People with sarcoidosis-associated pulmonary hypertension who have reduced physical fitness or worse gas exchange capacity live significantly shorter times without requiring a transplant, a new study indicates.
The study, “Physiological Predictors of Survival in Patients with Sarcoidosis Associated Pulmonary Hypertension,” was published in the European Respiratory Journal.
Nearly all people with sarcoidosis will experience some kind of lung disease. Pulmonary hypertension — elevated pressure in the blood vessels that supply the lungs — is a relatively uncommon lung manifestation of sarcoidosis that is associated with poor outcomes.
Given that sarcoidosis-associated pulmonary hypertension (SAPH) is fairly rare, it is unclear what factors are most important for predicting clinical outcomes in people with the condition.
Researchers analyzed data from the Registry for Sarcoidosis Associated Pulmonary Hypertension (ReSAPH, NCT01467791), a database that collects clinical and demographic information for people with SAPH from multiple treatment centers in the U.S., the Netherlands, the U.K., and Saudi Arabia.
Their study included data from 215 people enrolled in ReSAPH between 2011 and 2017. Of these, 60% were from the U.S., 24% from Europe, and 16% from Saudi Arabia. Not all data was available for every individual.
Most patients had precapillary pulmonary hypertension (73.9%), where high blood pressure is caused by alterations to the lung’s blood vessels themselves. This is distinct from postcapillary pulmonary hypertension, which is caused by alterations to the heart.
The researchers focused their analysis on the 159 patients in the precapillary group, which were mainly female (72.3%) and African American (56%). Their average age was 56.9 years, and a diagnosis of SAPH was made a median of 12.6 years after their sarcoidosis diagnosis.
About half of these patients (50.9%) were enrolled in ReSAPH within one year of their SAPH diagnosis (the incident group); the remaining 49.1% had been diagnosed for more than a year before enrollment in the database (the prevalent group).
These two groups were demographically similar except there was a lower proportion of African Americans in the incident group (46.9% vs. 65.4%).
The incident group also had significantly less pulmonary obstruction, as indicated by a higher ratio of forced expiratory volume in one second (FEV1) to forced vital capacity (FVC), and significantly higher diffusion capacity, which is a measurement of how well oxygen can be transferred from the lungs to the bloodstream.
Of note, the ratio of FEV1 to FEV measures the proportion of air a person can exhale in one second to the full amount of air a person can exhale in one breath.
After an average follow-up time of 2.4 years, 41 individuals died and nine received lung transplants. The overall transplant-free survival rate — the proportion of patients who were alive without lung transplants — was 89.2% after one year, 78.2% after three years, and 71.3% after five years. There were no significant differences in these values between the more and less recently diagnosed groups.
The researchers constructed statistical models to look for factors that significantly predicted transplant-free survival. They used two types of models: univariate models, which look at factors one-at-a-time, and multivariate models, which look at factors collectively.
Age and diffusion capacity was significantly associated with transplant-free survival in univariate models, but not multivariate ones.
The six minute walk test (6MWT) is a common measure of physical fitness in ambulatory people. It measures the distance a person can walk in six minutes. In both univariate and multivariate models, higher 6MWT scores were significantly predictive of a longer transplant-free survival, and this remained significant in both incident and prevalent subgroups.
“In this analysis, the 6MWD was by far the strongest predictor of mortality,” the researchers wrote. “This association provides support for the use of the 6MWD as a functional and potentially modifiable surrogate endpoint for future clinical trials in SAPH.”
The only other factor that was significantly predictive of transplant-free survival in the multivariate models was pulmonary obstruction. Higher FEV1/FVC ratios — indicating less pulmonary obstruction — were significantly predictive of worse transplant-free survival.
“We speculate that SAPH patients with evidence of obstruction may represent a subset with predominantly airway involvement with possibly less likelihood for contiguous vascular disease, thus portending a better outcome,” the researchers wrote.
In other words, the results could be due to people with low FEV1/FVC ratios scores having more problems with the lungs themselves, but not necessarily more problems with the lung’s blood vessels. Another explanation the researchers posited is that people with better lung function could be less adherent to their care. Further research will be needed to clarify these findings.
“Although this analysis has inherent limitations of registry data including some missing data, it clearly demonstrates that functional impairment (as demonstrated by the 6MWD) and reduced diffusing capacity are associated with decreased survival in SAPH patients,” the researchers concluded.
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