Influence of end-tidal CO(2) on cerebral blood flow during orthostatic stress in controls and adults with myalgic encephalomyelitis/chronic fatigue syndrome.

Abstract

Brain perfusion is sensitive to changes in CO(2) levels (CO(2) reactivity). Previously, we showed a pathological cerebral blood flow (CBF) reduction in the  majority of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) patients  during orthostatic stress. Limited data are available on the relation between  CO(2) and CBF changes in ME/CFS patients. Therefore, we studied this relation  between ME/CFS patients and healthy controls (HC) during tilt testing. In this  retrospective study, supine and end-tilt CBF, as measured by extracranial Doppler  flow, were compared with P(ET) CO(2) data in female patients either with a normal  heart rate and blood pressure (HR/BP) response or with postural orthostatic  tachycardia syndrome (POTS), and in HC. Five hundred thirty-five female ME/CFS  patients and 34 HC were included. Both in supine position and at end-tilt, there  was a significant relation between CBF and P(ET) CO(2) in patients (p < 0.0001),  without differences between patients with a normal HR/BP response and with POTS.  The relations between the %CBF change and the P(ET) CO(2) reduction were both  significant in patients and HC (p < 0.0001 and p = 0.0012, respectively). In a  multiple regression analysis, the patient/HC status and P(ET) CO(2) predicted  CBF. The contribution of the P(ET) CO(2) to CBF changes was limited, with low  adjusted R(2) values. In female ME/CFS patients, CO2 reactivity, as measured  during orthostatic stress testing, is similar to that of HC and is independent of  the type of hemodynamic abnormality. However, the influence of CO(2) changes on  CBF changes is modest in female ME/CFS patients.