Camera-based evaluation of deep breathing effects on plantar foot microcirculation - A pilot study on young healthy

Microvascular function, particularly of the plantar foot, reflects overall vascular health and is influenced by physiological oscillators such as heart rate, respiratory, myogenic, and neurogenic rhythms. Slow deep breathing modulates autonomic nervous system activity and affects peripheral microcirculation. This study investigates the effects of slow deep breathing on plantar foot perfusion using photoplethysmography imaging (PPGI).

Twenty healthy young adults participated in a four-stage protocol: baseline, deep breathing test (DBT), and two recovery stages (REST1 and REST2). PPGI was used to measure changes in plantar foot perfusion, focusing on energy, amplitude, and phase synchronization within frequency bands corresponding to key physiological oscillators. Time-frequency analyses and advanced signal processing were applied to assess these parameters.

Significant increases in energy were observed in all frequency bands during DBT, with slow frequency oscillators (SFOs) maintaining elevated activity up to 5 min after DBT. Amplitude analysis revealed a significant decrease in the first and second harmonic components of the heart rate signals during DBT. Phase synchronization between medial and lateral foot regions improved for respiratory, myogenic, and neurogenic frequency bands during DBT, with myogenic synchronization persisting for up to 2.5 min after DBT.

Slow deep breathing enhances microvascular perfusion and synchronizes autonomic oscillators in healthy individuals. PPGI proved effective in capturing these dynamics, indicating its potential as a non-invasive tool for assessing autonomic and microvascular function. Future research should explore its applicability in detecting early autonomic or vascular dysfunction in clinical populations.