ASSESSMENT OF ARTERIAL COMPLIANCE : plethismographic vs ultrasonographic method

Early functional changes in the arterial wall leading to a reduced arterial compliance may be used to identify individuals at risk of vascular disease well before the onset of the sintomatic disease. We have proposed a new plethysmographic method useful for measuring forearm arterial compliance (AC). This method was previously validated by evaluating its capacity to detect pharmacological-induced changes as well as to detect differences between hypercholesterolemic patients and normal controls. The present study was designed to further validate this method vis-à-vis measurements made with an echotracking device, the technological “gold standard” for AC measurements. Twelve subjects were selected for the study. The between-method agreement was evaluated comparing 36 compliance measurement obtained with both methods. The area under the compliance/BP curve ranged from 2.41x10-2 to 6.73x10-2 ml•100ml-1 forearm•mmHg-1•mmHg, with a mean value of 4.15x10-2±1.10x10-2, when measured with the plethysmographic method (FACauc), and from 1.06x10-2 to 5.64x10-2 mm2/mmHg x 10-3•mmHg, with a mean value of 3.27x10-2 ±1.12x10-2, when measured with the echotracking device (RACauc). The bias between readings was –0.87x10-2±0.61x10-2, with a repeatability coefficient of 2.13x10-2. The mean absolute difference between the two measurements was 0.93x10-2±0.53x10-2, with a CV of 11.7% and a correlation coefficient of 0.85 (p < 0.0001). The FACauc and the RACauc responses to reactive hyperemia was evaluated in 3 subjects. Although not identical in absolute terms, the kinetics of compliance changes during reactive hyperemia was clearly appreciable using both the methodology. Finally, the FACauc and the RACauc were evaluated in 5 subjects also after sublingual GTN administration. In these subjects a dose dependent variation of RACauc was observed. All the compliance changes detected with the echotracking system were also detected with the plethysmographic device. Indeed, although different in terms of absolute values, the trends of compliance changes during reactive hyperemia as well as those induced by sublingual GTN are essentially identical for the two methods, thus indicating that the plethysmographic method describeed here provides reliable technology for arterial compliance measurements, applicable to clinical trials. Thus, although the plethysmographic method may not be considered as interchangeable with the echotracking one, both provide essentially the same kind of information. In conclusion, the proposed technique appears to be highly sensitive and may be considered as an alternative to ultrasound, as a potentially useful tool to detect and monitor in vivo compliance changes induced by arterial occlusion.