Biomedical Engineering Reference
In-Depth Information
course of the reduction in inflammatory markers in the two groups, though
there was considerable variation in levels observed. Although there is a sug-
gestion that exacerbations in alphal-antitrypsin patients may be more
severe, peak flow changes with therapy did not differ and this suggests that
response to therapy is similar in the two patient groups. Whether the
increased inflammatory response at exacerbation in alphal-antitrypsin
deficiency plays a part in the accelerated decline in FEV1 requires further
studies with larger patient numbers.
III. VIRAL INFECTIONS
COPD exacerbations are frequently triggered by upper respiratory tract
infections and these are commoner in the winter months with colder tem-
peratures (16), when there are more respiratory viral infections prevalent
in the community. Patients may also be more prone to exacerbations in
the winter months as lung function in COPD patients shows small but
significant falls with reduction in outdoor temperature during winter (16).
Further evidence that respiratory viral infections are important
triggers of exacerbations comes from the association of colds with exacerba-
tions. In a prospective analysis of 504 exacerbations, where daily monitoring
was performed, larger falls in peak flow were associated with symptoms of
dyspnoea, presence of colds, and related to longer recovery time from
exacerbations (17). We have reported that up to 64% of exacerbations were
associated with symptomatic colds as assessed using daily diary card mon-
itoring and thus it is likely that these exacerbations were precipitated by
viruses (8). The commonest virus associated with COPD exacerbations are
rhinoviruses and other viruses include coronavirus, RSV (respiratory syncy-
tial virus), influenza, parainfluenza, and adenovirus.
Rhinovirus is the virus that is responsible for the common cold and is
currently the most important cause of COPD exacerbation. Since the intro-
duction of influenza immunization for patients with chronic lung disease,
influenza has become a less prominent cause of exacerbation, though this
is still likely to be an important factor at times of influenza epidemics
(18). Together with enteroviruses, rhinoviruses belong to the picornavirus
group of RNA viruses. Rhinoviruses are spread directly from one person
to another by infected respiratory secretions. Although rhinovirus has been
recognized as an important cause of asthmatic exacerbations (19,20), till
recently rhinovirus has not been considered to be of much significance dur-
ing exacerbations of COPD, as the techniques for detection used only
isolation by cell culture and serology. This virus has fastidious growth
requirements and over 100 serotypes making detection by culture or serolo-
gical methods very difficult.
Early studies using serological and cell culture diagnostic methods
reported relatively small effects of rhinovirus at COPD exacerbations
