It is proposed that the maximum in cuff pressure oscillations during oscillometry is due to the buckling of the brachial artery under a cuff. This theory is investigated by means of a mathematical model of oscillatometry that includes the mechanics of the occlusive arm cuff, the arterial pressure pulse waveform, and the mechanics of the brachial artery. A numerical solution is provided for the oscillations in cuff pressure for one cycle of cuff inflation and deflation. The buckling pressure is determined from actual arterial data and the von Mises buckling criteria. The buckling of an artery under a cuff occurs near -2 to 0 mm Hg transmural pressure. This effect corresponds with a maximum arterial compliance and maximum cuff pressure oscillations when cuff pressure is nearly equal to mean arterial pressure (MAP), in support of the suggested theory. The model was also found to demonstrate the basic characteristics of experimental oscillometry, such as an increasing and decreasing amplitude in oscillations as cuff pressure decreases, the oscillations that occur when cuff pressure is above systolic pressure, maximum oscillation amplitudes in the range of 1 to 4 mm Hg, and an oscillatory maximum at cuff pressure equal to MAP. These findings support the case that the model is representative of oscillometry. Finally, the model predicted values for the systolic and diastolic detection ratios of 0.593 and 0.717, respectively, similar to those found empirically. These ratios alter with blood pressure, but the tightness of the cuff wrap did not change their value.

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The role that the pattern of vessel wall growth plays in determining pressure-lumen area (P-A) and pressure-compliance curves was examined. A P-A vessel model was developed that encompasses the complete range of pressure, including negative values, and accounts for size given the fixed length, nonlinear elastic wall properties, constant wall area, and collapse. Data were obtained from excised canine carotid and femoral arteries, jugular veins, and elastic tubing. The mean error of estimate was 8 mmHg for all vessels studied and 2 mmHg for blood vessels. The P-A model was employed to examine two patterns of arterial wall thickening, outward growth and remodeling (constant wall area), under the assumption of constant wall properties. The model predicted that only outward wall growth resets compliance such that it increases at a given arterial pressure, explaining previously contradictory data. In addition, it was found that outward wall growth increases the lumen area between normal and high pressures. Remodeling resulted in lumen narrowing and a decrease in compliance for positive pressures.