Influence of arm soft tissue on non-invasive blood pressure measurements: An experimental and mathematical study

We investigated the possible influence of arm soft tissue on the accuracy of blood pressure measurements performed with indirect techniques. To this end we measured arterial pressure repeatedly on 36 patients by means of an automatic procedure based on the Riva-Rocci method and controlled by a personal computer. Measurement results point out that, in about 1/3 of patients, squeezing of arm tissue by repeated cuff pressure measurements can cause a significant decrease (0.66–1.33 kPa, i.e. 5–10 mmHg) in the estimated systolic and diastolic pressure values. This phenomenon may be ascribed to alterations in the elastic properties of arm tissue.

Mathematical analyses, performed with a finite element model of the upper arm, show that pressure transmission across the arm can be significantly affected by the elastic parameters of the soft tissue, especially by a decrease in tissue compressibility. Decreasing the Poisson ratio from 0.45 to 0.3, in fact, causes a fall in pressure transmission as high as 1–2 kPa (7.5–15 mmHg).

In order to achieve individual identification of the elastic parameters of arm tissue, we developed an original non-invasive experimental procedure, based on two contiguous cuffs placed around the same upper arm and separately inflated. The possibility of achieving a unique theoretical identificability of the elastic parameters with this procedure is demonstrated.