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Pulmonary arterial hypertension (PAH) occurs when the pressure in blood vessels that transport blood from the heart to the lungs is unusually high.

The results of seventeen clinical trials involving data pertaining to 5,440 patients who have PAH sent researchers on a mission to discover why obese patients with PAH had a higher rate of survival than those with normal weight. Assistant professor Nadine Al-Naamani, at Pennsylvania’s Perelman School, provided the information about the trials in an article published by Healio. Professor Al-Naamani said that the team is investigating whether a person’s body size has an effect on PAH treatment response.

The Obesity Paradox

Statistics show an increase in the number of older PAH patients who are overweight or obese. This correlates to the rise in obesity in the U.S. and other areas.

The University study analyzed individual participant data from seventeen Phase III trials that assessed treatment submitted to the Food and Drug Administration for approval between 2000 and 2015. Participants were randomized and all had a diagnosis of PAH. The weight status of each patient was established by BMI that was recorded at the onset of their respective trials. A total of nine drugs belonging to five drug classes were studied in the trials.

Primary endpoints were changes in the six-minute walk distance plus the WHO functional class.

The researchers examined BMI in relation to clinical and demographic characteristics, blood flow (hemodynamics), and baseline exercise capacity.

At the onset of the trials, the obese patients had a reduced six-minute walk distance and a lower WHO functional class when compared to PAH patients who had normal weight.

The team assumed that obese and overweight PAH patients would derive a benefit from pulmonary vasodilators (blood vessel dilators). The researchers also assumed that there would be varied responses by body size to the vasodilators. It was expected that PAH patients would show improvement in the six-minute walk distance and also in their WHO functional class. Yet this did not occur

On the contrary, at the conclusion of the University study, the researchers found no improvement in the six-minute walk distance or the WHO functional class. However, survival benefits for obese PAH patients improved; thus the obesity paradox.

It is a fact that obesity leads to a lower quality of life, as well as increased hospitalizations, but for reasons not yet established, obesity leads to improved survival in PAH patients.

In conclusion, Professor Al-Naamani suggests that future research should include clinical trials that involve patients in varied weight categories and explore other possible causes of an “obesity paradox.”