Patients with pulmonary arterial hypertension (PAH) had lower pulmonary gradient of methemoglobin compared with control patients and oxyhemoglobin tracked with disease severity and survival, according to study results published in Respiratory Research.

Blood samples were obtained during right heart catheterization from the pulmonary artery and pulmonary artery wedge in patients with and without PAH. Co-oximetry was used to determine pulmonary gradients of oxyhemoglobin, carboxyhemoglobin, and methemoglobin, and these results were compared between groups.

Of the 130 participants, 65 had group 1 PAH, 40 had group 2 to 5 PH, and 25 had no PH. In all 3 groups, pulmonary artery wedge blood had higher pH, carboxyhemoglobin, and lactate, as well as lower partial pressure of carbon dioxide than pulmonary artery blood. In patients with group 1 PAH, methemoglobin in the pulmonary artery wedge blood was lower than in pulmonary artery blood. Furthermore, this was directly associated with the degree of change in pulmonary vascular resistance during inhaled nitric oxide test.

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Oxyhemoglobin levels in both the pulmonary artery and pulmonary artery wedge blood were associated with adjusted survival in PAH (hazard ratio [HR], 0.90; 95% CI, 0.82-0.99; P =.04 and HR, 0.9; 95% CI, 0.84-0.98; P =.003, respectively). Lower levels were independently associated with worse survival.

The researchers wrote, “[w]e found that [carboxyhemoglobin] is higher in the [pulmonary artery wedge] compared to [pulmonary artery] blood in all groups of patients, suggesting pulmonary production and systemic metabolism of carbon monoxide.”

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Khirfan G, Mostafa A, Faulx M, Dakkak W, Dweik RA, Tonelli AR. Gasometric gradients between blood obtained from the pulmonary artery wedge and pulmonary artery positions in pulmonary arterial hypertensionRespir Res. 2019;20(1):6.