Development of an intraluminal intestinal photoplethysmography sensor

Intestinal ischemia is a serious medical condition and can lead to life threatening sepsis. Currently, there are no reliable techniques available for directly monitoring intestinal viability for prolonged periods of time, and intraoperatively, the majority of the surgeons still rely on subjective methods, such as visual inspection to assess viability of the intestine. The development of an intraluminal optical sensor for monitoring intestinal viability is being proposed. The sensor will continuously monitor changes in blood volume and oxygen saturation. The developed reflectance photoplethysmography/pulse oximetry sensor comprises of two emitters (red and infrared) and a photodiode. A photoplethysmography processing and data acquisition system was also utilized. The prototype sensor was evaluated in a pilot study in the buccal mucosa of 12 healthy volunteers, given the locations similarity to the intestinal mucosa and its easy accessibility. Good quality photoplethysmography signals with high signal-to-noise ratio were acquired from the buccal mucosa in all the volunteers. Preliminary blood oxygen saturation values from the intraluminal sensor were in broad agreement with the standard finger pulse oximeter probes

The effects of optical sensor-tissue separation in endocavitary photoplethysmography

Objective: Intestinal anastomotic failure that occurs mainly due to ischaemia is a serious risk in colorectal cancer patients undergoing surgery. Surgeons continue to rely on subjective methods such as visual inspection to assess intestinal viability during surgery and there are no clinical tools to directly monitor viability postoperatively. A dual-wavelength reflectance optical sensor has been developed for continuous and dynamic monitoring of intestinal viability via the intestinal lumen. Maintaining direct contact between the sensor and the inner intestinal wall can be difficult in an intraluminal design, therefore impacting on signal acquisition and quality. This paper investigates the effect of direct contact versus variable distances between the sensor and the tissue surface of the buccal mucosa as a surrogate. Approach: The in vivo study involved 20 healthy volunteers to measure the effect of optical sensor-tissue distances on the ability to acquire photoplethysmography signals and their quality. Signals were acquired from the buccal mucosa at five optical sensor-tissue distances. Main results: Distances between 0 mm (contact) to 5 mm were the most optimal, producing signals of high quality and signal-to-noise ratio, resulting in reliable estimations of the blood oxygen saturation. Distances exceeding 5 mm compromised the acquired signals, and were of poor quality, thereby unreliably estimating the blood oxygen saturation. Significance: The developed optical sensor proved to be reliable for acquiring photoplethysmography signals for cases where distances between the optical sensor-tissue may arise during the assessment of intraluminal intestinal viability

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

In silico and in vivo investigations using an endocavitary photoplethysmography sensor for tissue viability monitoring

Significance: Colorectal cancer is one of the major causes of cancer-related deaths worldwide. Surgical removal of the cancerous growth is the primary treatment for this disease. A colorectal cancer surgery, however, is often unsuccessful due to the anastomotic failure that may occur following the surgical incision. Prevention of an anastomotic failure requires continuous monitoring of intestinal tissue viability during and after colorectal surgery. To date, no clinical technology exists for the dynamic and continuous monitoring of the intestinal perfusion. Aim: A dual-wavelength indwelling bowel photoplethysmography (PPG) sensor for the continuous monitoring of intestinal viability was proposed and characterized through a set of in silico and in vivo investigations. Approach: The in silico investigation was based on a Monte Carlo model that was executed to quantify the variables such as penetration depth and detected intensity with respect to the sensor–tissue separations and tissue perfusion. Utilizing the simulated information, an indwelling reflectance PPG sensor was designed and tested on 20 healthy volunteers. Two sets of in vivo studies were performed using the driving current intensities 20 and 40 mA for a comparative analysis, using buccal tissue as a proxy tissue-site. Results: Both simulated and experimental results showed the efficacy of the sensor to acquire good signals through the “contact” to a “noncontact” separation of 5 mm. A very slow wavelength-dependent variation was shown in the detected intensity at the normal and hypoxic states of the tissue, whereas a decay in the intensity was found with the increasing submucosal-blood volume. The simulated detected-to-incident-photon-ratio and the experimental signal-to-noise ratio exhibited strong positive correlations, with the Pearson product-moment correlation coefficient R ranging between 0.65 and 0.87. Conclusions: The detailed feasibility analysis presented will lead to clinical trials utilizing the proposed sensor

Investigation of splanchnic perfusion utilising an intraluminal opto-electronic sensor placed in the duodenum

The splanchnic region (abdominal gastrointestinal organs) is sometimes known as the “canary of the body” for its susceptibility to develop hypoxia at an earlier stage, analogue to the old times practice in coal mining. When the neuroendocrine response is activated, it exhibits regulation of blood flow and extraction of oxygen, facilitating redistribution of blood to vital organs. This can ultimately lead to systemic inflammatory response and multiple organ failure. The vital need to monitor the perfusion of the splanchnic region in critically ill patients has not yet been met by existing techniques. The goal of this research was to evaluate the feasibility of using the technique of photoplethysmography intraluminally in the duodenum in order to measure the haemodynamic changes occurring in the splanchnic circulation in a minimally invasive fashion. A bespoke processing system and data acquisition virtual instrument were designed and developed to allow continuous and simultaneous monitoring of two probes: an existing miniaturised PPG probe intended for intraluminal use and optically- identical finger PPG probe. Nine anaesthetised patients undergoing elective open laparotomy surgery were recruited and consented for the clinical trial at The Royal London Hospital. Due to the great proximity to the surgical site, monitoring of duodenal pulse oximetry signals could not be done in a continuous way. Also, the presence of moderate respiratory modulation in otherwise good quality, high amplitude signals seemed to result in an underestimation of arterial blood saturation of 2%. A frequency domain algorithm was thus applied to the data with results in agreement with both the finger PPG probe and commercial pulse oximeter. Blood oxygen saturation estimation at respiratory frequency yielded values within the physiological range expected for venous blood. For three of the patients, PPG signals were also acquired from the stomach, with results showing a similar pattern to the ones obtained from the duodenum. During the clinical trials, two patients experienced hypotension. PPG signals obtained before, during and after showed a great decrease in estimated blood oxygen saturations, which remained low even when monitored haemodynamical variables were back to normal values. Finger PPG probe estimations and commercial pulse oximetry values did not demonstrate this change. This suggests the possibility of photoplethysmography identifying changes in tissue oxygenation and blood volume in the splanchnic circulation resulting from external and/or internal regulatory mechanisms. This clinical trial thus show the great promise of pulse oximetry as complementary monitoring for patients at risk of developing splanchnic ischaemia

Overview of biofluids and flow sensing techniques applied in clinical practice

This review summarizes the current knowledge on biofluids and the main flow sensing techniques applied in healthcare today. Since the very beginning of the history of medicine, one of the most important assets for evaluating various human diseases has been the analysis of the conditions of the biofluids within the human body. Hence, extensive research on sensors intended to evaluate the flow of many of these fluids in different tissues and organs has been published and, indeed, continues to be published very frequently. The purpose of this review is to provide researchers interested in venturing into biofluid flow sensing with a concise description of the physiological characteristics of the most important body fluids that are likely to be altered by diverse medical conditions. Similarly, a reported compilation of well-established sensors and techniques currently applied in healthcare regarding flow sensing is aimed at serving as a starting point for understanding the theoretical principles involved in the existing methodologies, allowing researchers to determine the most suitable approach to adopt according to their own objectives in this broad field.This research was supported by the Consejo Nacional de Ciencia y Tecnología (CONACYT) of México through Ph.D. grant 472102 and by the Ministerio de Economía y Competitividad through grant FIS2017-89850R.Peer ReviewedPostprint (author's final draft

Intra-operative optical monitoring of bowel tissue viability based on photoplethysmography and laser doppler flowmetry

Determination of bowel viability in patients undergoing bowel resection is essential in gastrointestinal surgery. One of the most common operations in gastrointestinal surgery is bowel resection for patients who have different kinds of bowel cancer or any other occlusion in which anastomosis has to be carried out following the removal of an unhealthy segment of the bowel. Monitoring blood flow in abdominal surgery especially intraoperatively would be a valuable tool for prevention of a postoperative anastomosis complication (e.g. anastomotic leak, which is the main complication after colorectal resection). The development of a continuous method for monitoring perfusion of bowel tissue would assist in early detection of inadequate blood supply which then help to reduce the occurrence of an anastomosis complication. Although various monitoring techniques have been proposed to assess intestinal viability intraoperatively, none of these techniques have proved to be reliable enough to replace visual observation. Therefore, to date there is no widely accepted and readily available intraoperative technique to reliably assess the viability of bowel tissue. The aim of this study was to combine the established techniques, laser Doppler flowmetry (LDF) and Photoplethysmography (PPG), into one probe intended for assessment of perfusion in abdominal tissue during bowel resection intraoperatively. In PPG, changes in transmission of light through tissue due to pulsation of small arteries can be monitored whereas in LDF microcirculatory blood cell velocity and flux can be studied. Such a probe could alert the surgeon immediately of any compromise in blood flow so further investigation and, if necessary, therapeutic steps can be applied immediately to prevent severe consequences. Therefore, custom reflectance PPG along with LDF sensor was designed and built in the form of a probe to investigate the changes in blood volume, blood flow and arterial oxygen saturation in patients undergoing bowel resection. The instrumentation was designed successfully and the data was saved for the further analysis. Twenty-four patients undergoing bowel resection were recruited for monitoring of perfusion and blood flowintraoperatively; twenty had undergone laparoscopy and the remainder had a laparotomy operation. Eight different measurements were performed during each trial. The results revealed that the probe could be an indicator of evaluating perfusion and blood flow changes at different stages of the surgery. The results also suggest that laser Doppler is more sensitive to artefact compared to PPG. Differences in amplitude of PPG between different measurements reveal that the sensor does detect changes in blood volume and flow confirming that it has the ability to verify that pulsatile flow is being preferentially preserved at the last step of the resection procedure (at the edges of the anastomosis sites after anastomosis is been constructed

Venous hypertensive microangiopathy : evaluation with laser doppler flowmetry

Imperial Users onl

Advanced analyses of physiological signals and their role in Neonatal Intensive Care

Preterm infants admitted to the neonatal intensive care unit (NICU) face an array of life-threatening diseases requiring procedures such as resuscitation and invasive monitoring, and other risks related to exposure to the hospital environment, all of which may have lifelong implications. This thesis examined a range of applications for advanced signal analyses in the NICU, from identifying of physiological patterns associated with neonatal outcomes, to evaluating the impact of certain treatments on physiological variability. Firstly, the thesis examined the potential to identify infants at risk of developing intraventricular haemorrhage, often interrelated with factors leading to preterm birth, mechanical ventilation, hypoxia and prolonged apnoeas. This thesis then characterised the cardiovascular impact of caffeine therapy which is often administered to prevent and treat apnoea of prematurity, finding greater pulse pressure variability and enhanced responsiveness of the autonomic nervous system. Cerebral autoregulation maintains cerebral blood flow despite fluctuations in arterial blood pressure and is an important consideration for preterm infants who are especially vulnerable to brain injury. Using various time and frequency domain correlation techniques, the thesis found acute changes in cerebral autoregulation of preterm infants following caffeine therapy. Nutrition in early life may also affect neurodevelopment and morbidity in later life. This thesis developed models for identifying malnutrition risk using anthropometry and near-infrared interactance features. This thesis has presented a range of ways in which advanced analyses including time series analysis, feature selection and model development can be applied to neonatal intensive care. There is a clear role for such analyses in early detection of clinical outcomes, characterising the effects of relevant treatments or pathologies and identifying infants at risk of later morbidity

Acute cardiovascular responses to slow and deep breathing

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonSlow and deep breathing (SDB) has long been regarded as a nonpharmacological method for dealing with several physiological and emotional imbalances, and widely used for relaxation purposes. There is, however, limited understanding of the putative mechanisms by which SDB acutely impacts the cardiovascular and autonomic systems to elicit chronic adaptations. The present thesis explored how the manipulation of breathing pattern and intrathoracic pressure during SDB could further the understanding of the regulatory mechanisms that underpin the acute cardiovascular response to SDB. This thesis makes an original contribution to the existing knowledge by reporting a previously undescribed inversion of normal within-breath (inspiration vs. expiration) left ventricular stroke volume (LVSV) pattern for breathing frequencies < 8 breaths∙min-1. This finding might reflect the influence of a lag between enhanced right atrial filling and right ventricular stroke volume during inspiration, and its expression in left ventricular stroke volume; this lag results from the time required for blood to transit the pulmonary circulation. Furthermore, blood pressure variability (BPV) was reduced significantly at the lowest breathing frequencies, likely due to the involvement of baroreflex mediated responses. The pattern of responses was consistent with the buffering of respiratory-driven fluctuations in left ventricular cardiac output (Q̇) and arterial blood pressure (ABP) by within breath fluctuations in heart rate (fc), i.e., respiratory sinus arrhythmia (RSA) (Chapter 4). Chapter 5 demonstrated that magnifying negative intrathoracic pressure with inspiratory loading during SDB increased inspiratory pressure-driven fluctuations in LVSV and fc, and enhanced Q̇, independently of changes in VT and fR. The data support an important contribution to the amplification of RSA, during SDB, of previously underappreciated reflex, and/or ‘myogenic’, cardiac response mechanisms. The findings in Chapter 6 confirmed that inspiratory loading during SDB amplified the effects observed with un-loaded SDB (reported in chapter 5). In contrast, expiratory loading increased ABP and attenuated RSA, LVSV and Q̇ during SDB. A lower RSA for higher ABP, supports the presence of a formerly underappreciated contribution of sinoatrial node stretch to RSA, and throws into question the clinical benefits of expiratory resisted SDB, particularly in hypertensive populations. In conclusion, the findings of the present thesis provide novel information regarding the mechanisms contributing to acute cardiovascular response to SDB. These new insights may contribute to the development of more effective SDB interventions, geared towards maximising the perturbation to the cardiovascular control systems