Understanding Airway Tissue Mechanics is a Step Towards Improving Treatments in OSA

973 Editorial—Brennick In this issue of SLEEP, Brown and colleagues1 report the results of a new study examining breath-to-breath changes in the movement of upper airway tissues in patients with obstructive sleep apnea (OSA). In doing so, they successfully provided a method to measure soft tissue movement and developed an analysis protocol that can account for various patterns of movement that can occur among the heterogeneous and multifunctional structures in the upper airway. More than 20 years ago, a method was developed to apply a temporary grid pattern of fiducial markers on cardiac soft tissues so that within a short time period (approximately one second) a series of images could be obtained that would show how the grid lines moved during the cardiac cycle and thus very accurate measurements of specific tissue motion could be evaluated.2,3 This MRI protocol—named spatial modulation of magnetization (SPAMM)—is now available on most medical scanners used in cardiac evaluation and has become particularly useful in the assessment of regional ventricular function (e.g., systolic wall thickening or systolic circumferential strain) and in the detection of pericardial adhesion and myocardial involvement.4-6 Although noninvasive methods have been available, large scale controlled studies with 3D computed tomography (CT) are difficult to justify in consideration of unnecessary x-ray dosage,7 while MRI studies without a specific method of tissue tracking and time sensitive acquisition and analysis do not yield precise information on breathto-breath or respiratory related movement of the airway tissues.8 Application of SPAMM MRI to the airways in rodent studies have provided detailed information as to how tongue muscle stimulation dilates the oral airway in a primarily ventral-dorsal airway expanding motion,9 while noninvasive tissue motion studies on the effect of obesity in the airways of Zucker rats10 showed an overall narrowing of obese airways in expiration and inspiration but fewer differences in airway wall motion between the obese and non-obese rat airways. One of the challenges to such studies is deciding how to segment the airways for comparison and how to compare differences in motion between similar wall structures but in different airspaces such as the nasopharyngeal and oropharyngeal airways. What is unique in the study by Brown and colleagues1 is that they developed methods to examine the whole respiratory cycle EDITORIAL