Do hypertensive patients have a different diurnal pattern of electrolyte excretion?

Abstract

SUMMARY Studies generally indicate that excretion of sodium, potassium, and water is greater during the day than during the night. To determine whether hypertensive patients exhibit this same pattern of excretion, diurnal variations in excretion of sodium, potassium, creatinine, and water were examined in 107 hypertensive men and women from a clinical trial on control of hypertension by nonpharmacological means -the Hypertension Control Program. Each participant provided two carefully timed 24-hour urine collections divided into daytime and overnight specimens. The median ratios of 24-hour to 8-hour overnight excretion were 2.84,3.95,2.99, and 2.77 for sodium, potassium, creatinine, and water, respectively. Thus, more than half of this hypertensive group exhibited a greater rate of sodium and water excretion during sleep than during daytime hours, a reversal of the usual pattern. When the group was subdivided based on age, sex, race, trial randomization group, use of diuretics, and hypertension severity, women had significantly lower ratios of 24-hour to overnight excretion for sodium and water than men and blacks had significantly lower 24-hour to overnight ratios for water and potassium than whites. When the 24-hour to overnight ratios for these hypertensive patients were compared with those for a group of 30 men and women with high-normal blood pressure, those with high-normal blood pressure had significantly larger ratios for sodium and water excretion than the hypertensive group. The results of this study suggest that hypertensive patients may have a different diurnal pattern of sodium and water excretion than normotensive subjects and that further research is needed to clarify this issue. (Hypertension 10: 417-424, 1987) KEY WORDS • hypertension • electrolytes • diurnal patterns D IURNAL variations in urinary excretion of sodium, chloride, potassium, and water have long been recognized, with excretion of water and electrolytes generally reaching a maximum some-

Blood pressure and diurnal variation in sodium, potassium, and water excretion

“…40,43,[47][48][49]52 Diurnal variations in excretion of sodium, chloride, potassium, and water have been observed in many studies. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Creatinine excretion has generally been reported to be fairly constant over 24 h, 2,7,11,26,28 and on average this was the case for the men in this study. Water and electrolyte excretion in healthy individuals generally reaches a maximum sometime around midday and a minimum toward the end of sleep.…”

“…26 With respect to reproducibility of ratios over the three 24-h periods, the intra-class correlation of the three ratios was 0.518 for sodium, 0.441 for potassium, 0.340 for volume, and 0.338 for creatinine. These correlations indicate that for the ratio of 8-h overnight to 24-h excretion of sodium calculated from a single 24-h urine collection, approximately half the observed variation in the ratio is due to true between person variation and half to within-person variation.…”

“…The rationale behind this correction is that this and other studies indicate that creatinine excretion is on average constant throughout the day, 2,7,11,26,28 ie, the total amount of creatinine excreted in a 16-h daytime collection should on average be approximately twice the amount excreted in an 8-h overnight collection. Under this assumption, the creatinine term in the denominator of the second equation, ie, (2 × Cr o )/Cr d , should be close to one.…”

“…The results for creatinine are not unexpected given the relatively smaller standard deviations of the overnight to 24-hour creatinine ratios compared to those for sodium, potassium, and volume, and the finding in this and other studies that creatinine excretion is on average constant throughout the day. 2,7,11,26,28 Correlations with possible confounding variables Systolic BP was significantly correlated with age, BMI, and heart rate and DBP with BMI and heart rate ( Table 2). While SBP and DBP were positively correlated with log alcohol intake, these correlations did not differ significantly from zero.…”

“…10,[17][18][19][20][21][22] Investigators have also reported a reversal or flattening of the usual cycle of sodium and chloride excretion in hypertensives. 17,[23][24][25][26][27] In a previous report, Dyer et al 26 found on average no diurnal variation in excretion of sodium and water in a group of hypertensive men and women, with more than half showing a higher rate of sodium and water excretion at night than during the day. A stronger association between blood pressure (BP) and overnight excretion of sodium, compared to daytime or 24-h excretion, has also been reported.…”