Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC283
Overnight changes in neck circumference and pharyngeal calibre in heart failure patients with obstructive sleep apnoea
T. Carlisle1,2, N. Ward1,2, A. Atalla1,2, M. Cowie1,2, A. Simonds1,2, M. Morrell1,2
1. National Heart and Lung Institute, Imperial College London, London, United Kingdom. 2. Biomedical Research Unit, Royal Brompton and Harefield NHS Foundation Trust, London, United Kingdom.
The prevalence of obstructive sleep apnoea (OSA) in congestive heart failure (CHF) patients is approximately 15%(1), compared to 2-4% in the general population(2). A possible mechanism for OSA in CHF is that lower extremity oedema may shift to the neck when supine, causing an increase in transmural pharyngeal pressure overnight. The aim of this study was to test the hypothesis that nocturnal fluid shift results in increased neck circumference and decreased pharyngeal calibre in the morning compared to the evening. Neck circumference (NC) was measured between the cricoid and thyroid cartilages using a tape measure. Pharyngeal calibre was assessed non-invasively by measuring the mean pharyngeal area (APmean) between the mouth and the epiglottis using standard methods of acoustic reflection(3). Both measurements were performed while participants were awake and in a supine posture, in the evening after 5 minutes of lying supine (between 19:00 and 20:00) and in the morning immediately after waking up but before sitting up from bed (between 06:00 and 07:00). The Kruskal-Wallis test and the Mann-Whitney U test with a Bonferroni correction were used to test for significant differences (p=0.05). Six CHF patients with OSA (6 male, mean±SD: age 72.3±2.6 years; body mass index (BMI) 25.1±12.4 kg/m2; left ventricular ejection fraction (LVEF) 40±15.8%; apnoea-hypopnoea index (AHI) 27.5±11.3 events/hour), 6 CHF patients without OSA (6 male, mean±SD: age 75.7±8.0 years; BMI 27.0±3.2 kg/m2; LVEF 40.4±18.6%; AHI 5.8±2.0 events per hour) and 6 healthy volunteers (5 male, mean±SD: age 58.2±6.1 years; BMI 25.7±2.0 kg/m2; AHI 0.7±1.2 events/hour) were studied. Measurements of NC and APmean are presented in Table 1. In summary, CHF with OSA had a significantly greater NC in the morning compared to evening, but this was not reflected in the APmean, which was unchanged in this group of patients. In contrast, CHF patients without OSA and healthy volunteers had no significant increase in NC but their APmean decreased overnight. Our findings indicate that nocturnal fluid shift towards the neck may be a mechanism of OSA in CHF patients but this is not reflected in changes in pharyngeal calibre.
Where applicable, experiments conform with Society ethical requirements