Effects of Preventing Fluid Retention in the Legs on Overnight Airway Narrowing in Asthma

Cristina de Oliveira Francisco (1), Susan Tarlo (2, 3), Matthew Stanbrook (2, 3), Mark Inman (4), Azadeh Yadollahi (1, 5)

1) KITE, Toronto Rehabilitation Institute – University Health Network, 2) Department of Medicine, University of Toronto, 3) Toronto Western Hospital – University Health Network, 4) Faculty of Medicine (Respirology), McMaster University, 5) Institute of Biomaterials and Biomedical Engineering, University of Toronto

Background: In Canada, asthma is not well-controlled in 90% of asthmatics, despite the advances in pharmacological treatments. Nocturnal worsening is a common feature of asthma. Recent studies showed that rostral fluid shift from the legs to the thorax during supine posture is a potential contributor to nocturnal worsening of asthma. We hypothesized that preventing fluid retention in the legs during the day by wearing compression stockings improves airway resistance in asthma before and after sleep.
Methods: Individuals with diagnosis of asthma based on Global Initiative for Asthma (GINA) guidelines performed two full in-laboratory sleep studies two weeks apart. Before and after sleep while supine, we measured leg fluid volume (LFV) using bioelectrical impedance and respiratory resistance at 5Hz (R5) with oscillometry. After the first sleep study, the participants received below knee compression stockings (pressure of 20-30mmHg). The participants were instructed to wear the stockings for 2 weeks, during the day, for at least 8hr/day.
Results: Eleven asthmatics, 7 male and 4 female, age: 56.5±11.4 years, BMI 28.8±6.1 kg/m2, FEV1/FVC%: 68.6±7.8% participated in the study. After two weeks of wearing compression stockings, LFV and R5 decreased in the evening (ΔLFV: -192.6±248.3ml, p=0.024 and ΔR5: -0.7±0.9cmH2O/L.s, p=0.03). However, no differences in LFV and R5 were found in the morning (ΔLFV: -197.7±330.5ml, p=0.1 and ΔR5: -0.3±1.0 cmH2O/L.s, p=0.3). Also, there were no differences in the overnight fluid shift or overnight airway resistance between the nights (p>0.05).
Conclusions: Preventing fluid retention during the day reduced airway resistance in the evening but not in the morning. The mechanisms by which changes in fluid affect airway resistance remain unclear. Our participants were mild asthmatics without nocturnal asthma symptoms or fluid retaining conditions. This could be one of the reasons that compression stockings did not reduce rostral fluid shift as they did not have much fluid retention in the legs to start with. Future studies should include asthmatics with more severe asthma and those with nocturnal symptoms.
Acknowledgements: This study was supported by Canadian Respiratory Research Network and Allergen NCE.