Quantitative elastography and its application to blood pressure estimation: theoretical and experimental results

Reliability and Validity of Non-invasive Blood Pressure Measurement System Using Three-Axis Tactile Force Sensor

Blood pressure (BP) is a physiological parameter reflecting hemodynamic factors and is crucial in evaluating cardiovascular disease and its prognosis. In the present study, the reliability of a non-invasive and continuous BP measurement using a three-axis tactile force sensor was verified. All the data were collected every 2 min for the short-term experiment, and every 10 min for the long-term experiment. In addition, the effects on the BP measurement of external physical factors such as the tension to the radial artery on applying the device and wrist circumference were evaluated. A high correlation between the measured BP with the proposed system and with the cuff-based non-invasive blood pressure, and reproducibility, were demonstrated. All data satisfied the Association for the Advancement of Medical Instrumentation criteria. The external physical factors did not affect the measurement results. In addition to previous research indicating the high reliability of the arterial pulse waveforms, the present results have demonstrated the reliability of numerical BP values, and this implies that the three-axis force sensor can be used as a patient monitoring device.

Real-Time Blood Pressure Estimation From Force-Measured Ultrasound

OBJECTIVE

Our objective is to create a blood pressure measurement device, which may provide a way to easily acquire frequent measurements. Common techniques to measure blood pressure include an arterial catheter, an oscillometric pressure cuff, or an auscultatory pressure cuff.

METHODS

The approach takes as input ultrasound images of an artery and contact force between the ultrasound array and subject. A subject may perform the self-measurements. Image and force data is analyzed for its quality and used to provide guidance or reject poor measurements. Tissue motions, due to probe contact forces and pulsing blood pressure, are estimated from the ultrasound image. Tissues elasticities and blood pressure are found by optimally fitting the observed tissue motion versus applied forces to a table of predicted motion-pre-generated with a finite element tissue deformation model. The output of the optimization is an estimate of systolic and diastolic blood pressure, arterial stiffness, and surrounding tissue stiffness.

RESULTS

The real-time implementation of the algorithm was validated on a cohort of 21 single-visit volunteers and on four volunteers self-monitored longitudinally. The systolic and diastolic pressures were compared to oscillometric cuff readings. Regression and Bland-Altman analyses were performed.

CONCLUSION

Systolic pressure and diastolic pressure can be estimated in real-time and by the subject using this novel non-invasive ultrasound-based method (systolic accuracy/precision: -5.2 mmHg/10.7 mmHg; diastolic accuracy/precision: -3.9/8.0 mmHg).

SIGNIFICANCE

The method occupies a middle ground between the arterial catheter and cuff-based techniques. It has the potential to give calibration-free results.

Noninvasive Blood Pressure Estimation Using Ultrasound and Simple Finite Element Models

OBJECTIVE

Many commercially available arterial blood pressure measurement devices suffer from a range of weaknesses. For example, common weaknesses include being inaccurate, invasive, and ad hoc; many also require explicit user calibration or cut off blood flow to a limb. A novel algorithmic approach is presented to accurately estimate systolic and diastolic blood pressure in a way that does not require any explicit user calibration, is noninvasive, and does not cut off blood flow.

METHODS

The approach uses ultrasound images of the arterial wall and corresponding contact force data to obtain blood pressure estimates. To acquire data, an ultrasound probe was placed on the patient's carotid artery and the contact force was increased from 1.5 to 12 N. The artery was then algorithmically segmented from the recorded DICOM B-Mode data. The segmentation data and the contact force were used as input into the Levenberg-Marquardt optimization method to solve for the parameters, including blood pressure, of a simple finite element model of the carotid artery.

RESULTS

The algorithm was validated on 24 healthy volunteers. Algorithm arterial blood pressure predictions were compared to oscillometric blood pressure cuff readings. Regression and Bland-Altman analyses were performed on the data.

CONCLUSION

Both systolic pressure and diastolic pressure can be estimated using this novel noninvasive ultrasound-based method (systolic accuracy/precision: $-$ 2.36 mmHg/10.21 mmHg; diastolic accuracy/precision: $-$ 0.32/8.23 mmHg).

SIGNIFICANCE

The method occupies a clinical middle ground between the arterial catheter and cuff-based techniques. It has the potential to give accurate results for patients with hypertension and atherosclerosis.

Arterial blood pressure estimation using ultrasound: Clinical results on healthy volunteers and a medicated hypertensive volunteer

This study presents a non-occlusive and non-invasive ultrasound-based technique to measure blood pressure. Most popular clinically-used arterial blood pressure measurement techniques suffer from important weaknesses including being inaccurate, invasive, or occlusive. In the proposed technique, an ultrasound probe is placed on the patient's carotid artery and the contact force between the probe and the tissue is slowly increased while ultrasound images and contact force data are recorded. From this data, the artery is segmented and the segmentation data is sent into an optimization procedure; after post-processing, blood pressure is displayed to the user. This technique was applied to 24 healthy single-visit volunteers, one multi-visit healthy volunteer, and one multi-visit medicated hypertensive volunteer. Compared to the oscillometric cuff, the accuracy and precision of the algorithm-reported systolic pressure is -2.4 ± 10.2 mmHg, and for diastolic pressure is -0.3 ± 8.2 mmHg. This method has the potential to occupy a clinical middle-ground between the arterial catheter and the oscillometric cuff.