Abnormal blood lactate accumulation during repeated exercise testing in myalgic encephalomyelitis/chronic fatigue syndrome.

Abstract

Post-exertional malaise and delayed recovery are hallmark symptoms of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Studies on repeated  cardiopulmonary exercise testing (CPET) show that previous exercise negatively  affects oxygen uptake (VO(2) ) and power output (PO) in ME/CFS. Whether this  affects arterial lactate concentrations ([La(a) ]) is unknown. We studied 18  female patients (18-50 years) fulfilling the Canadian Consensus Criteria for  ME/CFS and 15 healthy females (18-50 years) who underwent repeated CPETs 24 h  apart (CPET(1) and CPET(2) ) with [La(a) ] measured every 30th second. VO(2) at  peak exercise (VO(2peak) ) was lower in patients than in controls on CPET(1)  (P < 0.001) and decreased in patients on CPET(2) (P < 0.001). However, the  difference in VO(2peak) between CPETs did not differ significantly between  groups. [La(a) ] per PO was higher in patients during both CPETs (P(interaction)  < 0.001), but increased in patients and decreased in controls from CPET(1) to  CPET(2) (P(interaction)  < 0.001). Patients had lower VO(2) (P = 0.02) and PO  (P = 0.002) at the gas exchange threshold (GET, the point where CO(2) production  increases relative to VO(2) ), but relative intensity (%VO(2peak) ) and [La(a) ]  at GET did not differ significantly from controls on CPET(1) . Patients had a  reduction in VO(2) (P = 0.02) and PO (P = 0.01) at GET on CPET(2) , but no  significant differences in %VO(2peak) and [La(a) ] at GET between CPETs. Controls  had no significant differences in VO(2) , PO or %VO(2peak) at GET between CPETs,  but [La(a) ] at GET was reduced on CPET(2) (P = 0.008). In conclusion, previous  exercise deteriorates physical performance and increases [La(a) ] during exercise  in patients with ME/CFS while it lowers [La(a) ] in healthy subjects.