michigan hypertension core curriculum - State of Michigan
michigan hypertension core curriculum - State of Michigan
michigan hypertension core curriculum - State of Michigan
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Figure 3. Hemodynamic Consequences <strong>of</strong> Aortic Stiffening<br />
2. Blood Pressure Measurement<br />
A variety <strong>of</strong> techniques are available for the measurement <strong>of</strong> arterial BP. The primary, though<br />
not exclusive, method used in clinical settings is indirect estimation <strong>of</strong> brachial artery pressure using an<br />
appropriately sized sphygmomanometer. The arm should be at the level <strong>of</strong> the heart with the palm facing<br />
upward. The BP cuff is inflated above the level <strong>of</strong> systolic BP by ~ 20 mm Hg. How do you know how<br />
high to inflate the BP cuff to determine the SBP level ~ 20 mm Hg above where the systolic BP likely is?<br />
Before you listen for Korotk<strong>of</strong>f sounds, apply an appropriate size cuff to the arm, inflate it until the radial<br />
pulse is no loner palpable. Now you are ready to listen for Korotk<strong>of</strong>f sounds – inflate the cuff ~ 20 mm Hg<br />
above the systolic pressure level where the radial pulse was no longer palpable. This stops all blood flow<br />
in the brachial artery. Next the cuff is gradually deflated and as the pressure inside the brachial artery<br />
exceeds that in the cuff, tapping (Korotok<strong>of</strong>f phase 1) sounds become audible. The cuff is continually<br />
deflated. However, the flow <strong>of</strong> blood through the brachial artery remains episodic until the pressure in<br />
the brachial artery during diastole exceeds the external pressure supplied exerted by the cuff. When this<br />
occurs, blood flow during becomes continuous and the tapping sounds disappear (Phase V Korotok<strong>of</strong>f<br />
sound). In some patients the Korotok<strong>of</strong>f sounds may muffle before they disappear - the BP level <strong>of</strong> this<br />
muffling is (Phase IV Korotok<strong>of</strong>f sounds). In adults, the Phase I and V Korotok<strong>of</strong>f sounds are what are<br />
recorded as the SBP and DBP, respectively.<br />
Systolic blood pressure may vary by 10 or more mm Hg between the arms in ~ 25% <strong>of</strong> hypertensives.<br />
Blood pressure values over the popliteal artery are either as high or more than 20 mm Hg higher than BP<br />
determinations obtained over the brachial artery (arm).<br />
3. Central Aortic Blood Pressure<br />
Central aortic blood pressure is typically lower than the BP level obtained clinically in the brachial<br />
artery. Central aortic blood pressure is likely to be a more important determinant <strong>of</strong> cardiovascular<br />
complications such as stroke and heart failure than peripheral (brachial) blood pressures. This is<br />
because aortic SBP is the pressure that the left ventricle ejects blood against and aortic DBP is a major<br />
determinant <strong>of</strong> coronary perfusion pressure. Moreover, central aortic pressure is the pressure that the<br />
vasculature in the brain is exposed to. Several non-invasive devices that can be used in clinical settings<br />
now allow estimation <strong>of</strong> central aortic pressure from either radial or carotid pulse waveforms using a<br />
validated generalized transfer function. Antihypertensive drugs have been shown to differentially affect<br />
central aortic blood pressure.<br />
B. Elevated or Hypertensive BP Levels<br />
Blood pressure elevations are considered <strong>hypertension</strong> at different levels <strong>of</strong> elevation dependent<br />
NKFM & MDCH 27