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Biomedical subjects

G Cornelissen

Publications and source records attributed to G Cornelissen.

At least 19 recordsLinked to original sources
PubMed2002

New insights into circadian aspects of health and disease.

Early awakening and early to bed as well as good conduct, thought, diet, interpersonal dealings and physical activity have been suggested for healthy life in Ayurveda. Circadian rhythms, coordinated in part by the parietal hypothalamic-pituitary and adrenal mechanisms, have been reported in almost all variables examined thus far, including the circulation. It is possible that all metabolic functions undergo circadian rhythms. It remains to be explored whether these rhythms may be optimized by Ayurvedic practices. The onsets of myocardial ischemia, unstable angina, acute myocardial infarction, sudden cardiac death, and strokes have been reported to exhibit a circadian variation, with increased frequency in the second quarter of the day. An increased physical and mental load caused by an attempt to prepare for the day may be important in triggering acute cardiovascular events. Depending on their timing, meditation (Ayurvedic practice), n-3 fatty acids, coenzyme Q10, beta-blockers and estrogens may have beneficial effects, whereas progestins and mental load may have adverse effects on heart rate and blood pressure variability, which may be expressed by different circadian patterns. Around the clock serial recordings of blood pressure and heart rate during usual activities and lifestyles may be recorded and may be analyzed by computer-implemented curve fitting to assess the about 24-hour (circadian) variation, among other rhythmic, chaotic, and trend components of the time structure (chronome) of these variables. The new disease risk syndrome circadian hyper-amplitude-tension (CHAT), a condition characterized by an excessive circadian amplitude of blood pressure, cannot be ascertained on the basis of single casual blood pressure measurements. The International Chronome Ecological Study of Heart Rate (and blood pressure) Variability in various ethnic groups aims at collecting further evidence regarding the role of blood pressure and heart rate variability in the pathogenesis of cardiovascular events, while also examining any role played by ethnicity and lifestyle-associated factors.

Blood Pressure↗
PubMed2001

A simple Tenax extraction method to determine the availability of sediment-sorbed organic compounds.

A simple method to determine the availability of sediment-sorbed organic contaminants was developed and validated. For 10 polycyclic aromatic hydrocarbons, 4 polychlorinated biphenyls, and 9 chlorobenzenes in 6 sediments, we measured the fraction extracted by Tenax in 6 and 30 h. These fractions were compared with the rapidly desorbing fractions determined by consecutive Tenax extraction. Extraction by Tenax for 30 h completely removed the rapidly desorbing fraction plus some part of the slowly desorbing fraction. The fraction removed after 30 h was about 1.4 times the rapidly desorbing fraction. The fraction extracted by Tenax after 6 h is about 0.5 times the rapidly desorbing fraction for chlorobenzenes (CBs)/polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). The rapidly desorbing fraction probably represents the fraction of sorbed organic compound that poses actual risks for transport to (ground) water and determines the uptake by organisms and that can be microbially degraded. Extraction by Tenax for 6 h provides an easy way to address these issues more accurately than does the measurement of total concentrations.

Adsorption↗
PubMed2001

The power of size. 1. Rate constants and equilibrium ratios for accumulation of organic substances related to octanol-water partition ratio and species weight.

Most of the thousands of substances and species that risk assessment has to deal with are not investigated empirically because of financial, practical, and ethical constraints. To facilitate extrapolation, we have developed a model for accumulation kinetics of organic substances as a function of the octanol-water partition ratio (Kow) of the chemical and the weight, lipid content, and trophic level of the species. The ecological parameters were obtained from a previous review on allometric regressions. The chemical parameters, that is, resistances that substances encounter in water and lipid layers of organisms, were calibrated on 1,939 rate constants for absorption from water for assimilation from food and for elimination. Their ratio was validated on 37 laboratory bioconcentration and biomagnification regressions and on 2,700 field bioaccumulation data. The rate constant for absorption increased with the hydrophobicity of the substances with a Kow up to about 1,000 and then leveled off, decreasing with the weight of the species. About 39% of the variation was explained by the model, while deviations of more than a factor of 5 were noted for labile, large, and less hydrophobic molecules as well as for algae, mollusks, and arthropods. The efficiency for assimilation of contaminants from food was determined mainly by the food digestibility and thus by the trophic level of the species. A distinction was made between substances that are stable, that is, with a minimum elimination only, and those that are labile, that is, with an excess elimination probably largely due to biotransformation. The rate constant for minimum elimination decreased with the hydrophobicity of the substance and the weight of the species. About 70% of the variation was explained by the model, while deviations of more than a factor of 5 were noted for algae, terrestrial plants, and benthic animals. Labile substances were eliminated faster than isolipophilic stable compounds, but differences in laboratory elimination and accumulation were small compared with those in field accumulation. Excess elimination by vertebrates was faster than by invertebrates. Differences between terrestrial and aquatic species were attributed to water turnover rates, whereas differences between trophic levels were due to the food digestibility. Food web accumulation, expressed as organism-organic solids and organism-food concentrations ratios could be largely explained by ecological variables only. The model is believed to facilitate various types of scientific interpretation as well as environmental risk assessment.

Absorption↗
PubMed2000

Slow desorption of PCBs and chlorobenzenes from soils and sediments: relations with sorbent and sorbate characteristics.

The kinetics of slow desorption were studied for four soils and four sediments with widely varying characteristics [organic carbon (OC) content 0.5-50%, organic matter (OM) aromatic content (7-37%)] for three chlorobenzenes and five polychlorinated biphenyls (PCBs). Slowly and very slowly desorbing fractions ranged from 1 to 50% (slow) and 3 to 40% (very slow) of the total amount sorbed, and were observed for all compounds and all soils and sediments. In spite of the wide variations in sorbate K(OW) (factor 1000) and sorbent characteristics, the rate constants of slow (k(slow), around 10(-3) h(-1)) and very slow (k(very slow), 10(-5)-10(-4) h(-1)) desorption appeared to be rather constant among the sorbates and sorbents (both within a factor of 5). There was a good correlation (r(2) above 0.9) between the distribution over the slow, very slow and rapid sediment fractions and log K(OC), indicating that sorbate hydrophobicity may be important for this distribution. No correlation could be found between sorbent characteristics [OC, N, and O in the organic matter, polarity index C/(N+O), OC aromaticity as determined by CP-MAS (13)C-NMR] and slow desorption parameters (slowly/very slowly desorbing fractions+corresponding rate constants). The absence of (1) a correlation between k(slow) and k(very slow), respectively, and OC content, and (2) the narrow range of k(slow) and k(very slow) values, indicates that intra-OM diffusion is not the mechanism of slow or very slow desorption, because on the basis of this mechanism it would be expected that increasing OC content would lead to longer diffusion pathlengths and, consequently, to smaller rate constants. In addition, it was tested whether differential scanning calorimetry would reveal a glass transition in the soils/sediments. In spite of the sensitivity of the equipment used (changes in heat flow in the micro-Watt range were measurable), a glass transition was not observed. This means that activation enthalpies of slow desorption can be calculated from desorption measurements at various temperatures. In the present study these values ranged from 60 to 100 kJ/mol among the various soils and sediments studied.

Journal Article↗
PubMed2000

The cosmos and CHAT, prompting blood pressure and heart rate monitoring for Dérer's week.

BACKGROUND: The effects of natural environmental factors upon health, documented in Minnesota, support the proposition of Bratislava's champions of the cosmos and of the biological week, gauged via circaseptan rhythms by the late Ladislav Dérer, whose "macro-rhythm" lasted "most frequently about 6 days". MAIN PURPOSE: To introduce 7-day monitoring of blood pressure and heart rate into routine practice. STARTING POINTS AND METHODS: Cosinor analysis on 7-day series determines (conventionally ignored) consistent blood pressure overswinging, i.e., circadian hyper-amplitude-tension (CHAT), a disease risk syndrome, whether it is associated with a normal average blood pressure or a high blood pressure. RESULTS: Summary of information understandable by the general population on the dynamics of blood pressure. CONCLUSIONS AND MEANING FOR PRACTICE AND THEORY: Space weather reports may prompt preventive measures. Caution dictates in any event monitoring blood pressure and heart rate for 7 days to attempt to prevent strokes, rather than to ignore the greatest yet detectable risk of catastrophic vascular disease, CHAT, a risk greater than old age or high blood pressure. (Tab. 1, Fig. 3, Ref. 31.)

Blood Pressure Monitoring, Ambulatory↗
PubMed1999

Blood pressure and heart rate rhythmicity: differential effects of late pregnancy.

Arterial blood pressure (BP) and heart rate (HR) of 31 hospitalized pregnant women at low risk of hypertension were automatically monitored for 48 h at 15-min intervals. Each of the recorded 56 data series for systolic arterial pressure (SAP), diastolic arterial pressure (DAP), and HR was chronobiologically assessed by linear-nonlinear rhythmometry. The rhythm-adjusted mean (MESOR), circadian amplitude, circadian acrophase, and best-fitting period were grouped by pregnancy trimester and further subjected to analysis of variance. BP MESOR remained unaltered, whereas HR MESOR increased significantly in middle and late pregnancy. Ultradian rhythms, with an amplitude higher than that of the circadian rhythm, were found in 25% of the SAP records in the second and third trimester. Such ultradian rhythms were not detected in the simultaneously recorded HR. Finally, the group BP and HR circadian acrophases coincided in the first trimester, but were significantly apart in mid and late pregnancy. These observations support the notion that the coordination of BP and HR rhythmicity involves different physiological mechanisms. Analysis of the individual variability in the chronobiological end points (based on the records of nine women monitored in each pregnancy trimester) revealed that only the BP MESOR was well reproducible in the course of pregnancy and may be useful in early diagnosis of gestational hypertension.

Activity Cycles↗
PubMed1999

Circadian rhythm of gene expression of myocardial contractile protein, left ventricular pressure and contractility.

Objective. A number of cardiovascular variables exhibit a circadian rhythm. Whether myocardial contractile response and gene expression of the contractile protein also show changes with a similar period was here investigated. Method. Circadian variabilities in the left ventricular developed pressure (LVP) and contractility (LV dp/dt max) were measured in 24 Sprague-Dawley rats by directly left ventricular catheterizing and compared with changes in the gene expression of alpha-myosin heavy chain (alpha-MHC) in myocytes obtained from the same animals by dot blotting analysis. Results. A circadian rhythm was seen in the variability of LVP (P<0.001), LV dp/dt max (P<0.001) and the biochemically measured expression of the alpha-MHC gene (P<0.01). As compared to the amplitude of the rhythm in alpha-MHC gene expression, the amplitude of the contractility rhythm was large (P<0.01) and the circadian amplitude of the LVP (P<0.001) was the largest, representing perhaps a composite of intracardiac plus any extracardiac contributions. Conclusion. One of factors determining the circadian rhythm of myocardial contractile function is alpha-MHC gene expression level.

Animals↗
PubMed1997

Age, gender and fractal scaling in heart rate variability.

1. The fractal scaling of heart rate variability, gauged by the correlation dimension (CD), is hypothesized to be characterized by a time structure (chronome), which in health shows differences as a function of gender and age. 2. From 24 h Holter records of 44 clinically healthy male subjects in four age groups (5-10, 20-25, 40-45 and 60-65 years; n = 11 in each group), 500 s sections at 4 h intervals for 24 h were analysed for smoothed R-R intervals sampled at 4 Hz. Using an algorithm modified from Grassberger and Procaccia (Physica D 1983; 9: 189-208), the correlation integral was estimated for embedding dimensions from 1 to 20 with a 1.0 s time lag for each section. Nightly (02.00 hours-06.00 hours) ECG records were similarly analysed in 72 additional clinically healthy subjects of both genders, 5-70 years of age. The single cosinor assessed the circadian characteristics; one- and two-way analyses of variance and linear regression were used to examine changes as a function of gender and age. 3. The 24 h average of CD is largest in the 20-25-year-old men and decreases with age there-after (P < 0.05). These changes apply in particular to the nightly CD values, which are higher in female than in male subjects (P < 0.001). Increasing age is associated with a decrease in the amplitude and an advance in the phase of the circadian rhythm in CD (P < 0.05). 4. A chaotic end-point from fractal scaling, yielding a non-linear index, such as the correlation integral, undergoes a circadian rhythm and changes with gender and age. This assessment in the chronome represents an added diagnostic tool in cardiology, and provides new end-points for the study of coherence among internal variables of autonomic mechanisms and of influences by external environmental variables upon them.

Adolescent↗
PubMed1997

Meta-analyzed heart rate variability, exposure to geomagnetic storms, and the risk of ischemic heart disease.

The aim was to examine how heart rate variability (HRV) relates to the risk of ischemic heart disease (IHD) and may provide a means to assess effects of exposure to geomagnetic storms. In Stockholm, the 24-hour SD of hourly estimates of heart rate (HR) were obtained by Holter monitoring from 50 men who had had an acute myocardial infarction or had angina pectoris and compared to that of 50 clinically healthy men of similar age. In Tokyo, the HR 121 normotensives and 176 treated hypertensives was monitored. The incidence of IHD was recorded prospectively for 6 years. These results are aligned with those of a retrospective analysis of archived data on all crews of the Soyuz spacecraft for 1990-1994 focused on ECG from cosmonauts (47 male and 2 female) at times corresponding to geomagnetic storms. The results clearly indicate a decrease in HRV in association with IHD (20.5%, p=0.002 in Stockholm, 20.0%, p=0.04 in Tokyo). By comparison, the about 30% decrease (p=0.041) in rms SD of HR in cosmonauts studied during a geomagnetic storm as compared to cosmonauts monitored on quiet days adds supportive evidence to the proposition that exposure to geomagnetic disturbances increases cardiovascular disease risk.

Adult↗
PubMed1996

An energy budget model for the biodegradation and cometabolism of organic substances.

Expression of bacterial cellular processes (maintenance, heat loss, growth, cometabolism and substrate degradation) into energy units yielded surprisingly realistic figures on the bacterial energy balance in spite of the severe approximations and assumptions that had to be made. For studies without cometabolism, 47-83% of the calculated amount of available energy was consumed by growth; for maintenance + heat loss this percentage was 20-35%. When involved, cometabolism consumed 7-13% of the total energy budget. Overall, 67-118% of the calculated amount of energy generated was spent on these energy-consuming processes. This shows that the model is internally consistent. Relationships between growth and cometabolism may offer predictions of persistence of cometabolizable chemicals under different conditions. The energy budget model as presented provides a starting point for the development of such relationships. In addition, the method is used to explain threshold concentrations, below which normally degradable compounds are not degraded.

Bacteria↗
PubMed1996

Resonance of about-weekly human heart rate rhythm with solar activity change.

In several human adults, certain solar activity rhythms may influence an about 7-day rhythm in heart rate. When no about-weekly feature was found in the rate of change in sunspot area, a measure of solar activity, the double amplitude of a circadian heart rate rhythm, approximated by the fit of a 7-day cosine curve, was lower, as was heart rate corresponds to about-weekly features in solar activity and/or relates to a sunspot cycle.

Adult↗
PubMed1996

[From Pavlov's recording of time and conditioned reflexes to the chronophysiology of human nutrition].

That I. P. Pavlov understood how important to record the time factor allowed him to anticipate the chronobiological approach in physiology. As compared to the conditioned reflexes, the body's biological rhythms appeared to have a deeper basis - chronomes coded in the genes. The authors comparatively characterize the homeostatic approach used by I. P. Pavlov and the chronobiological approach proposed by F. Halberg both for biology and medicine.

Animals↗
PubMed1994

From circadians of the fifties to chronomes in vitro as in vivo.

In a recent review of cellular mechanisms of entrainment, an ocular circadian rhythm of Bulla was reported (1). The isolated retina of this marine mollusk is described to contain a circadian oscillator. A glance at the spontaneous impulse frequency from eyes recorded in darkness at 15 degrees C suggests lower-frequency modulations of the about 24-h rhythm and prompts the quantitative assessment of the broader time structure, the chronome, in this extensively used model of a budding neurochronophysiology. The cultured retina of mollusks is interpreted by the original authors as descriptive of similar cellular mechanisms that may underlie mammalian as well as molluscan physiology. We report here the rhythmometric analysis of the original data by Block et al. (2), taken from Figure 2 of the article by Colwell et al. (1), resolved by computer just as the microscope resolves cellular structure. The results are further compared with those obtained on data kindly provided by Stephan Michel on another retina of Bulla. The findings of multiple chronome components (beyond the circadian system) are placed into the broader context of cell biophysics and its implications for biomedicine within the scope of an international chronome endeavor.

Action Potentials↗
PubMed1993

Rhythms and blood pressure.

The time (chronos) structure of life (bios) is the topic of a computer-implemented science (logos), chronobiology. Chronobiologic methods for resolving physiologic time structure provide a more reliable mean, the MESOR, and other parametric dynamic measures of blood pressure variability. The amplitude is a measure of predictable extent of change and the acrophase a measure of timing of overall high values within each cycle of the rhythmic function. Such chronobiologic endpoints are often more sensitive than the mean for separating groups at different risk of developing high blood pressure. About 24-h (circadian) rhythms account for a sizeable part of predictable variability in blood pressure. Methodology to assess the characteristics of circadian blood pressure rhythms also provides time-varying reference limits for the interpretation of single measurements. Deviant blood pressures can be quantified by reference to such circadian-stage-dependent limits, derived from the automatically monitored blood pressure profiles of healthy peer groups. Excess or deficit in blood pressure can also be assessed as a hypertensive or hypotensive index integrated over 24 h. Chronobiologic monitoring has wide uses in practice as well as research, whether it is carried out by self- or automatic measurements, once the data are analyzed by appropriate computer methods that are now readily available.

Adult↗
PubMed1993

[24-hour monitoring of blood pressure in patients with essential hypertension].

The aim of the study was to determine the efficiency of enalapril therapy during 24-hours blood pressure monitoring. A group of healthy subjects (C, n = 11), a group of patients with essential hypertension without therapy (EH, n = 9) and a group of patients with essential hypertension II (WHO) treated with enalapril (Acepril Lachema) in once a day doses (13.0 +/- 2.1 mg per kg) during at least 10 months (EH A, n = 8). In all groups of patients and healthy subjects 24-hours blood pressure measurement was provided using Accutracker II equipment. The mean values of systolic (SBP) and diastolic blood pressure (DBP) from 24-hours measurement (+/- SD) were in the group of healthy subjects C 121.38 +/- 10.49/74.79 +/- 7.88 mmHg, in the group EH 146.58 +/- 12.20/88.0 +/- 8.97 mmHg, in the group EH A 127.38 +/- 8.36/74.71 +/- 6.08 mmHg. The differences between the maximum and minimum mean blood pressure values during 24 hours (SBP/DBP) were in the group C 33/27 mmHg, EH 37/29 mmHg, EH A 29/21 mmHg. The smaller difference in SBP and DBP in EH A patients was significant in comparison to C and EH (t-test, p < 0.05). Cosinor analysis proved the results. From our results we can conclude that the Acepril therapy decreases blood pressure more during the day-hours then during night and it is preferable in connection to the risk of night hypotension with hypoxia.

Blood Pressure↗