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Henrik Jensen

Publications and source records attributed to Henrik Jensen.

At least 19 recordsLinked to original sources
PubMed2005

Dynamic protein adsorption in microchannels by "stop-flow" and continuous flow.

This work addresses two ways of loading proteins on microchannel surfaces for immunoassay applications: the "stop-flow" and the continuous flow processes. The "stop-flow" method consists of successive static incubation periods where the bulk solution depletes upon the adsorption process. In the present paper, a multi-step "stop-flow" protein coating is studied and compared to a coating under continuous flow conditions. For the "stop-flow", a non-dimensional parameter is here introduced, indicating the adsorbing capacity of the system, by which it is possible to calculate the number of loads necessary to reach the optimum coverage. For the continuous flow, the effects on the adsorption of the kinetic rates, flow velocity and wall capacity have been considered. This study shows the importance of a careful choice of the fluid velocity to minimise the sample waste. For diffusion controlled and kinetics controlled processes, two flow velocity criteria are provided in order to obtain the best possible coverage, with the same amount of sample as with the "stop-flow".

Adsorption↗
PubMed2005

Childhood mortality after oral polio immunisation campaign in Guinea-Bissau.

Though previous studies have suggested a non-specific beneficial effect of oral polio vaccine (OPV), there has been no evaluation of the mortality impact of national polio immunization days. On the other hand, studies examining the effect of OPV and diphtheria-tetanus-pertussis (DTP) vaccines, which are usually administered together in routine immunisation programmes in low-income countries, have found no beneficial or even a negative effect on infant survival. In 1998, we used the opportunity of two national immunisation days to examine the impact of OPV administered alone on survival for the 6103 children less than 5 years of age in the Bandim Health Project's study area in Guinea-Bissau. Survival was ascertained through regular surveillance from March 1998 until the beginning of the war on June 7, 1998, the end of 1998, or the end of 1999, respectively. The child register was linked with a register for the only paediatric ward in Bissau to determine the risk of hospitalisations. Among children under 5 years of age, 82% had received 1 or 2 doses of polio vaccines during the campaign. Though polio vaccination during the campaign was associated with slightly lower mortality, this difference was not significant for all children under 5 years of age (mortality ratio (MR)=0.46 (0.18-1.15)). However, oral polio vaccination was associated with a beneficial effect for children under 6 months of age at the time of the campaign, the mortality ratio being 0.09 (95% CI 0.01-0.85) in the 3 months before the war controlling for significant background factors, including routine immunizations, antenatal consultations, and arm circumference. The polio-vaccinated children aged 0-5 months had fewer hospitalisations than children who had not been polio vaccinated (RR=0.27 (0.10-0.76)). With longer follow-up to December 1998 or December 1999, the difference in mortality gradually disappeared, the MR for polio-vaccinated children being 0.61 (0.32-1.14) and 0.83 (0.51-1.34), respectively. Among children aged 6-59 months of age, measles vaccine was associated with a 56% reduction in mortality (MR=0.44 (0.28-0.69)) and no effect of oral polio vaccine was measurable in this age group. The effect of polio vaccine among children less than 6 months of age could be due to selection bias but might also represent a non-specific beneficial immune stimulation and there is nothing to suggest that OPV might have a negative effect on infant survival. Studies of the possible non-specific effects of oral polio vaccine are warranted before OPV is withdrawn.

Adolescent↗
PubMed2005

Acute lower respiratory tract infections and respiratory syncytial virus in infants in Guinea-Bissau: a beneficial effect of BCG vaccination for girls community based case-control study.

Among measles unvaccinated infants in Guinea-Bissau, we tested whether case infants with acute lower respiratory tract infection (ALRI), especially ALRI caused by respiratory syncytial virus (RSV), were more likely to be Bacille Calmette Guerin (BCG)-unvaccinated and to have no scar after BCG vaccination than were control infants without symptoms of ALRI. Three hundred and eighty-six case infants with ALRI were identified at a paediatric clinic (N=84), a health centre (N=82), and in a community morbidity surveillance system (N=220). Control infants were matched on sex, age, and district and were also measles unvaccinated. In ALRI case infants, the adjusted OR of being BCG unvaccinated was 2.87 (1.31-6.32), 1.72 (0.48-6.19) in boys and 4.45 (1.48-13.4) in girls. Among BCG vaccinated ALRI case infants, the adjusted OR of having no BCG scar was 1.54 (0.86-2.75), 0.93 (0.45-1.91) in boys and 2.70 (1.21-6.02) in girls. In ALRI case infants with RSV infection, similar trends were observed. BCG vaccination may have a non-targeted protective effect against ALRI, the effect being most marked in girls.

BCG Vaccine↗
PubMed2005

Numerical simulation of two-phase partition chromatography in microchannels for moderated log P measurements.

A finite element simulation has been used in order to study the partition chromatography process of one species between an aqueous mobile phase and an organic stationary phase located at the bottom of a rectangular microchannel. The transient model incorporates convection--diffusion of the species in the water phase coupled to the diffusion in the stationary organic phase by the way of the partition kinetics at the interface. The time evolution of the injected species concentration is analyzed versus the velocity of the mobile phase, the detecting position and the thickness of the stationary phase. The comparison of simulation results with both experimental data and analytical model confirm its validity. These simulations show that thin channels can be used to measure log P of molecules from their retention time. Finally, we have shown how the sample velocity can be optimized for a given geometry of the channel and diffusion coefficient of the species.

Calibration↗
PubMed2005

Routine vaccinations associated with divergent effects on female and male mortality at the paediatric ward in Bissau, Guinea-Bissau.

Several studies have suggested that routine childhood immunisations may have non-specific effects on mortality. To examine which disease categories might be affected, we investigated whether immunisation status had an impact on the case fatality for hospitalised children. Between 1990 and 1996, the Bandim Health Project maintained a register of all children from the study area hospitalised at the paediatric ward of the central hospital in Bissau, Guinea-Bissau. The study included 2079 hospitalised children aged 1.5-17 months coming from the Bandim study area. Among children whose vaccination card had been seen at admission, the case fatality ratio for measles-vaccinated children versus measles-unvaccinated children was 0.51 (0.27-0.98), the beneficial effect being significantly stronger for girls than for boys (test of interaction, p=0.050). The protective effect of measles vaccine remained unchanged when hospitalised measles cases were excluded from the analysis (0.49 (0.26-0.94)). The effect of measles vaccine was strongest for children with pneumonia (MR=0.28 (0.07-0.91)) and presumptive malaria (MR=0.40 (0.13-1.18)). For measles-vaccinated children, the female to male case fatality ratio was 0.54 (0.28-0.97). Among children having received diphtheria-tetanus-pertussis (DTP) and oral polio (OPV) as the last vaccines, girls had higher case fatality than boys, the mortality ratio being 1.63 (1.03-2.59). The female to male ratios were significantly inversed for DTP and OPV versus measles vaccine (test of interaction, p=0.003). These results remained unchanged if 1-month post-discharge deaths were included in the analysis, and in multivariate analyses controlling for determinants of mortality. In conclusion, measles vaccine was associated with reduced mortality from diseases other than measles, the beneficial effect being stronger for girls than for boys. On the other hand, DTP and OPV vaccine were associated with higher case fatality for girls than for boys. Understanding the divergent non-specific effects of common vaccines may contribute to better child survival in developing countries.

Confidence Intervals↗
PubMed2005

BCG vaccination scar associated with better childhood survival in Guinea-Bissau.

BACKGROUND: Recent studies have suggested that Bacille Calmette-Guerin (BCG) vaccination may have a non-specific beneficial effect on infant survival and that a BCG scar may be associated with lower child mortality. No study has previously examined the influence of BCG vaccination on cause of death. METHODS: Two cohorts (A and B) were used to describe the mortality pattern for children with and without BCG scar and to determine specific causes of death. In cohort A (n = 1813), BCG scar was assessed at 6 months of age and as previously described children with a BCG scar had lower mortality over the next 12 months than children with no BCG scar. In cohort B, 1617 children aged 3 months to 5 years of age had their BCG scar status assessed in a household-based survey and mortality was assessed during a 12-month period. Causes of death were determined by verbal autopsy (VA) and related to BCG scar status in a cause-specific hazard function. RESULTS: Controlling for background factors associated with mortality, there was lower mortality for children with a BCG scar than without in cohort B, the mortality ratio (MR) being 0.45 (95% CI 0.21-0.96). Exclusion of children exposed to TB did not have any impact on the result. In a combined analysis of cohorts A and B, the MR was 0.43 (95% CI 0.28-0.65) controlling for background factors. There were no large differences in distribution of the five major causes of death (malaria, pneumonia, acute diarrhoea, chronic diarrhoea, and meningitis/encephalitis) according to BCG scar status in the two cohorts. Having a BCG scar significantly reduced the risk of death from malaria [MR 0.32 (95% CI 0.13-0.76)]. CONCLUSIONS: A BCG scar is a marker of better survival among children in countries with high child mortality. BCG vaccination may affect the response to several major infections including malaria.

BCG Vaccine↗
PubMed2005

Salt removal during Off-Gel electrophoresis of protein samples.

The Off-Gel technology was recently described for protein fractionation in a solution placed on top of an immobilized pH gradient gel. In addition, this process was found to remove salts from the biological samples to analyze. This desalting effect is studied experimentally in a conductometric prototype cell. A simplified analytical model is developed to understand this process and a good agreement is found with the conductivity measurements. To illustrate the desalting of a biological sample, a 1 mg.mL(-1) solution of beta-lactoglobulin A in 0.1 M NaCl is subjected to electrophoresis in a single compartment Off-Gel cell. The analysis of the resulting sample by ESI-MS demonstrates the effective removal of salt. A finite element diffusion-migration model is also used to illustrate how the nonuniformity of the electric field in the cell, associated with the salt migration, can slow down the desalting process.

Electric Conductivity↗
PubMed2005

Pre-equilibrium capillary zone electrophoresis or frontal analysis: advantages of plateau peak conditions in affinity capillary electrophoresis.

The feasibility of using the affinity CE methodologies pre-equilibrium CZE and CE frontal analysis was tested on interaction systems exhibiting rapid on-and-off kinetics. Experimentally, the methodologies differ only with respect to the volume of sample introduced into the capillary. Pre-equilibrium CZE has been considered amendable to interactions with slow on-and-off kinetics only; however, it has recently been applied in studies of interactions with fast on-and-off kinetics. The effect of varying the sample volume introduced hydrodynamically into the capillary on the apparent degree of complexation was studied. For two different binding systems, the fraction of free analyte was found to be overestimated using pre-equilibrium CZE as compared to volumes providing plateau peak conditions as used with frontal analysis. Results indicate that frontal analysis conditions lead to more robust binding assays and thus more reliable data. The validity of data obtained by pre-equilibrium CZE may be low, thus the use of an experimental setup providing plateau peaks is highly recommended. It is suggested that the effect of altering the sample volume on the degree of binding should be investigated as part of method development and validation.

Benzoic Acid↗
PubMed2004

Protein adsorption in static microsystems: effect of the surface to volume ratio.

A numerical model for the adsorption kinetics of proteins on the walls of a microchannel has been developed using the finite element method (FEM) to address the coupling with diffusion phenomena in the restricted microchannel volume. Time evolutions of the concentration of one species are given, both in solution and on the microchannel walls. The model illustrates the adsorption limitation sometimes observed when the microdimensions of these systems induce a global depletion of the bulk solution. A new non-dimensional parameter is introduced to predict the final value of the coverage of any microsystem under static adsorption. A working curve and a criteria (h/K[Gamma](max) > 10) are provided in order to choose, for given adsorption characteristics, the value of the volume-to-surface ratio (i.e. the channel height h) avoiding depletion effects on the coverage (relative coverage greater than 90% of the theoretical one). Simulations were compared with confocal microscopy measurements of IgG antibody adsorption on the walls of a PET microchannel. The fit of the model to the experimental data show that the adsorption is under apparent kinetic control.

Adsorption↗
PubMed2004

Vaccination technique, PPD reaction and BCG scarring in a cohort of children born in Guinea-Bissau 2000-2002.

The rates of positive tuberculin skin test (TST) reactions and BCG scarring after BCG vaccination vary between studies and populations. Tuberculin reactivity and BCG scarring may be related to better child survival in low-income countries. We therefore studied determinants for TST reaction and scarring in Guinea-Bissau. In a cohort of children born in suburban Bissau from March 2000 to July 2002, we assessed a Mantoux test with Purified protein derivative (PPD) (SSI, 2 T.U.) at 2 (2689 children), 6 (N=2148) and 12 months (N=1638) of age, and BCG scar was assessed at 2 (N=2698) and 6 months (N=2225) of age. In a subgroup of the children the vaccination technique was monitored by direct observation of post-vaccination wheal and route of administration. Three different types of BCG vaccine supplied by the local Extended Programme on Immunization were used. At 6 months of age the rate of PPD reactors (>1mm) after BCG vaccination was 25% and the rate of scarring was 89%. One BCG strain was associated with fewer PPD reactors (OR=0.54 (0.31-0.91)) and BCG scars (OR=0.13 (0.05-0.37)) and larger post-vaccination wheals produced more PPD reactions (OR 1.21 (95% CI 1.02-1.43)) and BCG scars (OR 1.66 (1.24-2.21)). In the multivariable analyses of BCG-vaccinated children assessed at 6 months of age, monitoring of vaccination technique and type of BCG vaccine were important. This was not changed by control for other determinants, including sex, season, vaccination place, birthplace, ethnic group, low birth weight, place of residence, education and civil status of mother. We reason that vaccination technique and BCG strain are important for PPD reaction and scarring in response to BCG vaccination. Considering that these responses are associated with better infant survival, the importance of monitoring vaccination technique and of different BCG strains should be evaluated with respect to infant mortality.

BCG Vaccine↗
PubMed2004

Oral polio vaccination and low case fatality at the paediatric ward in Bissau, Guinea-Bissau.

Oral polio vaccine (OPV) and diphtheria-tetanus-pertussis (DTP) vaccines are given simultaneously in routine immunisation programmes in developing countries. It is therefore difficult to determine the separate effects of these vaccines on survival. We used the shortage of DTP vaccine in Bissau to examine the impact of OPV on the case fatality at the paediatric ward in Bissau. For 719 children less than 5 years of age whose vaccination card had been seen at admission and who had not yet received measles vaccine, having received OPV only was associated with a case fatality of 6% compared with 15% for children having received combined DTP and OPV vaccinations, the case fatality ratio (CFR) being 0.29 (95% confidence interval (CI) 0.11-0.77). Even if children fleeing the hospital were assumed to have died shortly after leaving the hospital, the case fatality would still be lower for children having received OPV only (CFR = 0.41; (95% CI 0.20-0.81)). The tendency was similar for children hospitalised with pneumonia, diarrhoea, and presumptive malaria. Control for background factors had no impact on the estimate. In areas with high mortality, OPV administered alone may have non-specific beneficial effects or DTP may have a negative effect for children who had received both DTP and OPV.

Adolescent↗
PubMed2004

A flexible sample introduction method for polymer microfluidic chips using a push/pull pressure pump.

A push/pull sample introduction method based on push/pull pressure flow for microfluidic systems (cross, double T and multichannel structures) is presented. This leads to well-defined and controllable sample plugs even when dealing with long channels. By tuning the relative push/pull pressure, it is shown that the size of the sample plug can effectively be controlled. Good signal reproducibility upon continued sample introduction and subsequent chip electrophoresis employing fluorescence detection is demonstrated for different chip geometries (i.e. short channels and long channels). Since the performance of the method is relatively insensitive to chip geometry, it is particularly useful for polymeric prototype microchips as tedious optimization is not required. Furthermore, the push/pull sample introduction is extended to multichannel chips thus demonstrating the possibilities of applying the methodology for realizing single chip high throughput sample analysis.

Equipment Design↗
PubMed2004

Passive conductivity detection for capillary electrophoresis.

A passive electrochemical detection principle that can be applied to capillary electrophoresis is presented. The separation electrical field is used to generate a potential difference between two electrodes located along the channel. For constant-current electrophoresis, the generated signal is proportional to the resistance of the solution passing between the two electrodes. Contrary to conductivity detectors that are ac driven and need to be decoupled from the separation field, the passive detection directly takes advantage of the separation field. The signal is simply measured by a high-impedance voltmeter. The detection concept has been validated by numerical simulations showing how the magnitude of the signal is related to the ratio between the electrode distance and the length of the sample plug. As a proof of the principle, this detection concept has been demonstrated by the electrophoretic separation of three alkali ions on a polymer microchip. Based on preliminary results, a detection limit of 20 microM and a dynamic range of up to 3 orders of magnitude have been achieved.

Journal Article↗