Benefit of nasal CPAP in obstructive sleep apnea is due to positive pharyngeal pressure.

The purpose of this study was to determine if the mechanism of nasal continuous positive airway pressure's (CPAP's) effectiveness is to act as a pneumatic splint or to increase functional residual capacity (FRC) and consequently, upper airway caliber. Four subjects with obstructive sleep apnea underwent 3 nights of polysomnography: night 1, control; night 2, nasal CPAP; night 3, external subatmospheric pressure (ESAP). ESAP, a negative pressure body suit, increases FRC. We measured the changes in FRC with nasal CPAP and ESAP using the weighted spirometer technique. The dose used for the ESAP night was the dose that produced the same FRC as the subject's prescribed nasal CPAP dose. The mean number of arousals and the respiratory events index were higher on ESAP and control nights. Less severe oxygen desaturation occurred during non-rapid-eye-movement sleep on the nasal CPAP and ESAP nights. These preliminary results show that increasing FRC alone does not account for the effectiveness of nasal CPAP, and splinting of the collapsible upper airway is necessary.

Measurement of pharyngeal volume by digitized magnetic resonance imaging. Effect of nasal continuous positive airway pressure.

Pharyngeal size is thought to play an important role in the pathogenesis of snoring and obstructive sleep apnea. It has been hypothesized that nasal continuous positive airway pressure (CPAP) works by enlarging pharyngeal size and splinting the airway open. In this study, we selected 12 heavy snorers and abolished their snoring with nasal CPAP in our sleep laboratory. Using magnetic resonance imaging and a computer program utilizing a digitizing pad, we measured these awake subjects' pharyngeal volumes without and with the nasal CPAP apparatus on at the level used to abolish their snoring. We found an average 27.7% increase in pharyngeal volume with nasal CPAP. We have visually shown an increase in pharyngeal size with the use of nasal CPAP in a cohort of heavy snorers.

Midazolam-associated alterations in cardiorespiratory function during colonoscopy.

Twenty patients undergoing clinically indicated elective colonoscopy were prospectively monitored noninvasively for alterations in cardiorespiratory function. Most of the patients were elderly and many had either cardiac or pulmonary disease. All subjects were premedicated with intramuscular meperidine and continuously monitored with ECG, blood pressure, earlobe pulse oximetry, nasal air flow by thermistor probe, and impedance pneumography. Any use of additional analgesic or sedative was determined by the endoscopist, who was blinded to the physiologic tracings, and dosages of medications given were titrated to each patient's tolerance of the procedures as assessed by the endoscopist. Seventeen patients (85%) required additional sedation with the benzodiazepine, midazolam. These patients exhibited frequent episodes of hypotension (reductions in mean arterial blood pressure of 23 +/- 12 mm Hg from baseline, means +/- SD) and respiratory depression (as noted by the greater number of apneas and arterial oxygen desaturation as low as 7.1 +/- 2% from baseline, means +/- SD). In addition, elderly patients and patients with an underlying history of cardiac or pulmonary disease had a greater incidence of potentially untoward cardiorespiratory events.

Massive tracheal necrosis complicating endotracheal intubation.

There are significant complications associated with endotracheal intubation. Massive tracheal necrosis secondary to tracheoesophageal space abscess developed in a 71-year-old man during mechanical ventilation. Elevated endotracheal tube cuff pressures, sepsis, hypotension, and other risk factors predispose to this disastrous consequence.