Fig. 4.

Correlations of the delta heart rate and the delta stroke volume index of healthy controls and ME/CFS patients. Legend to Fig. 4: The 95% prediction intervals (PI) of the relation of the stroke volume index decrease during the tilt versus the heart rate increase during the tilt in healthy controls, indicated by the two green lines. The blue line indicates the regression line of the relation SVI decrease versus the heart rate increase in healthy controls, the red line the same regression in ME/CFS patients. The gray area shows the ME/CFS patients with an abnormally low HR increase for the decrease in stroke volume index, meeting the study definition of chronotropic incompetence. Delta HR: heart rate increase during the tilt; delta SVI: stroke volume index decrease during the tilt; ME/CFS: myalgic encephalomyelitis/chronic fatigue syndrome.