DIURNAL BLOOD-PRESSURE VARIATIONS AND ONSET OF SUBARACHNOID HEMORRHAGE - A POPULATION-BASED STUDY

Objectives: To analyse the association between time of onset of subara chnoid haemorrhage and diurnal blood pressure variations of ambulant n ormo- and hypertensive subjects. Design: Retrospective, population-bas ed study. Setting: The population (246 000) of the Health Care Distric t of Central Finland. Patients: During 1980-1987 a total of 332 subjec ts in the study population had their first subarachnoid haemorrhage, T he hour of onset could be obtained for 287 patients, and these form th e basis of the present study. Results: The onset of subarachnoid haemo rrhage occurred significantly more often during the waking hours than during the night. The correlation between the hourly numbers of patien ts suffering a haemorrhage and the corresponding mean systolic and dia stolic blood pressure values of ambulant normo- and hypertensive subje cts was highly significant (r = 0.88, P < 0.001). The results were sim ilar when the 224 patients with proved aneurysmal bleed were analysed separately (r = 0.79-0.85, P < 0.001). Conclusions: The diurnal blood pressure variations of ambulant normo- and hypertensive subjects, espe cially the transient blood pressure peaks reaching much higher levels of pressure during the waking hours than during the night, may be cruc ial in determining the time of rupture of a critically weakened aneury sm wall.