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Biomedical subjects

T Kenner

Publications and source records attributed to T Kenner.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1986

[Sleep apnea in infants and the risk of SIDS].

The examination of the respiratory function in 184 sleeping infants gave evidence of a significant difference in several parameters between the so-called SIDS risk group and the control group. The risk group (97 babies) consists of 60 infants with frequent prolonged apneas, 30 infants with postnarcotic apneas and 7 near miss infants. Polygraphic registration during sleep showed significantly more apneas in the risk group. These apneas often appeared more frequently during certain periods. The average respiratory deficit expressed as the MA-value (MA = average apnea duration) in the risk group was significantly higher than in control infants. Besides that we were able to prove a more frequent pathological gastroesophageal reflux in the risk infants than in control infants.

Anesthesia, General↗
PubMed1985

[Model construction and systems analysis in physiology and pathology].

A model is the result of an epidemiological process which can be circumscribed by the words systems analysis and identification. Some characteristics of this process, as well as the problem of teleology and reason of different aspects of systems analysis are discussed in this essay using examples from circulation research. Such a description also makes it understandable that the essence of systems analysis can best be described in conjunction with the example of medical diagnostic procedure.

Blood Circulation↗
PubMed1985

Combined disturbance of respiratory regulation and esophageal function in early infancy.

An evident coincidence exists between increased and extended apneas during sleep and frequent gastroesophageal reflux as well as disturbances of propulsive esophageal peristalsis. The tendency to develop apnea and disturbed esophageal function are related to the degree of the maturity of the patient. This indicates that in some infants, a combined regulatory immaturity of the autonomic centers persists. Moreover, the gastroesophageal reflux fosters the clinical manifestation of sleep apneas. The risk of a reflex apnea accompanied by gastroesophageal reflux increases in proportion to the disturbance in the central respiratory regulation present at the same time. This pathomechanism can be considered one of the causes of the sudden infant death syndrome. The possibility of effective prophylaxis consists in treating the apneic tendency with aminophylline and the treatment of reflux by elevating the upper body and thickening the nourishment given.

Age Factors↗
PubMed1985

Effects of pressure-controlled intermittent coronary sinus occlusion on regional ischemic myocardial function.

Pressure-controlled intermittent coronary sinus occlusion has been reported to reduce infarct size in dogs with coronary artery occlusion, possibly because of increased ischemic zone perfusion and washout of toxic metabolites. The influence of this intervention on regional myocardial function was investigated in open and closed chest dogs. In six open chest dogs with severe stenosis of the left anterior descending coronary artery and subsequent total occlusion, a 10 minute application of intermittent coronary sinus occlusion increased ischemic myocardial segment shortening from 5.5 +/- 1.2 to 8.2 +/- 2.6% (NS) and from -0.1 +/- 2.1 to 2.3 +/- 1.2% (NS), respectively. In eight closed chest anesthetized dogs, intermittent coronary sinus occlusion was applied for 2.5 hours between 30 minutes and 3 hours of intravascular balloon occlusion of the proximal left anterior descending coronary artery. Standardized two-dimensional echocardiographic measurements of left ventricular function were performed to derive systolic sectional and segmental fractional area changes in five short-axis cross sections of the left ventricle. Fractional area change in all the severely ischemic segments (less than 5% systolic wall thickening) was -4.0 +/- 4.7% at 30 minutes after occlusion, and increased with subsequent 60 and 150 minutes of treatment to 13.1 +/- 3.3 and 7.0 +/- 3.3%, respectively (p less than 0.05). At the most extensively involved low papillary muscle level of the ventricle, regional ischemic fractional area change was increased by intermittent coronary sinus occlusion between 30 and 180 minutes of coronary occlusion from -0.4 +/- 0.1 to 14.4 +/- 4% (p less than 0.05), whereas a further deterioration was noted in untreated dogs with coronary occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Arteriovenous difference of the blood density in the coronary circulation.

The mechanical oscillator technique permits determining blood density continuously with high accuracy. Using this technique arteriovenous density gradients were recorded in the coronary vascular bed of anesthetized dogs. It was found that the coronary sinus blood has a higher density than arterial blood due to the loss of filtered fluid in the microcirculation. The amount of fluid loss corresponds to the lymph flow in the myocardium. Increase of venous pressure leads to an increase of the density gradient. Intermittent coronary sinus occlusion (ICSO) surprisingly leads to a reduction of the density gradient. Injection of osmotically hypertensive fluids influences the arteriovenous gradient by shifting extravascular fluid into the blood. The method permits the determination of filtration coefficients and to estimate the tissue volume available for fluid exchange.

Animals↗
PubMed1985

Rheological discrimination between native, rigid and aggregated red blood cells in oscillatory flow.

The viscoelastic behaviour of hardened or aggregated red blood cells is compared with the flow pattern of native red blood cells, all suspended in buffer solution at a hematocrit of 45%. The rheological properties are investigated under oscillatory shear at the constant frequency of 2Hz. Variation of the amplitude covers a range of shear-rates from 0.5/s to 200/s. It can be seen that rigidification of the red cells by treatment with glutardialdehyde leads to changes of the flow properties in the range of shear-rates above 10/s, whereas aggregate formation due to addition of dextran distinctly alters the flow properties in the range of shear-rates below 10/s.

Blood Viscosity↗
PubMed1984

Application of statistical methods for the analysis or interval related cardiac performance variations during cardiac arrhythmia in man.

To study the influence of the sequence of stimulation intervals on cardiac performance indices the relationship between properties of succeeding arrhythmic aortic pressure pulses of patients with atrial fibrillation has been analysed by methods of correlation and regression analysis. There are high correlations between properties of succeeding pulses and it can be shown that the pressure amplitude of one pulse correlates to the properties (diastole, diastolic pressure, pressure amplitude) of up to five preceding pulses. Furthermore, the diastolic pressure is also highly correlated with properties of more than one preceding pulse whereas the duration of the diastole and the RR-interval is independent of preceding pulse properties. We, therefore, conclude that there is no beat to beat regulation of intervals during atrial fibrillation. The relations between properties of succeeding pressure pulses have been summarised in a transfer function model, which allows the description of pulse properties from preceding pulse properties without lack of it. The parameters of the transfer function models are estimated from a sequence of arrhythmic pressure pulses and a parameter selection procedure was developed which identifies the optimal number of input variables (= properties of preceding pulses) required to describe the time course of one pulse property. In order to obtain informations about the presence of possible interval dependent potentiation effects, the transfer function model was used to stimulate the behaviour of the aortic pressure for different stimulation sequences, which have been used in the literature to study potentiation effect experimentally. From typical sequences of potentiation phenomena in the stimulated pulse sequence we conclude that frequency potentiation effects exist in the human myocardium.

Aorta, Thoracic↗