Post‐Exercise Intracranial Hypotension
Authors: Petersen Lonnie Grove , Grace Evan , Petersen Johan , Hargens Alan 
Published: June 2021

IntroductionPost‐exercise arterial hypotension is a well described normal phenomenon in healthy humans. While the exact integrated pathways and mechanisms are not fully described, the drop in mean arterial blood pressure (MAP) minutes to hours following exercise, results from a combination of sustained vasodilation of the previously active muscles, centrally mediated reduction in sympathetic nervous activity and resetting of arterial baro‐ and thermoreflexes. Despite a significant drop in MAP, cerebrovascular function, cerebral autoregulation and middle cerebral arterial flow velocity are generally well maintained following moderate exercise. We tested the hypothesis that intracranial pressure (ICP) is concomitantly decreased during post‐exercise arterial hypotension, thereby leaving cerebral perfusion pressure (CPP) maintained.MethodsEight healthy volunteers (5 female, age 20±2 years, height 169±10 cm, weight 64±12 kg) were included and baseline measurements recorded after 10 min rest in seated and supine postures in a temperature controlled room (23 C). Each subject completed 30 min exercise at 70% estimated maximum oxygen consumption on an upright ergonomic bicycle followed by a one‐hour recovery phase in supine position. MAP, heart rate (HR), stroke volume (SV), and total peripheral resistance (TPR) were recorded continuously by volume‐clamp method using a cuff around the right middle finger (Nexfin). Noninvasive ICP by evoked tympanic membrane displacement (Cerebral Cochlea Fluid Pressure device) was measured before, immediately after and repeated every 10 min during supine recovery. CPP was calculated as the difference between MAP at the level of the brain and ICP.ResultsICP decreased by 69±41% compared to supine baseline immediately following exercise (from 5.9±70.5 nL to −59.1±73.0 nL) and gradually returned to pre‐exercise supine values after 45 min (P=0.067). This trend was correlated to MAP (r2=0.81, P=0.006), which initially decreased (from 83.9±2.4 to 76.6±2.9 mmHg) and returned to supine resting values after approximately 30 min. The underlying vasodilation of exercised muscles and reduced venous return were reflected by decreased TPR and SV and correlated to the drop in ICP (r2=0.90, P=0.001 and r2=0.68, P=0.022, respectively), while HR was increased post‐exercise (P<0.05) and gradually returned to resting values. CPP was maintained during the supine recovery phase (P=0.1).DiscussionAlthough not reaching statistical significance, our data indicate a drop in ICP following 30 min of aerobic exercise with a gradual increase towards baseline supine values. This trend was significantly correlated with the concomitant decrease in MAP, TRP and SV, while CPP was maintained. Our data are limited by the non‐invasive method of obtaining ICP and the small N, which is insufficient to support any conclusion regarding gender differences. Ongoing trials will evaluate a possible augmented intracranial post‐exercise hypotension in females compared to males. Although speculative at this point, attenuated concomitant decrease in ICP would decrease CPP which might be a factor in post‐exercise syncope.Support or Funding InformationThis work was supported by Novo Nordic Foundation (NNF150C0019196) and NASA (NNX13AJ12G)