Hypocapnia, eucapnia, and hypercapnia during "Where's Waldo" search paradigms: Neurovascular coupling across the cardiac cycle and biological sexes.

This investigation explored the impact of partial pressure of end-tidal carbon dioxide (PCO) alterations on temporal neurovascular coupling (NVC) responses across the cardiac cycle and the influence of biological sex via a complex visual scene-search task (""). 10 females and 10 males completed five puzzles, each with 40 seconds of eyes open and 20 seconds of eyes closed, under PCO clamped at ∼40 mmHg (eucapnia), ∼55 mmHg (hypercapnia), and ∼25 mmHg (hypocapnia). Cerebral blood velocity (CBv) in the middle and posterior cerebral arteries (MCAv, PCAv) were measured via Transcranial Doppler ultrasound. Linear mixed-effects models with participants as a random effect analyzed NVC metrics, including baseline and peak CBv, relative increase, and area-under-the-curve (AUC30). During hypercapnic trials, reductions in PCAv and MCAv AUC30 were noted across the cardiac cycle (all ). Hypocapnic PCAv AUC30 was reduced (all ), as was systolic MCAv AUC30 (). Females displayed greater baseline PCA diastole (). No other biological sex differences were observed across conditions in baseline (all ), peak (all  > ), relative increase (all ), and AUC30 metrics (all ). Despite differences in responses to hypercapnic and hypocapnic stimuli, NVC responses to complex visual tasks remain robust, across the physiological CO range.