Effect of valve closure time on the determination of respiratory resistance by flow interruption
- 98 Downloads
The resistance of the respiratory system to flow may be conveniently assessed by the flow-interruption technique, in which the flow of gas at the mouth of a subject is suddenly interrupted, while the pressure just distal to the point of interruption, is recorded. There is a rapid change in pressure immediately upon interruption, presumably giving the resistive pressure drop across the pulmonary airways. This is followed by a further slow change in pressure reflecting stress relaxation in the respiratory system and possibly gas redistribution between different regions of the lung. The diagnostic potential of the post-occlusion pressure signal is dependent on the airway opening being occluded effectively instantaneously. We present a description of an occlusion valve we have designed and built for performing rapid airway occlusions. We are able to measure the closing characteristics of our valve precisely, and show that its finite closure time of 12 ms causes the initial rapid drop in pressure to be underestimated by about 7 per cent. A simple numerical correction scheme allows us to estimate this pressure drop correctly to within one or two per cent.
KeywordsAirways resistance Linear models of respiratory system
Unable to display preview. Download preview PDF.
- Bates, J. H. T., Rossi, A. andMilic-Emili, J. (1985) Analysis of the behaviour of the respiratory system with constant inspiratory flow.J. Appl. Physiol.,58, 1840–1848.Google Scholar
- Gottfried, S. B., Rossi, A., Calverley, P. M. A., Zocchi, L. andMilic-Emili, J. (1984) Interrupter technique for measurement of respiratory mechanics in anaesthetized cats.J. Appl. Physiol.,56, 681–690.Google Scholar
- Hyett, A. W. andMcDermott, M. (1959) A simple air-flow interrupter.J. Physiol. (Lond.),147, 40P.Google Scholar
- Jackson, A. C., Milhorn, H. T. andNorman, J. R. (1974) A reevaluation of the interrupter technique for airway resistance measurement.J. Appl. Physiol.,36, 264–268.Google Scholar
- Knudson, R. J., Mead, J. andKnudson, D. E. (1974) Contribution of airway collapse to supramaximal expiratory flows.,36, 653–667.Google Scholar
- Marshall, R. andDubois, A. B. (1956) The measurement of the viscous resistance of the lung tissues, in normal man.Clin. Sci.,15, 161–169.Google Scholar
- Mead, J. andWhittenberger, J. L. (1954) Evaluation of airway interruption technique as a method for measuring pulmonary air-flow resistance.J. Appl. Physiol.,6, 408–416.Google Scholar
- Shephard, R. J. (1963) Mechanical characteristics of the human airway in relation to use of the interrupter valve.Clin. Sci.,25, 263–280.Google Scholar
- von Neergaard, J. andWirz, K. (1927) Die Messung der Strömungswiderstände in den Atemwegen des, Menschen, insbesondere bei Asthma und Emphysem.Z. Klin. Med.,105, 51–82.Google Scholar