The inter-relationships of analysis procedures in the assessment of oxygen-uptake kinetics across PRBS and square-wave protocols

The kinetics of oxygen uptake (VO2) can be measured in response to numerous exercise protocols. Commonly, VO2 kinetics have been assessed as dynamic cardiopulmonary responses to abrupt changes in work, either as intermittently alternating work patterns (e.g a pseudo-random binary sequence (PRBS) protocol) or simple square wave transients. Complications of analysis procedures across protocols and the influence of different work rate intensities have meant that a meaningful comparison of results is difficult to achieve. METHODS Eight subjects (age: 20±3 years, body mass: 81.1±4.1, height: 179.8±5.4cm) agreed to participate in this study and performed three procedures: 1) a graded exercise test to exhaustion for the determination of VO2 max, 2) three repeats of a single square-wave exercise transient from walking to 80% Tvent, and 3) three repeats of a 300 s PRBS protocol on a cycle ergometer from 25W to 85W. Gas exchange was measured breath-by-breath. Data derived from PRBS exercise was analysed in three ways: 1) Fourier techniques (fou-PRBS) to attain amplitude ratios (ml·min-1.W-1) and phase shift (degrees) parameters, 2) comparison of auto- and cross-correlation signals to attain a 'peak cross-correlation time' (PCCT), and 3) the curve fitting of the cross-correlation function (CCF) from the ramp form of a two-component exponential model to derive a mean response time (prbs-MRT). Data derived from the square-wave exercise protocol was assessed using conventional mono-exponential modeling techniques to achieve time delay and time constant parameters for the subsequent expression of MRT (sw-MRT). RESULTS All forms of VO2 kinetics analysis were related to VO2max, with the highest significance being for both prbs-MRT (R2 = 0.68, p < 0.01) and sw-MRT (R2 = 0.7, p < 0.01). Both prbs- MRT (R2 = 0.71 p < 0.01) and individual harmonics of fou-PRBS (phase shift: 10 mHz - R2 = 0.79 p < 0.01) were significantly associated with sw-MRT. PCCT was unrelated to sw-MRT. CONCLUSIONS Although all forms of PRBS analysis showed significant inter-relationships, only the prbs-MRT and some individual elements of frequency domain analysis were related to both sw-MRT and VO2max. From the results of this study, the PCCT method seems to have limited application as a method of analysis. These findings support the preferential expression of VO2 kinetics in response to PRBS exercise by the prbs-MRT method.