Haemodynamic studies on arterial stenoses and the assessment of peripheral vascular disease.

Various methods of assessing peripheral vascular disease are studied by making measurements both on dogs, and patients with arterial disease. Theoretical and experimental models of blood flow in diseased arteries are reviewed. A new type of experimental inter-changeable stenosis is described; and the flow, pressure and Doppler ultrasound results from a number of dog experiments using the device are presented. The relationship between the pressure drop across a stenosis and the flow through it in-vivo is shown to differ from previously reported in-vitro values. The severity of a stenosis is shown to have little effect on peripheral resistance, and attention is drawn to the lack of concrete evidence in the literature suggesting that it does. A possible explanation for this finding is given. It is suggested that ultrasonic Doppler traces are influenced by the distal bed as well as by proximal stenoses. Experimental Doppler spectra are compared with spectra calculated from electromagnetic flow waveforms and found to be in good agreement. Measurements from over 150 vascular patients are presented, and the difficulty of determining the validity of these measurements discussed. The indirect pressure measurement method of assessing vascular disease is examined and shown to be of limited value. It is shown that an inflatable cuff can substantially alter the pressure distribution within an artery, and the possibility of worsening disease being reflected by a higher occlusive cuff pressure is introduced. It is shown that both Doppler ultrasonic velocity measurements and direct arterial pressure measurements agree with the clinical assessment in extreme cases, but that in equivocal cases the two tests often disagree with each other. The difficulty of adjudicating between tests is reaffirmed and a new method of objective evaluation suggested. Finally the problems consequent upon the dynamic nature of the disease are mentioned.