Objectives To study the relationship between ambulatory blood pressure monitoring parameters and carotid intima-media thickness in masked hypertensive patients.

Methods Two hundred and ten adults normotensives (office blood pressure < 140/90 mmHg) and one hundred hypertensives (office blood pressure ≥ 140/90 mmHg) underwent 24 hour ambulatory blood pressure monitoring. Based on the 24 h ambulatory blood pressure, all the patients were categorised into mased hypertensives (n = 82), normotensives (n = 128) and hypertensives (n = 100) respectively. Carotid intima-media thickness (IMT) was measured with high resolution ultrasound.

Results Nocturnal systolic blood pressure (nSBP), ambulatory arterial stiffness index (AASI), non-dipper blood pressure rhythm percentage, IMT were higher in masked hypertensives than in normotensives, but lower than those in hypertensives [nSBP(121.0 ± 10.7)vs (106.5 ± 9.8) vs (127.9 ± 10.2); AASI (0.53 ± 0.12) vs (0.41 ± 0.10) vs (0.58 ± 0.18); non-dipper blood pressure rhythm percentage (42.8%) vs (27.9%) vs (50.2%); IMT(0.91 ± 0.12) vs (0.72 ± 0.10) vs (1.01 ± 0.12); P< 0.01 or P < 0.05]. After adjusted for gender and age in masked hypertensives, multiple linear regression analysis showed that 24 hour systolic blood pressure (24 hSBP), nocturnal systolic blood pressure (nSBP), non-dipper blood pressure rhythm percentage and total cholesterols were independent risk factors for IMT (β values were 0.171, 0.204, 0.358, 0.293; all P < 0.05).

Conclusions Masked hypertension may be the prophase stage of persistent hypertension. More and more researches have verified that the risk of cardiovascular events in masked hypertensives are similar in hypertensives, meanwhile far higher than in normotensives. This study demonstrated that masked hypertensives have already appeared the descend of artery compliance, increased of arterial stiffness and IMT. Furthermore abnormal circadian rhythm of blood pressure independently influence IMT, and it could be related to the dysfunction of autonomic nervous system and the balance disorder of endothelium-derived vasoconstrictor factor and endothelium-derived relaxing factor. Conclusion The masked hypertensives had already existed IMT thickened and AASI increased, 24 hSBP, nSBP and non-dipper blood pressure rhythm percentage were the important influencing factors of IMT.