PubMed Health⌕ Search

Biomedical subjects

E O'Brien

Publications and source records attributed to E O'Brien.

At least 55 records · Page 3Linked to original sources
PubMed1990

Inaccuracy of seven popular sphygmomanometers for home measurement of blood pressure.

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.

Blood Pressure Determination↗
PubMed1990

Twenty-four-hour ambulatory blood pressure monitoring: a review of validation data.

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.

Blood Pressure Monitors↗
PubMed1990

Evaluation of blood pressure measuring devices with special reference to 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.

Blood Pressure Monitors↗
PubMed1990

The relative accuracy of simultaneous same arm, simultaneous opposite arm and sequential same arm measurements in the validation of automated blood pressure measuring devices.

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.

Adult↗
PubMed1990

The antihypertensive efficacy of ketanserin in the elderly evaluated by ambulatory blood pressure measurement.

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.

Aged↗
PubMed1989

Abnormalities in the mechanical properties of red blood cells caused by Plasmodium falciparum.

Although changes in the mechanical properties of infected red cells may contribute to the pathophysiology of malaria, such changes have not previously been described in detail. In this study, the physical properties of individual cells from both clinical and cultured samples infected with Plasmodium falciparum were tested using micropipette aspiration techniques. Cells containing ring forms took about 50% longer to enter 3 microns pipettes compared with nonparasitised cells, and there was a similar increase in the critical pressure required to induce cell entry. These abnormalities were similar in clinical and cultured samples. More mature cultured parasites (ie, trophozoites and schizonts containing pigment) caused much greater loss of deformability, with entry time and pressure increased four to sixfold. The decrease in deformability of the ring forms was attributable to a deficit in cell surface area/volume ratio (based on micropipette measurement of the surface area and volume of individual cells) and slight stiffening of the cell membrane (shear elastic modulus increased 13%, as measured by pipette aspiration of small membrane tongues). Measurement of the rate of cell shape recovery indicated that the membrane of parasitised cells was not more viscous. The main factor in the drastic loss of deformability of the trophozoites and schizonts was the presence of the large very resistant parasite itself. Otherwise, the cell surface area/volume deficit was slightly less and membrane rigidification slightly greater compared with ring forms. The above abnormalities should cause the trophozoites and schizonts to have great difficulty in traversing splenic or marrow sinuses and could contribute to microvascular occlusion and sequestration. On the other hand, the ring forms may be expected to circulate relatively unhindered.

Animals↗
PubMed1989

Do subjects with stiff arteries have high blood pressure?

It has been argued that age-related increases in arterial stiffness could lead to spuriously high indirect blood pressure measurements, with consequent overdiagnosis of hypertension in older patients. To study the relationship between arterial stiffness and blood pressure, we identified patients with 'arterial stiffness', using Osler's manoeuvre, and compared their blood pressure levels with patients of a similar age. A total of 250 hospital inpatients were assessed independently by two doctors. In the 198 patients (79%) where both observers agreed on Osler's manoeuvre status, positive Osler's manoeuvre was uncommon under the age of 50 years but became more common thereafter, rising to 58% of patients aged over 75 years. However, blood pressure levels were similar in each age group, irrespective of Osler's manoeuvre status. We conclude that increased arterial stiffness as measured by Osler's manoeuvre is not necessarily associated with raised blood pressure levels in the elderly.

Adolescent↗
PubMed1989

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.

Adult↗
PubMed1989

A double-blind evaluation of captopril in elderly hypertensives.

To establish the role of angiotensin converting enzyme inhibitors in the management of hypertension in the elderly, 16 patients were treated with captopril in a randomized double-blind placebo-controlled cross-over study. Clinic blood pressure, ambulatory blood pressure, renal function and mental performance, with emphasis on mood and psychological well-being, were assessed. Twelve patients, aged 73 (+/- 4.4) years, completed the study. The doses of captopril used were 50 mg (11 patients) and 25 mg (one patient) twice daily for 4 weeks. Mean (+/- s.e.m.) clinic sitting blood pressure during captopril therapy was significantly lower than during administration of placebo (172 +/- 4.5/83 +/- 25 versus 188 +/- 4.4/89 +/- 3.4 mmHg; P less than 0.001/P less than 0.05). Mean ambulatory blood pressure was also significantly lower on captopril treatment than during administration of placebo (166 +/- 5.3/87 +/- 1.6 versus 179 +/- 5.1/94 +/- 2.4 mmHg; P less than 0.02/P less than 0.02) and this effect was sustained over the dosing interval. Renal blood flow and mental performance were unaltered by treatment. Gastrointestinal discomfort occurred in two patients, one of whom was withdrawn and cough developed in one patient. We conclude that captopril is effective as monotherapy in lowering blood pressure in the elderly.

Aged↗
PubMed1989

Discrepancy between clinic and ambulatory blood pressure measurement in the evaluation of two antihypertensive agents.

Discrepancies between clinic and ambulatory BP measurements may be important in the assessment of antihypertensive drug efficacy. Trimazosin (50-200 mg twice daily) and propranolol (40-160 mg twice daily) were compared in 22 hypertensive subjects in a randomised double-blind cross-over study. Daytime ambulatory BP was measured with a non-invasive portable recorder (Remler M2000). Clinic BP measurements were made with a random zero sphygmomanometer. While both drugs reduced clinic supine BP (trimazosin by 16/10 mmHg, P less than 0.01/P less than 0.001; propranolol by 25/14 mmHg, P less than 0.001/P less than 0.001), equivalent decreases on ambulatory measurement occurred with propranolol (28/11 mm/Hg, P less than 0.001/P less than 0.001) but not trimazosin (8/3 mmHg, P less than 0.05/NS). This difference in drug efficacy persisted throughout the 12-hour dosing interval. We conclude that clinic BP measurements alone cannot be relied upon to reflect accurately changes in BP induced by antihypertensive drugs. Moreover this study confirms the necessity for ambulatory BP measurement in the evaluation of antihypertensive drugs.

Ambulatory Care↗
PubMed1989

The need for a standardized protocol for validating non-invasive ambulatory blood pressure measuring devices.

Increasing interest in ambulatory blood pressure measurement has resulted in the proliferation of non-invasive measurement systems. This paper discusses the problems associated with validation of these systems. There is an urgent requirement for a standardized protocol for validation of ambulatory systems which is practicable, universally applicable and which is acceptable to investigators, publishing houses and the manufacturing industry.

Blood Pressure Determination↗