Updated: May 17, 2010
A rather delicate topic, you may say. Well, if you feel offended or whatnot, please stop reading now. However, if you want to explore the physics of a very common phenomenon inflicting half the human population at least once a day, then please do continue reading.
I would like to calculate the max. theoretical limit of a male erection, one that would cause the owner to faint instantly from the massive surge of blood away from vital organs into the nether regions. We've all heard and read stories about this guy and that guy, and even though some required medications and others used tripods, none of these exhibited any of the signs of massive blood loss or unconsciousness while under the influence of manhood.
The question is, if our tissue and blood pressure permitted limitless mischief, what kind of monstrosity should we expect before blacking out? How much blood would we need lose before fainting? What would that blood loss result in, physically? What kind of heart beat and blood pressure would the owner have to maintain to support such an exhibit, before losing consciousness, that is? Well, if you're in for some adult fun, scroll down and enjoy.
Blood
Our blood is very precious. We carry only a few liters. Losing even one can be dangerous, but probably not fatal. Reading online, I discovered that most studies agree on 2 liters being the max. quantity of blood an average human can lose before dying. Two liters means 2,000 cc of blood, not necessarily 2 kg of liquid, since blood is more dense than water, due to all the little thingies floating in it, like proteins, metals and whatnot. We will use this later on. For now, we agree than 2 liters is the max.
Where does it all go?
Into corpus spongiosum, of course! Let's ignore the actual tissue, as it usually takes very little volume and will not make much difference in the final calculation. We will also assume infinite elasticity, i.e. the organ can stretch indefinitely while maintaining rigidity. Our estimated average diameter is about 5cm. Therefore, we need a cylinder-shaped vessel, with the base of 5 cm, capable of containing 2,000 cc of blood.
Using some very simple mathematics, we get:
So, we would require a member that is 101 cm long! That's quite a bit, eh?
Blood pressure & heart rate
Let's see what kind of pumping power we would require to maintain such a majestic foundation!
The normal systolic blood pressure is about 120 mm Hg or roughly 0.15 bar, whereas the diastolic pressure is about 80 mm Hg or roughly 0.1 bar, with the average heart rate of 72 beats/min. For the sake of simplicity, we will assume the diastolic pressure is two thirds of the systolic.
The pressure at the base of our erection is 2,000 cc of blood on an area just shy of 20cm2. The only question remaining is, how thick the blood is, with all the foreign particles in it. Again, referring to all kinds of medical articles online, we derive the average blood density is 1.05 gr/cm3. So, we have 2.1 kg blood, pressing on an area of 0.002 m2. This is: 10500 Pa or 0.105 bar.
This means that we would require a blood pressure of about 0.26 bars or almost 200 mm Hg to maintain the erection. Some of you may think this is not much. Just note that a very high blood pressure is clinically rated as 150 mm Hg and higher.
Note: Image taken from Wikipedia; licensed under CC-BY-SA 2.0
The only thing left to calculate is the heart beat required. I have not found any reliable source showing a direct relation between the blood pressure and heart rate, so I'll assume the simplest one - linear. Therefore, the heart beat would have to go up to about 120 beats/min, which is a decent workout.
End result
Just before fainting, maintaining the ultra-big erection of 101 cm would make your blood pressure so high, you would probably go blind after a short while, if it were left to its own devices, and you would be panting like someone just finished with a decent 5-km jog. And then, you'd lose too much blood and faint. This would be very much like pulling G in an airplane, without a G-suit! Your blood rushes into nether regions, you breathe heavily and you blackout. Hilarious! An aerobatic wang effect!
This also partially explains why men are getting more stupid when aroused. They don't have enough blood in their brains. Capillary action also plays a part, methinks, but since we have Sequoia trees that tower tens of meters, this is probably not an issue here. And that's all!
Conclusion
Ah, another pseudo-physical masterpiece! Bio-physics this time, if you will. Today, we have learned many important things. The first and foremost, the direct relation between temporal intelligence and erection. The second, the reason why human males do not have very large members and, if average intelligence has anything to do with it, why large is not quite the adjective you would use. Thirdly, we have learned about the physical limits of human arousal, mostly bounded by the fatality of blood loss rather than pressure limitations.
I hope you've enjoyed it. If you have other weird topics you'd like explored, feel free to suggest them.
Dedoimedo out.