Chronic sustained hypoxia (CH) occurs in populations living at high altitude and in patients with chronic pulmonary disease. Exposure to CH produces ventilatory acclimatization to hypoxia (VAH) and increases the hypoxic ventilatory response (HVR) by mechanisms that involve areas of the brainstem that control breathing. The nucleus tractus solitarius (NTS) is a sensory integrative center in the medulla receiving carotid body afferents and known to be crucial for VAH. Our previous results demonstrated that glia cells in the rat NTS contribute to VAH but these mechanisms have not been studied in mice exposed to CH beyond 24 hours. We hypothesized that CH produces an early transient activation of astrocytes and microglia in the mouse brainstem as observed in rats. To study the activation of glial cells with CH, we exposed mice to normobaric hypoxia (10% FiO2) for 0.5, 1 and 4 hours and 1 and 7 days. Mice were perfused with 4% paraformaldehyde and brainstem sections were obtained. We quantified astrocyte activation by measuring glial fibrillary acidic protein (GFAP) intensity with immunofluorescence, and microglial activation using image analysis to measure changes in branch morphology. Exposure to CH significantly increased GFAP intensity after 30 minutes and 1day but it returned to normoxic control levels after 1 week of CH. Measurements of microglia during 7 days of CH have not been completed. The results differ from those in rats (Stokes et al., 2017) but suggest that astrocyte activation in the NTS may be an initial step in VAH.

Neuron-glia communication in the central nervous system is emerging as an important component of neuronal signaling in respiratory control centers of the brainstem. To investigate glial cell contributions to ventilatory acclimatization to hypoxia, I measured the time course of activation of microglia and astrocytes’ neural circuits that control breathing following different lengths of exposure to sustained hypoxia (10% O2). Rats were exposed to sustained hypoxia at the following time points: 30 minutes, 1-, 4-, and 24-hours, 4- and 7-days. Activation of glial cells was measured in two respiratory control centers: the nucleus tractus solitarius (NTS), a sensory integrative center known to be important for ventilatory acclimatization to hypoxia, and the hypoglossal (XII) motor nucleus, a respiratory motor nucleus adjacent to the NTS. Microglia (Iba-1 positive cells) show an active morphology (shorter and fewer branches measured with image analysis, IMARIS) after 1 hour of hypoxia in the NTS and XII and return to the resting ramified state (longer filaments and extensive branching) after 4 hours of hypoxia. The number of microglia stayed constant throughout activation. Astrocytes (glial fibrillary acidic protein, GFAP positive cells) increased GFAP antibody immunofluorescent intensity after 4 hours of sustained hypoxia in the NTS but not until 7 days in XII. Astrocyte proliferation was only observed after 7 days of sustained hypoxia in the hypoglossal motor nucleus. These results show that glial activation with sustained hypoxia occurs sequentially with microglia activation preceding astrocyte activation and a time course that is unique in different medullary respiratory centers. This indicates an important role for glia in neural plasticity with sustained hypoxia and ventilatory acclimatization to hypoxia.

California is the largest cement producing state in the U.S., accounting for between 10 percent and 15 percent of U.S. cement production and cement industry employment. The cement industry in California consists of 31 sites that consume large amounts of energy, annually: 1,600 GWh of electricity, 22 million therms of natural gas, 2.3 million tons of coal, 0.25 tons of coke, and smaller amounts of waste materials, including tires. The case study summarized in this paper focused on providing background information, an assessment of energy-efficiency opportunities and barriers, and program recommendations that can be used by program planners to better target products to the cement industry. The primary approach to this case study involved walk-through surveys of customer facilities and in depth interviews with customer decision makers and subsequent analysis of collected data. In addition, a basic review of the cement production process was developed, and summary cement industry energy and economic data were collected, and analyzed. The analysis of secondary data provides background information on the cement industry and identification of potential energy-efficiency opportunities. The interviews provide some understanding of the customer perspective about implementation of energy-efficiency projects.

Asthma is defined by its intermittence. Periods of normal function are interrupted by intermittent bouts of airflow obstruction, and the severity and frequency of these bouts define the severity of the disease. Asthma also varies in space just as it does in time. Patches of the lung become compromised during an asthma attack, while the rest of the lung continues to function normally. This dissertation explores the intersection of these two modes of variation – what causes bronchoconstriction to occur in patches, and will it cause the same patches to emerge time after time?

A seminal modeling study predicted that lung units under smooth muscle stress exhibit a type of emergent behavior; self-organized patches of constriction can arise from the small airways because of the interdependence of airflow through the airway tree. In a sense, airways “communicate” with each other through flow patterns in a way that allows large-scale patterns to emerge.

One goal of this dissertation work was to empirically verify the findings of this model. We chose to perform studies in healthy normal subjects to ensure that the patterns of constriction we observed were due to interdependence and not to underlying inflammation or remodeling. The results of our first study (Chapter 2) found that bronchoconstriction – provoked with methacholine – in healthy subjects did indeed occur in a spatially patchy pattern.

Further, we found that this patchy pattern was recurrent in challenges weeks to months apart. We showed that, although subjects each had a characteristic pattern of constriction, there was an overall tendency for the dependent lung to constrict when supine. Our second study (Chapter 3) showed that this was due to the interaction between gravitational compression of tissue and the underlying topography of the airway tree structure.

Our final study (Chapter 4) showed that healthy subjects did not recover from constriction immediately after albuterol inhalation, even though traditional metrics of lung function indicated that they had. We interpreted this as evidence for the power and utility of functional imaging in detecting and characterizing pathologic function.

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