LFCT measures the time for oxygen to travel from the lungs to the fingertip, as assessed via sleep studies. It is determined by the time interval between the end of a respiratory event and the nadir of oxygen saturation (SpOâ‚‚).

The following quartile ranges for Lung-to-Finger Circulation Time (LFCT) have been used in research studies-

  1. 1st Quartile (Q1): 4–15 seconds
  2. 2nd Quartile (Q2): >15–18 seconds
  3. 3rd Quartile (Q3): >18–22 seconds
  4. 4th Quartile (Q4): >22–52 seconds

These ranges were used to analyze and stratify the participants’ risk of cardiovascular and all-cause mortality.

The following PSG tracings shows how to measure LFCT-

Please click on this link to understand detailed methodology for calculating LFCT for entire sleep study- https://doi.org/10.1016/j.chest.2020.10.025

A recent study reported Prolonged lung-to-finger circulation time (LFCT) is independently associated with both cardiovascular (CV) and all-cause mortality in older men with sleep-disordered breathing (SDB). https://doi.org/10.1016/j.chest.2020.10.025

  • Individuals in the highest quartile of LFCT (>22 seconds) demonstrated a significantly higher risk of mortality compared to those in the lowest quartile (<15 seconds).

LFCT Potential Clinical Utility: https://doi.org/10.1016/j.chest.2020.10.025

    • LFCT may serve as a novel physiological marker for subclinical cardiovascular disease (CVD) and poor outcomes in patients with SDB.
    • It could complement traditional metrics, such as apnea-hypopnea index (AHI) and hypoxic burden, to improve risk stratification and guide clinical decision-making.

    LFCT Mechanistic Insights: https://doi.org/10.1016/j.chest.2020.10.025

      • Prolonged LFCT reflects delayed circulation, potentially indicating low cardiac output, subclinical heart failure, or other cardiovascular dysfunctions.
      • LFCT captures the combined effects of oxygen transport and peripheral oxygen uptake, which are crucial for assessing cardiac function.

      LFCT Association Beyond SDB: https://doi.org/10.1016/j.chest.2020.10.025

        • The association between LFCT and all-cause mortality persisted regardless of the severity of SDB, suggesting its relevance as a broader marker of cardiovascular vulnerability.
        • CV mortality showed a stronger association with LFCT in individuals with significant SDB (AHI ≥15/hr), potentially indicating a synergistic effect.

        LFCT Threshold Effect: https://doi.org/10.1016/j.chest.2020.10.025

          • The association of LFCT with mortality was most pronounced in the highest quartile, suggesting a threshold effect where prolonged circulation time reaches a level that predicts adverse outcomes.

          LFCT and Independent of Conventional Metrics: https://doi.org/10.1016/j.chest.2020.10.025

            • LFCT remains predictive of mortality even after adjusting for conventional SDB metrics, including AHI and hypoxic burden, highlighting its unique prognostic value.

            LFCT Clinical Implications: https://doi.org/10.1016/j.chest.2020.10.025

              • LFCT can be derived from routine sleep studies, making it a readily available and cost-effective tool for identifying at-risk individuals.
              • Future research is needed to explore its reproducibility, validity across diverse populations, and potential integration into clinical practice.

              Limitations and Future Directions: https://doi.org/10.1016/j.chest.2020.10.025

                • The study only included older men, limiting generalizability to women and younger populations.
                • LFCT derived from a single-night sleep study may have variability that requires further investigation.
                • Additional studies are necessary to explore the potential benefits of interventions targeted at individuals with prolonged LFCT.