Increased respiratory drive relates to severity of dyspnea in systemic sclerosis

Dyspnea may be a presenting symptom in progressive systemic sclerosis (SSc). Respiratory drive (mouth occlusion pressure, MOP, at rest and during CO2 rebreathing, 7% CO2, 93% O2) is a major determinant of dyspnea and may relate to the magnitude of dyspnea.

In a prospective design, MOP at 0.1 sec (P0.1) was measured in 73 SSc patients while breathing room air and during CO2 rebreathing. An abnormal V'E/P0.1 is defined as < 8 L/min/cm H2O. Dyspnea scores were assessed by a shortness of breath questionnaire (UCSD dyspnea scale).

Mean P0.1 in patients with normal V'E/P0.1 (n = 45) was 1.1 ± 0.04 and 1.6 ± 0.08 cm H2O in patients with abnormal V'E/P0.1 (n = 28), p <0.001. ∆P0.1/∆PetCO2 differed significantly between these groups (0.45 versus 0.75 cm H2O/mmHg, P < 0.001), but no significant difference was present in ∆V'E/∆PetCO2. 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).

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.