Platelets get trapped in lungs in PH patients with heart failure: Study
This aggregation is associated with low platelet counts, high bleeding risk
Platelets, or cell fragments in blood that help stop or prevent bleeding, tend to cluster in lung blood vessels of people with decompensated pulmonary hypertension (PH), a lung disease characterized by sudden worsening of clinical signs of right heart failure, followed by other severe complications, a study has found.
This clustering, or aggregation, is associated with low platelet counts in these patients, increasing their risk of bleeding.
Normally, most platelets travel unimpeded through the tiny blood vessels of the lungs. However, “the vascular, endothelial and immune abnormalities associated with PH may contribute to platelets trapping within lung capillaries [tiny blood vessels],” scientists wrote. The endothelium is a cell layer lining the inner side of blood vessels.
The study, “Platelet aggregates in lung capillaries in severely decompensated pulmonary hypertension” was published in Thorax.
In PH, or high blood pressure in the pulmonary arteries that supply the lungs, acute decompensation is characterized by rapid worsening symptoms of right heart failure, which can lead to other life-threatening complications such as failure of multiple organs.
20% of PH patients develop thrombocytopenia, or low platelet levels
About 20% of PH patients develop thrombocytopenia, or low platelet levels in the blood. Platelets are produced from precursor cells called megakaryocytes. Acute PH decompensation alters blood flow and the endothelium, while also promoting inflammation. All these changes may promote inflammation.
The study aimed to determine whether platelet aggregation in the lungs could explain the low platelet count in patients with decompensated PH. The data were retrospectively collected from patients who underwent high-priority lung transplants between July 2012 and July 2022.
All patients studied had decompensated PH, treated with catecholamines (a type of chemical made by nerve cells and used in cell communication) when they were admitted to the intensive care unit before their lung transplant. Most had pulmonary arterial hypertension.
The researchers narrowed their study to 16 patients, dividing them into two groups of eight: one with low platelet counts and the other with normal platelet counts. Also included were seven participants who had other chronic lung diseases and had undergone a lung transplant.
Results showed PH patients with low platelet counts had significantly more platelet aggregates in their lung tissue samples compared to the control group. The number of megakaryocytes was also higher in the patients with thrombocytopenia, though the difference was not statistically significant.
In addition, the study found significant correlations between platelet counts, megakaryocytes, and platelet aggregates. “The number of lung platelet aggregates and megakaryocytes correlated with the severity of thrombocytopenia,” the team wrote.
Platelet counts returned to normal after lung transplant
Once the patients underwent their lung transplant, their platelet blood counts returned to normal.
According to the scientists, one explanation for these findings is that in PH, as lung blood pressure is higher and blood flow is altered, the formation of platelet aggregates may be promoted, further obstructing blood flow. This potentially creates “a vicious circle of PH-related flow disturbances, platelet aggregation, lumen [blood vessel] obstruction and further flow disturbances,” the researchers wrote.
Another possible mechanism involves megakaryocytes, which were higher in patients and may trigger a compensatory response by lowering platelet counts, the scientists suggested.
The inclusion of different PH types is a noteworthy study limitation. “Including only pulmonary arterial hypertension would have been more compelling, but such patients are rare,” the researchers wrote. Additionally, the technique used to quantify platelet aggregates provides only an estimate.
“Our study suggests that platelets may aggregate within the lungs during acute PH decompensation,” the investigators concluded, which could affect treatment decisions about platelet transfusion. They suggested platelet transfusion should be used cautiously, only in cases of active bleeding or early in lung transplant procedures, as it may be harmful in other circumstances.
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