Asthmatics most "at risk of death" from their asthma are those that have severe asthma with a history of severe life threatening attacks (SLTAs). Some asthmatics are poor perceivers of the severity of their asthma. It is not known whether these two groups form a homogeneous population. The aim of this thesis was to establish whether this was the case by comparing the sensitivity of asthmatics classified as severe with a history of severe life threatening attacks, asthmatics without a history of SLTAs, mild and moderate asthmatics, and matched controls to externally added resistive loads during inspiration. It also aimed to establish whether poor sensitivity to externally added resistive loads during inspiration was associated with diminished amplitude or increased latency of scalp potentials evoked by inspiratory occlusion. Two studies were conducted to meet the first aim. The first study tested the applicability of the equal variance normal-normal model of signal detection theory as a descriptor of subjects' performance when discriminating between different levels of externally added resistive loads during inspiration. Twelve subjects rated their capacity to distinguish between pairs of resistive loads ranging from 2-33cmH2O/L/s presented during a single inspiration. Data were collected for 100, 200 and 300 single breath trials. The results showed that the model fitted the data well; that 200 trials provided performance indices that were sufficiently precise to distinguish between relatively low, average and high levels of sensitivity; and that, for the modality tested, respiratory sensation complied with Weber’s Law. The second study applied the validated procedure to test the ability of 25 asthmatics classified either as severe, or mild or moderate, and 25 matched controls to distinguish between pairs of external resistive loads ranging from 2-33cmH2O/L/s presented during a single inspiration. Analysis of the data (ANOVA) showed that there were no significant differences in the ability of subjects to distinguish between resistive loads regardless of whether they were severe asthmatics with or without a history of SLTAs, mild or moderate asthmatics, or matched controls. It was concluded that asthmatics with poor sensitivity to the respiratory sensation tested and asthmatics most "at risk of death" from their asthma were not a homogeneous group, but poor sensitivity coupled with severe asthma, and a history of SLTAs most likely increased the risk of death to that patient. Four studies were conducted to meet the second aim. The first three studies were concerned with determining the reproducibilty of the scalp potential evoked by inspiratory occlusion (designated respiratory event related evoked potentials, RREP) and establishing a reliable recording protocol for the RREP that was relatively free of artefact. The results showed that the RREP was relatively stable over time and the best recording sites were cephalic electrode pairs C3-Cz and C4-Cz (10-20 International System). The fourth study examined the relationship between the ability of 25 asthmatic subjects and their matched controls to distinguish between levels of resistive loads added to inspiration and the latencies and amplitudes of the first positive and first negative components of the RREP. Correlation analysis showed that there was no relationship between sensitivity to added resistive loads during inspiration and RREP component parameters. It was concluded that diminution or absence of the early components of the RREP was not indicative of impaired perception of respiratory sensation though some issues regarding the appropriateness of the analysis still require resolution. / Whole document restricted, but available by request, use the feedback form to request access.
| Identifer | oai:union.ndltd.org:ADTP/277122 |
| Date | January 1994 |
| Creators | Gaeta, Helen |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Whole document restricted but available by request. Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated., http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm, Copyright: The author |
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