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Altitude Modulates Concussion Incidence: Implications for Optimizing Brain Compliance to Prevent Brain Injury in Athletes.

Smith DW, Myer GD, Currie DW, Comstock RD, Clark JF, Bailes JE - Orthop J Sports Med (2013)

Bottom Line: When concussion rates were dichotomized by altitude using the median, elevated altitude was associated with a reduction in concussion rates overall (rate ratio [RR], 1.31; P < .001), in competition (RR, 1.31; P < .001), and in practice (RR, 1.29; P < .001).The results of this epidemiological investigation indicate increased physiological responses to altitude may be associated with a reduction in sports-related concussion rates, especially in collision sports.Future research that focuses on the potential prophylactic effect of optimizing outflow impedance and thus reduction of intracranial compliance (a "tighter fit") in humans is warranted to determine the most effective approaches to mitigate sport-related concussion, especially in football players.

View Article: PubMed Central - PubMed

Affiliation: Division of Sports Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA. ; Department of Neurosurgery, NorthShore University HealthSystem, Evanston, Illinois, USA.

ABSTRACT

Background: Recent research indicates that the volume and/or pressure of intracranial fluid, a physiology affected by one's altitude (ie, elevation above sea level), may be associated with the likelihood and/or severity of a concussion. The objective was to employ an epidemiological field investigation to evaluate the relationship between altitude and concussion rate in high school sports.

Hypothesis: Because of the physiologies that occur during acclimatization, including a decline in intracranial compliance (a "tighter fit"), increased altitude may be related to a reduction in concussion rates in high school athletes.

Study design: Cohort study; Level of evidence, 3.

Methods: Data on concussions and athlete exposures (AEs) between 2005-2006 and 2011-2012 were obtained from a large national sample of high schools (National High School Sports-Related Injury Surveillance System [High School RIO]) and were used to calculate total, competition, and practice concussion rates for aggregated sports and for football only.

Results: Altitude of participating schools ranged from 7 to 6903 ft (median, 600 ft), and a total of 5936 concussions occurred in 20,618,915 exposures (2.88 per 10,000 AEs). When concussion rates were dichotomized by altitude using the median, elevated altitude was associated with a reduction in concussion rates overall (rate ratio [RR], 1.31; P < .001), in competition (RR, 1.31; P < .001), and in practice (RR, 1.29; P < .001). Specifically, high school sports played at higher altitude demonstrated a 31% reduction (95% confidence interval [CI], 25%-38%) in the incidence of total reported concussions. Likewise, concussion rates at increased altitude were reduced 30% for overall exposures, 27% for competition exposures, and 28% for practice exposures in football players (P < .001).

Conclusion: The results of this epidemiological investigation indicate increased physiological responses to altitude may be associated with a reduction in sports-related concussion rates, especially in collision sports. Future research that focuses on the potential prophylactic effect of optimizing outflow impedance and thus reduction of intracranial compliance (a "tighter fit") in humans is warranted to determine the most effective approaches to mitigate sport-related concussion, especially in football players.

No MeSH data available.


Related in: MedlinePlus

Cerebral volume must rise by 3 to 4 mL before pressure starts to rise. (Reprinted with permission from Löfgren J, Zwetnow NN. Cranial and spinal components of the cerebrospinal fluid pressure–volume curve. Acta Neurol Scand. 1973;49:575-585. ©1973, Wiley.)
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fig1-2325967113511588: Cerebral volume must rise by 3 to 4 mL before pressure starts to rise. (Reprinted with permission from Löfgren J, Zwetnow NN. Cranial and spinal components of the cerebrospinal fluid pressure–volume curve. Acta Neurol Scand. 1973;49:575-585. ©1973, Wiley.)

Mentions: In the chronic phase of adaptation at altitude, erythropoietin stimulates increased blood synthesis with further polycythemia. Initially, hemoglobin and hematocrit rise and blood volume declines, but as acclimatization occurs, an increase in erythrocyte volume is manifested.40 In long-term acclimatization, increased arterial oxygen content is sustained by expansion of erythrocyte volume.40 Vasogenic edema in the brain leads to increased extravascular water. These 2 adaptations would also lead to tighter packaging of the brain (less compliance = tight fit) with increased blood cell content surrounding the brain. It has been noted that cerebral volume must rise by only 3 to 4 mL before pressure starts to rise and take up the compliance with brain tissues.17,26Figure 1 presents this continuum and a potential mechanistic model that may be associated with the reduced rate of concussion observed at higher altitude in this study.17 The primary pathophysiological response of cerebral concussion is felt to be due to the movement of the intracranial contents inside the skull, leading to the potential for both cellular and microstructural brain injury. The concept of Slosh has emerged as a descriptive and physiological mechanism whereby there is differential motion between the skull and brain.10,32 The notion that mild internal jugular vein compression can cause an immediate increase in intracranial blood volume and protect the brain from concussion is an emerging theory that has been demonstrated in a standard rodent mTBI model.10,32 In rat models (during a 900-g impact, per Marmarou protocol19), findings of increased brain pressure and volume were thought to reduce intracranial Slosh effects and were associated with mitigated traumatic axonal injury.10,32 The differences between just the supine and upright postures include a 1.8-fold increase in the intracranial volume, a 2.4-fold reduction in the cerebrospinal fluid oscillatory volume, and a 2.8-fold increase in the intracranial compliance index with a corresponding decrease in pressure.23 These orthostatic changes are likely associated with intracranial hydrodynamic changes. Therefore, it is reasonable to suppose that such changes in volume, pressure, and compliance could occur with increases in elevation similar to those seen with orthostatic dynamics. The noted physiological responses to increased altitude may influence a similar reduction in potential brain Slosh leading to a decreased risk of concussion at increased altitudes.


Altitude Modulates Concussion Incidence: Implications for Optimizing Brain Compliance to Prevent Brain Injury in Athletes.

Smith DW, Myer GD, Currie DW, Comstock RD, Clark JF, Bailes JE - Orthop J Sports Med (2013)

Cerebral volume must rise by 3 to 4 mL before pressure starts to rise. (Reprinted with permission from Löfgren J, Zwetnow NN. Cranial and spinal components of the cerebrospinal fluid pressure–volume curve. Acta Neurol Scand. 1973;49:575-585. ©1973, Wiley.)
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4555510&req=5

fig1-2325967113511588: Cerebral volume must rise by 3 to 4 mL before pressure starts to rise. (Reprinted with permission from Löfgren J, Zwetnow NN. Cranial and spinal components of the cerebrospinal fluid pressure–volume curve. Acta Neurol Scand. 1973;49:575-585. ©1973, Wiley.)
Mentions: In the chronic phase of adaptation at altitude, erythropoietin stimulates increased blood synthesis with further polycythemia. Initially, hemoglobin and hematocrit rise and blood volume declines, but as acclimatization occurs, an increase in erythrocyte volume is manifested.40 In long-term acclimatization, increased arterial oxygen content is sustained by expansion of erythrocyte volume.40 Vasogenic edema in the brain leads to increased extravascular water. These 2 adaptations would also lead to tighter packaging of the brain (less compliance = tight fit) with increased blood cell content surrounding the brain. It has been noted that cerebral volume must rise by only 3 to 4 mL before pressure starts to rise and take up the compliance with brain tissues.17,26Figure 1 presents this continuum and a potential mechanistic model that may be associated with the reduced rate of concussion observed at higher altitude in this study.17 The primary pathophysiological response of cerebral concussion is felt to be due to the movement of the intracranial contents inside the skull, leading to the potential for both cellular and microstructural brain injury. The concept of Slosh has emerged as a descriptive and physiological mechanism whereby there is differential motion between the skull and brain.10,32 The notion that mild internal jugular vein compression can cause an immediate increase in intracranial blood volume and protect the brain from concussion is an emerging theory that has been demonstrated in a standard rodent mTBI model.10,32 In rat models (during a 900-g impact, per Marmarou protocol19), findings of increased brain pressure and volume were thought to reduce intracranial Slosh effects and were associated with mitigated traumatic axonal injury.10,32 The differences between just the supine and upright postures include a 1.8-fold increase in the intracranial volume, a 2.4-fold reduction in the cerebrospinal fluid oscillatory volume, and a 2.8-fold increase in the intracranial compliance index with a corresponding decrease in pressure.23 These orthostatic changes are likely associated with intracranial hydrodynamic changes. Therefore, it is reasonable to suppose that such changes in volume, pressure, and compliance could occur with increases in elevation similar to those seen with orthostatic dynamics. The noted physiological responses to increased altitude may influence a similar reduction in potential brain Slosh leading to a decreased risk of concussion at increased altitudes.

Bottom Line: When concussion rates were dichotomized by altitude using the median, elevated altitude was associated with a reduction in concussion rates overall (rate ratio [RR], 1.31; P < .001), in competition (RR, 1.31; P < .001), and in practice (RR, 1.29; P < .001).The results of this epidemiological investigation indicate increased physiological responses to altitude may be associated with a reduction in sports-related concussion rates, especially in collision sports.Future research that focuses on the potential prophylactic effect of optimizing outflow impedance and thus reduction of intracranial compliance (a "tighter fit") in humans is warranted to determine the most effective approaches to mitigate sport-related concussion, especially in football players.

View Article: PubMed Central - PubMed

Affiliation: Division of Sports Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA. ; Department of Neurosurgery, NorthShore University HealthSystem, Evanston, Illinois, USA.

ABSTRACT

Background: Recent research indicates that the volume and/or pressure of intracranial fluid, a physiology affected by one's altitude (ie, elevation above sea level), may be associated with the likelihood and/or severity of a concussion. The objective was to employ an epidemiological field investigation to evaluate the relationship between altitude and concussion rate in high school sports.

Hypothesis: Because of the physiologies that occur during acclimatization, including a decline in intracranial compliance (a "tighter fit"), increased altitude may be related to a reduction in concussion rates in high school athletes.

Study design: Cohort study; Level of evidence, 3.

Methods: Data on concussions and athlete exposures (AEs) between 2005-2006 and 2011-2012 were obtained from a large national sample of high schools (National High School Sports-Related Injury Surveillance System [High School RIO]) and were used to calculate total, competition, and practice concussion rates for aggregated sports and for football only.

Results: Altitude of participating schools ranged from 7 to 6903 ft (median, 600 ft), and a total of 5936 concussions occurred in 20,618,915 exposures (2.88 per 10,000 AEs). When concussion rates were dichotomized by altitude using the median, elevated altitude was associated with a reduction in concussion rates overall (rate ratio [RR], 1.31; P < .001), in competition (RR, 1.31; P < .001), and in practice (RR, 1.29; P < .001). Specifically, high school sports played at higher altitude demonstrated a 31% reduction (95% confidence interval [CI], 25%-38%) in the incidence of total reported concussions. Likewise, concussion rates at increased altitude were reduced 30% for overall exposures, 27% for competition exposures, and 28% for practice exposures in football players (P < .001).

Conclusion: The results of this epidemiological investigation indicate increased physiological responses to altitude may be associated with a reduction in sports-related concussion rates, especially in collision sports. Future research that focuses on the potential prophylactic effect of optimizing outflow impedance and thus reduction of intracranial compliance (a "tighter fit") in humans is warranted to determine the most effective approaches to mitigate sport-related concussion, especially in football players.

No MeSH data available.


Related in: MedlinePlus