Biomedical subjects

André E Aubert

Publications and source records attributed to André E Aubert.

12 recordsLinked to original sources

PubMed2006

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). All participants performed a one-year fitness training programme in which training intensity and frequency were specifically chosen to be compliant for the majority of the participants (2-3 sessions per week at moderate intensity). At the same time, a reference group consisting of 15 sedentary age-matched men (age 64.2 +/- 6.5 years) did not change their habitual physical activity. Measurements were performed before and after the training intervention. Cardiac autonomic control was inferred from resting values (supine and standing) of heart rate variability (HRV) computed in the frequency domain over 10-min intervals. Endurance capacity was evaluated during a maximal incremental bicycle ergometer test. In spite of an increase in peak oxygen consumption (VO2peak) by 6.4% after training, heart rate in the training group remained unchanged at rest and at the same metabolic demand. No changes in resting parameters of HRV were shown for either groups or positions. Results from this study provide no evidence of a clinically meaningful increase in the vagal modulation to the sinus node at rest after one year of low-volume and moderate-intensity fitness training in men aged 55-75 years.

Aged↗

PubMed2006

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. RESULTS: CHF patients presented a loss of circadian variation in both FD and conventional time- and frequency-domain HRV indices. FD was higher in the CHF population both during the day and night. In the CHF population the correlation between FD and high-frequency power of HRV was lost. CONCLUSION: Day-night variations of heart rate fluctuations are lost in heart failure. Changes in FD reflecting physiological and pathophysiological changes were observed.

Algorithms↗

PubMed2005

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. Nonlinear scaling properties were studied by using 1/f slope (where f is frequency), fractal dimension, and detrended fluctuation analysis short- and long-term correlations (DFAalpha(1) and DFAalpha(2), respectively). Nonlinear complexity was described with correlation dimension (CD), Lyapunov exponent (LE), and approximate entropy (ApEn). The population consisted of 135 women and 141 men (age, 18-71 yr). Twenty-four hour ECG recordings were obtained by using Holter monitoring. The recordings were split into daytime (8 AM-9 PM) and nighttime (11 PM-6 AM). A day-night variation was present in all nonlinear heart rate variability (HRV) indexes, except for the CD in the female population. During the night the percentage of CD values of surrogate data files differing from the CD value of the original data increased. All nonlinear indexes were significantly correlated with age. Deeper analysis per age category of 10 yr showed a stabilization in the age decline of the fractal dimension and ApEn at the age of > or =40 yr. The vagal pathways seemed to be more involved in the generation of nonlinear fluctuations. Higher nonlinear behavior was evident during the night. No clear difference between men and women was found in the nonlinear indexes. Nonlinear indexes decline with age. This can be related to the concept of decreasing autonomic modulation with advancing age.

Adult↗

PubMed2005

Spectral characteristics of heart rate fluctuations during parabolic flight.

Parabolic flight is used to create short successive periods of changing gravity in a range between 0 and 1.8 Gz (1 Gz: 9.81 m/s(2)). The purpose of the present study was to evaluate whether cyclic variations in heart rate during +/-20 s periods of stable gravity in parabolic flight reflect autonomic modulation of cardiac chronotropy. During the 29th and 32nd ESA parabolic flight campaign ECG and respiration were recorded in 13 healthy volunteers in both standing and supine postures. We developed and validated a spectral algorithm especially adapted to study frequency components of heart rate among ultrashort (+/-20 s) stable gravity periods of parabolic flight. A low frequency (LF) component, starting from the lowest measurable frequency (+/-0.05 Hz) up to 0.15 Hz was distinguished from a high frequency (HF) component, ranging from 0.16 Hz up to 0.4 Hz. Powers were calculated by integration between corresponding limits and represented in normalized units (nu). With our method, we were able to reproduce normal findings in the upright posture at 1 Gz, i.e., less power in the HF component compared to supine (HFnu: 0.18+/-0.09 vs. 0.40+/-0.16). These postural related differences are shown to be eliminated at 0 Gz (HFnu: 0.30+/-0.12 vs. 0.32+/-0.13) and amplified at 1.8 Gz phases (HFnu: 0.15+/-0.10 vs. 0.39+/-0.16) of parabolic flight. In the supine position no coherent differences were shown in the measured variables among different gravity phases. Our observations strongly indicate that spectral characteristics of heart rate fluctuations among stable gravity periods of parabolic flight reflect parasympathetic nervous system control of cardiac chronotropy. At 1 Gz, there is a normal upright situation with less parasympathetic modulation of heart rate compared to supine. This effect is augmented during 1.8 Gz-conditions due to a suppressed parasympathetic control of heart rate in the upright posture. Alternatively, at 0 Gz, increased parasympathetic control in standing position eliminates differences in cardiac chronotropy compared to supine.

Adult↗

PubMed2005

Cardiovascular function and basics of physiology in microgravity.

Space exploration is a dream of mankind. However, this intriguing environment is not without risks. Life, and the human body, has developed all over evolution in the constant presence of gravity, especially from the moment on when living creatures left the ocean. When this gravitational force is no longer acting on the body, drastic changes occur. Some of these changes occur immediately, others progress only slowly. In the past 40 years of human space flight (first orbital flight by Yuri Gagarin on 12 April, 1961) several hazards for the human body have been identified. Bone mineral density is lost, muscle atrophy and cardiovascular deconditioning occur; pulmonary function, fluid regulating systems of the body, the sensory and the balance system are all disturbed by the lack of gravity. These changes in human physiology have to be reversed again when astronauts return to earth. This can cause adaptation problems, especially after long-duration space flights. Also the reaction of human physiology to radiation in space poses a huge risk at this moment. In this review the accent will be on cardiovascular function in space: how normal function is modified to reach a new equilibrium in space after short- and long-duration exposure to microgravity. In order to make long-duration space flight possible the mechanisms of this physiological adaptation must be understood to full extent. Only with this knowledge, effective countermeasures can be developed.

Adaptation, Physiological↗

PubMed2004

Different evolutions in heart rate variability after heart transplantation: 10-year follow-up.

BACKGROUND: After heart transplantation, the donor heart is extrinsically denervated. No input of sympathetic or vagal nerves can influence the heart rate, resulting in a flat power spectrum of the beat-to-beat variability. The occurrence and the significance of reinnervation remain controversial. METHODS AND RESULTS: We monitored the evolution of heart rate variability (HRV) after heart transplantation, starting from a few weeks postoperatively up to 10 years after surgery. Twenty-four-hour Holter recordings of 216 heart-transplant patients were analyzed using time and frequency domain analysis of HRV. Analysis of all data revealed an increase in 24-hour and night-time total power starting from 2 years after transplantation. Low-frequency oscillations calculated over the total 24 hours, day- and nighttime increased significantly starting from year 4 and onward (year 4-8: P < 0.005). No evolution was found in high-frequency power. Subgroup analysis revealed a group with a clear spectral component (n = 16), a group with a small component (n = 124), and a group with a flat spectrum (n = 76). Only the first group revealed an evolution in both high- and low-frequency power. CONCLUSION: These results indicate three different types of evolution in HRV, with reinnervating patterns present in only a minority of the patients. The vast majority of the patients show no signs of reinnervation.

Blood Pressure↗

PubMed2004

HICOPS: human interface computer program in space.

BACKGROUND: During long experimental set ups, a protocol book usually guides cosmonauts. This is not very easy to work with in microgravity conditions and is not very efficient. For the cardiovascular physiology experiment CARDIOCOG during the Belgian Soyuz Mission (Odissea, November 2002) we developed a software program that guided the cosmonauts through the experiment. The software was developed in LabVIEW, thoroughly tested by CNES and the Russian space authorities and transported to the ISS as a stand-alone application. An adapted version was used during the Spanish Cervantes Mission in October 2003. RESULTS: This program provided several advantages: (1) error procedures could be easily dealt with in using the program's incorporated error structure; (2) the experimental sequences were easy to follow for the cosmonauts; (3) the experimental duration was exactly the same for all repetitions of the experiment, since the program imposed the timing; (4) after the flight, we were able to reconstruct all sequences of the experiment using a log-file that was automatically created during the different steps of the experiment; and (5) we were able to impose exact breathing frequencies to the cosmonauts using a visual aid. CONCLUSION: Less training was necessary for the cosmonauts to learn the experiment. Reconstruction of the experiment timing was easy. Exact breathing frequencies were obtained at each repetition. The program HICOPS worked to the overall satisfaction of the cosmonauts and they preferred working with HICOPS instead of with paper flow sheets. Data for the cardiovascular experiment during both missions were obtained in a standardised way.

Aerospace Medicine↗

PubMed2004

Heart rate and heart rate variability in chicken embryos at the end of incubation.

Our immediate goal was to study heart rate variability (HRV) in chicken embryos in the egg. Instantaneous heart rate data were needed for this purpose, and accordingly an ECG recording method in the egg was developed. The aim of this work was to test the hypothesis that autonomic nervous cardiac modulation, as shown from HRV parameters, is present at the end of development and that it reaches a constant value during the last days of incubation. Embryonic chicken heart rate was obtained at the final incubation period (days 19 and 20) from ECG recordings. Tachograms were computed and time- and frequency-domain indices of HRV were determined. No significant differences were found between HRV indices from day 19 and day 20. The power spectra extended in two frequency bands with centre frequency around 0.6-0.7 Hz (low frequency (LF) component), and another around 1.2-1.5 Hz (high frequency (HF) component); the latter was shown to reflect respiratory sinus arrhythmia. A relation between mean RR interval and some HRV parameters (rMSSD, pNN5 and HF power) was shown. HRV results obtained from embryonic chickens, showed the presence of modulation of cardiovascular function by the autonomic nervous system. The results suggested that sympathetic and parasympathetic activities have already reached a constant level at day 19 of incubation. High frequency oscillations (0.78-2.5 Hz) were detected and are considered to reflect respiratory sinus arrhythmia.

Animals↗

PubMed2003

Heart rate variability in athletes.

This review examines the influence on heart rate variability (HRV) indices in athletes from training status, different types of exercise training, sex and ageing, presented from both cross-sectional and longitudinal studies. The predictability of HRV in over-training, athletic condition and athletic performance is also included. Finally, some recommendations concerning the application of HRV methods in athletes are made.The cardiovascular system is mostly controlled by autonomic regulation through the activity of sympathetic and parasympathetic pathways of the autonomic nervous system. Analysis of HRV permits insight in this control mechanism. It can easily be determined from ECG recordings, resulting in time series (RR-intervals) that are usually analysed in time and frequency domains. As a first approach, it can be assumed that power in different frequency bands corresponds to activity of sympathetic (0.04-0.15 Hz) and parasympathetic (0.15-0.4 Hz) nerves. However, other mechanisms (and feedback loops) are also at work, especially in the low frequency band. During dynamic exercise, it is generally assumed that heart rate increases due to both a parasympathetic withdrawal and an augmented sympathetic activity. However, because some authors disagree with the former statement and the fact that during exercise there is also a technical problem related to the non-stationary signals, a critical look at interpretation of results is needed. It is strongly suggested that, when presenting reports on HRV studies related to exercise physiology in general or concerned with athletes, a detailed description should be provided on analysis methods, as well as concerning population, and training schedule, intensity and duration. Most studies concern relatively small numbers of study participants, diminishing the power of statistics. Therefore, multicentre studies would be preferable. In order to further develop this fascinating research field, we advocate prospective, randomised, controlled, long-term studies using validated measurement methods. Finally, there is a strong need for basic research on the nature of the control and regulating mechanism exerted by the autonomic nervous system on cardiovascular function in athletes, preferably with a multidisciplinary approach between cardiologists, exercise physiologists, pulmonary physiologists, coaches and biomedical engineers.

Autonomic Nervous System↗

PubMed2002

Association between restoration of autonomic modulation in the native sinus node and hemodynamic improvement after cardiac transplantation.

BACKGROUND: Little is known about the autonomic control of the native sinus node (NSN) after heart transplantation because its electrical activity is difficult to detect with skin electrodes. METHODS AND RESULTS: The intracardiac electrogram of the NSN and the donor heart electrocardiogram were measured simultaneously. A total of 351 recordings of 107 heart transplant patients (age 53.6+/-12.3 years) were obtained up to 1 year after transplantation. In a subgroup of 41 patients, consecutive recordings were made. Eleven recordings of heart failure patients (age 56.2+/-6.5 years) awaiting cardiac transplantation were used as controls. To examine a relationship between autonomic indices of the NSN and hemodynamics of the donor heart, intracardiac pressures and cardiac output were recorded in the same session. Heart rate variability (HRV) parameters in time and frequency domain of the NSN showed a significant increase starting at 6 months after transplantation, whereas heart rate of the NSN tended to decrease. Heart rate and HRV parameters remained constant over the first year in the donor heart. Higher values of low-frequency and high-frequency powers in the NSN were associated with lower values of right ventricular, pulmonary artery, and mean atrial pressure and cardiac output. Recordings of patients with rejection could not be distinguished from those without rejection based on the spectral content of HRV of either the NSN or the donor heart. CONCLUSIONS: These data suggest a restoration of autonomic modulation of the NSN. This restoration is associated with hemodynamic improvement of the donor heart.

Autonomic Nervous System↗

PubMed2002

Cardiovascular autonomic function in conscious rats: a novel approach to facilitate stationary conditions.

BACKGROUND: An experimental setting and software were developed to evaluate cardiovascular autonomic function in conscious rats. A restrained approach was used, which, upon proper habituation, induced little or no stress in the rats and limited motion artifacts. METHODS: The ECG and arterial blood pressure were recorded. Time- and frequency-domain indices of heart rate variability (HRV) and blood pressure variability (BPV) were calculated. The spontaneous baroreflex sensitivity (spBRS) was estimated using the method of statistical dependence. RESULTS: The power spectra clearly concentrated in a frequency band with center frequency around 0.4 Hz, the low frequency (LF) component, and one at the respiratory frequency at 1.5 Hz, the high frequency (HF) component. In baseline conditions, a direct association existed between mean R-R and especially HRV parameters denoting vagal modulation such as rMSSD, pNN5, and HF power. Beta-adrenergic blockade by propranolol diminished basal heart rate. Vagal indices increased while there was an exclusive decrease in the low frequency band of HRV. Alpha-adrenergic blockade with phentolamine produced a depressor response with tachycardia, and a clear decrease in the LF component of BPV. Both the LF and HF component in the HRV spectrum were virtually absent. Cholinergic blockade with atropine did not significantly alter BP but induced a clear tachycardia with decreased vagal indices. The HF component of HRV was completely abolished and the LF band was reduced. CONCLUSIONS: Both alpha- and beta-adrenergic blockade left spBRS virtually unaltered, while cholinergic blockade profoundly diminished spBRS. Spectral fluctuations of beta-sympathetic tone were restricted to the LF range of HRV, while the HF respiratory component represented vagal modulation. The alpha-sympathetic system played a dominant role in the LF oscillations of BPV. A role of the vagus in the HF oscillations of BPV in the rat is questioned. The baroreflex depended mainly on changes in vagal activity.

Adrenergic alpha-Antagonists↗

PubMedDate not supplied

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. 2. In 13 conscious rats, heart rate and aortic blood pressure were measured continuously before, during and after autonomic blockade with atropine, phentolamine and propranolol. Non-linear scaling properties were studied using 1/f slope, fractal dimension and long- and short-term correlation. Non-linear complexity was described with correlation dimension, Lyapunov exponent and approximate entropy. Non-linear indices were compared with linear time and frequency domain indices. 3. Beta-adrenoceptor blockade did not alter the non-linear characteristics of HRV and BPV, although low-frequency power of HRV was depressed. Alpha-adrenoceptor blockade decreased the scaling behaviour of HRV, whereas cholinergic blockade decreased the complexity of the non-linear system of HRV. For BPV, the scaling behaviour was increased during alpha-adrenoceptor blockade and the complexity was increased during cholinergic blockade. The linear indices of HRV and BPV were decreased. 4. The present results indicate that the beta-adrenoceptor system has little involvement in the generation of non-linear HRV and BPV in rats. 5. Alpha-adrenoceptor blockade mostly influenced the scaling properties of the time series, whereas cholinergic blockade induced changes in the complexity measures. 6. The absence of the baroreflex mechanism can trigger a compensatory feed-forward system increasing the complexity of BPV.

Adrenergic alpha-Antagonists↗