Unevenness of ventilation assessed by the expired CO2 gas volume versus VT curve in asthmatic patients

2004 
Abstract Recently, we have shown that the expired CO 2 gas volume versus tidal volume ( V CO 2 – V T ) curve is a useful tool for assessing unevenness of ventilation because it allows the separation of tidal volume into three functional compartments: (a) the CO 2 -free expired air ( V 0 ), (b) the transitional volume ( V tr ), (c) the alveolar volume ( V A ) and the measurement of alveolar F CO 2 during resting breathing in normal subjects and patients with COPD. In this paper, we have investigated whether changes pertaining to unevenness of ventilation taking place immediately after the administration of methacholine can be assessed using the V CO 2 – V T curve in asthmatic patients. The V CO 2 – V T curve was obtained during tidal breathing from 16 stable asthmatic patients who underwent a methacholine challenge test. It has been found that the V tr , and hence Bohr’s dead space ( V D,Bohr = V 0 + V tr ), over tidal volume ratios were significantly increased immediately after the methacholine administration, whilst the V 0 over tidal volume ratio was not affected. The change of the above ratios was not related to the percentage decrease of FEV 1.0 following methacholine administration.
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