Gas exchange during exercise pinpoints PAH severity
medwireNews: Including gas exchange measurements during the 6-minute walk distance (6MWD) test may give a better indication of disease severity in patients with pulmonary arterial hypertension (PAH) than the walk test alone, researchers report.
“Results of this study could provide clinicians and researchers the opportunity to incorporate these relatively simple measures into clinical practice and add incremental value in the management of PAH patients”, they write in Respirology.
In all, 76 PAH patients completed the 6MWD test during which simultaneous gas exchange measurements, including oxygen uptake (VO2), carbon dioxide production (VCO2), oxygen saturation, minute ventilation to carbon dioxide output (VE/VCO2) and end-tidal partial pressure for carbon dioxide (PETCO2) were taken.
Among the patients, 24 were classified as New York Heart Association functional class (NYHA FC) III and these patients had poorer gas exchange than the 52 who were FC II, as indicated by significantly higher VE/VCO2 (approximately 45 vs 41) and lower PETCO2 (24 vs 28 mmHg). A higher FC was also associated with a shorter 6MWD.
Evidence of an association between ventilatory dysfunction during exercise and disease severity was also seen in patients receiving triple therapy who, despite a similar 6MWD performance, had significantly higher VE/VCO2 and lower PETCO2 than those receiving monotherapy, the researchers led by Norman Morris (Griffith University, Queensland, Australia) report.
Although patients on triple therapy are “possibly well compensated” says the team, they “may well have more advanced disease compared with those on monotherapy”. They add: “If we looked at the 6MWD alone, this would not be obvious.”
Neither 6MWD performance nor ventilatory function differed significantly according to PAH subtype, with the 28 patients with idiopathic PAH (IPAH), the 24 with connective tissue disease-related PAH (CTD-PAH) and the 24 with congenital heart disease-related PAH (CHPAH) having comparable VE/VCO2 and PETCO2 measures at the end of the exercise.
CHPAH and CTD-PAH patients did have significantly lower VO2 (0.76 and 0.87 L/min, respectively) and VCO2 (0.85 and 1.00 L/min) during exercise compared with the IPAH patients (1.10 and 1.22 L/min), but these associations were lost after accounting for body mass.
This suggests that the IPAH group have slightly greater cardiac output during exercise than the other two groups, the team explains.
CHPAH patients also had significantly lower end-exercise VE and O2 pulse compared with IPAH patients and significantly greater oxygen desaturation during 6MWD than both IPAH and CTD-PAH participants.
The researchers point out that gas exchange abnormalities could be measured during the 6MWD test using a portable system, which, unlike during cardiopulmonary exercise testing, would require no medical supervision or use of an unfamiliar fixed ergometer, such as a treadmill or cycle ergometer.
By Lucy Piper
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