Changes of nocturnal blood pressure dipping status in hypertensives by nighttime dosing of alpha-adrenergic blocker, doxazosin - Results from the HALT study

Abnormal nocturnal blood pressure (BP) dipping status may be partly determi ned by nocturnal sympathetic activity. We studied the effect of nighttime d osing of an alpha(1)-adrenergic blocker, doxazosin, on the BP dipping statu s of 118 hypertensives, all of whom underwent 24-hour ambulatory BP monitor ing before and after treatment. The mean nighttime/daytime ratio of systoli c BP was increased (0.91 after therapy versus 0.89 at baseline, P<0.05). Th e patients were initially divided into 4 groups on the basis of their dippi ng status at the baseline assessment: 18 (15%) were extreme dippers, with a nighttime systolic BP fall of at least 20% of daytime BP; 46 (39%) were di ppers (fall between 10% and 20%); 48 (41%) were nondippers (fall between 0% and 10%); and 6 (5%) were risers (nocturnal increase of systolic BP). A sh ift in dipping status toward less nocturnal BP dipping was observed after d oxazosin therapy (P<0.05). Dipping status was determined by nighttime more than by daytime BP, and this was not explained by differences in the number of daytime and nighttime readings. The effects of doxazosin on the mean no cturnal systolic BP changes were an increase of 4.3 mm Hg in extreme dipper s and decreases of 0.7 mm Hg in dippers, 12 mm Hg in nondippers, and 18 mm Hg in risers; the reduction was only significant in the latter 2 groups (bo th P<0.01). To estimate the effects of regression to the mean on the change s in dipping status, we also defined dipping status with the average of the BPs before and after doxazosin and found no difference in the degree of ni ghttime BP reduction among each group. The reduction of daytime BP was now significantly greater in the subgroups with less dipping: 6.4 mm Hg for ext reme dippers and 16 mm Hg for risers (P<0.05). In conclusion nighttime dosi ng with doxazosin markedly affects the nocturnal BP dipping status of hyper tensives, but the apparently greater reduction in nighttime pressure in non dippers and risers may be, at least partly, due to the effect of regression to the mean. The most important determinants of the effect of doxazosin we re the absolute BP levels, both day and night, rather than dipping status p er se.