Hill’s sign

Myxomatous aortic valve histology – a cause of aortic insufficiency
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• Hills’s sign refers to the increased systolic blood pressure recorded in the lower limb in cases of aortic insufficiency
• Normally,  the lower limb systolic blood pressure is 10-20mm higher than the upper limb pressure
• This is appreciated only when using the indirect method of blood pressure measurement (using sphygmomanometer)
• Direct blood pressure measurement using intra arterial probes do not show the pressure difference

Mechanism of Hill’s sign:

• The increased blood pressure is the result of summation of reflected pressure waves
• The lower limb vessels are more muscular compared to the upper limb vessels
• Also they are a direct continuation of the aorta unlike the upper limb vessels which arise at a 90 degree angle
• As a result, the pressure wave is transmitted at high speed in the wall of the lower limb vessels, gets reflected at the end and summates with the incoming wave
• This results in the apparent increase in lower limb blood pressure

What happens in aortic regurgitation?

• In aortic regurgitation, the increased momentum of ejection results in greater amplitude of the pressure wave
• Hence, the pressure wave summation effects are greater resulting in increased blood pressure difference

Grading of aortic regurgitation using Hill’s sign

Severity of Aortic Regurgitation	Blood pressure difference (mm of Hg)
Mild	20-40
Moderate	40-60
Severe	>60

Image credits : Nephron