Assessment of age-dependent changes in circadian blood pressure rhythm in patients with essential hypertension

The effects of age on the circadian blood pressure rhythm of patients with untreated essential hypertension (n = 133, World Health Organization stage I or II) were compared with those of normotensive subjects (n = 91). Subjects were classified into three groups by age: young (< 40 years old), adult (40-59 years old) and old (≥ 60 years old). Blood pressure was monitored every 5 min for 24 h, using a finger volume oscillometric device under fixed external conditions. The single cosinor method was used to evaluate circadian rhythm. There was no difference in the amplitude of circadian systolic or diastolic blood pressure rhythm among the different normotensive and essentially hypertensive age groups although a wide distribution of amplitude was noted within each group. The distribution of amplitude was wider in the hypertensive than in the normotensive groups. The amplitude of circadian blood pressure rhythm was independent of the mesor level. On the other hand, the amplitude of circadian heart rate rhythm decreased with increasing age both in normotensive subjects (P < 0.05, young versus adult or old) and hypertensive patients (P < 0.01, young and old versus adult). The acrophase of circadian systolic blood pressure rhythm in young hypertensives was greater than that in adult or old hypertensives (P < 0.05, for both). Such age-dependent changes were not observed in the normotensive groups. Consequently, the acrophase of circadian systolic or diastolic blood pressure rhythm in young hypertensives was larger than that in young normotensives (P < 0.05, for both systolic and diastolic blood pressure). The acrophase of heart rate did not differ between any of the groups. The amplitude of circadian systolic or diastolic blood pressure rhythm was greater in adult hypertensives than in adult normotensives (P < 0.05, for both systolic and diastolic blood pressure). Such information may be useful in the diagnosis and treatment of essential hypertension and warrants further study to clarify the mechanisms responsible for the alteration of circadian blood pressure rhythm.