A review of machine learning techniques in photoplethysmography for the non-invasive cuff-less measurement of blood pressure

Hypertension or high blood pressure is a leading cause of death throughout the world and a critical factor for increasing the risk of serious diseases, including cardiovascular diseases such as stroke and heart failure. Blood pressure is a primary vital sign that must be monitored regularly for the early detection, prevention and treatment of cardiovascular diseases. Traditional blood pressure measurement techniques are either invasive or cuff-based, which are impractical, intermittent, and uncomfortable for patients. Over the past few decades, several indirect approaches using photoplethysmogram (PPG) have been investigated, namely, pulse transit time, pulse wave velocity, pulse arrival time and pulse wave analysis, in an effort to utilise PPG for estimating blood pressure. Recent advancements in signal processing techniques, including machine learning and artificial intelligence, have also opened up exciting new horizons for PPG-based cuff less and continuous monitoring of blood pressure. Such a device will have a significant and transformative impact in monitoring patients’ vital signs, especially those at risk of cardiovascular disease. This paper provides a comprehensive review for non-invasive cuff-less blood pressure estimation using the PPG approach along with their challenges and limitations

Price impact of block trades in the Saudi stock market

This paper examines the price impact of block trades for the 124 companies that comprise all listed firms in the Saudi stock market (SSM). We use high frequency intraday data (one minute intervals) for the period 2005-2008 to provide out of sample evidence of the determinants of price impact. We find an asymmetric price impact of 0.5% for block purchases and -0.38% for block sales. We document a price continuation post block trades and a price reversal after block sales. Sellers of block trades in the Saudi market pay higher liquidity premiums than buyers of block trades. However, on average, the price effect of a block trade is small and short-lived suggesting that resiliency is high in the market. Moreover, we find a direct relationship between the size of the trades and the level of information asymmetry in the market. Despite the structural differences of the SSM, the intraday pattern of price impacts is similar to patterns documented in other markets, namely an inverse J-shaped pattern. Finally, sophisticated traders can gain abnormal profits in the SSM through “free riding”, a trader can benefit from the overreaction before the block trade and price reversal after the block trade

Can market frictions really explain the price impact asymmetry of block trades? Evidence from the Saudi stock market

We empirically examine the price impact of block trades, in the Saudi Stock Market over the time period of 2005-2008. Using a unique dataset of intraday data consisting of 2.3 million block buys and 1.9 million block sales, we find an asymmetry in the price impact of block purchases and sales. The asymmetry persists even when we account for the bidask bias in block trades, which is contrary to the previous literature. Overall, our findings suggest that in an emerging market where institutional trading is relatively scarce, market microstructure cannot explain the asymmetry n the price impact of large trades

A Multilayer Monte Carlo Model for the Investigation of Optical Path and Penetration Depth at Different Perfusion States of the Colon

There is a great interest in monitoring the oxygen supply delivered to the colon. Insufficient oxygen delivery may lead to hypoxia, sepsis, multiorgan dysfunction and death. For assessing colonic perfusion, more information and understanding is required relating to the light-interaction within the colonic tissue. A multilayer Monte Carlo model of a healthy human colon has been developed to investigate the light-tissue behavior during different perfusion states within the mucosal layer of the colon. Results from a static multilayer model of optical path and reflectance at two wavelengths, 660 nm and 880 nm, through colon tissue, containing different volume fractions of blood with a fixed oxygen saturation are presented. The effect on the optical path and penetration depth with varying blood volumes within the mucosa for each wavelength has been demonstrated. The simulation indicated both wavelengths of photons penetrated similar depths, entering the muscularis layer

Direct pulse oximetry within the esophagus, on the surface of abdominal viscera, and on free flaps

Pulse oximetry is a noninvasive photometric technique that provides information about arterial blood oxygen saturation (SpO2) and heart rate and has widespread clinical applications. This is accomplished via peripheral pulse oximetry probes mainly attached to the finger, toe, or earlobe. The direct application of pulse oximetry to an organ, such as the esophagus, liver, bowel, stomach or free flap, might provide an indication of how well perfused an organ or a free flap is. Also, the placement of a pulse oximetry probe at a more central site, such as the esophagus, might be more reliable at a time when conventional peripheral pulse oximetry fails

Estimation of Venous oxygenation saturation using the finger Photoplethysmograph (PPG) waveform

In this study, finger photoplethysmograph data obtained from twelve patients undergoing cardiothoracic surgery were analyzed in order to estimate the venous saturation utilizing the modulations created by the positive pressure ventilation in the AC Photoplethysmograph (PPG) signals. The PPG signals were analyzed in the time-domain using a conventional pulse oximetry algorithm to produce estimations of arterial oxygen saturation. The instantaneous arterial and venous saturations were estimated by utilizing time-frequency analysis technique of Smoothed-pseudo Wigner-Ville Distribution (SPWVD). The results showed that there was no significant difference in the traditionally-derived (time-domain) arterial saturation and the instantaneous arterial saturation. However, the instantaneous venous saturation was found to be significantly lower than the time-domain estimated and instantaneous arterial saturation (P=<;0.001)

Development and in vitro evaluation of an artificial spinal disc loading cell

One of the common diseases for chronic low back pain is Disc Degeneration Disease (DDD). In this disease, spinal intervertebral disc loses its ability to safely handle the mechanical stresses. The knowledge of the in-vivo loading on the spinal disk is of great importance in the understanding of low back pain. In this study a loading cell has been developed utilizing an artificial spinal disc which was loaded with strain gauges and piezoresistive sensors in an effort to investigate the behavior of the sensors during in vitro loading of the disc. The artificial disc with all sensors was loaded in a laboratory environment. The in vitro loading produced reliable and repeatable results and therefore suggesting that such approach might aid in the development of an artificial intelligent disc which will contribute in the better understanding of the in vivo loading of the human spine

Temperature sensor technology

Human body temperature is of vital importance to the well being of the person and therefore it is routinely monitored to indicate the state of the person’s health. Despite the fact that temperature measurement in humans seems so simple, a wide variety of devices are available to record a temperature from skin, oral or rectal mucosa or the tympanic membrane. The choice of clinical thermometers for health professionals and parents has never been so complicated. This chapter makes an attempt to provide an overview of temperature sensing technologies in medicine. The introductory sections give a brief and general description of temperature and its effect on the human body. A synoptic historical review on the evolution of the thermometer including the clinical thermometer is given in section 3. Section 4 describes the main sensors/transducers used in the development of clinical thermometers, such as thermocouples, thermistors, Resistance Temperature Detectors (RTDs), semiconductor temperature sensors, liquid crystal temperature sensors, and infra-red radiation sensors. These thermometers have been designed and developed for application in various parts of the body such as the rectum, the mouth, the axilla, the esophagus, the bladder, the ear, the temporal artery, the skin, and this will be the content of section 5. It will be almost impossible for this chapter to cover every possible application and evaluation study relating to different thermometers; however an effort is made in section 6 to provide an integrative review of studies comparing selected invasive and non-invasive temperature measurement methods

Evaluation of the Linear Relationship Between Pulse Arrival Time and Blood Pressure in ICU Patients: Potential and Limitations

A variety of techniques based on the indirect measurement of blood pressure (BP) by Pulse Transit Time (PTT) have been explored over the past few years. Such an approach has the potential in providing continuous and non-invasive beat to beat blood pressure without the use of a cuff. Pulse Arrival Time (PAT) which includes the cardiac pre-ejection period has been proposed as a surrogate of PTT, however, the balance between its questioned accuracy and measurement simplicity has yet to be established. The present work assessed the degree of linear relationship between PAT and blood pressure on 96 h of continuous electrocardiography and invasive radial blood pressure waveforms in a group of 11 young ICU patients. Participants were selected according to strict exclusion criteria including no use of vasoactive medications and presence of clinical conditions associated with cardiovascular diseases. The average range of variation for diastolic BP was 60 to 79 mmHg while systolic BP varied between 123 and 158 mmHg in the study database. The overall Pearson correlation coefficient for systolic and diastolic blood pressure was −0.5 and −0.42, respectively, while the mean absolute error was 3.9 and 7.6 mmHg. It was concluded that the utilization of PAT for the continuous non-invasive blood pressure estimation is rather limited according to the experimental setup, nonetheless the correlation coefficient performed better when the range of variation of blood pressure was high over periods of 30 min suggesting that PAT has the potential to be used as indicator of changes relating to hypertensive or hypotensive episodes

An exploration in visibility: some experiences of Indian women accountants

Many studies have emerged in the accounting field that explore women’s experiences in developed economies. However, little research has been undertaken to investigate the experiences and realities facing practising women accountants in India. The study offers exploratory insights into this area, (against the backdrop of the internationalisation and globalisation of accounting). The study involved seventeen women accounting practitioners from four major commercial cities in Indian: Mumbai, Chennai, Bangalore and Hyderabad. The results indicate that several practitioners experienced difficulties in certain areas of practice, whereas others reported that they did not experience any barriers to advancement. A discussion concerning limitations and areas for further research are presented in the conclusion