Seasonal differences in diurnal blood pressure of hypertensive patients living in a stable environmental temperature.
To determine whether there is a seasonal variation in blood pressure in hypertensive patients whose daily lifestyle is similar in summer and in winter, and who live almost entirely indoors in a stable environmental temperature. During summer and winter, blood pressure was measured by ambulatory blood pressure monitoring in outpatients with essential hypertension, and environmental temperature was measured by electrothermometer while the patients were awake. The 24-h blood pressure data were analysed after being divided into four groups: morning, afternoon, night-time and sleeping periods. We studied 25 outpatients (mean +/- SD age 57 +/- 12 years) who spend virtually the entire day indoors in both summer and winter. Measurements of systolic and diastolic blood pressure in the morning and night-time periods were significantly higher in winter than in summer (differences of 7.5 +/- 14.7 and 4.1 +/- 8.8 mmHg and 8.2 +/- 14.8 and 4.5 +/- 8.1 mmHg, respectively). Blood pressure measured in the afternoon and during sleeping periods did not differ significantly. No correlation was observed between the seasonal change in blood pressure in the morning and that at night. Environmental temperatures were significantly higher in the morning, afternoon and night-time periods during summer than those during winter. The differences among these periods were not statistically significant. There is a seasonal variation in blood pressure in the morning and night-time periods during winter in hypertensive patients who live essentially indoors in a relatively stable environmental temperature. Pressor factor(s) may differ between morning and night-time periods during winter.