Blood Pressure Increases in OSA due to Maintained Neurovascular Sympathetic Transduction: Impact of CPAP

Abstract

Study objectives: To test the hypothesis that greater resting sympathetic activity in obstructive sleep apnea (OSA) syndrome would not induce a lesser sympathetic neurovascular transduction.

Design: Case-controlled cohort study.

Participants: 33 patients with newly diagnosed OSA without comorbidities and 14 healthy controls.

Interventions: 6 months of continuous positive airway pressure (CPAP) treatment for OSA patients and follow-up for 9 healthy controls.

Measurements and results: We assessed resting sympathetic outflow and sympathetic neurovascular transduction. Sympathetic activity was directly measured (microneurography) at rest and in response to sustained isometric handgrip exercise. Neurovascular transduction was derived from the relationship of sympathetic activity and blood pressure to leg blood flow during exercise. Despite an elevated sympathetic activity of ∼50% in OSA compared to controls, neurovascular transduction was not different (i.e., absence of tachyphylaxis). After six months of CPAP, there were significant declines in diastolic pressure, averaging ∼4 mm Hg, and in sympathetic activity, averaging ∼20% with no change in transduction.

Conclusions: Greater sympathetic activity in obstructive sleep apnea does not appear to be associated with lesser neurovascular transduction. Hence, elevated sympathetic outflow without lesser transduction may underlie the prevalent development of hypertension in this population that is well controlled by continuous positive airway pressure treatment.

Keywords: arterial blood pressure; continuous positive airway pressure; hypertension; obstructive sleep apnea; sympathetic nervous system.

© 2015 Associated Professional Sleep Societies, LLC.

Figures

Figure 1

Subject enrollment and study design.

Figure 2

Diastolic blood pressure, resting sympathetic nerve activity, and sympathetic neurovascular transduction in patients with OSAS and age-matched controls.

Figure 3

Diastolic blood pressure and sympathetic nerve activity before and after 6 months of CPAP therapy.

Figure 4

The relation between sympathetic neurovascular transduction and resting sympathetic activity before and after 6 months of CPAP therapy.

Figure 5

The relation between diastolic blood pressure and leg vascular resistance before and after 6 months of CPAP therapy.