Study objectives: Nocturnal and early morning elevation of blood pressure are common acute manifestations of obstructive sleep apnea (OSA) that do not always carry over into a sustained daytime hypertension. Using pulse wave analysis, we examined the effect of OSA on arterial stiffness and central aortic blood pressure to assess whether each would be elevated independent of diurnal changes in peripheral blood pressure.
Design: Cross-sectional sleep laboratory cohort study.
Setting: Two university teaching hospitals.
Patients: 57 male nonsmokers referred for suspected OSA and free of known cardiovascular disease or blood-pressure and lipid-lowering medications.
Measurements and results: The augmentation index, a quantification of augmentation of central aortic pressure due to the reflected component of the pulse pressure waveform, and brachial and aortic blood pressure were determined in the evening and early morning. The augmentation index consistently increased from evening to morning (P < .001) and was accompanied by an increase in central systolic blood pressure (P = .007) and a decrease in pulse pressure amplification (P < .001). However, these changes were unaccompanied by any changes in peripheral blood pressure. Overnight changes in mean blood pressure and heart rate were the only predictors of this effect, but they only accounted for a third of the variance (r2 = 0.339, P = .002). After adjustment for known confounders, the respiratory disturbance index was positively correlated with augmentation index at both time points (PM: P = .008, am: P = .016). The respiratory disturbance index did not correlate with any indexes of peripheral or central blood pressure.
Conclusions: Systemic arterial stiffness is positively correlated with OSA severity and, in addition, is increased in magnitude in the early morning independent of OSA severity.