# Pulmonary Function and Nocturnal Hypoxemia Patterns in Patients with Obstructive Sleep Apnea

## TL;DR

The study finds that obesity and lung function affect nighttime oxygen levels in sleep apnea patients, with different patterns suggesting distinct management approaches.

## Contribution

The paper identifies distinct nocturnal hypoxemia patterns in OSA patients, linking them to pulmonary function and obesity, which can guide therapeutic decisions.

## Key findings

- Higher BMI correlates with more frequent and severe nocturnal oxygen drops.
- Lower FEV1 is associated with lower average oxygen saturation and longer periods of low oxygen.
- Patients with OSA and COPD show a tendency for lower average nocturnal oxygen levels.

## Abstract

Background/Objective: Obesity is a documented risk factor for impaired pulmonary function and abnormal oxyhaemoglobin levels during sleep. This functional impairment becomes more significant when there are additional respiratory pathologies, such as obstructive sleep apnea (OSA) and/or chronic obstructive pulmonary disease (COPD). Overnight pulse oximetry may offer an effective evaluation of nocturnal oxyhaemoglobin levels/waveform patterns. We evaluated the correlation between obesity, overnight pulse oximetry (parameters, waveform patterns) and pulmonary function in patients diagnosed with moderate–severe OSA and normal oxyhaemoglobin saturation levels during waking hours. We also compared the overnight oxyhaemoglobin saturation levels between patients with OSA alone and those with associated COPD. Methods: This was a retrospective, transversal, non-interventional study on consecutive patients with moderate–severe OSA diagnosed using overnight cardiorespiratory polygraphy over a period of 18 months. After analyzing the study population’s characteristics, the patients were divided into two subgroups: one consisting of patients with OSA alone (Group A), and the second with coexisting OSA and COPD (Group B). Results: Seventy-six patients were included in the study, and 18% were diagnosed with COPD. A higher body mass index (BMI) correlated with a higher number of ≥3% SpO2 drops/h (ODI3) and percentage of time with oxyhaemoglobin saturation < 90% (t90) and a lower average nocturnal oxyhaemoglobin saturation (avgSpO2). ODI3 correlated negatively with avgSpO2 and positively with t90. After eliminating BMI as a confounding factor, lower values of forced expiratory volume in the first second (FEV1) were associated with lower avgSpO2 and higher t90. FEV1 did not corelate with ODI3. After dividing the study population into the two subgroups, patients from Group B had a tendency towards lower average nocturnal SpO2 levels compared to Group A. Conclusions: Different phenotypes/patterns of nocturnal hypoxemia can be identified using quantitative and qualitative analyses of overnight pulse oximetry: repetitive, consecutive obstructive respiratory events with a characteristic intermittent (saw-tooth) hypoxemia pattern and alveolar hypoventilation, resulting in a continuous (plateau) hypoxemia pattern. According to our findings, nocturnal hypoxemia is more important at lower FEV1 values (correlating with lower avgSpO2/higher t90, but not with ODI3). The presence of a continuous hypoxemia pattern in patients with OSA may suggest that pulmonary function tests should be performed in order to differentiate patients with alveolar hypoventilation secondary to obesity (restrictive syndrome) from those with associated COPD (obstructive syndrome). This can have an impact on the management of the case and the therapeutic approach (positive pressure therapy with/without supplemental oxygen).