Lower ventilation rates and higher occupant density lead to accumulation of carbon dioxide (CO 2 ) accompanied by human bioeffluents inside built environments. Research had been conducted to evaluate the effect of CO 2 and bioeffluents using physiological measurements and correlated with reduced cognitive performance. However, no study has reported the underlying mechanism for the reduction in cognitive performance when exposed to elevated CO 2 concentration with bioeffluents. It is suggested that the reduction in cognitive performance is due to CO 2 retention in human, caused by the reduced gas transfer in lungs. The aim of the study was to obtain the lung performance functions at varying CO 2 concentrations with bioeffluents and to investigate their influence on the gas exchange mechanism. A spirometric analysis was made with eight healthy male volunteers at four different exposure conditions—ambient, 1000 ppm, 2000 ppm, and 3000 ppm—for a 3-h duration. The important parameters such as forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) showed reduced value, whereas FEV1/FVC showed a stable value across exposure conditions. Evidences for a restrictive lung behavior were reported, indicating a reduced gas transfer in the lung region. The partial pressure of CO 2 in lungs was derived from a literature experimental database and found to be increasing during elevated CO 2 concentration with bioeffluents. The underlying mechanism for the CO 2 retention in humans is elaborated. © 2018 Elsevier Ltd