| Summary: | Background: Mean arterial pressure (MAP) is required for many hemodynamic calculations. Most automated devices do not report MAP and a form factor (FF) is used to estimate it from systolic and diastolic blood pressure (BP). The appropriate choice of FF in the brachial artery is controversial: 0.33 is the traditional value, but invasive measurements report a value of 0.4. [1] Non-invasive studies have provided some support for FF = 0.4 but have usually not measured MAP directly, nor used brachial blood pressure waveforms, or accounted for BP measurement errors. We addressed these issues in a sample of white Europeans drawn from the Southall and Brent Revisited study.
Methods: BP was measured using a Pulsecor device (USCOM). Form factors (FFosc and FFwave) were calculated as (MAP-diastolic BP)/(systolic BP-diastolic BP) using MAPosc calculated by oscillometry and MAPwave calculated as the waveform mean respectively.
Results: Data are mean ± SD of 527 observations (Table 1). FFosc was lower than FFwave and use of FF = 0.4 (MAP0.4) overestimated MAPosc. Allowing for measurement errors based on [2–3] gave estimates of MAPwave that were more similar to MAPosc.
Conclusions: Measurement errors confound estimation of MAP using FF. Measurement errors vary substantially between devices [4] precluding a single FF for all studies. Non-invasive MAP should be estimated by oscillometric methods.
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