The more precise and sensitive auscultatory method is utilized to measure systolic pressure and estimate diastolic pressure. By applying a stethoscope to the skin of the antecubital space over the brachial artery, the practitioner listens for specific sounds. When the pressure in the cuff surpasses systolic pressure, the brachial artery is blocked, resulting in the absence of sounds. As the inflation pressure falls just below the systolic level, a small amount of blood escapes the cuff's occluding pressure, producing tapping sounds known as Korotkoff sounds. The pressure at which the first sound is heard represents systolic pressure and is closely aligned with the directly measured systolic pressure. As the cuff's inflation pressure continues to decrease, more blood escapes per beat, leading to louder sounds. When the inflation pressure approaches the diastolic level, the Korotkoff sounds become muted. When the inflation pressure falls just below the diastolic level, the sounds disappear, indicating diastolic pressure. The origin of the Korotkoff sounds is the result of intermittent blood spurts passing under the cuff and encountering a stationary column of blood beyond the cuff, generating audible vibrations. Once the inflation pressure falls below the diastolic pressure, blood flow becomes continuous in the brachial artery, and no sounds are heard. 

Veins play a vital role in returning blood from tissues back to the heart and serve as a large reservoir, containing up to 70% of the blood in circulation. This reservoir function allows veins to adjust the volume of blood returning to the heart, also known as preload, in order to meet the body's needs when cardiac output is altered. This high capacitance is a crucial characteristic of veins.

The ankle-brachial index (ABI) is a measurement of the ratio between the systolic blood pressures at the ankle (dorsalis pedis artery) and the brachial artery. The ABI is a simple indicator of potential peripheral artery disease and has also been proposed as a predictor of cardiovascular and cerebrovascular disease risk. Individuals with a normal ABI ratio of 1.1 to 1.4 have a lower incidence of coronary or cerebrovascular events compared to those with a ratio of 0.9 or lower. Additionally, as the ABI ratio increases over time, the incidences of cardiovascular morbidity and mortality also increase.
The auscultatory method is a more sensitive and therefore more precise technique for measuring systolic pressure, and it also enables diastolic pressure to be estimated. The practitioner listens with a stethoscope applied to the skin of the antecubital space over the brachial artery. While the pressure in the cuff exceeds systolic pressure, the brachial artery is occluded, and no sounds are heard (see
Fig.
17.20B ). When the inflation pressure falls just below the systolic level (120 mm Hg in
Fig. 17.20A ), a small spurt of blood escapes the occluding pressure of the cuff, and slight tapping sounds (called Korotkoff sounds) are heard with each heartbeat. The pressure at which the first sound is detected •Fig. 17.19 Pulse Pressure Curves Recorded From Various Sites in the Arterial Trees of Humans at Different Ages. Inthe24-yearold,thearterialpulsedisplaysstrikingchangesinthepulsepressureamplitudeandcontourasitpassesdownthearterialtree.Thepulsepressurewaveinthe68-year-oldshowslittleamplificationandisrelativelyunchangedasthepulsetravelsbecausethereislesswavereflection.(ReproducedbypermissionofHodderEducationfromNicholsWW,O’RourkeM,eds.McDonald’s Blood Flow in Arteries: Theoretical, Experimental and Clinical Principles. 5thed.London:Arnold;2005.) represents systolic pressure. It usually corresponds closely to the directly measured systolic pressure. As the inflation pressure of the cuff continues to fall, more blood escapes under the cuff per beat and the sounds become louder. When the inflation pressure approaches the diastolic level, the Korotkoff sounds become muffled. When the inflation pressure falls just below the diastolic level (80 mm Hg in
Fig. 17.20A ), the sounds disappear; the pressure reading at this point indicates diastolic pressure. The origin of the Korotkoff sounds is related to the discontinuous spurts of blood that pass under the cuff and meet a static column of blood beyond the cuff; the impact and turbulence generate audible vibrations. Once the inflation pressure is less than diastolic pressure, flow is continuous in the brachial artery, and sounds are no longer heard (see
Fig. 17.20C
The Venous System
Veins are elements of the circulatory system that return blood to the heart from tissues. Moreover, veins constitute a very large reservoir that contains up to 70% of the blood in the circulation. The reservoir function of veins makes them able to adjust the volume of blood returning to the heart,
Theankle-brachialindex(ABI)istheratioofsystolicbloodpressuresattheankle(dorsalispedisartery)tothatinthebrachialartery.TheABI,whichisobtainedbysimplemeasurements,isanindicatorofpossibleperipheralarterydisease.TheABIhasalsobeenproposedasapredictorofriskforcardiovascularandcerebrovasculardisease.PeoplewithanormalABIratioof1.1to1.4havealowerincidenceofeithercoronaryorcerebrovasculareventsthandothosewitharatioof0.9orlower.Inaddition,astherateofABIincreaseswithtime,theincidencesofcardiovascularmorbidityandmortalityalsoincrease.
or preload, so that the needs of the body can be matched when cardiac output is altered (see
Chapter 19). This high capacitance is an important property of veins.