Detection of pulmonary vasculopathy by novel analysis of oxygen uptake in patients with systemic sclerosis: association with pulmonary arterial pressures.

OBJECTIVES: During cardiopulmonary exercise testing (CPET) compromised pulmonary vasculature in patients with systemic sclerosis (SSc) may lead to increases in pulmonary arterial pressures (PAP) and decreased oxygen uptake. We hypothesised that this may lead into a disproportional heart rate (HR) increase with a corresponding V'O2/HR breakpoint and relates to systolic PAP at rest. METHODS: In a prospective design we evaluated V'O2/HR slopes for breakpoints. To understand its physiological meaning, we evaluated V'O2/HR and V'O2/mPAP slopes for breakpoints in a historic data set of SSc patients, in which CPET and right heart catheterisation was performed simultaneously. V'O2/HR slopes with a peak oxygen uptake outside the normal range were defined as pathologic. RESULTS: A breakpoint occurred in both V'O2/mPAP and V'O2/HR slope in 16/34 patients in the historic dataset and occurred in the V'O2/mPAP slope at a lower V'O2in 15 patients. In the prospective dataset, 73/121 patients showed a V'O2/HR breakpoint and achieved a significantly lower peak oxygen uptake compared to 48/121 patients without a V'O2/HR breakpoint (p=0.036). Mean systolic PAP in 41/121 patients with a pathologic V'O2/HR slope differed significantly from patients without a pathologic V'O2/HR slope (p=0.027). In 27/121 patients with a systolic PAP < 35 mmHg a pathologic V'O2/HR slope was observed. CONCLUSIONS: SSc patients with a V'O2/HR breakpoint are characterised by a decreased oxygen uptake, likely caused by sudden PAP increases during exercise. Importantly, in patients with normal resting SPAP pathologic V'O2/HR slopes were observed. This suggests that these patients are at risk for developing pulmonary hypertension.