Characterization of Perineum Elasticity and Pubic Bone-Perineal Critical Distance with a Novel Tactile Probe: Results of an Intraobserver Reproducibility Study

Non-Invasive Radial Artery Blood Pressure Monitoring Using Error Compensated Tactile Sensors and Patient Specific Oscillometry

This paper presents a new method of measuring non-invasive blood pressure at the radial artery based on oscillometry and tonometry. A localized capacitive tactile sensor array is used with a novel algorithm based on waveform features for optimizing oscillometry ratios. A novel tonometer is presented with typically 1% base measurement error, with sensor errors compensated using a custom error model, and applied to blood pressure measurement at the radial artery. The tonometer gives a direct arterial waveform, and uses a manual pressure sweep to determine blood pressure. Key points on the oscillogram are correlated with optimal ratios for minimizing mean errors and standard deviation for an individual. This paper details an initial assessment into the dominant sources of error, for the purpose of determining feasibility and directing future research. Over a limited clinical trial of N_p = 20, No = 180, the reported BP accuracy is MAE = 0.61/0.38mmHg and 1SD = 7.14/5.91mmHg for systolic and diastolic measurements respectively. The average load on the patient is in the order of 5N, compared with around 1000N for a brachial cuff, which represents a clear improvement in patient comfort. This is a positive result, indicating larger scale performance within AAMI and BHS standards, and stands as a useful benchmark for further development of the system into a clinical product for rapid and comfortable BP measurement. Clinical Relevance This paper demonstrated that direct tonometry can measure blood pressure if sensor error is compensated by the designer. This method uses 200x less load than conventional cuffs suitable for long term and supine use.

Feasibility and safety of antepartum tactile imaging

Introduction and hypothesis

Quantitative characterization of the birth canal and critical structures before delivery may provide risk assessment for maternal birth injury. The objective of this study was to explore imaging capability of an antepartum tactile imaging (ATI) probe.

Methods

Twenty randomly selected women older than 21 years with completed 35th week of pregnancy and a premise of vaginal delivery were enrolled in the feasibility study. The biomechanical data were acquired using the ATI probe with a double-curved surface, shaped according to the fetal skull and equipped with 168 tactile sensors and an electromagnetic motion tracking sensor. Software package COMSOL Multiphysics was used for finite element modeling. Subjects were asked for assessment of pain and comfort levels experienced during the ATI examination.

Results

All 20 nulliparous women were successfully examined with the ATI. Mean age was 27.8 ± 4.1 years, BMI 30.7 ± 5.8, and week of pregnancy 38.8 ± 1.4. Biomechanical mapping with the ATI allowed real-time observation of the probe location, applied load to the vaginal walls, and a 3D tactile image composition. The nonlinear finite element model describing the stress–strain relationship of the pelvic tissue was developed and used for calculation of Young’s modulus (E). Average perineal elastic modulus was 11.1 ± 4.3 kPa, levator ani 4.8 ± 2.4 kPa, and symphysis–perineum distance was 30.1 ± 6.9 mm. The pain assessment level for the ATI examination was 2.1 ± 0.8 (scale 1–4); the comfort level was 2.05 ± 0.69 (scale 1–3).

Conclusions

The antepartum examination with the ATI probe allowed measurement of the tissue elasticity and anatomical distances. The pain level was low and the comfort level was comparable with manual palpation.