Reactivity of Ambulatory Blood Pressure to Physical Activity Varies With Time of Day

• Published in: Hypertension (Dallas, Tex. 1979) Vol. 47; no. 4; pp. 778 - 784
• Main Authors: Jones, Helen, Atkinson, Greg, Leary, Andrew, George, Keith, Murphy, Michael, Waterhouse, Jim
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Heart Association, Inc 01-04-2006; Hagerstown, MD Lippincott
• Subjects: Adult; Arterial hypertension. Arterial hypotension; Biological and medical sciences; Blood and lymphatic vessels; Blood Pressure; Blood Pressure Monitoring, Ambulatory; Cardiology. Vascular system; Circadian Rhythm; Clinical manifestations. Epidemiology. Investigative techniques. Etiology; Diastole; Female; Fundamental and applied biological sciences. Psychology; Heart Rate; Hemodynamics. Rheology; Humans; Hypertension - diagnosis; Hypertension - physiopathology; Male; Medical sciences; Middle Aged; Motor Activity; Systole; Vertebrates: cardiovascular system; Physical exercise; Human; Hypertension; Morning; Cardiovascular disease; exercise; Circadian rhythm; Heart rate; Chemotherapy; Sleep; blood pressure monitoring, ambulatory; Arterial pressure; Blood pressure; Ambulatory; Monitoring
• ISSN: 0194-911X; 1524-4563; 1524-4563
• DOI: 10.1161/01.HYP.0000206421.09642.b5

Blood pressure (BP) fluctuates over a 24-hour period, but it is unclear to what extent this variation is governed completely by changes in physical activity. Our aim was to use a BP “reactivity index” to investigate whether the BP response to a given level of physical activity changes during a normal sleep–wake cycle. Hypertensive patients (n=440) underwent simultaneous 24-hour ambulatory BP, heart rate (HR), and activity monitoring. BP and HR were measured every 20 minutes. Actigraphy data were averaged over the 15 minutes that preceded a BP measurement. Individual BP and HR reactivity indices were calculated using least-squares regression for twelve 2-hour periods. These indices were then analyzed for time-of-day differences using a general linear model. Systolic BP and HR were generally more reactive to physical activity than diastolic BP. The highest reactivity of systolic BP (mean±SE=4±1 mm Hg per logged unit change in activity) was observed between 8:00 am and 10:00 am (P=0.014). Between 10:00 am and 12:00 pm, BP reactivity then decreased (P=0.048) and showed a secondary rise in the early afternoon. These 24-hour changes in BP reactivity did not differ significantly between groups formed on the basis of early and late wake times (P=0.485), medication use, age, and sex (P>0.350). In conclusion, under conditions of normal living, the reactivity of BP and HR to a given unit change in activity is highest in the morning and shows a secondary rise in the afternoon.