Estimation of respiratory rate from photoplethysmographic imaging videos compared to pulse oximetry.

We present a study evaluating two respiratory rate estimation algorithms using videos obtained from placing a finger on the camera lens of a mobile phone. The two algorithms, based on Smart Fusion and empirical mode decomposition (EMD), consist of previously developed signal processing methods to detect features and extract respiratory induced variations in photoplethysmographic signals to estimate respiratory rate. With custom-built software on an Android phone, photoplethysmographic imaging videos were recorded from 19 healthy adults while breathing spontaneously at respiratory rates between 6 to 32 breaths/min. Signals from two pulse oximeters were simultaneously recorded to compare the algorithms' performance using mobile phone data and clinical data. Capnometry was recorded to obtain reference respiratory rates. Two hundred seventy-two recordings were analyzed. The Smart Fusion algorithm reported 39 recordings with insufficient respiratory information from the photoplethysmographic imaging data. Of the 232 remaining recordings, a root mean square error (RMSE) of 6 breaths/min was obtained. The RMSE for the pulse oximeter data was lower at 2.3 breaths/min. RMSE for the EMD method was higher throughout all data sources as, unlike the Smart Fusion, the EMD method did not screen for inconsistent results. The study showed that it is feasible to estimate respiratory rates by placing a finger on a mobile phone camera, but that it becomes increasingly challenging at respiratory rates greater than 20 breaths/min, independent of data source or algorithm tested.

Usability and Feasibility of PIERS on the Move: An mHealth App for Pre-Eclampsia Triage.

BACKGROUND: Pre-eclampsia is one of the leading causes of maternal death and morbidity in low-resource countries due to delays in case identification and a shortage of health workers trained to manage the disorder. Pre-eclampsia Integrated Estimate of RiSk (PIERS) on the Move (PotM) is a low cost, easy-to-use, mobile health (mHealth) platform that has been created to aid health workers in making decisions around the management of hypertensive pregnant women. PotM combines two previously successful innovations into a mHealth app: the miniPIERS risk assessment model and the Phone Oximeter. OBJECTIVE: The aim of this study was to assess the usability of PotM (with mid-level health workers) for iteratively refining the system. METHODS: Development of the PotM user interface involved usability testing with target end-users in South Africa. Users were asked to complete clinical scenario tasks, speaking aloud to give feedback on the interface and then complete a questionnaire. The tool was then evaluated in a pilot clinical evaluation in Tygerberg Hospital, Cape Town. RESULTS: After ethical approval and informed consent, 37 nurses and midwives evaluated the tool. During Study 1, major issues in the functionality of the touch-screen keyboard and date scroll wheels were identified (total errors n=212); during Study 2 major improvements in navigation of the app were suggested (total errors n=144). Overall, users felt the app was usable using the Computer Systems Usability Questionnaire; median (range) values for Study 1 = 2 (1-6) and Study 2 = 1 (1-7). To demonstrate feasibility, PotM was used by one research nurse for the pilot clinical study. In total, more than 500 evaluations were performed on more than 200 patients. The median (interquartile range) time to complete an evaluation was 4 min 55 sec (3 min 25 sec to 6 min 56 sec). CONCLUSIONS: By including target end-users in the design and evaluation of PotM, we have developed an app that can be easily integrated into health care settings in low- and middle-income countries. Usability problems were often related to mobile phone features (eg, scroll wheels, touch screen use). Larger scale evaluation of the clinical impact of this tool is underway.

Development of diagnostic sensors for infant dehydration assessment using optical methods.

Dehydration resulting from acute diarrhea is one of the leading causes of infant mortality in the developing world. Safe assessment of an infant's hydration level is essential to determine appropriate clinical intervention strategies. However, clinical hydration scales, which are the current gold standard for non-invasive hydration assessment, are often unreliable in lower resource settings. This study presents the development and testing of non-invasive, optical sensors for the objective assessment of dehydration based on the quantitative measurement of skin recoil time, capillary refill time and skin temperature. The results obtained have demonstrated the basic feasibility of using optical sensors for the objective assessment of dehydration. However, several challenges must be overcome before these sensors can be applied in a clinical setting.

Development of a diagnostic dehydration screening sensor based on infrared spectrometry.

The clinical assessment of dehydration is highly subjective and requires experienced and highly trained clinical personnel. At present no objective method for quantitatively determining an individual's dehydration status exists. The aim of this study is to address this deficiency by presenting the development and testing of a novel diagnostic tool for dehydration detection based on infrared spectrometry. Laboratory testing and two clinical studies were conducted to evaluate the efficacy of the device in both adults and infants. The results were promising for the infant study with a clear trend exhibited. However, a number of challenges must be overcome before this sensor can be applied in a clinical setting.

Application of an artificial neural network and morphing techniques in the redesign of dysplastic trochlea.

Segmentation and computer assisted design tools have the potential to test the validity of simulated surgical procedures, e.g., trochleoplasty. A repeatable measurement method for three dimensional femur models that enables quantification of knee parameters of the distal femur is presented. Fifteen healthy knees are analysed using the method to provide a training set for an artificial neural network. The aim is to use this artificial neural network for the prediction of parameter values that describe the shape of a normal trochlear groove geometry. This is achieved by feeding the artificial neural network with the unaffected parameters of a dysplastic knee. Four dysplastic knees (Type A through D) are virtually redesigned by way of morphing the groove geometries based on the suggested shape from the artificial neural network. Each of the four resulting shapes is analysed and compared to its initial dysplastic shape in terms of three anteroposterior dimensions: lateral, central and medial. For the four knees the trochlear depth is increased, the ventral trochlear prominence reduced and the sulcus angle corrected to within published normal ranges. The results show a lateral facet elevation inadequate, with a sulcus deepening or a depression trochleoplasty more beneficial to correct trochlear dysplasia.

Design of an interactive medical guideline application for community health workers.

Clinical guidelines, such as the Integrated Management of Childhood Illness (IMCI), are used worldwide to support community health workers in the assessment of severely ill children. These guidelines are distributed in paper form, complicating their use at the point-of-care. We have developed a framework for building advanced clinical guideline applications for the Android mobile phone OS. The framework transfers clinical guidelines into a flexible and interactive electronic format using an XML interpreter. The resulting application supports intuitive navigation of guidelines while assessing the patient, easy integration of patient management tools, and logging of performed assessments and treatments. The novel approach transforms clinical guidelines from a mere paper dictionary into a working tool that integrates into the daily workflow of community health workers and simplifies their task at the care and administrative levels.

Evaluation of the use of frequency response in the diagnosis of pleural effusion on a phantom model of the human lungs.

Pleural effusion is one of the most widespread respiratory diseases in the world. Current diagnostic techniques include a combination of medical history and x-ray or CT scan imaging of the chest. However, these techniques are expensive and impractical in resource limited settings. We propose a new method based on sound transmission into the respiratory system through the chest wall. To evaluate this technique, a sine sweep signal with a frequency range between 100 Hz and 1000 Hz was transmitted into a phantom model of the human lungs capable of simulating healthy and effused conditions. The frequency response of the model under both conditions was computed and compared to evaluate the diagnostic performance of the new method. The results indicate that there is a significant difference between the frequency response of healthy and effused lungs, which suggests that the new technique may be suitable for the clinical diagnosis of pleural effusion.

Sharing Vital Signs between mobile phone applications.

We propose a communication library, ShareVitalSigns, for the standardized exchange of vital sign information between health applications running on mobile platforms. The library allows an application to request one or multiple vital signs from independent measurement applications on the Android OS. Compatible measurement applications are automatically detected and can be launched from within the requesting application, simplifying the work flow for the user and reducing typing errors. Data is shared between applications using intents, a passive data structure available on Android OS. The library is accompanied by a test application which serves as a demonstrator. The secure exchange of vital sign information using a standardized library like ShareVitalSigns will facilitate the integration of measurement applications into diagnostic and other high level health monitoring applications and reduce errors due to manual entry of information.

Respiratory rate assessment from photoplethysmographic imaging.

We present a study investigating the suitability of a respiratory rate estimation algorithm applied to photoplethysmographic imaging on a mobile phone. The algorithm consists of a cascade of previously developed signal processing methods to detect features and extract respiratory induced variations in photoplethysmogram signals to estimate respiratory rate. With custom-built software on an Android phone (Camera Oximeter), contact photoplethysmographic imaging videos were recorded using the integrated camera from 19 healthy adults breathing spontaneously at respiratory rates between 6 and 40 breaths/min. Capnometry was simultaneously recorded to obtain reference respiratory rates. Two hundred and ninety-eight Camera Oximeter recordings were available for analysis. The algorithm detected 22 recordings with poor photoplethysmogram quality and 46 recordings with insufficient respiratory information. Of the 232 remaining recordings, a root mean square error of 5.9 breaths/min and a median absolute error of 2.3 breaths/min was obtained. The study showed that it is feasible to estimate respiratory rates by placing a finger on a mobile phone camera, but that it becomes increasingly challenging at respiratory rates higher than 20 breaths/min.

Development of a smart backboard system for real-time feedback during CPR chest compression on a soft back support surface.

The quality of cardiopulmonary resuscitation (CPR) is often inconsistent and frequently fails to meet recommended guidelines. One promising approach to address this problem is for clinicians to use an active feedback device during CPR. However, one major deficiency of existing feedback systems is that they fail to account for the displacement of the back support surface during chest compression (CC), which can be important when CPR is performed on a soft surface. In this study we present the development of a real-time CPR feedback system based on an algorithm which uses force and dual-accelerometer measurements to provide accurate estimation of the CC depth on a soft surface, without assuming full chest decompression. Based on adult CPR manikin tests it was found that the accuracy of the estimated CC depth for a dual accelerometer feedback system is significantly better (7.3% vs. 24.4%) than for a single accelerometer system on soft back support surfaces, in the absence or presence of a backboard. In conclusion, the algorithm used was found to be suitable for a real-time, dual accelerometer CPR feedback application since it yielded reasonable accuracy in terms of CC depth estimation, even when used on a soft back support surface.

Development of a diagnostic glove for unobtrusive measurement of chest compression force and depth during neonatal CPR.

Optimizing chest compression (CC) performance during neonatal cardiopulmonary resuscitation (CPR) is critical to improving survival outcomes since current clinical protocols often achieve only a fraction of the native cardiovascular perfusion. This study presents the development of a diagnostic tool to unobtrusively measure the CC depth and force during neonatal CPR using sensors mounted on a glove platform. The performance of the glove was evaluated by infant manikin tests using the two-thumb (TT) and two-finger (TF) methods of CC during simulated, unventilated neonatal CPR. The TT method yielded maximum CC depths and forces of as much as 25.7 ± 3.2 mm and 35.9 ± 2.2 N while the TF method produced CC depths and forces of as much as 21.6 ± 2.2 mm and 23.7 ± 2.9 N. These results are consistent with clinical findings which suggest that TT compression is more effective than TF compression since it produces greater CC depths and forces.

Recognition of correct finger placement for photoplethysmographic imaging.

In mobile health applications, non-expert users often perform the required medical measurements without supervision. Therefore, it is important that the mobile device guides them through the correct measurement process and automatically detects potential errors that could impact the readings. Camera oximetry provides a non-invasive measurement of heart rate and blood oxygen saturation using the camera of a mobile phone. We describe a novel method to automatically detect the correct finger placement on the camera lens for camera oximetry. Incorrect placement can cause optical shunt and if ignored, lead to low quality oximetry readings. The presented algorithm uses the spectral properties of the pixels to discriminate between correct and incorrect placements. Experimental results demonstrate high mean accuracy (99.06%), sensitivity (98.06%) and specificity (99.30%) with low variability. By sub-sampling pixels, the computational cost of classifying a frame has been reduced by more than three orders of magnitude. The algorithm has been integrated in a newly developed application called OxiCam where it provides real-time user feedback.

Detection of the optimal region of interest for camera oximetry.

The estimation of heart rate and blood oxygen saturation with an imaging array on a mobile phone (camera oximetry) has great potential for mobile health applications as no additional hardware other than a camera and LED flash enabled phone are required. However, this approach is challenging as the configuration of the camera can negatively influence the estimation quality. Further, the number of photons recorded with the photo detector is largely dependent on the optical path length, resulting in a non-homogeneous image. In this paper we describe a novel method to automatically detect the optimal region of interest (ROI) for the captured image to extract a pulse waveform. We also present a study to select the optimal camera settings, notably the white balance. The experiments show that the incandescent white balance mode is the preferable setting for camera oximetry applications on the tested mobile phone (Samsung Galaxy Ace). Also, the ROI algorithm successfully identifies the frame regions which provide waveforms with the largest amplitudes.

The lateral tibial tunnel: does it allow for adequate fixation in ACL surgery?

UNLABELLED: The purpose of this cadaver study about the ACL graft was to compare a "Lateral Tibial Tunnel" (LTT) and a "classic, anteroMedial Tibial Tunnel" (MTT), as to fixation strength and mode of failure. Ten pairs of fresh frozen human proximal tibias were used. In one of both tibias a classic anteromedial tunnel was used, versus a lateral tibial tunnel in the contralateral knee. Autologous doubled semitendinosus and gracilis tendons were fixed in the tunnels. A maximum load to failure test was performed to determine the stiffness and the strength of the graft-tibia complex. CONCLUSION: for none of the measurements was there any significant difference between both tunnels. The tibial fixation strength of a human autologous doubled hamstring graft in ACL surgery is similar, whether a lateral or an anteromedial tibial tunnel is used. This is the first study investigating fixation strength of an ACL graft in a lateral tibial tunnel.

Optimal chest compression in cardiopulmonary resuscitation depends upon thoracic and back support stiffness.

A biomechanical analysis of the constant peak displacement and constant peak force methods of cardiopulmonary resuscitation (CPR) has revealed that optimal CC performance strongly depends on back support stiffness, CC rate, and the thoracic stiffness of the patient being resuscitated. Clinically the results presented in this study suggest that the stiffness of the back support surfaces found in many hospitals may be sub-optimal and that a backboard or a concrete floor can be used to enhance CC effectiveness. In addition, the choice of optimal CC rate and maximum sternal force applied by clinicians during peak force CPR is ought to be based on a general assessment of the patient's thoracic stiffness, taking into account the patient's age, gender, and physical condition; which is consistent with current clinical practice. In addition, it is important for clinicians to note that very high peak sternal forces, exceeding the limit above which severe chest wall trauma and abdominal injury occurs, may be required for optimal CC during peak force CPR on patients with very stiff chests. In these cases an alternative CPR technique may be more appropriate.

Reducing subsidence risk by using rapid manufactured patient-specific intervertebral disc implants.

BACKGROUND CONTEXT: Intervertebral disc implant size, shape, and position during total disc replacement have been shown to affect the risk of implant subsidence or vertebral fracture. Rapid manufacturing has been successfully applied to produce patient-specific implants for craniomaxillofacial, dental, hip, and knee requirements, but very little has been published on its application for spinal implants. PURPOSE: This research was undertaken to investigate the improved load distribution and stiffness that can be achieved when using implants with matching bone interface geometry as opposed to implants with flat end plate geometries. STUDY DESIGN: The study design comprises a biomechanical investigation and comparison of compressive loads applied to cadaveric vertebrae when using two different end plate designs. METHODS: Four spines from male cadavers (ages 45-65 years, average 52 years), which had a total of n=88 vertebrae (C3-L5), were considered during this study. Bone mineral density scans on each spine revealed only one to be eligible for this study. Twenty remaining vertebrae (C3-L3) were potted and subjected to nondestructive compression tests followed by destructive compression tests. Custom-made nonfunctional implants were designed for this experiment. Ten implants were designed with matching end plate-to-bone interface geometry, whereas the other 10 were designed with flat end plates. Testing did not incorporate the use of a keel in either design type. I-Scan pressure sensors (Tekscan, Inc., MA, USA) were used during the nondestructive tests to assess the load distribution and percentage surface contact. RESULTS: Average percent contact area measured during nondestructive tests was 45.27% and 10.49% for conformal and flat implants, respectively-a difference that is statistically significant (p<.001). A higher percent contact area was especially observed for cervical vertebrae because of their pronounced end plate concavity. During destructive compression tests, conformal implants achieved higher failure loads than flat implants. Conformal implants also performed significantly better when stiffness values were compared (p<.0001). CONCLUSIONS: One of the main expected benefits from customizing the end plate geometry of disc implants is the reduced risk and potential for subsidence into the vertebral bone end plate. Subsidence depends in part on the stiffness of the implant-bone construct, and with a 137% increase in stiffness, the results of this study show that there are indeed significant potential benefits that can be achieved through the use of customization during the design and manufacture of intervertebral disc implants.

Design challenges for camera oximetry on a mobile phone.

The use of mobile consumer devices as medical diagnostic tools allows standard medical tests to be performed anywhere. Cameras embedded in consumer devices have previously been used as pulse oximetry sensors. However, technical limitations and implementation challenges have not been described. This manuscript provides a critical analysis of pulse oximeter technology and technical limitations of cameras that can potentially impact implementation of pulse oximetry in mobile phones. Theoretical and practical examples illustrate difficulties and recommendations to overcome these challenges.

Classification of gender and race in the distal femur using self organising maps.

In this study gender and race differences in distal femoral morphology were investigated. Reliable anatomic knee measurements were obtained for 60 knees via MRI and direct scanning of cadaver specimens. The MRI data comprised of 20 White males and 22 White females while the cadaver specimens comprised of 18 Black males. Possible differences were investigated using a type of artificial neural network to classify the data, namely the self-organising map (SOM). The SOM suggested that clear differences are present between genders when absolute measurements are used. Male knees tended to be larger over all the measurements considered. However, when data were normalised for size, the clear differences were diminished and definite clusters were difficult to define. Black male knees tended to have larger condyle radius to anterior-posterior length ratios compared to White males. White male knees tended to be wider than White female knees. It is however suggested than when corrected for size, there exists a large variation among individual knees regardless of gender or race. It is argued that with the large variation in populations it can become advantageous not to think about gender-specific or race-specific knee replacement designs, but rather patient-specific.

Development and testing of patient-specific knee replacements.

This study presents a design methodology for designing and manufacturing patient-specific unicompartmental knee replacements. The design methodology uses mathematical modeling and an artificial neural network to predict the original and healthy articulating surfaces of a patient's knee. The models are combined with medical images from the patient to create a knee prosthesis that is patient-specific. These patient-specific implants are then compared to conventional implants with respect to contact stresses and kinematics. The patient-specific implant experienced lower contact stresses at the tibiofemoral joint compared to a fixed-bearing design. Both the UKRs showed similar kinematic patterns to the normal knee using two different test rigs. The patient-specific UKR showed good results and with the other benefits it shows potential to dramatically improve clinical outcomes of knee replacement surgery.

In vitro characterization of an aortic bioprosthetic valve using Doppler echocardiography and qualitative flow visualization.

A 19 mm diameter prototype bioprosthetic valve mounted in a cardiac pulse duplicator was characterized using Doppler echocardiography and qualitative flow visualization at a heart rate of 72 bpm. Analysis of the flow visualization images revealed that the prototype and control valve leaflets open symmetrically but close asymmetrically. The asymmetry in the closing of the valves is likely due to the large pressure gradients across the valves and may have implications for the long term mechanical failure of the valves. The relatively high peak systolic velocity of 309.9 cm/s, which was measured in the prototype 19 mm valve, can be attributed to the small valve diameter and the high cardiac output used in the current study.