Increased lung arterial obstruction is significantly associated with greater airflow obstruction in people with chronic thromboembolic pulmonary hypertension (CTEPH) and without a smoking history, a study shows.
Notably, airflow obstruction, reflected by a reduced ability to exhale quickly, was lessened with reduced arterial obstruction and improved blood flow following pulmonary thromboendarterectomy, or PEA — CTEPH’s mainstay treatment, a surgery to remove blood clots from major blood vessels in the lungs.
These findings suggest that blood vessel and flow changes seen in CTEPH patients may contribute to airflow obstruction.
Larger studies are needed to confirm this association and clarify its underlying mechanisms, the researchers noted.
The study, “Vascular involvement in chronic thromboembolic pulmonary hypertension is associated with spirometry obstructive impairment,” was published in the journal BMC Pulmonary Medicine.
CTEPH is a rare type of pulmonary hypertension (PH) caused by blood clots in the lung arteries, which increase their blood pressure, force the heart to work hard to pump blood, and cause exercise-induced shortness of breath.
In standard lung tests, these patients often show patterns of airflow obstruction, even in the absence of a smoking history (a known contributor). A previous study showed that CTEPH patients tended to have a low FEV1 relative to healthy people.
FEV1 refers to the amount of air forced from the lungs during a forced breath in one second. Lower-than-normal FEV1 indicates airflow obstruction, as it is very difficult for a person with such an obstruction to exhale quickly due to the increase in airway resistance.
“However, the relationship between the lung mechanics and [blood flow dynamics] is unclear,” the researchers wrote.
To address this, a team of researchers at Chiba University, in Japan, retrospectively analyzed blood flow and lung function data from 135 CTEPH patients (108 women and 27 men) with no smoking history and seen at their hospital from January 2000 to December 2019.
Blood flow parameters, such as mean pulmonary artery pressure (mPAP) and pulmonary vascular resistance (PVR), were assessed through an invasive method called right heart catheterization. PVR is the internal resistance to blood flow within the lung arteries.
Lung arterial obstruction was determined with the computed tomography angiography (CTA) obstruction score. CTA consists of injecting a contrast solution into a person’s blood vessels to identify blood flow blockages in lung CT scans.
Lung function was assessed with a standard test called spirometry that included parameters such as FEV1 and forced vital capacity, or the amount of air that can be forcibly exhaled from your lungs after taking the deepest breath possible.
Patients’ mean age was 64 years (range 52 to 70) and 41% had an acute pulmonary embolism episode, or a blockage in one of the lung arteries that resulted in symptoms.
Results showed that one quarter of the patients (25.2%) had significantly lower-than-normal FEV1 and FEV1/FVC ratio, indicative of obstructive airflow.
Notably, among evaluated lung function parameters, the percentage of predicted FEV1 (%FEV1) was inversely associated with mPAP, PVR, and CTA obstruction score. This meant that CTEPH patients with lower %FEV1, or greater airflow obstruction, were more likely to have worse blood flow dynamics and greater CT-proven arterial obstruction.
When adjusting for potential influencing factors, the team found that the CTA obstruction score was an independent predictor of lower %FEV1.
Moreover, data from the 54 patients who underwent PEA showed that %FEV1 was significantly improved in some, but not all, patients one year after surgery. An increase in %FEV1 was significantly associated with reduced mPAP, reflecting improved blood flow.
In the 29 patients whose CTA obstruction score could be assessed after PEA, reductions in the CTA obstruction score were significantly associated with increases in FEV1.
These findings highlight that arterial blood flow obstruction in CTEPH patients may contribute to airflow obstruction.
The researchers hypothesized that lung tissue death due to low blood supply near obstructed arteries may cause the collapse of air sacs and air passages, and that blood clot-induced inflammatory molecules may promote air passage contraction, all affecting local airflow.
Multicenter studies focused on obstructive lung impairment in CTEPH patients are needed to confirm these findings and “shed new light on the [underlying mechanisms] of CTEPH,” the team wrote.
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