Induced sputum differential cell counts have been advocated as a method of
non-invasively assessing airway inflammation in asthma and other airway dis
eases. Since sputum induction usually involves delivering hypertonic saline
via a high output ultrasonic nebulizer there have been concerns about its
safety in asthma. There are relatively little data on the effects of sputum
induction in large numbers of patients. We have examined the success rate
and effect of sputum induction on forced expiratory volume in 1 sec (FEV1)
in 100 inductions performed on 79 patients using a low output nebulizer. Th
irty-seven patients had asthma, 29 had miscellaneous conditions (mainly chr
onic cough) and 13 were subjects without respiratory symptoms. Sputum was i
nduced 10 min after 200 mu g of inhaled salbutamol by sequential 5-min inha
lations of 3, 4 and 5% saline delivered via a Fisoneb ultrasonic nebulizer
and FEV1 was measured after each inhalation. Sputum induction resulted in a
sample suitable for analysis in 92% of asthmatics, 90% of those with misce
llaneous conditions and 100% of normal subjects. The mean (SEM) maximum per
cent fall in FEV1 was 5.4% (0.1), 4.3% (1.0) and 2.6%(1.1)in subjects with
asthma, miscellaneous conditions and in asymptomatic subjects respectively
. Only 13 inductions resulted in a >10% fall in FEV1, and only three of the
se resulted in a >20% fall. The maximum per cent fall in FEV1 did not corre
late with baseline FEV1 % predicted (r = - 0.17), the log sputum eosinophil
count (r = - 0.12), or the methacholine PC20 (r = - 0.14). We conclude tha
t sputum induction using a relatively low output ultrasonic nebulizer with
premedication with salbutamol is successful and safe in the majority of pat
ients with asthma and other airway conditions.