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Biomedical subjects

N Atkins

Publications and source records attributed to N Atkins.

At least 37 records · Page 2Linked to original sources
PubMed1995

A new audiovisual technique for recording blood pressure in research: the Sphygmocorder.

OBJECTIVE: To devise a method of blood pressure measurement capable of being substituted for the fallible human observer in validation of blood pressure measuring devices. DESIGN: A number of components used to measure blood pressure have been combined innovatively with audiovisual recording technology to produce a system, named the Sphygmocorder, which consists of a mercury sphygmomanometer, an occluding cuff, an inflation source, a stethoscope, a microphone capable of detecting Korotkoff sounds, a camcorder and a display screen. METHODS: To determine the accuracy of the Sphygmocorder against the trained human observer, the Sphygmocorder has been validated in three separate studies in which three devices for self-measurement of blood pressure, the Omron HEM-705CP, the Phillips HP5332 and the Nissei DS-175, were being validated against two trained observers in 85 subjects with a wide range of blood pressure according to the protocol of the British Hypertension Society. RESULTS: The Sphygmocorder was as accurate as at least one of the observers in each of the validation studies and therefore allows replacement of trained observers by the new device. CONCLUSION: The Sphygmocorder, which retains the time-honoured technique of blood pressure measurement with a mercury sphygmomanometer and an auscultating observer, and provides, in addition, objective evidence of the measurement recorded, which can be stored and re-examined, can be used as a substitute for human observers in validation studies of blood pressure-measuring devices.

Blood Pressure Determination↗
PubMed1995

Factors influencing validation of ambulatory blood pressure measuring devices.

With the introduction of 24 h ambulatory blood pressure monitoring into clinical practice a vast market for ambulatory blood pressure monitoring devices has been created. To satisfy this market manufacturers are producing an array of ambulatory blood pressure monitoring devices. There is no obligation on manufacturers to have such devices validated independently, even though two national protocols, one from the British Hypertension Society (BHS) and the other from the Association for the Advancement of Medical Instrumentation (AAMI), call for independent validation and state the means of doing so. However, many factors can influence the validation procedure. They include compliance to the protocol being employed; the accuracy of the standard; establishing precisely the model being validated; the influences of blood pressure level, age and exercise on device accuracy; the provisions necessary for special populations, such as pregnant women, the elderly and children; the influence of oscillometric versus Korotkoff sound detection and electrocardiographic gating on comparative measurements; the assessment of performance as distinct from accuracy; and the relevance of general factors, such as the algorithm being employed and computer compatibility. Forty-three ambulatory blood pressure monitoring devices have been marketed for ambulatory blood pressure measurement and of those only 18 have been validated according to either the BHS or the AAMI protocol. The influence of the factors listed above on the validation studies of those devices will be considered and the relevance of validation procedures to the clinical use of ambulatory blood pressure monitoring devices will be discussed.

Association↗
PubMed1994

Using Hawksley random zero sphygmomanometer as a gold standard may result in misleading conclusions.

We combined a database of paired blood pressure measurements taken using the Hawksley random-zero sphygmonanometer and a standard mercury sphygmomanometer and a database of paired measurements made on a SpaceLabs 90202 ambulatory blood pressure recorder and standard sphygmomanometer to determine how the SpaceLabs 90202 would have fared if it had been assessed against the Hawksley random-zero sphygmomanometer instead of a standard sphygmomanometer. The pooled database contained 255 triplicate readings. Using the standard sphygmomanometer as gold standard, the Spacelabs had a median error of 2 mm/Hg for both systolic and diastolic. Against the Hawksley random-zero sphygmomanometer, median error was -3 mm systolic and -6 mm diastolic. The proportion of errors > 10 mm rose from 11% (systolic) and 9% (diastolic) with the standard sphygmomanometer to 16% and 29% with the Hawksley random-zero sphygmomanometer. Because it underestimates systolic and diastolic pressures, the use of the Hawksley random-zero sphygmomanometer as a gold standard may have resulted in misleading conclusions about performance of some automated BP recorders.

Adult↗
PubMed1994

Ambulatory blood pressure in normotensive and hypertensive subjects: results from an international database.

OBJECTIVE: To delineate more precisely an operational threshold for making clinical decisions based on ambulatory blood pressure (ABP) measurement by studying the ABP in subjects who were diagnosed as either normotensive or hypertensive by conventional blood pressure (CBP) measurement. SUBJECTS: Twenty-four research groups recruited 7069 subjects. Of these, 4577 were normotensive (CBP < or = 140/90 mmHg), 719 were borderline hypertensive (systolic CBP 141-159 mmHg or diastolic CBP 91-94 mmHg) and 1773 were definitely hypertensive. Of the subjects in the last of these categories, 1324 had systolic hypertension (systolic CBP > or = 160 mmHg) and 1310 had diastolic hypertension (diastolic CBP > or = 95 mmHg). Combined systolic and diastolic hypertension was present in 861 subjects. Hypertension had been diagnosed from the mean of two to nine (median two) CBP measurements obtained at one to three (median two) visits. RESULTS: The 95th centiles of the ABP distributions in the normotensive subjects were (systolic and diastolic, respectively) 133 and 82 mmHg for 24-h ABP, 140 and 88 mmHg for daytime ABP and 125 and 76 mmHg for night-time ABP, respectively. Of the subjects with systolic hypertension, 24% had 24-h systolic ABP < 133 mmHg. Similarly, 30% of those with diastolic hypertension had 24-h diastolic ABP < 82 mmHg. The probability that hypertensive subjects had 24-h ABP below these thresholds tended to increase with age and was two- to fourfold greater if the CBP of the subject had been measured at only one visit and if fewer than three CBP measurements had been averaged for establishing the diagnosis of hypertension. By contrast, for each 10-mmHg increment in systolic CBP, this probability decreased by 54% for 24-h systolic ABP and by 26% for 24-h diastolic ABP, and for each 5-mmHg increment in diastolic CBP it decreased by 6 and 9%, respectively. In comparison with 24-h ABP, the overlap in the daytime and night-time ABP between normotensive and hypertensive subjects was of similar magnitude and was influenced by the same factors. CONCLUSIONS: The ABP distributions of the normotensive subjects included in the present international database were not materially different from those in previous reports in the literature. One-fifth to more than one-third of hypertensive subjects had an ABP which was below the 95th centile of the ABP of normotensive subjects, but this proportion decreased if the hypertensive subjects had shown a higher CBP upon repeated measurement. The prognostic implications of elevated CBP in the presence of normal ABP remain to be determined.

Adolescent↗
PubMed1994

A comparison of the British Hypertension Society and Association for the Advancement of Medical Instrumentation protocols for validating blood pressure measuring devices: can the two be reconciled?

BACKGROUND: Experience with the original protocols of the Association for the Advancement of Medical Instrumentation (AAMI) and the British Hypertension Society (BHS) for validating blood pressure has provided valuable insight into the methodological problems associated with device validation and has influenced both the BHS and the AAMI in revising their protocols. OBJECTIVES: To review the revisions of the original BHS and AAMI protocols; to compare the protocols; and, using the BHS protocol as a framework for validation, to determine how it should be modified to a protocol that will fulfil the criteria of both the AAMI and the BHS. CONCLUSIONS: The revised protocols have many similarities but there are some important differences. These differences merit consideration so as to facilitate manufacturers seeking to validate devices for acceptance in both Europe and the United States. Of the two protocols, the BHS protocol is the more elaborate in that (1) it takes particular care to ensure that observers are trained to a very high standard, (2) it makes provision for special group validation and (3) it recommends in-use validation of all devices. By modifying the BHS protocol, it is possible to validate blood pressure measuring devices (ambulatory devices require special consideration) to satisfy the criteria of both protocols.

Blood Pressure Determination↗
PubMed1994

A consistent reference frame for ambulatory blood pressure monitoring is found in different populations.

This study investigated the consistency of a reference frame for ambulatory pressure monitoring, which using various approaches was determined in two different populations. The two reference groups were 718 subjects randomly selected from the population and 895 bank employees. The reference values derived in these two groups were subsequently tested in 591 untreated hypertensive patients. The ambulatory pressures equivalent to a conventional pressure of 140 mmHg systolic and 90 mmHg diastolic were calculated by regression analysis in all subjects. In addition, in subjects who were normotensive by conventional sphygmomanometry, the mean +2 and +3 standard deviations and the 90th, 95th and 99th percentiles of the ambulatory measurements were determined. The distributions of the ambulatory measurements were similar in the two reference groups and the aforementioned parameters therefore agreed within 4 mmHg in the two populations. There was considerable overlap in the ambulatory pressures between the two reference groups and the hypertensive patients. Classification of the patients according to the means +3 standard deviations and the regression limits gave the same results because in both reference groups these boundaries approximated to each other within 1 mmHg. For the 24 h pressures in the population sample these boundaries were 140 mmHg systolic and 88 mmHg diastolic. Of the patients with systolic hypertension (> or = 160 mmHg on conventional measurement), 39% had a 24 h systolic pressure of < 140 mmHg and of those with diastolic hypertension (> or = 95 mmHg), 44% had a 24 h diastolic pressure of < 88 mmHg; if the corresponding boundaries derived in the bank employees (143/90 mmHg) were applied, these proportions were 47% and 44%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Measurement error in the Hawksley random zero sphygmomanometer: what damage has been done and what can we learn?

The Hawksley random zero sphygmomanometer is used in all aspects of blood pressure research, from clinical trials to evaluation of new blood pressure recorders. It is designed to reduce observer bias in blood pressure measurement. The problem is that it also underestimates blood pressure. Furthermore, this was first reported more than two decades ago. In this paper Rónán Conroy and colleagues explore the consequences of using an inaccurate instrument for important research and why prestigious organisations like the World Health Organisation continue to use it.

Blood Pressure Determination↗
PubMed1993

Comparative accuracy of six ambulatory devices according to blood pressure levels.

OBJECTIVE: To assess the accuracy of six ambulatory blood pressure measuring systems at low, medium and high blood pressures. RESULTS: The CH-Druck, Profilomat, SpaceLabs 90207 and Novacor DIASYS 200R, having previously achieved A to C grading for systolic and diastolic blood pressures according to the British Hypertension Society (BHS) protocol and having fulfilled the criteria of the Association for the Advancement of Medical Instrumentation, have been recommended for measurement of ambulatory blood pressure in clinical practice; the Pressurometer IV and Takeda TM-2420, achieved only C and D grades and failed to satisfy the Association for the Advancement of Medical Instrumentation criteria. In this study the data from the original validations are re-analysed for three pressure ranges of systolic and diastolic blood pressures: low range < or = 130/80 mmHg, medium range 130-160/80-100 mmHg and high range > or = 160/100 mmHg. All six devices maintained their overall grading or improved them slightly in the low and medium blood pressure ranges, but in the high blood pressure range the CH-Druck slipped from an overall A/A grading to B/C, the Profilomat from B/A to C/D, the SpaceLabs from B/B to C/C and the Pressurometer IV from C/D to D/D. The Takeda remained unchanged with a D grading, but the results within this grading were worse in the higher blood pressure range, and the Novacor rose from C/C to C/B. CONCLUSIONS: This analysis suggests that the CH-Druck is the most accurate ambulatory system across the pressure range, although it does not perform as well in the high blood pressure range as in the medium and low blood pressure ranges. The SpaceLabs 90207 is accurate in the low and medium blood pressure ranges and reasonably accurate in the high blood pressure range. If blood pressures only in the low and medium ranges are to be measured, a wider selection of ambulatory systems becomes available because, in addition to the CH-Druck and SpaceLabs 90207, the Profiloat and Novacor DIASYS 200R are accurate.

Blood Pressure↗
PubMed1993

Twenty-four-hour ambulatory blood pressure measurement in a primigravid population.

OBJECTIVE: To establish the profiles of 24-h non-invasive ambulatory blood pressure measurement (ABPM) during the trimesters of pregnancy and the puerperium in normotensive healthy primigravidae. DESIGN: A prospective study in which 24-h ABPM was performed on five occasions in each subject: in the first trimester between 9 and 16 weeks' gestation; in the second trimester between 18 and 24 weeks; in the third trimester between 26 and 32 weeks and between 33 and 40 weeks; and finally at 6 weeks post partum. METHOD: One hundred and six Caucasian primigravid women who were normotensive at their first booking visit were recruited consecutively from the antenatal clinic and had 24-h ABPM performed with the SpaceLabs 90207 ambulatory system. RESULTS: Of the 106 women recruited, 98 completed 24-h ABPM on four of the five measurement occasions. Four women delivered prematurely before 33 weeks' gestation, thereby missing one ABPM measurement. Changes during pregnancy and the puerperium were assessed against the ABPM performed in the first trimester. There was no difference for daytime or night-time systolic blood pressure between 9 and 33 weeks, but it rose significantly from 33 to 40 weeks. At 6 weeks post partum, systolic blood pressure was not significantly different from the daytime pressure in the first-trimester ABPM but was raised significantly at night. Diastolic blood pressure decreased significantly between 18 and 24 weeks for both daytime and night-time. From 33 to 40 weeks it increased in parallel with systolic blood pressure, and at 6 weeks post partum it was raised significantly compared with first-trimester values for daytime and night-time. The nocturnal fall in blood pressure was preserved throughout pregnancy with a significant difference between daytime and night-time measurements present on all measurement occasions for systolic, diastolic and mean blood pressures and heart rate. There were significant differences between daytime ABPM and clinic blood pressure for both systolic and diastolic blood pressure up to 33 weeks. From 33 weeks until 6 weeks post partum there was no significant difference between daytime ambulatory and clinic blood pressures. CONCLUSION: This study provides reference values for ABPM in healthy primigravidae with generally uncomplicated pregnancies.

Adult↗
PubMed1993

Antihypertensive therapy and circadian blood pressure profiles: a retrospective analysis utilising cumulative sums.

The results of previous studies on the effects of antihypertensive agents on circadian blood pressure patterns are inconclusive, possibly due to the lack of a simple, objective, universally accepted method of quantifying circadian blood pressure profiles. In order to investigate for differences in the effects of antihypertensive drugs on circadian changes we utilised a recently described modified cumulative sums technique to quantify circadian alteration magnitude (CAM). CAM is simply calculated as the difference between crest and trough blood pressures, the mean blood pressures of the 6-h periods of highest and lowest sustained pressures respectively. The records from all 24-h ambulatory blood pressure monitoring performed over a 7 year period on subjects either on no medication (1208), or on treatment with a single first-line antihypertensive agent (578), were examined retrospectively. A sample (n = 40) stratified for trough diastolic blood pressure, age and sex was randomly selected from each of the following 5 groups: subjects on no medication, and subjects being treated with bendrofluazide, atenolol, class 2 calcium-channel blockers or captopril alone. Untreated subjects, those on bendrofluazide and those on a class 2 calcium channel blocker had similar circadian patterns. Subjects on atenolol therapy (25.9 +/- 1.7/18.3 +/- 1.3, systolic CAM +/- SE/diastolic CAM +/- SE) had attenuated circadian changes (p < 0.05) when compared to the untreated group (29.8 +/- 1.8/23.6 +/- 1.1), while those on captopril (34.9 +/- 2.4/25.7 +/- 1.8) exhibited markedly increased systolic and diastolic circadian blood pressure swings, which differed from those of the atenolol treated group (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Evaluation of blood pressure measuring devices.

Validation of blood pressure measuring devices is a relatively new field of research. There are two national protocols for validating blood pressure measuring devices: the protocol of the American Association for the Advancement of Medical Instrumentation (AAMI) and the protocol of the British Hypertension Society (BHS), each of which has recently been revised. 19 blood pressure measuring devices have been validated according to one or both of these protocols. These protocols have been beneficial in drawing attention to the potential inaccuracy of blood pressure measuring systems, they permit comparison between devices and they have brought manufacturers of blood pressure measuring devices into closer contact with the profession. There are some inherent weaknesses in both protocols which include the fallibility of the 'gold standard', the lack of provision for validation in special circumstances and in special groups, such as the elderly and pregnant women, and failure to allow for deteriorating accuracy with higher pressure levels. The revised BHS protocol attempts to redress these deficiencies.

Blood Pressure Monitors↗
PubMed1993

Short report: ambulatory blood pressure in normotensive compared with hypertensive subjects. The Ad-Hoc Working Group.

OBJECTIVE: To delineate more precisely an operational threshold for making clinical decisions based on ambulatory blood pressure (ABP) measurement by studying the ABP in subjects who were diagnosed as either normotensive or hypertensive by conventional blood pressure (CBP) measurement. SUBJECTS: Twenty-four research groups recruited 7069 subjects. Of these, 4577 were normotensive (CBP < or = 140/90 mmHg), 719 were borderline hypertensive (systolic CBP 141-159 mmHg or diastolic CBP 91-94 mmHg) and 1773 were definitely hypertensive. Of the subjects in the last of these categories, 1324 had systolic hypertension (systolic CBP > or = 160 mmHg) and 1310 had diastolic hypertension (diastolic CBP > or = 95 mmHg). Hypertension had been diagnosed from the mean of two to nine (median two) CBP measurements obtained at one to three (median two) visits. RESULTS: The 95th centiles of the 24-h ABP distributions in the normotensive subjects were (systolic and diastolic, respectively) 133 and 82 mmHg. Of the subjects with systolic hypertension, 24% had 24-h systolic ABP < 133 mmHg. Similarly, 30% of those with diastolic hypertension had 24-h diastolic ABP < 82 mmHg. The probability that hypertensive subjects had 24-h ABP below these thresholds tended to increase with age and was two- to fourfold greater if the CBP of the subject had been measured at only one visit and if fewer than three CBP measurements had been averaged for establishing the diagnosis of hypertension. By contrast, for each 10-mmHg increment in systolic CBP, this probability decreased by 54% for 24-h systolic ABP and by 26% for 24-h diastolic ABP, and for each 5-mmHg increment in diastolic CBP it decreased by 6 and 9%, respectively. CONCLUSIONS: The ABP distributions of the normotensive subjects included in the present international database were not materially different from those in previous reports in the literature. One-fifth to more than one-third of hypertensive subjects had an ABP which was below the 95th centile of the ABP of normotensive subjects, but this proportion decreased if the hypertensive subjects had shown a higher CBP upon repeated measurement. The prognostic implications of elevated CBP in the presence of normal ABP remain to be determined.

Adolescent↗
PubMed1993

Defining normal ambulatory blood pressure.

Providing normal reference values and the means to interpret such values in practice is an urgent issue requiring consensus. Five basic approaches to defining normalcy for 24 h blood pressures (BP) are considered: 1) the relationship of ambulatory blood pressure (ABP) to morbidity and mortality, 2) the relationship of ABP to end-organ involvement, 3) ABP levels in normal populations, 4) the relationship of ABP to clinic BP, and 5) the relationship of 24 h indices to risk. Although there now is considerable evidence demonstrating that ambulatory measurement correlates more strongly with end-organ damage, the first two approaches are scientifically the best. It will be some time before levels of normalcy can be derived. There is a large volume of data on population samples permitting derivation of normalcy for clinical practice. Rounded upper limits of normal can be calculated as 140/90 mm Hg for 24 h ambulatory pressure, 150/90 mm Hg for daytime pressure, and 130/80 mm Hg for nighttime pressure. There are, however, considerable differences for age and gender which need to be taken into consideration.

Ambulatory Care↗