Some Experiences with Electronic Simulation of BTPS Conditions in Body Plethysmography1

Woitowitz, H.‐J.; Günthner, W. A.; Woitowitz, R. H.

doi:10.1159/000386234

Cited by 8 publications

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“…The thermal component may then be eliminated by subtracting from Vpl a signal proportional to V with the appropriate amplitude (subtraction method [6][7][8]); the method is equivalent to extracting the component of Vpl which is in phase with flow, and using it to compute sRaw.…”

mentioning

confidence: 99%

Frequency dependence of specific airway resistance in a commercialized plethysmograph

Peslin¹,

Duvivier²,

Malvestio³

et al. 1996

Eur Respir J

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Specific airway resistance (sRaw) measured by body plethysmography has been shown to decrease markedly with decreasing breathing frequency when the inspired air is not conditioned to body temperature, atmospheric pressure and saturation with water vapour (BTPS). The phenomenon has been attributed to noninstantaneous gas warming and wetting in the airways. The aim of this investigation was to assess whether the phenomenon was also present in a commercialized plethysmograph featuring an "electronic BTPS correction".Airway resistance (Raw) and sRaw were measured in 15 healthy subjects at six breathing frequencies ranging 0.25-3 Hz, using a constant volume plethysmograph in which a correction for non-BTPS gas conditions was applied by electronically flattening the box pressure-airway flow loop (Jaeger Masterscreen Body, version 4.0).The temperature and water vapour saturations in the box averaged 26.5±1.3°C and 59±6%, respectively. Raw and sRaw exhibited a clear positive frequency dependence in all but one subject. From 0.25 to 3 Hz Raw increased from (mean±SD) 0.62±0.55 to 1.71±+0.76 hPa·s·L -1 (p<0.001), and sRaw from 2.34±1.90 to 7.55±3.08 hPa·s (p<0.001). The data are consistent with a simple model, in which gas conditioning in the airways and external dead space occurred with a time constant of 0.39 s.We conclude that the electronic BTPS correction of the instrument was inadequate, probably because it is assumed that gas conditioning in the airways is instantaneous. We recommend that, with similar instruments, airway resistance be measured using as high a panting frequency as feasible. Eur Respir J., 1996Respir J., , 9, 1747Respir J., -1750 When a subject breathes ambient air inside a body plethysmograph, the largest part of the volume variations measured by the instrument (Vpl) is due to the warming and humidification of inspired air in the airway during the inspiratory phase and to its partial cooling during the expiratory phase. Computed according to the equation of DRORBAUGH and FENN [1] the change in Vpl occurring when a tidal volume of 0.6 L at 22°C and 50% water vapour saturation (SH 2 O) is conditioned to body temperature, atmospheric pressure and saturation with water vapour (BTPS) amounts to about 57 mL. This thermal component of Vpl is more than 10 times larger than the airway resistance (Raw) component expected in a normal subject (specific Raw (sRaw=5 hPa·s)) at a flow rate of 1 L·s -1 .

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confidence: 99%

Frequency dependence of specific airway resistance in a commercialized plethysmograph

Peslin¹,

Duvivier²,

Malvestio³

et al. 1996

Eur Respir J

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“…The last strategy that allows to attenuate the thermal and metabolic artifacts is to subtract from ΔV S , electronically or digitally, a signal proportional to ΔV th + ΔV met (electronic or digital compensation). This task is far from simple, as warming and humidification of air in the airways during inspiration, and cooling and loss of water vapor in the box during expiration are not instantaneous processes, nor have the same kinetics [ 13 , 14 ], as once believed [ 15 , 16 ]. Indeed, in a technical note appeared in 1996, concerns were risen regarding the appropriateness of the compensation, as R aw , measured in healthy subjects with a plethysmograph equipped with electronic compensation, was found to increase with increasing respiratory rate faster than it could be expected on physiological ground [ 17 ].…”

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Diagnostic Insights from Plethysmographic Alveolar Pressure Assessed during Spontaneous Breathing in COPD Patients

et al. 2021

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Since its introduction in the clinical practice, body plethysmography has assisted pneumologists in the diagnosis of respiratory diseases and patients’ follow-up, by providing easy assessment of absolute lung volumes and airway resistance. In the last decade, emerging evidence suggested that estimation of alveolar pressure by electronically-compensated plethysmographs may contain information concerning the mechanics of the respiratory system which goes beyond those provided by the simple value of airway resistance or conductance. Indeed, the systematic study of expiratory alveolar pressure-flow loops produced during spontaneous breathing at rest has shown that the marked expansion of expiratory loops in chronic obstructive pulmonary disease patients mainly reflects the presence of tidal expiratory flow-limitation. The presence of this phenomenon can be accurately predicted on the basis of loop-derived parameters. Finally, we present results suggesting that plethysmographic alveolar pressure may be used to estimate non-invasively intrinsic positive end-expiratory pressure (PEEPi) in spontaneously breathing patients, a task which previously could be only accomplished by introducing a balloon-tipped catheter in the esophagus.

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Berufliche Asbeststaubexposition und obstruktive Ventilationsstörungen

Woitowitz¹

1970

Internationales Archiv Für Arbeitsmedizin / International Archives of Occupational Health

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Some Experiences with Electronic Simulation of BTPS Conditions in Body Plethysmography1

Cited by 8 publications

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Frequency dependence of specific airway resistance in a commercialized plethysmograph

Frequency dependence of specific airway resistance in a commercialized plethysmograph

Diagnostic Insights from Plethysmographic Alveolar Pressure Assessed during Spontaneous Breathing in COPD Patients

Berufliche Asbeststaubexposition und obstruktive Ventilationsstörungen

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