Does diurnal variation in blood pressure exist in CAPD patients?

The existence of diurnal variation in CAPD remains controversial. We therefore attempted to delineate the blood-pressure (BP) pattern in CAPD patients by ambulatory blood-pressure monitoring (ABPM). Initially ABPM was performed in 31 patients (21 M, 10 F), mean age 65.4 years (26–87) using the Spacelabs model 90207. The maximal normal BP preset on the recorder was 140/90 mmHg. Daytime and night-time readings, recorded every 30 min, were defined as those from 0600 to 2100 and 2100 to 0600 hours respectively. Mean duration of dialysis was 15.2 months (3–76).There were 14 hypertensive patients, defined as a basal BP > 140/90 mmHg, or those on antihypertens-ive medications. Taking the group as a whole a significant difference between day and night-time readings was found as regards minimal systolic BP (118 versus 107.6 mmHg), maximal systolic BP (181.6 versus 171.2 mmHg), mean diastolic BP (83.9 versus 79.6 mmHg), and maximal diastolic BP (121.7 versus 104.5 mmHg), P<0.05. Diurnal variation, defined in the initial study as a 10% decrease of MAP occurring during any consecutive 4-h period, was present in 21 patients. In three the diurnal variation manifested as a paradoxical reduction of BP during the day. The only significant difference between those with diurnal variation and those without was the duration of dialysis, being 19.2 ±19.9 versus 13.3 ±17.3 months respectively, (P<0.05).In a second study 18 hypertensive CAPD patients were subjected to ABPM. Nine of them had participated in the first study. These patients were specifically asked to detail their periods of sleep and arousal. Diurnal variation was here defined as a 10% decrease of MAP occurring 2 h after the onset of sleep. Diurnal variation was found to exist in 10 patients (55%). Comparing the day to night-time readings in this group, no significant differences were found in mean systolic and MAP. When, however, the arousal versus sleep period readings were compared, a significant difference was observed in mean diastolic BP (83±14 versus 77±17mmHg, P<0.01), and in the MAP (104 ± 18 versus 98±20.5 mmHg, P<0.01). The mean systolic BP just failed to reach statistical significance (141±26 versus 137±30 mmHg) due probably to the small sample size.We conclude that diurnal variation exists in the majority of CAPD patients. Our findings support the concept that the set point model of diurnal variation, in which the major determinant is activity or arousal is the operative one in these patients. Due to disordered sleep patterns in patients on CAPD, diurnal variation might thus be better elicited when taking into account a decrease of MAP occurring during any consecutive 4-h period.