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Biomedical subjects

B Oeseburg

Publications and source records attributed to B Oeseburg.

At least 37 records · Page 2Linked to original sources
PubMed1999

Hypoxia, the subsequent systemic metabolic acidosis, and their relationship with cerebral metabolite concentrations: An in vivo study in fetal lambs with proton magnetic resonance spectroscopy.

OBJECTIVE: The relationship among decreased fetal arterial oxygen saturation, the subsequent systemic metabolic acidosis, and changes in cerebral metabolite concentrations in the fetal lamb brain was investigated by means of quantitative proton magnetic resonance spectroscopy. STUDY DESIGN: Fetal hypoxia was induced in 6 fetal lambs by gradual reduction of the oxygen supply to the anesthetized pregnant ewe. In vivo proton magnetic resonance spectroscopy was performed on the fetal lamb brain simultaneously with repeated measurements of fetal arterial oxygen saturation and acid-base balance. RESULTS: Proton magnetic resonance spectra showed metabolites such as inositol, choline compounds, creatine, and N-acetylaspartate. A signal for cerebral lactate was below the detection level under normoxic conditions and increased during hypoxia to indicate concentrations varying from 2.8 to 11.1 mmol/kg wet weight brain tissue. N -Acetylaspartate signals decreased during hypoxia, whereas signals of inositol, choline compounds, and creatine remained constant. CONCLUSION: These results support the view that fetal cerebral anaerobic metabolism in fetal lambs does not start under hypoxic conditions if the arterial blood pH is >7.28 or the base excess is >-8 mmol/L.

Acidosis↗
PubMed1999

Reproducibility of the alterations in circulation and cerebral oxygenation from supine rest to head-up tilt.

Cardiovascular stability, as affected by several diseases, may be assessed by head-up tilt testing. Follow-up studies are essential in both evaluating interventions and assessing progression. However, data on the reproducibility of the changes in circulatory status and cerebral oxygenation provoked by head-up tilt testing are fundamental to follow-up studies. The aim of this study was, therefore, to assess the reproducibility of the alterations in stroke volume (SV), mean arterial pressure (MAP), as well as oxygenated ([O2Hb]) and deoxygenated haemoglobin ([HHb]) concentration in cerebral tissue from supine rest (SUP) to head-up tilt (HUT). SV was calculated by Modelflow, a pulse contour method, from the finger arterial pressure wave measured by Portapres, the portable version of Finapres. [O2Hb] and [HHb] were measured using near-infrared spectroscopy (NIRS). Ten healthy individuals visited the laboratory on two different days. On both days, they underwent 10 min SUP followed by 10 min 70 degrees HUT twice. SV decreased, which was (in part) compensated for by an increased heart rate, while MAP increased slightly during HUT compared with SUP. Although [HHb] increased during HUT, no presyncope symptoms were experienced. The circulatory variables (SV, HR and MAP) as well as [HHb] showed an acceptably small systematic and random error as well as reproducibility error compared with the observed difference between HUT and SUP and were similar between and within visits. Therefore, it is concluded that MAP measured by Portapres and SV calculated by Modelflow as well as HHb measured by NIRS seem to be reproducible and may therefore be used in follow-up studies.

Adult↗
PubMed1999

Non-invasive cardiac output assessment during moderate exercise: pulse contour compared with CO2 rebreathing.

The arterial pulse contour method called Modelflow 2.1 calculates stroke volume continuously, beat to beat, from the non-invasive blood pressure signal measured by Finapres or Portapres. Portapres is the portable version of Finapres. The purpose of this study was to compare cardiac output (CO) calculated using Modelflow 2.1 (COmf) with CO obtained by the CO2 rebreathing method (COre) during steady state at moderate exercise levels. Twelve subjects visited the laboratory twice and performed submaximal exercise on a bicycle ergometer at 20%, 40% and 60% of their individual peak power output (POpeak). The averaged correlation between COmf and COre gives an r-value of 0.69, whereas the slope and intercept of the regression line were 1.06 and 1.65 respectively. The averaged difference between COmf and COre was 2.27 +/- 3.91 min-1 (mean +/- standard deviation). However, the test-retest difference between COmf and COre was 2.5 +/- 3.1 and 0.5 +/- 1.31 min-1 respectively. These results suggest that Modelflow 2.1 is not an accurate method for estimating CO from non-invasive blood pressure data collected by Portapres during exercise at up to 60% of the individual POpeak corresponding with daily life activity.

Adult↗
PubMed1999

Induction of acute metabolic acid/base changes in humans.

The aim of this study was to induce acute metabolic acid/base changes of > or = 2 mequiv.l-1 change in base excess (BE) to aid future investigations of respiratory parameters under these conditions. Ammonium chloride (NH4Cl) was administered to induce acidification and furosemide was used to induce alkalization. Nine healthy volunteers (six men and three women aged 35 +/- 18 years) ingested a calculated amount of NH4Cl at t = 0 and a repeat dose after 60 min. Eight healthy volunteers (three men and five women aged 37 +/- 16 years) consumed 40 mg of furosemide. Arterialized capillary blood gases were measured at t = 0, 30, 60, 90, 120 and 180 min. In the case of acute metabolic acidosis, the target acidification of 2 mequiv.l-1 was attained after 30 min and the greatest change was achieved at 90 min: -4.9 (2.2) mequiv.l-1. In the case of acute metabolic alkalosis, the target alkalization of 2 mequiv.l-1 was reached between 120 and 180 min and the greatest change was seen at 180 min: +2.2 (1.4) mequiv.l-1. Significant (P < 0.05) changes in acidification compared with baseline BE values were found between 60 and 180 min; significant (P < 0.05) changes in alkalization were found between 120 and 150 min. PaCO2 did not change significantly in either condition. We conclude that NH4Cl and furosemide induce a steady state of pure metabolic acid/base conditions in humans, which is buffered in an isocapnic manner.

Acid-Base Equilibrium↗
PubMed1999

Why is training effective in the treatment of patients with intermittent claudication?

Patients with peripheral arterial obstructive disease (PAOD) often have complaints of intermittent claudication. This causes a great limitation in the quality of life because of reduction in walking ability. PAOD is associated with increased morbidity and mortality. Beside other therapies, training has been shown to be an effective treatment option for patients with intermittent claudication. Exercise training significantly increases walking distance and consequently the functional behaviour of the patient. Several authors have identified different mechanisms involved in this beneficial effect. The most important are discussed in this review, namely adaptation or redistribution of the peripheral blood flow, inhibition of the progression of the atherosclerotic disease, changes in blood rheology, metabolic changes, changes in skeletal muscle morphology, economisation of walking, a change in pain perception and an effect on the cardiovascular system. It is concluded that training works through a combination of mechanisms. Further research is needed to clarify the precise mechanisms.

Exercise Therapy↗
PubMed1998

Proton magnetic resonance spectroscopy of fetal lamb brain during hypoxia.

Proton magnetic resonance spectroscopy of fetal lamb brain was performed simultaneously with repeated measurements of fetal arterial oxygen saturation during decrease of oxygen supply. Magnetic resonance spectra displayed the same metabolite peaks as detected in the human fetal brain. Cerebral lactate signals could be detected during fetal hypoxia.

Animals↗
PubMed1997

ATP content measured by 31P NMR correlates with post-ischaemic recovery of external work output in an isolated rat heart perfused with erythrocyte suspension.

The limited capacity of the heart to survive ischaemia presents a recognized problem during open-heart surgery. In order to provide a baseline for the study of cardioprotection we subjected a series of isolated rat hearts to periods of ischaemia of increasing duration, and sought correlations between phosphate metabolite levels as measured by 11P NMR and post-ischaemic recovery of external work output. A strong linear correlation was found between the fraction of ATP measured after reperfusion expressed as a ratio. RATP to the pre-ischaemic level, and the fractional recovery of external work output, RW: Rw = 1.06 (SE 0.27) RATP + 0.01 (SE 0.21) (Spearman rank correlation coefficient 0.72, two-tailed P value 0.006).

Adenosine Triphosphate↗
PubMed1997

Near infrared spectroscopy for noninvasive assessment of claudication.

The purpose of this study was to explore the application of near-infrared spectroscopy (NIRS) to the assessment of peripheral arterial occlusive disease (PAOD). Muscle blood flow, oxygen consumption, arterial inflow capacity, O2 resaturation, and recovery times were determined at rest, under ischemic and hyperemic conditions, and continuously during and after walking exercise in 11 claudicants and 15 nonclaudicants. Blood flow and oxygen consumption (VO2) at rest and blood flow following walking exercise did not differ significantly between claudicants and nonclaudicants. In contrast, VO2 after walking exercise was increased by a factor 4.1 in claudicants compared to a factor of 1.7 in nonclaudicants. The oxygen resaturation rate after arterial occlusion and the oxygen resaturation rate after walking exercise were significantly lower in claudicants. Claudicants showed a higher degree of hemoglobin deoxygenation during walking exercise than nonclaudicants. A high postexercise VO2 is correlated with a low ankle-branchial index (ABI). The resaturation rates and recovery times following walking exercise and arterial occlusion correlated significantly with ABI parameters. A significant negative correlation was found between hemoglobin deoxygenation during exercise and the ABI parameters. A high correlation was observed between the oxygenated hemoglobin (O2Hb) recovery time and the ABI recovery time after walking exercise. NIRS appears to be an effective noninvasive method for assessing the imbalance between oxygen demand and oxygen delivery in the leg muscles of PAOD patients at rest and during exercise.

Adult↗
PubMed1997

Post-ischemic 31P NMR determination of myocardial intracellular pH in vivo using ATP peak.

31P NMR allows non-invasive measurement of intracellular pH, which drops during tissue hypoxia or ischemia. Determination is usually based on the chemical shift between the inorganic phosphate (P(i)) and phosphocreatine (PCr) peaks. During reperfusion, P(i) is taken up to form PCr and ATP, and in our model at least (an isolated, working rat heart perfused with an erythrocyte suspension), the level of P(i) reduces well below the pre-ischemic level, making pH determination difficult. The chemical shifts of the three ATP peaks also depend on pH, and the level of ATP remains high during reperfusion, so these might be used to determine pH. The results of one experiment are presented in detail, showing the time course of high energy phosphate levels before, during and after a 32 min ischemic insult, and close agreement between the pH determinations from the Pi and gamma-ATP peaks can be seen. The formula used to calculate pH from the ATP peak was: pH (ATP) = 0.59 delta 2-5.0 delta + 15.9 where delta is the shift in ppm between PCr and gamma-ATP. All pH readings by both methods from a series of seven experiments were compared and a 1:1 agreement demonstrated (correlation coefficient 0.63, p < 0.0001). Although the ATP shifts also depend on magnesium complexation which we have ignored, this appears to be justifiable within the errors of the method; the good agreement between the results of the two methods, and the ability to determine pH during reperfusion suggest that calculation of intracellular pH from the chemical shift of gamma-ATP is a useful technique.

Adenosine Triphosphate↗
PubMed1997

Coronary flow response after myocardial ischemia may predict level of functional recovery.

Is there a quantity, potentially measurable in the operating theater, which predicts rapid recovery of heart power output after surgical intervention with ischemia? We have enhanced our blood-perfused, ejecting, isolated rat heart model for use inside the magnet of an NMR spectrometer, in order to conduct fundamental research into cardioprotective techniques. To provide a baseline, we investigated the effect of normothermic ischemic insults of varying duration. Hemodynamic and metabolic data were collected, and analyzed to seek measures predictive of rapid recovery of aortic power output, which was selected as the most important measure of function. The presence of erythrocytes in the perfusate ensures that oxygen supply is sufficient to support a physiological workload, and that there is reserve coronary flow. On reperfusion, reactive hyperemia occurs: coronary flow increases to a peak, then declines to a steady value. This response was mathematically modeled, and the data for each of fifteen experiments were fitted to the model. Correlating power output recovery against time to reach peak coronary flow yielded the following equation: R = -0.45 log10tp + 1.74 where R is the ratio of power output ten minutes after reperfusion to that before the ischemic insult, and tp is the time taken to reach peak coronary flow, in seconds. The correlation is very significant (p = 0.005). In the clinic, coronary flow response on reperfusion could be used to predict the patient's need for post-operative support.

Animals↗
PubMed1997

Relative exercise intensity of long-distance marching (120 km in 4 days) in 153 subjects aged 69-87 years.

The aim of this study was to determine the relative exercise intensity (oxygen uptake during the march/maximal oxygen uptake, VO2march/VO2max) during a long-distance march in subjects or over 70 years of age. Secondly, the effect of hypertension, cardiovascular and pulmonary diseases on the relative exercise intensity was evaluated. One hundred and fifty-three subjects, 97 men aged 76.7 (4.6) years and 56 women aged 72.8 (3.6) years who completed the 1993 Nijmegen day long-distance march (30 km x day(-1) on 4 consecutive days) participated in the study. Oxygen uptake (VO2) during walking at different velocities (v) was measured in a subgroup of nine men and nine women, selected randomly from the population under study. With these data, regression equations describing the relationship between VO2 and v were made. VO2march was estimated with the obtained regression equations from an average of the v(march) measured in all participants. VO2max was determined using incremental cycle ergometry in all subjects. VO2march was 13.7 (1.8) ml x kg(-1) x min(-1) in men and 15.2 (1.3) ml x kg x min(-1) in women at a mean v of 5 km x h(-1) in both sexes. This corresponded to 52% of VO2max in men and 63% in women. In both sexes subjects with cardiovascular and/or pulmonary diseases walked at a slower v and thus lower VO2march compared to subjects without these diseases. Due to the lower VO2max in subjects with these diseases there was no difference in the relative exercise intensity between the groups. A multiple linear regression analysis showed that and not age on the prevalence of hypertension, cardiovascular and/or pulmonary that VO2max was the most important predictor of the variance in self-selected v(march). This study demonstrates that these active people aged over 70 years could maintain a high relative exercise intensity during endurance walking on 4 subsequent days. Furthermore, it shows that the relative exercise intensity of marching is within the range recommended for improving fitness and reducing the risk of cardiovascular diseases. Finally, these results demonstrate that VO2max has a more important influence on performance than does age or chronic diseases in active elderly people.

Aged↗
PubMed1997

The effect of blood transfusion and haemodilution on cerebral oxygenation and haemodynamics in newborn infants investigated by near infrared spectrophotometry.

UNLABELLED: The objective of this study was to investigate the influence of blood transfusion and haemodilution on cerebral oxygenation and haemodynamics in relation to changes in cerebral blood flow velocity (CBFV) and other relevant physiological variables in newborn infants. Thirteen preterm infants with anaemia (haematocrit < 0.33) and ten infants with polycythaemia (haematocrit > 0.65) were studied during blood transfusion and haemodilution respectively using adult red blood cells and partial plasma exchange transfusion. Changes in cerebral concentrations of oxyhaemoglobin (cO2Hb), deoxyhaemoglobin (cHHb), total haemoglobin (ctHb), (oxidized-reduced) cytochrome aa3 (cCyt.-aa3) were continuously measured using near infrared spectrophotometry throughout the whole procedure. Simultaneously, changes of mean CBFV in the internal carotid artery were continuously measured using pulsed Doppler ultrasound. Heart rate, transcutaneous partial pressure of oxygen and carbon dioxide, and arterial O2 saturation were continuously and simultaneously measured. Blood transfusion resulted in increase of cO2Hb, cHHb, ctHb and red cell transport (product of CBFV and haematocrit), whereas CBFV decreased. The increase of cO2Hb exceeded that of cHHb, reflecting improvement of cerebral O2 supply. Haemodilution resulted in a decrease of cO2Hb, cHHb and ctHb, whereas CBFV increased. Red cell transport was unchanged. The decrease of cO2Hb exceeded that of cHHb, reflecting decreased cerebral O2 supply. cCyt.aa3 decreased after blood transfusion and remained unchanged after haemodilution, but the reliability of these results is uncertain. With the exception of a small, but significant increase in transcutaneous partial pressure of oxygen after blood transfusion, the other variables showed no changes. Each blood withdrawal during exchange transfusion resulted in only a significant increase in heart rate without changes in the other variables measured, suggesting unchanged cerebral perfusion. CONCLUSION: In newborn infants blood transfusion in anaemia results in improvement of cerebral oxygenation, but haemodilution in polycythaemia does not improve cerebral oxygenation despite possible improvement of cerebral perfusion.

Anemia↗
PubMed1997

Accuracy of fetal pulse oximetry and pitfalls in measurements.

Pulse oximetry is a technique for estimating arterial oxygen saturation continuously and non-invasively. Reflectance pulse oximetry might become useful for monitoring the fetus during labour but it is much more susceptible to all kinds of physiological variations than the well-established transmission pulse oximetry for neonatal or adult monitoring. This review focuses on the accuracy of reflectance pulse oximetry. Results of human, animal, in vitro and theoretical models indicate that factors such as; blood volume fraction differences, haematocrit, and blood flow differences are major sources for inaccurate pulse oximetry readings in the fetal arterial oxygen saturation range of 10-80%. These factors cannot be overcome by systems using two wavelengths sensors with the 660/890 or 940 nm combination. Reported precision values (S.D. of difference between pulse oximeter and blood sample saturation) range between 2.5 and 12.9% for various 660 nm sensors. Most sensors were tested only once with a limited number of animals. A new 735/890 nm sensor (Nellcor Puritan Bennett) demonstrates a promising accuracy (precision around 5%) in two studies. Various other sensors have also been developed, but are not or scarcely evaluated. Without thorough establishment of the reliability of this technique, clinical fetal oxygen saturation data are still of limited value.

Animals↗
PubMed1997

Validation of reflectance pulse oximetry: an evaluation of a new sensor in piglets.

OBJECTIVE: A new reflectance pulse oximetry sensor, developed for intrapartum estimation of arterial oxygen saturation (SaO2), was calibrated and evaluated. The sensor contains two light emitting diodes of 735 and 890 nm, and a photodetector at a distance of 14 mm from both light emitting diodes. METHODS: In seven Yorkshire/Hampshire piglets, the reflectance sensor (Nellcor Puritan Bennett Inc.) was calibrated using blood sample SaO2 values. The resulting calibration line was evaluated in four Dutch piglets, by comparing pulse oximetry saturation readings (SpO2) with blood sample and intravascular fiberoptic oximetry SaO2 values. Several reflectance sensors were fixed on each animal. Desaturation levels were obtained by changing the gas mixture of oxygen/ nitrous oxide via a tracheal catheter. RESULTS: In the Yorkshire/ Hampshire piglets, the standard deviation of difference (SpO2-SaO2) was 4.7% (n = 364), over an SaO2 range of 17% to 100%. In the Dutch piglets, the mean difference (SpO2-SaO2) was -1.6% and the standard deviation of difference was 5.4%, over the same SaO2 range (n = 254). Comparisons of continuous recordings of reflectance SpO2 and fiberoptic SaO2 revealed variation in individual regression lines. CONCLUSIONS: This new 735/890 nm reflectance sensor demonstrates acceptable accuracy in piglets. A further evaluation during labor should assess its feasibility for fetal surveillance.

Animals↗
PubMed1997

Cerebral and circulatory haemodynamics before vasovagal syncope induced by orthostatic stress.

Vasovagal syncope is usually described as a sudden and transient loss of consciousness that resolves spontaneously. Cardiocirculatory changes are well described during and before syncope. However, changes in the cerebral oxygenation are not well defined. In this study, near-infrared spectroscopy (NIRS) was used to assess the cerebral oxygenation directly during 80 degree head-up (HU) tilt. To simulate central hypovolaemia, 500 ml of blood was drawn from each of 10 healthy subjects. Oxygenation index (OI) was defined as the difference between oxy- and deoxyhaemoglobin concentration. Blood pressure, heart rate and cardiac output were monitored using a finger plethysmographic device. The protocol was divided into two stages, each consisting of a 15-min stabilization period in the supine (SUP) position, 15 min in HU position and another 10 min in SUP position. Between both stages, blood was drawn from the subject. Haemoglobin concentration and haematocrit were measured before and 30 min after withdrawal of blood. No compensatory haemodilution was observed. During HU position in the second stage, six subjects showed signs of presyncope (F) and four did not (NF). A significant difference between F and NF was found in the observation that, before fainting, the OI of F showed a steady and significant (P = 0.02) decrease (-1.4 +/- 0.5 microM min-1) compared with NF (-0.18 +/- 0.16 microM min-1). This indicates that the onset of (pre)syncope is preceded by a mismatch between oxygen demand and oxygen supply in the cerebrum. Using NIRS enabled us to monitor this mismatch and to predict the onset of a syncope before clear signs in cardiocirculatory variables were visible.

Adult↗