The Effect of Different Breathing Conditions on Cerebral Blood Flow in Young Males During Maximal Aerobic Exercise: A Pilot Study

During aerobic exercise, cerebral blood flow (CBF) decreases past 70% of maximal oxygen uptake (VO2), but transient hypercapnia could mitigate the reduction. To examine the effect of oral (OB), nasal (NB), and combined (CB) breathing on CBF during a graded maximal exercise test (GXT). Six young males (age: 21.8 ± 2.3 years) performed three GXTs until volitional fatigue using a randomized breathing condition (OB, NB, or CB) order. Respiratory gases were assessed via a metabolic cart. Ultrasound sonography (7.5 MHz linear transducer) was utilized to assess the peak systolic velocity (PSV), end-diastolic velocity (EDV), and vessel diameter of the internal (ICA) and external (ECA) carotid artery. A one-way ANCOVA, with VO2 as a covariate, followed by a Bonferroni post-hoc analysis, was utilized to examine the differences between the breathing conditions. The end-tidal partial pressure of CO2 (PetCO2) was significantly greater (p = 0.006) during NB (33.16 ± 1.37 mmHg) than that of CB (26.63 ± 1.32 mmHg) and OB (26.72 ± 1.37) at 100% VO2max. There was a trend of a greater PSV in the ICA throughout the entire GXT that was only significantly greater (p = 0.027) during NB (126.12 ± 7.51 cm/s) compared to OB (92.47 ± 7.34 cm/s) but not CB (111.91 ± 7.14 cm/s) at 70% VO2max. During a GXT, NB demonstrated a superior capacity to increase CBF, denoted by a higher PSV in the ICA compared to CB and OB, which might be partly related to an increased PetCO2.