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Biomedical subjects

E O'Brien

Publications and source records attributed to E O'Brien.

At least 37 records · Page 2Linked to original sources
PubMed1991

The effects of age on platelet intracellular free calcium concentrations in normotensives and hypertensives.

We have investigated relationships between age, blood pressure and intracellular calcium concentration in platelets from normotensives and hypertensives. In normotensives, there were positive correlations between age and platelet intracellular calcium concentration (r = 0.76, P less than 0.001), age and mean arterial pressure (MAP; r = 0.55, P less than 0.01) and MAP and platelet intracellular calcium concentration (r = 0.45, P less than 0.01). Multiple regression analysis revealed that age was the primary determinant of platelet intracellular calcium concentration in normotensives. The effect of MAP on platelet intracellular calcium concentration when adjusted for age was not significant (P = 0.73). In hypertensives, there was no significant relationship between age and platelet intracellular calcium concentration (r = 0.15, P = 0.43), age and MAP (r = 0.17, P = 0.37) or MAP and platelet intracellular calcium concentration (r = -0.27, P = 0.15). Overall, platelet intracellular calcium concentration was significantly higher in hypertensives than in age-matched normotensives (P less than 0.05). Within the age groups examined, platelet intracellular calcium concentration was significantly higher only in younger hypertensives when compared with controls of a similar mean age (P less than 0.001). Thus, age, in addition to hypertension, is an important determinant of platelet intracellular calcium concentration.

Adult↗
PubMed1991

Ambulatory blood pressure measurement in the diagnosis and management of hypertension.

Before the diagnostic potential of 24-hour non-invasive BP measurement can be assessed, the accuracy of ambulatory recorders must be established, and normal reference values determined. The accuracy criteria of four ambulatory BP measuring systems (the SpaceLabs 90207, the Novecor DIASYS 200, the Takeda TM-2420 and the Del Mar Avionics Pressurometer IV) have been assessed according to the British Hypertension Society (BHS) protocol, and the Medilog, Suntech Accutracker II and the SpaceLabs 90202 according to the standard of the Association for the Advancement of Medical Instrumentation (AAMI). The SpaceLabs 90202 and 90207, the DIASYS 200 and the Medilog fulfilled the AAMI criteria. The best devices with the BHS grading system are the SpaceLabs 90207 and the DIASYS 200. Normal reference values for daytime, night-time and 24-hour ambulatory BP have been provided by the Allied Irish Bank study of 815 healthy individuals, which showed clear age and sex differences. The mean 24-hour ambulatory pressure for the entire group was 118/72 mm Hg. 24-hour ambulatory BP measurement possesses clear advantages over conventional clinic measurement in evaluating drug efficacy, as it provides many more readings, allowing for the possibility of reducing the number of patients in antihypertensive drug studies and eliminating the need for a placebo-controlled crossover design. It allows assessment of night-time BP, which is important in view of the fact that excessive BP reduction may put patients at risk of myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Validation requirements for ambulatory blood pressure measuring systems.

The increasing application of ambulatory blood pressure measurement in clinical practice has stimulated the manufacture of a large number of ambulatory systems which must be independently validated. The British Hypertension Society protocol for the evaluation of blood pressure measuring devices has now been used to evaluate eight ambulatory systems. Based on this experience recommendations are made for improving validation techniques for the evaluation of ambulatory devices.

Blood Pressure Monitors↗
PubMed1991

The role of twenty-four-hour ambulatory blood pressure measurement in clinical practice.

Twenty-four-hour ambulatory blood pressure monitoring is passing from research into clinical practice and it is necessary to clarify circumstances for which 24-h ambulatory measurement will be most beneficial. Devices should be accurate and reasonably priced. The operator should be able to interpret 24-h recordings and be familiar with the operation of the equipment. The subject must be capable of complying with the instructions necessary for successful use of the device. In diagnosis, 24-h ambulatory blood pressure measurement is particularly useful in deciding whether subjects with borderline hypertension have a genuinely elevated blood pressure, in identifying white-coat hypertension, in determining dipper status and in diagnosing symptomatic hypotension. In the management of antihypertensive drug treatment, the technique helps the clinician to select the drug best suited to the individual patient in terms of duration of action and suitability for the individual 24-h profile; the technique also identifies any excessive reduction in blood pressure and provides a means of assessing resistant cases of hypertension.

Antihypertensive Agents↗
PubMed1991

Clinical application of ambulatory blood pressure measurement in pregnancy.

Eclampsia and pre-eclampsia are the most important obstetric causes of maternal mortality in the Western world. The current definitions of hypertensive disorders in pregnancy rely on arbitrary blood pressure limits based on intermittent clinic readings which are subject to bias and error. Twenty-four-hour ambulatory blood pressure monitoring can overcome many of these deficiencies but has only recently been introduced into antenatal care. Five pregnancy studies using ambulatory blood pressure monitoring are currently underway in Birmingham, Glasgow, Grenoble, Oxford and Dublin. The results so far indicate that ambulatory blood pressure monitoring is an acceptable method of measuring blood pressure in pregnancy. It is also concluded that ambulatory blood pressure monitoring may have several roles in the future antenatal management of hypertension, including modification of existing classification systems, a clinical confirmatory role and a possible predictive role for pre-eclampsia.

Blood Pressure↗
PubMed1991

Ambulatory blood pressure measurement in the elderly.

A number of problems relating to clinic measurements of blood pressure may be particularly relevant to elderly patients with isolated systolic hypertension. First, there are large discrepancies in the blood pressure levels measured by these two techniques in the elderly population. Second, while blood pressure is universally accepted as one of the most important risk factors for the development of cardiovascular morbidity, its predictive value in the individual is relatively poor. Clinic and 24-h ambulatory recordings from 318 patients aged 17-80 years, diagnosed as having isolated systolic hypertension on clinic measurement, were compared with reference values determined from 815 healthy bank employees. In the isolated systolic hypertension group, mean systolic blood pressure by daytime ambulatory measurement was 27 mmHg lower than that recorded in the clinic, while diastolic pressure was similar (151 +/- 17/87 +/- 11 versus 178 +/- 28/84 +/- 9 mmHg). This discrepancy was greater in women than men, increased slightly but significantly with age (r = 0.12, P less than 0.05) and raised the crucial question as to which of the two measurements might best predict prognosis in this population. In a further study of the association between electrocardiographic (ECG) voltages and blood pressure measured in the clinic and by ambulatory monitoring in 216 patients with isolated systolic hypertension, the sum of SV1 + RV5 and the sum of SV1 + RV6 were significantly and positively related to systolic pressure both in the clinic and with daytime and night-time ambulatory measurement.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Evaluation of the SpaceLabs 90202 non-invasive ambulatory recorder according to the AAMI Standard and BHS criteria.

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.

Adult↗
PubMed1991

Ambulatory blood pressure measurement: therapeutic implications.

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.

Ambulatory Care↗
PubMed1991

A comparison of the twenty-four-hour blood pressure profile in normotensive and hypertensive subjects.

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.

Adult↗
PubMed1991

Training and assessment of observers for blood pressure measurement in hypertension research.

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)

Blood Pressure Determination↗
PubMed1990

Inaccuracy of the Hawksley random zero sphygmomanometer.

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.

Adolescent↗
PubMed1990

The British Hypertension Society protocol for the evaluation of automated and semi-automated blood pressure measuring devices with special reference to ambulatory systems.

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.

Blood Pressure Monitors↗