Biomedical subjects

Bart Verheyden

Publications and source records attributed to Bart Verheyden.

9 recordsLinked to original sources

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

RNA extraction for quantitative enterovirus RT-PCR: comparison of three methods.

Quantification of virus-like RNA sequences in biological fluids, like serum and cerebrospinal fluid, requires an RNA extraction method that is both reproducible and fast. Three RNA extraction methods were tested on enteroviruses: (1) the acid guanidine thiocyanate-phenol/chloroform (AGPC) method; (2) a method based on differential precipitation of the RNA and (3) a 'bind-wash-elute' system based on silica-gel membrane binding. The latter two methods yielded a comparable detection limit as measured by RT-PCR ELISA. The detection limit for the AGPC method was 10 times higher. The relative standard deviation for the bind-wash-elute method (3%) was superior to that of the other methods tested (both 20%) and provides a reliable and fast method to extract (viral) RNA from biological fluids for quantification by RT-PCR.

Enterovirus↗

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↗