MRI study of regional variations of pharyngeal wall  compliance in cats

Brennick, Michael J.; Ogilvie, Malcolm D.; Margulies, Susan S.; Hiller, Luke; Gefter, Warren B.

doi:10.1152/jappl.1998.85.5.1884

Cited by 14 publications

(12 citation statements)

References 32 publications

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“…Although the strengths and limitations of our experimental model have been addressed in detail previously (4, 9, 52), here I review some technical issues that are particularly relevant to the present experimental design. First, my goal was to measure responses to dynamic pressure changes, as opposed to the nonphysiological static changes that have been used to measure pharyngeal compliance by others (7,23,31) and us (3). This is an important issue because collapse off the pharyngeal airway in patients with sleep apnea is a dynamic event, occurring in the face of airflow, and collapse can occur when flow is in either the inspiratory or expiratory direction (43).…”

Section: Discussionmentioning

confidence: 99%

“…Results for each measured variable were analyzed with two-way repeated-measures ANOVA, with VP segment (i.e., slices [1][2][3][4][5][6][7][8] and stimulation/no-stimulation the main factors. If the results of ANOVA were significant, differences between stimulation and no-stimulation conditions for each slice were evaluated with Bonferroni post hoc tests (Graph Pad Prism Software, San Diego, CA).…”

Section: Methodsmentioning

confidence: 99%

“…1. Schematic representation of the experimental configuration used in this and in previous studies from our laboratory (4,7,52). The bottom portion shows an enlargement of the ventral neck region and depicts the location of the tracheotomy tube, hypopharyngeal catheter, and site of application of positive and negative pressures.…”

Section: Methodsmentioning

confidence: 99%

“…However, we know little about the influence of tongue muscle contraction on VP volume changes in either human subjects or animal models, and recent studies suggest that the VP is a complex pharyngeal region that does not behave uniformly along its length in cats or rats (7,52). For example, the VP in the adult rat is only ϳ10 mm long, but it shows differences in compliance between its most rostral and caudal regions (52).…”

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Influence of tongue muscle contraction and dynamic airway pressure on velopharyngeal volume in the rat

Fregosi¹

2008

Journal of Applied Physiology

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Fregosi RF. Influence of tongue muscle contraction and dynamic airway pressure on velopharyngeal volume in the rat. J Appl Physiol 104: 682-693, 2008. First published December 13, 2007 doi:10.1152/japplphysiol.01043.2007.-The mammalian pharynx is a collapsible tube that narrows during inspiration as transmural pressure becomes negative. The velopharynx (VP), which lies posterior to the soft palate, is considered to be one of the most collapsible pharyngeal regions. I tested the hypothesis that negative transmural pressure would narrow the VP, and that electrical stimulation of extrinsic tongue muscles would reverse this effect. Pressure (Ϫ6, Ϫ3, 3, and 6 cmH 2O) was applied to the isolated pharyngeal airway of anesthetized rats that were positioned in a 4.7-T MRI scanner. The volume of eight axial slices encompassing the length of the VP was computed at each level of pressure, with and without bilateral hypoglossal nerve stimulation (0.1-ms pulse, one-third maximum force, 80 Hz). Negative pressure narrowed the VP, and either whole hypoglossal nerve stimulation (coactivation of protrudor and retractor muscles) or medial nerve branch stimulation (independent activation of tongue protrudor muscles) reversed this effect, with the greatest impact in the caudal one-third of the VP. The dilating effects of medial branch stimulation were slightly larger than whole nerve stimulation. Positive pressure dilated the VP, but tongue muscle contraction did not cause further dilation under these conditions. I conclude that the narrowest and most collapsible segment of the rat pharynx is in the caudal VP, posterior to the tip of the soft palate. Either coactivation of protrudor and retractor muscles or independent contraction of protrudor muscles caused dilation of this region, but the latter was slightly more effective. apnea; functional electrical stimulation; hypoglossal nerve; magnetic resonance imaging; pharynx; upper airway THE PHARYNX IS A MUSCULAR tube with little skeletal support and is thus subject to collapse as its transmural pressure becomes negative during inspiratory contractions of the diaphragm and accessory inspiratory muscles. Various skeletal muscles residing within the pharyngeal walls (e.g., pharyngeal constrictor muscles), or lying within and adjacent to the pharynx (e.g., tongue and palatal muscles), are capable of dilating and/or stiffening it. Indeed, the posterior segment of the tongue comprises a large portion of the anterior pharyngeal wall, so movement and/or stiffening of the tongue can have a marked impact on the dimensions and compliance of the oropharynx and velopharynx (VP). For both anatomic and physiological reasons, neuromuscular activation is inadequate in at least some patients with primary snoring, upper airway resistance syndrome, or obstructive sleep apnea (41, 54). These patients cannot maintain a positive pharyngeal transmural pressure during sleep, leading to periodic pharyngeal collapse with associated hypoventilation and hypoxia throughout the night.At present, the favored treatme...

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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confidence: 99%

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Influence of tongue muscle contraction and dynamic airway pressure on velopharyngeal volume in the rat

Fregosi¹

2008

Journal of Applied Physiology

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“…Patients with sleep disordered breathing often have narrow or floppy pharyngeal airways (''anatomic hypothesis'') (1-3) and/or poor neuromuscular control of pharyngeal airway muscles (''neural hypothesis'') (4)(5)(6)(7)(8)(9). It is generally believed that the velopharynx, or ''retropalatal airway'', is the pharyngeal region that is most susceptible to collapse, (1,(10)(11)(12)(13)(14)(15) and recent data suggest that static compliance varies along its rostral-caudal extent (16). The influence of pharyngeal muscle activation on velopharyngeal compliance and size is poorly understood.…”

Section: Introductionmentioning

confidence: 99%

Regional velopharyngeal compliance in the rat: influence of tongue muscle contraction

et al. 2007

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The velopharynx is the most collapsible segment of the upper airway in patients with obstructive sleep apnea. However, we do not know if velopharyngeal compliance is uniform throughout its length, or if compliance is modified by contraction of upper airway muscles. We tested the hypothesis that rostral and caudal velopharyngeal (VP) compliance differs, and that tongue muscle contraction reduces compliance. High-resolution MR images of the VP were made at nasopharyngeal pressures ranging from -9 to 9 cmH(2)O in anesthetized rats. Images were obtained twice at each pressure, once with and once without bilateral hypoglossal nerve stimulation. The volume of the caudal and rostral VP was computed at each pressure. The caudal VP was significantly (P = 0.0058) more compliant than the rostral VP, but electrical stimulation of the tongue muscles did not change compliance. VP critical pressure (Pcrit; pressure at zero airway volume) averaged -25.2 and -12.1 cmH(2)O in the rostral and caudal VP, respectively (P < 0.0001). Coactivation of tongue protrudor and retractor muscles or contraction of protrudor muscles alone dilated the VP and made Pcrit more negative (P < 0.0001), but only in the caudal VP. In the rat, the caudal VP is more collapsible than the rostral VP, and either coactivation of tongue protrudor and retractor muscles or contraction of protrudor muscles alone makes this region more difficult to close. Thus, tongue muscle contraction protects the caudal VP, which appears to be a particularly vulnerable segment of the nasopharyngeal airway. With suitable modification, the methods described here, including tongue muscle stimulation at different pharyngeal pressures, may be appropriate for experiments in human subjects.

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Disorders of the Respiratory System

Davis¹

2018

Equine Internal Medicine

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MRI study of regional variations of pharyngeal wall compliance in cats

Cited by 14 publications

References 32 publications

Influence of tongue muscle contraction and dynamic airway pressure on velopharyngeal volume in the rat

Influence of tongue muscle contraction and dynamic airway pressure on velopharyngeal volume in the rat

Regional velopharyngeal compliance in the rat: influence of tongue muscle contraction

Disorders of the Respiratory System

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