The aim of this pilot study was to determine if there was a relationship between disease severity, measured by right ventricular systolic pressure (RVSP), and gas exchange, measured by oxygen consumption, during the six-minute walk test (6MWT) in ten patients with idiopathic PAH. In addition, we sought to determine if there was a relationship between the change in RVSP and the change in gas exchange following several months of therapy with the goal of reducing RVSP. The optimal treatment (medication) was determined by the subjects' doctors and was not recorded for this study. For test 1, we found a negative non-significant relationship between end-tidal carbon dioxide (PETCO2) and RVSP (r=-0.6, p=0.094) and a negative non-significant correlation between PETCO2 and RVSP (r=-0.7, p=0.13) for test 2. We also found a positive, non-significant correlation between minute ventilation (VE) relative to carbon dioxide production (VE/VCO2) assessed at the mouth and RVSP (r=0.6, p=0.06) for test 1 and a positive non-significant correlation between VE/VCO2 and RVSP (r=0.5, p=0.33) for test 2. We found a significant drop in RVSP (p=0.049), PETCO2 (p=0.023) and VE/VCO2 (p=0.025) between test 1 and test 2. We found no relationship between the change in RVSP and the change in PETCO2; we found a moderate, non-significant, relationship between change in RVSP and change in VE/VCO2 (r= 0.7, p=0.09). Due to the small sample size there was no significant relationship between the change in RVSP and the change in VE/VCO2; however, the trend towards significance suggests that the assessment of the gas exchange parameter VE/VCO2 may be sensitive enough to determine changes in disease severity in patients with pulmonary hypertension in a study with a larger sample size. In support of this, we performed a post-hoc power analysis and determined that a study with a sample size of 16 would be sufficient to determine changes in RVSP and changes in VE/VCO2. Future studies should look at the relationship between the change of RVSP and the change of VE/VCO2 with a larger sample size under standard conditions in regards to treatment and timing between the tests.
University of Minnesota M.S. thesis. May 2014. Major: Kinesiology. Advisor: Eric Snyder. 1 computer file (PDF); v, 46 pages, appendix p. 34-46.
Is there a relationship between change in disease severity and change in gas exchange during a six-minute walk test in patients with idiopathic pulmonary arterial hypertension?.
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