Increased respiratory drive relates to severity of dyspnea in systemic sclerosis

BACKGROUND: Dyspnea may be a presenting symptom in progressive systemic sclerosis (SSc). Respiratory drive (mouth occlusion pressure, MOP, at rest and during CO(2) rebreathing, 7% CO(2), 93% O(2)) is a major determinant of dyspnea and may relate to the magnitude of dyspnea. METHODS: In a prospective design, MOP at 0.1 sec (P0.1) was measured in 73 SSc patients while breathing room air and during CO(2) rebreathing. An abnormal V’E/P0.1 is defined as < 8 L/min/cm H(2)O. Dyspnea scores were assessed by a shortness of breath questionnaire (UCSD dyspnea scale). RESULTS: Mean P0.1 in patients with normal V’E/P0.1 (n = 45) was 1.1 ± 0.04 and 1.6 ± 0.08 cm H(2)O in patients with abnormal V’E/P0.1 (n = 28), p <0.001. ∆P0.1/∆PetCO(2) differed significantly between these groups (0.45 versus 0.75 cm H(2)O/mmHg, P < 0.001), but no significant difference was present in ∆V’E/∆PetCO(2). V’E/P0.1 showed the highest significant correlation with the UCSD dyspnea score (r = -0.76, p <0.001). UCSD cut-off value for abnormal V’E/P0.1 was 8.5 (sensitivity 93%, specificity 96%, area under the curve 0.98). CONCLUSIONS: In SSc patients an abnormal V’E/P0.1 better relates to the severity of dyspnea than traditional lung function parameters and can easily be assessed at first outpatient consultation.