Biomedical subjects

A F Verbraak

Publications and source records attributed to A F Verbraak.

7 recordsLinked to original sources

PubMed1992

A quasi steady state ramp method for the estimation of the ventilatory response to CO2.

There are two suitable methods for estimating the ventilatory response to CO2: the steady state or the Read method. The latter is usually applied because of its shorter duration and its stimulus, near to tissue PCO2. From recent studies on a physiological model but also on the dynamics of the ventilatory CO2 response (G liters min-1 kPa-1), it can be shown, both theoretically and experimentally, that the Read method markedly overestimates the steady-state estimate of the ventilatory CO2 response (Gss). We have, therefore, applied two ramp approaches: one with an initial end-tidal PCO2 (PetCO2) step of 0.5 kPa and a mean PetCO2 ramp slope of 0.41 kPa/min (step-ramp method, SR) and one without an initial step and a mean ramp slope of 0.21 kPa/min (ramp method; R). As predicted by theory, the ventilatory CO2 response from the R method (GR) during the second 4-min interval of the 8-min procedure and the ventilatory CO2 response from the SR method (GSR) from the whole 6-min procedure, except for the first 30 s, should yield a good approximation of Gss. In a group of 12 normal volunteers we indeed found no differences between these estimates, and, as predicted by theory, we found both estimates to be larger than GR from the first 4-min interval. From the interindividual spread, only the difference with respect to GSR was significant (p less than 0.02). The volunteers preferred the R approach because of the lower PetCO2 attained and the smaller ventilation increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Serial lung model for simulation and parameter estimation in body plethysmography.

A serial lung model with a compressible segment has been implemented to simulate different types of lung and airway disorders such as asthma, emphysema, fibrosis and upper airway obstruction. The model described can be used during normal breathing, and moreover the compliant segment is structured according to more recent physiological data. A parameter estimation technique was applied and its reliability and uniqueness were tested by means of sine wave input signals. The characteristics of the alveolar pressure/flow patterns simulated with the model agree to a great extent with those found in the literature. In the case of absence of noise the parameter estimation routine produced unique solutions for different simulated pathologic classes. The sensitivity of the different parameters depended on the values belonging to each class of pathology. Some more simplified models are presented and their advantages over the complex model in special types of pathology are demonstrated. Noise added to the simulated flow appeared to have no influence on the estimated parameters, in contradiction to the effects with noise added to the pressure signal. In that case effective resistance was accurately estimated. Where parameters had no influence, as for instance upper airway resistance in emphysema or peripheral airway resistance in upper airway obstruction, the measurement accuracy was less. In all other cases, a satisfactory accuracy could be obtained.

Humans↗

PubMed1991

A lung function information system.

A lung function information system (LFIS) was developed for the data analysis of pulmonary function tests at different locations. This system was connected to the hospital information system (HIS) for the retrieval of patient data and the storage of the lung function variables of patients to generate follow-up reports and to support financial and administrative management. The application programs were developed in such a way that high flexibility was obtained with respect to the patient-computer-technician interaction. The sampled data are stored on a disc to correct earlier decisions, perform recalculations and reanalyse the data for research purposes. When the measurements performed on a patient are authorized, the sampled data are deleted, except for when they are needed for future research. A distributed computer system was chosen to combine the benefits of a centralized system with those of several stand-alone systems. The main tasks of the central unit are to store collected data and computer programs, generate a final lung function report on laser printer and provide a connection to the HIS. In the satellite computers, which are located close to the lung function equipment, the signals and raw data are processed. Furthermore, the satellite computers were in use for program development and several research projects, and for the offline data processing of the lung function measurements from two other hospitals by means of a modem connection. The LFIS improved the quantity and quality of data acquisition. It resulted in an increased capacity of about 50% concerning spirometry, and facilitated time-consuming complex analyses. It also avoided miscalculations and mistakes in reports previously experienced with hand calculations.

Computer Systems↗

PubMed1989

Dose-effect relationship of terbutaline using a multi-dose powder inhalation system ('Turbuhaler') and salbutamol administered by powder inhalation ('Rotahaler') in asthmatics.

A study was carried out in 8 patients with chronic stable bronchial asthma to compare the bronchodilator response with terbutaline, administered by a recently developed powder inhalation system ('Turbuhaler') and equipotent doses of salbutamol administered by a widely used powder inhaler ('Rotahaler'). Dose-effect relationships with usually applied clinical doses of the bronchodilators were estimated by maximal expiratory flow-volume analysis and airway resistance estimates from body plethysmography. There was no significant difference in clinical response using either inhaler. The equal and opposite changes in forced vital capacity and residual volume with increasing dose indicate an improvement in peripheral airway resistance and, therefore, adequate peripheral powder deposition of the bronchodilators. Only at the highest dose was a mild increase noted in pulse frequency and tremor score with both systems. It is suggested that, because of the multi-dose character, absence of additives, easy handling (no capsule loading) and low inspiratory flow needed for actuation, the 'Turbuhaler' system may be considered preferable for the application of a bronchodilator in children and severely obstructed adults.

Administration, Inhalation↗

PubMed1987

Maximal expiratory and inspiratory flow-volume curves in bilateral vocal-cord paralysis. Changes after surgical treatment and comparison with glottic resistance characteristics.

The maximal expiratory flow-volume (MEFV) and maximal inspiratory flow-volume (MIFV) curve present maximal attainable flows, plotted against the displaced volume at the mouth during a forced expiratory manoeuvre from total lung capacity (TLC) and a subsequent forced inspiratory manoeuvre from residual volume (RV), respectively. Depending on the glottic resistance characteristics, the usual flow limitation may be absent during forced expiration, drastically influencing the form of MEFV curves. During forced inspiration however, the flow remains effort-dependent. We tested this hypothesis by comparing the form of MEFV and MIFV curves, and the glottic resistance characteristics, before and after an endolaryngeal superolateralization of a vocal cord, in 12 patients with bilateral vocal-cord paralysis. Peak expiratory and inspiratory flows were estimated with the aid of the measured glottic resistance characteristics on the assumption that the maximal alveolar pressures were normal during the manoeuvres. The estimated values agreed well with measured values. The form of the MEFV and MIFV curves was also found to be closely linked to the glottic resistance characteristics. It is concluded that the MEFV and MIFV curves are sensitive indicators of flow limitation in patients with upper-airway obstructions.

Adult↗

PubMed1986

Effective airway resistance: a reliable variable from body plethysmography.

Since the introduction of whole-body plethysmography in pulmonary function routines, airway resistance measurements by this method have been plagued by a side-effect of the ventilation process. Warming up and humidifying of inspired air and the cooling and condensation of expired air lead to a change in volume of the gas in the system and thus to a change in pressure in the body box which is superimposed on the regular box pressure. One generally applied solution is to compensate electronically for the disturbing pressure change. However, the required adjustment of the size of the compensating signal is difficult or impossible to obtain with patients who have obstructive lung diseases. In this paper we show that if no correction at all is applied the measurement error in the effective airway resistance remains relatively small. Moreover the magnitude of the error appears to depend on certain symmetrical and asymmetrical properties of the mouth flow curve. The maximum error in the effective resistance, as computed from a number of measured flow patterns, was found to be -18% for the normal persons and -9% for patients with obstructive lung diseases. We conclude that the uncorrected effective airway resistance is reasonably accurate. Alternatively, a good accuracy can be obtained with only a coarse adjustment of the correction circuit.

Airway Resistance↗

PubMed1986

A simplified procedure for exponential fitting of pressure-volume curves of normal and diseased lungs.

Exponential fitting of mammalian pressure-volume curves requires least squares approaches, using computer facilities. We have developed a simplified fit procedure which can be performed by hand or by a small pocket calculator. First the asymptotic value of the volume axis, Vm, is estimated from a series of volume data at equal pressure-intervals. Subsequently, the 'pressure constant' (comparable with a time constant) and the intersection of the curve with the pressure axis (Po) are determined graphically. A comparison of the fit parameters with those obtained from a non-linear least squares procedure, performed on a medium-size computer, yielded an accuracy sufficient for practical purposes. We conclude that the simplified fit procedure may be a valuable tool for a quick and accurate interpretation of mammalian pressure-volume curves in pulmonary function routine.

Biometry↗