Fig. 1

Changes in ΔF _CO, \( \dot{V}_{\text{CO}} ,\) \( \dot{V}_{{{\text{O}}_{ 2} }} , \) \( \dot{V}_{\text{E}} \) against time and the relationship between \( \dot{V}_{{{\text{O}}_{ 2} }} \) and \( \dot{V}_{\text{CO}} ,\) and between \( \dot{V}_{\text{E}} \) and \( \dot{V}_{\text{CO}} \) in one non-smoker (N-1). Note that ΔF _CO gradually decreased, but \( \dot{V}_{\text{CO}} \) increased linearly during ramp exercise, similar to the changes of \( \dot{V}_{{{\text{O}}_{ 2} }} \) and \( \dot{V}_{\text{E}} \). A significant correlation was observed between \( \dot{V}_{{{\text{O}}_{ 2} }} \) and \( \dot{V}_{\text{CO}} ,\) and between \( \dot{V}_{\text{E}} \) and \( \dot{V}_{\text{CO}} \) (lower panel)