We thank G. Giannakoulas and co-workers for their interest in our study 1. Unfortunately, haemodynamic measurements at rest or during exercise were not performed in our patients with interstitial lung diseases. Therefore, we were unable to evaluate the relationship between exercise tolerance and those physiological adjustments. In line with these results, however, we did find that oxygen pulse, an index of stroke volume in some circumstances 2, was positively related to the number of steps climbed in 6 min (r = 0.64; p<0.01). Conversely, there was an inverse relationship between oxygen pulse and the nadir of oxyhaemoglobin desaturation at exercise cessation (r = -0.57; p<0.01).
Additional studies are needed to better characterise the haemodynamic responses to stepping and walking in these patients and their relationships with resting echocardiographic parameters and the severity of chronic hypoxaemia. We have preliminary data (data not published) suggesting that the step test also provides prognostic information in these patients and that it might constitute a more practical test paradigm than walking tests performed in clinical settings.
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