Recordings of sympathetic nerve activity, respiratory rate, and intra-arterial blood pressure in the same individual when awake, with OSA during rapid eye movement (REM) sleep, and with elimination of OSA episodes by continuous positive airway pressure (CPAP) therapy during REM sleep. Sympathetic nerve activity is very high during wakefulness, but increases even further secondary to obstructive apnea during REM sleep. Blood pressure increases from 130/65 mm Hg when the individual is awake to 256/110 mm Hg at the end of the apneic episode. Elimination of apneic episodes by CPAP therapy results in decreased sympathetic activity and prevents blood pressure surges during REM sleep. Reproduced with permission from Somers et al.¹²

Abnormalities associated with obstructive sleep apnea may be intermediary mechanisms that contribute to the initiation and progression of cardiac and vascular pathology. These mechanisms may interact with each other, thus potentiating their pathophysiological implications.

*These conditions are associated with OSA. The associations may be due, in part, to common risk factors; they may also reflect a role of OSA in their etiology.

Solid thick line represents estimates from nonparametric logistic regression; dashed lines, 95% confidence limits for the nonparametric logistic regression estimates; solid thin line, adjusted odds ratio estimated from conventional logistic regression using the categories shown in Table 4. Odds ratios adjusted for demographics, body mass index, neck circumference, and waist-to-hip ratio. Hypertension is defined in Table 4.

Diagnostic group refers to those patients excluded because of diagnostic group as outlined in the "Methods" section (chronic obstructive pulmonary disease after the first year, spinal cord injury, obstructive sleep apnea). It is not possible to provide numbers for those patients who met inclusion and exclusion criteria but were not approached for consent (patient or physician refusal or no apparent attempt made to recruit the patient) who developed respiratory distress (ie, would have been eligible for the study) because this was not recorded. Of those randomized, the flow of patients through the trial is also illustrated. DNR indicates do not resuscitate; NPPV, noninvasive positive-pressure ventilation.