A reasonable correlation exists between invasive and non-invasive methods of measuring systemic blood pressure. However, there are frequent individual differences between these methods and these variations have often caused the validity of the non-invasive measurement to be questioned. The hypothesis that certain invasive systolic blood pressures may represent a pressure impulse rather than a flow-generating pressure was used to classify the invasive pulse pressure contour into various types,

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... d the invasive pressure measurement was then correlated with the non-invasive. There was a significantly greater difference between these two methods of measuring systolic blood pressure in patients exhibiting prominent inotropic pressure pulse phenomena compared with patients without such phenomena. Since non-invasive monitors measure blood pressure by volume displacement or flow detection and invasive ones measure pressure impulses rather than flow, it was concluded that the pressure measured by the non-invasive monitor more accurately reflects the propulsive pressure-causing flow when inotropic pressure pulse phenomena are present.