Abstract
The mechanical properties of the soft palate can be associated with breathing abnormalities. Dorsal displacement of the soft palate (DDSP) is a naturally occurring equine soft palate disorder caused by displacement of the caudal edge of the soft palate. Snoring and a more serious, sometimes life-threatening, condition called obstructive sleep apnea (OSA) are forms of sleep-related breathing disorders in humans which may involve the soft palate. The goal of this study was to investigate the effect of injecting the protein crosslinker genipin into the soft palate to modify its mechanical properties for the treatment of equine DDSP with potential implications for the treatment of snoring and OSA in humans. Ex vivo experiments consisted of mechanical testing and a wind tunnel study to examine the effect of genipin on the mechanical properties, displacement, and vibration of equine soft palates. A pilot in vivo study was completed using DDSP and control horses to test the safety and effectiveness of injecting a genipin reagent into the soft palate. The wind tunnel testing demonstrated a greater than 50% decrease in transient deformation and a greater than 33% decrease in steady-state vibrations for all doses of genipin tested. Ultimate tensile stress, yield stress, and Young's modulus were higher in the genipin-treated distal soft palate specimens by 52%, 53%, and 63%, respectively. The pilot in vivo study showed a reduction of snoring loudness in all DDSP horses and elimination of DDSP in at least one of three horses. The difficulty of using a 1-meter-long endoscopic injection needle contributed to a consistent overinjection of the equine soft palates, causing excessive stretching (pillowing) and related degradation of the tissue. These ex vivo and in vivo results demonstrated reduced vibration amplitude and flaccidity and increased strength of genipin-treated soft palates, suggesting that genipin crosslinking could become an effective and safe treatment for soft palate related breathing abnormalities.
Highlights
Whether the result of repetitive insult or a congenital condition, a flaccid soft palate can be involved in upper airway obstruction and sound generation in animals and humans
Dorsal displacement of the soft palate (DDSP) is a naturally occurring soft palate disorder caused by displacement of the caudal edge of the soft palate, interfering with normal expiratory airflow through the nasopharynx, producing mechanical property deficiencies, snoring, and temporary obstruction of the airway [1]
The limitations of this simplified wind tunnel model, especially with regard to the airflow associated with equine DDSP, may suggest that the effects of genipin protein crosslinking in this wind tunnel model may not accurately reflect the magnitudes of clinical effects in horses
Summary
Whether the result of repetitive insult or a congenital condition, a flaccid soft palate can be involved in upper airway obstruction and sound generation in animals and humans. With some similarities, snoring is a condition that affects people of all ages, including 48% of men and 34% of women [11,12,13] Another sleep-related breathing disorder, obstructive sleep apnea (OSA), is a more serious, and sometimes lifethreatening, condition that occurs in approximately 4.2% of Americans aged 16 and older [14,15,16,17,18]. Both snoring and OSA are the result of obstructed airflow during inhalation due to abnormalities in the geometry of the air passages and the propensity for aberrant deformation of the soft palate [19, 20]. This fibrotic tissue can be expected to exhibit inferior mechanical properties and a decrease of structural integrity compared to normal tissues, leading to the eventual loss of some initial treatment-related benefits [20,21,22,23,24,25,26,27,28,29]
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