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Portable blood pressure recorder Accuracy and preliminary use in evaluating intradaily variations in pressure
Portable Accuracy intradaily
blood pressure recorder and preliminary use in evaluating va,riations in pressure
Allen T. H&man, M.D. Btrnard T. Engel, Ph.D. Arthur F. Bickford, M.D. San Francisco, Calif.
T
he inherent variability of the blood pressure has led to problems in the diagnosis, lr2 treatment,3 and prognosis4-6 of hypertension. Knowing how the blood pressure fluctuates with the stresses and strains of everyday life should help in assessing the severity of hypertension, the response to treatment, and the prognosis in individual cases. The portable blood pressure recorder described in this report was developed as a means of obtaining new information on variations in blood pressure throughout the day. The recorder is worn by the subject as he carries out his daily routine, the readings are taken semiautomatically, and the results are recorded on tape. Otherwise, the technique of determining the blood pressure is similar to that of the standard auscultatory method. This similarity allows comparison of determinations by the two methods and the use of established standards in evaluating the results. This report deals with preliminary observations on measurements of blood presFrom
sure with the portable recorder in normotensive subjects. The purpose of the studies was (1) to compare the values obtained with the portable instrument with those obtained with the standard auscultatory method, and (2) to measure the variability of blood pressure under everyday living conditions. Materials
and
methods
Portable blood pressure recorder. The portable recorder* (for convenience, also referred to as portometer) is illustrated in Fig. 1. It consists of a standard blood pressure cuff with bulb, a button microphone, a frequency-modulated pressure transducer and appropriate electronic equipment, a tape recorder controlled by a pressure switch, and a twin-light signal system. The recorder is worn by the subject as shown in E’ig. 2. The blood pressure cuff is wrapped around the upper arm and secured with adhesive tape. The inflating bulb is placed in the axillary area, and the microphone, which acts as a substitute
the Department of Medicine and the Cardiovascular Research Institute, University of California School of Medicine, San Francisco, Calif. Development of this instrument was made possible by grants from the Mrs. William A. Hewitt-Deere Estate and Mr. I. W. Hellman. Research was supported in part by grants from the San Francisco Heart Association, and from the United States Public Health Service (H-754). Received for publication Nov. 14, 1961. *The recorder used in these studies was assembled by the Alpha Scientitic Laboratory, Berkeley. Calif., under the direction of Dr. J. R. Singer. An improved modd. smaller and lighter in weij&t, is being developed by tbe Remler Company. San Francisco. Calif.
663
664
Hinman,
Engel, and Bickford
OR/G/h’AL DESIGN -JUNE 8, ALLEN 7: HlNMAh UN/ VERS/IY OF CAL /FORN/A SCHOOL OF /WED/C/NE SAN FRANC/SC0
Fig.
1. Diagram
of portable
blood
pressure
recording
for the stethoscope, is taped over the brachial artery. The tape recorder is carried in one shoulder bag, and the batteries, transducer, and electronic equipment in the other. The weight of, the present equipment is 5 45 pounds. Method of recording. The pressure switch is set at a level above systolic pressure; this setting is not known to the subject. In order to minimize noise from clothing, the subject is asked to extend the arm and avoid unnecessary movement. To start the recording cycle, the subject inflates the cuff. At a cuff pressure of 50 mm. Hg, the pressure switch turns on the pressure transducer, the tape recorder, and the low lamp of the signal system. Inflation is continued until lighting of the high lamp signals to the subject that the cuff has been inflated above systolic pressure and that inflation should be stopped. The cuff deflates in approximately 30 seconds through an adjustable needle valve. As the cuff pressure decreases, the air-flow aperture increases in size, producing a linear drop in cuff pressure. During deflation, the pressure in the cuff is continuously recorded on the tape through the transducer. The pulse sounds (Korotkoff) are picked up by the microphone over the brachial artery and recorded on the tape. When the pressure in the cuff reaches 50 mm. Hg, the pressure switch
1957
system.
opens, stopping the tape recorder and the transducer. It also turns off the low signal lamp; the subject can then deflate the cuff completely. When a set of recordings has been completed, the tape is decoded through a system calibrated with a mercury manometer. The frequency-modulated pressure signal is converted into a direct-current potential which is played back through a pen recorder. The arterial sounds are converted to deflections on the pen recorder and at the same time are monitored by means of an audiosystem. Experimental
observations
Simultaneous bilateral determinations of blood jwessure. The validity of measurements by the portable recorder was determined in studies on 5 normotensive subjects. In each study, the subject’s blood pressure was determined by using the portable recorder on one arm and the standard auscultatory pressure cuff on the other, as shown in Fig. 3. Readings by the two methods were taken simultaneously at 2-minute intervals, and the pattern of recording was kept constant. The portometer was used for 6 determinations on the left arm, was shifted to the right arm for 12 determinations, and was then changed back to the left arm for an additional 6 determinations, while an
Volume Number
63 5
Fig. 2. Subject wearing recorder. Left shoulder and electronic equipment, contains the tape recorder.
Portable blood pressure recorder
portable blood pressure bag contains transducer and right shoulder bag
equal number of auscultatory readings were taken on the opposite arm. In this manner, 24 simultaneous recordings were taken, 12 on each arm by each method, as shown in the representative study presented in Fig. 4. This technique enabled us to detect bilateral inequalities in the subject’s blood pressure and to balance the effect of adaptation. Determinations of blood pressure were made, as described, on 9 occasions. The systolic and diastolic pressures recorded in the left and right arms of the subjects, the average of 12 readings by each method, are compared in Fig. 5. In the left arm, the average systolic pressures measured by the portometer were in almost exact agreement with the auscultatory readings in 3 experiments, were lower-in 5 experiments, and higher in 1. With one exception (Subject R. T., Experiment 2), the pressures recorded in the left arm by the two methods did not differ by more than 6 mm. Hg. In the right arm, the systolic pressures recorded by the portometer were lower than the auscultatory readings in 7 experiments and higher in 2. Here, the difference between the two readings was 9 mm. Hg or less. Comparison of the levels recorded during the 9 studies showed that the recorder underestimated systolic pressure a total of 5 times in the left arm and 7 times in the right arm. The average error,
665
however, was negligible. If the one experiment on Subject R. T. is excluded, the underestimation amounted to less than 2 mm. Hg in the left arm and less than 4 mm. Hg in the right arm. Readings of diastolic pressure by the portable recorder were less satisfactory. In general, the diastolic pressures appeared to be recorded at a point between the muffling and the disappearance of the sound. As shown in Fig. 5, the average recorded pressures were intermediate between Phase IV and Phase V in the 9 determinations on the right arm and in 6 of the 9 determinations on the left arm. These differences were in the range of 4 mm. Hg. In the other 3 determinations on the left arm the inaccuracy was greater (see Subjects K.C., M.C., and R.T. in Fig. 5). In these instances the pressures recorded by our instrument were closer to Phase IV than to Phase V. The finding of different pressures in the two arms (Fig. 5), although incidental to this study, deserves mention. Our subjects consistently had higher systolic pressures in the right arm than in the left, amounting to as much as 15 mm. Hg in some cases, and with two exceptions (Subjects C.T. and K.C.) the diastolic pressures in the right arm were also higher. Similar disparities in the levels of pressure in the
/NFL&l r/o,4 CUFFS D”LD FOR BOTH Fig. 3. Technique for taking simultaneous readings of blood pressure with portable blood pressure recorder and by standard auscultatory method. Both cuffs are inflated simultaneously by means of bulb and Y tube; deflation is regulated by needle valve of portable recorder.
666
H&man,
Am. Heart I. May, 1962
Engel, and Bickford
Fig. 4. Results of 24 simultaneous bilateral blood normotensive Subject K.C. x = Reading taken with ing taken by standard auscultatory method.
right and left arms have been noted in other studies.7 In determining the validity of measurements by the portable recorder, we also took simultaneous readings on the same arm with the stethoscope in the usual position. This necessitated placing the microphone over the brachial artery but proximal to the stethoscope, which, in our opinion, introduced another variable. For this reason, we preferred to use the bilateral method. Use of portable recorder in determining variations in pressure. Additional studies were carried out to evaluate the use of the portable recorder in measuring variations in the level of blood pressure throughout the day. Three subjects, one of whom had levels which were frequently in the higher ranges, wore the portable recorder for various periods while following their usual daily routines. Each recorded his blood pressure at intervals and noted his activity at the time at which each reading was taken.
pressure readings the portable blood
in representative pressurerec0rder.o
study on = Read-
The subjects were able to wear the portometer for as long as 8 to 11 hours without discomfort, although the present equipment is somewhat heavy and cumbersome. The pressures recorded by each of the 3 subjects and his activity at the time of the reading are indicated in Figs. 6, 7, and 8. Subject B.T.E. recorded his pressure 24 times in a period of 8 hours. During this time his level of systolic blood pressure ranged from 93 to 140 mm. Hg, averaging 113 mm. Hg (S.D. 12.9), and his diastolic pressure ranged from 71 to 93 mm. Hg, averaging 77 mm. Hg (SD. 5.9). In a similar study, Subject A.H. recorded 22 readings of blood pressure over a lohour period. His systolic pressure ranged from 100 to 170 mm. Hg, averaging 130 mm. Hg (S.D. 6.2), and his diastolic pressure ranged from 63 to 104 mm. Hg, averaging 81 mm. Hg (S.D. 10.6). In the third study the pressure syitch was set at 250 mm. Hg. Because the cuff was uncomfortably tight when inflated, the subject made
Volume
63
Portable blood pressure recorder
Nfimber 5
667
level of blood pressure in patients with hypertension. Our preliminary observations
on normotensive
subjects
indicated
that the portable recorder is sufficiently accurate for this purpose. Although the levels of blood pressure established by the portometer and the standard auscultatory method were not in complete agreement, the discrepancies were not serious. The disparity between the systolic pressures recorded by the two methods was slight. The difference between the diastolic pressure readings, although greater in degree, NAME
: A.H.
DATE:
10-I-59
I SYSTOLIC DlASTOLlt
PRESSURE PRESSURE
220-
Fig. 5. Comparison of blood pressure readings obtained simultaneously by portable recorder and standard auscultatory method in experiments on 5 normotensive subjects. Each value represents the average of 12 readings on one arm. NAMEi D.T.5. DATE
: 10-S-59
SYSTOLIC I DIASTOLIC
PRESSURE PRESSURE
220 I:
tt 180 ’ 1 0,200
‘u s
200
-
P g
ISO-
-
4
160-
f
140-
c 2
120-
8
IOO-
s Q
80-
-
6Ot /
I
(0
160-
II
I
I
I
(2
1
2
I
I
3 4 TIME-HOURS
A.M.
I
I
I
I
I
5
6
7
6
9
1 10 PM.
-
Fig. 7. Levels of blood pressure determined with the portable recorder by Subject A.H. over a lohour period. Activities included driving in traffic (1:00 P.M.), speaking at a meeting (2:00 to 3:30 P.M.), and resting at home (9:45 P.M.). NAME: DATE:
P.M.
Fig. 6. Levels of blood pressure determined with the portable recorder by Subject B.T.E. during the routine of a normal day. Activities included reading (11:00 to 12:00 A.M.), technical discussions at work (12:30 to 2:00 P.M.), driving in traffic (5:45 P.M.), and playing with his children (6:30 P.M.).
only 9 determinations during an 11-hour period. The recordings during this time showed that his systolic pressure ranged from 138 to 190 mm. Hg, averaging 171 mm. Hg (S.D. 25.9), and that his diastolic pressure varied from 93 to 139 mm. Hg, averaging 120 mm. Hg (S.D. 19.8). Discussion
The portable blood pressure recorder was designed primarily to provide information on intradaily variations in the
220
-
200
-
P t
180
F ’
160-
A.=. 10-22-59
1 SYSTOLIC DlASTOLlC
PRESSURE PRESSVRE
.I
: -
““I 10
AM.
II
,2
1
2
3 TIME
4 5 -HOURS
6
7
6 P.M.
Fig. 8. Levels of blood pressure determined with the portable recorder by Subject A.Z. The first 4 determinations were made when the subject was alone and reading quietly; the next 2 were made when he was in a heated discussion about some phase of his work, and the last 3 were made when he was at home caring for his children.
668
Hinman,
Am. Heart 1. May, 1962
Engel, and Bickford
does not invalidate readings obtained with the portable recorder, particularly since the auscultatory method is somewhat unreliable because of differences in keenness of hearing among observers and the difficulty sometimes found in identifying Phases IV and V. In addition, our special interest lay in determining changes in pressure over a period of time, and in a series of such determinations any constant error would tend to be cancelled. The differences in blood pressure determinations with the portable recorder were usually in multiples of 4 mm. Hg. This is the drop in pressure in the cuff between two heartbeats, indicating that the present instrument does not always record the first heartbeat, probably because of faulty coupling of the microphone to the skin. Imperfect coupling was also thought to be mainly responsible for the inaccuracy in recording diastolic pressures. The tape recorder may have been partly at fault, since the frequency of pulse however, waves in the Phase IV to Phase V band is below the lower distortion-free limit of our present apparatus (about 100 cycles per second). Technical improvements to minimize errors in recording and to reduce the size and weight of the equipment are currently under way. Despite some limitations of the present equipment, the portable recorder offers a practical technique for measuring the blood pressure. It has the advantage of allowing frequent recordings during the day, in contrast to the usual single casual reading by the auscultatory method. Since the subject initiates the recordings, the pressor effect which results from the presence of a physician or observer1 is eliminated. In addition, the subject is not aware of the level of his blood pressure. Preliminary data obtained with the portometer indicate that the blood pressure varies significantly during the course of a day, and that these variations can be related to experiences in the everyday life of the subject. In the future, comparable studies on hypertensive patients should yield useful information for diagnostic and prognostic purposes, as well as for regulating drug therapy.
Summary
The portable blood pressure recorder described in this report offers a practical technique for determining intradaily variations in the level of pressure. The instrument is worn by the subject, enabling him to record his blood pressure at frequent intervals during the day while in his usual environment and performing his usual tasks. The readings are taken semiautomatically, and the aid of a physician or technician is not required. The subject does not know the levels recorded by the instrument. Preliminary observations on normotensive subjects showed that the portable recorder is sufficiently accurate for clinical purposes. In additional experiments, 3 subjects recorded their levels of pressure at intervals while carrying out their daily routines. The results indicated that the portable recorder provides valid data on variations in blood pressure throughout the day. Expanded studies on hypertensive patients should yield useful information for evaluating the highly variable natural history of hypertension. REFERENCES 1. Ayman, D., and Goldshine, A. D.: Blood pressure determinations by patients with essential hypertension. I. The difference between clinic and home readings before treatment, Am. J. M. SC. 200:465, 1940. 2. Smirk, F. H.: High arterial pressure, Springfield, Ill., 19.57, Charles C Thomas, Publisher. 3. Freis, E. D.: The discrepancy between home and office recordings of blood pressure in patients under treatment with pentapyrrolidinium. Importance of home recordings in adjusting dosages, M. Ann. District of Columbia 23:363, 19.54. 4. Janeway, T. C. : A clinical study of hypertensive cardiovascular disease, Arch. Int. Med. 12:755, 1913. 5. Blood Pressure Study, 1939. The Actuarial Society of America and the Association of Life Insurance Medical Directors, New York, 1940, 6. Sokolow, M., and Perloff, D.: The prognosis of essential hypertension treated conservatively, Circulation 23:697, 1961. 7. Amsterdam, B., and Amsterdam, A. L.: Disparity in blood pressures in both arms in normals and hypertensives and its clinical significance: a study of 1,000 normals and 272 hypertensives, New York J. M. 43:2294, 1943.
blood pressure recorder and preliminary use in evaluating va,riations in pressure
Allen T. H&man, M.D. Btrnard T. Engel, Ph.D. Arthur F. Bickford, M.D. San Francisco, Calif.
T
he inherent variability of the blood pressure has led to problems in the diagnosis, lr2 treatment,3 and prognosis4-6 of hypertension. Knowing how the blood pressure fluctuates with the stresses and strains of everyday life should help in assessing the severity of hypertension, the response to treatment, and the prognosis in individual cases. The portable blood pressure recorder described in this report was developed as a means of obtaining new information on variations in blood pressure throughout the day. The recorder is worn by the subject as he carries out his daily routine, the readings are taken semiautomatically, and the results are recorded on tape. Otherwise, the technique of determining the blood pressure is similar to that of the standard auscultatory method. This similarity allows comparison of determinations by the two methods and the use of established standards in evaluating the results. This report deals with preliminary observations on measurements of blood presFrom
sure with the portable recorder in normotensive subjects. The purpose of the studies was (1) to compare the values obtained with the portable instrument with those obtained with the standard auscultatory method, and (2) to measure the variability of blood pressure under everyday living conditions. Materials
and
methods
Portable blood pressure recorder. The portable recorder* (for convenience, also referred to as portometer) is illustrated in Fig. 1. It consists of a standard blood pressure cuff with bulb, a button microphone, a frequency-modulated pressure transducer and appropriate electronic equipment, a tape recorder controlled by a pressure switch, and a twin-light signal system. The recorder is worn by the subject as shown in E’ig. 2. The blood pressure cuff is wrapped around the upper arm and secured with adhesive tape. The inflating bulb is placed in the axillary area, and the microphone, which acts as a substitute
the Department of Medicine and the Cardiovascular Research Institute, University of California School of Medicine, San Francisco, Calif. Development of this instrument was made possible by grants from the Mrs. William A. Hewitt-Deere Estate and Mr. I. W. Hellman. Research was supported in part by grants from the San Francisco Heart Association, and from the United States Public Health Service (H-754). Received for publication Nov. 14, 1961. *The recorder used in these studies was assembled by the Alpha Scientitic Laboratory, Berkeley. Calif., under the direction of Dr. J. R. Singer. An improved modd. smaller and lighter in weij&t, is being developed by tbe Remler Company. San Francisco. Calif.
663
664
Hinman,
Engel, and Bickford
OR/G/h’AL DESIGN -JUNE 8, ALLEN 7: HlNMAh UN/ VERS/IY OF CAL /FORN/A SCHOOL OF /WED/C/NE SAN FRANC/SC0
Fig.
1. Diagram
of portable
blood
pressure
recording
for the stethoscope, is taped over the brachial artery. The tape recorder is carried in one shoulder bag, and the batteries, transducer, and electronic equipment in the other. The weight of, the present equipment is 5 45 pounds. Method of recording. The pressure switch is set at a level above systolic pressure; this setting is not known to the subject. In order to minimize noise from clothing, the subject is asked to extend the arm and avoid unnecessary movement. To start the recording cycle, the subject inflates the cuff. At a cuff pressure of 50 mm. Hg, the pressure switch turns on the pressure transducer, the tape recorder, and the low lamp of the signal system. Inflation is continued until lighting of the high lamp signals to the subject that the cuff has been inflated above systolic pressure and that inflation should be stopped. The cuff deflates in approximately 30 seconds through an adjustable needle valve. As the cuff pressure decreases, the air-flow aperture increases in size, producing a linear drop in cuff pressure. During deflation, the pressure in the cuff is continuously recorded on the tape through the transducer. The pulse sounds (Korotkoff) are picked up by the microphone over the brachial artery and recorded on the tape. When the pressure in the cuff reaches 50 mm. Hg, the pressure switch
1957
system.
opens, stopping the tape recorder and the transducer. It also turns off the low signal lamp; the subject can then deflate the cuff completely. When a set of recordings has been completed, the tape is decoded through a system calibrated with a mercury manometer. The frequency-modulated pressure signal is converted into a direct-current potential which is played back through a pen recorder. The arterial sounds are converted to deflections on the pen recorder and at the same time are monitored by means of an audiosystem. Experimental
observations
Simultaneous bilateral determinations of blood jwessure. The validity of measurements by the portable recorder was determined in studies on 5 normotensive subjects. In each study, the subject’s blood pressure was determined by using the portable recorder on one arm and the standard auscultatory pressure cuff on the other, as shown in Fig. 3. Readings by the two methods were taken simultaneously at 2-minute intervals, and the pattern of recording was kept constant. The portometer was used for 6 determinations on the left arm, was shifted to the right arm for 12 determinations, and was then changed back to the left arm for an additional 6 determinations, while an
Volume Number
63 5
Fig. 2. Subject wearing recorder. Left shoulder and electronic equipment, contains the tape recorder.
Portable blood pressure recorder
portable blood pressure bag contains transducer and right shoulder bag
equal number of auscultatory readings were taken on the opposite arm. In this manner, 24 simultaneous recordings were taken, 12 on each arm by each method, as shown in the representative study presented in Fig. 4. This technique enabled us to detect bilateral inequalities in the subject’s blood pressure and to balance the effect of adaptation. Determinations of blood pressure were made, as described, on 9 occasions. The systolic and diastolic pressures recorded in the left and right arms of the subjects, the average of 12 readings by each method, are compared in Fig. 5. In the left arm, the average systolic pressures measured by the portometer were in almost exact agreement with the auscultatory readings in 3 experiments, were lower-in 5 experiments, and higher in 1. With one exception (Subject R. T., Experiment 2), the pressures recorded in the left arm by the two methods did not differ by more than 6 mm. Hg. In the right arm, the systolic pressures recorded by the portometer were lower than the auscultatory readings in 7 experiments and higher in 2. Here, the difference between the two readings was 9 mm. Hg or less. Comparison of the levels recorded during the 9 studies showed that the recorder underestimated systolic pressure a total of 5 times in the left arm and 7 times in the right arm. The average error,
665
however, was negligible. If the one experiment on Subject R. T. is excluded, the underestimation amounted to less than 2 mm. Hg in the left arm and less than 4 mm. Hg in the right arm. Readings of diastolic pressure by the portable recorder were less satisfactory. In general, the diastolic pressures appeared to be recorded at a point between the muffling and the disappearance of the sound. As shown in Fig. 5, the average recorded pressures were intermediate between Phase IV and Phase V in the 9 determinations on the right arm and in 6 of the 9 determinations on the left arm. These differences were in the range of 4 mm. Hg. In the other 3 determinations on the left arm the inaccuracy was greater (see Subjects K.C., M.C., and R.T. in Fig. 5). In these instances the pressures recorded by our instrument were closer to Phase IV than to Phase V. The finding of different pressures in the two arms (Fig. 5), although incidental to this study, deserves mention. Our subjects consistently had higher systolic pressures in the right arm than in the left, amounting to as much as 15 mm. Hg in some cases, and with two exceptions (Subjects C.T. and K.C.) the diastolic pressures in the right arm were also higher. Similar disparities in the levels of pressure in the
/NFL&l r/o,4 CUFFS D”LD FOR BOTH Fig. 3. Technique for taking simultaneous readings of blood pressure with portable blood pressure recorder and by standard auscultatory method. Both cuffs are inflated simultaneously by means of bulb and Y tube; deflation is regulated by needle valve of portable recorder.
666
H&man,
Am. Heart I. May, 1962
Engel, and Bickford
Fig. 4. Results of 24 simultaneous bilateral blood normotensive Subject K.C. x = Reading taken with ing taken by standard auscultatory method.
right and left arms have been noted in other studies.7 In determining the validity of measurements by the portable recorder, we also took simultaneous readings on the same arm with the stethoscope in the usual position. This necessitated placing the microphone over the brachial artery but proximal to the stethoscope, which, in our opinion, introduced another variable. For this reason, we preferred to use the bilateral method. Use of portable recorder in determining variations in pressure. Additional studies were carried out to evaluate the use of the portable recorder in measuring variations in the level of blood pressure throughout the day. Three subjects, one of whom had levels which were frequently in the higher ranges, wore the portable recorder for various periods while following their usual daily routines. Each recorded his blood pressure at intervals and noted his activity at the time at which each reading was taken.
pressure readings the portable blood
in representative pressurerec0rder.o
study on = Read-
The subjects were able to wear the portometer for as long as 8 to 11 hours without discomfort, although the present equipment is somewhat heavy and cumbersome. The pressures recorded by each of the 3 subjects and his activity at the time of the reading are indicated in Figs. 6, 7, and 8. Subject B.T.E. recorded his pressure 24 times in a period of 8 hours. During this time his level of systolic blood pressure ranged from 93 to 140 mm. Hg, averaging 113 mm. Hg (S.D. 12.9), and his diastolic pressure ranged from 71 to 93 mm. Hg, averaging 77 mm. Hg (SD. 5.9). In a similar study, Subject A.H. recorded 22 readings of blood pressure over a lohour period. His systolic pressure ranged from 100 to 170 mm. Hg, averaging 130 mm. Hg (S.D. 6.2), and his diastolic pressure ranged from 63 to 104 mm. Hg, averaging 81 mm. Hg (S.D. 10.6). In the third study the pressure syitch was set at 250 mm. Hg. Because the cuff was uncomfortably tight when inflated, the subject made
Volume
63
Portable blood pressure recorder
Nfimber 5
667
level of blood pressure in patients with hypertension. Our preliminary observations
on normotensive
subjects
indicated
that the portable recorder is sufficiently accurate for this purpose. Although the levels of blood pressure established by the portometer and the standard auscultatory method were not in complete agreement, the discrepancies were not serious. The disparity between the systolic pressures recorded by the two methods was slight. The difference between the diastolic pressure readings, although greater in degree, NAME
: A.H.
DATE:
10-I-59
I SYSTOLIC DlASTOLlt
PRESSURE PRESSURE
220-
Fig. 5. Comparison of blood pressure readings obtained simultaneously by portable recorder and standard auscultatory method in experiments on 5 normotensive subjects. Each value represents the average of 12 readings on one arm. NAMEi D.T.5. DATE
: 10-S-59
SYSTOLIC I DIASTOLIC
PRESSURE PRESSURE
220 I:
tt 180 ’ 1 0,200
‘u s
200
-
P g
ISO-
-
4
160-
f
140-
c 2
120-
8
IOO-
s Q
80-
-
6Ot /
I
(0
160-
II
I
I
I
(2
1
2
I
I
3 4 TIME-HOURS
A.M.
I
I
I
I
I
5
6
7
6
9
1 10 PM.
-
Fig. 7. Levels of blood pressure determined with the portable recorder by Subject A.H. over a lohour period. Activities included driving in traffic (1:00 P.M.), speaking at a meeting (2:00 to 3:30 P.M.), and resting at home (9:45 P.M.). NAME: DATE:
P.M.
Fig. 6. Levels of blood pressure determined with the portable recorder by Subject B.T.E. during the routine of a normal day. Activities included reading (11:00 to 12:00 A.M.), technical discussions at work (12:30 to 2:00 P.M.), driving in traffic (5:45 P.M.), and playing with his children (6:30 P.M.).
only 9 determinations during an 11-hour period. The recordings during this time showed that his systolic pressure ranged from 138 to 190 mm. Hg, averaging 171 mm. Hg (S.D. 25.9), and that his diastolic pressure varied from 93 to 139 mm. Hg, averaging 120 mm. Hg (S.D. 19.8). Discussion
The portable blood pressure recorder was designed primarily to provide information on intradaily variations in the
220
-
200
-
P t
180
F ’
160-
A.=. 10-22-59
1 SYSTOLIC DlASTOLlC
PRESSURE PRESSVRE
.I
: -
““I 10
AM.
II
,2
1
2
3 TIME
4 5 -HOURS
6
7
6 P.M.
Fig. 8. Levels of blood pressure determined with the portable recorder by Subject A.Z. The first 4 determinations were made when the subject was alone and reading quietly; the next 2 were made when he was in a heated discussion about some phase of his work, and the last 3 were made when he was at home caring for his children.
668
Hinman,
Am. Heart 1. May, 1962
Engel, and Bickford
does not invalidate readings obtained with the portable recorder, particularly since the auscultatory method is somewhat unreliable because of differences in keenness of hearing among observers and the difficulty sometimes found in identifying Phases IV and V. In addition, our special interest lay in determining changes in pressure over a period of time, and in a series of such determinations any constant error would tend to be cancelled. The differences in blood pressure determinations with the portable recorder were usually in multiples of 4 mm. Hg. This is the drop in pressure in the cuff between two heartbeats, indicating that the present instrument does not always record the first heartbeat, probably because of faulty coupling of the microphone to the skin. Imperfect coupling was also thought to be mainly responsible for the inaccuracy in recording diastolic pressures. The tape recorder may have been partly at fault, since the frequency of pulse however, waves in the Phase IV to Phase V band is below the lower distortion-free limit of our present apparatus (about 100 cycles per second). Technical improvements to minimize errors in recording and to reduce the size and weight of the equipment are currently under way. Despite some limitations of the present equipment, the portable recorder offers a practical technique for measuring the blood pressure. It has the advantage of allowing frequent recordings during the day, in contrast to the usual single casual reading by the auscultatory method. Since the subject initiates the recordings, the pressor effect which results from the presence of a physician or observer1 is eliminated. In addition, the subject is not aware of the level of his blood pressure. Preliminary data obtained with the portometer indicate that the blood pressure varies significantly during the course of a day, and that these variations can be related to experiences in the everyday life of the subject. In the future, comparable studies on hypertensive patients should yield useful information for diagnostic and prognostic purposes, as well as for regulating drug therapy.
Summary
The portable blood pressure recorder described in this report offers a practical technique for determining intradaily variations in the level of pressure. The instrument is worn by the subject, enabling him to record his blood pressure at frequent intervals during the day while in his usual environment and performing his usual tasks. The readings are taken semiautomatically, and the aid of a physician or technician is not required. The subject does not know the levels recorded by the instrument. Preliminary observations on normotensive subjects showed that the portable recorder is sufficiently accurate for clinical purposes. In additional experiments, 3 subjects recorded their levels of pressure at intervals while carrying out their daily routines. The results indicated that the portable recorder provides valid data on variations in blood pressure throughout the day. Expanded studies on hypertensive patients should yield useful information for evaluating the highly variable natural history of hypertension. REFERENCES 1. Ayman, D., and Goldshine, A. D.: Blood pressure determinations by patients with essential hypertension. I. The difference between clinic and home readings before treatment, Am. J. M. SC. 200:465, 1940. 2. Smirk, F. H.: High arterial pressure, Springfield, Ill., 19.57, Charles C Thomas, Publisher. 3. Freis, E. D.: The discrepancy between home and office recordings of blood pressure in patients under treatment with pentapyrrolidinium. Importance of home recordings in adjusting dosages, M. Ann. District of Columbia 23:363, 19.54. 4. Janeway, T. C. : A clinical study of hypertensive cardiovascular disease, Arch. Int. Med. 12:755, 1913. 5. Blood Pressure Study, 1939. The Actuarial Society of America and the Association of Life Insurance Medical Directors, New York, 1940, 6. Sokolow, M., and Perloff, D.: The prognosis of essential hypertension treated conservatively, Circulation 23:697, 1961. 7. Amsterdam, B., and Amsterdam, A. L.: Disparity in blood pressures in both arms in normals and hypertensives and its clinical significance: a study of 1,000 normals and 272 hypertensives, New York J. M. 43:2294, 1943.