[Reply: the factual matter is the most important].
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Biomedical subjects
Publications and source records attributed to G Sjönell.
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The outcome of a Swedish mammographic screening programme has been studied by analysis of official health statistics for 1987-96. The study series comprised 605,260 women (70 per cent of those aged 50-69 years at inclusion in the mammography programme), representing 4,908,176 woman-years, 1,932,353 mammographies, and 6,713 deaths due to breast cancer. The observed number of deaths was 55 (0.8%) less than would have been expected had the screening not been performed (ns), whereas findings in the Two County Council study suggest that the reduction in mortality should have been 28 per cent (n = 739) for the group and period studied. Thus, the cost of saving a single life was estimated to have been SEK 18-25 million (approximately GBP 1.3(1.8 m. USD 2.36(3.17 m).
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We studied 20 patients with moderate to severe obesity (body mass index 37 +/- 8 kg/m2) with obese arms (arm circumference 37 +/- 4 cm). Their blood pressure was measured directly in the brachial artery in one arm and simultaneously indirectly in the other arm using either a large standard cuff (rubber bag 12 x 35 cm) or a new cuff (the Tricuff, Pressure Group AB, Stockholm) containing three rubber bags of different sizes, which automatically selected the appropriately sized bag in relation to arm circumference. Both cuffs showed a significant overestimation of the diastolic blood pressure (standard cuff 13 mm Hg, P < .001, Tricuff 6 mm Hg, P < .01). The error of the standard cuff was significantly greater than that of the Tricuff (P < .001). The differences in systolic blood pressure between the intraarterially and the indirectly measured results were small (0.2 to 3 mm Hg) and not statistically significant with either cuff. The new Tricuff offered an advantage as compared to a large standard cuff in terms of a lesser overestimation of the diastolic blood pressure. In practical terms, this should lead to a reduction in the overestimation of diastolic hypertension in obese individuals.
Fifty-eight patients, 31 women and 27 men, with a wide range of upper arm circumferences (20-43 cm), ages (16-82 years) and body mass indices (16-55 kg m-2) were studied. The direct blood pressure was measured in the brachial artery in one arm and simultaneously the indirect pressure was measured in the other arm using a large standard cuff (rubber bag 12 x 35 cm). The mean intra-arterial blood pressure was (systolic/diastolic) 137 +/- 25 mmHg (SD)/76 +/- 10 mmHg. With the cuff the mean blood pressure was 134 +/- 23 mmHg/85 +/- 11 mmHg. The cuff significantly underestimated the systolic blood pressure (3.2 +/- 11.4 mmHg, range -25-30 mmHg) while the diastolic pressure was overestimated significantly (8.8 +/- 8.5 mmHg, range -32-14 mmHg). The direct/indirect blood pressure difference correlated significantly to the intra-arterial systolic and diastolic pressures (systolic/diastolic; r = 0.44, P = 0.0006/r = 0.36, P = 0.0062), but only to the auscultatory diastolic pressure (r = -0.02, P = 0.9/r = -0.45, P = 0.0004). The direct/indirect difference correlated significantly to the arm circumference (r = -0.33, P = 0.01/r = -0.30, P = 0.02) as did the diastolic direct/indirect difference to pulse rate (r = 0.34, P = 0.009). Age did not correlate significantly to the direct/indirect blood pressure difference in this study (r = -0.02, P = 0.9/r = -0.10, P = 0.5). It can be concluded that in addition to the ratio between the arm circumference and the width of the cuff (rubber bag), there are other sources of systematic errors of indirect blood pressure measurement, in particular pulse rate and the level of indirect blood pressure. If corrections could be made with regard to these variables, it is obvious that the reliability of the indirect method, especially when used in epidemiological contexts, would increase.
This study compares blood pressures measured with a standard cuff (rubber bag 12 x 35 cm) with concomitantly measured intra-arterial pressures in 48 subjects. With the standard cuff, and using a diagnostic cut-off limit for diastolic hypertension of 90 mmHg, 15/48 patients were found to be hypertensive, whereas only 4/48 had intraarterial pressure above 90 mmHg. Thus, the specificity of the non-invasive method was only 75%. If higher diagnostic cut-off limits were used, e.g. 95 mmHg, specificity increased to 84%, and with lower cut-offs specificity was 63% for 85 mmHg and 52% for 80 mmHg. A specificity of only 75% is very poor for a method commonly used in screening examinations and may lead to considerable over-diagnosis of mild hypertension.
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