Noninvasive monitoring of elevated intramuscular pressure in a model compartment syndrome via quantitative fascial motion

Abstract

Compartment syndromes, conditions of elevated intramuscular pressure (IMP) resulting from trauma or chronic overuse, frequently require invasive IMP monitoring for accurate diagnosis. Our objective was to test a noninvasive ultrasound technique for estimating IMP based on fascial displacement waveforms from arterial blood pressure pulses. IMP was increased in the legs of 23 healthy adult subjects up to 80 mmHg using two blood pressure cuffs covering the region from the knee to the ankle. Receiver operator characteristic curves and recursive partitioning were used to determine the sensitivity and specificity of diagnosing elevated IMP using fascial displacement. For one curve, in which several ultrasonic measurement parameters were used along with subject body mass index and blood pressure, the sensitivity and specificity for diagnosing normal IMP (below 30 mmHg) from elevated IMP (30 mmHg and up) was 0.61 and 0.94, respectively. Recursive partitioning, in which IMP was divided into three ranges (normal <30 mmHg, midrange of 30-40 mmHg, and elevated >or=50 mmHg), resulted in improved diagnostic sensitivity (0.77) with almost no change in specificity (0.93).

Figures

Figure 1

Tissue displacement waveform displayed over a five second interval.

Figure 2

Comparison of the mean displacement amplitude (top left) on the cuffed leg (dark) versus the uncuffed leg (light) at each pressure level over the 23 individuals tested. Similar comparisons of the displacement harmonic ratio (top right), mean backscatter amplitude (bottom left), and mean backscatter harmonic ratio (bottom right) are also provided.

Figure 3

Sensitivity and specificity measurements using a full effect model ROC curves (left), an ROC curve based on displacement amplitude only (middle) and recursive partitioning (right). The area under the curve for the first ROC curve was 0.83, while for the second it was 0.82.

Figure 4

Example tissue displacement readings for two individuals tested. The decrease in tissue displacement at pressures of 70 mmHg and 80 mmHg that occur in the first subject (left) appear to be linked to low blood pressure, as the first subject had a blood pressure of 112/46 while the second subject had a blood pressure of 116/75.