Latent overhydration and nocturnal hypertension in diabetic nephropathy

With the aim of studying the diurnal variation in blood pressure in relation to degree of fluid retention, 24-h ambulatory blood pressure monitoring was performed in 31 insulin-dependent diabetic patients with nephropathy. The extracellular volume was calculated from the distribution volume of 51Cr-EDTA after a single injection. The study population was arbitrarily divided into two groups, depending on their extracellular volume. Group 1 included 15 patients with a lower extracellular volume and group 2, 16 patients with a higher extracellular volume. Ambulatory blood pressure was measured with a portable monitor using an oscillometric technique. In all patients, the mean +/- SD 24-h ambulatory blood pressure was 135/79 +/- 14/7 mmHg. Day and night-time blood pressure were 136/81 +/- 14/7 and 133/75 +/- 17/8, respectively (p < 0.02). The ambulatory blood pressure was 135/80 +/- 14/7 in group 1 and 136/78 +/- 15/6 mmHg in group 2. The nocturnal change in blood pressure was significantly greater in group 1 than in group 2, -9/-9 +/- 10/5 mmHg and 1/-3 +/- 10/6 mmHg, respectively (p = 0.005/0.01). There were no other significant differences between the groups than the diurnal blood pressure pattern. There were significant correlations between day ambulatory blood pressure and night ambulatory blood pressure and 24-h ambulatory blood pressure and urinary albumin excretion. There was no correlation between ausculatatory clinic blood pressure on the one hand and albuminuria on the other. Latent fluid retention therefore may contribute to nocturnal hypertension in diabetic nephropathy.