Effects of Systemic Hypoxia on Motor Control Performance and Brain Blood Flow in Healthy, Young Humans

Abstract

The brain is an oxygen dependent organ of the human body and adequate blood flow is imperative. To maintain adequate perfusion, in response to stimuli like hypoxia, vasodilation occurs. Fine motor control skills are essential, particularly for in‐flight piloting. Despite the possibility of encountering hypoxia in flight conditions, there is a lack of data on how motor control may be impacted by hypoxia and the corresponding changes in brain blood flow. We hypothesized that motor control would be impaired during hypoxia, despite increased cerebral blood flow. A group of seven subjects between the ages of 20 to 22 performed a motor control task in two counterbalanced conditions, the control (21% O2, 0.03% CO2, nitrogen balance) and the hypoxic exposure (10% O2 with nitrogen balance mix). The motor control task consisted of lateral joystick movements to adjust the angle of a computer visual beam to roll and stop a ball into one of 4 targets (40 targets total in MATLAB). Throughout each trial, heart rate (HR; 3‐lead ECG), beat‐beat arterial blood pressure (MAP; finger photoplethysmography), end‐tidal CO2 (sampling line) and bilateral middle cerebral artery velocity (MCAv; transcranial doppler), an indicator of cerebral blood flow (CBF), were measured. The motor control program recorded the time to target, beam angle, and ball velocity. In poikilocapnic conditions, hypoxic and normoxic gas mixtures were delivered via facemask and on average the subjects desaturated to an SpO2value of 84.1 ± 4.9%. Contrary to our hypothesis, hypoxia had minimal impact on motor control based on time to task completion for both individual trials and overall task (188.9 ± 21.9 s vs 194.7 ± 19.9 s p=0.613). Physiologically, as anticipated, hypoxia increased heart rate significantly in the transition from normoxic to hypoxic stimulus (86.1 ± 4.6 vs 75.7 ± 7.3 bpm; p<0.001) but was not significantly greater in hypoxic motor control (82.7 ± 9.0 bpm) than hypoxia alone (p=0.180). During the motor control task, MCAv (average of both sides) was similar in normoxic (51.6 ± 7.7 cm/sec) and hypoxic conditions (54.2 ± 8.7 cm/sec; p=0.414). However, MCA during hypoxic motor control was higher than that in hypoxic rest (49.1±10.3 cm/sec; p=0.025), whereas motor control during normoxia did not significantly increase MBV from rest (49.7 ± 7.4; p=0.17). Results were similar when analyzed based on cerebral vascular conductance (MBV/MAP). The present results suggest that mild systemic hypoxia does not impact performance in a simple motor control task, and this may be because of an increase in brain blood flow.