Showing papers by "Maastricht University published in 1992"

A new approach for the determination of ventilatory and lactate thresholds.

Abstract: In order to determine the ventilatory threshold (VT) and the lactate threshold (LT) in a reliable way, a new method is proposed and compared with conventional methods. The new method consists of calculating the point that yields the maximal distance from a curve representing ventilatory and metabolic variables as a function of oxygen uptake (VO2) to the line formed by the two end points of the curve (Dmax method). Male cyclists (n = 8) performed two incremental exercise tests a week apart. Ventilatory/metabolic variables were measured and blood was sampled for later lactate measurement during each workload and immediately after exercise. No statistical differences were observed in the threshold values (expressed as absolute oxygen uptake; VO2) determined by the Dmax method and the conventional linear regression method (according to O2 equivalent; EqO2) and venous blood at the onset of blood lactate (OBLA), while VT assessed with the conventional linear method (according to the slope of CO2 output; Vslope) yielded significantly lower threshold values. Similar results were obtained from the reproducibility test. Thus, the Dmax method appears to be an objective and reliable method for threshold determination, which can be applied to various ventilatory or metabolic variables yet yield similar results. The results also showed that breathing frequency can be used to determine VT.

Measuring quantity and frequency of drinking in a general population survey: a comparison of five indices.

Abstract: This article compares five indices of alcohol consumption in a general population survey conducted in 1985 in the Netherlands. Self-reports of consumption were obtained with a prospective diary, a retrospective 7-day recall method, and three summary measures, such as a quantity-frequency index. The coverage of sales data appeared highest for the diary (67%), which suggests a higher validity. Special attention was given to comparisons of quantity and frequency of drinking between the diary, on the one hand, and the weekly recall and summary measures, on the other. It was found that underreporting, relative to the diary reports, was generally higher in the frequency than in the quantity domain. This result, together with the finding from longitudinal studies that intraindividual variation is also higher for drinking frequency, leads to the conclusion that forgetting is a potent source of undercoverage in surveys and to the hypothesis that large differences in overall drinking pattern between populations (e.g., in regularity of drinking) may account for the large differences in coverage rates of sales data. Furthermore, the subjectively assessed probability of drinking by means of a "usual" frequency question appeared a poor predictor of (diary) drinking frequency for respondents reporting a low or moderate frequency. For subjects claiming a high "usual" drinking frequency, a reasonable correspondence between diary and summary measures was found. This mitigates the fear often expressed that heavy drinkers particularly underreport their consumption.

Release of heart fatty acid-binding protein into plasma after acute myocardial infarction in man

Abstract: The release of cytoplasmic heart fatty acid-binding protein (H-FABP) into the plasma of cardiac patients up to 38 hr after the onset of the first clinical symptoms of acute myocardial infarction (AMI) was studied, using a sensitive direct and noncompetitive Enzyme Linked Immunosorbent Assay of the antigen capture type (sandwich ELISA), newly developed for the measurement of small amounts of human H-FABP in plasma samples. Plasma levels of H-FABP were compared with plasma activity levels of the myocardial cytoplasmic enzymes creatine kinase MB (CK-MB) and alpha-hydroxybutyrate dehydrogenase (α-HBDH). Upper normal levels of H-FABP (19μg/l), CK-MB (10 U/l) and α-HBDH (160 U/l) as determined in plasma from 72 blood donors served as threshold levels. H-FABP levels were significantly elevated above their threshold level within 3 hr after AMI. Peak levels of H-FABP, CK-MB and α-HBDH were reached 4.1 ± 0.9 hr, 8.4 ± 1.4 hr and 25.0 ± 9.5 hr (means ± S.D., n = 10) after acute myocardial infarction, respectively. Serial time curves of the plasma contents of H-FABP reveal that after myocardial infarction H-FABP is released in substantial amounts from human hearts. In 18 out of 22 patients with established AMI the plasma FABP level was at or above the threshold level in blood-samples taken within 3.5 hr after the first onset of symptoms of AMI, while for CK-MB this applied to 9 patients and for α-HBDH to 6 patients. These findings suggest that for an early indication of acute myocardial infarction in man cytoplasmic heart fatty acid-binding protein is more suitable than heart type creatine kinase MB and/or alpha-hydroxybutyrate dehydrogenase. (Mol Cell Biochem116: 155–162,1992)

The effectiveness of manual therapy, physiotherapy, and treatment by the general practitioner for nonspecific back and neck complaints. A randomized clinical trial.

Abstract: In a randomized trial, the effectiveness of manual therapy, physiotherapy, continued treatment by the general practitioner, and placebo therapy (detuned ultrasound and detuned short-wave diathermy) were compared for patients (n = 256) with nonspecific back and neck complaints lasting for at least 6 weeks. The principle outcome measures were severity of the main complaint, global perceived effect, pain, and functional status. These are presented for 3, 6, and 12 weeks follow-up. Both physiotherapy and manual therapy decreased the severity of complaints more and had a higher global perceived effect compared to continued treatment by the general practitioner. Differences in effectiveness between physiotherapy and manual therapy could not be shown. A substantial part of the effect of manual therapy and physiotherapy appeared to be due to nonspecific (placebo) effects.

Long-term effect of physical activity on energy balance and body composition

Abstract: We studied the effect of an increase in physical activity on energy balance and body composition without interfering with energy intake (EI). Sixteen women and sixteen men, aged 28-41 years, body mass index 19.4-26.4 kg/m2, not participating in any sport before the start of the experiment, prepared to run a half-marathon competition after 44 weeks. Measurements of body composition, EI and energy expenditure (EE) were performed before (0 weeks), and 8, 20, and 40 weeks after the start of training. Body composition was measured with hydrodensitometry and isotope dilution, and EI with a 7 d dietary record. EE was measured overnight in a respiration chamber (sleeping metabolic rate (SMR)) and in a number of subjects over 2-week intervals with doubly-labelled water (average daily metabolic rate (ADMR)). ADMR showed an average increase of 30% in both sexes from the start of training onwards while SMR tended to decrease. EI showed a tendency to drop from week 20 to week 40 in the men and a tendency to increase from week 20 to week 40 in the women. Body mass (BM) did not change in both sexes until the observation at 40 weeks when the median value of the change in men was -1.0 kg (P < 0.01; Wilcoxon signed-rank) while the corresponding change of -0.9 kg in the women was not statistically significant. Body composition changes were most pronounced in men as well. Based on changes in BM, body volume and total body water, men lost 3.8 kg fat mass (FM) (P < 0.001; Wilcoxon signed-rank) and gained 1.6 kg protein mass (P < 0.01; Wilcoxon signed-rank) while the corresponding changes in women were 2.0 kg (P < 0.05; Wilcoxon signed-rank) and 1.2 kg (P < 0.05; Wilcoxon signed-rank). In men the loss of FM was positively correlated with the initial percentage body fat (Pearson r 0.92, P < 0.001). In conclusion, body fat can be reduced by physical activity although women tend to compensate for the increased EE with an increased EI, resulting in a smaller effect on BM and FM compared with men.

Randomised clinical trial of manipulative therapy and physiotherapy for persistent back and neck complaints: results of one year follow up.

Abstract: OBJECTIVE--To compare the effectiveness of manipulative therapy, physiotherapy, treatment by the general practitioner, and placebo therapy in patients with persistent non-specific back and neck complaints. DESIGN--Randomised clinical trial. SETTING--Primary health care in the Netherlands. PATIENTS--256 patients with non-specific back and neck complaints of at least six weeks' duration who had not received physiotherapy or manipulative therapy in the past two years. INTERVENTIONS--At the discretion of the manipulative therapists, physiotherapists, and general practitioners. Physiotherapy consisted of exercises, massage, and physical therapy (heat, electrotherapy, ultrasound, shortwave diathermy). Manipulative therapy consisted of manipulation and mobilisation of the spine. Treatment by general practitioners consisted of drugs (for example, analgesics), advice about posture, home exercises, and (bed)rest. Placebo treatment consisted of detuned shortwave diathermy (10 minutes) and detuned ultrasound (10 minutes). MAIN OUTCOME MEASURES--Changes in severity of the main complaint and limitation of physical functioning measured on 10 point scales by a blinded research assistant and global perceived effect measured on a 6 point scale by the patients. RESULTS--Many patients in the general practitioner and placebo groups received other treatment during follow up. Improvement in the main complaint was larger with manipulative therapy (4.5) than with physiotherapy (3.8) after 12 months' follow up (difference 0.9; 95% confidence interval 0.1 to 1.7). Manipulative therapy also gave larger improvements in physical functioning (difference 0.6; -0.1 to 1.3). The global perceived effect after six and 12 months' follow up was similar for both treatments. CONCLUSIONS--Manipulative therapy and physiotherapy are better than general practitioner and placebo treatment. Furthermore, manipulative therapy is slightly better than physiotherapy after 12 months.

To Combine or not to Combine? Issues of Combining Forecasts

Abstract: This paper addresses issues such as: Does it always pay to combine individual forecasts of a variable? Should one combine an unbiased forecast with one that is heavily biased? Should one use optimal weights as suggested by Bates and Granger over twenty years ago? A simple model which accounts for the main features of individual forecasts is put forward. Bayesian analysis of the model using noninformative and informative prior probability densities is provided which extends and generalizes results obtained by Winkler (1981) and compared with non-Bayesian methods of combining forecasts relying explicitly on a statistical model for the individual forecasts. It is shown that in some instances it is sensible to use a simple average of individual forecasts instead of using Bates and Granger type weights. Finally, model uncertainty is considered and the issue of combining different models for individual forecasts is addressed.

Physiological changes in male competitive cyclists after two weeks of intensified training.

Abstract: To study the physiological response to heavy training, seven male competitive cyclists intensified their normal training program for two weeks (IIT) in order to achieve a state of short-term overtraining. The subjects underwent a graded cycle ergometer test to exhaustion, an outdoor 8.5 km time trial and a computerized test to study reaction time and visual perception, before, during and after the two weeks of intensified training and after two weeks of recovery. Furthermore subjects kept a daily log in the form of a questionnaire. After two weeks of IIT all subjects showed symptoms of overtraining: the general state of well being declined as indicated by the questionnaire while performances on time trial (mean +/- SEM: 830 +/- 14 sec-871 +/- 19 sec), contests and maximal power output (mean +/- SEM: 336 7 watt-310 +/- 5 watt) declined significantly. Maximal (mean +/- SEM 11.8 +/- 1.1 mmol.l-1-5.9 +/- 0.5 mmol.l-1) and submaximal lactate values were significantly lowered during ergometer test after the IIT, while the workload at the 4 mmol point increased significantly (mean +/- SEM 234 +/- 10 watt-267 +/- 13 watt). Sleeping heart rate increased significantly (mean +/- SEM 49.5 +/- 9.3 BPM-54.3 +/- 8.8 BPM). Maximal heart rate (mean +/- SEM 185 +/- 3 BPM-178 +/- 2 BPM, mean heart rate during the time trial (mean +/- SEM 178 +/- 2 BPM-169 +/- 2 BPM) and VO2max (mean +/- SEM 4801 +/- 121 ml.min-1-4409 +/- 101 ml.min-1) were all significantly lowered by the IIT.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II receptor blockade after myocardial infarction in rats: effects on hemodynamics, myocardial DNA synthesis, and interstitial collagen content.

Abstract: Angiotensin-converting enzyme (ACE) inhibitors are widely used for treatment of heart failure after myocardial infarction (MI). The beneficial effects consist of a combination of hemodynamic effects and interference with cardiac structural alterations. These effects are believed to depend on inhibition of angiotensin II (AII) formation and thus diminished angiotensin receptor stimulation. We administered the angiotensin II-1 (AT-1) receptor antagonist losartan during and after completion of the repair phase of an MI to investigate involvement of the AT-1 receptor in the above described effects of captopril. MI reduced cardiac output (CO) (sham 94 +/- 4 ml/min, MI 78 +/- 5 ml/min) and maximal CO (sham 154 +/- 4, MI 107 +/- 5 ml/min, respectively). Losartan (15 mg/kg/day) resulted in a rightward shift of the AII pressor dose-response curve by a factor of 32-40. Neither CO nor COVL,max was affected by losartan treatment in either phase (late treatment CO = 78 +/- 5, COVL,max = 118 +/- 9 ml/min). Although early treatment with losartan reduced cardiac hypertrophy measured as heart weight, DNA synthesis was reduced only slightly. In contrast, collagen deposition was inhibited completely. The results suggest that the effects of captopril in rats after MI are not dependent on AT-1 receptor-mediated mechanisms.

To combine or not to combine? issues of combining forecasts

Abstract: This paper addresses issues such as: Does it always pay to combine individual forecasts of a variable? Should one combine an unbiased forecast with one that is heavily biased? Should one use optimal weights as suggested by Bates and Granger over twenty years ago? A simple model which accounts for the main features of individual forecasts is put forward. Bayesian analysis of the model using noninformative and informative prior probability densities is provided which extends and generalizes results obtained by Winkler (1981) and compared with non-Bayesian methods of combining forecasts relying explicitly on a statistical model for the individual forecasts. It is shown that in some instances it is sensible to use a simple average of individual forecasts instead of using Bates and Granger type weights. Finally, model uncertainty is considered and the issue of combining different models for individual forecasts is addressed.

Exploring the Relationship between R&D and Productivity in French Manufacturing Firms

Abstract: This paper uses a newly available dataset on the R&D performance of individual French manufacturing firms for the 1980s to replicate and update a series of studies on French R&D and productivity growth at the firm level during the 1970s. The focus of the paper is on the use of a single dataset to evaluate the robustness of the methods commonly used to measure the private returns to R&D. We investigate the consequences of varying specifications and estimations. and in particular that of using different measures of R&D (knowledge) capital and of double counting corrections. Our main findings are the following: first. having a longer history of R&D expenditures helps in predicting the productivity growth of firms, but the choice of depreciation rate for R&D capital makes little difference to the results. Second, the correction for double counting of R&D expenditures in capital and labor is important and converts a measured "excess" rate of returns to a total rate of return to R&D. Third. we show that the direct production function approach to measuring the returns to R&D capital is preferred on several grounds over the rate of returns variation which has been used in the past. Finally, the productivity, of knowledge capital in the production function is uniformly positive, fairly robust, and correlated with permanent firm or industry effects.

Anticoagulant activity of beta 2-glycoprotein I is potentiated by a distinct subgroup of anticardiolipin antibodies.

Abstract: Plasmas of 16 patients positive for both IgG anticardiolipin (aCL) antibodies and lupus anticoagulant (LA) antibodies were subjected to adsorption with liposomes containing cardiolipin. In 5 of these plasmas both the anticardiolipin and the anticoagulant activities were co-sedimented with the liposomes in a dose-dependent manner, whereas in the remaining cases only the anticardiolipin activity could be removed by the liposomes, leaving the anticoagulant activity (LA) in the supernatant plasma. aCL antibodies purified from the first 5 plasmas were defined as aCL-type A, while the term aCL-type B was used for antibodies in the other 11 plasmas, from which 2 were selected for this study. Prolongation of the dRVVT was produced by affinity-purified aCL-type A antibodies in plasma of human as well as animal (bovine, rat and goat) origin. aCL-type B antibodies were found to be devoid of anticoagulant activity, while the corresponding supernatants containing LA IgG produced prolongation of the dRVVT only in human plasma. These anticoagulant activities of aCL-type A and of LA IgG's were subsequently evaluated in human plasma depleted of beta 2-glycoprotein I (beta 2-GPI), a protein which was previously shown to be essential in the binding of aCL antibodies to anionic phospholipids. Prolongation of the dRVVT by aCL-type A antibodies was abolished using beta 2-GPI deficient plasma, but could be restored upon addition of beta 2-GPI. In contrast, LA IgG caused prolongation of the dRVVT irrespective of the presence or absence of beta 2-GPI.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropsychological deficits in patients with persistent symptoms six months after mild head injury.

Abstract: There is much debate on the nature and duration of cognitive deficits and postconcussive symptoms (PCS) after mild head injury. Most studies performed so far have compared head-injured patients with subjects who had not suffered a concussion, instead of directly comparing patients with and w

The time sequence of electrical and mechanical activation during spontaneous beating and ectopic stimulation

Abstract: The relation between the sequence of electrical (E) and mechanical (M) activation was studied at the LV anterior wall of open-chest dogs (n = 11). M activation was defined as the onset of epicardial fibre shortening, as measured with a recently developed video technique. E activation was determined with a brush of extracellular electrodes. The delay between activation of basal and apical regions was consistently larger for M activation than for E activation: during spontaneous beating: 20.5 +/- 7.30 ms vs 8.8 +/- 3.31 ms, during right ventricular outflow tract pacing: 50.3 +/- 7.69 ms vs 39.0 +/- 5.31 ms and during left ventricular apex pacing 40.1 +/- 10.03 ms vs 25.4 +/- 9.30 ms, respectively (P less than 0.05 in all cases). The E-M time interval was consistently shorter in early than in late activated regions: 32 +/- 10 vs 41 +/- 8 ms during RV outflow tract pacing (P = 0.09) and 24 +/- 30 vs 40 +/- 24 ms during LV apex pacing (P less than 0.05). Electrical asynchronies larger than 40 ms resulted in decreases of systolic blood pressure and stroke volume. This study shows that the asynchrony of cardiac motion exceeds that of electrical activation because the time interval between electrical activation and onset of fibre shortening is larger the later a particular region is activated. Possible explanations for this phenomenon are discussed.

Intelligent decision support systems

Abstract: This paper explores the basic ingredients of intelligent decision support systems in partial contrast to approaches followed by expert systems.

The Microcirculation and Hypertension

Abstract: The role of the microcirculation is increasingly being recognized in the pathophysiology of cardiovascular disease. It is the major site of control of vascular resistance. In addition, the microcirculation is a major site of damage in most target organs of cardiovascular disease, such as the heart, brain, and kidney. In this chapter, we review the main methods used to assess the microcirculation. These methods include intravital microscopy, video capillaroscopy, Doppler flowmetry, and the use of isolated small arteries. Recently, important advances have been made in retinal microvascular imaging. These methods have led to important new insights in the role of changes in microcirculation both as a cause and a consequence of hypertension. We propose a major role for a defect in angiogenesis as a cause of microvascular rarefaction.