TABLE 3.

Multiple regression analysis to predict CBF from other variables.

Variable	CBF supine	CBF end‐tilt	%CBF decrease	CBF supine	CBF end‐tilt	%CBF decrease
	Patients (n = 535)			Patients and healthy controls (n = 569)
PETCO2 a	7.222	4.943	0.432	6.656	4.897	0.487
Age	−1.186	ns	0.083	−1.146	ns	ns
HR a	ns	ns	ns	ns	ns	ns
MAP a	ns	ns	ns	ns	ns	ns
Pat‐HC	–	–	–	ns	−104.273	−18.188
Disease duration	ns	ns	ns	–	–	–
Moderate disease	ns	ns	−2.485	–	–	–
Severe disease	ns	ns	−3.077	–	–	–
normBPHR‐POTS	ns	ns	ns	ns	ns	ns
Constant	332.47	297.65	−25.445	349.30	391.76	−8.369
P of model	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001
Adj R 2 of model	0.07	0.13	0.19	0.07	0.24	0.47

Abbreviations: Adj, adjusted CBF, cerebral blood flow; HC, healthy controls; HR, heart rate in bpm; MAP, mean arterial pressure; moderate and severe disease: ME disease severity criteria (Carruthers et al., 2011); normHRBP, normal heart rate and blood pressure during tilt test; P, significance of the model; Pat, ME/CFS patients; P_ETCO₂, end‐tidal carbon dioxide pressure in mmHg; POTS, postural orthostatic tachycardia syndrome during tilt test; R, correlation coefficient of the model.

^a P_ETCO₂, heart rate and mean arterial pressure data of supine, end‐tilt, and the differences, were taken for the supine, end‐tilt, and CO₂ reactivity analysis, respectively.