Worse measures of blood flow, arterial oxygenation, and cardiac function may underlie the poor clinical condition of chronic thromboembolic pulmonary hypertension (CTEPH) patients who also have obstructive sleep apnea (OSA), according to a new study.
The research, “Obstructive sleep apnea in patients with chronic thromboembolic pulmonary hypertension,” was published in the Journal of Thoracic Disease.
OSA is a risk factor for cardiovascular diseases such as pulmonary hypertension (PH), heart failure, and coronary artery disease. Prior research also showed that OSA is an independent risk factor for venous thromboembolism (VTE), which refers to the formation of a blood clot in a deep vein — usually in the leg — later migrating to the lungs and blocking an artery, an occurrence known as a pulmonary embolism.
CTEPH, characterized by chronic obstruction of the major pulmonary arteries and microvascular disease, is a long-term complication of an acute pulmonary embolism. Specific risk factors for VTE have been identified as risk factors for CTEPH, which is in line with the high prevalence of OSA in patients with CTEPH. However, data on the link between CTEPH and OSA is still scarce.
Aiming to address this gap, a team from Fuwai Hospital, National Center for Cardiovascular Diseases, in China, conducted a single-center, retrospective study in 57 adult patients with a stable clinical status who had been diagnosed with CTEPH by right heart catheterization (RHC) from September 2015 to December 2017. Factors associated with OSA in CTEPH were explored.
Baseline patient characteristics were collected, including their age, sex, body mass index (BMI), smoking history, six-minute walking distance (6MWD) — an assessment of exercise capacity —, World Health Organization (WHO) functional class, biochemical parameters, and co-morbidities. Patients also underwent measurements of pulmonary function testing, as well as partial pressures of oxygen and carbon dioxide.
All patients underwent a sleep study — polysomnography — before or after RHC. Their nasal airflow, finger pulse oximetry (to monitor oxygen saturation), thoracic and abdominal movement, body position and snoring were recorded.
Of the 57 CTEPH patients enrolled, 32 had OSA (21 men). These patients were older (57 vs. 50 years), had higher mean BMI (24.98 vs. 23.32), and worse WHO functional class than the 25 CTEPH patients without OSA. They also had higher levels of hemoglobin (163.47 vs. 155.24 g/L), the protein that carries oxygen in the blood.
Having OSA did not significantly affect pulmonary function. However, CTEPH patients with OSA had significantly lower partial pressure of oxygen (60.13 vs. 68.22%) and oxygen saturation (90.32 vs. 93.26%), which is in line with previous research.
Sleep data showed that the group with OSA had a higher apnea-hypopnea index (AHI, 16.74 vs. 2.43), and oxygen desaturation index (an indicator of OSA severity, 13.35 vs. 3.50), but a lower minimum oxygen saturation (77.25 vs. 80.28%). Of note, AHI is calculated by dividing the total number of apnea events (a decrease of nasal airflow by more than 90%) and hypopnea events (more than 30% decrease in nasal airflow) by the number of sleeping hours.
As for factors associated with OSA in CTEPH, the team identified hemoglobin, oxygen saturation, WHO functional classes III–IV (representing worse disease severity), and N-terminal pro-brain natriuretic peptide (which is produced in response to changes in pressure inside the heart and is a biomarker of pulmonary arterial hypertension).
In addition, hemodynamic (blood flow) parameters such as mean right atrium (one of the heart’s upper chambers) pressure, mean pulmonary arterial pressure, cardiac index — cardiac output divided by body surface area — and pulmonary vascular resistance also were associated with OSA in CTEPH.
Subsequent analysis showed that the cardiac index was independently associated with OSA in CTEPH.
Overall, the the team concluded that “OSA may aggravate the clinical status of CTEPH patients to some degree,” they wrote.
“In turn, a worse hemodynamics, oxygenation state and cardiac function are associated with OSA in CTEPH after being adjusted for age, sex and BMI. Among them, CI [cardiac index] is the most important parameter in indicating the coexistence of OSA and CTEPH,” the researchers added.
These results underscore the importance of recognizing and treating OSA in CTEPH patients.