Age-related Changes in Microcirculatory Control Mechanisms Show in Distinct Frequency Bands of Fast Fourier Transform of Photoplethysmograms

Reflection photoplethysmography (PPG) is an inexpensive and non-invasive method of assessing microcirculatory function in the skin. Blood flow in the microcirculation is controlled by factors that show up as distinct frequency bands in Laser Doppler Flowmetry or PPG recordings. The established frequency bands associated with the control mechanisms for the microcirculation are: 0.40 – 1.60 Hz (cardiac), 0.15 – 0.40 (respiratory), 0.05 – 0.15 (myogenic), 0.02 – 0.05 (neurogenic) and < 0.02 (endothelial). Aging affects the microcirculation; hence, we hypothesized that PPG would show changes in the microcirculatory frequency bands when the waveform is subjected to Fast Fourier Transform (FFT). PPG was recorded with hardware and software developed by Laumann Medizin Technick, (Selb, Germany). The hardware is based on reflectance PPG and includes a finger clip that has a sensor with two emitters giving off light at 840nm (Near Infra-red, NIR) and 640nm (Red light), a photodetector, and a temperature probe. PPG recordings were obtained for two minutes from healthy volunteers at rest having regular breathing or during deep breathing. PPG records from the NIR was analyzed with an in-house customized python script to generate the FFT. The study involved two groups of volunteers: Group 1 (n=26) comprised persons aged 18 – 27 years old (average age of 24±2.4, mean±sd); Group 2 (n=27) comprised persons aged 53 – 71 years old (average age of 59±4.3). During regular breathing, Group 2 (older cohort) had significantly lower amplitude compared to Group 1 in the neurogenic (p < 0.01), myogenic (p =.02), and respiratory (p <.01) frequency bands; and in the aggregate of all the bands (p =.012). During deep breathing, Group 2 had significant reduction compared to Group 1 in the myogenic (p <.01) and respiratory bands (p=.025); and in the aggregate of the bands (p <.01). When comparing regular versus deep breathing for each cohort, Group 1 had significant increases during deep breathing in the neurogenic (p =.018), myogenic and respiratory bands (p <.01), and the aggregate of all bands (p <.01). In Group 2, there were significant increases during deep breathing in the myogenic and respiratory bands, and the aggregate of the bands (p <.01 in all cases). FFT of the PPG showed age-related reduction in the control mechanisms of the cutaneous microcirculation, especially in the neurogenic and myogenic bands; these are consistent with aging-related changes in these two control mechanisms. Given that the PPG is an inexpensive, non-invasive, and safe method of data collection, it could be further automated and used to monitor microvascular control mechanisms in conditions with microvascular damage such as diabetes mellitus. Funding: Campus Research Fund, University of the West Indies, Trinidad & Tobago This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.