Pulmonary ˙VO2 kinetics at the onset of exercise is faster when actual changes in alveolar O2 stores are considered.

Breath-by-breath (BbB) oxygen uptake rate (˙VO2 ) 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 ˙VO2 values were calculated correctingMO ˙VO2 values by (i) estimating (GR); and (ii) measuring (opto-electronic plethysmography, OEP) BbB lung O2 store changes. ˙VO2 kinetics was then described by a bi-exponential model. GR yielded larger values of the time constants (2) of the primary phase of ˙VO2 kinetics. The mean response times (MRTs) calculated by analysing GR BbB ˙VO2 values were larger than (i) those obtained by using MO and OEP at 90W; and (ii) that by using MO at 120 W. OEP corrected ˙VO2 yielded the highest normalised amplitude of the cardiodynamic phase of the ˙VO2 on-response. Correction of BbB ˙VO2 for actual BbB changes of lung O2 stores by OEP thus seems more appropriate for the study of the early cardiodynamic phase of ˙VO2 kinetics than GR.