Respiratory pressure effects on echo-planar image (EPI) deoxy-hemoglobin and flow signals from human brain

We have noted that EPI signals from the cranial midline varied with respiration, and hypothesized that this was related to changes in volume of the sagittal sinus. This study explores the effects of respiratory alterations in intrathoracic pressure (and venous pressure/volume) on signals from deoxyhemoglobin. Six awake volunteer subjects were studied in the supine posture at 1) rest with normal breathing, 2) breath-hold of up to one minute to tolerance, 3) breathing against a PEEP valve at pressure of 5, 10, and 20cm H2O for one minute. 512 sequential gradient recalled echo-planar images were examined for time and frequency analysis, selecting the midline region. The results below show variation with both respiratory and cardiac cycles. Breath-holding attenuates the respiratory signals but increases the cardiac ones, while serial PEEP increases both. %Change from rest %Change in %Change in in signal magnitude respiration peak cardiac peak Breath-hold 11 ±4 -76±19 63 ±14 PEEP (5mmHg) -7±3 23±11 54±9 PEEP (20mmHg) -17±8 37±17 71±19 These results support signal origination from volume and flow change in the sagittal sinus. The technique may be adaptable for further non-invasive study of the cerebral circulation.