Biomedical subjects

Frank Beckers

Publications and source records attributed to Frank Beckers.

12 recordsLinked to original sources

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

MsbA is not required for phospholipid transport in Neisseria meningitidis.

The outer membrane of Gram-negative bacteria contains phospholipids and lipopolysaccharide (LPS) in the inner and outer leaflet, respectively. Little is known about the transport of the phospholipids from their site of synthesis to the outer membrane. The inner membrane protein MsbA of Escherichia coli, which is involved in the transport of LPS across the inner membrane, has been reported to be involved in phospholipid transport as well. Here, we have reported the construction and the characterization of a Neisseria meningitidis msbA mutant. The mutant was viable, and it showed a retarded growth phenotype and contained very low amounts of LPS. However, it produced an outer membrane, demonstrating that phospholipid transport was not affected by the mutation. Notably, higher amounts of phospholipids were produced in the msbA mutant than in its isogenic parental strain, provided that capsular biosynthesis was also disrupted. Although these results confirmed that MsbA functions in LPS transport, they also demonstrated that it is not required for phospholipid transport, at least not in N. meningitidis.

ATP-Binding Cassette Transporters↗

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

Lipopolysaccharide transport to the bacterial outer membrane in spheroplasts.

The mechanism of lipopolysaccharide (LPS) transport in Gram-negative bacteria from the inner membrane to the outer membrane is largely unknown. Here, we investigated the possibility that LPS transport proceeds via a soluble intermediate associated with a periplasmic chaperone analogous to the Lol-dependent transport mechanism of lipoproteins. Whereas newly synthesized lipoproteins could be released from spheroplasts of Escherichia coli upon addition of a periplasmic extract containing LolA, de novo synthesized LPS was not released. We demonstrate that LPS synthesized de novo in spheroplasts co-fractionated with the outer membranes and that this co-fractionation was dependent on the presence in the spheroplasts of a functional MsbA protein, the protein responsible for the flip-flop of LPS across the inner membrane. The outer membrane localization of the LPS was confirmed by its modification by the outer membrane enzyme CrcA (PagP). We conclude that a substantial amount of LPS was translocated to the outer membrane in spheroplasts, suggesting that transport proceeds via contact sites between the two membranes. In contrast to LPS, de novo synthesized phospholipids were not transported to the outer membrane in spheroplasts. Apparently, LPS and phospholipids have different requirements for their transport to the outer membrane.

ATP-Binding Cassette Transporters↗

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↗

PubMed2004

Role of the pilot protein YscW in the biogenesis of the YscC secretin in Yersinia enterocolitica.

The YscC secretin is a major component of the type III protein secretion system of Yersinia enterocolitica and forms an oligomeric structure in the outer membrane. In a mutant lacking the outer membrane lipoprotein YscW, secretion is strongly reduced, and it has been proposed that YscW plays a role in the biogenesis of the secretin. To study the interaction between the secretin and this putative pilot protein, YscC and YscW were produced in trans in a Y. enterocolitica strain lacking all other components of the secretion machinery. YscW expression increased the yield of oligomeric YscC and was required for its outer membrane localization, confirming the function of YscW as a pilot protein. Whereas the pilot-binding site of other members of the secretin family has been identified in the C terminus, a truncated YscC derivative lacking the C-terminal 96 amino acid residues was functional and stabilized by YscW. Pulse-chase experiments revealed that approximately 30 min were required before YscC oligomerization was completed. In the absence of YscW, oligomerization was delayed and the yield of YscC oligomers was strongly reduced. An unlipidated form of the YscW protein was not functional, although it still interacted with the secretin and caused mislocalization of YscC even in the presence of wild-type YscW. Hence, YscW interacts with the unassembled YscC protein and facilitates efficient oligomerization, likely at the outer membrane.

Bacterial Outer Membrane Proteins↗

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

Pore formation and function of phosphoporin PhoE of Escherichia coli are determined by the core sugar moiety of lipopolysaccharide.

The lipid matrix of the outer membrane of Gram-negative bacteria is an asymmetric bilayer composed of a phospholipid inner leaflet and a lipopolysaccharide outer leaflet. Incorporated into this lipid matrix are, among other macromolecules, the porins, which have a sieve-like function for the transport or exclusion of hydrophilic substances. It is known that a reduced amount of porins is found in the outer membrane of rough mutants as compared with wild-type bacteria. This observation was discussed to be caused by a reduced number of insertion sites in the former. We performed electrical measurements on reconstituted planar bilayers composed of lipopolysaccharide on one side and a phospholipid mixture on the other side using lipopolysaccharide from various rough mutant strains of Salmonella enterica serovar Minnesota. We found that pore formation by PhoE trimers that were added to the phospholipid side of the bilayers increased with the increasing length of the lipopolysaccharide core sugar moiety. These results allow us to conclude that the length of the sugar moiety of lipopolysaccharide is the parameter governing pore formation and that no particular insertion sites are required. Furthermore, we found that the voltage gating of the porin channels is strongly dependent on the composition of the lipid matrix.

Escherichia coli Proteins↗

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↗