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On the pressure response in the brain due to short duration blunt impacts.

Pearce CW, Young PG - PLoS ONE (2014)

Bottom Line: As such, the head impact literature to date has focussed almost exclusively on impact scenarios which lead to a quasi-static pressure response in the brain.We demonstrate that short duration head impacts can lead to potentially deleterious transients of positive and negative intra-cranial pressure over an order of magnitude larger than those observed in the quasi-static regime despite reduced impact force and energy.The onset of this phenomenon is shown to be effectively predicted by the ratio of impact duration to the period of oscillation of the first ovalling mode of the system.

View Article: PubMed Central - PubMed

Affiliation: College of Engineering, Mathematics and Physical Sciences, University of Exeter, Harrison Building, North Park Road, Exeter, EX4 4QF, United Kingdom.

ABSTRACT
When the head is subject to non-penetrating (blunt) impact, contusion-type injuries are commonly identified beneath the impact site (the coup) and, in some instances, at the opposite pole (the contre-coup). This pattern of injury has long eluded satisfactory explanation and blunt head injury mechanisms in general remain poorly understood. There are only a small number of studies in the open literature investigating the head's response to short duration impacts, which can occur in collisions with light projectiles. As such, the head impact literature to date has focussed almost exclusively on impact scenarios which lead to a quasi-static pressure response in the brain. In order to investigate the response of the head to a wide range of impact durations, parametric numerical studies were performed on a highly bio-fidelic finite element model of the human head created from in vivo magnetic resonance imaging (MRI) scan data with non-linear tissue material properties. We demonstrate that short duration head impacts can lead to potentially deleterious transients of positive and negative intra-cranial pressure over an order of magnitude larger than those observed in the quasi-static regime despite reduced impact force and energy. The onset of this phenomenon is shown to be effectively predicted by the ratio of impact duration to the period of oscillation of the first ovalling mode of the system. These findings point to dramatically different pressure distributions in the brain and hence different patterns of injury depending on projectile mass, and provide a potential explanation for dual coup/contre-coup injuries observed clinically.

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Normalised peak positive and negative intra-cranial pressures.(A) Non-dimensionalised pressures against non-dimensionalised impact durations at the coup, and (B) at the contre-coup. Solid lines represent results of the parametric study conducted using the simpler two-phase head model, and bold markers represent three case studies utilising the full bio-fidelic model.
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pone-0114292-g003: Normalised peak positive and negative intra-cranial pressures.(A) Non-dimensionalised pressures against non-dimensionalised impact durations at the coup, and (B) at the contre-coup. Solid lines represent results of the parametric study conducted using the simpler two-phase head model, and bold markers represent three case studies utilising the full bio-fidelic model.

Mentions: As before, the recorded peak intra-cranial pressures were normalised over the analytically predicted peak pressures ±Pquasi, so resulting in a measure of pressure magnification, i.e. the factor by which the pressure response of a particular short duration head impact is increased in comparison to a conventional quasi-static head impact with equal peak force. Impact durations TP were normalised over the period of oscillation of the first equivoluminal mode of vibration of the head TΩ. The normalised results for a range of impacts are presented in Fig. 3 in terms of non-dimensional pressure against the log of non-dimensional duration at both the coup and contre-coup. The results of the three case studies using the full bio-fidelic head model can be seen to exhibit non-dimensional pressure magnifications against impact duration which agree well with those of the simpler parametric study. The non-dimensional ratio TP/TΩ neatly collapses the system's response: above a value of approximately TP/TΩ = 2 the pressure distribution in the brain will be quasi-static and below this value increasingly large positive and negative pressure transients are observed. It is noteworthy that the most commonly adopted measure of head impact severity, the Head Injury Criterion (HIC) [28], correlates decidedly poorly with the observed pressure magnitudes in the brain; indeed the light fragment and golf ball impacts have low computed HIC values of 52 and 835 respectively, whilst the heavy impactor HIC score is 2650, yet in the case of the two lighter impactors the resulting peak positive pressures were observed to be between 5.3 to 8.8 times greater and negative pressures were 4.0 to 6.5 times greater.


On the pressure response in the brain due to short duration blunt impacts.

Pearce CW, Young PG - PLoS ONE (2014)

Normalised peak positive and negative intra-cranial pressures.(A) Non-dimensionalised pressures against non-dimensionalised impact durations at the coup, and (B) at the contre-coup. Solid lines represent results of the parametric study conducted using the simpler two-phase head model, and bold markers represent three case studies utilising the full bio-fidelic model.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4257587&req=5

pone-0114292-g003: Normalised peak positive and negative intra-cranial pressures.(A) Non-dimensionalised pressures against non-dimensionalised impact durations at the coup, and (B) at the contre-coup. Solid lines represent results of the parametric study conducted using the simpler two-phase head model, and bold markers represent three case studies utilising the full bio-fidelic model.
Mentions: As before, the recorded peak intra-cranial pressures were normalised over the analytically predicted peak pressures ±Pquasi, so resulting in a measure of pressure magnification, i.e. the factor by which the pressure response of a particular short duration head impact is increased in comparison to a conventional quasi-static head impact with equal peak force. Impact durations TP were normalised over the period of oscillation of the first equivoluminal mode of vibration of the head TΩ. The normalised results for a range of impacts are presented in Fig. 3 in terms of non-dimensional pressure against the log of non-dimensional duration at both the coup and contre-coup. The results of the three case studies using the full bio-fidelic head model can be seen to exhibit non-dimensional pressure magnifications against impact duration which agree well with those of the simpler parametric study. The non-dimensional ratio TP/TΩ neatly collapses the system's response: above a value of approximately TP/TΩ = 2 the pressure distribution in the brain will be quasi-static and below this value increasingly large positive and negative pressure transients are observed. It is noteworthy that the most commonly adopted measure of head impact severity, the Head Injury Criterion (HIC) [28], correlates decidedly poorly with the observed pressure magnitudes in the brain; indeed the light fragment and golf ball impacts have low computed HIC values of 52 and 835 respectively, whilst the heavy impactor HIC score is 2650, yet in the case of the two lighter impactors the resulting peak positive pressures were observed to be between 5.3 to 8.8 times greater and negative pressures were 4.0 to 6.5 times greater.

Bottom Line: As such, the head impact literature to date has focussed almost exclusively on impact scenarios which lead to a quasi-static pressure response in the brain.We demonstrate that short duration head impacts can lead to potentially deleterious transients of positive and negative intra-cranial pressure over an order of magnitude larger than those observed in the quasi-static regime despite reduced impact force and energy.The onset of this phenomenon is shown to be effectively predicted by the ratio of impact duration to the period of oscillation of the first ovalling mode of the system.

View Article: PubMed Central - PubMed

Affiliation: College of Engineering, Mathematics and Physical Sciences, University of Exeter, Harrison Building, North Park Road, Exeter, EX4 4QF, United Kingdom.

ABSTRACT
When the head is subject to non-penetrating (blunt) impact, contusion-type injuries are commonly identified beneath the impact site (the coup) and, in some instances, at the opposite pole (the contre-coup). This pattern of injury has long eluded satisfactory explanation and blunt head injury mechanisms in general remain poorly understood. There are only a small number of studies in the open literature investigating the head's response to short duration impacts, which can occur in collisions with light projectiles. As such, the head impact literature to date has focussed almost exclusively on impact scenarios which lead to a quasi-static pressure response in the brain. In order to investigate the response of the head to a wide range of impact durations, parametric numerical studies were performed on a highly bio-fidelic finite element model of the human head created from in vivo magnetic resonance imaging (MRI) scan data with non-linear tissue material properties. We demonstrate that short duration head impacts can lead to potentially deleterious transients of positive and negative intra-cranial pressure over an order of magnitude larger than those observed in the quasi-static regime despite reduced impact force and energy. The onset of this phenomenon is shown to be effectively predicted by the ratio of impact duration to the period of oscillation of the first ovalling mode of the system. These findings point to dramatically different pressure distributions in the brain and hence different patterns of injury depending on projectile mass, and provide a potential explanation for dual coup/contre-coup injuries observed clinically.

Show MeSH
Related in: MedlinePlus