Increased physiological dead space at exercise is a marker of mild pulmonary or cardiovascular disease in dyspneic subjects.

: The characteristics of cardiopulmonary exercise testing (CPET)-derived parameters for the differential diagnosis of exertional dyspnea are not well known. We hypothesized that increased physiological dead space ventilation (VD/Vt) is a marker for mild pulmonary or cardiovascular disease in patients with exertional dyspnea. We used receiver operating characteristic analysis to determine the performance of individual CPET parameters for identifying subjects with either mild pulmonary or cardiovascular disease, among 77 subjects with mild-to-moderate exertional dyspnea (modified Medical Research Council scale 1-2). : In comparison with subjects without disease, subjects with pulmonary disease ( = 31) had higher VE/V'CO slope, higher VD/Vt, and lower ventilatory reserve. Subjects with cardiovascular disease ( = 14) had lower heart rate and cardiovascular double product and higher VD/Vt at peak exercise. At a threshold of 28%, the sensitivity and specificity of VD/Vt at peak exercise for identifying pulmonary or cardiovascular disease were 89% (95% CI: 64-98%) and 72% (95% CI: 46-89%), respectively. : Increased physiological VD/Vt at exercise is a sensitive and specific marker of mild pulmonary or cardiovascular disease in dyspneic subjects.