Ohasama Study

Background/Questions

The Ohasama Study was initiated in 1986 and led by Yutaka Imai (currently of the Department of Clinical Pharmacology and Therapeutics, Tohoku University Graduate School of Pharmaceutical Science and Medicine). The study addressed primarily the relationship of resting home and ambulatory blood pressure in residents of Ohasama to their cardiovascular disease risk over an average of 10-years. Until Imai’s research, there was little knowledge of the epidemiology of 24-hour ambulatory blood pressure monitoring and home blood pressure measurement or their relationship to reference values and the distribution of casual blood pressure. The study sought to establish the variance for each modality.

Method/Design

Ohasama, a population of roughly 7,000 in Iwate prefecture, is a typical rural community mainly involved in the cultivation of fruit. In Ohasama, the medical checkups involved collecting home blood pressure measurements on all adults on three occasions, the first from 1986-1995, the second from 1997-2000 and the third from 2001-2005.

Results

24-hour monitoring

1. Compared to casual blood pressure measurements, 24-hour ambulatory blood pressure monitoring
   yields superior predictive value for morbidity and mortality from cardiovascular and cerebrovascular disease.
2. Mean 24-hour ambulatory blood pressure greater than 135/80 mmHg is classified as having hypertension.
3. Lowered mean blood pressure at night predicts lower rates of mortality from cerebrovascular and cardiovascular disease.
4. Large daytime variability in blood pressure and small daytime variability in pulse rate predicts higher rates of mortality from cerebrovascular and cardiovascular disease.

Home blood pressure measurements:

1. The predictive value for morbidity and mortality from cardiovascular and cerebrovascular disease is superior for home blood pressure measurements compared to casual resting blood pressure, irrespective of the number of measurements.
2. Home mean blood pressure measurements greater than 135/85 mmHg are classified as hypertension.
3. The predictive value for mortality for cardiovascular and cerebrovascular disease is superior in home systolic blood pressure measurements compared to diastolic.
4. Greater home mean pulse rate is associated with a higher risk of mortality from cardiovascular and cerebrovascular disease.
5. “White coat hypertension” predicts true hypertension eight years later.

Conclusions:

Both home and 24-hour monitored mean blood pressure add information for prediction of CVD events beyond casual survey or office resting blood pressure.

The 1997 Report of the Joint National Committee in the United States, the 1999 WHO/ISH Hypertension Guideline, the 2003 ESH/ESC Hypertension Guideline, and other international guidelines derived part of the standards for home blood pressure measurement and for 24-hour ambulatory blood pressure monitoring from the Ohasama study, making it a unique Japanese contribution to clinically relevant issues. (HU)