Respiratory sinus arrhythmia: why does the heartbeat synchronize with respiratory rhythm?

Although its true function remains unclear, sleep is considered critical to human physiological and cognitive function. Equally, since sleep loss is a common occurrence prior to competition in athletes, this could significantly impact upon their athletic performance. Much of the previous research has reported that exercise performance is negatively affected following sleep loss; however, conflicting findings mean that the extent, influence, and mechanisms of sleep loss affecting exercise performance remain uncertain. For instance, research indicates some maximal physical efforts and gross motor performances can be maintained. In comparison, the few published studies investigating the effect of sleep loss on performance in athletes report a reduction in sport-specific performance. The effects of sleep loss on physiological responses to exercise also remain equivocal; however, it appears a reduction in sleep quality and quantity could result in an autonomic nervous system imbalance, simulating symptoms of the overtraining syndrome. Additionally, increases in pro-inflammatory cytokines following sleep loss could promote immune system dysfunction. Of further concern, numerous studies investigating the effects of sleep loss on cognitive function report slower and less accurate cognitive performance. Based on this context, this review aims to evaluate the importance and prevalence of sleep in athletes and summarises the effects of sleep loss (restriction and deprivation) on exercise performance, and physiological and cognitive responses to exercise. Given the equivocal understanding of sleep and athletic performance outcomes, further research and consideration is required to obtain a greater knowledge of the interaction between sleep and performance.

Sleep and athletic performance: the effects of sleep loss on exercise performance, and physiological and cognitive responses to exercise.

Background: Depression is associated with an unusually high rate of aging-related illnesses and early mortality. One aspect of ‘‘accelerated aging’’ in depression may be shortened leukocyte telomeres. When telomeres critically shorten, as often occurs with repeated mitoses or in response to oxidation and inflammation, cells may die. Indeed, leukocyte telomere shortening predicts early mortality and medical illnesses in non-depressed populations. We sought to determine if leukocyte telomeres are shortened in Major Depressive Disorder (MDD), whether this is a function of lifetime depression exposure and whether this is related to putative mediators, oxidation and inflammation. Methodology: Leukocyte telomere length was compared between 18 unmedicated MDD subjects and 17 controls and was correlated with lifetime depression chronicity and peripheral markers of oxidation (F2-isoprostane/Vitamin C ratio) and inflammation (IL-6). Analyses were controlled for age and sex. Principal Findings: The depressed group, as a whole, did not differ from the controls in telomere length. However, telomere length was significantly inversely correlated with lifetime depression exposure, even after controlling for age (p,0.05). Average telomere length in the depressed subjects who were above the median of lifetime depression exposure ($9.2 years’ cumulative duration) was 281 base pairs shorter than that in controls (p,0.05), corresponding to approximately seven years of ‘‘accelerated cell aging.’’ Telomere length was inversely correlated with oxidative stress in the depressed subjects (p,0.01) and in the controls (p,0.05) and with inflammation in the depressed subjects (p,0.05). Conclusions: These preliminary data indicate that accelerated aging at the level of leukocyte telomeres is proportional to lifetime exposure to MDD. This might be related to cumulative exposure to oxidative stress and inflammation in MDD. This suggest that telomere shortening does not antedate depression and is not an intrinsic feature. Rather, telomere shortening may progress in proportion to lifetime depression exposure.

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Leukocyte telomere length in major depression: correlations with chronicity, inflammation and oxidative stress--preliminary findings.

Research into cardiovascular variabilities intersects both human physiology and quantitative modelling. This is because respiratory and Mayer wave (or 10 s) cardiovascular oscillations represent the integrated control of a system through both autonomic branches by systemic haemodynamic changes within a fluid-filled, physical system. However, our current precise measurement of short-term cardiovascular fluctuations does not necessarily mean we have an adequate understanding of them. Empirical observation suggests that both respiratory and Mayer wave fluctuations derive from mutable autonomic and haemodynamic inputs. Evidence strongly suggests that respiratory sinus arrhythmia both contributes to and buffers respiratory arterial pressure fluctuations. Moreover, even though virtual abolition of all R-R interval variability by cholinergic blockade suggests that parasympathetic stimulation is essential for expression of these variabilities, respiratory sinus arrhythmia does not always reflect a purely vagal phenomenon. The arterial baroreflex has been cited as the mechanism for both respiratory and Mayer wave frequency fluctuations. However, data suggest that both cardiac vagal and vascular sympathetic fluctuations at these frequencies are independent of baroreflex mechanisms and, in fact, contribute to pressure fluctuations. Results from cardiovascular modelling can suggest possible sources for these rhythms. For example, modelling originally suggested low frequency cardiovascular rhythms derived from intrinsic delays in baroreceptor control, and experimental evidence subsequently corroborated this possibility. However, the complex stochastic relations between and variabilities in these rhythms indicate no single mechanism is responsible. If future study of cardiovascular variabilities is to move beyond qualitative suggestions of determinants to quantitative elucidation of critical physical mechanisms, both experimental design and model construction will have to be more trenchant.

Short‐term cardiovascular oscillations in man: measuring and modelling the physiologies

Heart rate is a vital sign, whereas heart rate variability is an important quantitative measure of cardiovascular regulation by the autonomic nervous system. Although the design of algorithms to compute heart rate and assess heart rate variability is an active area of research, none of the approaches considers the natural point-process structure of human heartbeats, and none gives instantaneous estimates of heart rate variability. We model the stochastic structure of heartbeat intervals as a history-dependent inverse Gaussian process and derive from it an explicit probability density that gives new definitions of heart rate and heart rate variability: instantaneous R-R interval and heart rate standard deviations. We estimate the time-varying parameters of the inverse Gaussian model by local maximum likelihood and assess model goodness-of-fit by Kolmogorov-Smirnov tests based on the time-rescaling theorem. We illustrate our new definitions in an analysis of human heartbeat intervals from 10 healthy subjects undergoing a tilt-table experiment. Although several studies have identified deterministic, nonlinear dynamical features in human heartbeat intervals, our analysis shows that a highly accurate description of these series at rest and in extreme physiological conditions may be given by an elementary, physiologically based, stochastic model.

https://www.physiology.org/doi/pdf/10.1152/ajpheart.00482.2003

A point-process model of human heartbeat intervals: new definitions of heart rate and heart rate variability.

Usefulness of complex demodulation (CDM) in assessing the frequency components of cardiovascular variability was assessed and, subsequently, this technique was utilized to determine the time-depend...

Continuous assessment of hemodynamic control by complex demodulation of cardiovascular variability

Depressive symptoms are independently correlated with lipid peroxidation in a female population: comparison with vitamins and carotenoids.

Related factors of low back pain (LBP) among school personnel were investigated. We designed a cross-sectional study employing questionnaires, which included a Japanese version of the Job Content Questionnaire. Subjects consisted of 3306 male and 3184 female school personnel in all public schools and kindergartens operated by Nagoya City, Japan. Prevalence of LBP in each work category was compared to that in general teachers of each gender after adjusting for age. Male teachers at schools for the handicapped and in classrooms for the handicapped showed significantly higher LBP prevalence. Among female participants, teachers at schools for the handicapped, physical education teachers, kindergarten personnel and school nurses displayed higher LBP prevalence. In work categories which demonstrated high LBP prevalence, low social support and low job satisfaction were related to LBP of school nurses despite low physical loads. High job demand and physical loads correlated to LBP in kindergarten personnel.

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Psychosocial factors related to low back pain among school personnel in Nagoya, Japan.

Purpose
We examined the risk factors for automobile accidents caused by falling asleep while driving in subjects with obstructive sleep apnea syndrome (OSAS).

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Risk factors for automobile accidents caused by falling asleep while driving in obstructive sleep apnea syndrome

Objective Obstructive sleep apnea syndrome (OSAS) often accompanies obesity and diabetes mellitus. This study was performed to investigate the prevalence of glucose intolerance and to determine independent predictors for insulin resistance in patients with OSAS. Methods A cross-sectional study of 679 OSAS patients with an apnea-hypopnea index (AHI)≥5/h and 73 controls subjects (AHI 3) (odds ratio: 1.272, 95% confidence interval 1.206-1.343, p<0.0001). Conclusion Glucose intolerance was more common in patients with OSAS. Insulin resistance was associated not with AHI but rather with BMI.

Reiko Hori

Papers

Continuous assessment of hemodynamic control by complex demodulation of cardiovascular variability

Depressive symptoms are independently correlated with lipid peroxidation in a female population: comparison with vitamins and carotenoids.

Psychosocial factors related to low back pain among school personnel in Nagoya, Japan.

Risk factors for automobile accidents caused by falling asleep while driving in obstructive sleep apnea syndrome

Glucose intolerance in Japanese patients with obstructive sleep apnea.