SEASONAL-VARIATION IN BLOOD-PRESSURE IN NORMOTENSIVE WOMEN STUDIED BYHOME MEASUREMENTS

1. The factors influencing the seasonal variation in blood pressure me asured at home in normotensive women were examined. 2. Sixteen female subjects (56.3 +/- 7.9 years old, mean +/- SD) measured their blood pr essure and pulse rate at home each morning for more than 20 times per month for at least 1.5 years, Blood pressure and body weight were also determined in the office once or twice a month in that period, Monthl y means of outdoor and indoor temperatures and daytime length were obt ained from the Meteorological Observatory. The single cosinor method w as used to evaluate circannual rhythm. 3. We observed a biphasic seaso nal variation in self-recorded blood pressure measured at home, enviro nmental temperature and daytime length but found no apparent seasonal variation in body weight and blood pressure measured in the office, Th e lowest levels of systolic and diastolic blood pressure measured at h ome were observed in July, The longest daytime length was recorded in June, while the highest outdoor temperature and indoor temperature wer e recorded in August, indicating that the longest daytime length prece ded and the highest environmental temperature lagged behind the lowest level of blood pressure. The shortest daytime length is in December, The lowest outdoor and indoor temperature were observed in January, wh ile the highest levels of self-recorded systolic blood pressure and di astolic blood pressure were in January and December, respectively. Hal f-amplitudes of self-recorded systolic and diastolic blood pressure we re 2.6 +/- 1.0 mmHg and 2.0 +/- 0.8 mmHg, respectively. 4. These findi ngs indicate the importance of a seasonal effect, i.e. daytime length and the environmental temperature, on the Mood pressure of individuals .