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This dissertation attempts to show how the study of the variations in demographic experience between different types of communities can advance the understanding of the processes of English population growth in the past, particularly during the period of rapid economic change in the eighteenth century. Attention is concentrated on an area of fifty-two parishes, centered around the border of North East Somerset and West Wiltshire, which contained communities involved in a variety of economic activities. The principal objective is to demonstrate the relationships between economic developments and demographic change and more especially to emphasize the inter-relatedness of events in different communities, each of which fits into a complex regional system. The process of investigation is in three stages: first, aggregated annual totals of baptisms, burials and marriages (taken from parish registers and related documents) are used to analyse the general chronology of population change in the area as a whole and explanations for the acceleration and timing of growth are discussed. Secondly, similarities in the experiences of the constituent communities are studied and these provide the basis for the definition ~f groups of parishes with common sets of attributes. Movements of people between these groups are found to be an important element of regional population change. And thirdly, more detailed analytical techniques are used to investigate the processes of population change within individual communities. This indicates significant spatial differences in the fertility of populations and a study of the persistency of families identifies to what extent these differences arose because of spatial variations in environmental and economic conditions or because of the redistribution of population. The overall conclusion is that population change in a particular place, at a particular time cannot be fully explained without an understanding of changes that took place in other parts of the region in earlier generations.

Breathlessness during activity is increasingly recognized as a common symptom in the elderly, in older individuals with minor airway obstruction due to tobacco smoking, and in those with obesity. The underlying mechanisms of perceived respiratory difficulty in each of these populations remain unknown and are largely unstudied. Objective: The main purpose of this original research was to elucidate the alterations in central ventilatory drive and in dynamic ventilatory mechanics that might explain the origin of increased breathlessness during exercise in these three populations. General Hypothesis: In individuals with largely preserved resting pulmonary function, increased intensity of breathlessness during activity will arise as a result of measurable abnormalities of dynamic ventilatory mechanics, central respiratory drive, or both in combination. General Methods: We examined sensory-mechanical relationships during cardio-pulmonary exercise testing in each population (total n=146). We compared indices of ventilatory control (ventilation, pulmonary gas exchange and metabolic load), dynamic mechanics (breathing pattern and operating lung volumes) and ratings of dyspnea intensity in three well characterized cohorts: elderly versus younger; smokers with minor airway obstruction versus age-matched non-smokers, and obese versus lean participants. Results: Individuals across all three study populations had preserved resting pulmonary function. Compared with their respective control groups all three symptomatic groups demonstrated consistent abnormalities in dynamic airway function during exercise [expiratory flow limitation (EFL), dynamic increases in end expiratory lung volume, and restricted tidal volume response]; all had greater ventilatory requirements reflecting variable ventilation-perfusion and metabolic abnormalities. In all three groups, intensity of breathlessness increased as ventilatory demand approached capacity. In the elderly (with or without airway obstruction), breathlessness intensity ratings at a standardized ventilation during exercise correlated with indices of mechanical volume restriction secondary to EFL. In obese individuals, increased ventilatory drive secondary to increased metabolic loading (and not mechanical abnormalities) was the primary factor contributing to exertional breathlessness. Conclusion: Although the origin of breathlessness during physical exertion in the elderly (with or without minor airway obstruction) and in obese individuals is multi-factorial, we identified the central etiological importance of the combination of increased ventilatory drive and restrictive dynamic mechanical constraints to increasing ventilation. / Thesis (Ph.D, Physiology) -- Queen's University, 2008-07-02 14:17:41.602

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The aim of this thesis was to examine the effects of exercise on gas mixing in the lung during exercise. There were four major stages. Firstly, the existing equipment used with resting subjects was applied to the exercising subject and was found to be inappropriate. Secondly, an in-line system of measuring flow and gas concentration was devised. Thirdly this system was validated with the aid of a physical model and resting subjects. Finally, nitrogen wash-out data were collected from 24 subjects at rest and during progressive exercise at three standard exercise intensities. The dynamic response characteristics of the bag-in-box spirometer at high breathing frequencies (50 min-1) were such that tidal volume was underestimated by almost 50%. The box was too small and its response too a linear for adequate correction factors to be applied. The in-line system, based on a linear relationship between flow and several argon, oxygen, carbon dioxide and nitrogen mixtures ( r = + 0.99, p < 0.01 , Y = 0.2687 FAr + 0.995 ), measured tidal volumes reliably ( CV < 1% ) when expired flow was maintained at 35&deg; C. Thirty-six wash-outs of a 2.4 litre bell jar produced a mean value of 2.461 litres ( SD. 0.034, CV. 1.4% ). The capacity of the in-line system to measure gas mixing efficiency reliably was tested on resting subjects ( six trials each on two days ). Mean values were 76.7% ( SD. 7-5% ) and 76.8% ( SD 4.7% ); mean CV for all trials was 8%. Progressive exercise resulted in significant reduction in lung volume as measured by recovered nitrogen; there was evidence that at the greatest exercise intensity all the nitrogen was not recovered. Decreased diffusion time as a result of greater respiratory frequency may have been responsible. The significantly greater tidal volumes and respiratory frequencies observed on exercise resulted in bigger minute volumes. Both series and alveolar deadspaces increased, but the greater minute volume more than compensated for the growing dead spaces, and so the inspired volume available for mixing was increased. Ventilatory and gas mixing efficiency improved significantly as exercise progressed, but the greatest improvement occurred at the first power output of 50W; thereafter, there was very little change in gas mixing efficiency in spite of three-fold increase in ventilation. It is possible that gas mixing efficiency functions optimally at FRC and that, unlike some other physiological measures, there is little reserve capacity. However, the possibility of gas mixing deficiencies at maximal exercise leading to a ventilatory limit to maximal oxygen uptake remains, and this issue still needs to be investigated.

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