Rationale, design and methods planned in a prospective study concerning the circadian rhythm of heart rate asymmetry in healthy subjects

Heart rate asymmetry (HRA) is a physiological phenomenon caused by an unequal (asymmetric) contribution of heart rate decelerations and accelerations to the variability (variance) and microstructure of the heart rhythm of sinus origin. HRA has been studied in healthy people and patients with heart failure, diabetes, obstructive sleep apnoea, ischaemic heart disease, and survivors of myocardial infarction. HRA is a particular form of the heart rate variability (HRV) phenomenon related to the changes in the duration of cardiac cycles of sinus origin. HRV is influenced by physical activity, age, gender or time of day. It has been reported that HRA expression differs between day and night. However, its circadian rhythm has not been analysed so far. Moreover, the differences in HRA expression related to gender, level of physical activity or age have not been investigated either. With this study, we aim to explore the circadian rhythm of the HRA features, as well as the relation of the HRA expression to gender, physical activity, sleep pattern and body composition in a group of at least 100 healthy adults of both sexes aged between 19 and 60. This study might provide reference values for HRA as well as confirming or dismissing the existence of circadian rhythm of this physiological phenomenon.

Titin and dystrophin serum concentration changes in patients affected by thyroid disorders

INTRODUCTION

It is well established that thyroid hormones significantly affect skeletal muscle function, causing symptoms like myalgia and muscle weakness. Hypothyroid patients present increased levels of creatine kinase (CK), indicating muscle destruction. Lately, we proposed new serum markers of muscle disturbances in thyroid disorders: titin (TTN) and dystrophin (DMD). The aim of this study is to determine the association between thyroid status, muscle metabolism, and serum levels of TTN and DMD in patients affected by hypoand hyperthyroidism, before and after the treatment.

MATERIAL AND METHODS

In the study 56 subjects were enrolled. The studied group consisted of 16 patients with newly diagnosed overt hypothyroidism and 20 patients with hyperthyroidism. Twenty healthy controls were also included in the study. Body composition, thyroid hormones, and biochemical markers of muscle deterioration levels were evaluated before and after restoration of euthyroidism.

RESULTS

Dystrophin and TTN levels were noticeably lower in the hypothyroid group and hyperthyroid group in comparison with controls, at the border of statistical significance. Along with the thyroid hormones and CK normalisation, DMD levels increased in the hypothyroid group, with no significant lowering of TTN levels. However, TTN concentrations and the fT3/fT4 ratio became significantly lower than in controls. Hyperthyroid patients experienced no significant changes in TTN and DMD.

CONCLUSIONS

The presented data indicate that TTN and DMD are potential new markers of musculoskeletal deterioration in thyroid disorders. In addition, the shift in TTN and DMD serum concentrations after the treatment of hypothyroidism accompanied by decreased fT3/fT4 ratio suggest the influence of the chosen therapeutic approach on muscle metabolism.

Asymmetric properties of heart rate microstructure

The duration of each cardiac cycle is measured on ECG as the distance between the peaks of consecutive R waves (RR interval). Its inverse value corresponds to the heart rate (HR) changing in a beat-to-beat manner. HR accelerations are reflected as the shortenings of RR intervals while HR decelerations as the lengthening of RR intervals. HR asymmetry is a physiological phenomenon caused by an unequal input of HR decelerations and accelerations to the HR variability. Naturally occurring consecutive values of RR intervals create time series which are composed of acceleration and deceleration runs of different length. Some examples are a single HR acceleration, a pair of HR decelerations, a run consisting of five consecutive HR decelerations or a run composed of eight accelerations in a row. These runs make up the so-called heart rate microstructure that has asymmetric properties due to unequal contribution of acceleration and deceleration runs. Asymmetry of HR microstructure is a physiological finding in healthy people. However, the asymmetric properties of HR microstructure have been shown to significantly alter in some clinical conditions such as myocardial infarction, obstructive sleep apnea, chronic obturatory pulmonary disease or sepsis in infants. An abnormal HR microstructure has predictive value in survivors of myocardial infarction or patients with clinical indications for exercise treadmill stress test, e.g., for total mortality. In this review, we present and explain how the asymmetric properties of HR microstructure can be quantified, and summarise available data on the clinical and predictive value of this phenomenon and its analysis.

Relative Consistency of Sample Entropy Is Not Preserved in MIX Processes

Relative consistency is a notion related to entropic parameters, most notably to Approximate Entropy and Sample Entropy. It is a central characteristic assumed for e.g., biomedical and economic time series, since it allows the comparison between different time series at a single value of the threshold parameter r. There is no formal proof for this property, yet it is generally accepted that it is true. Relative consistency in both Approximate Entropy and Sample entropy was first tested with the M I X process. In the seminal paper by Richman and Moorman, it was shown that Approximate Entropy lacked the property for cases in which Sample Entropy did not. In the present paper, we show that relative consistency is not preserved for M I X processes if enough noise is added, yet it is preserved for another process for which we define a sum of a sinusoidal and a stochastic element, no matter how much noise is present. The analysis presented in this paper is only possible because of the existence of the very fast NCM algorithm for calculating correlation sums and thus also Sample Entropy.

Grip strength is associated with markers of central hemodynamics

Objectives. Reduced muscular strength (measured by grip strength) has been associated with an increased risk of cardiovascular complications. Further research is needed to identify how muscular strength is associated with various markers of cardiovascular function to provide at least some mechanistic explanation for observed interrelations. We, therefore, addressed the question of whether handgrip (HG) strength is associated with descriptors of peripheral and central hemodynamics in the population of healthy individuals. Design. Two hundred thirty-one healthy volunteers (90 men and 141 women, mean age 54 years) were studied. Patients were asked to perform the maximum handgrip trial in the standing position with the dominant arm, using hydraulic hand dynamometer. Applanation tonometry was used to execute the non-invasive assessment of the pressure waveform. Results. HG strength was associated with various markers of hemodynamics and clinical characteristics, e.g. correlated significantly and positively with BMI [body mass index, r = 0.21, p = .001], PPA [pulse pressure amplification, r = 0.43, p < .0001], Tr [time to return of pressure wave, r = 0.43, p < .0001] and significantly and negatively with AP [augmentation pressure, r = -0.45, p < .0001]. Multiple linear regression showed that sex, handgrip and mean blood pressure were independently associated with AP (R² = 0.38), PPA (R² = 0.21) and Tr (R² = 0.29). Conclusions. Our study demonstrated the association between handgrip strength and central hemodynamic metrics. These interactions may add a mechanistic explanation for the role of muscle strength as a risk marker for incident cardiovascular complications.

Monitoring the skin NADH changes during ischaemia and reperfusion in humans

Nicotinamide adenine dinucleotide (NADH/NAD+) is involved in many important biochemical reactions in human metabolism, including participation in energy production by mitochondria. Flow Mediated Skin Fluorescence (FMSF) is a non-invasive method to study dynamic changes in the content of the reduced form of NADH by measuring the optical properties of NADH related to the emission of the autofluorescent light (460 nm) after an earlier excitation by ultraviolet light. This review summarises the available studies using this method to describe its potential and limitations.

Testing heart rate asymmetry in long, nonstationary 24 hour RR-interval time series

OBJECTIVE

Heart rate asymmetry is a phenomenon in which the contribution of heart rate decelerations to short-term heart rate variability is greater than that of accelerations, and the contribution of accelerations to long-term and total variability is greater than that of decelerations. This has been established for short, stationary recordings, so our aim is to do it for long recordings.

APPROACH

In this paper, we analyze heart rate asymmetry in 87 long, 24 h electrocardiogram Holter recordings from healthy people. We show that in the whole recording all types of asymmetry are observable, clear and highly statistically significant. To analyze the local changes of asymmetry in time, we analyzed the recordings by disjoint jumping windows of 300 beats.

MAIN RESULTS

This analysis revealed that the local, averaged measures of all types of asymmetry also demonstrate its presence which is highly statistically significant. Additionally, we introduce in this paper a statistical test for asymmetry in a single long recording, as opposed to the current approach in which whole groups are tested. We do this by introducing the proportion of time spent in asymmetry for each recording and using it in the binomial tests.

SIGNIFICANCE

We found that for all the recordings most of the time is spent in asymmetry.

The Effect of Exercise on the Skin Content of the Reduced Form of NAD and Its Response to Transient Ischemia and Reperfusion in Highly Trained Athletes

Reduced nicotinamide adenine dinucleotide (NADH) is synthesized in the cellular nucleus, cytoplasm and mitochondria but oxidized into NAD+ almost exclusively in mitochondria. Activation of human skin by the 340 nm ultraviolet light triggers natural fluorescence at the light length of 460 nm, which intensity is proportional to the skin NADH content. This phenomenon is used by the Flow Mediated Skin Fluorescence (FMSF) which measures changes in the skin NADH content during transient ischemia and reperfusion. We examined the effects of exercise to exhaustion on the skin changes of NADH in response to 200 s forearm ischemia and reperfusion in 121 highly trained athletes (94 men and 27 women, long-distance running, triathlon, taekwondo, rowing, futsal, sprint running, fencing, and tennis). We found that exercise until exhaustion changes the skin content of NADH, modifies NADH turnover at rest, during ischemia and reperfusion in the most superficial living skin cells. Compared to the pre-exercise, there were significant increases in: mean fluorescence recorded during rest as the baseline value (B mean) (p < 0.001), the maximal fluorescence that increased above the baseline during controlled forearm ischemia (FImax) (p < 0.001, only in men), the minimal fluorescence after decreasing below the baseline during reperfusion (FRmin) (p < 0.001 men; p < 0.01 women) and the difference between B mean and FRmin (R min) (p < 0.01), and reductions in the difference between FImax and B mean (I max) (p < 0.001) and I max/IRampl ratio (CImax) (p < 0.001) after the incremental exercise test. There was no statistical difference between pre- and post-exercise the maximal range of the fluorescence change during ischemia and reperfusion (IRampl). In conclusion, exercise to exhaustion modifies the skin NADH content at rest, during ischemia and reperfusion as well as the magnitude of changes in the NADH caused by ischemia and reperfusion. Our findings suggest that metabolic changes in the skin NADH accompanying exercise extend beyond muscles and affect other cells and organs.

A thousand words about the cardiopulmonary exercise test in respiratory system diseases

The cardiopulmonary exercise test (CPET) is designed to measure some physiological variables related to the function of the cardiovascular and respiratory systems during exercise. Usually, the CPET is performed either on a treadmill or a cycle ergometer. In this mini‑review, we describe a set of parameters which are most commonly used to quantify CPET. We also summarize clinical indications for this test and interpretation of the obtained results in patients with respiratory system diseases. The CPET, if made appropriately, may deliver valuable information helpful in the diagnosis, e.g., of unexplained dyspnea, and prognosis, e.g., in chronic obturatory pulmonary disease, pulmonary hypertension, or interstitial lung diseases.

A thousand words about running fitness tests

Running is undertaken for different reasons, including improvement or maintenance of health and fitness. Many tests are employed for the estimation of the fitness in runners. In this review, we describe five field tests (Cooper test, Conconi test, 6-Minute Walk Test, 20-meter Multistage Fitness Test, and Harvard Step Test) and one laboratory cardiopulmonary exercise test (CPET) on a treadmill. A properly selected fitness test may help to estimate or measure the maximal oxygen consumption (VO2), thresholds for the aerobic and anaerobic metabolism, or restitution after the exercise. Such information is used for planning the training process, monitoring the progress of physical fitness or predicting the target distance or speed during competitions. In patients with cardiovascular or pulmonary diseases, this information may help to plan the intensity of daily activity or physical rehabilitation. Testing physical fitness is challenging, however when made appropriately, it delivers valuable physiological and clinical information.

A thousand words about the link between red blood cell distribution width and heart failure

A link between the red blood cell distribution width (RDW) and clinical outcomes in heart failure (HF) was reported for the first time in 2007. Since then, many studies have shown that an increased RDW is an independent and strong predictor of mortality and morbidity in patients with acute, decompensated or chronic HF. The evidence for such a link comes from dozens of prospective and retrospective studies in which clinical data from hundreds or even thousands of patients were examined. Although many processes such as nutritional deficiencies (e.g. iron, folate, vitamin B12), inflammation (interleukin 6, tumour necrosis factor), malnutrition, renal failure or tissue and organ hypoxia have been proposed, no clear explanation exists or is commonly accepted. This mini‑review summarises the clinical evidence on the increased RDW as a predictor of adverse clinical outcomes in HF patients, and hypothetical mechanisms that might be responsible for this interesting clinical observation.

Comparison of beta2-adrenergic and hyperemia-induced arterial vasodilation assessed by digital pulse contour analysis

Introduction. The Reflection Index (RIDVP) derived from digital volume pulse (DVP) analysis has proved to be useful in the assessment of endothelium‑dependent vasodilation induced by albuterol. Little is known of the effect of shear‑stress‑induced vasorelaxation on RIDVP.Material and Methods. Thirty three healthy volunteers (22 females, 11 males, mean age 57 yrs) were recruited. Assessment of endothelium‑dependent vasorelaxation was performed by the analysis of digital volume pulse after albuterol challenge or locally‑induced hyperemia. Results. he hyperemia‑induced vasodilation led to a significant decrease of RIDVP in comparison with the values obtained at rest (∆RIHyper 69 ± 2 % vs 64 ± 2, p < 0.0001). Similarly albuterol administration resulted in a significant drop in RIDVP (∆RIAlb 71 ± 2 % vs 67 ± 2 %, p < 0.0001). There was no significant difference between ∆RIHyper and ∆RIAlb (5.2 ± 0.8 % vs 4.6 ± 1.0 %, p = 0.61). We observed a significant correlation between the small vessel reaction in response to albuterol or hyperemia (r = 0.52, p = 0.01).Conclusions. Our study demonstrated that hyperemia‑induced changes in the Reflexion Index derived from the digital volume pulse are similar to those observed after albuterol‑challenge and both are correlated.

Arterial excess‑reservoir pressure integral as a predictor of cardiovascular complications in patients with acute coronary syndrome

INTRODUCTION    The excess pressure-time integral (excess PTI) and reservoir pressure-time integral(reservoir PTI) are new measures derived from blood pressure (BP) waveform decomposition. Thesemarkers predict cardiovascular (CV) complications and are associated with target organ  damage inpa tients on antihypertensive treatment or those with chronic and acute heart failure. OBJECTIVES    We investigated whether reservoir PTI or excess PTI predict future CV events (death, stroke, myocardial infarction [MI]) in patients with acute coronary syndrome (ACS) and reduced ejection fraction (EF). PATIENTS AND METHODS    BP waveforms were obtained by radial tonometry in 251 patients with ACS (median age, 64 years) and reduced EF (median, 40%). Left ventricular EF was assessed by transthoracic echocardiography. Reservoir PTI and excess PTI were derived by decomposition of the BP waveform RESULTS    A total of 78 CV events occurred during the follow‑up (median, 1245 days). A Kaplan-Meier analysis showed that the highest tertile of excess PTI was a significant predictor of adverse outcome. A multivariate Cox regression analysis demonstrated that excess PTI was a predictor of CV events after adjustment for EF, age, history of stroke, MI, and coronary artery bypass grafting (hazard ratio, 1.9; 95% confidence interval, 1.1-3.3; P = 0.02). CONCLUSIONS    In conclusion, excess PTI, a new measure derived from reservoir-pressure analysis, predicts outcome in survivors of ACS with reduced EF.

The association between irisin and muscle metabolism in different thyroid disorders

BACKGROUND

Irisin is a new adipo-myokine, encoded by the FNDC5 gene. Currently, there is a discussion regarding the relation between thyroid function and irisin concentration. This prospective study assesses the influence of thyrometabolic changes on serum irisin concentration in association with altered muscle metabolism. This is performed on a large cohort of patients affected by severe hypo- or hyperthyroidism, as well as by the expression of the FNDC5 gene in thyroid tissue affected by different pathologies.

METHODS

The study group comprised 119 patients with newly diagnosed severe hyperthyroidism or hypothyroidism, and a control group of 45 healthy subjects. Body composition, serum irisin concentrations, and thyroid-related hormones, creatine kinase, dystrophin and titin concentrations were evaluated. FNDC5 expression was also analysed in tissue samples from 80 patients with nontoxic multinodular goitre, toxic goitre, Graves' disease and papillary thyroid cancer.

RESULTS

Irisin concentration was lower in patients with prolonged hypothyroidism. There was a tendency towards lower dystrophin and titin concentrations in patients with hypothyroidism and hyperthyroidism. Restoration of euthyroidism in patients with hypothyroidism resulted in a decreased muscle mass with an increase in irisin concentrations, while the hyperthyroid group showed an increase in fat mass. Statistically significant overexpression of FNDC5 gene was found in patients with toxic goitre as compared to Graves' disease, papillary thyroid cancer and controls.

CONCLUSIONS

The presented data support the theory that irisin concentration changes are associated with prolonged hypothyroidism and might primarily constitute the result of prolonged myopathy. These changes are most likely not related to the expression of the FNDC5 gene in the thyroid gland.