FAILURE OF THE CIRCULATORY-SYSTEM LIMITS EXERCISE PERFORMANCE IN PATIENTS WITH SYSTEMIC-SCLEROSIS

OBJECTIVE: To determine the mechanisms for exercise impairment in symp tomatic patients with systemic sclerosis (SSc) using breath-by-breath expired-gas analysis with incremental exercise testing. DESIGN: Prospe ctive, open trial. PATIENTS AND METHODS: Fifteen consecutive patients with SSc seen at the Medical University Hospital (a tertiary referral center) with complaints of exercise intolerance underwent pulmonary fu nction testing (spirometry, helium dilution lung volumes, and diffusin g capacity of carbon monoxide) and incremental exercise testing on a c ycle ergometer measuring oxygen consumption (VO2), carbon dioxide prod uction (VCO2), respiratory exchange ratio (R), oxygen saturation, bloo d pressure, and heart rate (HR). Values for oxygen uptake at anaerobic threshold (VO2AT) were derived graphically by blinded clinicians expe rienced in exercise testing, and the results were averaged. Ventilator y reserve and oxygen pulse were calculated from measured values, and a ll data were subjected to analysis by standard clinical algorithms. ME ASUREMENTS AND MAIN RESULTS: Of 15 patients studied, 14 had either res trictive lung disease or normal results of spirometry on pulmonary fun ction testing. One patient with a history of tobacco use had evidence of airways obstruction. Three patients were unable to exercise maximal ly (as determined by maximum respiratory exchange ratio [R(max)] great er than 1.09 or maximum heart rate [HR(max)] greater than 85% predicte d), and exercise testing was terminated in one with Mobitz type II atr ioventricular block. The following data (mean +/- SEM) were obtained f rom II maximally exercising patients. VO2max 795 +/- 75 mL oxygen (O2) /min, R 1.34 +/- 0.05, VO2AT/VO2max predicted 0.21 +/- 0.02, O2 Pulse 5.1 +/- 0.4 mL O2/beat, ventilatory reserve 0.52 +/- 0.06, and tidal v olume/forced vital capacity ratio 0.46 +/- 0.02. Of the 11 patients co mpleting breath-by-breath expired-gas analysis, all had circulatory im pairment to exercise, as determined by low O2 pulse and low VO2 at ana erobic threshold, and circulatory impairment was limiting in 9 of 11 p atients. Of those nine patients, four had evidence of impaired gas exc hange compatible with pulmonary vascular disease. Arterial oxygen desa turation occurred in 2 of 11 patients. CONCLUSION: Circulatory impairm ent to exercise is common in SSc patients with exercise intolerance. R estrictive lung disease, although also common, does not limit exercise tolerance in patients capable of maximal effort.