February 2001
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Differential Pressure Across Diaphragm Muscle: The Mechanism Responsible for Sensations of Intense Internal Pressure and Pain Caused by Blow to "Solar Plexus"

Almost everyone has, at one time or another in his life, "had the wind knocked of him", either by a blow to the torso or by a sudden and unexpected fall.

Blunt trauma to the "solar plexus", a large network of sympathetic nerves and ganglia located in the peritoneal cavity behind the stomach and having tracts that supply nerves to the abdominal viscera, is frequently cited by persons who have no medical knowledge about the cause of this discomfort. 

Blunt trauma to the abdomen or the thorax can cause a significant differential pressure across the diaphragm, which is the muscle that separates the abdominal cavity from the thoracic cavity. The differential pressure stretches and strains the diaphragm, and can cause the diaphragm muscle to involuntarily spasm and contract painfully. The painful muscle cramp, which is essentially a "charley horse" of the diaphragm, is what prevents a person from catching his breath in the moments immediately after the blow is received.

A violent and forceful blow to a relaxed abdomen often produces a feeling of intense internal pressure as the contents of the abdominal cavity are suddenly displaced across the diaphragm muscle and into the thoracic cavity.

These deleterious effects can be decreased substantially by flexing the muscles of the abdomen before and when the blow is landed.

A person's mindset is key as to whether or not he's temporarily incapacitated by this mechanism. Having "the wind knocked out of you", while painful indeed, is not a physiological incapacitation mechanism. Rather, its effects are psychological in nature, borne out of physical pain and discomfort. Most people are quite capable of performing willful activity during the period in which they've lost their breath. What these people choose to do, lie down, stand with their hands on their knees, walk around, shoot back, etc., is entirely their choice.

This mechanism is often cited as "proof" of the alleged incapacitating physiological effects of energy transfer and temporary cavity. However, while there is physiology involved the incapacitating effect is almost entirely psychological, and psychological reaction to being shot is erratic, unreliable and dependent on the mental state of the person who is shot. Drugs, alcohol, resolve combined with an acceptance of the risk of being shot, and psychosis are factors that decrease the chances of inflicting a debilitating psychological reaction.

When all else fails, a bullet must damage vitals that are critical to an attacker's immediate survival to produce reliable rapid incapacitation.

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Sectional Density: Rule-of-thumb Guide for Estimating Terminal Performance

Sectional density is a bullet's weight in pounds divided by the square of its diameter in inches. It plays an important role in bullet penetration. Bullets with greater sectional density tend to penetrate deeper.

As a rule-of-thumb guideline, sectional density can be used estimate and compare penetration performance. Bullets of similar sectional densities, propelled at similar velocities, and exhibiting similar percentages of expansion tend to penetrate to similar depths.

In the late 1980's the FBI adopted a reduced velocity 10mm 180gr cartridge. Many critics, gun writer and non-gun writer alike, voiced an opinion in which they believed the FBI had simply reinvented the .45 ACP 185gr cartridge. These critics apparently didn't understand the concept of sectional density. What the FBI adopted was essentially a .45 ACP 230gr bullet that was propelled about 100 fps faster, which gave the FBI the penetration performance it desired.

With few exceptions, most JHP bullets expand to between 150 and 180 percent of their pre-fired diameters. You'll notice in the table below that bullets considered heavy-weight, middle-weight and light-weight for their respective calibers and cartridge loadings all share similar sectional densities.

Heavy-weight bullets in .45 ACP, .40 S&W and 9mm all share a similar trait: their sectional densities are alike, all are propelled at similar subsonic velocities, all demonstrate similar expansion performance and all penetrate to approximately the same depths. The same is true for middle-weight and light-weight bullets in these same calibers.

The table below lists several popular cartridges and their sectional densities in descending order. It is intended as a useful guide to estimate bullet penetration for cartridges wherein terminal performance data is unavailable.

What's that?! The table above doesn't list your cartridge and you don't have a clue what its sectional density is?  Well, you're in luck! A formula for calculating sectional density was published in the July 1999 issue of Tactical Briefs. Click here for information about calculating sectional density.

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This Month's Features:

Click title to read article:

• Communicating Effectively with Police

• INS National Firearms Unit Ballistic Test Protocol Symposium

The INS's methodologies for testing and selecting duty ammunition are far more complicated than necessary. In our opinion, INS could simplify its protocol by awarding points for penetration depth performance and temporary cavity volume performance only, and make all other test events pass/fail based on minimum acceptable performance.

According to gun writer Ed Sanow, who was invited by INS to participate in its April 1998 symposium, the majority of INS shootings involve people who are heavily clothed, and this is the reason why the test event involving heavily clothed gelatin was given greatest scoring weight. Given that the INS apparently believes a bullet's temporary cavity is an important incapacitation mechanism, we're dumbfounded at the obvious incongruity of the INS's fascination with measuring temporary cavity volume in bare gelatin only. To us, it doesn't make sense to measure temporary cavity volume in bare gelatin when most of its shooting incidents involve heavy clothing.

When the Federal Bureau of Investigation researched and developed its terminal performance criteria for handgun ammunition, it published its knowledge and beliefs about incapacitation mechanisms. The paper, Handgun Wounding Factors and Effectiveness, describes in great detail the evidence and rationale that supports the FBI's terminal performance criteria. Unfortunately it appears INS has chosen not to document its knowledge and rational in a similar manner. It would be interesting indeed to learn what INS knows about the effects of temporary cavitation and why it believes temporary cavity volume, produced by a handgun bullet, is an important incapacitation mechanism. 

• INS-NFU Ballistic Gelatin Test Protocol
• INS National Firearms Unit Ballistic Protocol Survey
• 40 S&W 155 Grain Duty Ammunition Technical Evaluation

• Personal Defense Ammunition Terminal Performance Test Data:

• .45 ACP Federal 230gr HydraShok JHP fired from a Glock 30
• .40 S&W Winchester Ranger 180gr RA40T JHP fired from a Glock 27

Delivering you informative multimedia essays about the "battlefield problem-solving" tactical aspects of armed self-defense.

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