Respiratory pressure and split flow data collection device with rapid occlusion attachment.

Respiratory model-based methods require datasets containing enough dynamics to ensure model identifiability for development and validation. Rapid expiratory occlusion has been used to identify elastance and resistance within a single breath. Currently accepted practice for rapid expiratory occlusion involves a 100 ms occlusion of the expiratory pathway. This article presents a low-cost modular rapid shutter attachment to enable identification of passive respiratory mechanics. Shuttering faster than 100 ms creates rapid expiratory occlusion without the added dynamics of muscular response to shutter closure, by eliminating perceived expiratory blockage via high shutter speed. The shutter attachment fits onto a non-invasive venturi-based flow meter with separated inspiratory and expiratory pathways, established using one-way valves. Overall, these elements allow comprehensive collection of respiratory pressure and flow datasets with relatively very rapid expiratory occlusion.

Investigation of Narrow-band NIR LED Spectral Response Towards a Non-invasive Glucose Sensor.

Spectroscopy is utilised extensively in medical sensing technology. Typically, hand-held spectroscopy equipment uses miniature narrow-band light emitting diodes (LEDs) and photodiodes to emit and detect light, respectively. Photodiodes typically absorb light across a wide spectra so measurements can be corrupted by surrounding light. LEDs in the visible spectrum have a narrower spectral response and can be used in place of a traditional photodiode. However, the absorption characteristics of near infrared (NIR) spectrum LEDs is unknown. A discrete, low-cost spectrophotometer was designed to assess spectral response for 8 narrow band NIR LEDs. The normalised and raw spectral response determined the optimum detector for 1050 nm - 1300 nm is the 1450 nm LED, and the optimum detector for 1450 nm - 1650 nm emissions is the 1650 nm LED.Clinical relevance - Understanding the spectral response of narrow-band LEDs in the NIR spectrum will aid development of NIR hand-held spectroscopy medical devices.

Non-Invasive Assessment of Abdominal/Diaphragmatic and Thoracic/Intercostal Spontaneous Breathing Contributions.

(1) Background: Technically, a simple, inexpensive, and non-invasive method of ascertaining volume changes in thoracic and abdominal cavities are required to expedite the development and validation of pulmonary mechanics models. Clinically, this measure enables the real-time monitoring of muscular recruitment patterns and breathing effort. Thus, it has the potential, for example, to help differentiate between respiratory disease and dysfunctional breathing, which otherwise can present with similar symptoms such as breath rate. Current automatic methods of measuring chest expansion are invasive, intrusive, and/or difficult to conduct in conjunction with pulmonary function testing (spontaneous breathing pressure and flow measurements). (2) Methods: A tape measure and rotary encoder band system developed by the authors was used to directly measure changes in thoracic and abdominal circumferences without the calibration required for analogous strain-gauge-based or image processing solutions. (3) Results: Using scaling factors from the literature allowed for the conversion of thoracic and abdominal motion to lung volume, combining motion measurements correlated to flow-based measured tidal volume (normalised by subject weight) with R2 = 0.79 in data from 29 healthy adult subjects during panting, normal, and deep breathing at 0 cmH2O (ZEEP), 4 cmH2O, and 8 cmH2O PEEP (positive end-expiratory pressure). However, the correlation for individual subjects is substantially higher, indicating size and other physiological differences should be accounted for in scaling. The pattern of abdominal and chest expansion was captured, allowing for the analysis of muscular recruitment patterns over different breathing modes and the differentiation of active and passive modes. (4) Conclusions: The method and measuring device(s) enable the validation of patient-specific lung mechanics models and accurately elucidate diaphragmatic-driven volume changes due to intercostal/chest-wall muscular recruitment and elastic recoil.

Low-cost, low-power, clockwork syringe pump.

A low-cost ($120 NZD, $75 USD), low-power (1-year battery life), portable, and programmable syringe pump design is presented, which offers an alternative to high-cost commercial devices with limited battery life. Contrary to typical motor-driven syringe pumps, the design utilizes a compression spring coupled with a clockwork escapement mechanism to advance the syringe plunger. Full control over flow-rate and discrete (bolus) deliveries is achieved through actuation of a clockwork escapement using programmable, low-power electronics. The escapement mechanism allows the syringe plunger to advance a fixed linear distance, delivering a dose size of 0.001 ml in the configuration presented. The modular pump assembly is easily reconfigured for different applications by interchanging components to alter the minimum dose size. Testing to IEC 60601-2-24(2012), the average error of the clockwork syringe pump was 8.0%, 4.0%, and 1.9% for 0.001 ml, 0.002 ml, and 0.01 ml volumes, respectively. An overall mean error of 1.0% was recorded for a flow-rate of 0.01 ml h-1. Compared to a commercial insulin pump, the clockwork pump demonstrated reduced variability but greater average error due to consistent over-delivery. Further development of the design and/or manufacture should yield a device with similar performance to a commercial pump.

An identifiable model of lung mechanics to diagnose and monitor COPD.

BACKGROUND: Current methods to diagnose and monitor COPD employ spirometry as the gold standard to identify lung function reduction with reduced forced expiratory volume (FEV1)/vital capacity (VC) ratio. Current methods utilise linear assumptions regarding airway resistance, where nonlinear resistance modelling may provide rapid insight into patient specific condition and disease progression. This study examines model-based expiratory resistance in healthy lungs and those with progressively more severe COPD. METHODS: Healthy and COPD pressure (P)[cmH2O] and flow (Q)[L/s] data is obtained from the literature, and 5 intermediate levels of COPD and responses are created to simulate COPD progression and assess model-based metric resolution. Linear and nonlinear single compartment models are used to identify changes in inspiratory (R1,insp) and linear (R1,exp)/nonlinear (R2Φ) expiratory resistance with disease severity and over the course of expiration. RESULTS: R1,insp increases from 2.1 to 7.3 cmH2O/L/s, R1,exp increases from 2.4 to 10.0 cmH2O/L/s with COPD severity. Nonlinear R2Φ increases (mean R2Φ: 2.5 cmH2O/L/s (healthy) to 24.4 cmH2O/L/s (COPD)), with increasing end-expiratory nonlinearity as COPD severity increases. CONCLUSION: Expiratory resistance is increasingly highly nonlinear with COPD severity. These results show a simple, nonlinear model can capture fundamental COPD dynamics and progression from regular breathing data, and such an approach may be useful for patient-specific diagnosis and monitoring.

Determining Losses in Jet Injection Subcutaneous Insulin Delivery: A Model-Based Approach.

OBJECTIVE: Accurate, safe glycemic management requires reliable delivery of insulin doses. Insulin can be delivered subcutaneously for action over a longer period of time. Needle-free jet injectors provide subcutaneous (SC) delivery without requiring needle use, but the volume of insulin absorbed varies due to losses associated with the delivery method. This study employs model-based methods to determine the expected proportion of active insulin present from a needle-free SC dose. METHODS: Insulin, C-peptide, and glucose assay data from a frequently sampled insulin-modified oral glucose tolerance test trial with 2U SC insulin delivery, paired with a well-validated metabolic model, predict metabolic outcomes for N = 7 healthy adults. Subject-specific nonlinear hepatic clearance profiles are modeled over time using third-order basis splines with knots located at assay times. Hepatic clearance profiles are constrained within a physiological rate of change, and relative to plasma glucose profiles. Insulin loss proportions yielding optimal insulin predictions are then identified, quantifying delivery losses. RESULTS: Optimal parameter identification suggests losses of up to 22% of the nominal 2U SC dose. The degree of loss varies between subjects and between trials on the same subject. Insulin fit accuracy improves where loss greater than 5% is identified, relative to where delivery loss is not modeled. CONCLUSIONS: Modeling shows needle-free SC jet injection of a nominal dose of insulin does not necessarily provide metabolic action equivalent to total dose, and this availability significantly varies between trials. By quantifying and accounting for variability of jet injection insulin doses, better glycemic management outcomes using SC jet injection may be achieved.

Bench-Side Dose Accuracy of an Open-Source Ultra-Low-Cost Insulin-Pump, With Testing Conducted to IEC 60601-2-24.

With the prevalence of diabetes higher than ever, governments and people with diabetes are facing significant treatment and indirect costs associated with managing their condition. An ultra-low-cost insulin pump is a possible solution to improving health disparities. This article presents test results for an insulin-pump built from low-cost components (bill of materials < $US100). All testing was completed in accordance with IEC60601-2-24, and results were benchmarked against a commercial pump. Results showed the ultra-low-cost pump has comparable accuracy to the commercially available insulin pump with testing displaying an overall accuracy of 0.089% and -0.392%, respectively. These results show that an ultra-low-cost pump can accurately deliver insulin in limited bench testing. Testing in other environments and scenarios is required to fully meet IEC60601-2-24 standards.

Design of an open source ultra low cost insulin pump.

In this report we present a design for an open source low cost insulin pump. The pump has been designed to provide an alternative to commercially available pumps costing upwards of US$6500, making them inaccessible to many. The hardware described in this article can be produced for a materials cost of US$89.85. Compared to other devices on the market, the design presented has the obvious advantage of being low cost, but is also highly customisable as it is run using open source software. The device is housed in a case of size 85 mm x 55 mm x 25 mm making it small enough to fit in a pocket, and equivalent to other devices on the market. The device is designed to work with insulin cartridges currently available on the market. Power is provided through the use of AAA batteries, and the pump is able to be recharged through a USB mini port. The accuracy of the pump has been tested and compared to data obtained from an in-warranty commercial insulin pump model using an identical testing methodology, with the ultra-low-cost pump performing similarly to the commercial model. The system can be readily extended to be controlled from external bluetooth or wired mobile devices using their built in security, offloading computation from the device and onto a phone.

Respiratory bi-directional pressure and flow data collection device with thoracic and abdominal circumferential monitoring.

Non-invasive pressure and flow data from Venturi-based sensors can be used with validated models to identify patient-specific lung mechanics. To validate applied respiratory models a secondary measurement is required. Rotary encoder-based tape measures were designed to capture change in circumference of a subject's thorax and diaphragm. Circumferential changes can be correlated to measured or modelled change in lung volume and associated muscular recruitment measures (patient work of breathing). Hence, these simple measurement devices can expedite respiratory research, by adding low-cost, accessible, and clinically useful measurements.

CPAP pressure and flow data at 2 positive pressure levels and multiple controlled breathing rates from a trial of 30 adults.

OBJECTIVES: A unique dataset of airway flow/pressure from healthy subjects on Continuous Positive Airway Pressure (CPAP) ventilation was collected. This data can be used to develop or validate models of pulmonary mechanics, and/or to develop methods to identify patient-specific parameters which cannot be measured non-invasively, during CPAP therapy. These models and values, particularly if available breath-to-breath in real-time, could assist clinicians in the prescription or optimisation of CPAP therapy, including optimising PEEP settings. DATA DESCRIPTION: Data was obtained from 30 subjects for model-based identification of patient-specific lung mechanics using a specially designed venturi sensor system comprising an array of differential and gauge pressure sensors. Relevant medical information was collected using a questionnaire, including: sex; age; weight; height; smoking history; and history of asthma. Subjects were tasked with breathing at five different rates (including passive), matched to an online pacing sound and video, at two different levels of PEEP (4 and 7 cmH2O) for between 50 and 180 s. Each data set comprises ~ 17 breaths of data, including rest periods between breathing rates and CPAP levels.

Physiologic-range three/two-way valve for respiratory circuits.

A 3D-printed three/two-way valve compatible with respiratory circuits is presented. It is actuated by a servo motor (HXT12K), which is able to be controlled by any PWM-capable micro controller. The valve sufficiently isolates respiratory circuits to deliver fully customisable mechanical ventilation breathing cycles, with differences in driving and end-expiratory pressures of up to 30 cmH 2 O successfully demonstrated. It is suitable for multiplexing ventilators for in-series breathing, or providing separate ventilation to each individual lung in a single patient. Each switching valve costs approximately $16USD, $10 of which is the servo motor which can be reused, allowing subsequent devices for only $6USD of 3D printing and common engineering components. The valve has proven reliable for at least 50,000 state changes over at least one month.

Physiologic-range flow and pressure sensor for respiratory systems.

A low-cost but reliable flow and pressure sensor is an impediment to development of medical equipment, and studies of human respiratory function, which is characterised by relatively low pressures and flows. A Venturi tube ( D 1 = 15 mm , D 2 = 10 mm ) connected to a differential pressure sensor (SDP816-125 Pa) allows accurate measurement of flow between 5 - 75 L · min - 1 , with Pearson Correlation over 4 min at 50 Hz ⩾ 0.97 , and distance correlation ⩾ 0.96 . The pressure measurement was similarly accurate using a MPVZ4006GW7U. Both sensors provide an analogue output from a 5.0 V supply, aiding compatibility and customisation. Each populated PCB costs approximately $50USD, and each Venturi sensor costs approximately $1USD. Multiple configurations exist, allowing flow rates up to 250 L · min - 1 , increased resolution for specific ranges, and different physical characteristics.

Insulin Units and Conversion Factors: A Story of Truth, Boots, and Faster Half-Truths.

Conventional insulin concentration units (IU/mL or just U/mL) are bioefficacy based, whereas the Système International (SI) units (pmol/L) are mass based. In converting between these two different approaches, there are at least 2 well-accepted conversion factors, where there should be only 1. The correct value is not the most-used or well-accepted using online calculators, some journal styles, laboratory reports, and published articles. In short, an incorrect insulin conversion factor is widely used which underreports insulin concentrations by ~15%, with potentially significant research and clinical implications. This short commentary describes the history of insulin IU definitions and conversion factors, and highlights the widespread nature of conversion factor misuse, to provoke deeper interest and thought regarding numbers we so often use without thinking.

Determining the effects of insulin Detemir on endogenous secretion of insulin.

Type 2 diabetes (T2D) is a long-term metabolic disorder. A pilot trial was designed to investigate the effects of the long acting insulin Detemir on endogenous insulin secretion, to assess use in early T2D care. Provesn metabolic system models are used to identify patient-specific insulin sensitivity and endogenous insulin secretion from clinical data. Post-cardiac surgery patients with early T2D or pre-diabetes based on HbA1c were given a bolus of insulin Detemir on one day, and none on the second day in hospital. Blood glucose, insulin, C-Peptide, and all nutrition given are recorded. Early results from N=3 patients show 0.8-1.0U/hour insulin Detemir doses have no apparent suppression of endogenous insulin secretion, but does help lower glucose levels. The results show the model captures glucose-insulin dynamics in pre-diabetic post-surgical patients, and insulin Detemir may be useful to support individuals with pre-diabetes in reducing blood glucose levels. Tests with higher doses, need to be carried out to verify these results over a greater range of patients.