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.

<p>This is an examinaton of welfare officers and patients experiences of a course in mindfulnessbased stressreduction in primary care. The authors used a qualitative method and a phenomenological hermeneutics scientific philosophical position. The analys of the data appeared by using three theoretical perspectives; cognitive, coping and Antonovskys Sence of Coherence. The purpose was to get a deeper understanding of what mindfulness is, how a course in mindfulnessbased stressreduction can be arranged and how it is comprehended by the welfare officers and previous participators of the course. To get an opinion of the issue the authors wanted to know the welfare officers intention of the course, to which patients they provide the course, what the participators thought about their situation before and after the attendence and if they had assimilated the knowledge and if so how it was applicable. The results indicated that the welfare officers and the patients intentions of the course where incoherent. The welfare officers intention was to teach the patients a way of manner to incorporate and to handle stress and other disabilities. The patients intention was to get strategies to manage their stress and chronic pain. Their most customary strategies was breathing and consideration of their thoughts.</p>

This is an examinaton of welfare officers and patients experiences of a course in mindfulnessbased stressreduction in primary care. The authors used a qualitative method and a phenomenological hermeneutics scientific philosophical position. The analys of the data appeared by using three theoretical perspectives; cognitive, coping and Antonovskys Sence of Coherence. The purpose was to get a deeper understanding of what mindfulness is, how a course in mindfulnessbased stressreduction can be arranged and how it is comprehended by the welfare officers and previous participators of the course. To get an opinion of the issue the authors wanted to know the welfare officers intention of the course, to which patients they provide the course, what the participators thought about their situation before and after the attendence and if they had assimilated the knowledge and if so how it was applicable. The results indicated that the welfare officers and the patients intentions of the course where incoherent. The welfare officers intention was to teach the patients a way of manner to incorporate and to handle stress and other disabilities. The patients intention was to get strategies to manage their stress and chronic pain. Their most customary strategies was breathing and consideration of their thoughts.

Neurons in the Locus coeruleus (LC) play an important role in the central CO2 chemosensitivity. However, the molecular mechanisms for neuronal CO2 chemosensitivity remain unclear. To demonstrate the expression of pH/CO2 sensitive ion channels, we screened the inward rectifier K+ channels (Kir) and transient receptor protein (TRP) channels, as parallel studies in this lab suggested that certain Kir and TRP channels are involved in neuronal responses to high levels of CO2. Our results showed that several members of the Kir and TRP channel families were robustly expressed in the LC neurons at the mRNA level. Of particular interest are TRPC5, Kir4.1 and Kir5.1 channels that are all pH-sensitive. The rich expression of various pH-sensitive Kir and TRP channels suggests that these ion channels are likely to play a role in the chemosensitivity of LC neurons.

The purpose of the study was to investigate whether sleep-disordered breathing (SDB) impairs executive functioning in children. Additionally, the study sought to identify the executive functions at risk in SDB and the contribution of daytime sleepiness. SDB represents a spectrum of upper airway conditions that can be mild, such as snoring, or severe, such as obstructive sleep apnea (OSA). Children with these problems may present with excessive sleepiness, failure to thrive, and a variety of cognitive and behavioral dysfunctions including impaired executive functioning. Beebe and Gozal (2002) developed a theoretical model to explain the impact of sleepiness and hypoxia on executive functioning. This model provided a framework to examine links between the medical disorder and the neuropsychological consequences. Twenty-seven children with suspected SDB were tested with polysomnography (PSG) and a neuropsychological battery. Parents completed subjective measures of cognitive function and sleep symptoms. The children were ages 8 to 18 and had no congenital or acquired brain damage. They were matched for age and gender with 21 healthy controls. The executive function protocol included subtests from the Delis-Kaplan Executive Function System (D-KEFS), the digit span subtest from the Wechsler Intelligence Scale for Children (WISC-IV), the Tower of London-II-Drexel University (TOL-II), the Behavioral Rating Inventory of Executive Functioning (BRIEF), and the Conners’ Continuous Performance Test (CPT-II). Statistical analysis was performed using 2 statistical software packages, SAS and NCSS. Regression analysis was used to evaluate all variables. Due to significant group differences in socio-economic status (SES), SES was included as a covariate, along with IQ. No group differences in IQ were found. Significantly less robust executive function in children with SDB was identified in the domains of cognitive flexibility and impulsivity. Additionally, poorer executive planning and overall inattentiveness was also associated with SDB. Level of significance was set at 0.05 and trends (0.05 < p < 0.10) were acknowledged. Other areas of executive function, including working memory, behavioral and emotional inhibition, and processing speed were not associated with SDB. Moreover, academic functioning was significantly lower in children with SDB, although the differences can be shared equally with SDB, SES and IQ.

In the study, micro-PEM fuel cells are designed and fabricated in-house through a deep UV lithography SU-8 process and a wet etching technique for perforated holes plates (diameter is 750 £gm) of 50 £gm thickness of pure copper. Measurements of cell performance are performed using the low percentage of the weight concentration (1-10 wt. %) of NaOH solution, Al paper as the source material for hydrogen production, and different open ratios of the perforated plates to determine which best improves cell power density. Experimental results are presented in the form of polarization VI and PI curves under the above operating conditions. The experimental results show cell performance is enhanced by the self-heating, humidifying of hydrogen production, hydrogen internal circulation and accumulated pressure. Finally, the micro-PEM fuel cell system with DC/DC boost converter can generate 4.99 V for use in cellular phone accumulators charging.

In this thesis, a long-term operation direct methanol fuel cell (DMFC) stack is developed. In order to reach this goal required in many ways, including select highly chemical stability materials, operating conditions must also be stable, and avoid changing the MEA structure when preserved, then can cause the DMFC to maintain stable operation for a long time. First of all, in order to avoid contaminating electrode, this study find out the chemical instability materials. Second, this study design a device which does not require power then can stability supply consumption fuel, and apply this device in 16-cell DMFC. Finally compare with continuous fuel supply and without fuel supply, two operating conditions performance stability. From these experiments can find out, the DMFC indeed in stable operation for a long time under the appropriate supplement. Traditional fuel supply systems typically using the pump fuel recycling, so the structure is more complex, difficult to reduce the volume, and not conducive to carry. If using a passive operation, fuel completely stored in the reaction Chamber, even though the structure is simple there will be a problem with fuel supply. In recent years, someone use vapors of methanol to supply the fuel, although can use high concentration methanol to extend operating time, but the evaporation rate is difficult to control, the fuel can¡¦t be supplied in time, especially when the large current is needed, and CROSSOVER issues would be difficult to overcome. In our 16-cell DMFC, continues to add appropriate amount of fuel consumed which according to the different current. The fuel supply device with a sliding control plate which can control methanol and water diffusion rate respectively. This device only to provide consumed by reaction and leaked fuel in anode chamber, so that the methanol concentration can maintained in the proper range at anode chamber. This device only use diffusion and gravity effects, don't use a fuel pump, so will not consume DMFC power.

Abstract A one-watt portable air-breathing direct methanol fuel cell stack (called DMFC), which can supply fuel passively and operate steadily, is developed in this thesis. A DMFC to maintain its performance stable, the most important strategy is to keep the methanol concentration in reacting chamber to be proper and stable. A fuel supplying system will be in accordance with the depletion of chemical reaction and the leakage of fuel under different circuit current to supplying fuel. To regulate the methanol and water supplying, a fuel supplying system by gravitation and diffusion forces deliver methanol and water to fill up the consumed fuel to maintain the concentration of methanol solution in anode reaction chamber, by adjusting a sliding gate to control the area of a diffusive membrane and utilizing three cotton threads and hoses to distribute the fuel to proper location. In doing so, the methanol concentration in the anode chamber can keep within an appropriate range, so that the DMFC stack can operate stably for a longer period. Yet the diffusivity of the diffusive membrane is comparatively less, the supply system is not easy to downsize. To reduce the size of portable DMFC, we make use of a fuel plug tank to combine the supply tank and reacting chamber, and thus the cell package is more portable. Between the plug tank and the reacting chamber, the three cotton threads are used to distribute the fuel to proper location. The above two design with no extra auxiliary device; therefore, no extra energy will be consumed. To reduce the fuel leakage, and make more use of fuel, four block films is pasted on the bare area of the nafion membranes in a 16-cell DMFC stack. If no fuel is fed into reaction chamber, this will prolong the cell operation time. Under the condition of 3.7 V (cell phone rated voltage) and the operating current 225 mA, our experiments display that the stacks with the two fuel supplying systems can continuously operate for more than 3 hours with no obvious change in methanol concentration within reaction chamber. The experimental results show that this simple passive fuel supplemental system can really keep the DMFC stack operating stably for a sufficient long period.

A new type of heterogeneous carbon fiber bunch bipolar plate developed in our lab is applied to portable pure hydrogen proton exchange membrane fuel cell stacks. Several different types of bipolar plate structures have been designed, and the voltages and currents of these fuel cell stacks are measured to compare their performance. The new type of heterogeneous carbon fiber bunch bipolar plate is well in low contact resistance, weight low, small volume and the flexible geometry shape. Due to its flexible structure of carbon fiber bunch, the compressing pressure is small while assembling stack so that the electrode can not be over compressed and out of shape. Therefore the high porosity of diffusion layer can be keep and reaction gas can enter and distribute to all reaction areas easily. For using to portable equipments, a small 6-cell flat type of fuel cell stack are developed firstly. The total weight is about 75g and the total volume is about 68cm . The second stack is cylinder-type(I) fuel cell stack. The total weight is about 60g and the total volume is about 71cm . The third stack is cylinder-type (II). The total weight has been reduced to about 20g and the total volume has been reduced to about 30cm . Above three kinds of the 6-cell stacks the total electrode area is 13.5cm . Using Nafion, the catalyst content anode Pt 0.4mg/cm , cathode Pt 1.0mg/cm , On room temperature and inlet hydrogen gauge pressure 0.15atm air-breathing, total output power of the cylinder (II) can reach 1.85W, and the power density of unit area can reach about 137mW/cm^2.

In this research the effects of the fabrication processes of MEA on the output power of a DMFC stack are studied by changing hot-pressing conditions including pressure, temperature and time. Additionally, the effects of the various treatments of the MEAs on the output voltage and power are also studied after the hot-pressing process of MEA is finished. In the first experimental study the catalyst of cathode is 4.0mg/cm unsupported HP Pt black, Anode is 4.0mg/cm 80% HP Pt-Ru Alloy (1: 1), membrane is Nafion 117, and bipolar plates is heterogeneous carbon fiber bipolar plate developed by our fuel cell laboratory. The MEA for single cell includes the area of membrane 3*3 cm2 the active area of electrode 1.5*1.5 cm2. Under the hot-pressing conditions 120 oC, 100 bar and 90s, the maximum power density can reach a value of 18 mW/cm2 at the conditions of methanol concentration 3 M, air-breathing, and room temperature After several experiments, we observed that performances of MEAs decayed with time. So we designed a series of experiments to inspect the various possible reasons and try to solve this problem. The cylindrical DMFC is one of the most important developments in our lab. However, the MEAs made for plate-type DMFC do not fit the cylindrical DMFC stack properly. The electrodes easily pealed off from the membrane and the contact resistance increases after certain periods. So the hot-pressing device had been redesigned to fit the cylindrical DMFC stack. After that the total power of the 6-cell stack with total active area 15 cm2 can reach a value 135 mW. If the performance of each cell of the 6-cell stack is uniform, we expect that the total power of this stack can reach a higher value 195 mW, which can be applied to some portable electronic products.