ORIGINAL ARTICLE Associations between fluctuations in lung function and asthma control in two populations with differing asthma severity Cindy Thamrin, 1 Regula Nydegger, 1 Georgette Stern, 1 Pascal Chanez, 2 Sally E Wenzel, 3 Rosemary A Watt, 4 Susan FitzPatrick, 4 D Robin Taylor, 5 Urs Frey 1,6 ABSTRACT Background Lung function is a major criterion used to assess asthma control. Fluctuation analyses can account for lung function history over time, and may provide an additional dimension to characterise control. The relationships between mean and fluctuations in lung function with asthma control, exacerbation and quality of life were studied in two independent data sets. Methods Data from 132 adults with mild to moderate asthma and 159 adults with severe asthma were analysed separately. Fluctuations in twice-daily peak expiratory flow (PEF) over 6 months were measured by a, representing the strength of correlation with past lung function and potentially asthma stability. a and mean percentage predicted PEF (%predPEF) were plotted with and compared between patients grouped by asthma control defined by recent GINA (Global Initiative for Asthma) guidelines, the Asthma Control Questionnaire score, exacerbations and Asthma Quality of Life Questionnaire score. Associations of a and %predPEF with these outcomes were examined using multiple regression analyses. Results Both a and %predPEF differed with and were significantly associated with GINA-defined asthma control in both the mild to moderate and severe asthma groups. Only a was related to whether or not exacerbations occurred in mild to moderate asthma, while %predPEF was more significantly related than a in severe asthma. In those with severe asthma, only %predPEF was significantly related to Asthma Control Questionnaire and Asthma Quality of Life Questionnaire scores. Conclusion Lung function history quantified by fluctuation analysis provides additional information to mean lung function, and may help characterise the current state of asthma control. It may also potentially aid in phenotyping clinical asthma. INTRODUCTION Asthma control has most recently been defined as the extent to which the various components comprising asthmadthat is, symptoms, variable airway obstruction, airway hyper-responsiveness and inflammationdare improved in the presence of treatment. 1 2 Despite the existence of numerous research studies and clinical trials including a number of recent collaborative publications, there are still no definitive guidelines for the assessment of asthma control, which includes an assessment of current state as well as future risk. 3 4 This highlights the difficulty of characterising such a heterogenous, multidimensional condition as asthma, 5 complicated by the existence of different phenotypes which are themselves not yet fully described. What is clear, however, is that no single parameter is adequate to assess asthma control. 34 Lung function, as an assessment of variable airway obstruction, is one of the objective measures to assess asthma control. Recent guidelines recog- nise the need to assess control over periods of weeks rather than just at the moment of assessment, 467 and home monitoring of lung function provides one avenue by which this can be done. 48 Single points of assessment or mean values are frequently used to quantify lung function, which remove a great deal of information which might be derived from assessing changes over time. In this regard, tech- niques such as fluctuation analyses may account for changes in lung function history over time. 5 9 These techniques have been introduced to deter- mine the presence of certain correlation patterns in twice-daily peak expiratory flow (PEF), which in turn have been shown to vary with short- and long- acting b 2 -agonist treatment. 9 Past lung function history, assessed by such correlation patterns, has already been shown to be useful in the assessment of future risk for exacerbations. 10 It may provide an additional dimension to characterise the current state of asthma control. Key messages What is the key question? Is fluctuation analysis of past lung function history useful in assessing asthma control? What is the bottom line? In two separate populations of subjects with asthma, history of lung function fluctuations was related to asthma control measures and exacerba- tions, independently of mean lung function. Why read on? For the patient, the ability to assess asthma control using home-monitored peak flow fluctuations facil- itates self-management of asthma; for the clinician, it suggests lung function fluctuations should be additionally considered in the phenotyping of asthma. See Editorial, p 1019 < Additional methods and a table are published online only. To view these files please visit the journal online (http:// thorax.bmj.com). 1 Division of Respiratory Medicine, Department of Paediatrics, Inselspital and University of Bern, Switzerland 2 De ´partement des Maladies Respiratoires, AP-HM, INSERM CNRS U 600, UMR6212 AP-HM, Universite ´ de la Me ´diterrane ´e, Marseille, France 3 Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh Medical Center, Pennsylvania, USA 4 Centocor Research & Development, Inc., Malvern, Pennsylvania, USA 5 Dunedin School of Medicine, University of Otago, Dunedin, New Zealand 6 University Children’s Hospital (UKBB), University of Basel, Basel, Switzerland Correspondence to Professor Urs Frey, University Children’s Hospital (UKBB), PO Box, CH-4005 Basel, Switzerland; urs.frey@ukbb.ch. Received 30 November 2010 Accepted 7 April 2011 Published Online First 20 May 2011 1036 Thorax 2011;66:1036e1042. doi:10.1136/thx.2010.156489 Asthma group.bmj.com on October 24, 2016 - Published by http://thorax.bmj.com/ Downloaded from