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(Hypertension. 2008;52:e10.)
© 2008 American Heart Association, Inc.

Letters to the Editor

Nocturnal Blood Pressure Fall Changes in Correlation With Urinary Sodium Excretion

Hypertension Unit, Nephrology Division, University of São Paulo–School of Medicine, São Paulo, Brazil

To the Editor:

In the April 2008 issue of Hypertension, Bankir et al¹ analyzed the data of 325 subjects divided into tertiles of the day:night ratio of urinary sodium excretion. Subjects in tertile 3 were qualified as "high daytime sodium excretors" because they excreted sodium at a rate that was 46% higher during daytime than during nighttime, whereas subjects in tertile 1 were "low daytime sodium excretors" and excreted 3 times less sodium during daytime than during nighttime. The nocturnal blood pressure (BP) dipping was significantly lower in tertile 1 than in other tertiles, especially for systolic BP. Thus, the authors suggested that the capacity to excrete sodium during daytime is the main determinant of nocturnal BP and dipping.

However, the mechanisms associated with the reproducibility of the circadian BP pattern remain to be elucidated. It is well known that when ambulatory BP monitoring (ABPM) is repeated without interventions in the short² or long term,³ a spontaneous change may occur in the nocturnal BP.

Thus, we⁴ investigated whether individuals with a spontaneous change in the nocturnal BP fall have any differences in physiological mechanisms of BP control. Normotensive and hypertensive subjects underwent two 24-hour ABPM recordings separated by 30 days and also measurements in the same period of plasma renin activity, aldosterone, catecholamines, and 24-hour urinary sodium/potassium excretion.

Twenty-three individuals (50%) maintained the same nocturnal systolic and diastolic BP fall profile, "dipper" (n=14) or "nondipper" (n=9), designated as the "maintained" group. In 23 individuals (50%), the nocturnal BP fall profile changed, from dipper to nondipper (n=16) or from nondipper to dipper (n=7), called the "changed group." The maintained and changed groups were not different in relation to age, body mass index, gender, plasma renin activity, aldosterone, catecholamines, and 24-hour urinary potassium excretion.

However, it was observed that, in the changed group, the subgroup that changed from dipper (ABPM 1) to nondipper (ABPM 2) had a significant increase in nocturnal BP on ABPM 2 (123±16 to 131±19 mm Hg; P<0.05) and lower urinary sodium excretion (151±65 versus 112±48 mEq/24 hours; P<0.05) and a negative correlation between the difference in nighttime ambulatory systolic BP (ABPM 1 – ABPM 2) and in 24-hour urinary sodium excretion (r=–0.63; P=0.01).

A explanation for this finding could be that the subjects in this subgroup probably had an elevation in nocturnal systolic BP during the second 24-hour recording because of lower sodium excretion in the daytime, as showed by Bankir et al.¹ For a better understanding of this subject, further studies should be done to investigate the sodium excretion during daytime and nighttime in two 24-hour ABPM recordings.

	Acknowledgments

 
Source of Funding

This work was supported by a grant from FAPESP (03/08257-9).

Disclosures

None.

	References

Top References

 
1. Bankir L, Bochud M, Maillard M, Bovet P, Gabriel A, Burnier M. Nighttime blood pressure and nocturnal dipping are associated with daytime urinary sodium excretion in African subjects. Hypertension. 2008; 51: 891–898.[Abstract/Free Full Text]

2. Mochizuki Y, Okutani M, Donfeng Y, Iwasaki H, Takusagawa M, Kohno I, Umetani K, Ishii H, Ijiri H, Komori S, Tamura K. Limited reproducibility of circadian variation in blood pressure dippers and nondippers. Am J Hypertens. 1998; 11: 403–409.[CrossRef][Medline] [Order article via Infotrieve]

3. Omboni S, Parati G, Palatini P, Vanasia A, Muiesan ML, Cuspidi C, Mancia G. Reproducibility and clinical value of nocturnal hypotension: prospective evidence from the SAMPLE study. J Hypertens. 1998; 16: 733–738.[CrossRef][Medline] [Order article via Infotrieve]

4. Ortega KC, Mion D Jr. Sodium excretion and nocturnal blood pressure fall. World Congress of Nephrology 2007; April 21–25, 2007; Rio de Janeiro, Brazil. Book of Abstracts WCN T-PO-. 2007; 1171: 387.

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This Article Extract Full Text (PDF) All Versions of this Article: 52/2/e10    most recent HYPERTENSIONAHA.108.115394v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ortega, K. C. Articles by Mion, D. Search for Related Content PubMed PubMed Citation Articles by Ortega, K. C. Articles by Mion, D., Jr Related Collections Other hypertension Other diagnostic testing