F. Series et I. Marc, ACCURACY OF BREATH-BY-BREATH ANALYSIS OF FLOW-VOLUME LOOP IN IDENTIFYING SLEEP-INDUCED FLOW-LIMITED BREATHING CYCLES IN SLEEP APNEA-HYPOPNEA SYNDROME, Clinical science, 88(6), 1995, pp. 707-712
1. Inspiratory flow limitation is involved in the pathophysiology of s
leep-related breathing disorders, Since the definition of flow-limited
cycle is based on a dissociation between flow and respiratory efforts
, identification of inspiratory flow limitation requires upper airway
or intrathoracic pressure measurements, We examined the accuracy of th
e analysis of the flow-volume loop of a tidal breath in identifying in
spiratory flow limitation during sleep in ten patients with a sleep ap
noea-hypopnoea syndrome. 2. Measurements were taken during continuous
positive airway pressure trials, After data acquisition, the presence
of inspiratory flow limitation was identified by the presence of an in
spiratory plateau or decrease in inspiratory flow independently of the
increase in inspiratory efforts, The flow-volume loop was reconstruct
ed for each breathing cycle by plotting the instantaneous flow and the
tidal volume, The instantaneous inspiratory and expiratory flows were
measured at 50% of the respective portion of the tidal volume, and a
breath-by-breath analysis of the mid-tidal volume-flow ratio (inspirat
ory/expiratory ratio) was obtained, The analysis of the flow-volume lo
op was compared with standard inspiratory flow limitation criteria usi
ng different values of the inspiratory/expiratory ratio threshold, bel
ow which breathing cycles were classified as flow-limited, With a lowe
r limit of the normal inspiratory/expiratory ratio threshold of 0.97,
the sensitivity and specificity of the method were both 76%, In each s
ubject, the proportion of breathing cycles identified as flow-limited
according to the inspiratory/expiratory ratio progressively decreased
with an increasing positive pressure level. 3. We conclude that analys
is of the flow-volume curve is accurate in identifying most of the ins
piratory flow limitation breathings in sleep apnoeahypopnoea syndrome.