Abstract
The research presented in this thesis focuses on the identification and utilisation of
novel indices measured from tidal breathing expiratory flow patterns to assess airflow
obstruction in adults. The work is in two parts, firstly the development of the data collection
protocol and the identification of suitable indices and secondly the evaluation ofthe
reproducibility of these indices and their comparison with conventional indices and reported
symptoms.
The current routine method used to assess airflow obstruction is the measurement of
FEV], however this test requires patient understanding of the test procedure and maximal
effort to produce satisfactory results. Furthermore, forced expiration is not a breathing
manoeuvre that people perform in every day life. The usefulness of FEVi in assessing
reversibility to bronchodilation was studied in a retrospective study which showed that 41%
of patients who were identified as non-reversible by FEVi criteria showed reversibility of
forced or relaxed vital capacity, indicating that FEVi does not detect all the physiological
effects of bronchodilators. Iftidal breathing is measured, a number of the disadvantages of
FEVi are overcome. It is effort-independent, requires no learning of special breathing
manoeuvres on the patient's part and so can be performed even in acutely breathless patients.
A method ofrecording tidal breathing patterns was developed in which the type of
equipment and the measurement protocol was comfortable for the subject, applicable to the
routine clinical setting and impacted minimally on the tidal breathing pattern. A five-minute
collection time was chosen, recorded after a two-minute acclimatisation period. A method of
producing an averaged breath was developed from which a number of novel tidal indices
could be measured. After analysis of these indices in pilot studies, three indices, (TBEV i
(volume of air exhaled in the first second of a tidal breath), TPEF (peak tidal expiratory flow
rate) and EF25 (expiratory flow at end tidal volume plus 25% end tidal volume) were
identified which changed consistently following bronchodilators and these were
subsequently studied in more depth. Each of these indices correlated with specific
conductance (sGaw) at baseline and showed significant increases after bronchodilator but not
after placebo treatment in patients known to have reversible airflow obstruction.
placebo treatment in patients known to have reversible airflow obstruction.
For the tidal breathing method to be clinical acceptable it had to be shown to be
reproducible and ideally to correlate with patient perceived breathlessness. The final section
ofthe thesis reports studies of reversibility of these measures. Reproducibility was similar to
conventional indices of airway obstruction.
In summary this thesis describes development of a method for the measurement and
analysis of tidal breathing expiratory flow patterns, which yields consistent and
physiologically plausible changes in defined tidal indices following bronchodilator
treatment.
