A novel photoplethysmography technique to derive normalized arterial stiffness as a blood pressure independent measure in the finger vascular bed

Abstract

Stiffening of the small artery may be the earliest sign of arteriosclerosis. However, there is no adequate method for directly assessing small arterial stiffness. In this study, the finger arterial elasticity index (FEI) was defined as the parameter n which denotes the curvilinearity of an exponential model of pressure (P)-volume (V(a)) relationship (V(a) = a - b exp (-nP)). For the original estimation, the FEI was calculated from a compliance index from the finger photoplethysmogram whilst occluding the finger. A simple estimation of the FEI was devised by utilizing normalized pulse volume instead of the compliance index. Both estimations yielded close agreement with the exponential model in healthy young participants (study 1: n = 19). Since the FEI was dependent on finger mean blood pressure, normalized finger arterial stiffness index (FSI) was defined as standardized residual from their relationship: mean and standard deviation (SD) of the FSI were 50 ± 10 (study 2: n = 174). The mean coefficient of variation of the FSI for four measurements was 5.72% (study 3: n = 6). The mean and SD of the FSI in seven arteriosclerotic patients were 100.0 ± 13.5. In conclusion, the FEI and FSI by simple estimation are valid and useful for arteriosclerosis research.

iPhysioMeter: A new approach for measuring heart rate and normalized pulse volume using only a smartphone

“…The finger PPG was measured in the transmittance mode using an 810-nm near-infrared LED as the light source and a photodiode as the photo sensor, placed on opposite sides of the tip of the left middle finger. The sensors and an amplifier to which the sensors were connected were built in the authors' laboratory, as has been previously reported (Tanaka et al, 2011). A logarithmic transformation was applied to the NPV values (i.e., ln NPV) to normalize the distribution.…”

Potential for Health Screening Using Long-Term Cardiovascular Parameters Measured by Finger Volume-Oscillometry: Pilot Comparative Evaluation in Regular and Sleep-Deprived Activities

“…It has been reported that the FEI reflects structural (not functional) changes in the finger artery [17], [19], and the PP is also known to change with age following the progressive stiffening of larger arteries [16]. For these reasons, FEI and PP are generally recognized as long-term cardiovascular risk factors.…”

“…Although a definite reason for this is not yet clear, one possibility could be considered. According to Tanaka et al's measurement procedure [19], FEI is calculated from the average value of eight or nine measurements. Therefore, the one-shot measurement applied in the present prototype might be inadequate to evaluate the long-term elasticity of small arteries.…”

“…Finger-artery elasticity index (FEI), shown to be a valid index of finger vascular elasticity [17], [19], and measured by the volume-oscillometric procedure mentioned above, was defined as the absolute value of the slope that follows the curvilinearity in the pressure-volume function of the finger artery, and can be calculated from the linear relationship of the log-transformed compliance index (CI: = NPV/PP) to the transmural pressure (P tr : = MBP−P c ), giving the following equation: …”

“…Briefly, measurements are taken from a single finger, using photo-plethysmography for the detection of peripheral pulse volume signals. The instrument then calculates: 1) systolic, mean and diastolic blood pressure (SBP, MBP and DBP, respectively) using the volume-oscillometric method [13] - [15]; 2) pulse pressure (PP), which is a strong predictor of increased large artery stiffness and high cardiovascular risk [16]; 3) heart rate (HR); 4) normalized pulse volume (NPV), which reflects !-adrenalin-mediated sympathetic control of the finger arteriolar vessels [17], [18]; and 5) the finger-artery elasticity index (FEI) derived from a simple descriptive model of the exponential pressure-volume function for the finger vascular bed [17], [19], modified by the volume elastic modulus [20]. These cardiovascular indices are simultaneously obtained using the present instrument and, whilst each is of interest and significant in itself, the adoption of a comprehensive method for handling the combined datasets is necessary if they are to be of practical use.…”