Effects of heat stress on the blood pressure and heart rate variability in young men

Eighteen healthy military college cadets and university students were studied by means of a head-up-tilting test (HUT) in normal (temperature 22°, relative humidity 35%) and hot environment (42°C, 18%). During HUT the beat-to-beat mean blood pressure (MBP) and heart rate (HR) were continuously recorded with a differential oscillometric device. The MBP and HR variability were calculated in segments of 5 min using Fast Fourier Transform to obtain high frequency (HF, 0.15-0.4 Hz) and low frequency (LF, 0.04-0.15 Hz) components. In addition to that, we also computed the time domain indices rMSSD and pNN50 for HR variability analysis. Our study revealed that in the heat the mean values of HR were significantly higher in the supine as well as the tilted position compared to the situation in normothermia. At the same time, the mean values of MBP in the supine and tilted positions in normal as well as heat stress condition were not significantly different. The absolute values of LF and HF components of HR variability decreased in hyperthermia, while no significant changes in spectral indices of MBP variability and normalised values of HR variability were observed. © 2013 IFMBE

Coordination dynamics of circulatory and respiratory rhythms during psychomotor drive reduction

A 0.15-Hz rhythm band in cutaneous blood oscillations in awake human subjects was studied in cardiovascular-respiratory time series of five subjects relaxing naively or practicing hypnoid relaxation (autogenic training, or AT). Time series analysis used nonlinear algorithms, time-frequency distribution (TFD), postevent scan (PES) method, and linear fast Fourier transform (FFT) algorithm. This 0.15-Hz rhythm band caused phase synchronization with respiration at 1:2, 1:1, and 2:1 integer number (n/m) ratios for extended periods. During wave epochs, the 0.15-Hz rhythm band was amplified, causing the 0.15-Hz rhythm band to also appear in interbeat intervals and arterial blood pressure fluctuations. If phase synchronization of the 0.15-Hz rhythm band with respiration was established at a 1:1 integer number ratio, it was maintained and resulted in consensualization of all cardiovascular-respiratory oscillations at this frequency. Simultaneous cardiovascular and respiratory oscillations at about 0.1 Hz did not affect the appearance of the 0.15-Hz rhythm band in the photoplethysmography (PPG) signal. Recent evidence suggests the emergence of the 0.15-Hz rhythm band and n/m phase synchronization to result from nonequilibrium phase transitions operational in the network of lower brainstern neurons and associated parasympathetic neuronal effectors. These findings corroborate our notion of the 0.15-Hz rhythm band as a marker of the trophotropic mode of operation. (C) 2004 Elsevier B.V. All rights reserved

Cardiovascular rhythms in the 0.15-Hz band: common origin of identical phenomena in man and dog in the reticular formation of the brain stem?

Selected examples from experiments in humans and dogs with time series of reticular neurons, respiration, arterial blood pressure and cutaneous forehead blood content fluctuations were analysed using multiscaled time-frequency distribution, post-event-scan and pointwise transinformation. We found in both experiments a 0.15-Hz rhythm exhibiting periods of spindle waves (increasing and decreasing amplitudes), phase synchronized with respiration at 1:2 and 1: 1 integer number ratios. At times of wave-epochs and n:m phase synchronization, the 0.15-Hz rhythm appeared in heart rate and arterial blood pressure. As phase synchronization of the 0.15-Hz rhythm with respiration was established at a 1:1 integer number ratio, all cardiovascular-respiratory oscillations were synchronized at 0.15 Hz. Analysis of a canine experiment supplied evidence that the emergence of the 0.15-Hz rhythm and n:m phase synchronization appears to result from a decline in the level of the general activity of the organism associated with a decline in the level of activity of reticular neurons in the lower brainstem network. These findings corroborate the notion of the 0.15-Hz rhythm as a marker of the trophotropic mode of operation first introduced by W.R. Hess

Correlation analysis between surface electromyography and continuous-wave near-infrared spectroscopy parameters during isometric exercise to volitional fatigue

In this study, the process of muscular fatigue was examined using surface electromyography (sEMG) and continuous-wave near-infrared spectroscopy (cw-NIRS) simultaneously during an isometric hand grip exercise at 50% and 75% of the maximal voluntary contraction (MVC), sustained until volitional fatigue. The mean frequency of the sEMG decreased during the whole exercise, whereas the root mean square had a tendency to increase. Oxyhemoglobin/deoxyhemoglobin concentration changes computed with cw-NIRS were found to exhibit a fast linear decrease/increase in the first 10-20 s of the exercise, the so-called fast phase, followed by a plateau-like slow phase. The change rates were higher at 75% MVC for both the sEMG and cw-NIRS parameters. Significant correlations were found, especially at 50% MVC, between the sEMG parameters computed for the whole exercise and cw-NIRS parameters computed from the early region of the exercise, i.e. infection duration and amplitude changes to the inflection point. The findings emphasize the potential of cw-NIRS for muscle studies

DIFFERENT RECOVERY METHODS AND MUSCLE PERFORMANCE AFTER EXHAUSTING EXERCISE: COMPARISON OF THE EFFECTS OF ELECTRICAL MUSCLE STIMULATION AND MASSAGE

In this study we assessed the influence of the three different recovery interventions massage (MSG), electrical muscle stimulation (EMS), and passive rest (PR) on lactate disappearance and muscle recovery after exhausting exercise bouts. Twelve healthy male sport students participated in the study. They attended the laboratory on five test days. After measurement of (V) over dotO(2)max and a baseline Wingate test (WG(b)), the three recovery interventions were tested in random counterbalanced order. High intensity exercise, which consisted of six exhausting exercise bouts (interspersed with active recovery), was followed by MSG, EMS or PR application (24 minutes); then the final Wingate test (WG(f)) was performed. Lactate, heart rate, peak and mean power, rating of perceived exertion (RPE), and total quality of recovery (TQR) were recorded. In WG(f) mean power was significantly higher than in WG(b) for all three recovery modalities (MSG 6.29%, EMS 5.33%, PR 4.84% increase, p0.05). The heart rate response and the changes in blood lactate concentration were identical in all three interventions during the entire protocol (p=0.817, p=0.493, respectively). RPE and TQR scores were also not different among the three interventions (p>0.05). These results provide further evidence that MSG and EMS are not more effective than PR in the process of recovery from high intensity exercise

COMPARISON OF HEART RATE VARIABILITY IN DIFFERENT BODY POSITIONS ON LAND AND IN WATER

Karada ve sudaki farklı beden konumlarında elde edilen Kalp Hızı Değişkenliği (KHD) değerlerinin karşılaştırılması ve en etkili gevşeme konumunun belirlenmesi amacıyla yapılan bu araştırmaya, İstanbul’da bir eğitim kurumunda çalışan farklı statülerdeki çalışanlardan oluşan 18 kişi gönüllü olarak katılmıştır. Katılımcıların KHD değerleri, karada dikey ve yatay, suda watsu konumunda alınmıştır. Gurubun tüm ölçümleri farklı günlerde ve her konum için 4 kez tekrarlanmıştır. KHD’nin zaman boyutu parametresi olarak RMSSD, frekans alanı parametreleri olarakta HF% ve LF/HF oranı analiz edilmiştir. RR sinyali 1 milisaniye hassaslıkta kayıt edilmiştir. Bu parametrelerin karşılaştırmaları Tekrarlayan Ölçüm Varyans Analizi ile yapılmıştır. Watsu konumunda alınan ölçümlerin analizinde, RMSSD ve HF% parametrelerinde anlamlı artış bulunmuştur. Sempatik düzenlemenin bir yansıması olarak kabul edilen LF/HF oranı watsu konum ölçümleri, dikey ve yatay olarak yapılan kara ölçümlerinden anlamlı olarak düşük çıkmıştır. Sonuç olarak, en etkili gevşemenin sudaki watsu konumunda gerçekleştiği anlaşılmıştır.18 people including staff working at different sites in an education foundation in İstanbul participated voluntarily in this research which was carried out to compare HRV values obtained through various methods applied on land and in water and to determine the most effective relaxation method. Participants’ HRV values were measured at vertical and horizontal positions on land and in watsu in water. All measurements of group were taken in different days and repeated 4 times for each position. RMSSD was analyzed as time domain parameter and HF% and rate of LF/HF were analyzed as frequency domain in HRV analysis. RR signal was recorded with 1 millisecond sensitivity. Comparison of these parameters was performed by means of Variance Analysis of Repeated Measurements. The analysis of values of watsu position indicated significant increases in RMSSD and HF% parameters. LF/HF rate, which is regarded as reflection of sympathetic modulation, was significantly lower than values of vertical and horizontal land measurements. In conclusion, the most effective relaxation was provided by watsu practiced in water.

Monitoring Autonomic and Central Nervous System Activity by Permutation Entropy during Short Sojourn in Antarctica

The aim of this study was to monitor acute response patterns of autonomic and central nervous system activity during an encounter with Antarctica by synchronously recording heart rate variability (HRV) and electroencephalography (EEG). On three different time-points during the two-week sea journey, the EEG and HRV were recorded from nine male scientists who participated in "The First Turkish Antarctic Research Expedition". The recordings were performed in a relaxed state with the eyes open, eyes closed, and during a space quantity perception test. For the EEG recordings, the wireless 14 channel EPOC-Emotiv device was used, and for the HRV recordings, a Polar heart rate monitor S810i was used. The HRV data were analyzed by time/frequency domain parameters and ordinal pattern statistics. For the EEG data, spectral band power in the conventional frequency bands, as well as permutation entropy values were calculated. Regarding HRV, neither conventional nor permutation entropy calculations produced significant differences for the different journey time-points, but only permutation entropy was able to differentiate between the testing conditions. During the cognitive test, permutation entropy values increased significantly, whereas the conventional HRV parameters did not show any significant differences. In the EEG analysis, the ordinal pattern statistics revealed significant transitions in the course of the sea voyage as permutation entropy values decreased, whereas spectral band power analysis could not detect any significant difference. Permutation entropy analysis was further able to differentiate between the three testing conditions as well between the brain regions. In the conventional spectral band power analysis, alpha band power could separate the three testing conditions and brain regions, and beta band power could only do so for the brain regions. This superiority of permutation entropy in discerning subtle differences in the autonomic and central nervous system's responses to an overwhelming subjective experience renders it suitable as an analysis tool for biomonitoring in extreme environments

The Effects of Resistance and Aerobic Exercises on Adiponectin, Insulin Resistance, Lipid Profile and Body Composition in Adolescent Boys with Obesity

Introduction: This present study aimed to examine the effects of long-term resistance exercise (REG) and aerobic exercise (AEG) on the adiponectin, insulin resistance, lipid profile and body composition in adolescent boys with obesity. Methods: Sixteen obese adolescent boys (age: 16.81 +/- 0.91 years) who studied at high school in Istanbul voluntarily participated in the study. The participants were randomly divided into two groups of (REG; n=8) and (AEG; n=8). The participants followed their exercise schedule for six months (3 days/wk, 60 min/day). The serum lipid profile, adiponectin, glucose, insulin resistance (HOMA-IR) levels and body composition of the participants were evaluated at the beginning and end of the study. A Wilcoxon matched-pairs signed-rank test and Mann-Whitney U test were used for analyses, and the criterion for statistical significance was set at p<0.05. Results: HOMA-IR, insulin, glucose and serum lipid levels decreased in both groups (p<0.05). Adiponectin and high-density lipoprotein increased only in the AEG (p<0.05). Low-density lipoprotein level was statistically decreased only in the REG (p<0.05). Conclusion: These results indicated that both types of exercises had positive effects on insulin resistance, per cent body fat, weight and fat-free body mass. Long-term (6 months) aerobic and REG had different positive effects on adiponectin and the lipid profile. Although the effects of long-term aerobic exercise on biochemical parameters are higher than REG, it was remarkable that REG proved to be an alternative model to AEG