People with diabetes suffer from a high risk of developing foot related diseases. It is therefore important to perform a blood pressure measurement on the toe to be able to diagnose and treat in time. Using laser Doppler flowmetry has been proven to be a useful technique for this purpose during a standard blood pressure measurement procedure using a cuff. The laser Doppler probe detects once the blood flow returns which can then be related to the pressure value. However, the algorithm currently used by the company for detection of return of blood flow is in need of improvements. This thesis aims to develop an improved algorithm, which is more robust against artifacts. Furthermore, a warning system for uncertainties in the detection will be developed and integrated with the new algorithm. To create the algorithm an investigation of the signals’ appearances was performed to obtain an understanding of what artifacts and characteristics the algorithm should be able to handle. First three different basic approaches were implemented and tested, namely model curve, threshold and pulsations. These algorithms were then combined into two different more complex algorithms. One of them consisted of the model curve and the pulsation algorithm, the second combined algorithm consisted of the threshold algorithm and the pulsation algorithm. From the result it was found that the second combined algorithm performed best. It had a high accuracy and a well-functioning warning system. However, the algorithm had problems to correctly detect the return of flow when it is characterised by a slow increase of the perfusion. The biggest contribution by this thesis is the newly developed warning system. A false detection can lead to a false diagnose to be given if the operator is not attentive. The warning system is therefore an important feature since it can prevent this from occurring.

The aim of the present thesis was to assess the occurrence of early lower extremity arterial disease (LEAD) in patients with diabetes and to assess novel potential risk markers for development or worsening of LEAD in the same patients. In parallel different measures of impaired peripheral circulation were evaluated. The measurement of ankle-to- brachial blood pressure index (ABI) to screen for asymptomatic LEAD in diabetic subjects is unreliable since a large proportion of patients have stiff ankle arteries (mediasclerosis) and thus may display a too high ABI. We studied type 1-, type 2 diabetic and non-diabetic subjects without a previous history of LEAD and a composite variable of ankle – plus toe blood pressures and indices was compared to ABI alone in detecting LEAD. Significantly more subjects with reduced peripheral circulation were detected using the composite variable compared to ABI alone. This was particularly true in diabetic subjects, about 30% of whom had signs of impaired peripheral circulation. Thus, it was found that toe blood pressure measurements, alone or in combination with ankle blood pressure measurements, increase the sensitivity for finding early asymptomatic LEAD in diabetic subjects. No significant difference in reproducibility between measurements of absolute ankle- and toe blood pressure and indices was found, but a correlation between systemic (brachial) and toe blood pressure variations over time may suggest that indices are more correct in assessing peripheral arterial circulation. Furthermore, toe blood pressure measurements can be performed using either the great toe or dig II and a strong concordance is found between these measurements. In addition, since the pole-test, another non-invasive method to measure peripheral blood pressure which is less sensitive to the presence of mediasclerosis compared to ABI, correlated significantly with toe blood pressure measurements this method may be used as an alternative screening method in subjects with previously known LEAD. Age, hypertension and glycemic control are well known risk factors and, in addition, high tissue plasminogen activator (tPA) activity turned out to be a novel early marker for asymptomatic LEAD in diabetic subjects, particularly in patients with type 2 diabetes. Age and hyperglycemia are the most important risk factors for development and progression of subclinical lower extremity arterial disease in type 2 diabetic subjects. No independent associations between markers of inflammation, such as CRP, interleukin-6 and TNF-α and early asymptomatic LEAD were seen among non-diabetic or diabetic subjects. In conclusion, impaired arterial circulation in the lower extremities is common in diabetic subjects even in the absence of symptoms. Including toe blood pressure measurement when screening for asymptomatic LEAD in diabetic subjects improves the ability to detect reduced peripheral circulation and this method avoids falsely elevated blood pressures readings due to mediasclerosis in the ankle arteries. Moreover, an altered fibrinolytic activity should be further evaluated as an early marker of atherosclerosis and LEAD.

Diss. (sammanfattning) Umeå : Umeå universitet, 2009. / Härtill 4 uppsatser. Även tryckt utgåva.