Skin blood flow measurements on the breast areola.

Blood flow and thermally insulated skin temperature were measured in the aerolae of normal breasts by means of the non-invasive transient thermal clearance method. Both parameters showed high variability among different women, but also showed typical dependence on the subject's age: the two parameters were constant up to age 50, and then showed a decrease at higher ages. The decrease can be attributed to the normal decrease of tissue blood flow at higher age and to atrophy of the breast glandular tissue after menopause. Statistically significant higher values of blood flow and insulated skin temperature were found for the left breast relative to the right breast.

Power spectrum analysis of spontaneous fluctuations in the photoplethysmographic signal.

Direct measurement of variability in the peripheral circulation was performed by means of photoplethysmography, which provides assessment of blood volume in tissue and systolic blood volume increase. Both parameters showed oscillations at a relatively low frequency, about 0.02 Hz, and a relatively high frequency, about 0.3 Hz, which is related to respiration. These frequencies are similar to those found in measurements of heart rate variability--which is also obtained by measuring the photoplethysmographic period variability--but the powers of the different frequencies are different. The low frequency oscillation, which is attributed to the activity of the sympathetic nervous system, is more pronounced in the measurements of tissue blood volume and of systolic blood volume increase than in the measurement of heart rate.