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Furthermore, investigators have also found a poor agreement between the brands of peak flow
metres when tested at sea level (Jackson 1995), at altitude (Gardner, Crapo et al. 1992) and in
the clinic (Gregg 1991; Quanjer t992; Burge 1993; Dahlqvist, Eisen et al. 1993; Gregg 1998;
Nolan, Tolley et al. 1999) even after the technical requirements for meters were established
by the National Heart, Lung and Blood Institute in 1991 (National Heart Lung and Blood
Institute 1991). Differences have also been seen between the values obtained from new or old
meters of the same type (Douma, van der Mark et al. 1997; Nazir, Razaq et al. 2005).
Finally there is also a report of adverse reactions to peak flow monitoring with two patients
having a herniation of abdominal content and three having depression or neurotic
preoccupation with their PEF values which the authors calculated as a side effect incidence of
1.1 cases per thousand patients in the study population (Schoch, Nierhoff et al. 1998). There
has been a report about the potential of fungal contamination of peak flow devices (Ayres,
Whitehead et al. 1989). So PEF monitoring is also not the answer for accurate diagnosis and
may not offer significant advantage for long term monitoring in most asthmatic patients over
symptom assessment.
Airway challenges (both direct and indirect) have also been used to make an asthma
diagnosis, although this happens less often in paediatric field outside of the research arena.
Airway direct challenges have been used widely and are well standardised most commonly
using methacholine or histamine. These act as direct stimuli on the effector cells,
predominantly airway smooth muscle, but also on mucus glands and airway microvasculature,
causing airflow limitation (Adelroth, Hargreave et al. 1986; Woolcock, Anderson et al. 1991).
The responses follow a continuous distribution within the population, which leads to
difficulty when determining a normal, versus an asthmatic response @ehaut, Rachiele et al.
l9S3). This has been arbitrarily defined (currently set at