Auscultatory gap

An auscultatory gap is the interval of pressure where Korotkoff sounds indicating true systolic pressure fade away and reappear at a lower pressure point during the manual measurement of blood pressure. The improper interpretation of this gap may lead to blood pressure monitoring errors: namely, an underestimation of systolic blood pressure and/or an overestimation of diastolic blood pressure.

The auscultatory gap can be mistaken for the silence that occurs when the cuff pressure exceeds the systolic pressure. In this setting, the true systolic pressure can be elucidated by palpating the radial artery pulse. It is therefore recommended to palpate and auscultate when manually recording a patient's blood pressure. Typically the blood pressure obtained via palpation is around 10 mmHg lower than the pressure obtained via auscultation. In general, the examiner can avoid being confused by an auscultatory gap by always inflating a blood pressure cuff to 20-40 mmHg higher than the pressure required to occlude the brachial pulse.

There is evidence that auscultatory gaps are related to carotid atherosclerosis and to increased arterial stiffness in hypertensive patients, independent of age. Another cause is believed to be venous congestion within the limb that is being used for the measurement. Although these observations need to be confirmed prospectively, they suggest that auscultatory gaps may have prognostic relevance.