Central Aortic Systolic Pressure (CASP)
Central Aortic Systolic Pressure (CASP) is the blood pressure that is measured at the root of the aorta where it emerges from the heart pump (see figure 1). It is the largest artery in the body as blood is pumped out from the heart to the rest of the body.
The normal blood pressure measure from the arm (brachial) artery may sometimes not be reliable. For example, young people may have more compliant blood vessels wall that can give misleading high blood pressure. Conversely older people have stiffer blood vessels which could give a misleadingly low blood pressure and a much better indicator of cardiac health. CASP is therefore a better blood pressure measurement than the conventional arm (brachial) measurement.
It has been shown that CASP is a better predictor of high blood pressure effect on the various vital organs, i.e. heart, brain, kidneys and therefore correlate better with heart attack, stroke and kidney dysfunction when compared to the conventional blood pressure measurements.
The CASP is usually lower than the brachial (arm) pressure. This difference can be as much as 30 mmHg in young, healthy adults but approximates that of the arm pressure when one gets older. It also becomes closer to the arm pressure when one is suffering from conditions like high blood pressure, uncontrolled diabetes.
The increase in central blood pressure drives blood flow through the brain excessively and cause pathological changes in the large and small blood vessels supplying the brain, increasing the risk of stroke and a condition known as aneurysm which is dilatation of brain blood vessels leading to bleeding if there is a rupture of the aneurysm.
CASP is also the pressure that the heart has to pump against to get blood to flow to the rest of the body. A higher CASP therefore means the heart must work harder to do its job. This can eventually lead to thickening of the heart muscle, reduced blood supply and therefore increase the risk of heart attacks and also heart failure.
The increase in CASP similarly is associated with increased workload on the kidneys leading to renal dysfunction.
CASP can be measured non-invasively through the analysis of the radial (wrist) (see figure 2) artery pressure waveform using a special device .
Currently there are several methods of measuring CASP. The one used here involves wearing a wrist watch monitor to measure the pulse waves from the wrist. Using this pulse wave in conjunction with the systolic and diastolic blood pressure readings from the traditional inflatable cuff, this device is able to compute the CASP values with 99% correlation with the actual invasive measurement of CASP reading.
There is a normal CASP chart for Asian men and women which your doctor would use to assess your CASP.