- Title
- Lower limb vascular assessment techniques to detect the presence and severity of peripheral arterial disease
- Creator
- Casey, Sarah Louise
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2020
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Peripheral arterial disease (PAD) affects approximately 15% of the population, and is known to result in ulceration, gangrene and limb extremity amputation, as well as causing ischaemic pain in some individuals. PAD is also associated with a fourfold increase in the risk of death from cardiovascular causes, with highest mortality in people with critical limb ischaemia. Early intervention and appropriate management is associated with better outcomes, and for this reason, ongoing screening of people at risk of PAD is recommended. Given that PAD is progressive and reflective of central atherosclerosis, it is imperative that screening techniques are reliable and are diagnostically accurate. This thesis evaluates the non-invasive vascular assessment techniques commonly used in clinical practice to identify the presence and severity of PAD. The research focuses on the ankle brachial index (ABI), as this is widely recommended for conducting lower limb vascular assessment, and compares the performance of this test to two alternate testing methods: the toe brachial index (TBI) and systolic toe pressures (TP). The reliability of the ABI was investigated by performing a systematic review. Due to the small number of studies suitable for inclusion, and the lack of reported statistical data, meta-analysis could not be performed. The review found that, although ABI reliability appears to be acceptable, there is a lack of consistency in the way studies were conducted and reported, particularly with regard to premeasurement rest time, which varied from five to fifteen minutes. Subsequently, four investigations of measures of clinical utility of lower limb non-invasive vascular assessment were undertaken. Firstly, the variability in premeasurement rest times reported by studies included in the systematic review resulted in the development of a study to examine the effect of rest time on ankle systolic pressure. This study found that ankle systolic pressure stabilises after 10 minutes of rest, with longer rest time not resulting in any further significant pressure change. The findings of the rest time study revealed that rest time can affect ankle systolic pressure, and therefore the ABI value obtained. Secondly, due to the limited available data investigating reliability of the ABI identified by the systematic review, an evaluation of intra-rater reliability of the test was undertaken. This study demonstrated that, although the test is reliable, the variability of the measure means that a large change is required before it can be interpreted as being clinically meaningful. Regression analysis revealed an association between history of smoking, increasing age and male gender and increased likelihood of an abnormal ABI. Sub-analysis by diabetes status found slightly lower reliability in this cohort. Thirdly, a study was undertaken to compare the predictive ability of the ABI, TBI and TP for diagnosing PAD using colour duplex ultrasound (CDU) as the reference standard. This study also investigated the diagnostic accuracy of all three tests to detect PAD vs no PAD, moderate/occlusive PAD vs no/mild PAD, and occlusive vs no/mild/moderate PAD. It found that all tests demonstrate a good probability of detecting the presence of PAD but do not differentiate as well between the degree of artery stenosis. The TBI and TP demonstrated higher overall diagnostic accuracy than the ABI. The lower diagnostic accuracy of the ABI for PAD, and only moderate agreement of the test with TBI values, highlighted limitations in relying on the ABI to diagnose the disease. The study also found that none of the tests are suitable for use in isolation, and that a combination of vascular assessment techniques is required in order to identify the presence and likely severity of PAD. Finally, an investigation of the effect of Medial Arterial Calcification (MAC) on the diagnostic accuracy of the three tests (ABI, TBI and TP) was undertaken. Although there is evidence of this condition affecting the ABI value, there is little research investigating the effect of this pathology on TP and the TBI, which are recommended as alternative testing techniques where MAC is suspected. A retrospective, case-control study was undertaken to compare the effect of MAC on the diagnostic accuracy of the ABI, TBI and TP for PAD. The strength of association of each test with PAD severity in people with and without MAC was also assessed. The ABI was found to demonstrate the lowest global measures of diagnostic accuracy in participants with MAC, which supports existing advice to use an alternative test in the presence of MAC. The overall diagnostic accuracy of the TBI was found to be less affected by the presence of MAC than ABI and to have greater diagnostic accuracy than TP. These results support the TBI as the test of choice in patients with suspected MAC.
- Subject
- peripheral arterial disease; vascular assessment; ankle brachial index; toe brachial index; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1419509
- Identifier
- uon:37460
- Rights
- Copyright 2020 Sarah Louise Casey
- Language
- eng
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 9 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 645 KB | Adobe Acrobat PDF | View Details Download |