Submaximal exercise testing may be superior to the 6‐min walk test in assessing pulmonary arterial hypertension disease severity

Abstract

Submaximal exercise testing (SET) assesses functional exercise capacity in pulmonary arterial hypertension (PAH) patients and provides additional physiologic information compared with the 6-min walk test (6MWT). The relative correlations of the 6MWT and SET using SHAPE-HF™ with other markers of PAH severity, particularly echocardiogram (ECHO)-derived mean pulmonary artery pressure (MPAP), have not been investigated. (i) Examine the correlation between SHAPE measures with the 6-min walk distance (6MWD), and (ii) Compare SHAPE parameters and the 6MWD to clinical measures of PAH severity. Fifty-five consecutive group 1 PAH outpatients were evaluated in a single pulmonary hypertension referral center from March 2011 to June 2012. World Health Organization (WHO) functional class (FC), brain natriuretic peptide (BNP), ECHO, 6MWD and SHAPE results. Data are reported using mean ± standard deviation and Spearman correlation coefficients (r). Nine patients were excluded. Of the 46 remaining patients, 78% were women and the average age was 61 ± 13 years. PAH characteristics: WHO FC III-IV 48%; idiopathic PAH 52%; BNP 198 ± 277 pg/mL; 6MWD 399 ± 97 m; ECHO right atrial pressure (RAP) 7 ± 4, pulmonary artery systolic pressure (PASP) 63 ± 29 and MPAP 45 ± 17 mmHg. SET with SHAPE results: mean partial pressure of end-tidal (PET ) CO2 31 ± 6 mmHg at end-exercise; ventilatory efficiency (VE/VCO2 ) 43 ± 16. Significant correlations were found between the 6MWD and SHAPE variables: VE/VCO2 (r = -0.57, P < 0.0001) and end-exercise PET CO2 (r = 0.42, P = 0.004). VE/VCO2 correlated with WHO FC, BNP, RAP, MPAP and PASP and 6MWD only with WHO FC, BNP and PASP. SHAPE outperformed 6MWD in comparison with other measures of PAH disease severity.