The influence of controlled breathing on cerebrovascular control

High frequency breathing (HF; >0.2 Hz) may limit the influence of respiration at the low frequency (LF; 0.07–0.2 Hz) where cerebrovascular control is assessed. We tested the hypotheses that: 1) LF breathing will increase, and HF breathing will decrease LF coherence (COH) between mean arterial pressure (MAP) and mean middle cerebral artery velocity (MCAv mean ); and 2) reductions of COH expected when subjects breathe at 0.25 Hz are due, in part, to reduced CO 2 associated with faster breathing. We recorded ECG, finger arterial pressure (Finometer), MCAv mean (transcranial Doppler), respiratory rate, and end‐tidal CO 2 in 20 volunteers (28 ± 2 yrs). Four 7‐min breathing protocols were followed: 1) spontaneous breathing (SB); 2) paced breathing at 0.1 Hz; 3) paced breathing at 0.25 Hz; and 4) paced breathing at 0.25 Hz with CO 2 control (5% CO 2 bled in continuously; 0.25 Hz C). LF COH was assessed between MCAv mean and MAP. End‐tidal CO 2 was lower during 0.25 Hz breathing than all other conditions (P<0.05). COH was lower during 0.25 Hz breathing than both 0.1 Hz breathing and SB (P≤0.008). COH was indistinguishable during 0.25 Hz breathing with controlled and uncontrolled CO 2 (P =0.299). Controlled breathing in the HF limits contributing influences of respiration on cerebrovascular control despite moderate reductions in end‐tidal CO 2 .