Pathophysiology of upper airway closure during sleep

Article Abstract:

A review is presented of the forces that normally keep the upper airway or pharynx open and of the abnormalities associated with closure of the airway when inspiring air during sleep. (The pharynx is the part of the airway above the larynx or voicebox.) Such closure occurs hundreds of times during a typical night in people who suffer from obstructive sleep apnea (OSA). The anatomy and distensibility of the segments of the upper airway are explained: closure can occur in any pharyngeal segment. The airway is kept open during inspiration by a balance between the forces that arise from activation of the upper airway muscles (which keep the airway open) and those that result from the subatmospheric pressure within the pharynx (resulting from the expansion of the chest, keeping the airway closed). Reflex activation of the upper airway muscles, known to take place in animals, also occurs in awake humans but may be blunted during sleep. In fact, sleep itself causes an increase in resistance of the upper airway even in normal subjects as the muscle activity in the upper airway decreases. A sequence of events that could be present in OSA is outlined; the first step in pharyngeal narrowing is a decrease in upper airway muscle activity. Although tracheostomy (surgical creation of an airway directly into the trachea) is the most effective surgical treatment for OSA, it is associated with complications and is not well accepted by patients. The treatment of choice for OSA is continuous positive airway pressure (CPAP), or directing air under positive pressure into the pharynx. Surgical approaches include uvulopalatopharyngoplasty, in which the structures of the pharynx are altered to decrease the pressure at which the upper airway closes. This does not reliably cure OSA, however. Some treatments are aimed at correcting problems in the nasopharynx (behind the nose), such as septal deviation, polyps, or congestion, but they are not usually effective. Weight reduction can ameliorate the problem, as can postural adjustments. Patients with OSA who only experience symptoms when lying on their backs are encouraged to sew tennis balls in their pajamas. Other treatments are evaluated. (Consumer Summary produced by Reliance Medical Information, Inc.)

Sleep apnea syndromes, Sleep apnea, Pharynx

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Pulmonary function and airway responsiveness during long-term therapy with captopril

Article Abstract:

The effects of ambulatory treatment with captopril (an angiotensin-converting enzyme inhibitor) on lung function were studied in 15 hypertensive subjects in an attempt to determine why these inhibitors, which are used to treat high blood pressure, sometimes cause cough. A persistent cough related to captopril use developed in four subjects, but it was not associated with airflow obstruction or excess contraction of the air passages of the lung (bronchi) in response to experimental chemical stimulation (with methacholine). After eight weeks of captopril treatment, the amount of methacholine required to cut exhalation capacity by 20 percent dropped from 62 grams per liter before treatment to 44 grams per liter after 8 weeks of captopril treatment. It is concluded that captopril does not significantly alter lung function and that there is no association between cough while using captopril and airflow obstruction or overreaction of the bronchi to chemical stimulation.

Analysis, Causes of, Complications and side effects, Pulmonary function tests, Cough, Captopril

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High-Altitude Cerebral Edema Evaluated With Magnetic Resonance Imaging:Clinical Correlation and Pathophysiology

Article Abstract:

Patients with high-altitude cerebral edema (HACE) have specific brain abnormalities on an MRI scan, which could aid in the prompt diagnosis of this condition. Cerebral edema is characterized by an accumulation of fluid inside the brain. Researches gave MRI scans to nine men with HACE, three with mountain sickness but not HACE and three healthy people. Seven of the patients with HACE had abnormal scans in white matter areas of the brain, particularly in an area called the corpus callosum. No one in the other groups had abnormal scans. All patients recovered completely.

Cerebral edema, Brain damage, Mountain sickness, Altitude sickness

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