The severely obese patient has varying degrees of intrinsic reduction of expiratory flow rates and lung volumes. Thus, the severely obese patient is predisposed to postoperative atelectasis, ineffective clearing of respiratory secretions, and other pulmonary complications. This study evaluated the effect of bi-level positive airway pressure (Bi-PAP) on pulmonary function in obese patients following open gastric bypass surgery. Patients with a body mass index (BMI) of at least 40 kg/m2 who were undergoing elective gastric bypass were eligible to be randomized to receive either BiPAP during the first 24 h postoperatively or conventional postoperative care. Patients with significant cardiovascular and pulmonary diseases were excluded from the study. Forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1.0), peak expiratory flow rate (PEFR), and percent hemoglobin oxygen saturation (SpO2) were measured preoperatively, and on postoperative days 1, 2, and 3. Twenty-seven patients were entered in the study, 14 received BiPAP and 13 received conventional postoperative care. There was no significant difference preoperatively between the study and control groups in regards to age, BMI, FVC, FEV1.0, PEFR or SpO2. Postoperatively, expiratory flow was decreased in both groups. However, the FVC and FEV1.0 were significantly higher on each of the three consecutive postoperative days in the patients who received BiPAP therapy. The SpO2 was significantly decreased in the control group over the same time period. Prophylactic BiPAP during the first 12--24 h postoperatively resulted in significantly higher measures of pulmonary function in severely obese patients who had undergone elective gastric bypass surgery. These improved measures of pulmonary function, however, did not translate into fewer hospital days or a lower complication rate in our study population of other wise healthy obese patients. Further study is necessary to determine if BiPAP therapy in the first 24 postoperative hours would be of benefit in severely obese patients with comorbid illnesses who have undergone elective gastric bypass.

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No description available.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--Stellenbosch University, 2008. / This thesis is concerned with the development and testing of a non-invasive device that is unassailable, and can be placed on an aggressive psychiatric patient to monitor the vital signs of this patient. Two devices, a glove measuring oxygen saturation and another on the dorsal part (back) of the patient measuring heart rate via electrocardiography (ECG), skin temperature and respiratory rate were designed and implemented. The data is transmitted using wireless technology. Both devices connect to one central monitoring station using two separate Bluetooth connections ensuring a total wireless setup. All the hardware and software to measure these variables have been designed and implemented. A Matlab graphical user interface (GUI) was developed for signal processing and monitoring of the vital signs of the psychiatric patient. Detection algorithms were implemented to detect ECG arrhythmias such as premature ventricular contraction and atrial fibrillation. The prototype was manufactured and tested in a laboratory setting on five volunteers. Satisfactory test results were obtained and the primary objectives of the thesis were fulfilled

Optical Coherence Tomography (OCT) is a non-invasive three-dimensional imaging technique. OCT synthesizes a cross-sectional image from a series of lateral adjacent depth scans, and with a two-dimensional scanning scheme, three-dimensional intensity image of sample can be constructed. Due to its non-invasive capability, OCT has been widely applied in ophthalmology, cardiology and dermatology; and in addition to three-dimensional intensity image construction, various functional OCT imaging techniques have been developed for clinical application. My research is focused on developing functional OCT systems for application in ophthalmology, including polarization-sensitive optical coherence tomography (PS-OCT) for retinal nerve fiber layer (RNFL) birefringence measurement and dual-wavelength photothermal optical coherence tomography (DWP-OCT) for microvasculature blood oxygen saturation (SO2) measurement. In the study, a single-mode-fiber based polarization-sensitive swept-source OCT (PS-SS-OCT) with polarization modulator, polarization-sensitive bulk-optics balanced detection module is constructed and polarization processing methods based on Stokes vectors are applied to determine birefringence. PS-OCT is able to provide human subject's RNFL thickness, phase retardation, and birefringence information. Degradation in the degree of polarization (DOP) along depth is investigated and its difference between four quadrants of RNFL (superior, temporal, inferior and nasal) indicates the structural property difference. DWP-OCT is a novel functional OCT system consisting of a phase-sensitive optical coherence tomography system (PhS-OCT) and two photothermal excitation lasers. PhS-OCT is based on a swept-source laser operating in the 1060 nm wavelength range; the two photothermal excitation lasers with wavelength 770 nm and 800 nm are intensity modulated at different frequencies. PhS-OCT probe beam and two photothermal excitation beams are combined and incident on the sample, optical pathlength (op) change on the sample introduced by two photothermal excitation beams are measured and used for blood SO2 estimation. A polarization microscope is proposed for future study. The polarization microscope is an imaging technique providing molecular structure and orientation based on probe light's polarization state information. The polarization microscope uses a wavelength tunable light source, and can achieve any incident polarization state by a retarder-rotator combination. Specimen's birefringence can be determined based on the changing of detected light amplitude. / text

A wireless, battery operated pulse oximeter system with a forehead mounted optical sensor was designed in our laboratory. This wireless pulse oximeter (WPO) would enable field medics to monitor arterial oxygen saturation (SpO2) and heart rate (HR) information accurately following injuries, thereby help to prioritize life saving medical interventions when resources are limited. Pulse oximeters developed for field-based applications must be resistant to motion artifacts since motion artifacts degrade the signal quality of the photoplethysmographic (PPG) signals from which measurements are derived. This study was undertaken to investigate if accelerometer-based adaptive noise cancellation (ANC) can be used to reduce SpO2 and HR errors induced by motion artifacts typically encountered during field applications. Preliminary studies conducted offline showed that ANC can minimize SpO2 and HR errors during jogging, running, and staircase climbing. An 8th order LMS filter with ì = 0.01 was successfully implemented in the WPO's embedded microcontroller. After real-time adaptive filtering of motion corrupted PPG signals, errors for HR values ranging between 60 - 180BPM were reduced from 12BPM to 6BPM. Similarly, ambient breathing SpO2 errors were reduced from 5% to 2%.

Pulse oximetry is used to measure heart rate (HR) and arterial oxygen saturation (SpO2) from photoplethysmographic (PPG) waveforms. PPG waveforms are highly sensitive to motion artifact (MA), limiting the implementation of pulse oximetry in mobile physiological monitoring using wearable devices. Previous studies have shown that multichannel pulse oximetry can successfully acquire diverse signal information during simple, repetitive motion, thus leading to differences in motion tolerance across channels. In this study, we introduce a multichannel forehead-mounted pulse oximeter and investigate the performance of this novel sensor under a variety of intense motion artifacts. We have developed a multichannel template-matching algorithm that chooses the channel with the least amount of motion artifact to calculate HR and SpO2 every 2 seconds. We show that for a wide variety of random motion, channels respond differently to motion, and the multichannel estimate outperforms single channel estimates in terms of motion tolerance, signal quality, and HR and SpO2 error. Based on 31 data sets of PPG waveforms corrupted by random motion, the mean relative HR error was decreased by an average of 5.6 bpm when the multichannel-switching algorithm was compared to the worst performing channel. The percentage of HR measurements with absolute errors ≤ 5 bpm during motion increased by an average of 27.8 % when the multichannel-switching algorithm was compared to the worst performing channel. Similarly, the mean relative SpO2 error was decreased by an average of 4.3 % during motion when the multichannel-switching algorithm was compared to each individual channel. The percentage of SpO2 measurements with absolute error ≤ 3 % during motion increased by an average of 40.7 % when the multichannel-switching algorithm was compared to the worst performing channel. Implementation of this multichannel algorithm in a wearable device will decrease dropouts in HR and SpO2 measurements during motion. Additionally, the differences in motion frequency introduced across channels observed in this study shows precedence for future multichannel-based algorithms that make pulse oximetry measurements more robust during a greater variety of intense motion.

Doctor of Philosphy (PhD) / This thesis describes the work carried out during four treks, each over 10-11 days, from 1400m to 5000m in the Nepal Himalaya and further work performed during several two-night sojourns at the Barcroft Laboratory at 3800m on White Mountain in California, USA. Nineteen volunteers were studied during the treks in Nepal and seven volunteers were studied at White Mountain. All subjects were normal, healthy individuals who had not travelled to altitudes higher than 1000m in the previous twelve months. The aims of this research were to examine the effects on sleep, and the ventilatory patterns during sleep, of incremental increases in altitude by employing portable polysomnography to measure and record physiological signals. A further aim of this research was to examine the relationship between the ventilatory responses to hypoxia and hypercapnia, measured at sea level, and the development of periodic breathing during sleep at high altitude. In the final part of this thesis the possibility of preventing and treating Acute Mountain Sickness with non-invasive positive pressure ventilation while sleeping at high altitude was tested. Chapter 1 describes the background information on sleep, and breathing during sleep, at high altitudes. Most of these studies were performed in hypobaric chambers to simulate various high altitudes. One study measured sleep at high altitude after trekking, but there are no studies which systematically measure sleep and breathing throughout the whole trek. Breathing during sleep at high altitude and the physiological elements of the control of breathing (under normal/sea level conditions and under the hypobaric, hypoxic conditions present at high altitude) are described in this Chapter. The occurrence of Acute Mountain Sickness (AMS) in subjects who travel form near sea level to altitudes above 3000m is common but its pathophysiology not well understood. The background research into AMS and its treatment and prevention are also covered in Chapter 1. Chapter 2 describes the equipment and methods used in this research, including the polysomnographic equipment used to record sleep and breathing at sea level and the high altitude locations, the portable blood gas analyser used in Nepal and the equipment and methodology used to measure each individual’s ventilatory response to hypoxia and hypercapnia at sea level before ascent to the high altitude locations. Chapter 3 reports the findings on the changes to sleep at high altitude, with particular focus on changes in the amounts of total sleep, the duration of each sleep stage and its percentage of total sleep, and the number and causes of arousals from sleep that occurred during sleep at increasing altitudes. The lightest stage of sleep, Stage 1 non-rapid eye movement (NREM) sleep, was increased, as expected with increases in altitude, while the deeper stages of sleep (Stages 3 and 4 NREM sleep, also called slow wave sleep), were decreased. The increase in Stage 1 NREM in this research is in agreement with all previous findings. However, slow wave sleep, although decreased, was present in most of our subjects at all altitudes in Nepal; this finding is in contrast to most previous work, which has found a very marked reduction, even absence, of slow wave sleep at high altitude. Surprisingly, unlike experimental animal studies of chronic hypoxia, REM sleep was well maintained at all altitudes. Stage 2 NREM and REM sleep, total sleep time, sleep efficiency and spontaneous arousals were maintained at near sea level values. The total arousal index was increased with increasing altitude and this was due to the increasing severity of periodic breathing as altitude increased. An interesting finding of this research was that fewer than half the periodic breathing apneas and hypopneas resulted in arousal from sleep. There was a minor degree of upper airway obstruction in some subjects at sea level but this was almost resolved by 3500m. Chapter 4 reports the findings on the effects on breathing during sleep of the progressive increase of altitude, in particular the occurrence of periodic breathing. This Chapter also reports the results of changes to arterial blood gases as subjects ascended to higher altitudes. As expected, arterial blood gases were markedly altered at even the lowest altitude in Nepal (1400m) and this change became more pronounced at each new, higher altitude. Most subjects developed periodic breathing at high altitude but there was a wide variability between subjects as well as variability in the degree of periodic breathing that individual subjects developed at different altitudes. Some subjects developed periodic breathing at even the lowest altitude and this increased with increasing altitude; other subjects developed periodic breathing at one or two altitudes, while four subjects did not develop periodic breathing at any altitude. Ventilatory responses to hypoxia and hypercapnia, measured at sea level before departure to high altitude, was not significantly related to the development of periodic breathing when the group was analysed as a whole. However, when the subjects were grouped according to the steepness of their ventilatory response slopes, there was a pattern of higher amounts of periodic breathing in subjects with steeper ventilatory responses. Chapter 5 reports the findings of an experimental study carried out in the University of California, San Diego, Barcroft Laboratory on White Mountain in California. Seven subjects drove from sea level to 3800m in one day and stayed at this altitude for two nights. On one of the nights the subjects slept using a non-invasive positive pressure device via a face mask and this was found to significantly improve the sleeping oxyhemoglobin saturation. The use of the device was also found to eliminate the symptoms of Acute Mountain Sickness, as measured by the Lake Louise scoring system. This finding appears to confirm the hypothesis that lower oxygen saturation, particularly during sleep, is strongly correlated to the development of Acute Mountain Sickness and may represent a new treatment and prevention strategy for this very common high altitude disorder.

Introduction: Oxygen delivery, or utilization, is a function of retinal blood flow and blood oxygen saturation. The retinal pigment epithelium (RPE), in particular, has been shown to have the highest levels of metabolic activity within the human body. Oxygen delivery is therefore of extreme importance to the maintenance of the health and integrity of the retina. Animal models presuppose that the oxygen tension in the retina is highest in the innermost layers at the level of the choriocapillaris, less in the photoreceptors and further decreases throughout the outer retinal structures. The choroid provides by far the largest component of the oxygen for consumption by the photoreceptors. A lack of oxygen stores in the inner retina therefore makes a constant supply crucial for its normal functioning. Blood flow dysfunction and subsequent hypoxia are both a feature in the pathogenesis of several major ocular diseases such as retinopathy of prematurity (ROP), age-related macular degeneration (ARMD), diabetic retinopathy (DR) and glaucoma. The development of methods to measure retinal blood flow and blood oxygen saturation is crucial to improve understanding of the patho-physiology of major ocular diseases. Purpose: The aims of this work were, firstly, to determine the least variable (range ± standard deviation) wavelength combination (610/548, 600/569 and 605/586) and subsequent ODR with the prototype HRC device. Secondly, using the ODR with the lowest measurement variability, we sought to quantify retinal blood SO2 in arterioles and venules and investigate the relationship between retinal blood SO2 and total retinal blood flow (TRBF) in response to stepwise changes in PETO2 in healthy participants. Retinal blood SO2 and TRBF were assessed using the IRIS HRC (Photon etc. Inc. Montreal, Canada) and the RTvue Doppler Fourier Domain OCT (Optovue Inc, Freemont, CA) instruments, respectively. Methods: Ten healthy participants between the ages of 23 and 37, with an average age of 28.3 years were evaluated in two descriptive cross-sectional studies. Two gas provocation protocols; hyperoxia (end-tidal oxygen; PETO2 of 100, 200, 300, 400mmHg) and hypoxia (PETO2 of 100, 80, 60, 50mmHg) were administered in a fixed sequential order. In each phase of gas provocation (via modulation of PETO2), retinal blood SO2 and TRBF measurements were acquired with the HRC and Doppler FD-OCT. The precise and repeated control of the partial end tidal pressures of oxygen (PETO2) and carbon dioxide (PETCO2) over the pre-determined phase duration, irrespective of the individuals’ respiratory rate, was made possible with the RespirAct (Thornhill Research Inc., Toronto, Canada); a sequential re-breathing gas delivery Results: In arterioles, the group range (±SD) of ODR values for baseline measurements (PETO2 of 100mmHg) was 0.169±0.061 for the 605/586 wavelength combination, 0.371±0.099 for the 600/569 wavelength combination and 0.340±0.104 for the 610/548 wavelength combination. In venules, the group range (±SD) of ODR values was 0.600±0.198 for the 605/586 wavelength combination, 0.569±0.169 for the 600/569 wavelength combination and 0.819±0.274 for the 610/548 wavelength combination. With the 605/586 combination at baseline 1 and 2 in arterioles, the group range (±SD) of ODR values was 0.607 ± 0.224 and 0.619 ± 0.158, respectively (p = 0.370), while in venules the group range (±SD) of ODR at baseline 1 and 2 was 0.289±0.750 and 0.284 ± 0.729, respectively (p = 0.714). For the 600/569 combination at baseline 1 and 2 in arterioles, the group range (±SD) of ODR values was 0.747±0.350 and 0.761±0.391, respectively (p = 0.424) while in venules the group range (±SD) of ODR at baseline 1 and 2 was 0.329±0.675 and 0.366±0.659, respectively (p = 0.372). For the 610/548 combination at baseline 1 and 2 in arterioles, the group range (±SD) of ODR values was 0.604±0.263 and 0.685±0.450, respectively (p = 0.056) while in venules, the group range (±SD) of ODR at baseline 1 and 2 was 0.292±0.746 and 0.285±1.009, respectively (p = 0.131). There was no statistical difference found between baseline ODR values (baseline 1 and 2) across all three wavelength combinations in both arterioles and venules. The mean retinal blood SO2 value at baseline in arterioles for 4 participants was 95.19% ± 31.04% and venules was 53.89% ± 17.24% (p = 0.115). There was a negative linear relationship between group retinal blood SO2 and TRBF values in the 10 participants studied, although the results of any of the 10 individuals did not show evidence of such a relationship using the described methodology. The Pearson’s correlation coefficient (r) between TRBF and SaO2 was r = -0.354 and p = 0.001 and between TRBF and SvO2 was r = - 0.295, p = 0.008 Conclusion: Of the three wavelength combinations investigated (605/586, 600/569 and 610/548), the 605/586 combination was shown to have the overall least variability. It would be unwise at this stage to adopt this wavelength combination for clinical usage, however, since it is presupposed that the 605/586 combination is also the most reliable combination to detect change in retinal blood SO2 i.e. lower variability of the 605/586 combination may be irrelevant if this combination proves to be insensitive to change in retinal blood SO2. The absolute mean ± SD retinal blood SO2 in the arterioles (SaO2) was 95.19% ± 31.04% and in the venules (SvO2) was 53.89% ± 17.24%. These values fell within the range expected and described in the literature. The magnitude of the difference between the SaO2 and SvO2 was also consistent with the literature. These findings were all appropriate for a low flow, high oxygen exchange vascular network typical of the inner retinal vascular system. Using group rather than individual data, TRBF was found in this study to relate inversely with SaO2 (r = -0.354 and p = 0.001) and SvO2 (r = – 0.295 and p=0.008), respectively. This relationship between TRBF and SaO2 and SvO2, was as expected based upon data derived primarily from animal models. This study is ground-breaking and unique, in that, it is the first study to concomitantly measure both retinal blood SO2 and TRBF in human participants. Individual data showed extensive variability and noise, thus limiting the strength of the association between TRBF and SaO2 and SvO2..

Simultaneous blood perfusion and oxygenation monitoring is crucial for patients undergoing a transplant procedure. This becomes of great importance during the surgical recovery period of a transplant procedure when uncorrected loss of perfusion or reduction in oxygen saturation can result in patient death. Pulse oximeters are standard monitoring devices which are used to obtain the perfusion level and oxygen saturation using the optical absorption properties of hemoglobin. However, in cases of varying perfusion due to hemorrhage, blood clot or acute blockage, the oxygenation results obtained from traditional pulse oximeters are erroneous due to a sudden drop in signal strength. The long term goal of the project is to devise an implantable optical sensor which is able to perform better than the traditional pulse oximeters with changing perfusion and function as a local warning for sudden blood perfusion and oxygenation loss. In this work, an optical sensor based on a pulse oximeter with an additional source at 810nm wavelength has been developed for in situ monitoring of transplant organs. An algorithm has been designed to separate perfusion and oxygenation signals from the composite signal obtained from the three source pulse oximetry-based sensor. The algorithm uses 810nm reference signals and an adaptive filtering routine to separate the two signals which occur at the same frequency. The algorithm is initially applied to model data and its effectiveness is further tested using in vitro and in vivo data sets to quantify its ability to separate the signals of interest. The entire process is done in real time in conjunction with the autocorrelation-based time domain technique. This time domain technique uses digital filtering and autocorrelation to extract peak height information and generate an amplitude measurement and has shown to perform better than the traditional fast Fourier transform (FFT) for semi-periodic signals, such as those derived from heart monitoring. In particular, in this paper it is shown that the two approaches produce comparable results for periodic in vitro perfusion signals. However, when used on semi periodic, simulated, perfusion signals and in vivo data generated from an optical perfusion sensor the autocorrelation approach clearly (Standard Error, SE = 0.03) outperforms the FFT-based analysis (Standard Error, SE = 0.62).