Infrared sauna as exercise-mimetic? Physiological responses to infrared sauna vs exercise in healthy women: A randomized controlled crossover trial

Dissociation between ACE activity and autonomic response to ACE inhibition in patients with heart failure

Four-month longitudinal within-subject exercise training study. Although body-weight supported treadmill training (BWSTT) has not shown promise as a means of improving ambulation in individuals with motor-complete spinal cord injury (SCI), it may still improve cardiovascular health and function in this population. The purpose of this study was to (i) investigate the effects of BWSTT on peripheral muscular and elastic artery dimension and function and measures of heart rate variability (HRV) and blood pressure variability (BPV) in individuals with motor-complete SCI, and (ii) to make a preliminary examination of what factors may predict favourable cardiovascular outcomes following BWSTT in this population. Centre for Health Promotion and Rehabilitation, McMaster University, Hamilton, Ontario, Canada. Six individuals (four male, two female; age 37.7+/-15.4 years) with chronic SCI (C4-T12; ASIA A-B; 7.6+/-9.4 years post-injury) were included in the present investigation. Doppler ultrasound was used to determine femoral (exercising; muscular), carotid (elastic) and brachial (non-exercising control; muscular) artery dimension and function before and after 4 months of BWSTT. Continuous heart rate and blood pressure were also recorded before and after 4-months of BWSTT to determine frequency domain measures of HRV and BPV; clinically valuable indices of neurocardiac and neurovascular control, respectively. Two-way ANOVA (vessel x time) revealed no exercise-induced change in femoral or carotid artery cross-sectional area, blood flow or resistance and no change in carotid artery compliance following the 4 months of BWSTT compared to the non-exercising control brachial artery. However, there was a significant exercise-induced increase in femoral artery compliance. There were no exercise-induced changes in HRV or BPV when all participants were considered together. However, the results suggest that the subgroup of individuals who had a substantial heart rate response to BWSTT (n=3), experienced exercise-training induced changes in HRV reflective of a relative shift toward cardiac vagal predominance and reductions in BPV. BWSTT may cause an increase in femoral artery compliance in individuals with motor-complete SCI and therefore, should be encouraged as a means of improving cardiovascular health in this population. BWSTT may also cause modest improvements in measures of HRV and BPV in a select subgroup of individuals who respond to ambulation with moderate to large increases in HR. In the present study, factors associated with a substantial HR response to BWSTT were a propensity to orthostatic intolerance and muscular spasticity.

Introduction: Large-artery stiffness is an independent predictor of hypertension which is a leading cause of excess cardiovascular morbidity and mortality. Carotid-femoral pulse wave velocity (cf-PWV) is considered the ‘gold-standard’ measure of arterial stiffness because it measures along the aorto-iliac pathway, which makes the largest contribution to the arterial buffering function. While there is well-documented evidence on the health benefits of aerobic and resistance exercise, the information for the effect of stretching on arterial stiffness is limited. Previous studies have shown that arterial stiffness is associated with trunk flexibility. Stretching exercise targeted to improve flexibility may exert a beneficial effect on reducing arterial stiffness. Purpose: This study aimed (1) to determine the association between trunk flexibility and arterial stiffness and (2) to examine whether one bout of stretching exercise will increase trunk flexibility and decrease arterial stiffness. Methods: Thirty healthy women (mean age = 44.37 years) were instructed to follow a 20-minute DVD demonstration of whole-body stretching. Before and after stretching, cf-PWV and trunk flexibility were measured by using the SphygmoCor system and by sit-and-reach test, respectively, as well as systolic and diastolic blood pressure (SBP and DBP) and heart rate (HR) by using a Welch Allyn Monitor. All data were measured after taking a 10-minute rest in a supine position. Results: cf-PWV was not related to trunk flexibility, however, cf-PWV was significantly decreased after stretching compared with before stretching (mean difference [MD]=.63, , p=.01). Trunk flexibility was also significantly increased after stretching (MD=-3.08, p=.00). Furthermore, while SBP and DBP did not change significantly, HR was significantly reduced after stretching compared with before stretching (MD=3.12, p=.00). Conclusions: Our results showed that one bout of stretching exercise had significant effects on reducing arterial stiffness and heart rate. Further testing of long-term effects of stretching exercise is warranted for development of preventative interventions to reduce arterial stiffness, an important subclinical biomarker of cardiovascular disease.

Studies have assessed changesin autonomic variables in terms of heart rate variability (HRV) during meditation, but their results have been conflicting. Recently, Telles and colleagues’ excellent study 1 compared changes in HRV measures during the first four meditative states—cancalata (random thinking), ekagrata (nonmeditative focusing), dharana (meditative focusing), and dhyana (effortless meditation)— described in traditional yoga texts. Their results revealed that the discrepancy in changes in HRV measures might be due to the different stages. At the end of the Discussion section, the authors mention the ultimate state in yoga, samadhi, which manifests with breath suspension. They did not explore this advancedmeditativestateintheirstudy.Therefore,wewould like to share our results about changes in HRV measures during breath suspension. We collected and compared HRV measures in time and frequency domains, along with heart rate and blood pressure, during random thinking, breath meditation, and the advanced meditative stage with breath suspension in 10 meditative sessions conducted by an experienced meditator. The results (Table 1) show that none of HRV measures of time and frequency domains differed significantly during meditation. In contrast, heart rate and systolic blood pressure reliably decreased as meditation advanced. Because the meditation technique used in this study is close to meditative focusing, the results are concordant with the dharana state described in Telles and colleagues’ study. By using a device to monitor the chest circumstance of the meditator, the current study confirmed that the timing of breath suspension coincided with the subjective experience of breath suspension, complete quiescence, and absence of self-boundary. HRV measures, on the other hand, did not concord with the subjective experience of pure quiescence. Because other authors have argued that HRV is not an index of autonomic control of the circulation, 2 whether HRV can be an ideal index of sympathetic or parasympathetic activities remains questionable. According to the current results, the variations of HRV measures, manifested as the ratio of standard deviation to mean, are much greater than those of heart rate and blood pressure. This has also been shown in previous studies. 1,3,4 According to this view, HRV measures cannot be accurate indexes. The current results suggest that heart rate itself is a better HRV measure for meditation and agree with findings from Mukherjee et al. 5 These authors examined the sensitivity to mental effort and reliability of various HRV measures. Their

Background: It is well known that exercise training has positive effects on both cardiac autonomic function and arterial stiffness (AS). However, it is not clear that which exercise training variables, intensity or volume, or both, play a crucial role in this regard. This study investigates the chronic effects of high-volume moderate-intensity training (HVMIT) and low-volume high-intensity training (LVHIT) on heart rate variability (HRV) and AS in sedentary adult men.Materials and Methods: Notably, 45 males (age: 42 ± 5.7 years) were randomly assigned to a control (n = 15), HVMIT (n = 15), or LVHIT (n = 15). The HVMIT group ran three times per week on a treadmill at 50–60% of VO2max for 45–60 min, while the LVHIT trained at 70–85% of VO2max for 25–40 min. Both training protocols were equated by caloric expenditure. HRV, pulse wave velocity (PWV), hemodynamic variables, and body composition were measured before and after 12 weeks.Results: Both protocols (i.e., HVMIT and LVHIT) significantly increased the SD of normal sinus beat intervals (SDNN) and high-frequency (HF) bands (p < 0.05) after 12 weeks. Whereas the low-frequency (LF)-HF ratio decreased significantly in both training protocols (p < 0.05); however, these changes were significantly greater in the LVHIT protocol (p < 0.05). Furthermore, the root mean square of successive RR interval differences (RMSSD) significantly increased only in the LVHIT (p < 0.05). Moreover, a significant decrease in LF and PWV was only observed following the LVHIT protocol (p < 0.05). Some measures of HRV and PWV were significantly correlated (r = 0.275–0.559; p < 0.05).Conclusion: These results show that the LVHIT protocol was more efficient for improving HRV variables and PWV than the HVMIT protocol after 12 weeks of continuous running training. Interestingly, changes in some HRV parameters were related to changes in PWV. Further studies should elaborate on the link between central and peripheral cardiovascular adaptations after continuous and intermittent training regimens differing in intensity.

ObjectiveHeart rate variability (HRV) reflects integrity of the autonomic nervous system. However, no study has investigated the impact of therapeutic hypothermia (TH) on HRV measures in infants with hypoxic-ischemic encephalopathy (HIE). In this study, we evaluate the influence of temperature on measures of HRV for a group of infants with favorable outcomes, as compared to a control group of infants with unfavorable outcomes.Study DesignTerm-born infants with moderate-severe HIE underwent standard TH treatment and prospective EEG and ECG recording. Infants with favorable outcome (no seizures, normal/mild EEG scores at 96h, no MRI brain injury, and normal neurodevelopmental scores at 18–24 months) were matched on gestational age, sex and worst encephalopathy score to a group of infants with unfavorable outcomesTime and frequency domain HRV measures were calculated from 60 min of ECG data obtained at three time points: 24h (hypothermia), 48h (hypothermia), and 96h (normothermia). The effect of time and temperature were evaluated using repeated-measures ANOVA.ResultsSixteen infants were included (8 favorable, 8 unfavorable). For both groups of infants, an increase in the HR, RR and HF power was associated with an increase in temperature, but was not associated with any other HRV measure. In contrast, measures of HRV increased over time, as encephalopathy decreased, for infants with favorable outcomes (reflecting increased cortical-autonomic integration), but not for those with unfavorable outcomes.ConclusionIn general, the effect of hypothermia on measures of HRV is limited to changes in heart rate (bradycardia) and respiratory rate, as opposed to changes in true variability. This supports the hypothesis that persistent changes in HRV are driven by the underlying brain injury and not by the process of TH.

Objective: Cardiac autonomic dysfunction is associated with increased cardiovascular mortality. No data on sympathovagal balance is available in patients with erectile dysfunction (ED), in whom cardiovascular risk is high. The aim of the study was to assess blood pressure variability (BPV) and heart rate variability (HRV) in patients with hypertension and erectile dysfunction. Design and method: We studied 215 untreated hypertensives (104 diagnosed with ED, mean age 53.9 ± 10.3 and 111 controls, mean age 48.3 ± 11.8). Cardiac autonomic function was evaluated by analysis of short-term BPV and HRV measures over 24-h, daytime, and nighttime using 24-h ambulatory blood pressure monitoring and the standard deviation of the measurements. Echocardiography was also performed and left ventricular mass index (LVMI) was estimated with the Demereux formula. ANCOVA was applied and the comparison between the two groups was adjusted for age, office pulse pressure, body-mass index, history of diabetes, smoking status, LDL and high sensitivity C-reactive protein. Results: In comparison with controls, patients with ED had higher daytime diastolic blood pressure variability (11.2mmHg vs. 10.7mmHg, p = 0.046) and daytime HRV (10.5 beats per minute vs. 10.3 beats per minute, p = 0.033). All other daytime, nighttime and 24 h measurements of BPV and HRV were not different between groups (p > 0.05). At echocardiography, hypertensives with ED had similar LVMI compared to hypertensives without ED (p < 0.05). Conclusions: Compared to controls, ED patients showed a daytime sympathovagal imbalance, characterized by a relatively increased sympathetic activity. Whether this autonomic alteration has a prognostic role in hypertensive ED patients for future cardiovascular events warrants further investigation in prospective studies.

BackgroundCryostimulation and cold-water immersion (CWI) have recently gained widespread attention due to their association with changes in cardiovascular and cardiac autonomic control responses. Therefore, the aim of the present systematic review and meta-analysis was to identify the global impact of such cold exposures on cardiovascular and cardiac autonomic activity. MethodsThree databases (PubMed, Embase, Web-of-Science) were used. Studies were eligible for inclusion if they were conducted on healthy participants using cryostimulation and/or CWI. The outcomes included measurements of blood pressure (BP), heart rate (HR), and heart rate variability (HRV) indices: RR interval (RR), Root mean square of successive RR interval differences (RMSSD), low frequency band (LF), high frequency band (HF), and LF/HF ratio. ResultsAmong the 27 articles included in our systematic literature review, only 24 were incorporated into the meta-analysis. Our results reveal a significant increase in HRV indices: RMSSD (Standardized mean difference (SMD) = 0.61, p < 0.001), RR (SMD = 0.77, p < 0.001), and HF (SMD = 0.46, p < 0.001), as well as significantly reduced LF (SMD = −0.41, p < 0.001) and LF/HF ratio (SMD = −0.25, p < 0.01), which persisted up to 15 min following cold exposure. Significantly decreased heart rate (SMD = −0.16, p < 0.05), accompanied by slightly increased mean BP (SMD = 0.28, p < 0.001), was also observed. These results seem to depend on individual characteristics and the cooling techniques. ConclusionOur meta-analysis suggests that cryostimulation and/or CWI exposure enhance parasympathetic nervous activity. There is scarce scientific literature regarding the effect of individual characteristics on cold-induced physiological responses.

Monitoring collegiate soccer players during a congested match schedule: Heart rate variability versus subjective wellness measures.

Heart rate variability (HRV) is a noninvasive methodology for evaluating the autonomic nervous system modulation of the sinoatrial node and to identify patients at risk of cardiac disorders. The contemporary therapeutic use for the HRV analysis is for risk stratification in patients with post-myocardial infarction or heart failure who are prone to have arrhythmic death and who would benefit from implantable cardioverter-defibrillators (ICDs). Although multiple HRV measurements have been developed to achieve a better risk stratification, the HRV measurements have been rarely tested to see whether they harbor a significant power to serve as a practical risk predictor. To date, the only reliable metric to predict the benefit from an ICD is a severely reduced ejection fraction; however, the predictive value of the ejection fraction is relatively low. Because of the high negative predictive value of the HRV, a combination with the ejection fraction may be helpful to identify candidates who are unlikely to benefit from ICD therapy. A more sophisticated risk approach that combines the HRV and other known clinical measures should be developed to provide accurate estimates of the risk to allow patients to make informed treatment decisions. Another requirement is to explore the novel HRV measurements for atrial fibrillation. The prevalence of atrial fibrillation rapidly increases among the aging population and is independently associated with a higher risk of ischemic strokes and excess mortality. The HRV measurements specific for atrial fibrillation may facilitate the risk stratification in such a high-risk population.

BackgroundSex differences and causality of the association between heart rate variability (HRV) and atrial fibrillation (AF) in the general population remain unclear.Methods12,334 participants free of AF from the population-based Rotterdam Study were included. Measures of HRV including the standard deviation of normal RR intervals (SDNN), SDNN corrected for heart rate (SDNNc), RR interval differences (RMSSD), RMSSD corrected for heart rate (RMSSDc), and heart rate were assessed at baseline and follow-up examinations. Joint models, adjusted for cardiovascular risk factors, were used to determine the association between longitudinal measures of HRV with new-onset AF. Genetic variants for HRV were used as instrumental variables in a Mendelian randomization (MR) analysis using genome-wide association studies (GWAS) summary-level data.ResultsDuring a median follow-up of 9.4 years, 1302 incident AF cases occurred among 12,334 participants (mean age 64.8 years, 58.3% women). In joint models, higher SDNN (fully-adjusted hazard ratio (HR), 95% confidence interval (CI) 1.24, 1.04–1.47, p = 0.0213), and higher RMSSD (fully-adjusted HR, 95% CI 1.33, 1.13–1.54, p = 0.0010) were significantly associated with new-onset AF. Sex-stratified analyses showed that the associations were mostly prominent among women. In MR analyses, a genetically determined increase in SDNN (odds ratio (OR), 95% CI 1.60, 1.27–2.02, p = 8.36 × 10–05), and RMSSD (OR, 95% CI 1.56, 1.31–1.86, p = 6.32 × 10–07) were significantly associated with an increased odds of AF.ConclusionLongitudinal measures of uncorrected HRV were significantly associated with new-onset AF, especially among women. MR analyses supported the causal relationship between uncorrected measures of HRV with AF. Our findings indicate that measures to modulate HRV might prevent AF in the general population, in particular in women.Graphical abstractAF; atrial fibrillation, GWAS; genome-wide association study, IVW; inverse variance weighted, MR; Mendelian randomization, MR-PRESSO; MR-egger and mendelian randomization pleiotropy residual sum and outlier, RMSSD; root mean square of successive RR interval differences, RMSSDc; root mean square of successive RR interval differences corrected for heart rate, SDNN; standard deviation of normal to normal RR intervals, SDNNc; standard deviation of normal to normal RR intervals corrected for heart rate, WME; weighted median estimator.aRotterdam Study n=12,334bHRV GWAS n=53,174cAF GWAS n=1,030,836

Heart rate variability (HRV) is a known risk factor for mortality in both healthy and patient populations. There are currently no normative data for short-term measures of HRV. A thorough review of short-term HRV data published since 1996 was therefore performed. Data from studies published after the 1996 Task Force report (i.e., between January 1997 and September 2008) and reporting short-term measures of HRV obtained in normally healthy individuals were collated and factors underlying discrepant values were identified. Forty-four studies met the pre-set inclusion criteria involving 21,438 participants. Values for short-term HRV measures from the literature were lower than Task Force norms. A degree of homogeneity for common measures of HRV in healthy adults was shown across studies. A number of studies demonstrate large interindividual variations (up to 260,000%), particularly for spectral measures. A number of methodological discrepancies underlined disparate values. These include a systematic failure within the literature (a) to recognize the importance of RR data recognition/editing procedures and (b) to question disparate HRV values observed in normally healthy individuals. A need for large-scale population studies and a review of the Task Force recommendations for short-term HRV that covers the full-age spectrum were identified. Data presented should be used to quantify reference ranges for short-term measures of HRV in healthy adult populations but should be undertaken with reference to methodological factors underlying disparate values. Recommendations for the measurement of HRV require updating to include current technologies.

Extracorporeal carbon dioxide removal: Effect of short time infusion of 3 different metabolic acids

Slow breathing exercises, associated with meditation and other eastern style modalities like tai chi and hatha yoga, are now increasingly employed in mainstream medicine to reduce stress, attenuate moderate hypertension, and alleviate symptoms of lifestyle-related illnesses. The clinical literature on slow breathing exercises includes studies employing various physiological measurements, including heart rate variability (HRV), galvanic skin response, and changes in skin temperature. HRV has been increasingly used to measure the activity of the autonomic nervous system in various human studies employing healthy and chronically ill subjects. 1. Objective: To understand the effects of slow breathing exercises on heart rate variability as a complementary intervention for stress reduction. 2. Method: Four subjects, through repetitive trials, were instructed to slow down their breathing following a metronome at 10 breaths per minute or 6 breaths per minute or spontaneously relax to slow down their respiratory rate. The ECG, heart rate, and respiratory rate were recorded using a Powerlab set-up (ADI). 3. Key Results: Results showed an increase in amplitude of heart rate variability during these slow breathing exercises, either through the metronome-guided or spontaneous slow-breathing exercises, especially around a breathing frequency of 6 breaths per minute. The increased amplitude of heart rate variability can be seen as a positive sign, a marker for sympathovagal balance. 4. Conclusion: HRV measurements have shown that slow breathing exercises can increase heart rate variability. Future protocols for clinical trials are being projected using the HRV technique and other physiological measurements for studying effects of yoga-based complementary interventions for stress reduction.

Non-invasive positive pressure ventilation (NIPPV) is known to enhance hypoventilation and is particularly adopted as a treatment for patients diagnosed with obesity hypoventilation syndrome (OHS). The augmented risk of cardiovascular morbidity is known as a side effect of OHS. In this paper, this inference is examined that hypoventilation and the increased risk of morbidity can be diagnosed via the assessment of changes in heart rate variability (HRV). More specifically, the study investigates the effect of NIPPV on both HRV and hypoventilation among OHS patients. The linear relationship between different HRV measures and ventilation parameters is also examined. The reported results are attained via an interventional clinical trial study. HRV measures are evaluated before and after treatment, in a group of patients which are newly diagnosed with OHS and receive bi-level positive airway pressure (BiPAP) treatment for three months. The results are compared and interpreted via statistical analysis. Throughout the study, the relationship between hypoventilation and HRV is confirmed, as well as the effect of BiPAP on some HRV measures in both time and frequency domains. Particularly significant connections are observed between hypoventilation and low-frequency components of HRV. The enhanced respiration due to the application of BiPAP can improve the performance of autonomous nervous and cardiovascular systems, in terms of HRV. Moreover, it is suggested to consider some HRV parameters to control the cardiovascular side-effects of OHS and confine the resulting mortality rate in long term.