Oxygen pulse slope analysis during exercise testing identifies patients with systemic sclerosis at a possible risk for developing pulmonary vasculopathy

Abstract

Background:

Patients with systemic sclerosis (SSc) are at risk for developing obliteration of microvascular structures leading to pulmonary hypertension (PH) which warrants early detection.

Methods:

In an observational, prospective design, we studied 121 eligible patients with SSc in an assessment program including non-invasive CPET to analyse an abnormal V’O2/HR slope represented by a breakpoint in the slope. To study the pathophysiologic meaning of such a breakpoint we applied our method to a published data set of a similar population in which CPET and pulmonary arterial pressures were measured simultaneously.

Results:

A pathological V’O2/HR slope was observed in 41 of 121 (34%) patients. Their mean V’O2/HR slope was 6 ± 2 ml, of whom 27 patients (66%) had a normal echocardiographic pulmonary arterial systolic pressures (PASP) at rest. In a historic CPET data set we calculated a breakpoint in both the V’O2/HR slope and V' O2/mPAP slope in 16 of 45 SSc patients (36%). For each patient we calculated the difference in V’O2 between the two breakpoints. Mean difference in V’O2 was 127 ml ± 63 ml. In 15 patients, a breakpoint in the V’O2/mPAP slope occurred at a lower V’O2 than in the V’O2/HR slope.

Conclusions:

The oxygen pulse breakpoint analysis in non-invasive CPET is a mathematical tool to detect abnormal cardiopulmonary vascular responses to exercise. The breakpoint in the V’O2/mPAP slope occurred at a slightly lower V’O2, suggesting that a sudden increase in pulmonary arterial pressures results in a disproportional increase in heart rate during CPET.