Biomedical subjects
Publications and source records attributed to E O'Brien.
Explore the source record for details and available documents.
The SpaceLabs 90202, a non-invasive ambulatory blood pressure recorder for the measurement of 24 hr blood pressure, was assessed according to the standard of the Association for the Advancement of Medical Instrumentation (AAMI) and the grading criteria of the British Hypertension Society (BHS) protocol were applied to the results. Two observers measured BP simultaneously in the same arm with the SpaceLabs 90202 and a standard mercury sphygmomanometer at 4 mmHg deflation steps in 85 subjects [age range 22-79 years, BP range 96-212 mmHg (systolic) and 52-134 mmHg (diastolic)]. The mean difference was -2 +/- 5 mmHg (systolic) and -2 +/- 5 mmHg (diastolic). The mean difference (+/- SD) between observers was 1 +/- 3 (systolic) and -2 +/- 3 (diastolic). The SpaceLabs 90202 fulfills the criteria of the AAMI standard (5 +/- 8 mmHg) and a B grading for both systolic and diastolic pressure is achieved with the BHS criteria.
Conventional clinic measurement of blood pressure has many deficiencies, among which the most significant are its inability to indicate the duration of drug effect, or the influence of antihypertensive drugs on nocturnal blood pressure. The technique is, therefore, unreliable for assessing antihypertensive drug efficacy, either in clinical practice or hypertension research. Non-invasive 24 h ambulatory blood pressure measurement has a number of advantages over conventional measurement. In clinical practice it provides a profile of blood pressure over the 24 h period permitting the selection of the most appropriate antihypertensive drug for the individual patient. In studies of antihypertensive drug effect, ambulatory measurement detects white coat responders and, being free of regression to the mean and the placebo response, it is possible to consider efficacy studies which need not have a placebo phase. By providing considerably more observations than can be obtained with clinic measurement, ambulatory measurement increases the power of studies making it likely that fewer numbers of patients are needed for antihypertensive drug studies. 24 h ambulatory blood pressure measurement offers the opportunity to study antihypertensive drugs in fewer patients with greater accuracy than is possible with conventional clinic measurement and should be a mandatory requirement for such studies.
The aim of this study was to assess the relationship between blood pressure measured conventionally ('conventional' pressure) and 24 h ambulatory blood pressure measured with the SpaceLabs 90202 recorder, in a control population with normal blood pressure, and in patients with hypertension. Reference values for 24 h ambulatory blood pressure had been determined previously in a control population of 776 healthy bank employees (396 men and 380 women), aged 17-80 years, and were compared with those from a clinic population which comprised 805 patients referred to a blood pressure clinic for evaluation of hypertension. The clinic population was divided into two groups: 'normotensive' patients, whose conventional blood pressure was less than 160/90 mmHg (n = 168), and 'hypertensive' patients, whose conventional blood pressure was greater than or equal to 160/90 mmHg (n = 637). The clinic population had higher conventional (156/87 versus 119/76 mmHg), daytime (147/90 versus 125/79 mmHg) and night-time (129/75 versus 106/61 mmHg) ambulatory pressures compared with the control population. The clinic 'hypertensive' patients had higher conventional (175/97 versus 136/77 mmHg), daytime (153/93 versus 140/87 mmHg) and night-time (133/78 versus 124/72 mmHg) ambulatory pressures than the clinic normotensive population. Daytime ambulatory pressure was higher than conventional pressure (125/79 versus 119/76 mmHg) in the control population and in the clinic normotensive population (140/87 versus 136/77 mmHg). However, this relationship was reversed in the clinic hypertensive patients (153/93 versus 175/97 mmHg). It is concluded that while conventionally measured blood pressure tends to be lower than ambulatory daytime pressure in normotensive populations, this relationship is reversed in patients with hypertension.
Eight nurses were re-trained in the technique of measuring blood pressure firstly with an audiotape and secondly with a video and expert instruction. They were then assessed for accuracy in measurement in subjects with a range of BP. In the first session with the audiotape, criteria for accuracy were that the difference in readings (systolic and diastolic) between each pair of observers was to be 5 mm Hg or less in at least 85% and 10 mm Hg or less in at least 95% of the readings. Five out of the 28 observer pairs (18%) fulfilled these criteria for both systolic and diastolic pressures, six (21%) satisfied the criteria for systolic pressure and nine (32%) for diastolic pressure with eighteen pairs (64%) failing to meet the criteria for both systolic and diastolic pressure. In the second training session seven of the original eight observers underwent further training in which the audio-tape was replaced by the British Hypertension Society video and instruction was also given by an expert. The same requirements for accuracy were used except that, in addition, the difference between the trainee observer and the expert had to be within 5 mm Hg in at least 90% and within 10 mm Hg in at least 95% of the readings. Eighteen of the 21 observer pairs (86%) achieved the accuracy criteria, with the remaining three (14%) failing on diastolic pressure only. All seven observers were within the required criteria when assessed against the expert observer. It is concluded that training of observers is more effective with a video and expert instruction than by using audio-tapes.(ABSTRACT TRUNCATED AT 250 WORDS)
To examine the accuracy of the Hawksley random zero sphygmomanometer two studies were done with subjects with a wide range of blood pressure. When readings made by one observer on the UK model of the Hawksley sphygmomanometer were compared with readings by two independent observers on separate mercury sphygmomanometers, the Hawksley device underestimated systolic readings by a mean (SD) of 2.0 (2.4) and 0.5 (3.6) mm Hg and diastolic readings by a mean of 3.7 (2.7) and 2.8 (2.9) mm Hg. When readings made on the UK and US models of the Hawksley sphygmomanometer were compared with those made on mercury sphygmomanometers, with observers exchanging devices half way during the experiment, the UK Hawksley device underestimated systolic pressure by a mean of 3.8 (SD 3.5) mm Hg and diastolic blood pressure by 7.5 (3.8) mm Hg; and the US model by 2.6 (3.4) mm Hg for systolic pressure and 6.2 (3.7) mm Hg for diastolic pressure. There was better agreement between two observers using standard sphygmomanometers than between an observer using the Hawksley random zero sphygmomanometer and an observer using a standard sphygmomanometer. Thus, the quantitative aspects of blood pressure in epidemiological and intervention studies in which the Hawksley random zero sphygmomanometer was used need re-evaluation. Moreover, the Hawksley random zero sphygmomanometer, in its present design, should not be used in hypertension research.
Explore the source record for details and available documents.
With the increasing manufacture of expensive systems for the measurement of ambulatory blood pressure there is a need for potential purchasers to be able to satisfy themselves that the systems have been evaluated according to agreed criteria. The British Hypertension Society has, therefore, drawn up a protocol of requirements for the evaluation of these devices. This protocol incorporates many features of the American National Standard for Non-Automated Sphygmomanometers but includes many additional features, such as strict criteria for observer training, interdevice variability testing before and after a month of ambulatory use, and a new system of analysis which permits the test system to be graded. It is recommended that manufacturers of ambulatory blood pressure measuring devices should obtain an unbiased evaluation according to a recognized standard before a device is marketed.
Seven models, available commercially for the self-measurement of blood pressure, were subjected to a validation procedure in which three devices of each model were tested by observers who were trained to a high standard of accuracy. The models were the Omron HEM-400C, the Philips HP5308, the Healthcheck 'Cuffless' CX-5 060020, the Nissei Analogue Monitor, the Philips HP5306/B, the Systema Dr MI-150 and the Fortec Dr MI-100. The validation programme had a number of unique features which included assessment of interdevice variability before and after 1 month of home use, and a new form of analysis, which we term 'clinical', based on the likely influence of three grades of device inaccuracy on patient management. In the main validation phase, one device of each model was compared with simultaneous measurements made by two 'blinded' observers using a standard mercury sphygmomanometer (PyMaH Corporation, New Jersey, USA) in the same arm in 85 subjects with a wide range of blood pressures. Three models (the Healthcheck 'Cuffless' CX-5 060020, the Systema Dr MI-150 and the Fortec Dr MI-100) failed the interdevice variability tests and did not reach the main validation test. Two models (the Omron HEM-400C and the Philips HP5306/B) failed on the criteria set down by the American National Standard for Electronic or Automated Sphygmomanometers, as well as the 'clinical' criteria. The remaining two models (the Nissei Analogue Monitor and the Philips HP5308) were acceptable for the measurement of systolic blood pressure by both methods of analysis but failed in the 'clinical' analysis for diastolic blood pressure. The mercury sphygmomanometer was comfortably within the criteria for both methods of analysis.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
As the clinical applications for 24-h ambulatory blood pressure monitoring expand, market demands increase, and there are now at least 13 manufacturers producing elaborate and expensive systems for recording 24-h ambulatory pressures. It is often difficult to assess the accuracy and performance characteristics of these devices and failure to standardize validation makes it difficult to compare one system with another. The standard of the Association for the Advancement of Medical Instrumentation (AAMI) and the recently published protocol of the British Hypertension Society (BHS) provide standardized validation procedures which allow comparisons to be made between ambulatory devices. Thirty-three published reports on 18 ambulatory systems are listed. Five of these systems have been validated according to the AAMI standard; of these, the SpaceLabs 90202 and the Medilog have satisfied the standard, and the Pressurometer IV, the Accutracker II and the Takeda TM-2420 did not satisfy the AAMI standard. The results of recent validations of the SpaceLabs 90207, the Diasys 200, the Takeda TM-2420 and the Pressurometer IV according to the BHS protocol are awaited and should provide further data that will allow comparisons of the performance and the accuracy of different ambulatory systems.
As ambulatory blood pressure measurement becomes more widely accepted in hypertension research and in the clinical management of high blood pressure, the number of devices available on the market has increased considerably, reflecting the clinical demand. These devices are expensive, both in terms of capital and running costs. As we rely increasingly on data produced by ambulatory systems, it becomes increasingly important that they be shown to be accurate. Initially protocols for the validation of ambulatory devices were designed on an ad hoc basis, so that many studies were inadequately designed and comparison of data between studies was usually impossible. The American National Standard published by the Association for the Advancement of Medical Instrumentation (AAMI) remedied this situation in part, and the recent publication of the British Hypertension Society (BHS) protocol for the validation of ambulatory systems has further advanced the demand for accuracy. The BHS protocol includes most of the AMMI standard recommendations, but in addition there are sections on observer training, in-use assessment and inter-device variability. In addition, performance characteristics, computer facilities and details on such practical matters as cost and maintenance are sought. Finally, the BHS protocol provides a grading system of validation which allows comparisons between devices and studies.
With the increasing demand for accurate BP measuring devices there comes also the need for validation. Most validation procedures assess the accuracy of a test device against a known standard, most commonly a mercury sphygmomanometer. The best method for assessing device accuracy is to measure BP simultaneously in the same arm with the test device and a mercury sphygmomanometer. This is not always possible because the deflation mechanism of the test device interferes with the ability of an observer to auscultate the Korotkov sounds accurately. In this study a mathematical method of sequential comparison between the test device and a mercury standard in the same arm is described which is almost as accurate as simultaneous measurement in the same arm.
To assess the role of the serotonin antagonist ketanserin in the management of hypertension in the elderly, 12 patients with a mean age of 68 years (range 60-79 years) were treated with ketanserin in a randomised double-blind placebo-controlled cross-over trial. Clinic BP, ambulatory BP, renal function, and pharmacokinetics were assessed. The doses of ketanserin used were 40 mg (ten patients) and 20 mg (two patients) twice daily for 8 weeks. Mean clinic sitting BP was reduced from 169 +/- 5/98 +/- 2 on placebo to 155 +/- 5/88 +/- 3 mmHg (NS/P less than 0.05/P less than 0.05) and standing pressure from 168 +/- 6/100 +/- 3 to 157 +/- 5/91 +/- 3 mmHg (NS/P less than 0.01). Mean ambulatory systolic BP was unaffected by active treatment (167 +/- 7 vs 164 +/- 5) while diastolic pressure was lowered from 99 +/- 2 to 94 +/- 2 mmHg (P less than 0.05). This effect appeared to be mainly confined to the first two hours after drug administration. Renal blood flow was unaltered by treatment. The mean plasma half-life of ketanserin was 20.9 +/- 5.5 hours. Side effects were minimal. In conclusion, while ketanserin may be effective as assessed in the clinic, its efficacy on ambulatory monitoring is substantially less impressive.
Explore the source record for details and available documents.
Explore the source record for details and available documents.