Provocation studies

Aerobic exercise testing

Betsy Keller (New York, USA) talked about the superior ability of a 2-day CPET (cardiopulmonary exercise test) protocol to detect functional impairment in ME/CFS compared to either a single CPET, submaximal exercise test or a VO₂ prediction equation. The single CPET failed to identify functional impairment in 20% patients, and diminished functional capacity due to post-exertional malaise (PEM) could not be detected, yet occurred in 55% of subjects. Two serial CPET tests however did identify functional impairment in 98% subjects. Submaximal exercise tests were poor predictors of VO₂-max in CFS/ME as was using the predicted VO₂ equation. The results demonstrated the superiority of using two serial CPETs to delineate functional impairment in CFS/ME.

J Mark Van Ness (Stockton, USA) showed diminished pulmonary ventilation in CFS/ME patients during graded exercise tests. He postulated that this could be due to deconditioning. A second study showed that post-exertional effects seem to reduce the ventilator response further in CF/MES. These effects may be due to diminished ventilator muscle function during PEM or reduced ventilator neural “drive”.

Mitochondrial dysfunction

David Patrick (Vancouver, Canada) addressed the issue of whether screening for mitochondrial dysfunction and other metabolic disorders was important in CFS/ME. CPET often leads to symptom flare, and so alternative approaches were discussed. Changes in haemoglobin and oxyhaemoglobin in wrist extensors using grip tests were measured. Response to the test was compared between cases and controls by calculating the area under the curve of HHb over time. Submaximal exercise procedure did not distinguish between cases and controls, but HHb levels did vary between the cases and a subset of 19% met criteria that prompted further testing for mitochondrial disease. 3 cases had particularly low levels of HHb and 2 had adverse physical reactions. There was a greater level of self-assessed exertion in the ME/CFS group. Even submaximal testing was intolerable for a subset of ME/CFS patients and we should be mindful of using exercise for testing or treatment.

Oxygen extraction and lactate were found to be low in patients assessed by Ruud Vermeulen (Amsterdam, Holland). This would indicate a metabolic cause for exercise intolerance in the majority of 178 women with CFS/ME studied. The low lactate after exercise in the majority of these patients suggests that physical impairment in this group is caused by downregulation of carbohydrate metabolism.