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

Image credits : Nephron