SEASONAL CHANGE IN 24-HOUR BLOOD-PRESSURE AND HEART-RATE IS GREATER AMONG SMOKERS THAN NONSMOKERS

In general, blood pressure is higher in winter than in summer, and thi s factor may be partly responsible for the higher mortality from cardi ovascular disease in winter. Cigarette smoking causes an acute presser response that may interact with this cardiovascular response to cold exposure. We sought to determine whether the seasonal variation in blo od pressure and heart rate differs between cigarette smokers and nonsm okers. We evaluated 24-hour ambulatory systolic blood pressure (SEP), ambulatory diastolic blood pressure (DBP), and ambulatory heart rate o f 97 healthy men (73 nonsmokers and 24 smokers), 28 to 63 years of age , during the summer and winter, taking indoor temperatures into consid eration. Smokers and nonsmokers both had higher daytime ambulatory SBP s and DBPs in winter than in summer (after adjustment for potential co nfounders). However, the winter increase seen in the smokers was signi ficantly higher far mean daytime SEP (7.3 versus 2.7 mm Hg, P<.01), fo r mean daytime DBP (4.4 versus 3.1 mm Hg, P=.051), and for ambulatory heart rate (3.9 versus -1.7 beats/min, P<.001), The double product inc reased from summer to winter (daytime) by 10.53 for smokers and by onl y 0.11 for nonsmokers (P<.01). There was an independent interaction be tween season and smoking status that affected SEP (standardized beta=0 .66, P<.0001) and DBP (standardized beta=0.32, P<.0001). Smokers have a greater seasonal variation in blood pressure and heart rate than non smokers and show a larger increase in the cardiovascular load in winte r. Smoking apparently potentiates the cardiovascular response to vario us climatic conditions. Season should be taken into account in studies of blood pressure and in the diagnosis and treatment of hypertension, particularly among cigarette smokers.