What unique cardiovascular metrics can PPG measure that EEG or ECG cannot?

PPG (Photoplethysmography) technology can measure several unique cardiovascular metrics that EEG (Electroencephalography) and ECG (Electrocardiography) do not typically focus on:

Blood Oxygen Saturation (SpO2)

PPG is widely used to estimate blood oxygen levels through the absorption of light by oxygenated and deoxygenated hemoglobin. This is a critical metric for assessing respiratory function and is not measured by EEG or ECG[1].

Microcirculatory Blood Flow

PPG can provide insights into microcirculation, offering information about peripheral blood flow and vascular health, which is outside the scope of EEG and ECG measurements[1].

Arterial Stiffness

PPG can assess arterial stiffness by analyzing pulse wave velocity and other waveform characteristics. This metric is crucial for cardiovascular risk assessment and is not typically evaluated by EEG or ECG[1][4].

Respiration Rate

PPG can indirectly measure respiration rate by analyzing changes in the PPG signal associated with breathing patterns. EEG primarily focuses on brain activity, while ECG measures heart activity, making respiration rate a unique metric for PPG[1].

While ECG remains the reference standard for certain cardiac measurements, PPG offers advantages in terms of simplicity, portability, accessibility, and cost-effectiveness, making it a viable alternative for various health monitoring applications, especially in remote and continuous monitoring scenarios[2].

Citations:

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6426305/

[2] https://neurosky.com/2015/01/ecg-vs-ppg-for-heart-rate-monitoring-which-is-best/

[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4714443/

[4] https://www.mdpi.com/2079-9292/12/13/2923

[5] https://www.sciencedirect.com/science/article/pii/S1319157822001409

[6] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10130316/

[8] https://www.nature.com/articles/s41598-024-51395-y