Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC14
Effects of respiratory loading on global and stimulus evoked cerebral blood flow
A. Hayen1, M. Herigstad1, M. Kelly1, R. Wise2, K. Pattinson1
1. Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom. 2. School of Psychology, Cardiff University, Cardiff, United Kingdom.
To use functional magnetic resonance imaging (FMRI) to understand neuronal processing of respiratory disorders it is vital to understand the effects of alterations in intrathoracic pressure on cerebral blood flow (CBF). We investigated how resistive inspiratory and expiratory loading affect CBF and the stimulus-evoked CBF response. We studied 13 healthy volunteers (11 male; age 28+/-7) twice, first in a physiology laboratory, then in a 3 Tesla MRI scanner. Resistive loads were applied via a custom designed breathing system. Breathing room air, subjects were trained to maintain their end-tidal carbon dioxide (PETCO2) constant via visual feedback. 270-second blocks of inspiratory loading (-10cmH20), expiratory loading (+10cmH20) and no loading were alternated and a 2Hz flashing checkerboard was shown for 120 seconds every 240 seconds. Session 1: middle cerebral artery velocity (MCAV) and blood pressure were continuously recorded. Session 2: CBF perfusion was acquired with a whole-brain pseudo continuous arterial spin labeling (ASL) sequence. Data was analysed in FSL and Matlab. Session 1: We observed a transient CBF increase (first 30 seconds) after application of inspiratory load (Figure 1) and a simultaneous increase in PETCO2, but no change in mean arterial pressure (MAP) or heart rate (HR, Table 1). Removal of inspiratory load and application and removal of expiratory load caused no changes in CBF, MAP and HR. Session 2: Voxel wise analysis shows significant bilateral CBF increases in the visual cortex to visual stimulation (25.2%+/-37.1) and no interaction of visual activity with inspiratory or expiratory load. Inspiratory and expiratory loading caused no global changes in CBF. After a transient increase PETCO2 was maintained at 5.5% (+/-0.8). We show transient effects of respiratory loading on CBF in the first 30 seconds of application of inspiratory resistance. No significant global effects of respiratory load on CBF or on the stimulus evoked CBF response occurred over 270 seconds. Hence, longer applications of respiratory load can overcome potential confounds of transient CBF changes. FMRI is hence a useful tool for looking at brain mechanisms of respiratory conditions, either during external resistive loading or in disease conditions associated with altered airway dynamics.
Where applicable, experiments conform with Society ethical requirements