Character physiology in Blood & Bullet
I want a couple of key features in Blood & Bullet to be realistic. One of those are how characters are injured and what the effects of the injuries are. I am by no means an expert but I use the knowledge I have and what I'm able to find. Since the characters in my game are 2-dimensional I have to play some tricks to simulate the third and missing dimension.
The characters' bodies are composed of limbs, and to each limb I can attach what I call vital properties. When a limb is hit by a projectile I randomize which of the vital properties are hit based on probabilities for each of the properties. For instance hitting the spine inside the torso has a much lower probability than hitting the lungs, since the lungs cover a larger volume of the torso than the spine does.
Some of the vitals I can add to limbs are as follows.
These are bones that are necessary for the character to move. When these are damaged the character will start to limp and if the impact is powerful enough it will knock the character off its feet. This is used in all the limbs from the feet up to the pelvis.
Major blood vessels
If these are hit the limb will bleed at its maximum rate. Depending on which limb it is it may cause the character to bleed out and loose consciousness very quickly.
When the lungs are hit their capacity to store oxygen is reduced.
When the heart is hit it will function less efficiently and skip beats or stop completely. The amount of oxygen transferred to the blood is reduced.
When the spine is hit I want to turn off motor control to the limbs below the hit region but I can't do that yet. Now the character simply falls to the ground.
When the brain is even slightly damaged the character loses consciousness. Further it is divided into a couple of parts making it possible for the character to lose:
- Circulation control - the heart stops
- Respiration (breathing) control - respiration stops
- Motor control - muscles in limbs cramp or spasm
What it takes to stay alive
For a character to remain alive in Blood & Bullet its brain must be intact and supplied with oxygen. That is the only criteria. If the brain is too damaged the character dies. The brain receives damage both from trauma (projectile hits) and over time by lack of oxygen. The brain can be without oxygen for 30 seconds before it dies. That value is game-ified of course and it will probably be different depending on the level of difficulty selected.
For the brain to be supplied with sufficient oxygen both the character's respiration and circulation must function properly, meaning it needs to breath and the heart needs to beat. As you saw above, both of these can be impaired by trauma from being shot, or disabled completely if the brain is hit. The character is unable to remain conscious when the oxygen level becomes low and this happens long before brain death, so a character lying on the ground in Blood & Bullet is usually just unconscious and not dead.
On the characters I have a value that represents how hard they are working themselves physically. It becomes high when they are running and it's low when they are standing still, but everything they do takes work. Even breathing and pumping the heart takes some work.
This is the basis of the physiology in B&B:
- A character breathes and pumps blood to provide itself with oxygen.
- The level of work a character does directly affects how much oxygen is taken from its blood.
- When the amount of oxygen in a character's blood becomes low, its heart compensates by pumping faster. This removes oxygen from its lungs faster but provides more oxygen.
- When the amount of oxygen produced by a character's breathing becomes insufficient the character compensates by breathing faster.
This all fits together rather neatly. While tweaking it I was pleasantly surprised when I managed to strain the player character so hard by running that he lost consciousness!
Above: Pulse, blood pressure, respiration and work intensity during a walk.
The same values some time into a sprint. Note that also the blood pressure is higher during work because it must circulate faster. Diastolic pressure is the lowest pressure during the beat cycle that occurs while the heart muscle is relaxed.
How it affects gameplay
Now that you understand that the characters in Blood & Bullet have "real" pulses you can see that a character that has been working hard will bleed out faster than a character that was resting if they were injured, because the heart pumps the blood out of the wound faster.
You can see that stabilizing a downed suspect to make him bleed slower may buy you time to finish the mission before he dies. (Proper healthcare cannot be provided before you have secured the building.)
You can also see that it's equally important that you make sure unconscious characters don't suffocate from having their breathing obstructed.
You will have the option to equip your team members with medical kits that can stop or slow down bleeding. It will be up to you to decide when to use them. Some missions may be so time critical that you simply don't have the time to stop before you have cleared the whole building.
It is my hope that this adds to the gameplay and that it puts the use of force into some perspective. At least for the campaign missions. The sandbox mode is quite different in how it is played but the same character physiology is in place there as well.
Thanks for reading!