Dr Peter Rothwell and colleagues at the John Radcliffe Hospital, Oxford, found that, whatever patients' mean BP, episodes of high BP were strong predictors of stroke, heart failure, angina and MI.

Another study showed that drug-class effects on variability in BP explained differences in the drugs' efficacy in preventing stroke.

In a review paper Dr Rothwell examines the shortcomings of the view that variation in readings is random and that a measure of a ‘true' BP should be sought.

In an accompanying comment piece, Dr Bo Carlberg and Dr Lars Hjalmar Lindholm, of Umeå University Hospital in Sweden argue that it is too early to revise treatment guidelines because of the difficulties of translating clinical trial results into everyday practice. They argue that Dr Rothwell and his team paper ‘make a strong argument for also measuring BP variability because it supplements BP very well as a risk factor'.