Cardiovascular Responses to the Cold Pressor Test are Correlated with Resting Cerebral Blood Flow in Healthy Controls and Concussed Athletes

Abstract

IntroductionConcussed athletes (CA) have attenuated cardiovascular (CV) responses to sympathoexcitatory stimuli, such as the cold‐pressor test (CPT). Magnetic resonance imaging (MRI) data demonstrate abnormalities in cerebral blood flow (CBF), fractional anisotropy (FA) and mean diffusivity (MD) in the brainstem of CA. It is unclear if CA typically exhibit high or low FA and MD values. Further, it is unknown if physiological responses to the CPT are correlated to brainstem abnormalities in HC and CA.PurposeWe tested the hypotheses that symptomatic CA have lower resting CBF and FA but higher MD in the brainstem and insula compared to healthy controls (HC) and that resting CBF, FA, and MD will be inversely correlated with the peak CV responses during the CPT.MethodsA resting MRI and a cold‐pressor test (CPT) were completed on 10 symptomatic CA (5 ± 3 days post‐injury, 6 females, age: 20 ± 2 years) and 9 HC (6 females, age: 21 ± 2 years). We measured CBF via arterial spin labeling, and fractional anisotropy (FA) and mean diffusivity (MD) via diffusion tensor imaging in the insula and brainstem. The CPT was performed by immersing a hand up to the wrist in ice water (~0 °C) for 2 min. Heart rate (HR; ECG) and blood pressure (MAP, SBP and DBP; photoplethysomography) were measured continuously and analyzed in minute increments at baseline and during the CPT for the peak change from baseline (Δ).ResultsThere were no differences between groups for CBF in the insula (CA 66.82 ± 6.28 vs. HC 63.35 ± 7.70 mL/100 g/min; P= 0.16) or brainstem (CA 46.69 ± 11.20 vs. HC 51.04 ± 10.31 mL/100 g/min; P= 0.39). CA had lower MD in the brainstem compared to HC (0.589 ± 0.079 vs. 0.661 ± 0.073 μm2/sec; P= 0.03) but insula MD did not differ (0.714 ± 0.057 vs. 0.729 ± 0.026 μm2/sec) between groups. FA did not differ in the insula (CA 0.190 ± 0.02 vs. HC 0.192 ± 0.008; P= 0.39) or brainstem (CA 0.450 ± 0.06 vs. HC 0.447 ± 0.027; P= 0.44). The ΔHR (r= −0.48, P= 0.02), ΔMAP (r= −0.51, P= 0.02), and ΔSBP (r= −0.52, P= 0.02) were correlated to brainstem CBF. Insula CBF was only correlated to the ΔDBP (r=0.46, P= 0.03). There were no correlations between any of the peak CV responses to the CPT and FA (P > 0.27) and MD (P > 0.20) in the insula or FA (P > 0.22) and MD (P > 0.07) in the brainstem.ConclusionsThese results show that brainstem MD was lower in CA compared to HC. Despite lower MD, there were no correlations between MD and the CV responses to the CPT. Therefore, it appears as though the structural abnormalities do not contribute to CV responses to sympathoexcitatory stimuli. Collectively, peak CV responses during the CPT were correlated with brainstem CBF, which suggests that elevated resting CBF might play a role in lower CV responses to sympathoexcitatory stimuli.Support or Funding InformationNIH Grant UL1TR001412This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.