Accuracy and reliability of two indirect ambulatory blood pressure recorders: Remler M2000 and Cardiodyne Sphygmolog

Twenty-four-hour ambulatory blood pressure measurement in clinical practice and research: a critical review of a technique in need of implementation

This review presents evidence that ambulatory blood pressure measurement (ABPM) should be used more widely in clinical practice and hypertension research. The technique, which should be mandatory in trials of antihypertensive drugs, is not being used in all studies of antihypertensive drug efficacy. ABPM is also being under-used in outcome studies. The failure to implement ABPM in primary care and hypertension research is impeding patient management and scientific advancement. ABPM offers so many advantages in assessing the efficacy of blood pressure (BP)-lowering drugs that it should be mandatory in pharmacological trials. Likewise, the technique provides a means of achieving BP control in clinical practice, which is essential if we are to halt the epidemic of the cardiovascular consequences of hypertension. However, if ABPM is to be implemented for these purposes, certain requirements will need to be fulfilled. These include the availability of accurate, patient-friendly and inexpensive devices; standardization of the presentation and plotting of data with summary statistics for day-to-day practice; provision of comprehensive data analysis for research; an interpretative report to facilitate use in busy clinical practice; a trend report to demonstrate efficacy or otherwise of treatment in clinical practice and online transmission of data to provide immediate real-time data analysis. The reasons why ABPM is not being implemented are reviewed, and proposals are made to make the technique more acceptable.

Comparative accuracy of three automated techniques in the noninvasive estimation of central blood pressure in men

Automated devices have regularly replaced manual sphygmomanometry for the determination of blood pressure not only in homes and clinics, but also in emergency and critical care settings. Few studies exist that correctly assess the accuracy of these devices, and even fewer that specifically compare commercially available units that rely on different physiologic events for measurement. Six hundred pressure measurements were obtained from 120 subjects using 1 of 3 randomly selected blood pressure monitors. In addition, central arterial pressure measurements were obtained simultaneously and directly from the ascending aorta of each subject. Overall, these devices tended to overestimate diastolic (+2.5 mm Hg, p < 0.0001) and mean (+3.8 mm Hg, p < 0.0001) pressures, but not systolic (+0.7 mm Hg, p = NS) pressure. Compared with the other 2 devices, device I, relying on oscillometric detection, demonstrated a significantly smaller mean absolute error for diastolic pressure (4.9 +/- 3.0 vs 7.0 +/- 4.8 and 6.2 +/- 5.3 mm Hg, p < 0.0001) and mean pressure (4.0 +/- 3.2 vs 7.8 +/- 5.9 and 8.6 +/- 7.5 mm Hg, p < 0.0001), and a trend toward smaller error with systolic pressure (6.8 +/- 6.5 vs 7.3 +/- 6.8 and 8.0 +/-5.6 mm Hg, p = 0.19). Clinically significant (+/-10 mm Hg) errors were common with each device (24.8% overall), but serious (+/-20 mm Hg) errors were unusual (3.2%) and did not occur at all with device I during diastolic and mean pressure measurement. All of the devices tested could be expected to perform satisfactorily in most clinical settings provided that an average error of 4.0 to 8.6 mm Hg is tolerable. This level of accuracy typically extended throughout the range of pressures anticipated in most noncritical clinical situations. As implemented in the devices tested, noninvasive measurement by oscillometry with stepped deflation is more accurate than automated auscultation.

State of the market. A review of ambulatory blood pressure monitoring devices

The introduction of 24-hour ambulatory blood pressure measurement into clinical practice created a large market for ambulatory blood pressure measurement devices. Forty-three such devices from 31 manufacturers or suppliers are now available to satisfy a market demand that is likely to increase. The aim of this article is to identify the devices available and then to examine critically any validation studies assessing accuracy and performance. Of the 43 devices available 18 have been validated according to the protocols of the Association for the Advancement of Medical Instrumentation (AAMI) or the British Hypertension Society (BHS) in 25 reported studies. In 9 of these studies the protocol was not adhered to, and the results, which are therefore questionable, are noted but not considered further. Fourteen devices were evaluated according to the accuracy criteria of both protocols, and of these 9 fulfilled the requirements. From this review of 43 devices on the market it may be concluded that, at the time of writing, there is published evidence for only 9 devices meeting the generally accepted AAMI and BHS criteria for accuracy and performance; these are the A&D TM-2420 models 6 and 7 and TM-2421, CH-Druck, Nissei ABPM DS-240, Profilomat, QuietTrak, and SpaceLabs SL-90202 and SL-90207.

Ambulatory blood pressure monitoring

Non-invasive measurement of blood pressure in ambulatory humans began in the 1960s. Ambulatory devices have been modified over the years and are now pocket-sized, with almost noiseless pumps. Their accuracy must be validated by independent laboratories using a standardised protocol. Twenty-four-hour ambulatory monitoring offers considerable advantages over conventional measurement, including avoidance of error associated with conventional measurement, elimination of white-coat effect and the provision of a series of blood pressure readings over the time period rather than a one-off measurement. In clinical practice, 24-hr monitoring provides valuable assistance in both the diagnosis and treatment of hypertension, in particular, in the selection of drug and dosage regimen. In the research setting, 24-hr monitoring plays an important role in establishing dose-response relationships and the duration of action of new drugs. It also has a role in the design of antihypertensive trials by ensuring that those with white-coat hypertension are excluded and by reducing the number of subjects necessary for recruitment. Although 24-hr ambulatory blood pressure is a better predictor of target organ damage, definitive evidence as to whether it is a better predictor of prognosis in hypertension awaits the results of longitudinal studies, which are now underway.

A proposal for scientific validation of instruments for indirect blood pressure measurement at rest, during exercise, and in critical care

OBJECTIVE

The purpose of this study was to provide a critical review and comprehensive outline of published guidelines for the validation of monitors for indirect blood pressure (BP) measurement in light of recent research and practical clinical experience.

METHODS

Studies testing the reliability and validity of BP monitors and available guidelines for validation have been reviewed and compared.

RESULTS

The validation studies of instruments for indirect BP measurement have used a wide variety of sample pools, BP ranges, protocols, reference instruments, and statistical procedures, thereby making it impossible to reach a consensus. Few existing recommendations for validation have been found to be incomplete with respect to BP in various physiological states, sequence of procedures, sample, and statistical analysis.

CONCLUSIONS

A new sequence of procedures for validation, including assessment of instruments during exercise and in critical care, is introduced. Previously suggested sample sizes for study subjects, age, and BP groups, as well as margins of error, are statistically challenged. Insufficiency of linear relationship and aggregate agreement alone in determining the interchangeability between a reference and test instrument is demonstrated by quantification of agreement.

Double-blind, randomized comparative study of the antihypertensive effect of nicardipine slow-release and nifedipine slow-release in hypertensive patients with coronary heart disease

The main aim of this study was to investigate whether a new slow-release formation of nicardipine can control hypertension and whether its antihypertensive effect is manifest throughout the dose intervals. In a randomized, double-blind placebo-controlled study, the antihypertensive effect of two calcium antagonists (Type II) was investigated in two independent groups of hypertensive patients with coronary artery disease. One group of patients received 40 mg nicardipine slow-release b.i.d. and the other 20 mg nifedipine slow-release b.i.d. The effect of the active drugs on blood pressure (BP), heart rate, and hemodynamics was compared with placebo within each group. In addition, a group comparison was made to establish whether nicardipine had any advantage over nifedipine. Twenty-eight patients [27 female, 1 male; 55 (41-72) years old], 18 with previous myocardial infarction (MI) entered the study (nicardipine, 15 patients; nifedipine, 13 patients). A placebo period of 3 days was followed by a 13-day drug treatment period. From the first to last trial day, BP and heart rate were measured three times daily. At the end of the placebo and the active drug periods, the following measurements were carried out: ambulatory BP monitoring by half-hourly recording for 12.5 hours with the Remler system, ergometric tests with ECG, and right heart catheterization. Both drugs lowered the BP at rest, during exercise, and during usual daily activities. The antihypertensive effect of nicardipine was significant for the daytime mean arterial BP (MAP) and for systolic BP and diastolic BP at various stages of the exercise tests. The difference between the effect of nicardipine and nifedipine was not significant.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of slow-release nicardipine on ambulatory and clinic blood pressure in mild hypertension

1. The antihypertensive efficacy of a long acting formulation of the calcium channel blocking drug, nicardipine, was assessed using clinic and ambulatory (Remler M2,000) blood pressure measurements. 2. Eleven patients with essential hypertension (mean +/- s.e. mean; 173 +/- 6.6/103 +/- 1.9 mmHg) completed a randomised double-blind, placebo-controlled, cross-over study. The dose of nicardipine used was 60 mg twice daily for 4 weeks. 3. Mean ambulatory blood pressure was reduced from 164 +/- 5.3/97 +/- 2.9 to 151 +/- 5.2/88 +/- 2.4 mmHg (P less than 0.01); this effect was shown to be sustained for 8 h after the morning dose. Mean ambulatory heart rate was not significantly affected by treatment. 4. Clinic lying systolic blood pressure was reduced on treatment from 169 +/- 7.1 to 157 +/- 5.9 mmHg (P less than 0.2) and diastolic blood pressure from 99 +/- 3.6 to 89 +/- 3.9 mmHg (P less than 0.05). 5. One patient was withdrawn because of dizziness and flushing while on nicardipine; vasodilatory side effects such as headache, palpitations and flushing on nicardipine were noted by three patients. 6. We conclude that the long acting formulation of nicardipine studied in a dose of 60 mg twice daily is effective as monotherapy and is relatively well tolerated in mild hypertension. 7. This study highlights the importance of ambulatory blood pressure measurement in detecting significant changes in blood pressure, thereby permitting the study of small numbers of patients.

Placebo does not lower ambulatory blood pressure

The effects of 4 weeks of placebo on clinic and on ambulatory blood pressure, measured non-invasively using the Remler M 2000 portometer, were studied in 46 hypertensive patients who were included in three consecutive double-blind randomized placebo-controlled trials with antihypertensive drugs. Placebo significantly reduced clinic blood pressure, but had no significant effect on ambulatory blood pressure.

Effect of guanfacine on ambulatory blood pressure and its variability in elderly patients with essential hypertension

The effect of guanfacine (2 mg once daily) on ambulatory blood pressure was studied with the Remler M 2000 recorder in 16 elderly hypertensive patients during a randomized, double-blind, placebo-controlled, balanced, cross-over study. Guanfacine significantly reduced heart rate and systolic and diastolic ambulatory blood pressure. The antihypertensive effect was maintained over the whole recording period. Systolic and diastolic blood pressure variability was not changed by guanfacine, neither when defined as standard deviation or variation coefficient of the mean, nor when defined as the range between the highest and lowest ambulatory blood pressure, suggesting that blood pressure variability is unrelated to sympathetic nervous system activity.

Efficacy of a fixed-dose combination of 40 mg penbutolol with 6 mg piretanide in the treatment of mild to moderate hypertension: a double-blind study against placebo

The antihypertensive efficacy and tolerability of a fixed-dose combination containing 40 mg penbutolol (a beta-blocking agent) and 6 mg piretanide (a diuretic) in comparison to placebo was investigated in a double-blind, crossover study in 20 patients with mild to moderate essential hypertension. After a 1-week period on placebo, patients were allocated at random to receive 1 tablet daily for 4 weeks of either the combination preparation or placebo and were then crossed over to the alternative medication for a further 4 weeks. The reduction in systolic and diastolic blood pressure both at rest, during maximal ergometric exercise and isometric word load, and also in the diurnal blood pressure profile over 24 hours was significantly greater in the group treated with the fixed-dose combination than in the placebo group. Pulse rate was also decreased to a greater extent. Mean diastolic blood pressure before exercise was reduced to normal (85.5 mmHg) after 4-weeks' treatment with the fixed-dose combination. Biochemical, haematological and urinary parameters showed no clinically relevant changes after either treatment. One patient complained of transient dizziness during treatment with the fixed-dose combination. No patient withdrew prematurely from the study because of side-effects.

Home blood pressure recording

Blood pressure is an inherently variable phenomenon. In addition to this the level rises in the clinical setting; a response which is extremely variable. Problems therefore arise in the diagnosis and treatment of hypertension. Studies have shown that blood pressure can reliably be measured at home either with a stationary or ambulatory apparatus. The readings which are reproducible are generally lower than those obtained in the clinic. Ambulatory recordings are a more reliable guide to prognosis and to the response to hypotensive agents. Home recordings should therefore be more widely used in diagnosis and treatment of the disorder.

Nadolol in essential hypertension: effect on ambulatory blood pressure, renal haemodynamics and cardiac function

Chronic administration of nadolol has been reported to reduce blood pressure either without or with a concomitant fall of renal blood flow. We therefore studied the effects of nadolol 80 mg once daily on ambulatory blood pressure, renal and systemic haemodynamics in patients with mild to moderate essential hypertension. Ten patients took part in this randomized, double-blind, placebo-controlled, crossover study, each phase of which lasted 4 weeks. Nadolol significantly reduced ambulatory blood pressure and heart rate, but had no effect on blood pressure variability. Cardiac output was significantly reduced by nadolol and total peripheral resistance increased but without reaching statistical significance. Despite the fall in blood pressure and cardiac output, renal blood flow and glomerular filtration rate remained unchanged. The fraction of cardiac output reaching the kidneys rose significantly and renal vascular resistance was significantly reduced. Body weight, urinary sodium excretion and urine flow rate remained unchanged. We conclude that nadolol 80 mg once daily lowers ambulatory blood pressure in patients with mild to moderate hypertension without impairment of renal blood flow, indicating a redistribution of cardiac output to the kidneys. The mechanism of the renal vasodilator effect of nadolol remains to be determined.