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Biomedical subjects

T Kenner

Publications and source records attributed to T Kenner.

At least 37 records · Page 2Linked to original sources
PubMed1990

Methods in clinical hemorheology: the continuous measurement of arterial blood density and blood sound speed in man.

Both blood density and sound speed are closely related to total protein concentration in blood and, as a consequence, to rheologically important parameters of blood. Two methods that permit continuous measurement of these properties, the mechanical oscillator technique and the new ultrasonic technique, were used for measuring blood protein concentration over a continuous period of time in a group of hemodialysis patients and in volunteers. It was seen that the concentration of the components of blood varies considerably. This variability is related to transport phenomena within as well as to the flow of masses across the cardiovascular compartment. From the continuous measurement of concentrations during hemodialysis treatment, relative changes in blood volume can be recorded in order to control the fluid balance of the patient. Rapid fluctuations at the macroscopic scale with periods of 5 to 30 seconds are due to heterogeneities at the microscopic scale and to the particular rheological behaviour of the red blood cells at the level of the capillaries and the small blood vessels. The amplitude of rapid oscillations increased up to 1.2% in terms of hematocrit values when there was rhythmic, spontaneous breathing at various frequencies. The measurement of concentrations at an accessible measuring site may be used to investigate the rheology of blood in the human microvasculature.

Blood Flow Velocity↗
PubMed1990

Factors involved in the pathogenesis of unexpected near miss events of infants (ALTE).

Near miss events or apparent life threatening events (ALTE) are considered preliminary stages of sudden infant death syndrome (SIDS). The current definition of near miss SIDS postulates that such an event happens unexpectedly and that no life threatening cause of disease can be detected. However in 32 of 34 observations of ALTE pathological changes actually could be identified by through investigations: 11 central nervous diseases, 10 respiratory tract disturbances, 5 metabolic abnormalities, 5 disturbances of the digestive tract and 1 cardiac disease. There were 22 morphologically manifested causes as opposed to 10 functional failures mainly respiratory control and oesophageal disturbances. Irrespective of the main diagnosis sleep apnea syndrome (SAS) could be detected in 17 of 28 infants combined with bradycardia in 5 cases, and oesophageal disturbances in 16 of 17 infants. Four babies later died, two of them suffered from carnitine deficiency and one from organic acidopathy. It is our conclusion that numerous, even banal causes of disease are able to trigger ALTE if there is a coincidence with phases of increased instability of vital regulatory mechanisms of autonomous centres in infants.

Brain Diseases↗
PubMed1989

Characterization of isoelectric subspecies of asialo-beta 2-glycoprotein I.

Isoelectric focusing of purified beta 2-glycoprotein I (beta 2-G-I) revealed five major bands with isoelectric points (pI) between 5.1 and 6.1. Neuraminidase treatment decreased the number of bands to two (pI 8.0 and 8.2). The two asialo subfractions of beta 2-G-I were purified by cation-exchange column chromatography. The more basic isoform II was found to have a higher content of lysine. Western-blot analysis of different plasma samples confirmed the heterogeneity of beta 2-G-I in plasma. Plasma treated with neuraminidase showed two bands irrespective of the number of isoforms as well as of the concentration in native plasma. This led us to the conclusion that human plasma beta 2-G-I consists of two isoproteins that are sialylated to different extents.

Apolipoproteins↗
PubMed1989

[Are there pre- or perinatal risk factors for sudden infant death?].

The question was posed, whether a relationship could be established between prenatal and perinatal events and subsequent sudden infant death. The birth records of eighty mothers, whose infants died of sudden infant death syndrome (SIDS) between 1982 and 1987, were reviewed for obstetric complications. The records immediately following the respective SIDS cases served as controls. A family history of SIDS was found significantly more often in the SIDS group than in the control group (p less than 0.001). Oxytocin was administered significantly more often in the SIDS group than in the control group: 54/80 (= 68%) and 20/80 (= 25%, p less than 0.001), respectively. Smoking, hypotension requiring treatment and the administration of tocolytic agents were found significantly more frequently in the SIDS group than in the control group (p less than 0.01, p less than 0.001, and p less than 0.05). Transient fetal hypoxia, as a result of reduced flow in the uterine artery, seems possibly to be connected to the vasoactive agent Oxytocin when occurring in the three above named groups. Whether these situations are connected to a later development of SIDS, has not, to date, been confirmed.

Birth Weight↗
PubMed1989

Monitoring fluid shifts in humans: application of a new method.

Using the "mechanical oscillator technique," the mass density of antecubital venous blood and plasma samples was measured 5-20 times in order to study the influence of postural changes (gravity dependence) on human blood mass density with 0.01 g.L-1 precision, while performing tilt table tests in 17 men. Hemoglobin concentration was measured in 10, and hematocrit in all subjects. Postural fluid shifts were mirrored by accompanying changes in all variables. Blood density (BD) was monitored continuously in five additional experiments from one vein each using two independent densitometers. There were linear relations (p less than 0.01) between all possible combinations of BD, plasma density (PD), blood hemoglobin concentration (Hb), and hematocrit (Ht). Hb can be directly computed from BD (range +/- 10%); the accuracy of Ht determinations from BD increases (range +/- 0.02) if the individual erythrocyte density (ED) and the sample PD are used for calculation. ED was calculated and did not change with body position. ED values of different persons ranged between 1085 g.L-1 and 1095 g.L-1 and did not vary in 15 out of 17 individuals with time (5-75 d). We conclude that ED is closely regulated to an individual set point, that Ht can be computed from BD with higher accuracy if the individual ED and the actual PD values are known, and that BD allows for direct Hb calculation. On-line BD monitoring can be performed with high precision and reveals the individual time-course of spontaneous and postural capillary fluid shifts.

Adult↗
PubMed1988

The predictive value of behavioural risk factors for sudden infant death.

In order to examine the predictive value of risk factors for the Sudden Infant Death Syndrome (SIDS), we have interviewed the parents of 80 SIDS victims and 80 parents of a healthy control group. From these interviews a list of 24 clinical and behavioural symptoms was assembled which appeared to be associated with the risk for SIDS. Out of this list of 24 symptoms the average number of symptoms reported to be observable in SIDS victims was twice as large as the average number of symptoms reported for healthy controls. The following symptoms appeared markedly more often in SIDS victims than in the controls: difficulties in awakening the baby, shrill crying, apathy, few movements during sleep, and cyanosis. We have attempted to consider a possible bias in the report of the parents of deceased infants by the introduction of an "exaggeration factor". By application of Bayes' theorem the highest predictive probability, 2.7%, was found for difficulties in awakening the baby. This is approximately nine times the assumed a priori probability of SIDS of 0.3%. We conclude that behavioural risk factors have a low but still remarkable predictive probability. A behavioural pattern of apathy and sleepiness indicates risk with a high probability.

Austria↗
PubMed1988

Physiological approaches to respiratory control mechanisms in infants. Assessing the risk for SIDS.

We have examined in a group of normal infants and in an "at-risk" group with clinical sleep apnea syndrome the duration and frequency distribution of apneas during sleep. In order to improve the estimation of an apnea factor, we introduced a weighting function which is based on the expected frequency distribution of apnea durations of normal infants. We were able to observe a good agreement between clinical rating, based on anamnestic symptoms, and numerical scoring. All infants of the at-risk group were treated with aminophylline, and the respiratory state improved significantly in nearly all cases. Breathing hypoxic gas mixtures tended to depress respiration, especially in the at-risk group, with a pronounced drop of pO2-values. Investigations on the coordination of respiration, sucking, and swallowing during nutritive sucking demonstrated a correspondence between disturbed coordination ability and the sleep apnea syndrome (SAS). This relationship is interpreted to be a result of an immaturity of the autonomic nervous system. In order to evaluate possible hereditary components in conjunction with respiratory disorders and, possibly, SIDS, we studied siblings of SIDS victims, of near-miss infants, and of infants with SAS. Only siblings of SAS and near-miss infants showed clinical signs of respiratory disorders with a rather high prevalence, whereas most of the siblings of SIDS victims were completely lacking conspicuous respiratory symptoms. Our results suggest that not all infants with sleep apnea syndrome are necessarily at increased risk for SIDS.

Deglutition↗
PubMed1988

[Retrospective study of incidents of sudden death (SIDS) in 80 infants].

The parents of 80 victims of SIDS (Sudden Infant Death Syndrome) participated in this retrospective study. The semistructured interview included questions concerning events preceding infants' death and the situation at the discovery of the death. Fifty-eight of the 80 SIDS victims were male, twenty-two were female. Fourty-four of the babies underwent a postmortem examination. There was a high incidence of death during the winter months and concerning the hour of the day in the morning hours. Most families (91%) had no socioeconomic difficulties--in contrast to reports of other authors. In 34% of the SIDS cases the parents reported about stress or irregularities of the daily family life cycle (journey, mayor family events, quarrels) immediately before the death of the baby. About 20% of the victims were not in the usual surrounding at the time of death. In about 30% of the SIDS victims an infection was observed. Since between the 2nd and 4th month of life a major neuronal reorganization in the central nervous system is assumed (Prechtl, 1984), stress during this period may be particularly effective and dangerous for the baby. This would explain the high incidence of SIDS during this vulnerable phase (60%) in which the baby, apparently, is unable to react properly.

Cross-Sectional Studies↗
PubMed1987

Quick measurement of hematocrit and erythrocyte sedimentation-rate by means of a density tracking method.

An instrument to track the sedimentation properties of red blood cells quickly and automatically and to evaluate the hematocrit as well as the plasma density of a blood sample in the same operation is described. Erythrocyte-sedimentation basically is due to the density difference between the red blood cells and the plasma and the new method makes use of the mechanical-oscillator-technique, where the resonant frequency of the bending-type oscillations of a U-shaped glass tube is related to the density of the fluid with which the tube is filled. The oscillating U-tube is part of a sedimentation-tube of special dimensions and particular spatial orientation. The tube is tilted at 60 degrees, the tip of the U-tube being raised above the horizontal plane. Filling the sedimentation-tube with anticoagulated blood first permits recording of the density of the homogeneous suspension. Then, after a few minutes, the onset of erythrocyte-sedimentation produces a decrease in recorded density. The final value is related to the density of the supernatant plasma-fluid. Hematocrit, blood and plasma density of the undiluted blood sample as well as the sedimentation-rate of the anticoagulated sample are automatically calculated from the recorded sedimentation-curve. The particular arrangement of the tilted sedimentation-tube facilitates a determination of the maximum sedimentation-rate within 15 min at most.

Blood Sedimentation↗
PubMed1987

Viscoelastic properties of whole blood. Influence of fast sedimenting red blood cell aggregates.

Red blood cell (RBC) aggregation is known to be of deciding influence on erythrocyte sedimentation-rate (ESR) and on whole blood viscoelastic properties. The rheological behaviour of blood collected from a control-group with normal ESR is compared to the viscoelastic behaviour of blood collected from two groups with high to very high ESR, whose individuals are suffering from chronical polyarthritis and Morbus Bechterew, respectively. The rheological properties are evaluated by means of an oscillating-flow capillary-rheometer where the viscous (eta') and elastic (eta") component of the complex viscosity (eta) is measured at a constant frequency of 2 Hz. Correcting for the varying hematocrit of the different blood samples according to an exponential equation, the viscoelastic data are found to be elevated in the groups with high ESR. For the viscous properties this is only due to the increase of the plasma viscosity. A correction for the plasma viscosity, however, shows that the viscous properties at low shear- rates (2s-1) are significantly reduced, whereas elastic properties in a range of medium shear-rates (10s-1 to 50s-1) are significantly increased (P less than 0.001, t-test of Student). This result is discussed to be due to the high packing density of the RBC in fast sedimenting aggregates. High packing density reduces the effective volume of the RBC but increases the stiffness of the aggregates.

Adolescent↗
PubMed1986

On the role of optimization in the cardiovascular system.

This essay discusses in a very simple manner several aspects of the meaning of optimization in general and, particularly, the role of optimization in relation to the work and action of the heart. Starting out with historical considerations the role of the properties of the heart as a pump, its relation to the arterial system, the problem of pulsatility and blood pressure and the role of time intervals and coronary perfusion is discussed. Mathematical methods permit the calculation of the time course of the cardiac ejection which, under certain constraints, minimizes the energy consumption of the heart. The saving of energy by this optimization compared with a nonoptimal ejection pattern is rather small--in the order of a few percent. It is therefore interesting and important to discuss the physiological meaning of small variations of the cost-effect function. It seems that unexplained phenomena like synchronization of heart beat and respiration have something to do with an optimization process. The most important conclusion is that any optimization has to be seen as a process related to the functioning of the organism as a whole.

Animals↗
PubMed1986

Effects of naloxone on apnoea duration during sleep in infants at risk for SIDS.

The effects of intravenous injections of the opiate antagonist naloxone (0.005-0.4 mg/kg body weight) on respiratory pattern, apnoea duration and frequency were investigated in six infants with severe sleep apnoea syndrome. Since several authors found elevated plasma- and CSF-levels of endogenous opioids (endorphines) in infants with sleep apnoea syndrome, we wanted to determine whether the impairment of the control mechanisms of respiration during sleep is due to an effect of endogenous opioids. Independent of the dose, naloxone did not exert any effect on respiratory pattern and occurrence of periodic apnoea. We were unable to prove that endorphines play a major role in pathogenesis of sleep apnoea syndrome in infancy and possibly in sudden infant death syndrome (SIDS). We speculate that elevated levels of endorphines reported by some investigators rather seem to be a consequence of hypoxic stress than a cause for sleep apnoeas.

Aminophylline↗
PubMed1986

Analysis of coronary-sinus-occlusion pressure by iterating the convolution integral.

Intermittent coronary sinus occlusion (ICSO) has been shown to reduce infarct size and to improve regional myocardial function. Since the efficiency of the procedure is closely related to proper intervals of occlusion and release of the coronary sinus, the reactions of coronary haemodynamics to this intervention have to be investigated. Coronary sinus pressure measurements obtained from anaesthetized dogs are analysed for three different conditions: normal coronary perfusion, experimentally induced infarction of the LAD performed according to a specific time pattern. The mathematical modelling of the coronary sinus pressure (CSP) reaction upon ICSO is accomplished by a convolution integral, incorporating a memory function g(x). With the aid of a numerical technique this function is evaluated to reproduce the measured data as closely as possible. Since g(x) describes the CSP response in a universal manner it can serve subsequently to predict reactions to different occlusion and release patterns not actually measured. This use of a mathematical model may provide economical paths for future investigations by avoiding prohibitively large numbers of animal studies. For different physiological states; normal perfusion, infarction and reperfusion; we obtained different memory functions. These differences in g(x) are then shown to be precisely related to known characteristics of the normal and diseased state of the myocardium. Understanding the link between cardiovascular physiology and its mathematical representation is seen as an important aid in the selection of therapeutic interventions.

Animals↗