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Several measures exist to aid the diagnosis of upper airway obstruction (UAO). These include subjective clinical signs such as the presence of stridor and objective measures such as the pattern of the flow-volume curve. However, by far the simplest and easily measured, but yet relatively unknown and underutilised, is the forced expiratory volume in 1 second (FEV1) / peak expiratory flow (PEF) rat...
Several measures exist to aid the diagnosis of upper airway obstruction (UAO). These include subjective clinical signs such as the presence of stridor and objective measures such as the pattern of the flow-volume curve. However, by far the simplest and easily measured, but yet relatively unknown and underutilised, is the forced expiratory volume in 1 second (FEV1) / peak expiratory flow (PEF) ratio. We wish to reignite attention to the use of this uncomplicated measurement through presentation of an interesting clinical case.
A 57-year old lady presented to our respiratory clinic with a complaint of inspiratory stridor. She did not have any other significant respiratory symptoms. There were no overt symptoms of gastroesophageal reflux or oesophageal dysfunction. On direct questioning, she denied any symptoms consistent with collagen vascular disease or vasculitis, except Raynaud’s phenomenon. Her medications included losartan for hypertension and amitriptyline for depression. She is a never-smoker. Clinical examination was unremarkable apart from a soft inspiratory stridor, which was heard best above the suprasternal notch. Her blood biochemistry, haematology, autoimmune, and vasculitic screen were unremarkable. Spirometry showed FEV1 of 2.79L (110% predicted), forced vital capacity (FVC) of 3.57L (120% predicted), FEV1/FVC ratio of 78%, and PEF of 396L/min (105% predicted). Her calculated FEV1/PEF ratio was 7.05ml/L/min. The pattern of the expiratory flow-volume curve was normal with a slight plateau in the inspiratory flow-volume curve (Figure 1). Flexible fibre-optic bronchoscopy demonstrated a subglottic stenosis (Figure 2).
Several pioneering studies have previously determined the usefulness of the FEV1/PEF ratio in diagnosing UAO.1-3 FEV1 is defined as the volume measured during the initial 1 second of a forced expiration from full inspiration and PEF is defined as the maximum flow rate maintained for at least 10 milliseconds during a forced expiration from full inspiration. Therefore, in UAO where the embarrassment is in the pre-carina upper airway, one would intuitively expect the FEV1/PEF ratio to increase, as chronologically, PEF would be affected more than FEV1, with the former reflecting more proximal airway per se. Evidently, the FEV1/PEF ratio has been shown to be significantly higher in patients with UAO compared to patients with asthma, chronic obstructive pulmonary disease, and normal subjects.1;2 A value of above 10ml/L/min was initially thought to represent UAO,1;2 although this was subsequently found to vary between 7ml/L/min and 12ml/L/min depending on the different subgroups of UAO such as extrathoracic, fixed, and variable intrathoracic.3
Therefore, although definitive procedures such as flexible fibre-optic bronchoscopy are needed to confirm the diagnosis of UAO, straightforward practical measurements that are useful in day-to-day clinical practice such as the FEV1/PEF ratio, which is easily obtainable through simple spirometry, may aid in either prompting initial consideration or confirming clinical suspicion of such a diagnosis.
Daniel K C Lee, MB, BCh, MRCP, MD
Prashant S Borade, MB, BS, MD
Nicholas J Innes, MB, BS, FRCP
Department of Respiratory Medicine, Ipswich Hospital, Heath Road, Ipswich IP4 5PD, Suffolk, England, United Kingdom
Expiratory and inspiratory flow-volume curve
Subglottic stenosis found on flexible fibre-optic bronchoscopy