What is central blood pressure?

Central blood pressure is the pressure in the aorta, which is the large artery into which the heart pumps. The term “central blood pressure” usually refers to the pressure in the aorta near the heart.

How is central blood pressure different from normal blood pressure?

Normally, blood pressure is measured in the upper arm, which is a “peripheral” artery. Peripheral blood pressure is usually higher than central blood pressure due to the peripheral site being closer to locations from which echoes reverberate.

The degree to which the peripheral blood pressure is higher than central blood pressure depends partly on the stiffness of the arteries.

Why is central blood pressure important?

Central pressure has been shown to more strongly relate to vascular disease and outcome than traditional upper arm blood pressure [1-3]. It also can distinguish between the effects of different hypertension medications when upper arm blood pressure and pulse wave velocity do not [4].

Central blood pressure is the pressure that the heart has to pump against to get blood to flow to the rest of the body. Higher central blood pressures mean that the heart must work harder to do its job. This can eventually lead to heart failure. Central blood pressure also determines the pressure in the blood vessels feeding the brain. If central pressure is too high, it may cause aneurysms and strokes.

How is central blood pressure measured?

Central blood pressure can be directly measured only using a pressure sensor or catheter inserted into the aorta (usually through an artery in the groin or wrist). This procedure is invasive and can lead to complications.

How does BPplus measure central blood pressure non-invasively?

BPplus calculates central blood pressure using a physics-based model of the arteries between the aorta and the cuff. These models relate how pressure waves travel between the aorta and the occluded artery under the suprasystolic cuff, as shown in the diagram on the next page. More details are available in [5].

What are the advantages of the BPplus approach to central pressure?

Central pressure is estimated non-invasively by using a mathematical relationship to a peripheral pressure. The degree to which this mathematical relationship matches any individual determines the accuracy of the central pressure estimate in that subject.

The BPPlus technique has a number of advantages over empirical transfer function and statistical attempts at estimating central blood pressure.

• Upper arm measurement means the distance between the sensor and the heart is much shorter than wrist or finger measurements, meaning less variability between the arterial geometry of individuals.
• Cuff inflated to occlude the brachial artery means individual variations in downstream arteries can be ignored.
• Physics-based model is applicable where statistical and empirical relationships are invalid. This is particularly true for stiff arteries.

Does BPplus require calibration to estimate central blood pressure?

No external calibration is necessary to estimate central blood pressure using BPplus. Instead information already collected from the upper-arm blood pressure measurement is used.

Does BPplus assume central mean and diastolic pressures?

BPplus calculates central systolic, diastolic and mean pressures. Other technologies assume central diastolic and/or mean pressures are equal to peripheral blood pressures.

How accurate are BPplus central blood pressure estimates?

Central blood pressure estimates have been independently tested against an accepted non-invasive technique for central blood pressure estimation and indicates well within the requirements of American Association for the Advancement of Medical Instrumentation (AAMI) standard SP10. Details will be available in the Proceedings of Artery 2010.

Does the central pressure estimate require patient height, age, sex etc.?

The BPplus central pressure estimate is model-based, not statistics-based and does not require the use of any other patient measurements.

Does brachial artery, arm or cuff variation affect accuracy?

The suprasystolic waveform is calibrated from the peripheral blood pressure. Variations in the arm and cuff are therefore not significant.

The brachial artery isn’t nearly as affected by cardiovascular disease as other major blood vessels and so does not influence the accuracy of the artery model in this way.

Is Augmentation Index related to Central Blood Pressure?

Both augmentation index and central blood pressure are known to increase with the age of the subject and be related to cardiovascular outcome. However, they are thought to measure different aspects of arterial stiffness.

Blood pressure plays a significant role in determining the arterial wall structure. Elevated blood pressure can lead to remodelling of the arterial structure, to compensate for changes in wall stress [6] which would affect the augmentation index.

Are cholesterol and central blood pressure related?

Cholesterol is a blood chemical indicator, which may or may not relate to functional measures of cardiovascular health such as central blood pressure. Nevertheless, some research suggests that patients with hypercholesterolemia exhibit increased central pulse pressure compared with normocholesterolemic controls [7].