# Assessing cardiac function in obstructive sleep apnea using a novel metric: integrating the respiratory event frequency and desaturation duration

## TL;DR

A new metric called RERTA is introduced to better assess how obstructive sleep apnea affects heart function by combining event frequency and oxygen desaturation duration.

## Contribution

The novel RERTA metric integrates respiratory event frequency and desaturation duration to evaluate cardiac impact in obstructive sleep apnea.

## Key findings

- Severe OSA patients had lower left ventricular ejection fraction (LVEF) compared to mild-to-moderate OSA patients.
- Each increase in RERTA was associated with a significant decrease in LVEF after adjusting for age, gender, and BMI.
- RERTA provides a more comprehensive assessment of circulatory stress in OSA patients compared to traditional metrics.

## Abstract

Obstructive sleep apnea (OSA) is associated with impaired cardiac function, evidenced by a decreased left ventricular ejection fraction (LVEF). Traditional measures, including the apnea-hypopnea index (AHI) and lung-to-finger circulation time (LFCT), do not simultaneously consider the hypoxemic duration, frequency, and severity. This study introduces the respiratory event response time area (RERTA), integrating duration- and frequency-based OSA indices, and examined its associations with the LVEF.

We retrospectively analyzed data from individuals who underwent polysomnography (PSG) and echocardiography within the previous 6 months. LFCT was calculated as the mean time from desaturation onset after a respiratory event to the lowest recorded oxygen saturation (SpO2). The RERTA, a joint metric that reflects the event frequency and desaturation duration, was determined as the square root of the product of the AHI and mean LFCT. PSG parameters and related metrics were then examined for associations with echocardiographic measures.

Among 34 participants (10 with mild-to-moderate and 24 with severe OSA), the severe group exhibited a lower median LVEF than the mild-to-moderate group (64.00% [61.00%–68.50%] vs. 70.00% [66.50%–72.75%], p < 0.05). After adjusting for age, gender, and the body-mass index (BMI), each 1-event/h increase in the AHI was linked to a borderline reduction in the LVEF (-0.71%, 95% CI: -1.42 to 0.00; p = 0.05). A 1-unit increase in the RERTA corresponded to a 0.33% decrease in the LVEF (95% CI: -0.62% to -0.04%, p < 0.05).

The RERTA combines the AHI and mean LFCT, providing a joint assessment of circulatory stress in patients with OSA. This study highlights its potential utility in evaluating cardiac function associated with OSA, which can serve as a basis for future prospective research.

The online version contains supplementary material available at 10.1186/s12890-025-03974-6.