HUMAN CARDIOVASCULAR RESPONSES TO SIMULATED PARTIAL GRAVITY AND A SHORT HYPERGRAVITY EXPOSURE

Orthostatic intolerance (OI), i.e., the inability to maintain stable arterial pressure during upright posture, is a major problem for astronauts after spaceflight. Therefore, one important goal of spaceflight-related research is the development of countermeasures to prevent post flight OI. Given the rarity and expense of spaceflight, countermeasure development requires ground-based simulations of partial gravity to induce appropriate orthostatic effects on the human body, and to test the efficacy of potential countermeasures. To test the efficacy of upright lower body positive pressure (LBPP) as a model for simulating cardiovascular responses to lunar and Martian gravities on Earth, cardiovascular responses to upright LBPP were compared with those of head-up tilt (HUT), a well-accepted simulation of partial gravity, in both ambulatory and cardiovascularly deconditioned subjects. Results indicate that upright LBPP and HUT induced similar changes in cardiovascular regulation, supporting the use of upright LBPP as a potential model for simulating cardiovascular responses to standing and moving in lunar and Martian gravities. To test the efficacy of a short exposure to artificial gravity (AG) as a countermeasure to spaceflight-induced OI, orthostatic tolerance limits (OTL) and cardiovascular responses to orthostatic stress were tested in cardiovascularly deconditioned subjects, using combined 70º head-up tilt and progressively increased lower body negative pressure, once following 90 minutes AG exposure and once following 90 minutes of -6º head-down bed rest (HDBR). Results indicate that a short AG exposure increased OTL of cardiovascularly deconditioned subjects, with increased baroreflex and sympathetic responsiveness, compared to those measured after HDBR exposure. To gain more insight into mechanisms of causal connectivity in cardiovascular and cardiorespiratory oscillations during orthostatic challenge in both ambulatory and cardiovascularly deconditioned subjects, couplings among R-R intervals (RRI), systolic blood pressure (SBP) and respiratory oscillations in response to graded HUT and dehydration were studied using a phase synchronization approach. Results indicate that increasing orthostatic stress disassociated interactions among RRI, SBP and respiration, and that dehydration exacerbated the disconnection. The loss of causality from SBP to RRI following dehydration suggests that dehydration also reduced involvement of baroreflex regulation, which may contribute to the increased occurrence of OI

Human hypertension: observations on autonomic nervous system control mechanisms and clinical associations

Introduction: Sympathetic nerve activity (SNA) undergoes physiological modulation by respiration but it remains unclear whether this process is altered by age and hypertension. Aims: To establish relationship between respiration and neural regulation of the cardiovascular system in aging and hypertension. Methods: Multiunit muscle SNA, BP, respiratory parameters and heart rate were recorded at rest in young and older healthy men and hypertensive patients, then repeated in hypertensive group after acute and long-term device-guided slow deep-breathing (SDB) training. Results: Muscle SNA was higher in older subjects but showed similar modulation by respiration in both age groups. In young acute SDB reduced SNA, with no effect on sympathetic and cardiac baroreflex sensitivity. The sympathoinhibition was not related to changes in baroreflex sensitivity, but it reflected increases in lung inflation afferent input and/or reduction in central respiratory-sympathetic coupling. Long-term SDB training inhibited muscle SNA in hypertensive patients and led to acute increase in heart rate variability and longer-term BP reduction. There were no changes in baroreflex sensitivity, cardiac structure/function or arterial stiffness in response to SDB training. Conclusions: The study provides new mechanistic insights into sympathetic regulatory pathways in hypertension and aging, which may help to establish anti-hypertensive strategy based on respiratory modulation

Physiological time-series investigations of cardiovascular regulation in healthy young adults during physical exercise.

Physiological parameters may be recorded non-invasively to gain information on cardiovascular function which can then characterise populations with various pathologies. Physical exercise produces specific autonomic nervous system (ANS) changes. There has been no comprehensive profiling of cardiovascular function during exercise or simultaneous characterisation of the influence of exercise on cardiac ventricular function and electrical activity. This work aims to address that, using a combination of physiological parameters. Between-lead agreement for ambulatory electrocardiographic (EGG) depolarisation-repolarisation (QT) interval was quantified during rest and exercise. In contrast to cardiac interval (RR) data, between-lead bias and limits of agreement for QT interval data should be quantified when reporting results from an ambulatory EGG system and between-gender QT differences should also be accounted for. EGG electrode location appears to significantly affect QT-RR hysteresis, the shortening of the post-exercise QT interval relative to that at similar heart rates during exercise or pre-exercise rest, further emphasising the need for standardisation of EGG electrode placement. Sample entropy (SampEn) measures data complexity. Few studies have compared SampEn of RR data (SampEn-RR) during exercise, whilst none have examined SampEn for the corresponding QT interval (SampEn-QT). Fractal analysis assesses data correlation and scaling structures. Detrended fluctuation analysis (DFA) provides a scaling exponent (a) which describes these properties. This has not been quantified for RR interval data during post-exercise recovery and has not been reported for QT interval data. Differences in a magnitudes for RR and QT data suggest that these quantities have different fractal properties. Exercise perturbs the resting QT-RR relationship via hysteresis. The QT variability index (QTVI) quantifies the relative autonomic influence on the atrial and ventricular myocardium during rest and exercise. QTVI is a consistent measure of cardiac ventricular function and as such appears to be a more useful index than other parameters based on RR or QT interval alone

Autonomisen hermoston toimintakokeiden vaikutukset sydämen repolarisaatioon

The autonomic nervous system is an important modulator of ventricular repolarization and arrhythmia vulnerability. This study explored the effects of cardiovascular autonomic function tests on repolarization and its heterogeneity, with a special reference to congenital arrhythmogenic disorders typically associated with stress-induced fatal ventricular arrhythmias. The first part explored the effects of standardized autonomic tests on QT intervals in a 12-lead electrocardiogram and in multichannel magnetocardiography in 10 healthy adults. The second part studied the effects of deep breathing, Valsalva manouvre, mental stress, sustained handgrip and mild exercise on QT intervals in asymptomatic patients with LQT1 subtype of the hereditary long QT syndrome (n=9) and in patients with arrhythmogenic right ventricular dysplasia (ARVD, n=9). Even strong sympathetic activation had no effects on spatial QT interval dispersion in healthy subjects, but deep respiratory efforts and Valsalva influenced it in ways that were opposite in electrocardiographic and magnetocardiographic recordings. LQT1 patients showed blunted QT interval and sinus nodal responses to sympathetic challenge, as well as an exaggerated QT prolongation during the recovery phases. LQT1 patients showed a QT interval recovery overshoot in 2.4 ± 1.7 tests compared with 0.8 ± 0.7 in healthy controls (P = 0.02). Valsalva strain prolonged the T wave peak to T wave end interval only in the LQT1 patients, considered to reflect the arrhythmogenic substrate in this syndrome. ARVD patients showed signs of abnormal repolarization in the right ventricle, modulated by abrupt sympathetic activation. An electrocardiographic marker reflecting interventricular dispersion of repolarization was introduced. It showed that LQT1 patients exhibit a repolarization gradient from the left ventricle towards the right ventricle, significantly larger than in controls. In contrast, ARVD patients showed a repolarization gradient from the right ventricle towards the left. Valsalva strain amplified the repolarization gradient in LQT1 patients whereas it transiently reversed it in patients with ARVD. In conclusion, intrathoracic volume and pressure changes influence regional electrocardiographic and magnetocardiographic QT interval measurements differently. Especially recovery phases of standard cardiovascular autonomic functions tests and Valsalva manoeuvre reveal the abnormal repolarization in asymptomatic LQT1 patients. Both LQT1 and ARVD patients have abnormal interventricular repolarization gradients, modulated by abrupt sympathetic activation. Autonomic testing and in particular the Valsalva manoeuvre are potentially useful in unmasking abnormal repolarization in these syndromes.Autonominen, eli tahdosta riippumaton hermosto osallistuu moniin elimistön säätelytoimintoihin, vaikuttaen suoraan myös sydämeen. Autonominen hermosto jaetaan sympaattiseen hermostoon, joka aktivoituu äkillisissä elimistön kriisitilanteissa kuten vihastumisen, stressin ja rasituksen yhteydessä, sekä parasympaattiseen hermostoon, joka puolestaan toimii vilkkaammin elimistön lepotilassa. Äkillisesti lisääntynyt sympaattisen hermoston aktiivisuus lisää vakavien rytmihäiriöiden vaaraa mm. kasvattamalla ohimenevästi sydämen sähköiseen toipumisvaiheen (repolarisaatioon) keston alueellisia eroja. Tämän ilmiön merkitys korostuu tietyissä vakaville rytmihäiriöille altistavissa perinnöllisissä taudeissa, joissa repolarisaatio on valmiiksi poikkeava. Näille taudeille on tunnusomaista henkeä uhkaavan rytmihäiriön ilmaantumisen riski tilanteissa joissa autonomisen hermoston toiminta muuttuu äkillisesti. Väitöskirjatutkimuksessa selvitettiin vakioitujen autonomisen hermoston toimintakokeiden vaikutuksia sydämen repolarisaatioon, mittaamalla monikanavaisesta sydänsähkökäyrästä (EKG) repolarisaatiota kuvaavaa QT-aikaa lyönti lyönniltä. Erityisesti tutkittiin testisarjan (syväänhengityskoe, Valsalvan koe, henkinen stressitesti, isometrinen puristuskoe, kevyt rasitus) vaikutuksia QT-aikaan kahdessa perinnöllisessä rytmihäiriösairaudessa; 1-tyypin pitkä-QT oireyhtymässä (LQT1) ja oikean kammion arytmogeenisessä dysplasiassa (ARVD). LQT1-potilailla syketaajuuden nousu ja QT-ajan lyheneminen olivat normaalia vaimeampia sympaattiseen aktivaation aikana, ja tunnusomaista oli QT-ajan poikkeava piteneminen testien palautumisvaiheissa. Lisäksi Valsalvan kokeen ponnistusvaihe pidensi ohimenevästi T-aallon huipusta T-aallon loppuun mitattua aikaintervallia, mikä katsotaan olevan rytmihäiriöriskiä parhaiten kuvaava EKG-ilmiö tässä oireyhtymässä. ARVD-potilailla havaittiin merkkejä poikkeavasta oikean kammion repolarisaatiosta, ja sen muuttumisesta sympaattisen aktivaation vaikutuksesta. Tutkimuksessa esitettiin lisäksi uusi tapa kuvata repolarisaation epäyhtenäisyyttä, arvioimalla EKG:n avulla sydämen oikean ja vasemman kammion välistä repolarisaatiogradienttia. Gradientti oli normaalia suurempi ja suunnaltaan vasemmalta oikealle LQT1-potilailla, mutta päinvastainen eli oikealta vasemmalle ARVD-potilailla. Valsalvan kokeen ponnistusvaihe korosti entisestään gradienttia LQT1-potilailla ja käänsi ohimenevästi sen suuntaa ARVD-potilailla. Autonomisen hermoston testit ja niistä erityisesti Valsalvan koe osoittautuivat käyttökelpoiseksi poikkeavan repolarisaation paljastamisessa LQT1- ja ARVD-potilailla. Kuvatuista menetelmistä saattaa jatkossa olla apua näiden sairauksien hoitolinjauksissa ja rytmihäiriöriskin arvioimisessa

Mathematics and Digital Signal Processing

Modern computer technology has opened up new opportunities for the development of digital signal processing methods. The applications of digital signal processing have expanded significantly and today include audio and speech processing, sonar, radar, and other sensor array processing, spectral density estimation, statistical signal processing, digital image processing, signal processing for telecommunications, control systems, biomedical engineering, and seismology, among others. This Special Issue is aimed at wide coverage of the problems of digital signal processing, from mathematical modeling to the implementation of problem-oriented systems. The basis of digital signal processing is digital filtering. Wavelet analysis implements multiscale signal processing and is used to solve applied problems of de-noising and compression. Processing of visual information, including image and video processing and pattern recognition, is actively used in robotic systems and industrial processes control today. Improving digital signal processing circuits and developing new signal processing systems can improve the technical characteristics of many digital devices. The development of new methods of artificial intelligence, including artificial neural networks and brain-computer interfaces, opens up new prospects for the creation of smart technology. This Special Issue contains the latest technological developments in mathematics and digital signal processing. The stated results are of interest to researchers in the field of applied mathematics and developers of modern digital signal processing systems

Cardiac Arrhythmias

The most intimate mechanisms of cardiac arrhythmias are still quite unknown to scientists. Genetic studies on ionic alterations, the electrocardiographic features of cardiac rhythm and an arsenal of diagnostic tests have done more in the last five years than in all the history of cardiology. Similarly, therapy to prevent or cure such diseases is growing rapidly day by day. In this book the reader will be able to see with brighter light some of these intimate mechanisms of production, as well as cutting-edge therapies to date. Genetic studies, electrophysiological and electrocardiographyc features, ion channel alterations, heart diseases still unknown , and even the relationship between the psychic sphere and the heart have been exposed in this book. It deserves to be read

Activation of 5-HT1A Receptors in the Nucleus Tractus Solitarius Facilitate Ventilatory Responses to Hypoxic Hypercapnia and Promote Sympathetic Recovery Following Hypotensive Hemorrhage

The 5-HT1A receptor agonist, 8-OH-DPAT, improves recovery from hemorrhage by stimulating sympathetically-mediated venoconstriction and cardiac output. The sympathoexcitatory effect of 8-OH-DPAT is only observed in hypovolemic rats, and is attenuated by sinoaortic denervation. Lesion of serotonergic nerve terminals in the nucleus tractus solitarius (NTS) attenuates ventilatory and sympathetic responses to hemorrhage, and peripheral chemoreceptor stimulation. Thus, we propose that serotonin is released in the NTS during hemorrhage to activate 5-HT1A receptors which facilitate chemoreflex responses. We utilized viral-mediated knockdown of the rat 5-HT1A receptor in the caudal NTS (cNTS) to examine the role of 5-HT1A receptors on compensation following hemorrhage and ventilatory responses to hypoxic/hypercapnia. Sequences encoding a 5-HT1A shRNA or scrambled version of the same sequence were incorporated into adeno-associated viral vectors and injected into the cNTS of rats. After 4 weeks, rats injected with the 5-HT1A shRNA-encoding virus showed decreases in sympathetic recovery and elevated lactate accumulations following hemorrhage that were inversely correlated with 5-HT1A mRNA expression in the cNTS. We also found that knockdown of 5-HT1A receptors in the NTS attenuated the blood pressure recovery and sympathetic drive induced by systemic 8-OH-DPAT administration. 5-HT1A receptor mRNA in the NTS was inversely correlated with the latency to recover blood pressure and positively correlated with sympathetic activity induced by 8-OH-DPAT injection during hemorrhage. Lastly, we found that acidosis stimulated the activation of serotonin in regions that project to the NTS. The presence of acidosis also increased the number of NTS cells activated by hypoxia. We further found that 5-HT1A receptors in the cNTS mediate intermittent bouts of increased ventilatory frequency (sniffing behavior) that occur during combined exposure to acidosis and hypoxia. Together these data indicate that serotonin released in the NTS during hemorrhage activates 5-HT1A receptors to facilitate sympathetic-mediated compensation and tissue perfusion following severe blood loss. Our data further suggest that acidosis stimulates serotonin release in the NTS where it activates 5-HT1A receptors to increase arousal. This phenomenon may contribute to the beneficial hemodynamic effect of serotonin during hemorrhage