The cerebrovascular and executive function responses to increased inspiratory muscle work

We investigated the cerebrovascular and executive function responses to increased inspiratory muscle work. Eight healthy men (33 ± 6 years) performed two separate 10 min bouts of inspiratory pressure threshold loading (ITL) targeting 70 % of maximal inspiratory mouth pressure (P_Imax) (ITL-Load) and two separate 10 min bouts of ITL targeting 2 % of P_Imax (ITL-Control). The order in which each participant undertook ITL-Load and ITL-Control conditions was randomized. Transcranial Doppler ultrasonography was used to measure middle cerebral artery blood velocity (MCA_V) and executive function was measured using the trail making task (TMT) Parts A and B during the 4-6th min of ITL-Load and ITL-Control. The cerebrovascular conductance index (CVCi) and cerebrovascular resistance index (CVRi) were calculated. There were time x condition interactions (P < 0.01) for MCA_V, CVCi and CVRi. This demonstrated during ITL-Load a small time-dependent increase (P < 0.01) in MCA_V and CVCi, and a small time-dependent decrease (P < 0.01) in CVRi. Part A (P = 0.007) and Part B (P = 0.013) times for the TMT were slower for ITL-Load compared to ITL-Control. There were significant correlations between the change in MCA_V from rest to the end of ITL and TMT times for Part A (r = 0.81, P = 0.009) and Part B (r = 0.67, P = 0.048). This is the first study to demonstrate that high-intensity ITL results in an increase in MCA_V, and a decreased executive function measured by the TMT, and these two measures were related in that the increase in MCA_V resulted in slower TMT times.