9. Mathewson, F.A.L., Corne, R.A., Nelson, N.A. & Hill, N.L.: Blood pressure characteristics of a select group of North American males, followed for 20 years. Can Med Assoc J 106: 549-557, 1972.

This report describes the 20-year blood pressure behaviours of 3869 selected young North American males. Initial mean systolic and diastolic pressures were higher than those recorded five years later; after that pressures increased progressively. The effect of initial selection was evident for the first 10 years of exposure. A significant relationship was demonstrated between all initial systolic and diastolic levels and the 20-year blood pressure behaviour. Systolic pressure was not affected by age until age 50 and diastolic until age 45. After that a significant relationship was demonstrated. In 20 years multiple readings > 140 and/or > 90 mm.Hg were recorded in 26% of the population. Increases in pressure usually extended over many years. Commonly they were labile, fluctuating above and below 140/90 mm.Hg. In a small, clearly defined group, accelerated increases reached high levels in three to 10 years.