Exploratory study on oxygen consumption on-kinetics during treadmill walking in women with systemic lupus erythematosus

Abstract

Objective: To determine whether oxygen consumption (V o(2)) on-kinetics differed between groups of women with systemic lupus erythematosus (SLE) and sedentary but otherwise healthy controls.

Design: Exploratory case-control study.

Setting: Medical school exercise physiology laboratory.

Participants: Convenience samples of women with SLE (n=12) and sedentary but otherwise healthy controls (n=10).

Intervention: None.

Main outcome measures: V o(2) on-kinetics indices including time to steady state, rate constant, mean response time (MRT), transition constant, and oxygen deficit measured during bouts of treadmill walking at intensities of 3 and 5 metabolic equivalents (METs).

Results: Time to steady state and oxygen deficit were increased and rate constant was decreased in the women with SLE compared with controls. At the 5-MET energy demand, the transition constant was lower and MRT was longer in the women with SLE than in controls. For a similar relative energy expenditure that was slightly lower than the anaerobic threshold, the transition constant was higher in controls than in women with SLE.

Conclusion: V o(2) on-kinetics was prolonged in women with SLE. The prolongation was concomitant with an increase in oxygen deficit and may underlie performance fatigability in women with SLE.

Figure 1

Oxygen consumption during continuous exercise. t₀ is the onset of exercise and t₁ is the time taken to reach a steady state or an asymptote and (t₆) is 6-minute test endpoint. Area between Line A and the X-axis the resting VO₂ and Line B represents the energy demand of the activity being performed. The area above the trajectory line and under Line B is the oxygen deficit. VO₂ is the amplitude of change in oxygen consumption at the 6-minute test endpoint.

Figure 2

Time to steady state, rate constant, and oxygen deficit in women with SLE and controls. Error bars equal one standard deviation unit. * Significantly different main effects for women with SLE than for controls (p<0.005 rate constant, p<0.016 time to steady state, p<0.028 oxygen deficit)

Figure 3

Transition constant and mean response time in women with SLE. Error bars are one standard deviation unit. * significantly higher than 3-METS (p<0.004), + significantly higher than 3-METS in the women with SLE, **significantly higher than 3 METS (p<0.017).