Impaired Dynamic Cerebrovascular Autoregulation in Adolescent Concussion

Although cerebrovascular impairments are believed to contribute to concussion symptoms, little information exists regarding brain vasomotor control in adolescent concussion, particularly during changes in arterial blood pressure (ABP). This research tested the hypothesis that adolescent concussion is marked by impaired dynamic cerebral autoregulation (dCA). Thirty concussed adolescents and thirty healthy controls completed two sit-to-stand trials. Cerebral blood flow velocity and ABP were measured continuously. Cerebrovascular resistance (CVR) was calculated and the rate of drop in CVR relative to the change in ABP provided the rate of regulation (RoR). The concussed adolescents were followed through rehabilitation for up to 12-weeks. At the first visit, the concussed adolescents demonstrated reduced RoR compared with the healthy controls (0.16±0.04 vs. 0.21±0.07 sec-1; P≤0.001). At the concussed adolescents final visit, RoR recovers to levels seen in the healthy controls (0.21±0.08 vs. 0.21±0.07 sec-1; P=0.93). Concussed adolescents demonstrate an impairment in dCA that recovers with symptoms

Autonomic Dysregulation in Adolescent Concussion Is Sex- and Posture-Dependent

Objective: To study autonomic responses to postural changes in concussed adolescents. The influence of sex was also studied. Design: Longitudinal cohort observational study. Participants: Concussed adolescents (CONC; n = 65; 26 male adolescents; age 15 ± 1 years, range = 12-18 years) and a control (CTRL) group of nonconcussed adolescents of similar age and sport (CTRL; n = 54; 29 male adolescents; age 14 ± 1 years, range = 12-18 years). Interventions: Concussed participants were monitored through 6 weekly visits throughout usual physician care. Control participants underwent 2 visits separated by at least 1 week to account for intrapersonal variation in testing measures. Main Outcome Measures: Heart rate variability as the root mean square of successive differences in R–R intervals (RMSSD), heart rate (HR), and blood pressure [mean arterial pressure (MAP) and diastolic blood pressure (DBP)] were measured in supine, sitting, and standing postures. Results: A mixed analysis of variance revealed a group 3 sex 3 posture interaction (P = 0.04) where seated values of RMSSD were less in concussed female participants versus control female participants (42 ± 4 vs 61 ± 7 ms; P = 0.01; Mann–Whitney rank test). Compared with CTRL, CONC exhibited increased pretesting seated DBP (69 ± 1 vs 74 ± 1 mm Hg; P\u3c 0.01), MAP (83 ± 1 vs 86 ± 1 mm Hg; P = 0.02), and baseline seated HR (72 ± 1 vs 77 ± 2 bpm; P = 0.03). Values of DBP (P = 0.03) and MAP (P, 0.01) improved at clinical discharge, whereas the RMSSD in female participants did not (P \u3e 0.5). Data are mean ± SEM. Conclusions: A modest reduction in female cardiac autonomic regulation was observed during seated postures. Alterations in seated concussed DBP and MAP, but not RMSSD, resolved at clinical discharge (median = 37 days). The results indicate that, in adolescents, concussion may impair cardiovagal function in a sex- and posture-dependent manner. The findings also suggest that BP metrics, but not RMSSD, are associated with clinical concussion recovery

Autonomic Dysregulation in Adolescent Concussion Is Sex- and Posture-Dependent

Objective: To study autonomic responses to postural changes in concussed adolescents. The influence of sex was also studied. Design: Longitudinal cohort observational study. Participants: Concussed adolescents (CONC; n = 65; 26 male adolescents; age 15 ± 1 years, range = 12-18 years) and a control (CTRL) group of nonconcussed adolescents of similar age and sport (CTRL; n = 54; 29 male adolescents; age 14 ± 1 years, range = 12-18 years). Interventions: Concussed participants were monitored through 6 weekly visits throughout usual physician care. Control participants underwent 2 visits separated by at least 1 week to account for intrapersonal variation in testing measures. Main Outcome Measures: Heart rate variability as the root mean square of successive differences in R–R intervals (RMSSD), heart rate (HR), and blood pressure [mean arterial pressure (MAP) and diastolic blood pressure (DBP)] were measured in supine, sitting, and standing postures. Results: A mixed analysis of variance revealed a group 3 sex 3 posture interaction (P = 0.04) where seated values of RMSSD were less in concussed female participants versus control female participants (42 ± 4 vs 61 ± 7 ms; P = 0.01; Mann–Whitney rank test). Compared with CTRL, CONC exhibited increased pretesting seated DBP (69 ± 1 vs 74 ± 1 mm Hg; P\u3c 0.01), MAP (83 ± 1 vs 86 ± 1 mm Hg; P = 0.02), and baseline seated HR (72 ± 1 vs 77 ± 2 bpm; P = 0.03). Values of DBP (P = 0.03) and MAP (P, 0.01) improved at clinical discharge, whereas the RMSSD in female participants did not (P \u3e 0.5). Data are mean ± SEM. Conclusions: A modest reduction in female cardiac autonomic regulation was observed during seated postures. Alterations in seated concussed DBP and MAP, but not RMSSD, resolved at clinical discharge (median = 37 days). The results indicate that, in adolescents, concussion may impair cardiovagal function in a sex- and posture-dependent manner. The findings also suggest that BP metrics, but not RMSSD, are associated with clinical concussion recovery

Cerebrovascular Compliance in Humans

Pulsatile blood flow consists of two components: steady flow and oscillatory flow. Steady blood flow is primarily regulated by vascular resistance while vascular compliance represents a key mediator of oscillatory blood flow. However, most studies investigating the regulation of cerebral blood flow in humans have focused on vascular resistance. Recently, emerging evidence has implicated vascular compliance as an important contributor to the regulation of cerebral perfusion. Therefore, the research contained herein aimed to i) quantify cerebrovascular compliance responses to blood pressure alterations and ii) explore mechanisms regulating cerebrovascular compliance in humans. The studies employed a Windkessel modelling approach to calculate cerebrovascular compliance using blood pressure waveforms measured at the brachial artery and middle cerebral artery blood velocity waveforms. Study One evaluated the nature of the cerebrovascular compliance response to transient reductions in blood pressure induced by standing upright. The findings demonstrate rapid and large increases in cerebrovascular compliance that contribute to the preservation of systolic blood velocity during the hypotensive phase of standing. Study Two investigated the impact of cerebral vasodilation on cerebrovascular compliance. Two vasodilatory stimuli, hypercapnia acting primarily through endothelial pathways and sodium nitroglycerin acting through non-endothelial pathways, produced reductions in cerebrovascular compliance. Hypercapnia dilates the entire cerebral vascular bed while sodium nitroglycerin dilates only the large cerebral arteries. Nonetheless, similar reductions in cerebrovascular compliance were observed. Study Three examined the role of sympathetic innervation, cholinergic innervation, and myogenic mechanisms in regulating cerebrovascular compliance. Distinct blockade of -adrenergic receptors (phentolamine), endothelial muscarinic receptors (glycopyrrolate), and calcium channels (nicardipine), produced large increases in cerebrovascular compliance. Similar changes in cerebrovascular compliance were observed under baseline conditions and during oscillatory lower body negative pressure to induce blood pressure fluctuations. Overall, these studies provide support for the role of cerebrovascular compliance in regulating cerebral perfusion. Additionally, these studies generated new knowledge regarding neural, endothelial, and myogenic mechanisms governing human cerebrovascular compliance

Concussion in Adolescents Impairs Heart Rate Response to Brief Handgrip Exercise

OBJECTIVE: Test the hypotheses that (1) concussion in adolescents impairs autonomic neural control of heart rate (HR), and (2) HR reactivity improves with symptom resolution. DESIGN: Observational, case-control. PARTICIPANTS: Nineteen concussed adolescents (8 female adolescents; age 15 ± 2 years) and 16 healthy controls (6 female adolescents, age 15 ± 2 years). INTERVENTION: All participants performed an isometric handgrip (IHG) at 30% maximum voluntary contraction lasting 30 seconds. Heart rate (electrocardiogram) and hemodynamic responses (photoplethysmographic Finometer) were recorded from 30 seconds of baseline and the last 10 seconds of handgrip. MAIN OUTCOME MEASURES: The HR response (ΔHR) at the onset of moderate-intensity IHG using a mixed 1-way analysis of variance. RESULTS: A group × time interaction (P \u3c 0.005) indicated that handgrip evoked a greater ΔHR among control participants (13 ± 10 beats/min) compared with concussed (6.4 ± 6.3 beats/min; group P = 0.63; time P \u3c 0.001; d = 0.77). CONCLUSION: These preliminary results suggest that a concussion impairs the ability to elevate HR at the exercise onset and, given the nature of the task, this could be interpreted to reflect reduced ability to withdraw cardiovagal control. Therefore, the data support the hypothesis of neural cardiac dysregulation in adolescents diagnosed with concussion. CLINICAL RELEVANCE: The IHG test could aid concussion diagnosis and support return-to-play decisions