Non-Linear trends in the blood pressure of Japanese adults

Hypertension is one of the risk factors for the development of coronary artery disease as well as stroke. The National Nutrition Survey shows that the systolic and diastolic blood pressures of Japanese adults have decreased over time. These trends have plateaued during the last decade. We investigated national trends in blood pressure (BP) levels during these 10 years by plotting the relation between the mean BP levels during year t, BP(t), and those of the following year, BP(t+1). When we plotted the systolic BP levels of Japanese men and women aged 15 to 80 years, the trace revolved clockwise, with cycles of 4 to 5 years. The approximate center of the circular trace corresponding to data for 1985 through 1990 was at 134 mmHg in men and 129 mmHg in women, and the approximate center of a smaller circle was at 135 mmHg in men and 130 mmHg in women, respectively. In addition, with respect to the data for Japanese men in their 60s, the mean systolic BP level decreased linearly from 1982 to 1986, whereas it seemed to generate 4 circles after 1986. The approximate center of the first circle was 146 mmHg in the men. The center of the second circle was 145 mmHg and that of the third circle was 144 mmHg. Plotting of the data for Japanese women of the same age group yielded the same number of circles as the data for men. Our method of documenting changes in the mean BP levels in Japanese adults provided information about a chaotic oscillation that occurred in the populations we studied. The centers of Lorenz-plotted circles may thus provide essential information about trends in the BP levels in these populations.