Objective:To investigate the influence of abnormal blood pressure circadian rhythms and the morning surge on aortic stiffness in elderly patients with isolated systolic hypertension(ISH).Methods:A total of 300 untreated elderly(≥60 years)patients with ISH were enrolled.24-hour ambulatory blood pressure was measured by using a non-invasive portable ambulatory sphygmomanometer with an inflatable cuff.Brachial-ankle pulse wave velocity(baPWV)and the ankle-brachial pressure index(ABI)were measured by using an automated device.Patients were divided into the dipper(n=95), no-dipper(n=177)and extreme dipper(n=28)groups according to the rate of nocturnal blood pressure reduction.They were also divided into the morning surge(n=88)and no morning surge(n=212)groups according to the morning blood pressure surge(MBPS). Differences between the groups were compared.Correlations between the parameters were calculated by partial correlation analyses.The effects on baPWV and ABI were calculated by multiple linear regression analyses.Results:baPWV was higher in the extreme dipper group than in the dipper and no dipper groups[(1 402±234)cm/s vs.(1 467±114)cm/s vs.(1 538±140)cm/s, P<0.01], while ABI values were lower in the extreme dipper group than in the dipper group(0.98±0.10 vs.1.05±0.12, P<0.01)and the no dipper group(0.98±0.10 vs.1.03±0.12, P<0.05). Moreover, baPWV[(1 508±170)cm/s vs.(1 430±163)cm/s, P<0.01]was higher while ABI values(0.98±0.13 vs.1.06±0.11, P<0.01)were lower in the morning surge group than in the no morning surge group.baPWV was positively correlated with daytime Systolic blood pressure(dSBP)( r=0.169, P<0.01), 24 hSBPCV( r=0.143, P<0.05), and MBPS( r=0.157, P<0.01), while ABI was negatively correlated with dSBP( r=-0.146, P=0.011)and MBPS( r=-0.321, P<0.01). Age( P<0.01), dSBP( P<0.05)and 24 h systolic blood pressure variation coefficient( P<0.05)were independent factors for baPWV, while dSBP and MBPS were independent factors for ABI(all P<0.01). Conclusions:Abnormal blood pressure circadian rhythms and the morning surge are associated with increased aortic stiffness in elderly patients with ISH.