A key component of measuring a manual blood pressure is an understanding of the Korotkoff phases. The Korotkoff phases have been classified as 5 phases with phases I, IV, and V integral to obtaining an accurate blood pressure.
The Korotkoff sounds are believed to originate from a combination of turbulent blood flow and oscillations of the arterial wall. Of note, some believe that using the Korotkoff sounds instead of direct intra-arterial pressure typically gives lower systolic pressures, with one study finding a 25 mmHg difference between the 2 methods in some individuals. Furthermore, some disagreement exists as to whether Korotkoff phase IV or V correlates more accurately with the diastolic blood pressure. Typically, phase V is accepted as the diastolic pressure due to both the ease of identifying phase V and the lower discrepancy between intra-arterial pressure measurements and pressures obtained using phase V. Phase IV, alternatively, is used to measure the diastolic pressure if a 10 mmHg or greater difference exists between the initiation of phase IV and phase V. This may occur in cases of high cardiac output or peripheral vasodilatation, children under 13 years old or pregnant women.
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