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weight and/or adherence. However, a large multicenter double-blind, randomized
study employing a sham-CPAP control group demonstrated a dose-response rela-
tionship between CPAP adherence and weight gain, with greater CPAP use associ-
ated with more weight gain over 6 months of follow-up [ 52 ]. One possible
explanation for these results is greater energy expenditure due to increased work of
breathing in those with untreated OSA.
CPAP
Nocturnal continuous positive airway pressure is considered first-line therapy for
treating obstructive sleep apnea in the majority of patients. CPAP therapy involves
a small device that delivers a set air pressure via a mask that fits over the patient’s
nose or nose and mouth in order to pneumatically stent open the airway, thereby
eliminating the repetitive breathing pauses seen in OSA. CPAP is intended to be
used during all hours of sleep, whether at night or during daytime naps. CPAP ther-
apy effectively treats OSA in almost everyone and improves symptoms of OSA in
many [ 53 ]. The more consistently a patient adheres to PAP therapy, the more likely
he or she is to experience its benefits [ 54 ]. Greater hours of nightly PAP usage have
been associated with several different clinical outcomes including quality of life and
excessive daytime sleepiness [ 54 ]. Fortunately, all modern PAP devices come
equipped with data chips and/or modems that enable providers to objectively moni-
tor adherence and efficacy.
Effect of CPAP on Blood Pressure
Most trials suggest a modest but significant benefit of PAP on blood pressure reduc-
tion [ 55 ]. It is important to note that studies on PAP therapy are limited by several
factors. First, it is difficult to establish the true impact of a therapy with which
patients are variably and imperfectly adherent. Second, despite CPAP being, in
practice, more often a lifelong therapy that may render its benefit over years rather
than weeks, there are practical challenges with performing long-term studies in this
area. Indeed, although early studies suggested more significant effect sizes of CPAP
on BP, many of these were seen exclusively among PAP-compliant patients. Not
surprisingly, the effect of CPAP on blood pressure reduction does appear to be mod-
ified by CPAP adherence [ 56 ]. Somnolence status also appears to contribute to the
effect of CPAP on blood pressure, with sleepier patients gleaning more benefit from
CPAP. Figure 13.4 shows one example of the beneficial effect of CPAP on mean
arterial pressures in patients with OSA [ 57 ].
A prospective observational cohort study following patients with both OSA and
hypertension for 2 years found an average decline by 4.9 mmHg in 24-h mean blood
pressure after 6 months after PAP initiation [ 58 ]. Effects were greatest in patients
reporting greater hypersomnolence and higher baseline BMI, suggesting that perhaps
L.A. Tobias and F. Roux