Anirban Dutta Choudhury

A robust heart rate detection using smart-phone video

In this paper, the authors have presented a smartphone based robust heart rate measurement system. The system requires the user to place the tip of his/her index finger on the lens of a smart phone camera, while the flash is on. The captured video signal often contains noise generated due to (i) improper finger placement, (ii) imparting excessive pressure, which subsequently blocks normal blood circulation and (iii) movement of the fingertip. To mitigate the above issues, a two stage approach has been proposed. Firstly, the onset of good video signal is detected by formulating a finite state machine, which employs multiple window short time fast fourier transform. Only upon receiving sufficient acceptable video signal, the heart rate is computed. Results indicate that the proposed method has successfully identified and rejected noisy video signal, resulting in avoidance of erroneous output.

UbiHeld: ubiquitous healthcare monitoring system for elderly and chronic patients

Once the persons identity is established, the most important aspects of ubiquitous healthcare monitoring of elderly and chronic patients are location, activity, physiological and psychological parameters. Since smartphones have become the most pervasive computing platform today, it is only a logical extension to use the same in healthcare domain for bringing ubiquity. Besides smartphone, skeleton based activity detection and localization using depth sensor like Kinect make ubiquitous monitoring effective without compromising privacy to a large extent. Finally sensing mental condition is made possible by analysis of the subjects social network feed. This paper presents an end-to-end healthcare monitoring system code named UbiHeld (Ubiquitous Healthcare for Elderly) using the techniques mentioned above and an IoT (Internet of Things) based back-end platform.

Noise cleaning and Gaussian modeling of smart phone photoplethysmogram to improve blood pressure estimation

Photoplethysmography (PPG) signals, captured using smart phones are generally noisy in nature. Although they have been successfully used to determine heart rate from frequency domain analysis, further indirect markers like blood pressure (BP) require time domain analysis for which the signal needs to be substantially cleaned. In this paper we propose a methodology to clean such noisy PPG signals. Apart from filtering, the proposed approach reduces the baseline drift of PPG signal to near zero. Furthermore it models each cycle of PPG signal as a sum of 2 Gaussian functions which is a novel contribution of the method. We show that, the noise cleaning effect produces better accuracy and consistency in estimating BP, compared to the state of the art method that uses the 2-element Windkessel model on features derived from raw PPG signal, captured from an Android phone.

Estimating blood pressure using Windkessel model on Photoplethysmogram.

Simple and non-invasive methods to estimate vital signs are very important for preventive healthcare. In this paper, we present a methodology to estimate Blood Pressure (BP) using Photoplethysmography (PPG). Instead of directly relating systolic and diastolic BP values with PPG features, our proposed methodology initially maps PPG features with some person specific intermediate latent parameters and later derives BP values from them. The 2-Element Windkessel model has been considered in the current context to estimate total peripheral resistance and arterial compliance of a person using PPG features, followed by linear regression for simulating arterial blood pressure. Experimental results, performed on a standard hospital dataset yielded absolute errors of 0.78±13.1 mmHg and 0.59 ± 10.23 mmHg for systolic and diastolic BP values respectively. Results also indicate that the methodology is more robust than the standard methodologies that directly estimate BP values from PPG signal.

AcTrak - Unobtrusive Activity Detection and Step Counting Using Smartphones

In this paper we introduce “AcTrak”, a system that provides training-free and orientation-and-placement-independent step-counting and activity recognition on commercial mobile phones, using only 3D accelerometer. The proposed solution uses “step-frequency” as a feature to classify various activities. In order to filter out noise generated due to normal handling of the phone, while the user is otherwise physically stationary, AcTrak is armed with a novel algorithm for step validation termed as Individual Peak Analysis (IPA). IPA uses peak-height and inter-peak interval as features. AcTrak provides realtime step count. It also classifies current activity, and tags each activity with the associated steps, resulting in a detailed analysis of activity recognition. Using our model, a step-count accuracy of 98.9 % is achieved. Further, an accuracy of 95 % is achieved when classifying stationary, walking and running/jogging. When brisk-walking is added to the activity set, still a reasonable level of accuracy is achieved. Since AcTrak is largely orientation and position agnostic, and requires no prior training, this makes our approach truly ubiquitous. Classification of step-based activity is done as walking, brisk-walking and running (includes jogging). So, after a session of workout, the subject can easily self-assess his/her accomplishment.

Identifying coronary artery disease from photoplethysmogram

This paper presents the idea of a non invasive screening system for identifying Coronary Artery Disease (CAD) patients from fingertip Photoplethysmogram (PPG) signal. A combined feature set, related to heart rate variability (HRV) as well as shapes of PPG waveform has been defined for distinguishing CAD and non CAD subjects. Support Vector Machine (SVM) is used for classification. Our methodology yields sensitivity and specificity scores of 0.82 and 0.88 respectively in identifying CAD patients on a corpus of 112 subjects, selected from MIMIC II dataset. Further, we achieved sensitivity and specificity scores of of 0.73 and 0.87 on another dataset of 30 subjects, collected from an urban hospital using commercial oximeter device.

PhotoECG: Photoplethysmographyto estimate ECG parameters

This paper presents a simple method to indirectly estimate the range of certain important electrocardiogram (ECG) parameters using photoplethysmography (PPG). The proposed method, termed as PhotoECG, extracts a set of time and frequency domain features from fingertip PPG signal. A feature selection algorithm utilizing the concept of Maximal Information Coefficient (MIC) is presented to rank the PPG features according to their relevance to create training models for different ECG parameters. The proposed method yields above 90% accuracy in estimating ECG parameters on a benchmark hospital dataset having clean PPG signal. The same method results an average of 80% accuracy on noisy PPG signal captured by iPhone, indicating its feasibility to create phone applications for preventive ECG monitoring at home.

Blood pressure estimation from photoplethysmogram using latent parameters

Non-invasive cuff-less Blood Pressure (BP) estimation from Photoplethysmogram (PPG) is a well known challenge in the field of affordable healthcare. This paper presents a set of improvements over an existing method that estimates BP using 2-element Windkessel model from PPG signal. A noisy PPG corpus is collected using fingertip pulse oximeter, from two different locations in India. Exhaustive pre-processing techniques, such as filtering, baseline and topline correction are performed on the noisy PPG signals, followed by the selection of consistent cycles. Subsequently, the most relevant PPG features and demographic features are selected through Maximal Information Coefficient (MIC) score for learning the latent parameters controlling BP. Experimental results reveal that overall error in estimating BP lies within 10% of a commercially available digital BP monitoring device. Also, use of alternative latent parameters that incorporate the variation in cardiac output, shows a better trend following for abnormally low and high BP.

Smart phone based blood pressure indicator

In this paper, we propose a methodology to estimate the range of human blood pressure (BP) using Photoplethysmography (PPG). 12 time domain features and 7 frequency domain features are pointed out and extracted from the PPG signal. A feature selection algorithm based on Maximal Information Coefficient (MIC) is presented to reduce the dimensionality of the feature set to effective ones, thereby cutting down resource requirements. Support Vector Machine (SVM) is used to classify the BP values into separate bins. The proposed methodology is validated and tested on a standard benchmark clean dataset as well as phone captured noisy dataset to justify its robustness and efficiency. Apart from a commending performance improvement, BP estimation is achieved with minimal features and processing, making the algorithm light weight for porting on smart phones.

HeartSense: smart phones to estimate blood pressure from photoplethysmography

In this paper we propose to demonstrate a smart phone application, that estimates human blood pressure (BP) values from photoplethysmography (PPG) signal using Windkessel model. PPG signal is extracted from a video sequence of a users index fingertip, acquired using smart phone camera. A set of time domain PPG features are used to estimate different lumped parameters of Windkessel model to simulate arterial BP. Under most of the cases, the application estimates systolic and diastolic BP values, within a range of ±10% of clinical measurement.