Rahul Manoj, PhD

Variations in body fluids in a short time can lead to significant health issues. The risk due to body fluid variations increases for critically ill and bedridden patients. Changes in body weight in short intervals are the primary indicator of body fluid imbalances. The clinical practice for periodic monitoring of body weights of critically ill or bedridden patients includes a dedicated weighing scale or lift scale, detachable or built-in units of weighing scale on to the legs of hospital cots or as integrated bed scales attached permanently to the cot. However, these methods have limited mobility and usability in a practical setting and often require the involvement of multiple personnel to measure the body weight of a bedridden patient. Owing to such constraints, periodic monitoring of body weights is seldom recorded. In this work, we propose a novel measurement scheme for periodic monitoring of body weight. The prototype consists of an active (piston-based syringe pump) pressurized liquidfilled flexible and elastic channel sandwiched between the hospital cot and mattress. The required displacement of the syringe pump to achieve an optimal internal pressure is calibrated with the known weights. A calibration model (R2 = 0.99, p \textless 0.001) is developed that maps the displacement of the piston pump in mm to known weights in kg for the range 0 to 90 kg. Using the calibration model, the accuracy and precision of the system are characterized at various loading conditions. A practical scenario of rising body weights was emulated as an invitro-experiment, resulting in a maximum error of 3%. The design of the system is modular, so it can easily be integrated with any type of hospital bed. This design is proof of concept for using alternative technologies for weight measurement over periodic intervals, where conventional designs seem cumbersome.

Abstract The local pulse wave velocity (PWV) from large elastic arteries and its pressure-dependent changes within a cardiac cycle are potential biomarkers for cardiovascular risk stratification. However, pulse wave reflections can impair the accuracy of local PWV measurements. We propose a method to measure pressure-dependent variations in local PWV while minimizing the influence of pulse wave reflections. The PWV is computed from the pulse transit time between two forward-traveling pulse waveforms obtained across known path length, after measured/modelled flow-based wave separation analysis (WSA). An in-vivo study of 60 participants (24 female), was conducted to compare inter- and intra-cycle variations in PWV obtained from measured and forward pulse waves. For this, proximal and distal diameter waveforms from the carotid artery, along with carotid tonometry, were recorded using a custom bi-modal arterial probe. The carotid blood flow for WSA was captured with an ultrasound imaging system. The reference PWV was derived from the Bramwell-Hill equation. After WSA, the reliability of PWV measurement improved with coefficient of variation reducing from 25% to 10% near the peak of the pulse waves and matched the reference PWV with no statistically significant difference. The average PWV at foot of the pulse wave before and after WSA were comparable to the reference PWV with no statistically significant difference. The coherence of carotid pulse pressure obtained from the mean values of PWV within a cardiac cycle after WSA with that of the carotid pulse pressure from tonometry, substantiates the results obtained for reflection-free PWV. The reliability of measuring local PWV and its pressure dependent variations within a cardiac cycle is improved by combining transit-time approach with WSA.

Background: Wave separation analysis (WSA) performed at the common carotid artery (CCA) reveals insights into cerebral vascular pathophysiology; however, the conventional WSA (WSAREF) necessitates the availability of both pressure and flow waveforms measured from the same arterial site. Objective: We propose a method for performing WSA at CCA using a single pulse waveform (WSAm-RAY), by modelling the shape of the CCA flow using multi-Rayleigh curves. The WSAm-RAY reduces the measurement complexity, by modelling the flow waveform shape, targeted at scenarios with limited resources, where comprehensive equipment, specialized personnel and hospital settings are often lacking. The modelled flow was compared with the measured flow for accuracy in modelling the flow morphology. The performance of WSAm-RAY was evaluated by comparing the reflection quantification indices derived from WSAREF and WSAm-RAY. Methods: WSAm-RAY employs weighted and shifted multi-Rayleigh functions, time-optimized for characteristic flow peaks in the early and late systolic phase of the CCA flow waveform. The reliability of the modelled flow and performance of WSAm-RAY were validated on 70 (28 female) participants (age: 20 to 51 years). Continuous recording of CCA flow velocity and diameter waveforms were recorded from the participants. Results: The root-mean-squared-error in forward and backward pressure waves was 2.18 ± 0.97 mmHg (∼ 2.5% of the average mean arterial pressure of the study participants). A statistically significant and strong correlation (r > 0.76, p < 0.001) was observed among reflection quantification indices from WSAREF and WSAm-RAY. Conclusion: WSAm-RAY potentially expands the scope of vascular screenings using a single pulse measurement targeting resource constrained settings.

Jugular venous pulse (JVP) waveform contour is directly linked to right atrial hemodynamics and is a potential tool for diagnosing various cardiovascular diseases. The reference standard, central venous line catheterization, while precise, is restricted to critical care units owing to the necessity for surgical procedures and specialized operator skills. Conventional ultrasound imaging systems can reliably measure jugular venous vessel dynamics but are hindered by low operational frame rates, large form factors, and the requirement for trained operators. In this study, we propose a portable system using single-element ultrasound technology for reliable JVP waveform acquisition and methods for quantifying the JVP contour features. The performance of the system and method was validated against a reference ultrasound imaging system in a preclinical study on 65 asymptomatic volunteers (27 female). Operating at an acquisition rate of 250 Hz, the system reliably captures JVP waveforms with a temporal resolution of 4 ms. The maximum and minimum jugular venous diameter measurements showed a statistically significant and strong correlation with the reference measurements (r = 0.93 and r = 0.86, respectively, p < 0.001). The devised algorithms effectively segmented JVP cycles and analyzed their contour features with a sensitivity and specificity of 92%. These results provide preliminary evidence for the potential use of the developed system for high-fidelity JVP waveform acquisition and pulse contour feature assessment. The ability to accurately evaluate the JVP contour characteristics can provide insights into right atrial hemodynamics, potentially facilitating the early detection and monitoring of vascular anomalies.