Accurate measurement of N2 volumes during N2 washout requires dynamic adjustment of delay time

Brunner, Josef; Wolff, G.; Cumming, Gordon; Langenstein, H

doi:10.1152/jappl.1985.59.3.1008

Cited by 57 publications

(35 citation statements)

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“…Both signals are measured simultaneously, and no delay time correction is necessary. This is an important advantage, as several studies (6,20) have shown that when gas fractions are measured by sidestream sampling, there is a substantial delay between gas analysis signal and the mainstream gas flow measurement signal, mainly caused by the transport time of the sampled gas. Furthermore, flow measurement with a conventional pneumotachograph must be corrected for changes in gas viscosity during gas washout (21), requiring cumbersome calibration.…”

Section: Discussionmentioning

confidence: 99%

Measurement of Functional Residual Capacity in Rabbits and Children Using an Ultrasonic Flow Meter

Schibler

Henning

2001

Pediatr Res

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A sulfur hexafluoride (SF 6 ) washin/washout technique was developed using an ultrasonic flowmeter to measure functional residual capacity (FRC) during mechanical ventilation. The ultrasonic flowmeter measures simultaneously flow and molar mass of the mainstream gas. Ventilation distribution was studied using moment ratios analysis (alveolar-based mean dilution number). Accuracy and precision of the measurement technique were tested in a mechanical lung model, and the method's sensitivity to changes of FRC was assessed in seven ventilated rabbits and six children. In the mechanical lung model with a volume range from 10 to 60 mL, the mean error of FRC measurement was 0.096 Ϯ 0.9 mL (range, 0 -2 mL). In seven rabbits (mean body weight, 3.6 kg), measurements of FRC and alveolar-based mean dilution number were made at positive end-expiratory pressures (PEEP) of 0, 3, and 6 cm H 2 O. The mean coefficient of variation of 66 FRC-measurements was 5.5% (range, 0 -15.3%). As the applied PEEP increased, mean FRC per kilogram body weight increased from 13.3 Ϯ 3.4 mL/kg (PEEP of 0 cm H 2 O) to 16.7 Ϯ 3.6 mL/kg (PEEP of 3 cm H 2 O) and to 20.8 Ϯ 4.3 mL/kg (PEEP of 6 cm H 2 O). Alveolar-based mean dilution number decreased accordingly from 1.94 Ϯ 0.42 (PEEP ϭ 0; mean Ϯ SD), to 1.91 Ϯ 0.45 (PEEP ϭ 3) and to 1.59 Ϯ 0.35 (PEEP ϭ 6). In the six children, as applied PEEP increased, mean FRC per kilogram increased from 21.1 Ϯ 4.51 mL/kg (PEEP ϭ 0), to 22.4 Ϯ 1.8 mL/kg (PEEP ϭ 5) and 27.2 Ϯ 3.4 mL/kg (PEEP ϭ 10). FRC measurement using the ultrasonic flowmeter is accurate and simple to use in ventilated and spontaneously breathing children. The monitoring of FRC is an important tool for interpreting volume-dependent pulmonary mechanics (e.g. lung elastic recoil pressure or airway resistance). Since the open-circuit MBNW was first described by Darling et al. in 1940 (1), several investigators have used gas washout techniques to measure FRC in spontaneously breathing (2, 3) and mechanically ventilated patients (4 -6). Other gas washout techniques involve helium dilution (7), argon washout (8), or washout of SF 6 (9). Each of these techniques has its own limitations. The MBNW can only be accurately performed if the patient's oxygen requirement does not exceed a certain amount (4 -6).Although MBNW can be performed easily, the considerable changes in gas viscosity during the washout maneuver significantly affect the accuracy of the gas flow measurement by pneumotachography (10, 11). The helium dilution technique is based on a closed circuit, and a leak in the measuring system reduces its accuracy (7). SF 6 washout is a potentially suitable technique for children, including those who require near 100% oxygen to maintain normal Hb saturation. There are a few studies using SF 6 as a washout gas (12-14) and a mass spectrometer or an infrared analyzer to measure SF 6 concentration. Neither technique is commercially available for routine measurement. The infrared analyzer has a low signal-to-noise ratio and a response time of 20 ms or more. Ai...

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Section: Discussionmentioning

confidence: 99%

Measurement of Functional Residual Capacity in Rabbits and Children Using an Ultrasonic Flow Meter

Schibler

Henning

2001

Pediatr Res

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“…Alternatively the cumulative expired nitrogen volume is obtained by integrating the product of expiratory flow and nitrogen concentration and summing these over subsequent breaths. This method is technically demanding: it requires very careful dynamic synchronisation of flow and concentration signals, and linearisation of the nitrogen meter [160]. With both procedures errors can arise due to elimination of nitrogen from tissues and body fluids.…”

Section: Multibreath Nitrogen Wash-out Methodsmentioning

confidence: 99%

Lung volumes and forced ventilatory flows

Quanjer¹,

Tammeling²,

Cotes³

et al. 1993

European Respiratory Journal

4,535

982

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“…To characterize the patient's respiratory system, accessible pulmonary gas volume (APV) was determined using the nitrogen washout technique. The details of the wash-out technique including synchronization of flow and concentration signals have been described previously [18,19].…”

Section: Methodsmentioning

confidence: 99%

Time constant/volume relationship of passive expiration in mechanically ventilated ARDS patients

Guttmann¹,

Eberhard²,

Fabry³

et al. 1995

Eur Respir J

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T Ti im me e c co on ns st ta an nt t/ /v vo ol lu um me e r re el la at ti io on ns sh hi ip p o of f p pa as ss si iv ve e e ex xp pi ir ra at ti io on n i in n m me ec ch ha an ni ic ca al ll ly y v ve en nt ti il la at te ed d A AR RD DS S p pa at ti ie en nt ts s The mean values of τE for each volume slice did not differ significantly throughout expiration, averaging 690±218 ms (mean±SD of five slices and 12 patients). We show that the flow-dependent resistance of the endotracheal tube (RETT) is mainly responsible for the observed time constant homogeneity.We conclude that in ARDS patients during uninterrupted mechanical ventilation the time constants of passive expiration are markedly modified by the flow-dependent resistance of the endotracheal tube (RETT), and also by the external resistance of tubing and ventilator (REX). RETT and REX render τE about three times larger than the time constant of the patient's respiratory system alone.

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Accurate measurement of N2 volumes during N2 washout requires dynamic adjustment of delay time

Cited by 57 publications

References 0 publications

Measurement of Functional Residual Capacity in Rabbits and Children Using an Ultrasonic Flow Meter

Measurement of Functional Residual Capacity in Rabbits and Children Using an Ultrasonic Flow Meter

Lung volumes and forced ventilatory flows

Time constant/volume relationship of passive expiration in mechanically ventilated ARDS patients

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