The ability to measure the oxygen saturation, oximetry, of retinal blood both non-invasively and in-vivo has been a goal of eye research for years. Retinal oximetry can in principle be achieved from the measurement of the reflectance spectrum of the ocular fundus. Oximetry calculations are however complicated by the scattering of red blood cells, the different pathways of light through blood and the ocular tissues that light interacts with before exiting the eye. The goal of this thesis was to investigate the influence of red blood cell scattering for different light paths relevant to retinal oximetry. Results of in-vitro whole blood experiments found calculated oxygen saturation differences between blood samples measured under different retinal light paths, and these differences did not depend on the absorbance path length. We also showed that the calculated oxygen saturation value determined by a multiple linear regression Beer-Lambert absorbance model depended on the wavelength range chosen for analysis. The wavelength dependency on the calculated oxygen saturation value is due in part to the correlation that exists between the oxyhaemoglobin and deoxyhaemoglobin extinction coefficient spectra and to errors in the assumptions built into the Beer-Lambert absorbance model. A wavelength region with low correlation between the oxyhaemoglobin and deoxyhaemoglobin extinction coefficients was found that is hypothesized to be a good range to calculate oxygen saturation using a multiple linear regression approach.

The ability to measure the oxygen saturation, oximetry, of retinal blood both non-invasively and in-vivo has been a goal of eye research for years. Retinal oximetry can in principle be achieved from the measurement of the reflectance spectrum of the ocular fundus. Oximetry calculations are however complicated by the scattering of red blood cells, the different pathways of light through blood and the ocular tissues that light interacts with before exiting the eye. The goal of this thesis was to investigate the influence of red blood cell scattering for different light paths relevant to retinal oximetry. Results of in-vitro whole blood experiments found calculated oxygen saturation differences between blood samples measured under different retinal light paths, and these differences did not depend on the absorbance path length. We also showed that the calculated oxygen saturation value determined by a multiple linear regression Beer-Lambert absorbance model depended on the wavelength range chosen for analysis. The wavelength dependency on the calculated oxygen saturation value is due in part to the correlation that exists between the oxyhaemoglobin and deoxyhaemoglobin extinction coefficient spectra and to errors in the assumptions built into the Beer-Lambert absorbance model. A wavelength region with low correlation between the oxyhaemoglobin and deoxyhaemoglobin extinction coefficients was found that is hypothesized to be a good range to calculate oxygen saturation using a multiple linear regression approach.

Recent advances in retinal imaging have made it possible to take measurements of retinal oxygen saturation noninvasively in humans. This allows studying the supply of oxygen in healthy and diseased retinae, thereby advancing our understanding of both the normal functioning of the retina and of retinal pathologies. However, retinal oximetry is still a research tool only and requires further improvement before being used in a clinical setting. Here, a single-wavelength flickering light was used to increase retinal blood flow in healthy subjects. This increase is revealed by both vasodilation and an increase in retinal oxygen saturation. A flickering light stimulus provides the means to assess the sensitivity of any retinal oximetry system, as such systems should be able to pick up this increase in retinal blood flow. In addition, the flickering light allows for com- parison to be made within rather than between subjects and can be used to examine the activation of the eye. This reduces the influence of potential confounding factors between subjects including differences in fundus pigmentation and illumination. The most commonly used method to measure retinal oxygenation is the optical density ra- tio (ODR) approach. The standard approach is to compute the average ODR for each vessel segment by combining the hundreds of individual ODR readings and then to use the mean of these segment averages as a measure of oxygen saturation. Alternatively, it has been suggested that the peak location of Gaussian functions fitted to histograms of individual ODR readings can be used as an measure of retinal oxygenation. In response to a 10Hz flickering light, the venular diameter increased by 3.44% (SEM: ±0.53%) (n=16, p<0.05) and the arteriolar diameter by 1.87% (±0.72 %) (p<0.05). The optical density ratio, measured with the Gaussian fit, decreased in the venules from 0.713 (±0.015) to 0.694 (±0.015) (p<0.05). No changes in arteriolar optical density ratios were measured. The post-flicker measurement was computed as the average of up to four post-flicker datasets obtained at 10s, 20s, 30s and 40s after onset of flickering. These results suggest that the flickering light increased retinal blood flow. The mean absolute percentage error was lower in venules for the Gaussian fit method than for the gold standard method for datasets taken at 30s and 40s after onset of flickering. Thus, the Gaussian fit method was more robust. All measurements were taken with a custom-made retinal oximeter. The pixel intensity of the blood vessel and the intensity on either side of the vessel had to be extracted to compute the individual optical density ratios. This required the automatic extraction of the retinal vasculature. Two such algorithms were developed and applied to two databases of retinal fundus images: the DRIVE and the novel DR HAGIS database. One algorithm was purely based on the pixel intensities, while the other made use of oriented Gabor filters. These two algorithms segmented the images to a similar accuracy (DRIVE: 94.56% and 94.54%, DR HAGIS: 95.83% and 95.71% for the intensity and Gabor filter based algorithm, respectively) and performed as well as a human expert (DRIVE: 94.73%). These algorithms were of sufficient quality to extract individual segments for the oximetry study and to align fundus images.

The ability to measure the oxygen saturation, oximetry, of retinal blood both non-invasively and in-vivo has been a goal of eye research for years. Retinal oximetry can in principle be achieved from the measurement of the reflectance spectrum of the ocular fundus. Oximetry calculations are however complicated by the scattering of red blood cells, the different pathways of light through blood and the ocular tissues that light interacts with before exiting the eye. The goal of this thesis was to investigate the influence of red blood cell scattering for different light paths relevant to retinal oximetry. Results of in-vitro whole blood experiments found calculated oxygen saturation differences between blood samples measured under different retinal light paths, and these differences did not depend on the absorbance path length. We also showed that the calculated oxygen saturation value determined by a multiple linear regression Beer-Lambert absorbance model depended on the wavelength range chosen for analysis. The wavelength dependency on the calculated oxygen saturation value is due in part to the correlation that exists between the oxyhaemoglobin and deoxyhaemoglobin extinction coefficient spectra and to errors in the assumptions built into the Beer-Lambert absorbance model. A wavelength region with low correlation between the oxyhaemoglobin and deoxyhaemoglobin extinction coefficients was found that is hypothesized to be a good range to calculate oxygen saturation using a multiple linear regression approach.

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Submitted in partial fulfilment of the requirements for the Degree of Masters in Technology: Clinical Technology, Durban University of Technology, 2009. / Currently, off-pump coronary artery bypass surgery (OPCAB) is a selectively employed technique for myocardial revascularization used in the majority of heart units worldwide. This strategy obviates the documented deleterious effects of cardiopulmonary bypass. However the occurrence of neurological sequelae associated with OPCAB ranges from minor cognitive dysfunction to major stroke. Haemodynamic instability throughout the positioning, stabilization and interruption of coronary blood flow are regarded as important factors that affect the performance of off-pump surgery. Fluctuations during the perioperative period, in particular manipulation of the heart could result in temporary brain hypoperfusion and neurological sequelae. To predict those patients that are predisposed to cerebral complications, investigators have used neurological monitoring, in particular Near-infra red spectroscopy (NIRS) during cardiac surgery. Aims and Objectives of the study This prospective, observational study was carried out to assess the correlation between cerebral oxygen saturation and central venous saturation during OPCAB surgery. Central venous saturation is an important variable used to assess global tissue perfusion and could therefore be advocated as a surrogate measure of cerebral oxygen saturation. In addition variables such as mean arterial (MAP) pressure, heart rate (HR), patient oxygen saturation (SpO2), partial pressure of carbon dioxide (PcvCO2), haematocrit (Hct) and lactate were also measured to determine if they were independent predictors of cerebral desaturation. This study is one of the first done in the South African population group. iv Methodology Twenty patients undergoing OPCAB surgery from the Cardiothoracic unit at Inkosi Albert Luthuli Central Hospital, Durban, South Africa were recruited in the trial. Cerebral somasensors were placed on the patients forehead to measure left and right cerebral saturations. These sensors were linked by cables to the cerebral monitor (NIRS), INVOS model 5100C. Eight time periods throughout the surgical procedure whereby patients would be haemodynamically unstable were identified. These time periods included, post induction and pre sternotomy, pre and post placement of swabs beneath the heart, pre and post placement of the stabilizer device (Octopus), pre and post snaring of the LAD (left anterior branch of the coronary arteries), pre anastomosis and during anastomosis of the coronary arteries, second sample during anastomosis and post anastomosis, pre and post removal of swabs from beneath the heart, pre and post transfer of the patient to the ICU bed. These time periods constituted the sampling period pre and post manoeuvres. Eight paired measurements, i.e., MAP, PaCO2, HR, Hct, lactate, SpO2, central venous saturation (ScvO2) and cerebral oxygen saturation (rSo2) per patient were taken during these time periods. Recording of cerebral saturations and blood samples from the central venous line were taken during these eight time periods in order to determine the correlation between central venous and cerebral oxygen saturations. Results Strong positive correlations between central venous saturation and cerebral saturation presented in majority of the sampling time periods throughout the study (post induction and pre sternotomy, post placement of swabs beneath the heart, post snaring of the LAD (left anterior branch of the coronary arteries, pre anastomosis and during anastomosis of the coronary arteries, second sample during v anastomosis, pre and post transfer of the patient to the ICU bed). The positive correlation indicates that central venous saturation can be used as a surrogate measure of cerebral oxygen saturation during OPCAB surgery. Conclusion The absence or poor correlation of MAP, HR, PcvCO2, heamatocrit, lactate, and patient saturation to cerebral saturation in this study suggests that insertion of a central venous line (CVP) during OPCAB should be a fundamental clinical requirement.

Submitted in partial fulfilment of the requirements for the Degree of Doctor of Technology: Clinical technology, Durban University of Technology, 2011. / Surgical revascularization of the coronary arteries is a cornerstone of cardiothoracic surgery. The enduring nature of coronary artery bypass grafting (CABG) bespeaks of its history and proven efficacy. However, cerebral deoxygenation during on-pump coronary artery bypass graft surgery may be associated with adverse neurological sequelae. Advanced age and the incidence of preoperative co-morbidity in patients presenting for coronary artery bypass graft surgery increases the potential for stroke and other adverse perioperative outcomes (Murkin, Adams, Quantz, Bainbridge and Novick, 2007). It is hypothesized, that by using the brain as an index organ, interventions to improve cerebral oxygenation would have systemic benefits for cardiac surgical patients. In an attempt to predict those patients that are predisposed to cerebral complications, investigators have used neurological monitoring ie, Near infrared spectroscopy (NIRS) to enhance detection of hypoxic conditions associated with neurological injury (Hoffman, 2006). Serum S100B protein has been used as a biochemical marker of brain injury during cardiac surgery. Elevated levels serve as a potential marker of brain cell damage and adverse neurological outcomes (Einav, Itshayek, Kark, Ovadia, Weiniger and Shoshan, 2008). Aims and Objectives of the study This prospective, quantitative, interventional study was carried out to maintain cerebral tissue oxygen saturation during cardiopulmonary bypass above 75% of the baseline level by implementation of a proposed interventional protocol. The analysis of S100B which is a marker of neurological injury and optimization of regional cerebral oxygen saturation would allow for the formulation of an algorithm which could be implemented during on-pump coronary artery bypass graft surgery as a preventive clinical measure further reducing the risk of neurological injury. Central venous lines (CVP) are inserted routinely during cardiac surgery. Central venous oxygen saturation is a global marker of tissue oxygenation. A secondary aim of the study was to determine if a correlation existed between central venous and cerebral tissue oxygen saturations. If a positive correlation existed then central venous oxygen saturation could be used as a surrogate measure of cerebral tissue oxygen saturation during on-pump coronary artery bypass graft surgery. This study is one of the first done in the South African population group. Methods Forty (40) patients undergoing on-pump coronary artery bypass graft surgery were recruited at Inkosi Albert Luthuli Central Hospital. Patients were randomized into a control group (n=20) and interventional group (n=20) using a sealed envelope system. The envelope contained designation to either group. Envelopes were randomly chosen. Intraoperative regional cerebral oxygen saturation (rSO2 ) monitoring with active display and treatment intervention protocol was administered for the interventional group. In the control group regional cerebral oxygen saturation monitoring was not visible to the perfusionist operating the heart lung machine during cardiopulmonary bypass (blinded). Recording of regional cerebral saturation was conducted by an independent person (another perfusionist) who was not involved in the management of the case so as to ensure that no interventions were carried out on the control group. Arterial blood samples for the measurement of serum S100B were taken pre and postoperatively. An enzyme immunoassay (ELISA) was used for the quantitative and comparative measurement of human S100B concentrations for both groups. Central venous oxygen saturation was monitored from the CVP using the Edwards Vigileo monitor. Cerebral monitoring constituted the use of Near infrared spectroscopy monitoring using the Invos 5100c, Somonetics Corp, Troy MI monitor. Adhesive optode pads were be placed over each fronto- temporal area for cerebral oxygen measurement. During cardiopulmonary bypass, eight time period measurements of mean arterial pressure (MAP), heart rate, temperature, activated clotting time (ACT), patient oxygen saturation (SpO2), partial pressure of carbon dioxide (pCO2), haematocrit, lactate, pH, haemoglobin (Hb), base excess (BE), potassium (K+), sodium (Na+), glucose, calcium (Ca2+), central venous oxygen saturation (ScvO2), cerebral tissue oxygen saturation (rSO2), fraction inspired oxygen (FiO2 ), sweep rate, pump flow rate (cardiac index), and percentage isoflurane per patient were taken. The time periods when data was recorded included: 5 minutes after onset of cardiopulmonary bypass, aortic cross clamping, after cardioplegic arrest, during distal anastomosis, during proximal anastomosis, during rewarming, after aortic cross clamp release and before termination of cardiopulmonary bypass. Baseline measurements were also taken. Clinical data recorded for both groups included: the number of grafts performed, cardiopulmonary bypass time, cross clamp time, red blood cells administered (packed cells), amount of adrenalin infused and total cerebral desaturation time. A prioritized intraoperative management protocol to maintain rSO2 values above 75% of the baseline threshold during cardiopulmonary bypass was followed. Cerebral desaturation was defined as a decrease in saturation values below 70% of baseline for more than one minute. Interventions commenced within 15 seconds of decrease below 75% of baseline value. Results The results of the study show that there was a highly significant difference in the change in S100B concentrations pre and post surgery between the interventional and control groups. The intervention vii group showed a smaller increase in S100B concentration of 37.3 picograms per millilitre (pg/ml) while the control group showed a larger increase of 139.3 pg/ml. Therefore, the control group showed a significantly higher increase in S100B concentration over time than the intervention group (p < 0.001). Maximizing pump flow rates was the most common intervention used (45 times) followed by maintaining partial pressure of carbon dioxide to approximately 40 mmHg (28 times), increasing mean arterial pressure by administration of adrenalin (11 times) and administration of red blood cells to increase haematocrit (11 times). There was a highly statistically significant treatment effect within the intervention group for each of the above interventions compared with no intervention. The above mentioned interventions significantly affected right and left cerebral oxygen saturations. However, administration of red blood cells was not found to significantly increase right (p = 0.165) and left (p = 0.169) cerebral oxygen saturation within the intervention group. The study highlighted a significant difference between the intervention and control groups in terms of cerebral desaturation time (p <0.001). The mean desaturation time for the control group was 63.85 minutes as compared to 24.7 minutes in the interventional group. Cerebral desaturation occurred predominantly during aortic cross clamping, distal anastomosis of coronary arteries and aortic cross clamp release. Predictors of cerebral oxygen desaturation included, partial pressure of carbon dioxide (pCO2), temperature, pump flow rate (LMP), mean arterial pressure (MAP), haematocrit, heart rate (HR) and patient oxygen saturation (SpO2). Central venous oxygen saturation was not significantly related to right (p = 0.244) or left (p = 0.613) cerebral oxygen saturations. Therefore central venous oxygen saturation cannot be used as a surrogate measure of cerebral tissue oxygen saturation during on-pump coronary artery bypass graft surgery. viii Conclusion These findings demonstrate the positive effect of optimizing cerebral oxygen saturation using an interventional protocol on markers of neurological injury (S100B). Optimization of pump flow rate, partial pressure of carbon dioxide and mean arterial pressure would result in increased cerebral oxygen saturation levels and a reduction in neurological injury. Therefore, an algorithm incorporating these interventions can be formulated. Monitoring specifically for brain oxygen saturation together with an effective treatment protocol to deal with cerebral desaturation during on-pump CABG must be advocated.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes vita. Includes bibliographical references (p. 161-182).

Submitted by Haroudo Xavier Filho (haroudo.xavierfo@ufpe.br) on 2016-10-07T18:07:19Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Carolina Paim Gomes de Freitas - Dissertação.pdf: 2606222 bytes, checksum: c1285c239db0c6bae33863737f8e0bca (MD5) / Made available in DSpace on 2016-10-07T18:07:19Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Carolina Paim Gomes de Freitas - Dissertação.pdf: 2606222 bytes, checksum: c1285c239db0c6bae33863737f8e0bca (MD5) Previous issue date: 2016-02-26 / Fundamentos: A oximetria de pulso arterial foi descrita como um método de triagem para cardiopatias congênitas críticas. O estabelecimento de nomogramas para saturação pré- e pós-ductal no nosso meio pode colaborar para o refinamento de um método de triagem específico para nossa população. Objetivo: descrever e analisar os principais resultados dos nomogramas para saturação de oxigênio em neonatos triados para cardiopatias congênitas críticas na população paraibana. Metodologia: neonatos assintomáticos com idade gestacional a partir de 34 semanas foram triados para cardiopatias congênitas pelo exame físico e oximetria de pulso arterial em 20 centros do estado da Paraíba. Os resultados das saturações pré e pós-ductais foram comparadas entre diversos grupos com a utilização de testes não paramétricos. Resultados: um total de 44647 neonatos foram analisados. A média da saturação pré-ductal foi de 97,37% e a pós-ductal foi de 97,44%. Houve diferença estatística (p<0,001) entre as duas saturações em praticamente todos os grupos. A média da diferença entre as saturações foi de 0,062, com a grande maioria dos neonatos apresentando diferença ≤ 4%. Neonatos pré-termo tiveram saturações menores do que os nascidos a termo (p<0,001). Não houve diferenças entre os sexos. Conclusões: foram descritos os nomogramas das saturações de oxigênio pré e pósductal, assim como a diferença entre ambas, em mais de 44647 neonatos. Tais nomogramas podem ser úteis na elaboração de metodologias de triagem para cardiopatias congênitas críticas no nosso meio. / Fundamentals: the pulse oximetry was described as a method of screening for congenital heart defects. The establishment of nomograms for pre-and pós-ductal saturation among us can collaborate for the refinement of a screening method specific to our population. Objective: to describe and analyze the main results of nomograms for oxygen saturation in neonates screened for congenital heart defects in critical population of Paraiba. Methodology: asymptomatic neonates with gestational age from 34 weeks were screened for congenital heart disease by physical examination and blood pulse oximetry in 20 centers in the State of Paraíba. The results of the pre-and pós-ductais overruns were compared between groups using nonparametric tests. Results: a total of 44647 newborns were evaluated. The average pré-ductal was 97.37% saturation and the pós-ductal was 97.44%. There was statistical difference (p < 0.001) between the two buffer overruns in almost all groups. The average difference between was 0.062 overruns, with the vast majority of newborns showing difference ≤ 4%. Preterm neonates had smaller overruns than those born at term (p < 0.001). There was no difference between the sexes. Conclusions: nomograms were described of the oxygen saturations pre-and pósductal, as well as the difference between the two in more than 44647 newborns. Such nomograms can be useful in the elaboration of methodologies for screening for congenital heart disease in our reviews.