Orthostatic Intolerance Is Independent of the Degree of Autonomic Cardiovascular Adaptation after 60 Days of Head-Down Bed Rest.

Spaceflight and head-down bed rest (HDBR) can induce the orthostatic intolerance (OI); the mechanisms remain to be clarified. The aim of this study was to determine whether or not OI after HDBR relates to the degree of autonomic cardiovascular adaptation. Fourteen volunteers were enrolled for 60 days of HDBR.

Cardiovascular autonomic adaptation in lunar and martian gravity during parabolic flight.

Purpose: Weightlessness has a well-known effect on the autonomic control of the cardiovascular system. With future missions to Mars in mind, it is important to know what the effect of partial gravity is on the human body. We aim to study the autonomic response of the cardiovascular system to partial gravity levels, as present on the Moon and on Mars, during parabolic flight.

Is autonomic modulation different between European and Chinese astronauts?

Purpose: The objective was to investigate autonomic control in groups of European and Chinese astronauts and to identify similarities and differences.

Methods: Beat-to-beat heart rate and finger blood pressure, brachial blood pressure, and respiratory frequency were measured from 10 astronauts (five European taking part in three different space missions and five Chinese astronauts taking part in two different space missions). Data recording was performed in the supine and standing positions at least 10 days before launch, and 1, 3, and 10 days after return.

Inhalation/Exhalation ratio modulates the effect of slow breathing on heart rate variability and relaxation.

Slow breathing is widely applied to improve symptoms of hyperarousal, but it is unknown whether its beneficial effects relate to the reduction in respiration rate per se, or, to a lower inhalation/exhalation (i/e) ratio. The present study examined the effects of four ventilatory patterns on heart rate variability and self-reported dimensions of relaxation. Thirty participants were instructed to breathe at 6 or 12 breaths/min, and with an i/e ratio of 0.

Circadian rhythm of autonomic cardiovascular control during Mars500 simulated mission to Mars.

Introduction: The Mars500 project was conceived to gather knowledge about the psychological and physiological effects of living in an enclosed environment during 520 d as would be required for a real mission to Mars. Our objective was to investigate the circadian profile of heart rate variability (HRV) in the context of the Mars500 study.

Methods: Before, during, and after confinement, 24-h EKG records were obtained from the six crewmembers who participated in the mission.

Adaptation of autonomic heart rate regulation in astronauts after spaceflight.

Background: Spaceflight causes changes in the cardiovascular control system. The aim of this study was to evaluate postflight recovery of linear and nonlinear neural markers of heart rate modulation, with a special focus on day-night variations.

Material/methods: Twenty-four-hour Holter ECG recordings were obtained in 8 astronauts participating in space missions aboard the International Space Station (ISS).

Sleep-wake differences in heart rate variability during a 105-day simulated mission to Mars.

Introduction: In prolonged spaceflights the effect of long-term confinement on the autonomic regulation of the heart is difficult to separate from the effect of prolonged exposure to microgravity or other space-related stressors. Our objective was to investigate whether the sleep-wake variations in the autonomic control of the heart are specifically altered by long-term confinement during the 105-d pilot study of the Earth-based Mars500 project.

Methods: Before (pre), during (T1: 30, T2: 70, andT3: 100 d), and after (post) confinement, 24-h EKG records were obtained from the six crewmembers that participated in the mission.

Heart rate variability after heart transplantation: a 10-year longitudinal follow-up study.

Background: Cross-sectional studies suggest, by use of heart rate variability (HRV), that partial re-innervation of the sinus node may occur after heart transplantation (HTx). Our aim was to test this hypothesis by examining HRV in long-term longitudinal follow-up study of HTx recipients.

Methods And Results: 14 HTx recipients (11 men) were studied 1-48 (median 13) months (baseline) and 119-172 (median 141) months after HTx (follow-up).

Cardiovascular autonomic adaptation to long-term confinement during a 105-day simulated Mars mission.

Introduction: Long-term confinement and microgravity may entail alteration in the regulation of the cardiovascular system. A 105-d pilot study of a Mars mission simulation was conducted to test the cardiovascular response to slow-paced breathing and mental stress.

Methods: Finger blood pressure and beat-to-beat heart rate were monitored in six male volunteers taking part in a 105-d Mars mission simulation.

Haemodynamic adaptation during sudden gravity transitions.

Haemodynamic responses during parabolic flight were studied. The hypothesis that haemodynamic changes may be counteracted by a transient vagal reflex during acute gravity transitions was tested. ECG, arterial pressure and respiration were recorded continuously in seven male subjects during parabolic flight.

Effects of mental stress on autonomic cardiac modulation during weightlessness.

Sustained weightlessness affects all body functions, among these also cardiac autonomic control mechanisms. How this may influence neural response to central stimulation by a mental arithmetic task remains an open question. The hypothesis was tested that microgravity alters cardiovascular neural response to standardized cognitive load stimuli.

Adaptation of heart rate and blood pressure to short and long duration space missions.

To what extent does going to space affect cardiovascular function? Although many studies have addressed this question, the answer remains controversial. Even for such primary parameters as heart rate (HR) and blood pressure (BP) contradictory results have been presented. The purpose of this investigation was to evaluate HR and arterial BP in 11 male astronauts who each took part in nine different space missions aboard the International Space Station (ISS), for up to 6 months.

Cardiac autonomic regulation under hypnosis assessed by heart rate variability: spectral analysis and fractal complexity.

Objective: This study examined the effects of hypnosis on autonomic cardiac control. We hypothesized a modification of autonomic modulation of the heart rate with an enhanced vagal tone during hypnosis compared to baseline.

Methods: In 12 healthy subjects (6 men and 6 women, 22.

Respiratory variability preceding and following sighs: a resetter hypothesis.

Respiratory behavior is characterized by complex variability with structured and random components. Assuming that both a lack of variability and too much randomness represent suboptimal breathing regulation, we hypothesized that sighing acts as a resetter inducing structured variability. Spontaneous breathing was measured in healthy persons (N=42) during a 20min period of quiet sitting using the LifeShirt(®) System.

Complexity of cardiovascular regulation in small animals.

Oscillations of heart rate and blood pressure are related to the activity of the underlying control mechanism. They have been investigated mostly with linear methods in the time and frequency domains. Also, in recent years, many different nonlinear analysis methods have been applied for the evaluation of cardiovascular variability.

Steep fall in cardiac output is main determinant of hypotension during drug-free and nitroglycerine-induced orthostatic vasovagal syncope.

Background: How much of the hypotension occurring during postural syncope is cardiac output-mediated and how much can be ascribed to a fall in systemic vascular resistance are unknown. The contribution of both determinants may be influenced by the use of vasoactive drugs.

Objective: The purpose of this study was to assess the determinants of hypotension during drug-free and nitroglycerine (NTG)-induced vasovagal presyncope in routine tilt table testing.

Tilt training increases the vasoconstrictor reserve in patients with neurally mediated syncope evoked by head-up tilt testing.

Aims: Tilt training is a useful therapeutic option in neurally mediated syncope (NMS). We tested the hypothesis that tilt training will restore orthostatic tolerance by increasing the degree of vasomotor reserve during sustained orthostatic stress. METHODS AND RESULTS In this follow-up study we enrolled 17 patients (age 31 +/- 22 years, 11 females) with a clinical diagnosis of NMS and two consecutive positive tilt tests.

Cardiovascular function and gravity transitions during parabolic flight.

Cardiovascular function and gravity transitions during parabolic flight.

Impact of age on the vasovagal response provoked by sublingual nitroglycerine in routine tilt testing.

NTG (nitroglycerine) is used in routine tilt testing to elicit a vasovagal response. In the present study we hypothesized that with increasing age NTG triggers a more gradual BP (blood pressure) decline due to a diminished baroreflex-buffering capacity. The purpose of the present study was to examine the effect of NTG on baroreflex control of BP in patients with distinct age-related vasovagal collapse patterns.

Low-dose exercise training does not influence cardiac autonomic control in healthy sedentary men aged 55-75 years.

The purpose of this study was to evaluate the effects of a realistic, feasible, and commonly used fitness training programme on cardiac autonomic control in 14 sedentary men aged 62.0 +/- 6.1 years (mean +/- s).

Fractal dimension in health and heart failure.

Background: Non-linear analysis of heart rate variability (HRV) can give additional information about autonomic control of the heart rate. This study applied the fractal dimension (FD) in a congestive heart failure (CHF) population.

Methods: FD and HRV were evaluated in a healthy population (n=21) and an end-stage heart failure population (n=21) using 1-h segments during the day and night from Holter recordings.

Effects of autonomic blockade on non-linear cardiovascular variability indices in rats.

1. The present study assesses the effects of autonomic blockade (alpha- and beta-adrenoceptor and cholinergic) on cardiovascular function studied by heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity in rats using non-linear dynamics. Little is known about the influence of pharmacological autonomic nervous system interventions on non-linear cardiovascular regulatory indices.

Aging and nonlinear heart rate control in a healthy population.

In recent years more studies are using nonlinear dynamics to describe cardiovascular control. Because of the large dispersion of physiological data, it is important to have large studies with both male and female participants to establish a range of physiological healthy values. This study investigated the effect of gender and age on nonlinear indexes.