Assessing erectile neurogenic dysfunction from heart rate variability through a Generalized Linear Mixed Model framework

Gravitational Dose‐Response Curves for Acute Cardiovascular Hemodynamics and Autonomic Responses in a Tilt Paradigm

Background

The cardiovascular system is strongly dependent on the gravitational environment. Gravitational changes cause mechanical fluid shifts and, in turn, autonomic effectors influence systemic circulation and cardiac control. We implemented a tilt paradigm to (1) investigate the acute hemodynamic response across a range of directions of the gravitational vector, and (2) to generate specific dose‐response relationships of this gravitational dependency.

Methods and Results

Twelve male subjects were tilted from 45° head‐up tilt to 45° head‐down tilt in 15° increments, in both supine and prone postures. We measured the steady‐state hemodynamic response in a range of variables including heart rate, stroke volume, cardiac output, oxygen consumption, total peripheral resistance, blood pressure, and autonomic indices derived from heart rate variability analysis. There is a strong gravitational dependence in almost all variables considered, with the exception of oxygen consumption, whereas systolic blood pressure remained controlled to within ≈3% across the tilt range. Hemodynamic responses are primarily driven by differential loading on the baroreflex receptors, combined with differences in venous return to the heart. Thorax compression in the prone position leads to reduced venous return and increased sympathetic nervous activity, raising heart rate, and systemic vascular resistance while lowering cardiac output and stroke volume.

Conclusions

Gravitational dose‐response curves generated from these data provide a comprehensive baseline from which to assess the efficacy of potential spaceflight countermeasures. Results also assist clinical management of terrestrial surgery in prone posture or head‐down tilt positions.

Heart Rate Variability: A Risk Factor for Female Sexual Dysfunction

Heart rate variability (HRV) is a measure of autonomic nervous system activity, which reflects an individual's ability to adapt to physiological and environmental changes. Low resting HRV has been linked to several mental health conditions, including depression, anxiety, and alcohol dependence (Kemp et al. in Biological Psychiatry 67(11):1067-1074, 2010. doi:10.1016/j.biopsych.2009.12.012; Kemp et al. in PloS One, 7(2):e30777, 2012; Quintana et al. in Drug and Alcohol Dependence, 132(1-2):395-398, 2013. doi:10.1016/j.drugalcdep.2013.02.025). HRV has also been used as a method for indexing the relative balance of sympathetic nervous system (SNS) activity to parasympathetic nervous system activity. This balance--in particular, moderately dominant SNS activity--has been shown to play a significant role in women's genital sexual arousal in the laboratory; however, the role of SNS activity in clinically relevant sexual arousal function is unknown. The present study assessed the feasibility of using HRV as an index of women's self-reported sexual arousal function outside the laboratory. Sexual arousal function, overall sexual function, and resting HRV were assessed in 72 women, aged 18-39. Women with below average HRV were significantly more likely to report sexual arousal dysfunction (p < .001) and overall sexual dysfunction (p < .001) than both women with average HRV and women with above average HRV. In conclusion, low HRV may be a risk factor for female sexual arousal dysfunction and overall sexual dysfunction.

The relationship between resting heart rate variability and erectile tumescence among men with normal erectile function

INTRODUCTION

Individuals with erectile dysfunction (ED) have been shown to display lower heart rate variability (HRV), suggesting dysregulation of cardiac autonomic function. No studies have explored whether HRV is predictive of erectile response among men with clinically normal erectile function.

AIM

The study aims to examine associations between resting HRV and objective measures of genital response (i.e., resting penile circumference; erectile tumescence) and self-reported sexual function.

METHODS

The sample comprised 59 male community volunteers (mean age = 20.15 years; SD = 2.52) selected from the control conditions of two previously published studies. Participants reported erectile function in the normal range (scoring ≥ 26 on the International Index of Erectile Function [IIEF]) and had no history of cardiovascular disease or myocardial infarct. During a laboratory visit, self-report, anthropometric, cardiovascular, and electrocardiographic data were assessed, as well as resting penile circumference and erectile tumescence in response to viewing an erotic film.

MAIN OUTCOME MEASURES

Resting penile responses, erectile tumescence (circumferential change via penile plethysmography), self-reported sexual function per the IIEF, and both time-domain (standard deviation of beat-to-beat [NN] intervals, square root of the mean squared difference of successive NN intervals, and percent of NN intervals for which successive heartbeat intervals differed by at least 50 msec [pNN50]) and frequency-domain (low frequency [LF], high frequency [HF], LF/HF ratio) parameters of HRV were assessed.

RESULTS

Higher-resting HF power and lower-resting LF/HF ratio were associated with greater erectile tumescence. There were marginally significant positive associations between mean NN interval and pNN50 and penile tumescence. HRV was not associated with self-reported sexual function or with resting penile circumference.

CONCLUSIONS

Results suggested that, among men without ED, relatively elevated parasympathetic tone was predictive of larger erectile tumescence. Limited variance in sexual function scores may have accounted for the lack of association between HRV and IIEF scores.

Adoption of diagnostic technology and variation in caesarean section rates: a test of the practice style hypothesis in Norway

OBJECTIVE

To examine whether the introduction of advanced diagnostic technology in maternity care has led to less variation in type of delivery between hospitals in Norway.

DATA SOURCES

The Medical Birth Registry of Norway provided detailed medical information for 1.7 million deliveries from 1967 to 2005. Information about diagnostic technology was collected directly from the maternity units.

STUDY DESIGN

The data were analyzed using a two-level binary logistic model with Caesarean section as the outcome measure. Level one contained variables that characterized the health status of the mother and child. Hospitals are level two. A heterogeneous variance structure was specified for the hospital level, where the error variance was allowed to vary according to the following types of diagnostic technology: two-dimensional ultrasound, cardiotocography, ST waveform analysis, and fetal blood analyses.

PRINCIPAL FINDING

There was a marked variation in Caesarean section rates between hospitals up to 1973. After this the variation diminished markedly. This was due to the introduction of ultrasound and cardiotocography.

CONCLUSION

Diagnostic technology reduced clinical uncertainty about the diagnosis of risk factors of the mother and child during delivery, and variation in type of delivery between hospitals was reduced accordingly. The results support the practice style hypothesis.

Contrasting effects of climate change on rabbit populations through reproduction

BACKGROUND

Climate change is affecting many physical and biological processes worldwide. Anticipating its effects at the level of populations and species is imperative, especially for organisms of conservation or management concern. Previous studies have focused on estimating future species distributions and extinction probabilities directly from current climatic conditions within their geographical ranges. However, relationships between climate and population parameters may be so complex that to make these high-level predictions we need first to understand the underlying biological processes driving population size, as well as their individual response to climatic alterations. Therefore, the objective of this study is to investigate the influence that climate change may have on species population dynamics through altering breeding season.

METHODOLOGY/PRINCIPAL FINDINGS

We used a mechanistic model based on drivers of rabbit reproductive physiology together with demographic simulations to show how future climate-driven changes in breeding season result in contrasting rabbit population trends across Europe. In the Iberian Peninsula, where rabbits are a native species of high ecological and economic value, breeding seasons will shorten and become more variable leading to population declines, higher extinction risk, and lower resilience to perturbations. Whereas towards north-eastern countries, rabbit numbers are expected to increase through longer and more stable reproductive periods, which augment the probability of new rabbit invasions in those areas.

CONCLUSIONS/SIGNIFICANCE

Our study reveals the type of mechanisms through which climate will cause alterations at the species level and emphasizes the need to focus on them in order to better foresee large-scale complex population trends. This is especially important in species like the European rabbit whose future responses may aggravate even further its dual keystone/pest problematic. Moreover, this approach allows us to predict not only distribution shifts but also future population status and growth, and to identify the demographic parameters on which to focus to mitigate global change effects.

Dying like rabbits: general determinants of spatio-temporal variability in survival

1. Identifying general patterns of how and why survival rates vary across space and time is necessary to truly understand population dynamics of a species. However, this is not an easy task given the complexity and interactions of processes involved, and the interpopulation differences in main survival determinants. 2. Here, using European rabbits (Oryctolagus cuniculus) as a model and information from local studies, we investigated whether we could make inferences about trends and drivers of survival of a species that are generalizable to large spatio-temporal scales. To do this, we first focused on overall survival and then examined cause-specific mortalities, mainly predation and diseases, which may lead to those patterns. 3. Our results show that within the large-scale variability in rabbit survival, there exist general patterns that are explained by the integration of factors previously known to be important at the local level (i.e. age, climate, diseases, predation or density dependence). We found that both inter- and intrastudy survival rates increased in magnitude and decreased in variability as rabbits grow old, although this tendency was less pronounced in populations with epidemic diseases. Some causes leading to these higher mortalities in young rabbits could be the stronger effect of rainfall at those ages, as well as, other death sources like malnutrition or infanticide. 4. Predation is also greater for newborns and juveniles, especially in population without diseases. Apart from the effect of diseases, predation patterns also depended on factors, such as, density, season, and type and density of predators. Finally, we observed that infectious diseases also showed general relationships with climate, breeding (i.e. new susceptible rabbits) and age, although the association type varied between myxomatosis and rabbit haemorrhagic disease. 5. In conclusion, large-scale patterns of spatio-temporal variability in rabbit survival emerge from the combination of different factors that interrelate both directly and through density dependence. This highlights the importance of performing more comprehensive studies to reveal combined effects and complex relationships that help us to better understand the mechanisms underlying population dynamics.

Heart Rate Variability in Men with Erectile dysfunction

Purpose

The objective of this study is to investigate alteration of autonomic nervous system (ANS) activity in patients suffering from erectile dysfunction (ED) by comparing parameters of heart rate variability (HRV) between men with ED and healthy subjects.

Methods

A retrospective review was performed on 40 ED patients (mean age, 46.0±8.49 years) without any disease and 180 healthy control people (mean age, 44.4±7.83 years) without ED in our institution from June 2008 to July 2010. And electrocardiographic signals were obtained to measure HRV parameters for both patients and controls in a resting state.

Results

For the time domain analysis, square root of the mean differences between successive RR intervals (RMSSD) representing parasympathetic activity was lower in patients than controls although P-value was not statistically significant (P=0.060). For the frequency domain analysis, high frequency (HF) representing parasympathetic activity was lower in patients than controls (P=0.232) and low frequency (LF) representing mainly sympathetic activity was higher in patients than controls (P=0.416). Lastly, LF/HF ratio reflecting sympathetic/parasympathetic activity ratio was statistically higher in patients than controls (P=0.027).

Conclusions

Patients with ED exhibited different HRV parameters compared with normal controls. This suggests that the patients with ED may have some kind of imbalance in the ANS and it may be possible that general imbalance of the ANS is one of the causes of ED. Thus, HRV analysis may give valuable diagnostic information and serve as a rapid screening tool to evaluate altered ANS activity in patients with ED.