Correlation between wave components of the second derivative of plethysmogram and arterial distensibility

The ratio of two wave components (magnitude of b/a constituting the second derivative of the plethysmogram (SDPTG) was correlated with arterial distensibility. Eighty-two subjects (33-93 years old) were classified into three groups according to the thickness of the intima-media complex of the common carotid artery measured by B-mode ultrasonography. One group was non-atherosclerotic (without pathologic thickening) (nAS) and the other two groups atherosclerotic (mild and severe thickening, or plaque formation) (AS-1 and AS-2). Distensibility (D) of the common carotid artery was calculated from arterial dimensions and blood pressure: h/p = D, where h = (Ds-Dd)/Dd; Ds, Dd and p represent the inner diameter of the carotid artery at peak systole, at end diastole and brachial pulse pressure, respectively. The plethysmogram was recorded at the cuticle of the 2nd digit of the left hand, and the SDPTG was determined with a 10 msec time constant. D showed a significant negative correlation with age in all subjects and in the three separate groups. The correlation between age and magnitude of b/a was significantly negative in all subjects. This negative correlation was not observed in the nAS group, while it was significant in both AS-1 and AS-2. The correlation between magnitude of b/a and D was significantly positive in all subjects and in each group. Significant differences were found among the three groups for magnitude of b/a and D. These results suggest that a decrease in magnitude of b/a or in D was proportional to the thickness of the intima-media complex of the carotid artery, that is, the development of atherosclerosis. These results provide direct evidence that magnitude of b/a of the SDPTG is related to the distensibility of the peripheral artery, and suggest that magnitude of b/a is a useful non-invasive index of atherosclerosis and altered arterial distensibility.