Airway turbulence and changes in upper airway hydraulic diameter can be estimated from the intensity of high frequency inspiratory sounds in sleeping adults. (28th July 2014)

• Record Type: Journal Article
• Authors: Rembold, Christopher M.; Suratt, Paul M.
• Is Part Of: Journal of physiology. Volume 592:Number 17(2014:Sep.)
• Page Start: 3831
• Page End: 3839
• Publication Date: 2014-07-28
• Subjects: Physiology -- Periodicals; 612.005
• DOI: 10.1113/jphysiol.2014.272302
• Languages: English
• ISSNs: 0022-3751

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="tjp6266-sec-0010" sec-type="section"> <title>Key points</title> <p> <list id="tjp6266-list-0001" list-type="bullet"> <list-item> <p>Adults and children with obstructive sleep disordered breathing make loud high frequency inspiratory sounds (HFIS, defined as inspiratory sounds >2 kHz) while sleeping.</p> </list-item> <list-item> <p>In an <italic>in vitro</italic> model, the intensity of high frequency sounds was found to be an estimate of airflow turbulence as reflected by the Reynold's number (Re).</p> </list-item> <list-item> <p>Hydraulic diameter (<italic>D</italic>) of the <italic>in vitro</italic> model could be calculated using Re determined by sound intensity, the pressure gradient, the Swamee–Jain formula and the Darcy formula.</p> </list-item> <list-item> <p>In four adult humans, <italic>D</italic> was calculated from measured HFIS intensity and the pressure gradient across the upper airway (estimated with oesophageal pressure, <italic>P</italic><sub>es</sub>).</p> </list-item> <list-item> <p>At apnoea termination when the airway opens, we observed (1) an increase in HFIS intensity suggesting an increase in turbulence (higher Re), and (2) a larger calculated <italic>D</italic>.</p> </list-item> <list-item> <p>This method allows dynamic estimation of changes in relative upper airway <italic>D</italic> in sleeping humans with narrowed upper airways.</p> </list-item> </list> </p> </sec> <sec id="tjp6266-sec-0020" sec-type="section"> <title>Abstract</title> <p>Obstructive sleep disordered breathing can cause death and significant morbidity in adults and children. We previously found that children with smaller upper airways (measured by magnetic resonance imaging while awake) generated loud high frequency inspiratory sounds (HFIS, defined as inspiratory sounds > 2 kHz) while they slept. The purpose of this study was (1) to determine what characteristics of airflow predicted HFIS intensity, and (b) to determine if we could calculate changes in hydraulic diameter (<italic>D</italic>) in both an <italic>in vitro</italic> model and in the upper airways of sleeping humans. In an <italic>in vitro</italic> model, high frequency sound intensity was an estimate of airflow turbulence as reflected by the Reynold's number (Re). <italic>D</italic> of the <italic>in vitro</italic> model was calculated using Re, the pressure gradient, Swamee–Jain formula and Darcy formula. <italic>D</italic> was proportional to but smaller than the actual diameters (<italic>r</italic><sup>2</sup> = 0.94). In humans, we measured HFIS intensity and the pressure gradient across the upper airway (estimated with oesophageal pressure, <italic>P</italic><sub>es</sub>) during polysomnography in four adult volunteers and applied the same formulae to calculate <italic>D</italic>. At apnoea termination when the airway opens, we observed (1) an increase in HFIS intensity suggesting an increase in turbulence (higher Re), and (2) a larger calculated <italic>D</italic>. This method allows dynamic estimation of changes in relative upper airway hydraulic diameter (<italic>D</italic>) in sleeping humans with narrowed upper airways.</p> </sec> </abstract>