Interpretatie van indicator-verdunningscurven met behulp van een random walk model

Een veel gebruikte methode ter bepaling van het hartminuutvolume tijdens fysiologische experimenten en in klinische toepassingen is de indicator-dilutiemethode. De procedure die meestal wordt uitgevoerd om voor recirculatie van indicatordeeltjes te corrigeren is de semilogarithmische extrapolatie van het afdalende been van de indicator-dilutiecurve. Hierover merkte Wise in 1975 op: "This custom bas persistea a remarkably long time. Physical interpretations of this exponentlal have long been abandoned - even so, one gets the impression that neither applied mathematicians or statisticians have ever been consulted in this field. l"le would surely all agree that this estimate of the cardiac output is needlessly inaccurate because too little of the observed primary curve is used and because we do not know when the secondary distribution begins". Ook Norwjch (1977) onderstreepte de wenselijkheid om alle meetwaarden van de curve aan te passen aan een adequaat model. Hij stelde: "My own preferenee is for a random walk function because it bas at least some physical basis and bas been tested experimentally fora number of indicators". Uit het bovenstaande vloeit de vraag voort of random walk (diffusie met drif~ functies een praktisch toepasbare benadering vormen voor de analyse van indicator-dilutiecurven. Deze vraag is de kern van het hier gepresent~erdeonderzoek. Bovendien werd een onderzoek ingesteld naar specifieke toepassingsgebieden. Ook werd een analyse verricht van de functieparameters waarbij werd- nagegaan of deze relevante informatie kunnen verschaffen over de fysiologische eigenschappen van het onderzochte deel van het circulatiesysteem

Incentive Pay and Performance: Insider Econometrics in a Multi-Unit Firm

We exploit organizational reforms in a foreign-owned bank in Central-East Europe to study the implementation of modern HRM policies in an emerging market context. We have branch-level data and use our knowledge of the process that led to the adoption of the reforms to implement two estimators that address endogeneity bias in a complementary fashion: an IV approach and Generalized Propensity Score estimation. Our results show that some of the reforms had a positive impact on productivity, but they also underscore the risks of quantity-based incentives where quality is important

Computer-controlled mechanical lung model for application in pulmonary function studies

A computer controlled mechanical lung model has been developed for testing lung function equipment, validation of computer programs and simulation of impaired pulmonary mechanics. The construction, function and some applications are described. The physical model is constructed from two bellows and a pipe system representing the alveolar lung compartments of both lungs and airways, respectively. The bellows are surrounded by water simulating pleural and interstitial space. Volume changes of the bellows are accomplished via the fluid by a piston. The piston is driven by a servo-controlled electrical motor whose input is generated by a microcomputer. A wide range of breathing patterns can be simulated. The pipe system representing the trachea connects both bellows to the ambient air and is provided with exchangeable parts with known resistance. A compressible element (CE) can be inserted into the pipe system. The fluid-filled space around the CE is connected with the water compartment around the bellows; The CE is made from a stretched Penrose drain. The outlet of the pipe system can be interrupted at the command of an external microcomputer system. An automatic sequence of measurements can be programmed and is executed without the interaction of a technician

Controlled expiration in mechanically-ventilated patients with chronic obstructive pulmonary disease (COPD)

In patients with severe chronic obstructive pulmonary disease (COPD), lung emptying may be affected by flow limitation. We tested the hypothesis that the airway compression leading to flow limitation can be counteracted by controlling the expiratory flow. The effects of an external resistor on lung emptying were studied in six patients with COPD, who were mechanically ventilated whilst sedated and paralysed. Respiratory mechanics were obtained during ventilatory support with and without the resistor. Airway compression was assessed using the interruptor method. For the study, a turbulent resistor was applied with the highest resistance level that did not increase the end-expiratory lung volume. At this resistance level, external positive end-expiratory pressure (PEEP) was generated in all patients. As total PEEP levels remained unchanged at both settings during the controlled expiration, the levels of intrinsic PEEP were significantly decreased from 0.96+/-0.30 to 0.53+/-0.19 kPa (mean+/-SD). Comparison of the expiratory flow-volume curves at both settings revealed that, during the controlled expiration, the flows were significantly decreased during the first 40% of the expired volume and significantly increased during the last 60%. As the end-expiratory lung volumes remained unchanged during both settings, these increments in flow indicated a decrease in effective resistance. Airway compression was observed during unimpeded expirations in all patients using the interruptor method. During the application of the resistor, airway compression was no longer detectable. In patients with chronic obstructive pulmonary disease receiving ventilatory support, the application of an external resistor could decrease effective expiratory resistance by counteracting airway compression, without increments in end-expiratory lung volume

SWISH DataLab: A Web Interface for Data Exploration and Analysis

SWISH DataLab is a single integrated collaborative environment for data processing, exploration and analysis combining Prolog and R. The web interface makes it possible to share the data, the code of all processing steps and the results among researchers; and a versioning system facilitates reproducibility of the research at any chosen point. Using search logs from the National Library of the Netherlands combined with the collection content metadata, we demonstrate how to use SWISH DataLab for all stages of data analysis, using Prolog predicates, graph visualizations, and R

Assessment of accuracy and applicability of a portable electronic diary card spirometer for asthma treatment

AbstractA pocked-sized turbine flowmeter and spirometer device, integrated with an electronic diary card (EDC-spirometer, Micro Medical, U.K.), was tested with a mechanical calibrator, in an outpatient clinic and in the home situation. A screen pneumotachometer was used as flow and volume reference.Ten devices were tested; interdevice variability was small with a mean variation coefficient of 1·1% for both forced expiratory volume in 1 s (FEV1) and peak expiratory flow (PEF) (sd 0·5 and 0·4, respectively) for eight settings of the calibrator. Mean difference from reference was −0·131 (sd 0·04) for FEV1 (range 0·38–3·16) and 0·091 s−1 (sd 0·09) for PEF (range 4·2–11·7). No significant deviation from linearity was present.Results obtained in the outpatient clinic confirmed the accuracy of FEV1 and PEF data obtained with the calibrator. However, linear regression analysis showed a mean underestimation of 0·451 (sd of estimate 0·29) for forced vital capacity over the whole measurement range, probably due to a restricted integration time.In 10 optimally-treated chronic obstructive pulmonary disease patients in a family practice, PEF measurements were done in the home situation, both with the EDC spirometer and a mini-Wright peak flow meter. No significant differences in the diurnal variation of PEF were found. The PEF data from the mini-Wright meter were corrected for earlier reported flow-dependent systematic deviations. In the home situation, patients preferred the EDC spirometer. It is concluded that this device is applicable in the follow-up and treatment of asthma at home