13. Teklu B. Bronchial asthma at high altitude, a clinical and laboratory study in AddisAbaba. Thorax 1989;44(7):586-7. http://dx.doi.org/10.1136/thx. 44.7.586 14. Van Gemert F, van der Molen T, Jones R, Chavannes N. The impact of asthma and COPD in sub-Saharan Africa. Prim Care Respir J 2011;20:240-8. http://dx.doi.org/10. 4104/pcrj.2011.00027 Since the initial description of the flow-volume loop (FVL) by Miller and Hyatt in the early 1970's as a clinical predictor of upper airway obstruction (UAO), 1 its utility in clinical practice has been debated. Early case series' suggested that the FVL might be a sensitive indicator of UAO.
2Combining the FVL appearance with measurements of the forced mid-expiratory to mid-inspiratory flow ratios (FEF 50/FIF50) was reported to separate upper airway lesions into fixed lesions (ratio of 0.85), variable extrathoracic obstruction (ratio of 2.20) with inspiratory limb truncation, and variable intrathoracic obstruction (ratio of 0.32) with expiratory limb truncation. The diagnostic utility of the FVL can be variable. Since the FVL requires a maximal inspiratory and expiratory vital capacity manoeuvre, the most common cause of an abnormal FVL is submaximal patient effort or inadequate patient instruction in properly performing the required technique. Numerous conditions consistent with either a fixed or intermittent UAO can be considered for diagnosis or followed post-diagnosis using the FVL appearance and associated spirometric findings such as the FEF 50 /FIF 50 . Suspicion should be increased when abnormal test results occur in conjunction with symptoms such as dyspnoea and noisy breathing, or physical examination identifying stridor or wheezing. Diagnostic confirmation of an UAO can be made with airway imaging, laryngoscopy, or bronchoscopy. Anatomic obstructions such as airway tumors, tracheal stenosis, and bilateral vocal cord paralysis are specific disease processes where the FVL can be instrumental in raising suspicions for underlying disease if there is significant flow limitation. 4 However, imaging techniques such as computed tomography (CT) scanning can detect early anatomic lesions without significant flow limitation or FVL findings. Exterior compression of the trachea from goitres or anterior mediastinal masses may demonstrate FVL abnormalities depending upon patient positioning. Upright and supine spirometry with FVL was first advocated in 1984 to predict airway compromise in the supine position but limited combined data supported this approach.5 After the 1983 publication of the initial series of vocal cord dysfunction (VCD) patients, 6 emphasis has shifted to using the FVL to identify symptomatic episodes of inducible laryngeal obstruction (ILO) due to upper airway disorders such as VCD and exercise-induced laryngeal obstruction (EILO).Limited data exist on the predictive value of FVL appearance in determining the presence or absence of induced laryngeal obstruction. We previously reviewed inspiratory FVL appearance in our institution and identified 2...
