Salt sensitivity and circadian rhythm of blood pressure: the keys to connect CKD with cardiovasucular events

Abstract

In healthy subjects, blood pressure (BP) drops by 10-20% during the night. Conversely, in patients with the salt-sensitive type of hypertension or chronic kidney disease, nighttime BP does not fall, resulting in an atypical pattern of circadian BP rhythm that does not dip. This pattern is referred to as the 'non-dipper' pattern. Loss of renal functional reserve, due to either reduced ultrafiltration capacity or enhanced tubular sodium reabsorption, induces the salt-sensitive type of hypertension. When salt intake is excessive in patients with salt-sensitive hypertension, the defect in sodium excretory capability becomes evident, resulting in elevated BP during the night. This nocturnal hypertension compensates for diminished natriuresis during the daytime and enhances pressure natriuresis during the night. Nocturnal hypertension and the non-dipper pattern of circadian BP rhythm cause cardiovascular events. When excess salt intake is loaded in patients who are in a salt-sensitive state, glomerular capillary pressure is also elevated, resulting in glomerular sclerosis and eventual renal failure. In this way, salt sensitivity and excess salt intake contribute to both cardiovascular and renal damage at the same time. We propose that salt sensitivity of BP and excess salt intake have important roles in the genesis of the cardiorenal connection. Salt sensitivity and circadian rhythm of BP are the keys to understanding the connections between cardiovascular and renal complications.

Altered Cardiovascular Rhythmicity in Children Born Small for Gestational Age

“…5,6 Among other mechanisms, salt sensitivity, which has been associated with LBW, 31,32 probably because of a reduced kidney size and nephron number, 7 has been proposed as a possible reason for the changes in BP rhythmicity. [33][34][35] The only moderate agreement between circadian and ultradian amplitudes in our SGA cohort is in accordance with previous data from children with chronic kidney disease 29 and supports the autonomy of rhythms with different period length, probably influenced by different pathophysiological effects. HR rhythms showed analogous abnormalities to BP rhythms with decreased amplitude size compared with controls, but only the 24-hour HR and -BP amplitudes correlate positively with each other.…”

Second morning urine method is superior to the casual urine method for estimating daily salt intake in patients with hypertension

“…Thus, it remains unclear whether the present results would be applicable to patients with severe target organ damage and patients with accelerated hypertension, because such patients may have a different circadian rhythm of sodium excretion. 38 In conclusion, the CU method was shown to underestimate the daily salt intake of persons with a high salt intake when morning urine samples were employed, and this finding was supported by the analysis of data from our previous studies A, B and C. On the other hand, the CU method overestimated the salt intake of persons with a low salt intake when afternoon urine samples were used. Correlations with the 24UC method were weaker for the CU method (R¼0.57) than the SMU method (R¼0.85).…”

A Randomized Trial of Dietary Sodium Restriction in CKD

“…[28][29][30] Although it is difficult to directly compare studies without taking the many potential confounding factors into consideration, BP reductions found in the LowSALT CKD study were nearly double those seen in the aforementioned meta-analyses, providing support for the hypothesis that CKD patients may have increased susceptibility to the adverse effects of excessive dietary sodium. 31,32 Nevertheless, further research with larger sample sizes is needed to confirm this.…”