measurement of level and distribution in the time frame of baseline. The watermark with patient data or results of accompanying measurements is coded accordingly to mimic the noise. Replacement of the baseline noise with the watermark data ends the process. With 12-lead CSE files and respective reference borders of PQ and TP segments, the capacity of watermark achieved 3875 bits per second, while the diagnostic value of the ECG remains untouched.

VARIABILITY OF ELECTROCARDIOGRAM ELEMENTS IN 6-7 YEARS CHILDREN UNDER THE INFLUENCE OF PHYSICAL ACTIVITY IN THE CONDITIONS OF THE EUROPEAN NORTH

The Aim: to determine the duration of the ECG intervals of PP, PT, PQ, QT and TP segment in two groups of children of both sexes aged 6-7 years in control and under the influence of an active orthostatic test (AOP n = 20) and test- Martine-Kushelevsky (PM n = 15). Methods. We studied the duration of ECG intervals in the II standard lead before and after the application of orthostatic test and test- Martine-Kushelevsky. Indices after statistical analysis were presented by M ± SD and cardiointervalogramm. Results. During orthostatic test the heart rate increased by 24 %, the duration of the PP interval was down by15 % ( from 0.71 ± 0.1 s in the control to 0.60 ± 0.1 s ) PT - by 4 % (from 0.47 ± 0.03 s to 0.45 ± 0.03 s), QT - by 9 % (from 0.34 ± 0.02 s to 0.31 ± 0.01 s), segment of the TP - from 0.24 ± 0.1 s to 0.15 ± 0.1 s (38 %), and the duration of the PQ interval increased insignificantly by 8% (from 0.13 ± 0.01 s to 0.14 ± 0.01 s). During test- Martine-Kushelevsky, the heart rate increased by 21 %, the remaining indices changed by 17 % (from 0.64 ± 0.1 s to 0.53 ± 0.04 s), 5 % (from 0.44 ± 0.03 s to 0.42 ± 0.03 s), 3 % (0.31 ± 0.01 s to 0.28 ± 0.004 s) and 50 % (from 0.20 ± 0.1 s to 0.10 ± 0.03 s) respectively. The PQ interval remained unchanged. Correlations between the heart rate before and after the samples rs = 0.67 (AOP) and rs = 0.36 (PM), between РР rs = 0.69 (AOP) and rs = 0.26 (PM), between РТ rs = 0.93 (AOP) and rs = 0.74 (PM), between РQ rs = 0.78 (AOP) and rs = 0.67 (PM), between QT rs = 0.83 (AOP) and rs = 0.65 (PM) and between TP rs = 0.56 (AOP) and rs = 0.37 (PM). Conclusions. As a result of the action of two functional tests on the cardiovascular system of children aged 6-7 years, the heart rate increased and the duration of the ECG intervals was shortened. The variability of the indicators was less than in the control. The most significantly changed the parameters of the TP segment.

PP and PT Intervals and TP Segment in Human Electrocardiogram under Experimental Acute Normobaric Hypoxia

Seven male volunteers aged 22–27 years took part in the laboratory experiment for the determination of body response to acute normobaric hypoxia where they inhaled an oxygen–nitrogen gas mixture (9% of О2) for 25 min. At least 100 cardiac cycles at each of six experimental time points have been recorded by using an electrocardiogram (ECG) recording technique in standard lead II. Mean heart rate (±SD) before hypoxia was 64 ± 2 bpm; the duration of the PP interval was 0.94 ± 0.07 s, that of the PT interval was 0.51 ± 0.02 s, and that of the TP segment was 0.41 ± 0.07 s. Five minutes after hypoxia, it has been found that heart rate (HR) increased by 19%; the duration of the PP and PT intervals and TP segment decreased by 16%, 6%, and 30%, respectively. Twenty minutes after hypoxia, all the parameters reached their initial values. Five and fifteen minutes after hypoxia, HR reached 59 ± 3 bpm; PP interval and TP segment increased by 9% and 14%, respectively, compared to the initial values; PT interval was the same as the initial value at the baseline. The correlation coefficient rp (PP/PT) was 0.10–0.54; rp (PP/TP) was 0.94–0.99. The intervals PP and TP were found to be identical.