Clinical Science (1979) 57,291s-294s
Physical activity and the circadian rhythm of blood pressure
S. M A N N , M. W. M I L L A R C R A I G , D . I. M E L V I L L E , V. B A L A S U B R A M A N I A N A N D E. B. R A F T E R Y Department of Cardiology, Northwick Park Hospital and Clinical Research Centre, Harrow, MiaWesex. U X .
Summary
1. Ambulatory blood pressure monitoring was carried out in 10 subjects for a period of 48 h, the first Or second 24 part Of which was selected randomly to be a period of complete bed rest. 2. Heart rate was significantly lower throughout the O4'0OOf bed rest except for the 08.00 hours, when there was little difference. 3. The circadian variation of blood pressure was reduced during the day of bed rest but this was mainly due to higher night-time pressures. Key words: ambulatory monitoring, blood pressure, circadian variation, physical activity. Introduction
Current interest in the circadian rhythm of blood pressure has spawned a controversy over the degree to which this is dependent on concurrent physical activity. The importance of a daytime rhythm of blood pressure independent of physical activity is great, since if present it should significantly alter the interpretation of pressures ascertained at different times of the day in the course of management of hypertensive subjects. There has also been much debate about the trends in blood pressure during the night and whether the rise in pressure in the early morning merely reflects physical activity or mental arousal (Floras, Jones, Johnston, Brooks, Hassan & Sleight, 1978). We have used the method of continuous monitoring of intra-arterial pressure to assess trends in blood pressure by plotting hourly mean values over Correspondence: Dr E. B. Raftery, Department of Cardiology, Northwick Park Hospital, Watford Road, Harrow, Middlesex HA1 3UJ, U.K.
the course of the day and pooling the data for similar groups of subjects (Millar Craig, Bishop & Raftery, 1978a). For 2 consecutive days of free in this ambulation the way have been found to be highly reproducible (Mann, Millar Craig, Balasubramanian, Melville & Raftery, 1979). In this study we sought to compare the trends in heart rate and blood pressure during a freely ambulant day with those during a contiguous day of minimal physical activity where the subjects restedin bed.
Subjects
Ten subjects took part in this experiment (eight males and two females). Seven were patients attending the hypertension clinic with mild to moderate untreated essential hypertension and three were normotensive, one with a very low blood pressure. Ages ranged from 29 to 64 years (mean 44 years) and clinic blood pressures from 90/60 to 218/123 mmHg (mean 159/96 mmHg). Informed consent was obtained, the project having approval of the Hospital Ethical Committee. Methods
Ambulatory recording of intra-arterial blood pressure and ECG was performed by methods previously described (Millar Craig, Hawes & Whittington, 1978b). One 24 h period was spent freely ambulant (at work where appropriate) and sleeping at home. The other 24 h was spent in bed in a hospital side-ward with minimum disturbance. Subjects were not restricted to lying flat, and were allowed visitors and to visit the toilet. The order of 291s
292s
S. Mann et al.
the 2 days was randomly allocated at the time of recruitment so that five subjects were ambulant first and the other five had a reversed order. The patients used dictaphone tape recorders to record activities during the study and were specifically requested to note the times of going to sleep and waking and a subjective impression of the quality of sleep. Results for each hour of the day were combined for patients undergoing the same phase of the study. Recombination of the data around the time of waking was also performed to synchronize the recordings. Sections of 6 h each were also used to express daytime (12.00-18.00 hours) and nighttime (24.0046.00 hours) mean values as single entities. Differences between ambulant and bed-rest periods, and between day 1 values and day 2 values, were compared by a paired Student's t-test.
50
Y"
1
-
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
09.00 13.00 17.00 21.00 01.00 05.00 09.00 11.00 15.00 19.00 23.00 03.00 07.00
Time of day (hours)
Results
Diaries All patients were normally active during the ambulant day, nine out of the 10 going out to work. Although not all slept well, scores for subjective impression of length and quality of sleep were identical for both nights. There was no significant difference between sleep quality or daytime activity between the groups who were ambulant first or last. Ambulant day Six-hourly daytime values showed a mean rise in heart rate of 26 beatdmin (37%) above night time rates. Blood pressure also rose, systolic by 28 mmHg (25%) and diastolic by 23 mmHg. (38%). The circadian curves plotted from hourly mean values (Fig. 1) showed essentially similar patterns to those reported previously with these methods (Millar Craig, Mann, Balasubramanian & Raftery, 1978~). Bed-rest day Day to night differences were clearly reduced during this day. Heart rate was lower throughout the 24 h, significantly so (P < 0.05) for all hours except from 04.00 to 08.00 hours; the day to night change was only 1 1 beatdmin (17%) (P < 0.02) with respect to the change on the ambulant day. Blood pressure was lower during the day but higher
FIG. 1. Circadian curves derived from hourly mean values of heart rate, systolic and diastolic pressures on the ambulant day ( 0 )and the bed rest day (0).Statistical significance of the differences: * P
Physical activity and the circadian rhythm of blood pressure
S. M A N N , M. W. M I L L A R C R A I G , D . I. M E L V I L L E , V. B A L A S U B R A M A N I A N A N D E. B. R A F T E R Y Department of Cardiology, Northwick Park Hospital and Clinical Research Centre, Harrow, MiaWesex. U X .
Summary
1. Ambulatory blood pressure monitoring was carried out in 10 subjects for a period of 48 h, the first Or second 24 part Of which was selected randomly to be a period of complete bed rest. 2. Heart rate was significantly lower throughout the O4'0OOf bed rest except for the 08.00 hours, when there was little difference. 3. The circadian variation of blood pressure was reduced during the day of bed rest but this was mainly due to higher night-time pressures. Key words: ambulatory monitoring, blood pressure, circadian variation, physical activity. Introduction
Current interest in the circadian rhythm of blood pressure has spawned a controversy over the degree to which this is dependent on concurrent physical activity. The importance of a daytime rhythm of blood pressure independent of physical activity is great, since if present it should significantly alter the interpretation of pressures ascertained at different times of the day in the course of management of hypertensive subjects. There has also been much debate about the trends in blood pressure during the night and whether the rise in pressure in the early morning merely reflects physical activity or mental arousal (Floras, Jones, Johnston, Brooks, Hassan & Sleight, 1978). We have used the method of continuous monitoring of intra-arterial pressure to assess trends in blood pressure by plotting hourly mean values over Correspondence: Dr E. B. Raftery, Department of Cardiology, Northwick Park Hospital, Watford Road, Harrow, Middlesex HA1 3UJ, U.K.
the course of the day and pooling the data for similar groups of subjects (Millar Craig, Bishop & Raftery, 1978a). For 2 consecutive days of free in this ambulation the way have been found to be highly reproducible (Mann, Millar Craig, Balasubramanian, Melville & Raftery, 1979). In this study we sought to compare the trends in heart rate and blood pressure during a freely ambulant day with those during a contiguous day of minimal physical activity where the subjects restedin bed.
Subjects
Ten subjects took part in this experiment (eight males and two females). Seven were patients attending the hypertension clinic with mild to moderate untreated essential hypertension and three were normotensive, one with a very low blood pressure. Ages ranged from 29 to 64 years (mean 44 years) and clinic blood pressures from 90/60 to 218/123 mmHg (mean 159/96 mmHg). Informed consent was obtained, the project having approval of the Hospital Ethical Committee. Methods
Ambulatory recording of intra-arterial blood pressure and ECG was performed by methods previously described (Millar Craig, Hawes & Whittington, 1978b). One 24 h period was spent freely ambulant (at work where appropriate) and sleeping at home. The other 24 h was spent in bed in a hospital side-ward with minimum disturbance. Subjects were not restricted to lying flat, and were allowed visitors and to visit the toilet. The order of 291s
292s
S. Mann et al.
the 2 days was randomly allocated at the time of recruitment so that five subjects were ambulant first and the other five had a reversed order. The patients used dictaphone tape recorders to record activities during the study and were specifically requested to note the times of going to sleep and waking and a subjective impression of the quality of sleep. Results for each hour of the day were combined for patients undergoing the same phase of the study. Recombination of the data around the time of waking was also performed to synchronize the recordings. Sections of 6 h each were also used to express daytime (12.00-18.00 hours) and nighttime (24.0046.00 hours) mean values as single entities. Differences between ambulant and bed-rest periods, and between day 1 values and day 2 values, were compared by a paired Student's t-test.
50
Y"
1
-
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
09.00 13.00 17.00 21.00 01.00 05.00 09.00 11.00 15.00 19.00 23.00 03.00 07.00
Time of day (hours)
Results
Diaries All patients were normally active during the ambulant day, nine out of the 10 going out to work. Although not all slept well, scores for subjective impression of length and quality of sleep were identical for both nights. There was no significant difference between sleep quality or daytime activity between the groups who were ambulant first or last. Ambulant day Six-hourly daytime values showed a mean rise in heart rate of 26 beatdmin (37%) above night time rates. Blood pressure also rose, systolic by 28 mmHg (25%) and diastolic by 23 mmHg. (38%). The circadian curves plotted from hourly mean values (Fig. 1) showed essentially similar patterns to those reported previously with these methods (Millar Craig, Mann, Balasubramanian & Raftery, 1978~). Bed-rest day Day to night differences were clearly reduced during this day. Heart rate was lower throughout the 24 h, significantly so (P < 0.05) for all hours except from 04.00 to 08.00 hours; the day to night change was only 1 1 beatdmin (17%) (P < 0.02) with respect to the change on the ambulant day. Blood pressure was lower during the day but higher
FIG. 1. Circadian curves derived from hourly mean values of heart rate, systolic and diastolic pressures on the ambulant day ( 0 )and the bed rest day (0).Statistical significance of the differences: * P
