The assessment of aortoiliac narrowing.

The deficiencies of arteriography in the assessment of arterial narrowing proximal to the inguinal ligament are well recognised. This thesis has set out to examine the usefulness of continuous wave Doppler ultrasound as a method of providing more reliable diagnostic information in this segment. After a review of the literature, the methods used in the study are described. Two series of animal experiments are then presented. In the first, three methods of analysis are applied to Doppler waveforms recorded from below stenoses of known dimensions implanted in the canine iliac artery. Pressure and flow measurements are used to calculate peripheral and stenosis resistance. The conclusion from this study is that neither pulsatility index (PI) nor Laplace transform damping factor (LTD) is consistently sensitive to stenoses of less than 88% area reduction and that this is in part due to the effect on these parameters of peripheral resistance. A third method, principal component analysis (PCA) appeared to give slightly better results. In the second series of canine experiments, the extent of turbulence produced by stenoses of varying degree is investigated. There is a clear relationship between increased tightness of stenosis and increased turbulence propagation. In the final part of the thesis the same methods of Doppler waveform analysis are investigated in a clinical study. The main reference material for comparison with the Doppler methods is direct arterial pressure measurement rather than arteriography. Although there are clear trends seen with all the indices examined, there is marked overlap between their values for different clinical groups, especially for PI and LTD. In particular, the effect of superficial femoral artery disease on common femoral Doppler waveforms is identified as a major factor which limits the usefulness of the methods. Again PCA appears to perform best, although the use of two dimensional information seems necessary to get the most out of the technique. In practice, it seems unlikely that the use of these methods of Doppler waveform analysis will be helpful in those specific cases where there is genuine doubt about the state of the proximal vessels. In conclusion, none of these methods is sufficiently accurate to be recommended for widespread adoption without more research. The present work would suggest that the information about lesser degrees of proximal narrowing is simply not contained in the outline of the Doppler waveform. Direct pressure studies provide the best current method of assessing aortoiliac narrowing.