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Biomedical subjects

G Schmalisch

Publications and source records attributed to G Schmalisch.

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

In vitro investigations of jet-pulses for the measurement of respiratory impedance in newborns.

The aim of this in vitro study was to investigate the measuring range and accuracy of a miniaturized equipment for respiratory impedance (Zrs) measurements in newborns using jet-pulses. Brief flow pulses (peak flow=16 L x min(-1), width=10 ms) were generated by a jet-generator consisting of a solenoid valve and an injector, situated between pneumotachograph and outflow resistance. Serially arranged resistance-inertance-compliance (R-I-C) lung models (RM=1.3-6.4 kPa x L(-1) x s, CM=7.4-36.9 mL x kPa(-1), IM=1.5 Pa x L(-1) x s2) were used to measure the real and imaginary part of Zrs between 4 and 50 Hz and to determine R, C and I by means of the method of least squares. The median errors for R, C and I were -0.1 kPa x L(-1) x s (-2%), 2.4 mL x kPa(-1)(13%) and -0.2 Pa x L(-1) x s2 (-13%) for measurements without breathing signals and 0.11 kPa x L(-1) -s (3%), 3 mL x kPa(-1) (16%) and 0.28 Pa x L (-1) x s2 (19%) in mechanically ventilated models. During spontaneous breathing the influence of the breathing flow on Zrs was negligible. The equipment did not show any nonlinearity when different pulse amplitudes were used (Vmax=13-22 L x min(-1)). The investigations have shown that jet-pulses allow reliable measurements of respiratory impedance and have the potential to provide valuable information about lung mechanics in spontaneously breathing and mechanically ventilated newborns. The developed measuring head has a low apparatus dead space, is easy to disinfect, has standard connections and can be used as the T-piece in a ventilator circuit.

Airway Resistance↗
PubMed1998

Comparative investigations of algorithms for the detection of breaths in newborns with disturbed respiratory signals.

The correct detection of the beginning of inspiration and expiration in the respiratory signals is an essential prerequisite for accurate lung function testing in newborns. Five algorithms for breath detection using pneumotachographically measured flow and volume signals were investigated with regard to the error rate. To compare and to evaluate the reliability of these algorithms 12 minimally and 12 severely disturbed flow and volume signals from spontaneously breathing newborns were used. With the exception of an algorithm based on Walsh-transformed signals, all algorithms work reliably (error rate <1.1%) if disturbances are minimal. In severely disturbed signals there is a great difference between the algorithms. The most robust algorithm tested (trigger of the flow signal with an additional plausibility check of the recognized breath) resulted in an error rate of <3.4%. Not all algorithms tested are suitable for real-time applications because they differ considerably in delay time for breath detection.

Algorithms↗
PubMed1998

Assessment of functional residual capacity using nitrogen washout and plethysmographic techniques in infants with and without bronchopulmonary dysplasia.

OBJECTIVE: In normal infants, functional residual capacity using plethysmography (FRCpleth) exceeds FRC(N2) (using nitrogen washout) and the within-subject difference FRC(pleth-N2) indicates the part of pulmonary gas volume not ventilated during tidal breathing. We postulated that infants with bronchopulmonary dysplasia (BPD) have an elevated FRC(pleth-N2). DESIGN: In a prospective study, FRC(pleth-N2) in healthy newborns (controls n = 17) was compared to that in neonates recovering from the respiratory distress syndrome without BPD (noBPD, studied at discharge, n = 13) and with BPD (BPD1 n = 14, studied at 36 post-conceptional weeks; BPD2 n = 16, at discharge). MEASUREMENTS AND RESULTS: Paired measurements, FRCpleth and FRC(N2), were performed using a plethysmograph (Jaeger, Germany) and an open-circuit nitrogen washout technique (SensorMedics 2600, USA). In comparison to the controls (5.2 ml/kg), FRC(pleth-N2)/kg in noBPD (12.7 ml/kg, p < 0.001), in BPD1 (24.9 ml/kg, p < 0.001) and in BPD2 (13.5 ml/kg, p < 0.001) was significantly higher. Compared with that of the controls FRCpleth was significantly increased in BPD1 (p < 0.001) and FRC(N2) was decreased in noBPD and both BPD groups. CONCLUSION: The FRC(pleth-N2) is a reliable indicator for pulmonary inhomogeneities in infants with respiratory diseases.

Breath Tests↗
PubMed1998

Computer simulation of the measured respiratory impedance in newborn infants and the effect of the measurement equipment.

The forced oscillation technique (FOT) is a non-invasive method to investigate lung mechanics. FOT does not require active cooperation and therefore it seems to be useful for lung function measurements in newborn infants. The aims of this simulation study were to investigate the effects of development and growth of the lung, pulmonary inhomogeneities and the measurement equipment on the respiratory impedance (Zrs). The respiratory impedance was simulated by using four lung models with lumped parameters in the frequency range of 3-50 Hz considering resistive and elastic resistances of the respiratory system and the inertance of breathing air and tissue. The simulation has shown that the maturation of lungs produces only a parallel shifting of the real and imaginary part of the impedance curves whereas respiratory diseases change the course of the curves. Furthermore, a high influence of the measurement equipment (e.g. compliance of the face mask, endotracheal tube leaks) on Zrs was found. In conclusion, the simulation has shown that FOT offers a deeper insight in the structure of the respiratory system. However, the technical requirements for accurate measurements in newborns are very high.

Airway Resistance↗
PubMed1998

Accuracy of volume measurements in mechanically ventilated newborns: a comparative study of commercial devices.

OBJECTIVE: Ventilatory measurements in ventilated newborns are increasingly used to monitor and to optimize mechanical ventilation. The aim of this study was to compare the accuracy of volume measurements by different instruments using standardized laboratory conditions. METHODS: The accuracy of displayed volume values of different commercial devices (Bicore CP-100, Ventrak 1500, Ventrak 1550, Babylog 8000, PEDS IV and SensorMedics 2600) was investigated using adjustable calibration syringes (volume range 2-60 ml, breathing rates 30/min-60/min) and humidified (>95%), heated (35 degrees C) breathing gas with adjustable FIO2 (0.21-1.0). The pneumotach and also the tubes were placed within an incubator (37 degrees C). RESULTS: The relative volume error of all devices was in conformity with clinically allowed tolerances (Bicore CP-100 6.4+/-0.5% (mean +/- SD), Ventrak 1500 3.6+/-4.2%, Ventrak 1550 6.5+/-2.7%, Babylog 8000 -5.5+/-1.5%, PEDS IV -4.0+/-1.4%, SensorMedics 2600 3.5+/-1.75%) for the measuring range studied (10 ml < V < 60 ml, rate 30-60/min, FIO2 = 0.21). Unacceptable errors were obtained for volumes lower than 10 ml with Bicore CP-100 (-28.5+/-26%) and PEDS IV (-10.3+/-3.4%). Changes in FIO2 had an important influence on volume measurements and only the SensorMedics 2600 and the PEDS IV corrected properly for FIO2 changes. CONCLUSION: Most of the currently available neonatal spirometry devices allow sufficiently accurate volume measurements in the range of 10-60 ml and at frequencies between 30-60/min provided that an increased FIO2 is taken into account.

Female↗
PubMed1998

Leak measurements in spontaneously breathing premature newborns by using the flow-through technique.

A new method for measuring and correcting air leaks during lung-function testing in infants has been validated in vitro and in vivo by using a flow-through system that measured the inflow and outflow of a face mask. An adjustable leak was quantified by using suction flow to validate the accuracy of leak measurements. To validate the leak correction, the volume of a pump was measured with different air leaks (0-30%). The method developed was tested in 67 infants breathing spontaneously. There was good agreement between measured and simulated leaks (r = 0.998, P < 0.001; 95% limits of agreement were -0.3 and 0.1%, respectively). The volume was generally underestimated because of leaks, and the volume error was up to 94% compared with the maximum error of 5% after leak correction. With continuous leak measurements in vivo, there were <4% actual leaks (median 2.6%), and we did not observe any leaks in >7% of cases. The leak correction improved the accuracy of ventilatory measurements. The monitoring of leaks is helpful for airtight placement of the face mask and for prevention of serious measurement errors caused by leaks.

Algorithms↗
PubMed1998

The stable microbubble test on tracheal aspirate samples from newborn babies for diagnosis of surfactant deficiency and/or surfactant malfunction.

For predicting the risk of respiratory distress syndrome (RDS), lung surfactant in amniotic fluid can be assessed by observation of stable microbubbles (< 15 microns diameter). It was investigated if the stable microbubble test (MT) developed on amniotic fluid could be applied on tracheal aspirate samples (TA) obtained from newborn infants. Forty-four TA from 29 newborn infants without pulmonary diseases (group 1) and 65 TA from 21 newborn infants with respiratory insufficiency (group 2) were analyzed by the MT for predicting surfactant deficiency and/or surfactant malfunction. Ten microbubbles/ mm2 was defined as cutoff value of the MT. A specificity of 90% and a sensitivity of 52% was obtained with this cutoff value. A much lower rate of false negative results (sensitivity 91%) was noted after surface tension measurement of TA. The sensitivity of the MT (52%) does not encourage the use of the MT on TA.

Cohort Studies↗
PubMed1996

Surface tension measurements on pharyngeal and tracheal aspirate samples from newborns without and with respiratory distress syndrome.

A rapid test determining surfactant deficiency or dysfunction might help in controlling therapy of respiratory distress syndrome (RDS). Forty tracheal aspirate samples (TA) from 40 newborns with RDS (group 1) and 46 pharyngeal from 46 newborns without RDS (reference group) were analyzed by surface tension measurement with the pulsating bubble surfactometer. Five surface tension parameters were compared. Marked differences between both groups could be noted for the parameters: minimum surface tension (gamma min) and stability index (S), while maximum surface tension (gamma max), surface tension after a 10-second adsorption period and hysteresis area did not have striking differences. The parameters gamma min and S have the highest diagnostic value for determining surfactant deficiency or dysfunction. For a rapid test it is sufficient to compare gamma min with reference values, because S is calculated from gamma min and gamma max.

Body Fluids↗
PubMed1995

[Differential breast tumor diagnosis by comparing blood circulation of the tumor with the contralateral breast using color coded, pulsed Doppler ultrasound].

74 breast tumor patients were preoperatively examined by means of colour and pulsed-wave Doppler sonography using the ultrasonic instrument ALT Ultramark 9 HDI with a broad-band linear scanner, 5-10 MHz. The Doppler flow velocity waveforms, from the vessels of the mammary lesion (affected breast) and the corresponding quadrant of the contralateral breast (non-affected breast), respectively, were compared in respect of the four parameters maximal systolic velocity, minimal diastolic velocity, pulsatility index (PI) and resistance index (RI). In 48 cases we succeeded in representing arterial vessels both inside the affected and the contralateral breast. The aim of the study was to examine whether these parameters show a significantly different degree of deviation in correlation with the tumours being either benign or malign. In cases with benign lesions (n = 24) we did not find any significant differences in all the parameters that we examined. In cases with cancer, however (n = 18), a significantly higher systolic velocity was found in the affected breast compared to the contralateral breast, but there were no differences in the other parameters. Although the quantitative Doppler measurements are angle-dependent parameters, the study showed that the maximal velocity in the affected breast compared to the contralateral breast is the most useful parameter in differential diagnosis of breast tumours.

Blood Flow Velocity↗
PubMed1995

[Adjusting background flow in measuring ventilation of newborn infants and infants using the flow-through technique].

Ventilatory measurements especially in preterm infants are hampered by the additional apparatus dead space (face mask, pneumotach, shutter, ...). The apparatus dead space can be higher than the physiological dead space and affects gas exchange and blood gases significantly. For lung function testing in premature or term infants a background flow (flow-through technique) is frequently used to eliminate the apparatus dead space. This background flow must be higher than the maximum inspiratory flow (maxVin). For its optimization ventilatory measurements were performed in 62 sleeping infants aged 2 to 28 days (birth weight 760-5000 g). maxVin correlated strongly with minute ventilation VE (r = 0.90; p < 0.001). The ratio maxVin/VE decreased significantly (p < 0.05) with increasing frequency: from 4.4 +/- 0.8 (f < 40/min); 4.1 +/- 0.7 (f = 40-59/min); 3.8 +/- 0.5 (f = 60-79/min) to 3.4 +/- 0.4 (f > 80/min). With increasing frequency the flow signal becomes sinusoidal and the ratio maxVin/VE tends to pi. Therefore, during tidal breathing the background flow should be at least three but not more than the six times VE to avoid an impairment of measurements.

Carbon Dioxide↗
PubMed1995

[Effect of background flow on the accuracy of respiratory flow and respiratory volume measurement in newborn infants].

Measurement of ventilation, in particular in preterm infants, is greatly impaired by equipment dead space, with its significant effect on the ventilatory pattern and gas exchange. For patients of this age, therefore, dead-spacefree methods are needed for long-term measurements. Rebreathing can be avoided if the pneumotachograph (PNT) and face mask are flushed with a continuous background flow. The effect of this on the measurements has not yet been investigated in detail. A measuring system comprising two identical baby PNTs (Jaeger/Germany) permitting a background flow of between 0 and 7 l per min was used. Spontaneous breathing was simulated with a 100 ml calibration syringe employing volumes of 20, 40, 60 and 100 ml (Rudolph/USA) and a frequency of 30 min-1. The measurements were carried out with a T-piece from a respirator circuit, a hand mask (50 ml) and a face chamber having a volume of 850 ml (Siemens-Elema/Sweden). To investigate the dynamic properties of the equipment, we employed flow jumps generated with a magnetic valve (response time < 2 ms) and analysed the responses using Fourier analysis. We were unable to find any significant relationship between the accuracy of volume measurement and tidal volume for any of the measured volumes. An increase in background flow resulted in an underestimation of the volume with an error < 3%. We found no influence of the background flow or type of face mask on the frequency response.(ABSTRACT TRUNCATED AT 250 WORDS)

Equipment Design↗
PubMed1994

[Effect of physical properties of respiratory gas on pneumotachographic measurement of ventilation in newborn infants].

UNLABELLED: The measurement of ventilation in neonates has a number of specific characteristics; in contrast to lung function testing in adults, the inspiratory gas for neonates is often conditioned. In pneumotachographs (PNT) based on Hagen-Poiseuille's law, changes in physical characteristics of respiratory gas (temperature, humidity, pressure and oxygen fraction [FiO2]) produce a volume change as calculated with the ideal gas equation p*V/T = const; in addition, the viscosity of the gas is also changed, thus leading to measuring errors. In clinical practice, the effect of viscosity on volume measurement is often ignored. The accuracy of these empirical laws was investigated in a size 0 Fleisch-PNT using a flow-through technique and variously processed respiratory gas. Spontaneous breathing was simulated with the aid of a calibration syringe (20 ml) and a rate of 30 min-1. RESULTS: The largest change in viscosity (11.6% at 22 degrees C and dry gas) is found with an increase in FiO2 (21...100%). A rise in temperature from 24 to 35 degrees C (dry air) produced an increase in viscosity of 5.2%. An increase of humidity (0...90%, 35 degrees C) decreased the viscosity by 3%. A partial compensation of these viscosity errors is thus possible. Pressure change (0...50 mbar, under ambient conditions) caused no measurable viscosity error. With the exception of temperature, the measurements have shown good agreement between the measured volume measuring errors and those calculated from viscosity changes. CONCLUSIONS: If the respiratory gas differs from ambient air (e.g. elevated FiO2) or if the PNT is calibrated under BTPS conditions, changes in viscosity must not be neglected when performing accurate ventilation measurements. On the basis of the well-known physical laws of Dalton, Thiesen and Sutherland, a numerical correction of adequate accuracy is possible.

Airway Resistance↗
PubMed1993

[Techniques and clinical application of capnography in newborn infants and infants].

Capnography has not yet achieved wide application as a noninvasive method for monitoring and optimizing assisted ventilation in neonatological intensive care medicine. The development of new equipment will probably make it possible for capnography to find its place as a routine examination. The aim of this work is to evaluate the existing methods for CO2-analysis in newborns and infants using data from existing literature. A mainstream capnograph (Novametrix 7000) was used to demonstrate typical capnographic curves in newborns and prematurely born children. The results offer new possibilities for the optimization of assisted ventilation.

Carbon Dioxide↗