Evaluation of vascular wall elasticity of human digital arteries using alternating current-signal photoplethysmography

Figures & data

Figure 1 Schematic block diagram of a photoplethysmograph system for the human finger.

Notes: The light-emitting diode (LED) system generates an infrared light directed toward the finger. The pressure generator induces a vascular volume change through the occluding cuff. The photo sensor detects the reflected light from the finger. The electric current from the photo sensor is decomposed into an alternating current (AC) and a direct current (DC). The AC current is then filtered through a high-pass and a low-pass filter. The A/D converter converts the AC, DC, and cuff-pressure input signals to the digital outputs before storing them on the personal computer.

Figure 2 Example of the recorded output signals from the photoplethysmograph: the alternating current (AC), direct current (DC), and cuff-pressure (P_c) signals are shown.

Notes: The P_c started to compress and collapse the arterial system at 180 mmHg. The P_c gradually decreased because of the deflation of the occluding cuff. When the P_c was equal to the systolic blood pressure (P_sys), the fluctuation in the AC signal started to be recognized. When the P_c was equal to the mean blood pressure (P_m), the transmural pressure (P_tr) was zero and the amplitude of the AC signal reached its highest value. When the P_c was equal to or less than P_m, the amplitude of the AC signal implied the arterial volume difference between systole and diastole (ΔV). The relative volume difference (ΔV/ΔV₀) was derived from the light intensity of the AC signal using the ratio of the AC amplitude at any P_tr to the AC amplitude at zero P_tr.

Figure 3 Relationships between the transmural pressure (P_tr) and the relative volume difference (ΔV/ΔV₀) in subjects with moderately sized fingers according to the occluding cuff size: 20 mm (♦), 22 mm (■), and 24 mm (▲) diameter cuffs.

Notes: ΔV/ΔV₀ is shown as the mean ± standard deviation (n = 5). The ΔV/ΔV₀ decreased with P_tr. There was no significant differences among the P_tr –ΔV/ΔV₀ curves obtained from the three cuff sizes.

Figure 4 Relationships between the transmural pressure (P_tr) and the relative volume difference (ΔV/ΔV₀) in subjects with large fingers according to the occluding cuff size: 20 mm (♦), 22 mm (■) and 24 mm (▲) diameter cuffs.

Notes: ΔV/ΔV₀ is shown as the mean ± standard deviation (n = 3). The ΔV/ΔV₀ decreased with the transmural pressure. The curves for the 20 mm diameter cuff differed from the curves for the 22 and 24 mm diameter cuffs. The small cuff with the 20 mm diameter seemed to affect the P_tr –ΔV/ΔV₀ relationship in subjects with large fingers.

Figure 5 Average mean blood pressure (P_m), pulse pressure (ΔP), and heart rate in six groups of subjects (eight women and eight men, 20–25 years old; five women and five men, 32–45 years old; and six women and six men, over 50 years old) presented in five subfigures: (A) average P_m in the brachial (filled bars), and digital (open bars) arteries; (B) average ΔP in the brachial (filled bars), and digital (open bars) arteries; (C) average P_m (open bars), and ΔP (filled bars) in the brachial artery; (D) average P_m (open bars), and ΔP (filled bars) in the digital artery; and (E) average heart rate (filled bars).

Notes: *P < 0.025; **P < 0.0005.
Abbreviations: M, men; W, women.

Figure 6 Positive correlation between mean blood pressure (P_m) and age.

Notes: P_m tended to increase with advancing age. The correlation coefficient of the regression model was 0.27 (R² = 0.1179, P < 0.025, n = 38).

Figure 7 Relationships between transmural pressure (P_tr) and relative volume difference (ΔV/ΔV₀) in arterial elasticity analyses performed in six groups of subjects: eight women (○) and eight men (●), 20–25 years old; five women (△) and five men (A), 32–45 years old; and six women (□) and six men (■), over 50 years old.

Notes: The mean ± standard deviation of ΔV/ΔV₀ in each group was plotted against the individual mean of P_tr. The P_tr–ΔV/ΔV₀ curves for the over 50-year-old subjects obviously differed from the curves of the younger subjects. Sex had no impact on the difference among the P_tr –ΔV/ΔV₀ curves.

Figure 8 Relative volume differences (ΔV/ΔV₀) at a transmural pressure (P_tr) of 30 mmHg in six groups of subjects: eight women and eight men, 20–25 years old; five women and five men, 32–45 years old; and six women and six men, over 50 years old.

Notes: ΔV/ΔV₀ is shown as the mean ± standard deviation. ΔV/ΔV₀ values of those over 50 years old were significantly greater than those of the younger subjects (P < 0.025), while sex had no impact on the difference in the mean ΔV/ΔV₀ values at a P_tr of 30 mmHg.

Figure 9 Positive correlation between the mean relative volume difference (ΔV/ΔV₀) value at a transmural pressure (P_tr) of 30 mmHg and age.

Notes: Mean ΔV/ΔV₀ value at a P_tr of 30 mmHg tended to increase with advancing age. The correlation coefficient of the regression model was 0.0049 (R² = 0.2891, P < 0.0005, n = 38).

Figure 10 Average mean blood pressure (P_m), pulse pressure (ΔP), and heart rate in twelve subjects according to the three conditions: pre-cold-stress stimulation (Pre-CSS), cold stress stimulation (CSS), and post-cold-stress stimulation (Post-CSS) presented in five subfigures: (A) average P_m in the brachial (filled bars), and digital (open bars) arteries; (B) average ΔP in the brachial (filled bars), and digital (open bars) arteries; (C) average P_m (open bars), and ΔP (filled bars) in the brachial artery; (D) average P_m (open bars), and ΔP (filled bars) in the digital artery; and (E) average heart rate (filled bars).

Notes: *P < 0.05; **P < 0.001.

Figure 11 Relationships between transmural pressure (P_tr) and the relative volume difference (ΔV/ΔV₀) according to the effect of cold-stress stimulation separated into three conditions: pre-cold-stress stimulation (Δ), cold-stress stimulation (●), and post-cold-stress stimulation (+).

Notes: The mean ± standard deviation (n = 12) of the ΔV/ΔV₀ in each condition was plotted against the individual mean of the P_tr. There were no significant differences among the P_tr–ΔV/ΔV₀ curves obtained from all the three conditions.