“Pressure pushing down on me, pushing down on you…” Queen, Under Pressure
Pressure affects all of us. It’s inescapable. So as freedivers, in a sport where water pressure compresses the air in our lungs to incomprehensibly tiny volumes and crushes our bodies, we not only have to overcome the hurdles of pressure, but teach our bodies to embrace it.
My personal best dive this year brought me to 81m/266 feet, or 9.1 atmospheres of pressure. That doesn’t sound too bad until you consider that my body underwent pressures up to 133 pounds per square inch at depth.
While that can sound frightening or make the more claustrophobic among us running for wide open spaces, this pressure can actually be a boon as much as it can be a detriment. The gentle hug of water pressure helps us reach those depths at the same time that it creates obstacles.
Hurdles of Pressure
Every freediver at one point or another has felt the impact of water pressure on the air spaces in their body, namely their ears. As outside pressure increases on your body’s airspaces, you have to increase pressure on the inner airspaces to even everything out. But it’s not always as simple as is sounds. A little congestion, poor technique and even distractions can cause you to miss an equalization and hurt your ears (or other air volumes).
Firing Stretch Receptors
Otherwise known as “The Lying Bastard,” a stretch receptor that we all have in our bodies will fire signals to our brains as pressure increases, telling us we need to breathe. This stretch receptor is not governed by levels of oxygen or carbon dioxide and so is an inaccurate gauge on our need to breathe. It basically just sucks and makes you feel like you have to turn around to head to the surface.
Benefits of Pressure
As freedivers enter water, water pressure begins a process called blood shunt. Blood shunt occurs when your body pulls blood back from your extremities and centralizes it to the core, around the heart and brain. This helps conserve oxygen and prioritize the most vital organs in the body.
When descending to depth, freedivers’ lungs compress until they reach the point of residual volume, or the volume at which the lungs can no longer compress without experiencing tissue damage (well, you can go a LITTLE lower than residual, but I’m generalizing here). But divers often go far beyond their point of residual volume because of something called thoracic filling. Once your lungs reach the point of maximum compression your body will fill them will blood plasma. Blood plasma is incompressible and allows divers to continue deeper and deeper without imploding their lungs.
Breath-holding can trigger bradycardia, or extremely low heart rate, in divers but extreme pressures can also trigger this reflex as well. As divers head to depth and reach residual volume and beyond they can show drastic drops in heart rate, as low as 14 beats per minute in some no-limits divers. This reflex helps conserve oxygen, allowing the diver to not only increase depth but breath-hold times as well.
So while we often think of being “under pressure” as a bad thing, it’s often great for freedivers. Pressure may make it hard to clear our ears, but it also triggers the dive reflexes that allow us to accomplish amazing depths. So I say bring it on- freedivers can handle it. I figure that anyone who voluntarily deprives themselves of oxygen for several minutes at a time can probably handle a little pressure!