Implementing Effective Noise Reduction Techniques in Implantable NIRS Sensors.

Near-Infrared Spectroscopy (NIRS) is a noninvasive optical method widely used for evaluating tissue hemodynamics and various physiological characteristics. Despite its advantages, NIRS faces limitations in light sampling depth and spatial resolution, which has led to the development of implantable NIRS sensors. However, these implantable sensors are prone to Common-Mode Voltage (CMV) interference due to their increased sensor-to-tissue capacitance, which can compromise the signal-to-noise ratio and accuracy of measurements.In this paper, we present a novel active CMV reduction technique that enhances the signal-to-noise ratio of NIRS signals. We propose an electrical model of a patient's body and NIRS sensor to characterize the CMV interference and the active CMV cancellation (ACC) electronic circuit. The ACC circuit measures CMV through a common-mode amplifier, which then inverts and introduces the amplified signal to the patient's body via an additional surface electrode. This technique effectively attenuates the CMV (50 and 60 Hz) by 80 to 90 dB, significantly improving the signal quality without causing system instability.The method has been validated through both analytical simulations and experimental measurements, demonstrating the circuit's ability to suppress CMV within a bandwidth of 0.1 to 100 Hz. Experimental verification of the active noise cancellation method was conducted by recording data from the fingertip and palm, showing effective suppression of the CMV. The proposed method has substantial clinical relevance as it enhances the reliability and accuracy of implantable NIRS sensors, enabling more precise monitoring of internal organs and improved patient care.

The effect of cardiac output on the pharmacokinetics and pharmacodynamics of propofol during closed-loop induction of anesthesia.

BACKGROUND AND OBJECTIVE: Intraoperative hemodynamic stability is essential to safety and post-operative well-being of patients and should be optimized in closed-loop control of anesthesia. Cardiovascular changes inducing variations in pharmacokinetics may require dose modification. Rigorous investigational tools can strengthen current knowledge of the anesthesiologists and support clinical practice. We quantify the cardiovascular response of high-risk patients to closed-loop anesthesia and propose a new application of physiologically-based pharmacokinetic-pharmacodynamic (PBPK-PD) simulations to examine the effect of hemodynamic changes on the depth of hypnosis (DoH). METHODS: We evaluate clinical hemodynamic changes in response to anesthesia induction in high-risk patients from a study on closed-loop anesthesia. We develop and validate a PBPK-PD model to simulate the effect of changes in cardiac output (CO) on plasma levels and DoH. The wavelet-based anesthetic value for central nervous system monitoring index (WAVCNS) is used as clinical end-point of propofol hypnotic effect. RESULTS: The median (interquartile range, IQR) changes in CO and arterial pressure (AP), 3 min after induction of anesthesia, are 22.43 (14.82-36.0) % and 26.60 (22.39-35.33) % respectively. The decrease in heart rate (HR) is less marked, i.e. 8.82 (4.94-12.68) %. The cardiovascular response is comparable or less enhanced than in manual propofol induction studies. PBPK simulations show that the marked decrease in CO coincides with high predicted plasma levels and deep levels of hypnosis, i.e. WAVCNS < 40. PD model identification is improved using the PBPK model rather than a standard three-compartment PK model. PD simulations reveal that a 30% drop in CO can cause a 30% change in WAVCNS. CONCLUSIONS: Significant CO drops produce increased predicted plasma concentrations corresponding to deeper anesthesia, which is potentially dangerous for elderly patients. PBPK-PD model simulations allow studying and quantifying these effects to improve clinical practice.

Reversal of neuromuscular blockade with sugammadex during continuous administration of anaesthetic agents: a double-blind randomised crossover study using the bispectral index.

Sugammadex, a specific reversal agent for steroidal neuromuscular blocking drugs, has on occasion been reported to be associated with clinical signs of awakening. We performed a study to systematically search for an increase in bispectral index values and signs of awakening in patients maintained under general anaesthesia following sugammadex administration. Patients, scheduled to receive general anaesthesia with neuromuscular blockade, were included in this double-blind randomised crossover study. After surgery was completed, and while the train-of-four ratio was zero, intravenous anaesthesia was continued with the aim of maintaining the bispectral index in the range of 40-60. Patients then received either sugammadex 4 mg.kg-1 or saline. In cases of incomplete reversal of neuromuscular blockade after 5 min, patients received the other drug. Bispectral index and train-of-four monitoring were recorded every minute and clinical signs of awakening noted. Fifty-one patients completed the study. Median (IQR [range]) bispectral index values increased after sugammadex administration from 49 (43-53 [38-64]) to 63 (53-80 [45-97]) (p < 0.01) with an increase of ≥ 20 in 22 patients; 14 (27%) patients had clinical signs of awakening. Saline had no effect on bispectral index values, clinical signs of awakening or degree of neuromuscular blockade. This study confirms that reversal of neuromuscular blockade with sugammadex may be associated with clinical signs of awakening despite maintenance of anaesthesia. Intravenous anaesthesia should be maintained until complete recovery of muscle function is achieved, especially when sugammadex is administered.

Patient and health care professional perspectives on using telehealth to deliver pulmonary rehabilitation.

The objective of this study was to identify the necessary features of pulmonary telerehabilitation (P-TR) from the perspectives of individuals living with chronic lung disease and health care professionals (HCPs) who deliver pulmonary rehabilitation (PR). Focus groups were carried out with patients ( n = 26) and HCPs ( n = 26) to elicit and explore their opinions about the critical elements of in-person PR and ideas for how these elements could be supported using technology. A questionnaire was used to assess technology use, PR experience, and general health status. Four key elements of PR were identified as critical to P-TR: the social aspect of PR; communicating with HCPs for education and support; using biosensors for monitoring and promoting self-knowledge; and the evolution of support with progress over time. A range of technology-enabled devices and programs were suggested as means to recreate aspects of these integral elements. Consultations with patients and HCPs suggest that users are interested in technology and want to ensure it recreates the important aspects of PR. Patients and HCPs identified similar key elements for P-TR. The opinions and suggestions of patients and HCPs should be the driving force of innovation if P-TR is to succeed in improving health outcomes.

Changes in cardiac index and blood pressure on positioning children prone for scoliosis surgery.

In this prospective observational study we investigated the changes in cardiac index and mean arterial pressure in children when positioned prone for scoliosis correction surgery. Thirty children (ASA 1-2, aged 13-18 years) undergoing primary, idiopathic scoliosis repair were recruited. The cardiac index and mean arterial blood pressure (median (IQR [range])) were 2.7 (2.3-3.1 [1.4-3.7]) l.min(-1).m(-2) and 73 (66-80 [54-91]) mmHg, respectively, at baseline; 2.9 (2.5-3.2 [1.7-4.4]) l.min(-1).m(-2) and 73 (63-81 [51-96]) mmHg following a 5-ml.kg(-1) fluid bolus; and 2.5 (2.2-2.7 [1.4-4.8]) l.min(-1).m(-2) and 69 (62-73 [46-85]) mmHg immediately after turning prone. Turning prone resulted in a median reduction in cardiac index of 0.5 l.min(-1).m(-2) (95% CI 0.3-0.7 l.min(-1).m(-2), p=0.001), or 18.5%, with a large degree of inter-subject variability (+10.3% to -40.9%). The changes in mean arterial blood pressure were not significant. Strategies to predict, prevent and treat decreases in cardiac index need to be developed.

Photoplethysmogram signal quality estimation using repeated Gaussian filters and cross-correlation.

Pulse oximeters are monitors that noninvasively measure heart rate and blood oxygen saturation (SpO2). Unfortunately, pulse oximetry is prone to artifacts which negatively impact the accuracy of the measurement and can cause a significant number of false alarms. We have developed an algorithm to segment pulse oximetry signals into pulses and estimate the signal quality in real time. The algorithm iteratively calculates a signal quality index (SQI) ranging from 0 to 100. In the presence of artifacts and irregular signal morphology, the algorithm outputs a low SQI number. The pulse segmentation algorithm uses the derivative of the signal to find pulse slopes and an adaptive set of repeated Gaussian filters to select the correct slopes. Cross-correlation of consecutive pulse segments is used to estimate signal quality. Experimental results using two different benchmark data sets showed a good pulse detection rate with a sensitivity of 96.21% and a positive predictive value of 99.22%, which was equivalent to the available reference algorithm. The novel SQI algorithm was effective and produced significantly lower SQI values in the presence of artifacts compared to SQI values during clean signals. The SQI algorithm may help to guide untrained pulse oximeter users and also help in the design of advanced algorithms for generating smart alarms.

Usability testing of a prototype Phone Oximeter with healthcare providers in high- and low-medical resource environments.

To increase the use of pulse oximetry by capitalise on the wide availability of mobile phones, we have designed, developed and evaluated a prototype pulse oximeter interfaced to a mobile phone. Usability of this Phone Oximeter was tested as part of a rapid prototyping process. Phase 1 of the study (20 subjects) was performed in Canada. Users performed 23 tasks, while thinking aloud. Time for completion of tasks and analysis of user response to a mobile phone usability questionnaire were used to evaluate usability. Five interface improvements were made to the prototype before evaluation in Phase 2 (15 subjects) in Uganda. The lack of previous pulse oximetry experience and mobile phone use increased median (IQR [range]) time taken to perform tasks from 219 (160-247 [118-274]) s in Phase 1 to 228 (151-501 [111-2661]) s in Phase 2. User feedback was positive and overall usability high (Phase 1--82%, Phase 2--78%).

[Closed-loop titration of propofol guided by the bispectral index]. / Titration automatisée du propofol guidée par l'index bispectral.

This review analyzes the clinical studies concerning the automated perfusion, or closed-loop, of propofol guided by the bispectral index (BIS). To carry out the maintenance of general anaesthesia by a closed loop propofol-BIS is feasible as shown by studies comprising few low risk patients. We showed that induction of anaesthesia is feasible with a closed loop, haemodynamic stability being similar to a manual titration. A second study, bearing on the whole of the anaesthesia of patients ASA I to III undergoing very diverse surgical acts, showed that the closed loop propofol-BIS was more precise than a manual perfusion. This confirms that the closed loop propofol-BIS is not an esoteric research and that it represents a tool with a future for the clinician.

Modelling for computer controlled neuromuscular blockade.

In this paper we present data collection and methods for the selection of a model class with the goal of automated neuromuscular blockade (NMB). Neuromuscular response was measured in the presence of rocuronium in rabbits (N=5) and humans (N=14). An average response was formed and used to determine optimal ARX and Laguerre representations for a wide range of orders and parameters. A 6th order Laguerre model was selected based on its accuracy and simplicity. Models were identified for each subject. For each group, variation was measured by comparison to the average response. The standard deviation of the average impulse response static gain was 45.4 and 45.8% of the mean for the rabbit and human models, respectively. The range of static gain was 121 and 159% of the mean for the rabbit and human datasets. Frequency domain analysis showed differences in gain of 12 and 15dB, and phase of 45 and 75° for the rabbit and human models respectively. With this knowledge, design and development of appropriate controllers for NMB will proceed.