Pulmonary V˙O2 kinetics at the onset of exercise is faster when actual changes in alveolar O2 stores are considered

Breath-by-breath (BbB) oxygen uptake rate (V˙O2) was measured at the mouth (MO) and at the alveolar level, at the onset of square wave cycling exercise of moderate intensity in six healthy male subjects. Alveolar BbB V˙O2 values were calculated correcting MO V˙O2 values by (i) estimating (GR); and (ii) measuring (opto-electronic plethysmography, OEP) BbB lung O2 store changes. V˙O2 kinetics was then described by a bi-exponential model. GR yielded larger values of the time constants (τ2) of the primary phase of V˙O2 kinetics. The mean response times (MRTs) calculated by analysing GR BbB V˙O2 values were larger than (i) those obtained by using MO and OEP at 90 W; and (ii) that by using MO at 120 W. OEP corrected V˙O2 yielded the highest normalised amplitude of the cardiodynamic phase of the V˙O2 on-response. Correction of BbB V˙O2 for actual BbB changes of lung O2 stores by OEP thus seems more appropriate for the study of the early cardiodynamic phase of V˙O2 kinetics than GR.