Loss of nocturnal blood pressure fall in patients with renal impairment

Davidson et al reported an excellent study correlating a blunted nocturnal fall in BP with the subsequent decline in renal function. I would like to mention that the loss or reversal of the physiologic nocturnal fall in BP was demonstrated many years ago in chronic kidney disease, independently from external interfering factors. Patients with chronic nephropathies and patients with essential hypertension were matched by age, sex, and mean 24-hour BP values. Ambulatory BP monitoring was performed in an open hospital ward for 48 hours at 15-minute sampling intervals after standardization of diet, meal times, sleep times, and activity schedules. In essential hypertension, the nocturnal fall in BP was preserved as in normal conditions, whereas patients with renal impairment displayed blunted or reversed nocturnal BP and heart rate patterns. Hence, it appeared that casual measurements of BP confined to daytime may underestimate a hypertensive condition associated with chronic kidney disease. Increased sympathetic tone related to renal impairment was proposed to play a role in such a finding. Some years later, however, a polysomnographic study using continuous BP monitoring with a Finapres device (Finapres Medical Systems BV, Amsterdam, the Netherland) showed that nondipping status is also present in a minority (15%) of essential hypertensive patients and is strictly associated with undiagnosed sleep-related breathing disorder characterized by apneic snoring. Furthermore, only continuous BP recording during the night allowed the proper identification of the nondipping condition, since a notable proportion of cases were miscategorized as nondipping by ambulatory BP monitoring. It appeared that polysomnography is necessary to differentiate sleep apnea from other possible underlying mechanisms. In view of the higher amount of target organ damage, which is to be expected in patients with nondipping status (including the renal function deterioration reported by Davidson et al), and the high prevalence of undiagnosed sleep-related breathing disorder in the adult population, the recommendation that one should incorporate an assessment of the subject’s sleep history into the routine diagnostic screening of any type of hypertension seems justified.