- Email: [email protected]
Ambulatory blood pressure monitoring: Recent advances and clinical applications
Volume 101 Number 6
16.
17.
18.
19. 20.
21.
PGEl
taglandins in the circulation of the fetal lamb. Prostaglandins llAO41, 1976. Heymann MA, Rudolph AM: Neonatal manipulation: Patent ductus arteriosus. 1n Engle MA, editor: Pediatric cardiovascular disease. Philadelphia, 1981, FA Davis Company, pp 301-310. Heymann MA, Rudolph AM: Effects of congenital heart disease on fetal and neonatal circulation. Prog Cardiovasc Dis 15:115,1972. Starling MB, Elliott RB: The effects of prostaglandins, prostaglandin inhibitors, and oxygen on the closure of the ductus arteriosus, puhnonary arteries, and umbilical vessels in vitro. Prostaglandins 8:187, 1974. Elliott RB, Starling MB, Neutze JM: Medical manipulation of the ductus arteriosua Lancet 1:140, 1975. Olley, P.M., Coceani, F., and Bodach, E.: E-type prostaglandins: A new emergency therapy for certain cyanotic congenital heart malformations. Circulation 53:728, 1976. Heymann MA, Rudolph AM: Ductus arteriosus dilatation by prostaglandin E1 in infants with pulmonary atresia. Pediatrics 59:325, 1977.
22.
23.
24.
25.
26.
27.
therapy
in congenital
heart
disease
843
Neutze JM, Starling MB, Elliott RB, Barratt-Boyes BG: Palliation of cyanotic congenital heart disease in infancy with E-type prostaglandins. Circulation 55:238, 1977. Freed MD, Heymann MA, Lewis AB, Reischer S, Kensey RC: Prostaglandin E1 in infants with ductus arteriosus dependent congenital heart disease. The U.S. experience. Circulation (In press) Lewis AB, Freed MD, Heymann MA, Reiscber S, Kensey RC: Side effects of therapy with prostaglandin E1 in infants with critical congenital heart disease. The U.S. experience. Circulation (In press, November, 1981) Rudolph AM, Heymann MA, Spitznas U: Hemodynamic considerations in the development of narrowing of the aorta. Am J Cardiol 30~514, 1972. Heymann MA, Berman W Jr, Rudolph AM, Whitman V: Dilatation of the ductus arteriosus by prostaglandin E1 in aortic arch abnormalities. Circulation 59:169, 1979. Silove ED, Coe JY, Shiu MF, Brunt JD, Page AJF, Singh SP, Mitchell MD: Oral prostaglandin EZ in ductus-dependent pulmonary circulation. Circulation 83:682, 1981.
Ambulatory blood pressure monitoring: Recent advances and clinical applications Michael J. Horan, M.D., Neil E. Padgett, Baltimore,
Md.,
and
Long
Beach,
BS., and Harold
L. Kennedy,
M.D., M.P.H.
Calif.
Casual, office blood pressure determinations using a standard sphygmomamonometer have traditionally constituted the principal modality for the diagnosis and management of hypertension. There is substantial evidence, however, to suggest that office blood pressure determinations may not always reliably reflect blood pressure at rest in other settings or during ordinary daily activities. In 1940 Ayman and Goldshine conducted a study in which they compared blood pressures taken in the clinic with home blood pressures. In 30% of 34 patients studied the systolic blood pressures obtained at home were lower by 40 mm Hg or more than the systolic blood
pressures obtained in the clinic. In 24% of the same patients the diastolic blood pressures were 20 mm Hg lower than the diastolic blood pressures obtained in the clinic. A number of subsequent reports are in agreement with these observations.g-5 Although patient-recorded home blood pressures are valuable, limitations are imposed by patient cooperation, frequency of recordings, and sampling error+ Also generally precluded are pressures during sleep? exercise, and other activities. Techniques therefore emerged for recording blood pressures in the active, ambulatory patient. They have developed along two lines, direct (intraarterial) and indirect (noninvasive) continuous pressure monitoring.
From the Department of Medicine, The Johns Hopkins Hospit& Department of Medicine, Division of Cardiology, Memorial Medical Center.
DIRECT AMBULATORY MEASUREMENTS
Received
for publication
Reprint requests: Harold Center, Dept. of Medicine, Beach, CA 90801.
0002-8703/81/060843
Dec. 29, 198% accepted
and the Hospital
Feb. 27, 1981.
L. Kennedy, M.D., Memorial Hospital Medical Division of Cardiology, 2801 Atlantic Ave., Long
+ 06$00.60/00
198lThe
C.V.Mosby
Co.
BLOOD
PRESSURE
The earliest intra-arterial method of measuring ambulatory blood pressure was designed by Stott and introduced by Beven et al.6, 7 in 1966. Additional
8
Horan,
Padgett,
and Kennedy
Fig. I- Patient wearing portable, noninvasive, automatic pressurometer (Del Mar Avionics) that measures and records blood pressure (BP), heart rate, and heart rhythm for periods up to 24 houm 1 = microphone; 2 = %P cui$ 3 = pressurometer; 4 = Hoker recorder; 5 = ECG leads.
applications of this technology were described by Littler et al.,8-13 Goldberg et al.,14. G and West et al.16 This led to a refined version of an ambulatory blood pressure apparatus which used an Oxford continnous blood pressure recordere17 The system employs an intra-arterial cannula which is placed percutaneously in the brachial artery 3 to 5 cm above the antecubital fossa. The heparinized saline-filled cannula is attached to an automatic perfusion pump and strain gauge transducer. Continuous pressure measurements from the transducer and simultaneous EXG are recorded on the Oxford recorder. The perfusion pump continuously perfuses the arterial cannula with heparinized saline to prevent clotting9 but it must be serviced every E! hours. Sophisticated tape recording analyzers provide beat-to-beat> real-
time data which can be displayed graphically- Highspeed analysis techniques allow these data to be played back at 25 or 60 times real-time5 and more recently an analog preprocessor has been developed to detect systoiic, diastolic? and mean arterial pressures with the pulse interval for statistical evahmtion and histogram plots.16 Studies using this technology have provided some of the earliest observations of the influence of various activities on blood pressure. Such studies have shown that blood pressure in normal subjects and hypertensive patients may vary widely during ordinary activities, and are affected by the psychologic stimuli of physician visits, medical examinations, and sexual activitym7, 1Z Of potential importance has been the observation that many individuals may, during the course of a day9 be found to be hypertensive or normotensive, and in occasion the highest pressure has been greater than twice the lowest pressure.i, 8 Other investigations have confirmed these early observations, and have noted that the decrease in blood pressure routinely seen with sleep was more pronounced in the patienVs home environment as compared to the bospitaI.1:3 In addition, blood pressure was found to be generally stable during automobile drivingY9 reflective of a Valsaha response during micturition and defecation11 and elevated with a concurrent rise in beart rate angina pectoris commensurate with the provocative activities which induced such pain.1o However, in spontaneous or no6turnal angina pectoris, rises m arterial pressure were noted to occur IO to 15 minutes before the onset of angina pectoris.‘O Comparison of sphygmomanometric blood pressure measurements obtained by the physician in the outpatient clinic were generally found to agree with concomitant direct arterial measurements, but some hypertensive patients were found to have lower direct arterial readings. lZ Direct arterial blood pressure recordings have also helped demonstrate that some hypertensive patients manifest a persistent tachycardia throughout the day, indicative of a hyperkinetic state.ls Finally, direct mtra-arterial ambulatory blood pressure measurements have been used to assess the efficacy of antbypertensive tberapy in hypertensive patientP I*. E I9 and in differentiating between borderline and fixed hypertensionZo While it is apparent that the direct intra-arterial measurement of ambulatory blood pressure provides precise data, such measurement requires substantial resources in terms of experienced personnel and equipment. Furthermore, although comphcations are infrequent, moderate morbidity has been
Volume 101 Number 6
Ambulatory
reported including localized paresis due to median nerve palsy.1* Studies employing direct arterial measurements continue to be in progress, and are being performed predominantly in Great Britian. Ambulatory blood pressure recording in North America has primarily involved use of noninvasive, indirect blood pressure measurement methods. NONINVASIVE AMIBULATORY MEASUREMENTS
IBLOOD
PRESSURE
Indirect (noninvasive) ambulatory blood pressure recorders have employed semiautomatic and automatic methods. The patient is required to activate the semiautomatic models, whereas the automatic models are self-activating. The earliest indirect semiautomatic ambulatory blood pressure recorder was developed in 1962 by Hinman et al.*l It consisted of a blood pressure cuff with inflating bulb, button microphone, transducer and tape recorder, all of which weighed 5&X pounds. The patient inflated the cuff whenever blood pressure recording was desired. When systolic blood pressure readings were compared with manually obtained readings, agreement was found to be within 9 mm Hg for one subject and within 4 mm Hg for four other subjects. For diastolic pressure, agreement was less satisfactory, with the portable unit generally recording a diastolic pressure intermediate between the ausculatory phase IV and phase V diastolic blood pressure. In 1964 Pickering and Richardson et al.ZZ employed a Gallavardin double-cuff which inflated automatically at &minute intervals. Arterial pressures were estimated by observing the pulsations at the lower cuff. TYhese investigators were the first to use continuous blood pressure recorders to demonstrate that bloald pressure tends to fall during sleep. Sokolow et al.s3 in 1966 employed an updated model of Hinman’s semi-automatic blood pressure recorder, known as the Remler recorder, to determine the relationship between casual blood pressure determinations tind portable ambulatory recordings. They found that ambula.tory blood pressures were lower than oflice blood pressures in 80% of 393 untreated patients with essential hypertension.sa Ambulatory systolic blood pressures averaged 18 mm Hg less than office systolic pressures and ambulatory diastolic blood pressures averaged 10 mm Hg less than omce diastolic pressures. The correlation between blood pressures obtained in the ambulatory setting and those obtained in the office setting was 0.67 for systolic pressures and 0.65 for diastolic pressures. Although these correlation coeficients
blood pressure
recordings
845
appeared satisfactory, they did not account for a sufficient proportion of variance to permit ambulatory pressures to be readily predicted from oflice pressures in individual cases. Furthermore, the correlation between blood pressure level and the presence of end-organ involvement (retinopathy, impaired renal fun&ion, and ECG and chest x-ray evidence of left ventricular hypertrophy) was higher for ambulatory blood pressures (systolic r = 0.63; diastolic, r = 0.65) than for casual blood pressures (systolic, r = 0.48; diastolic, r = 0.53). In subsequent studies these authors documented the broad variability of blood pressure in hypertensive patients during waking hours,Zs and also showed the advantages of ambulatory blood pressures in helping to decide whether to treat patients with borderline hypertension and whether to augment therapy in seemingly uncontrolled, treated hypertensive patientsZ6 Between 1968 and 1975 Schneider et al.ZT-3”developed an automatic, indirect, ambulatory blood pressure recording system that incorporated a blood pressure cuff, programmable electronic timer, tape deck, pressurized nitrogen cartridge, crystal microphone, and force-pressure translator. Blood pressures recorded with this system were found to be within 5% of the blood pressures obtained by conventional use of the sphygmomanometer and within 15% of blood pressures obtained intra-arterially.Za Additional experience with this unit revealed, contrary to the experience with home blood pressures, that automatic blood pressures recorded at home and at work were higher (greater than IO mm Hg) than office blood pressures in one third of 22 normotensive subjects and equal in two thirds of individualsZy Possible explanations for this variation may have included the novelty of experience with the instrument, the startle effect of the cuff spontaneously inflating? the increased level of activity outside the hospital, or combinations of these factors Using the apparatus this group also documented the decline of blood pressure during sleep.3o More recently, another noninvasive, automatic ambulatory blood pressure system utilizing a lightweight motor to inflate the cuff has been developed. As shown in Fig. 1, a microphone (No. I) is placed over the brachial artery, beneath the blood pressure cuff (No. 2). These are connected to the pressurometer (No. 3) housing the miniature motor which automatically air-inflates the blood pressure cuff every 7.5, 15, or 30 minutes. The Holter recorder (No. 4) records the appearance and disappearance of the Korotkoff sounds as well as ECG data from
846
Horan,
Padgett,
JUiw1981
and Kennedy
American
&art
Jourr?a~
Fig. 2. Example of two types of computerized data provided by 24-hour ambulatory blood pressure recordings. Upperpanel: graphic display of data printout. Lowerpanel: graphic display of average hourly systolic and diastolic blood pressures and heart rate. chest leads (No 5). A newer model of this pressurometer, containing solid state memory for the storage of digital data, has ehminated the Halter
recorder, makmg the entire system less cumbersome. Approximately 125 to 200 blood pressure readings are obtained per 24-hour period (Figs 2). Harshfield, Pickering, and Laragh31 demonstrated high correlations with blood pressures obtained rising this apparatus compared to intra-arterial pressures (r = 0.98) and compared to sphygmomanometric pressures (r = 0.86 to 0.99). Kennedy et al.3z examined the practical aspects of the instrumentation in obtaining useful data and found it to be reliable with, only 19% loss of data, A&factual data, secondary usually due to artifact. to misinterpretation of sounds other than Korotkoff sounds? were most often due to muscular contraction noises and/or extraneous noises in the environ-
ment. Studies with this apparatus have confirmed previous observations concerning the reduction of blood pressure during sleep in normal subjectsz3; they have documented that patients with border&e hypertension have no increase in labihty of blood pressures4; and they have demonstrated the utility of ambulatory blood pressure recordings in verifying the control or lack of control of blood pressure in treated hypertensive patients.35 CLINICAL
IMPLICATKINS
Use of ambulatory blood pressure recordings has to date been confined primarily to the research setting. The use of intra-arterial catheters provides accurate blood pressure readings, but for wide scale use as well as for safety and comfort, the mdirect, occlusive cuff methods would seem more desirable. Technologic problems with the development of
VotumelOl Number 6
instrumentation for indirect measurement of ambulatory blood pressure have not been entirely eliminated, although great strides have been made in this area. The remaining technologic problems include the persistence of some artifact in the blood pressure recordings, which currently’ affects about 10% of measurements, and occasional failure of one or more of the components in these systems. The validation and reliability studies alluded to above suggest that the automatic ambulatory blood pressure recording devices are acceptable both for research and patient care purposes. At the present time, preliminary research has demonstrated the usefulness of this technology in the evaluation of borderline or labile hypertension;4. 36 as well as its value in the assessment of therapeutic efficacy in the treatment of Additional evaluation is needed, hypertension.35 however, before complete utility of this technology can be determined and before it can be ascertained which subsets of patients actually require ambulatory blood pressure recordings. The current cost of the automatic units ranges from $7,000 to $20,000. Depending upon duration of the recording and whether a Holter ECG is also obtained, charges for ambulatory blood pressure recordings have ranged from $130 to $305. Since the precise significance of ambulatory blood pressure recordings, methods of data analysis, and the differential utilities of the technology are still being evaluated, it would be premature at the present time, both from clinical and economic standpoints, to adopt this technology on a widespread basis. Nevertheless, it seems probable that in the near future such instrumentation will provide a useful adjunctive aid to the clinician who manages patients with high blood pressure.
Ambulatoy
847
include characterization of blood pressure In-ofiles in normotensive and hypertensive populations, evaluation of patients with borderline hypertension, and assessment of the effects of therapeutic interventions. Regarding widespread clinical application of this technology, further investigation is needed to properly define its future role as an adjunctive aid in the diagnosis and treatment of high blood pressure. The authors thank assistance and Ms. tion.
Mr. Madeleine Sharon Mitchell
A. Boruta for for manuscript
technical prepara-
REFERENCES
1.
2.
3.
4.
5.
6.
7. 8.
9.
Ayman D, Goldshine AD: Blood pressure determinations in patients with essential hypertension. I. The difference between clinic and home readings before treatment. Am J Med Sci 200:465, 1940. Freis ED: The discrepancy between home and office recordings of blood pressure in patients under treatment with pentapyrrolidinium: Importance of home recordings in adjusting dosages. Med Ann District Columbia 23:363, 1954. Dustan HP, Page IH, Tarazi RC, Frolich ED: Arterial pressure responses to discontinuing antihypertensive drugs. Circulation 37:370, 1968. Julius S, Ellis CN, Pascual AV, et al: Home blood pressure determination: Value in borderline (“labile”) hypertension. JAMA 229:663, 1974. Parijs J, Joossens JV, VanderLinden L, Verstreden G, Amery A: Moderate sodium restriction and diuretics in the treatment of hypertension. AM HEART J 8522, 1973. Bevan AT, Honour AJ, Stott FD: Portable recorder for continuous arterial pressure measurement in man. J Physiol (Lond) 38~186, 1966. Bevan A, Honour AJ, Stott FD: Direct arterial pressure recording in unrestricted man. Clin Sci 36:329, 1969. Littler WA, Honour AJ, Sleight P, Stott FD: Continuous recording of direct arterial pressure and electrocardiogram in unrestricted man. Br Med J 3:76, 1972. Littler WA, Honour AJ, Sleight P: Direct arterial pressure and electrocardiogram during motor car driving. Br Med J 2:273,
10.
CONCLUSIONS
Concern for the adequacy of blood pressure measurement prompted general investigations into the reliability of casual or office blood pressure determinations as early as 1940. These studies showed that in many instances office blood pressure determinations did not correlate well with pressures obtained at home. Subsequently, direct (intra-arterial) and indirect (noninvasive) methods were developed to obtain blood pressure data on active, ambulatory patients for periods of time up to and exceeding 24 hours. Early efforts were hampered by technologic problems which have now largely been overcome. Indirect, automatic methods have the advantage of being noninvasive, yet have a hjgh correlation with intra-arterial pressures. Current research uses for indirect, ambulatory blood pressure recording
blood pressure recordings
11.
12.
13.
14.
15.
16.
17.
1973.
Littler WA, Honour AJ, Sleight P, Stott FD: Direct arterial pressure and electrocardiogram in unrestricted patients with angina pectoris. Circulation 48:125, 1973. Littler WA, Honour AJ, Sleight P: Direct arterial pressure, pulse rate and electrocardiogram during micturition and defecation in unrestricted man. AM HEART J 88:205, 1974. Littler WA, Honour AJ, Sleight P: Direct arterial pressure, heart rate and electrocardiogram during human coitus. J Reprod Fertil 48:321, 1974. Littler WA, Honour AJ, Pugsley DJ, Sleight P: Continuous recording of direct arterial pressure in unrestricted patients: Its role in the diagnosis and management of high blood pressure. Circulation 51:1101, 1975. Goldberg AD, Raftery EB: Patterns of blood-pressure during chronic administration of post-ganglionic sympathetic blocking drugs for hypertension. Lancet 2:1052, 1976. Goldberg AD, Raftery EB, Cashman PMM, Stott FD: Study of untreated hypertensive subjects by means of continuous intraarterial blood pressure recordings. Br Heart J 40:656, 1978. West MJ, Sleight P, Honour AJ: Statistical analysis of the 24.hour blood pressure using pressure frequency histograms. Postgrad Med J 52:100, 1976. Goldberg AD, Raftery EB, Green HL: The Oxford contin-
18. 19.
20.
21.
22.
23.
24.
25.
26.
27.
uous blood pressure recorder-technical and clinical evaluation. Postgrad Med J 52:104, 1976. Littler WA: Median nerve palsy-complication of bra&al artery cannulation. Postgrad Med J 52:110, 1976. Millar Craig MW, Mann S, Balasubramanian V, Raftery EG: Circadian rhythm of blood pressure and modification by treatment. Am J Cardiol 43~419, 1979. Irvine JB. Brash HM, Kerr F. Kirbv BJ: The value of ambulatory monitoring in borderline and established hypertension. Postgrad Med J 52(snppl 7): I-127, 1976. Hinman AT, Engel BT, Bickford AF: Portable blood pressure recorder accriracy and preliminary use in evaluating intra-daily variations in pressure. AM HEART J 63:663? 1962. Richardson DW, Honour AJ, Fenton GW, Stott FD, Pickereing GW: Variations in arterial pressnre throughout the day and night. Ciin Sci 26:445, 1964. Sokolow M, Werdegar D, Kain HK, et al: Relationship between level of blood pressure measuring casually and by portable recorders and sever&y of complications in essential hypertension. Circulation 34:279, 1966. Perloff D, Sokolow M: The representative blood pressure: Usefulness of office, basal, home, and ambulatory readings. Cardiovasc Med 3:6X?, 1978. Sokolow M, Werdegar D, Perloff DB, et al: Preliminary studies relating portably recorded blood pressures to daily life events in patients with essential hypertension. Bib1 Psychiatr 144:164, 1970. Sokolow M, Perloff D, Cown R: The value of portably recorded blood pressures in the initiation of treatment of moderate hypertension. Clin Sci Mol Med 45:195s 1973. Schneider RA: A fully automatic portable blood pressure recorder. J Appl Physiol 24~115, 1968. -
”
28.
29.
30.
31.
32.
33.
34.
35.
36.
Schneider RA, Kimmell GO, Van Meter AP Jr: An improved fully automatic portable blood pressure recorder. J Appl Physiol 37~776, 1974. Schneider RA, Costiloe JP, Wolf S: Arterial pressmes recorded in hospital and during ordinary daily activities contrasting data in subjects with and without ischemic heart disease. ,J Chronic Dis 23:647, 1971. Schneider RA; Costiloe JP: Twenty-four hour automatic monitoring of blood pressme and heart rate at work and at home. AM HEART J S&695, 1975. Harshfield G, Pickering T, Laragh J: A validation study of the Del Mar Avionics ambulatory blood pressure system. Ambulatory Electrocardiography 4:7, 1979. Kennedy HL, Padgett, NE, Horan, MJ: Performance rehability of the Avionics ambulatory blood pressure instrument in clinical use. Ambulatory Electrocardiography 4:13, 1979. Kennedy HL, Padgett, NE, Pickett RA, Goldoerg RJ, Farid RD: 24-hour ambulatory blood pressure in clinical!y normal men (abstr). Clin Res 27:179A, 1979. Horan MJ, Kennedy HL, Padgett NE: Do borderline hypertensive patients have labile blood pressures? Ann Intern Med (In press). Kennedy HL, Padgett NE, Horan MJ, cation of physician assessment of antibypertensive therapy by ambulatory blood pressure recording (abstr). Am J Cardiol 45490, 1980. Pickering TG, Harshfield GA, Laragh JH: Use of ambulatory blood pressure monitoring in the evaluation of patients with borderline hypertension (abstr). Am J Cardiol 45:446, 1980.
16.
17.
18.
19. 20.
21.
PGEl
taglandins in the circulation of the fetal lamb. Prostaglandins llAO41, 1976. Heymann MA, Rudolph AM: Neonatal manipulation: Patent ductus arteriosus. 1n Engle MA, editor: Pediatric cardiovascular disease. Philadelphia, 1981, FA Davis Company, pp 301-310. Heymann MA, Rudolph AM: Effects of congenital heart disease on fetal and neonatal circulation. Prog Cardiovasc Dis 15:115,1972. Starling MB, Elliott RB: The effects of prostaglandins, prostaglandin inhibitors, and oxygen on the closure of the ductus arteriosus, puhnonary arteries, and umbilical vessels in vitro. Prostaglandins 8:187, 1974. Elliott RB, Starling MB, Neutze JM: Medical manipulation of the ductus arteriosua Lancet 1:140, 1975. Olley, P.M., Coceani, F., and Bodach, E.: E-type prostaglandins: A new emergency therapy for certain cyanotic congenital heart malformations. Circulation 53:728, 1976. Heymann MA, Rudolph AM: Ductus arteriosus dilatation by prostaglandin E1 in infants with pulmonary atresia. Pediatrics 59:325, 1977.
22.
23.
24.
25.
26.
27.
therapy
in congenital
heart
disease
843
Neutze JM, Starling MB, Elliott RB, Barratt-Boyes BG: Palliation of cyanotic congenital heart disease in infancy with E-type prostaglandins. Circulation 55:238, 1977. Freed MD, Heymann MA, Lewis AB, Reischer S, Kensey RC: Prostaglandin E1 in infants with ductus arteriosus dependent congenital heart disease. The U.S. experience. Circulation (In press) Lewis AB, Freed MD, Heymann MA, Reiscber S, Kensey RC: Side effects of therapy with prostaglandin E1 in infants with critical congenital heart disease. The U.S. experience. Circulation (In press, November, 1981) Rudolph AM, Heymann MA, Spitznas U: Hemodynamic considerations in the development of narrowing of the aorta. Am J Cardiol 30~514, 1972. Heymann MA, Berman W Jr, Rudolph AM, Whitman V: Dilatation of the ductus arteriosus by prostaglandin E1 in aortic arch abnormalities. Circulation 59:169, 1979. Silove ED, Coe JY, Shiu MF, Brunt JD, Page AJF, Singh SP, Mitchell MD: Oral prostaglandin EZ in ductus-dependent pulmonary circulation. Circulation 83:682, 1981.
Ambulatory blood pressure monitoring: Recent advances and clinical applications Michael J. Horan, M.D., Neil E. Padgett, Baltimore,
Md.,
and
Long
Beach,
BS., and Harold
L. Kennedy,
M.D., M.P.H.
Calif.
Casual, office blood pressure determinations using a standard sphygmomamonometer have traditionally constituted the principal modality for the diagnosis and management of hypertension. There is substantial evidence, however, to suggest that office blood pressure determinations may not always reliably reflect blood pressure at rest in other settings or during ordinary daily activities. In 1940 Ayman and Goldshine conducted a study in which they compared blood pressures taken in the clinic with home blood pressures. In 30% of 34 patients studied the systolic blood pressures obtained at home were lower by 40 mm Hg or more than the systolic blood
pressures obtained in the clinic. In 24% of the same patients the diastolic blood pressures were 20 mm Hg lower than the diastolic blood pressures obtained in the clinic. A number of subsequent reports are in agreement with these observations.g-5 Although patient-recorded home blood pressures are valuable, limitations are imposed by patient cooperation, frequency of recordings, and sampling error+ Also generally precluded are pressures during sleep? exercise, and other activities. Techniques therefore emerged for recording blood pressures in the active, ambulatory patient. They have developed along two lines, direct (intraarterial) and indirect (noninvasive) continuous pressure monitoring.
From the Department of Medicine, The Johns Hopkins Hospit& Department of Medicine, Division of Cardiology, Memorial Medical Center.
DIRECT AMBULATORY MEASUREMENTS
Received
for publication
Reprint requests: Harold Center, Dept. of Medicine, Beach, CA 90801.
0002-8703/81/060843
Dec. 29, 198% accepted
and the Hospital
Feb. 27, 1981.
L. Kennedy, M.D., Memorial Hospital Medical Division of Cardiology, 2801 Atlantic Ave., Long
+ 06$00.60/00
198lThe
C.V.Mosby
Co.
BLOOD
PRESSURE
The earliest intra-arterial method of measuring ambulatory blood pressure was designed by Stott and introduced by Beven et al.6, 7 in 1966. Additional
8
Horan,
Padgett,
and Kennedy
Fig. I- Patient wearing portable, noninvasive, automatic pressurometer (Del Mar Avionics) that measures and records blood pressure (BP), heart rate, and heart rhythm for periods up to 24 houm 1 = microphone; 2 = %P cui$ 3 = pressurometer; 4 = Hoker recorder; 5 = ECG leads.
applications of this technology were described by Littler et al.,8-13 Goldberg et al.,14. G and West et al.16 This led to a refined version of an ambulatory blood pressure apparatus which used an Oxford continnous blood pressure recordere17 The system employs an intra-arterial cannula which is placed percutaneously in the brachial artery 3 to 5 cm above the antecubital fossa. The heparinized saline-filled cannula is attached to an automatic perfusion pump and strain gauge transducer. Continuous pressure measurements from the transducer and simultaneous EXG are recorded on the Oxford recorder. The perfusion pump continuously perfuses the arterial cannula with heparinized saline to prevent clotting9 but it must be serviced every E! hours. Sophisticated tape recording analyzers provide beat-to-beat> real-
time data which can be displayed graphically- Highspeed analysis techniques allow these data to be played back at 25 or 60 times real-time5 and more recently an analog preprocessor has been developed to detect systoiic, diastolic? and mean arterial pressures with the pulse interval for statistical evahmtion and histogram plots.16 Studies using this technology have provided some of the earliest observations of the influence of various activities on blood pressure. Such studies have shown that blood pressure in normal subjects and hypertensive patients may vary widely during ordinary activities, and are affected by the psychologic stimuli of physician visits, medical examinations, and sexual activitym7, 1Z Of potential importance has been the observation that many individuals may, during the course of a day9 be found to be hypertensive or normotensive, and in occasion the highest pressure has been greater than twice the lowest pressure.i, 8 Other investigations have confirmed these early observations, and have noted that the decrease in blood pressure routinely seen with sleep was more pronounced in the patienVs home environment as compared to the bospitaI.1:3 In addition, blood pressure was found to be generally stable during automobile drivingY9 reflective of a Valsaha response during micturition and defecation11 and elevated with a concurrent rise in beart rate angina pectoris commensurate with the provocative activities which induced such pain.1o However, in spontaneous or no6turnal angina pectoris, rises m arterial pressure were noted to occur IO to 15 minutes before the onset of angina pectoris.‘O Comparison of sphygmomanometric blood pressure measurements obtained by the physician in the outpatient clinic were generally found to agree with concomitant direct arterial measurements, but some hypertensive patients were found to have lower direct arterial readings. lZ Direct arterial blood pressure recordings have also helped demonstrate that some hypertensive patients manifest a persistent tachycardia throughout the day, indicative of a hyperkinetic state.ls Finally, direct mtra-arterial ambulatory blood pressure measurements have been used to assess the efficacy of antbypertensive tberapy in hypertensive patientP I*. E I9 and in differentiating between borderline and fixed hypertensionZo While it is apparent that the direct intra-arterial measurement of ambulatory blood pressure provides precise data, such measurement requires substantial resources in terms of experienced personnel and equipment. Furthermore, although comphcations are infrequent, moderate morbidity has been
Volume 101 Number 6
Ambulatory
reported including localized paresis due to median nerve palsy.1* Studies employing direct arterial measurements continue to be in progress, and are being performed predominantly in Great Britian. Ambulatory blood pressure recording in North America has primarily involved use of noninvasive, indirect blood pressure measurement methods. NONINVASIVE AMIBULATORY MEASUREMENTS
IBLOOD
PRESSURE
Indirect (noninvasive) ambulatory blood pressure recorders have employed semiautomatic and automatic methods. The patient is required to activate the semiautomatic models, whereas the automatic models are self-activating. The earliest indirect semiautomatic ambulatory blood pressure recorder was developed in 1962 by Hinman et al.*l It consisted of a blood pressure cuff with inflating bulb, button microphone, transducer and tape recorder, all of which weighed 5&X pounds. The patient inflated the cuff whenever blood pressure recording was desired. When systolic blood pressure readings were compared with manually obtained readings, agreement was found to be within 9 mm Hg for one subject and within 4 mm Hg for four other subjects. For diastolic pressure, agreement was less satisfactory, with the portable unit generally recording a diastolic pressure intermediate between the ausculatory phase IV and phase V diastolic blood pressure. In 1964 Pickering and Richardson et al.ZZ employed a Gallavardin double-cuff which inflated automatically at &minute intervals. Arterial pressures were estimated by observing the pulsations at the lower cuff. TYhese investigators were the first to use continuous blood pressure recorders to demonstrate that bloald pressure tends to fall during sleep. Sokolow et al.s3 in 1966 employed an updated model of Hinman’s semi-automatic blood pressure recorder, known as the Remler recorder, to determine the relationship between casual blood pressure determinations tind portable ambulatory recordings. They found that ambula.tory blood pressures were lower than oflice blood pressures in 80% of 393 untreated patients with essential hypertension.sa Ambulatory systolic blood pressures averaged 18 mm Hg less than office systolic pressures and ambulatory diastolic blood pressures averaged 10 mm Hg less than omce diastolic pressures. The correlation between blood pressures obtained in the ambulatory setting and those obtained in the office setting was 0.67 for systolic pressures and 0.65 for diastolic pressures. Although these correlation coeficients
blood pressure
recordings
845
appeared satisfactory, they did not account for a sufficient proportion of variance to permit ambulatory pressures to be readily predicted from oflice pressures in individual cases. Furthermore, the correlation between blood pressure level and the presence of end-organ involvement (retinopathy, impaired renal fun&ion, and ECG and chest x-ray evidence of left ventricular hypertrophy) was higher for ambulatory blood pressures (systolic r = 0.63; diastolic, r = 0.65) than for casual blood pressures (systolic, r = 0.48; diastolic, r = 0.53). In subsequent studies these authors documented the broad variability of blood pressure in hypertensive patients during waking hours,Zs and also showed the advantages of ambulatory blood pressures in helping to decide whether to treat patients with borderline hypertension and whether to augment therapy in seemingly uncontrolled, treated hypertensive patientsZ6 Between 1968 and 1975 Schneider et al.ZT-3”developed an automatic, indirect, ambulatory blood pressure recording system that incorporated a blood pressure cuff, programmable electronic timer, tape deck, pressurized nitrogen cartridge, crystal microphone, and force-pressure translator. Blood pressures recorded with this system were found to be within 5% of the blood pressures obtained by conventional use of the sphygmomanometer and within 15% of blood pressures obtained intra-arterially.Za Additional experience with this unit revealed, contrary to the experience with home blood pressures, that automatic blood pressures recorded at home and at work were higher (greater than IO mm Hg) than office blood pressures in one third of 22 normotensive subjects and equal in two thirds of individualsZy Possible explanations for this variation may have included the novelty of experience with the instrument, the startle effect of the cuff spontaneously inflating? the increased level of activity outside the hospital, or combinations of these factors Using the apparatus this group also documented the decline of blood pressure during sleep.3o More recently, another noninvasive, automatic ambulatory blood pressure system utilizing a lightweight motor to inflate the cuff has been developed. As shown in Fig. 1, a microphone (No. I) is placed over the brachial artery, beneath the blood pressure cuff (No. 2). These are connected to the pressurometer (No. 3) housing the miniature motor which automatically air-inflates the blood pressure cuff every 7.5, 15, or 30 minutes. The Holter recorder (No. 4) records the appearance and disappearance of the Korotkoff sounds as well as ECG data from
846
Horan,
Padgett,
JUiw1981
and Kennedy
American
&art
Jourr?a~
Fig. 2. Example of two types of computerized data provided by 24-hour ambulatory blood pressure recordings. Upperpanel: graphic display of data printout. Lowerpanel: graphic display of average hourly systolic and diastolic blood pressures and heart rate. chest leads (No 5). A newer model of this pressurometer, containing solid state memory for the storage of digital data, has ehminated the Halter
recorder, makmg the entire system less cumbersome. Approximately 125 to 200 blood pressure readings are obtained per 24-hour period (Figs 2). Harshfield, Pickering, and Laragh31 demonstrated high correlations with blood pressures obtained rising this apparatus compared to intra-arterial pressures (r = 0.98) and compared to sphygmomanometric pressures (r = 0.86 to 0.99). Kennedy et al.3z examined the practical aspects of the instrumentation in obtaining useful data and found it to be reliable with, only 19% loss of data, A&factual data, secondary usually due to artifact. to misinterpretation of sounds other than Korotkoff sounds? were most often due to muscular contraction noises and/or extraneous noises in the environ-
ment. Studies with this apparatus have confirmed previous observations concerning the reduction of blood pressure during sleep in normal subjectsz3; they have documented that patients with border&e hypertension have no increase in labihty of blood pressures4; and they have demonstrated the utility of ambulatory blood pressure recordings in verifying the control or lack of control of blood pressure in treated hypertensive patients.35 CLINICAL
IMPLICATKINS
Use of ambulatory blood pressure recordings has to date been confined primarily to the research setting. The use of intra-arterial catheters provides accurate blood pressure readings, but for wide scale use as well as for safety and comfort, the mdirect, occlusive cuff methods would seem more desirable. Technologic problems with the development of
VotumelOl Number 6
instrumentation for indirect measurement of ambulatory blood pressure have not been entirely eliminated, although great strides have been made in this area. The remaining technologic problems include the persistence of some artifact in the blood pressure recordings, which currently’ affects about 10% of measurements, and occasional failure of one or more of the components in these systems. The validation and reliability studies alluded to above suggest that the automatic ambulatory blood pressure recording devices are acceptable both for research and patient care purposes. At the present time, preliminary research has demonstrated the usefulness of this technology in the evaluation of borderline or labile hypertension;4. 36 as well as its value in the assessment of therapeutic efficacy in the treatment of Additional evaluation is needed, hypertension.35 however, before complete utility of this technology can be determined and before it can be ascertained which subsets of patients actually require ambulatory blood pressure recordings. The current cost of the automatic units ranges from $7,000 to $20,000. Depending upon duration of the recording and whether a Holter ECG is also obtained, charges for ambulatory blood pressure recordings have ranged from $130 to $305. Since the precise significance of ambulatory blood pressure recordings, methods of data analysis, and the differential utilities of the technology are still being evaluated, it would be premature at the present time, both from clinical and economic standpoints, to adopt this technology on a widespread basis. Nevertheless, it seems probable that in the near future such instrumentation will provide a useful adjunctive aid to the clinician who manages patients with high blood pressure.
Ambulatoy
847
include characterization of blood pressure In-ofiles in normotensive and hypertensive populations, evaluation of patients with borderline hypertension, and assessment of the effects of therapeutic interventions. Regarding widespread clinical application of this technology, further investigation is needed to properly define its future role as an adjunctive aid in the diagnosis and treatment of high blood pressure. The authors thank assistance and Ms. tion.
Mr. Madeleine Sharon Mitchell
A. Boruta for for manuscript
technical prepara-
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CONCLUSIONS
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Schneider RA, Kimmell GO, Van Meter AP Jr: An improved fully automatic portable blood pressure recorder. J Appl Physiol 37~776, 1974. Schneider RA, Costiloe JP, Wolf S: Arterial pressmes recorded in hospital and during ordinary daily activities contrasting data in subjects with and without ischemic heart disease. ,J Chronic Dis 23:647, 1971. Schneider RA; Costiloe JP: Twenty-four hour automatic monitoring of blood pressme and heart rate at work and at home. AM HEART J S&695, 1975. Harshfield G, Pickering T, Laragh J: A validation study of the Del Mar Avionics ambulatory blood pressure system. Ambulatory Electrocardiography 4:7, 1979. Kennedy HL, Padgett, NE, Horan, MJ: Performance rehability of the Avionics ambulatory blood pressure instrument in clinical use. Ambulatory Electrocardiography 4:13, 1979. Kennedy HL, Padgett, NE, Pickett RA, Goldoerg RJ, Farid RD: 24-hour ambulatory blood pressure in clinical!y normal men (abstr). Clin Res 27:179A, 1979. Horan MJ, Kennedy HL, Padgett NE: Do borderline hypertensive patients have labile blood pressures? Ann Intern Med (In press). Kennedy HL, Padgett NE, Horan MJ, cation of physician assessment of antibypertensive therapy by ambulatory blood pressure recording (abstr). Am J Cardiol 45490, 1980. Pickering TG, Harshfield GA, Laragh JH: Use of ambulatory blood pressure monitoring in the evaluation of patients with borderline hypertension (abstr). Am J Cardiol 45:446, 1980.