Topical pharmacologic agents such as cocaine, phenylephrine, apraclonidine, or hydroxyamphetamine can be used to confirm a diagnosis of HS. Cocaine acts by blocking the reuptake of norepinephrine in the neuromuscular junction of the iris dilator muscle
, causing the pupil in a normal eye to dilate, while incomplete dilation is seen in HS.,
The possible mechanism for higher minimum SaO[sub]2 in PD + RBD patients may be the loss of atonia in upper airway dilator muscles
. Another explanation is that drugs that might increase muscle activity could also benefit OSA, such as paroxetine, mirtazapine, and glycinergic antagonists., Some investigators obtained similar results, finding that, in idiopathic RBD patients, OSA severity was also alleviated.
The pathophysiology of IFIS is not well understood, and current research is mostly focused on the direct effect of [alpha]1-adrenergic antagonists on the iris dilator muscle
. Chronic receptor blockade could lead to iris vascular dysregulation, subsequent secondary atrophy of the iris dilator muscle
, and finally, the anomalous iris behavior seen in IFIS.
The changes in upper airway diameter during respiration is thought to primarily result from increased activation (during inhalation) and decreased activation (during exhalation) of pharyngeal dilator muscles
such as the geniohyoid, sternohyoid, genioglossus, and stylopharyngeus muscles.
(9) In OSP, sympathetic denervation results in upregulation of a-receptors which, in turn, unmasks the weak effect of apraclonidine on a1-receptors in the pupil dilator muscle
by causing mydriasis.
Imaging studies during wakefulness, however, are complicated to interpret since ongoing pharyngeal dilator muscle
activity (greater in OSA than controls (59)) may lead to observed differences between groups based on non anatomical (i.e., neuromuscular) factors.
(1) The lack of response of the iris dilator muscle
may be attributable to the fact that it is largely [[alpha].sub.1] receptor-dependent.
hydroxyamphetamine) because of degeneration of the sympathetic terminals in the iris dilator muscle
, whereas in fact the response to such agents has been shown to be normal [23, 24] in elderly subjects.
* The balance of 'tone' in the autonomic nervous system arising from the sphincter muscle, which is under parasympathetic innervation (resulting in miosis), and the dilator muscle
, which is under sympathetic innervation (resulting in mydriasis)
Their larynx has a rigid fibrous structure and a dilator muscle
in addition to a constrictor muscle.
The dilator muscle
moves away from the pupil like bicycle spokes.