Thorax 1998;53:775-779 ( September )

Exhalation flow and pressure-controlled reservoir collection of exhaled nitric oxide for remote and delayed analysis

P Paredi,^{a b} S Loukides,^a S Ward,^c D Cramer,^c M Spicer,^d S A Kharitonov,^a P J Barnes^a

^a Department of Thoracic Medicine, Imperial College School of Medicine at the National Heart and Lung Institute, Dovehouse Street, London SW3 6LY, UK, ^b University Respiratory Hospital, Milan, Italy, ^c Lung Function Unit, ^d Biomedical Engineering Department, ^e Royal Brompton Hospital, London, UK

Correspondence to: Professor P J Barnes.

Received 10 November 1997; Returned to authors 22 January 1998; Revised version received 11 May 1998; Accepted for publication 13 May 1998

BACKGROUNDExpiratory flow rate, soft palate closure, and dead space air may influence exhaled levels of nitric oxide (NO). These factors have not been evaluated in the reservoir collection of NO.
METHODSExhaled NO was collected into a reservoir during a single flow and pressure controlled exhalation.
RESULTSNO collected in a reservoir containing silica gel was stable for 24 hours. Nasally delivered 4.8% argon measured by mass spectrometry did not contaminate exhaled argon levels (0.1 (0.02)%) in five volunteers during exhalation against a resistance (10 (0.5) cmH₂O), hence proving an effective soft palate closure. Exhaled NO in the reservoir was 11 (0.2) ppb, 8.6 (0.1) ppb, 7.1 (0.6) ppb, and 6.6 (0.4) ppb in five normal subjects and 48.3 (18) ppb, 20.3 (12) ppb, 16.9 (0.3) ppb and 10.1 (0.4) ppb in 10 asthmatic subjects at four studied expiratory flows (5-6, 7-8, 10-11, and 12-13 l/min, respectively), with NO levels equal to direct measurement (7.3 (0.5) ppb and 17.4 (0.5) ppb for normal and asthmatic subjects respectively, p<0.05) at the flow rate 10-11 l/min. Elimination of dead space proved necessary to provide NO levels comparable to the direct measurement. Exhaled NO collected into the reservoir without dead space during flow controlled exhalation against mild resistance provided close agreement (mean (SD) difference -0.21 (0.68), coefficient of variation 4.58%) with direct measurement in 74 patients (NO range 1-69 ppb).
CONCLUSIONSFlow and pressure controlled collection of exhaled NO into a reservoir with silica gel provides values identical to the direct measurement and may be used to monitor asthma at home and where analysers are not on site.

Keywords: exhaled nitric oxide; reservoir collection

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© 1998 by Thorax
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