All marine and land vertebrates tested so far, including humans, have the dive reflex. The goal is to reduce the amount of oxygen used by limb muscles and organs in the abdomen while diving, save oxygen for the brain, heart, and lungs, and delay any damage to the brain until breathing starts again. The diving reflex is very clear in dolphins, whales, and seals, which need to hold their breath for long periods of time to hunt or move. The dive reflex can also help you deal with anxiety.
The Dive Reflex (Mammalian Diving Reflex)
Physiologically, there are four main response of diving reflex:
Heartbeats slow down (Bradycardia)
When the face is submerged in water that is colder than the body’s temperature, the parasympathetic nervous system’s cold receptors in the ophthalmic branch and maxillary branch of the trigeminal nerve are activated. When Vagal motoneurons are stimulated more, the heart rate goes down (Shattock and Tipton, 2012). It will drop to about half of its normal level in people who often free dive, and animals who live in the ocean will react more quickly. In a test in California, seven small walruses (Odobenus rosmarus) with their hearts on land had an average heart rate of 107 beats per minute. When they dove into seawater, their average heart rate dropped to 39 beats per minute, which is a 64% drop. During a dive, emperor penguins (Aptenodytes forsteri) can slow their heart rate down to only three beats per minute.
Vasoconstriction in the periphery
When the heart rate goes down, so does the blood pressure in the arteries. This makes the sympathetic nervous system tighten the blood vessels in the skin, limb muscles, and organs, which slows the flow of blood to these areas. In addition to keeping the body’s core temperature stable, peripheral vasoconstriction keeps blood in the center of the body. This helps oxygen get to the brain, heart, and lungs first.
Spleen swells up
This response was first found in aquatic mammals, and the sympathetic nervous system is what makes it happen. Marine mammals have a spleen that is pretty big. When they dive, the spleen contracts and sends red blood cells into the bloodstream. This makes the blood carry more oxygen. The Weddell seal’s (Leptonychotes weddelliihematocrit) and hemoglobin levels went up by 48% and 44%, respectively, when it dove for 10–12 minutes (Qvist et al., 1986). Schagatay et al. (2001) did a study with 20 people. None of them had professional training in holding their breath, and half of them had had their spleens taken out. The people put their faces in water that was 10°C cold and held their breath for 5 minutes. The results showed that the number of red blood cells increased by 6.4% and the amount of hemoglobin increased by 3.3% in the people who still had their spleens. This was a lot more than what happened in the people whose spleens had been removed. Even though the oxygen content of the human spleen is very different from that of marine mammals, this study proved that the human diving response also involves the spleen contracting.
Blood shift
The thoracic cavity is another part of the body that changes because of depth (blood shift). The large air volume keeps going down, and at the same time, the blood pressure in the pulmonary vessels goes up. This makes the microvessels around the alveoli constrict and expand to keep the shape of the lungs and keep the alveoli from being pulled away from the intrapleural cavity as the volume goes down. And stung. The diaphragm, sternum, and ribs are all parts of the thorax. The pleural cavity is the space between the lungs and the chest. Normally, there is no air in the pleural cavity, which is under negative pressure. This means that the lungs can expand and take in air when the thoracic cavity gets bigger. gas. Different species have a wide range of differences in how much the thorax changes in size. For example, the sperm whale (Physeter macrocephalus) can dive up to 3000 meters deep, and most of its ribs are separate from its sternum. This gives its thorax a lot of room to move. in the ocean If you put a lot of water pressure on it, it will shrink.
The human thorax, on the other hand, is less active. After going deeper than the thorax can be squeezed while holding your breath, if the amount of air in your lungs keeps going down, the pleural cavity will be pulled and the alveoli will break. So, in 1960, scientists thought it was impossible for humans to dive more than 50 meters in one breath, not because they couldn’t hold their breath long enough but because the water pressure would damage their lungs by making their lungs hold less air. But since then, freedivers have broken this record many times and come back to the surface without getting hurt. Researchers have found that about 1 liter of blood can flow into a person’s chest cavity through blood transfer, based on the size of their lungs at different water depths. Under pressure, there isn’t much change in volume, and the extra blood that flows into the thoracic vessels can keep the lungs in shape. During the process of coming to the surface, the blood will leave the chest cavity through the vessels as the water pressure drops (Craig et al., 1968; Schaefer et al., 1968). Due to the overexpansion of microvessels at extreme depth and low oxygen levels, blood plasma has leaked into the alveoli and caused pulmonary edema or bleeding (Linér and Andersson, 2008). This doesn’t happen to scuba divers because the high-pressure gas in the tank gives the chest cavity the air pressure it needs to keep its size.
Another part that needs to be balanced is the space in the middle ear. When humans dive to great depths, they mostly use air to balance the pressure in their middle ears. However, some marine mammals use blood transfer to balance the pressure in their middle ears (Costa, 2007).
How the dive reflex improve anxiety symptom.
Introduction about anxiety / Panic Disorder
According to the DSM-5, panic disorder (PD) is a severe and long-lasting anxiety disorder that causes panic attacks (PAs) that happen on their own and happen over and over again. People with PD have irregular breathing patterns, mostly a thoracic pattern of breathing, abnormal breathing variability, and irregular breathing. PD has also been linked to a number of breathing problems, such as air hunger, dyspnea, rapid breathing, and a fast heart rate.
If you want to know more about anxiety, you can start from here:
All You Need To Know About Anxiety
Is The Dive Reflex Useful To Improve Anxiety?
According to the recent paper (The Implications of the Diving Response in Reducing Panic Symptoms). It is interesting to note that by activating the diving response and then slowing down one’s heart rate, one may be able to reduce the physical and mental signs of panic and possibly their sensitivity to CO2. This study showed that the CFI task could reduce the anxiety and panic that the CO2 challenge caused. People with panic disorder say that their racing or pounding hearts are one of the scariest things that happen to them. So, lowering the heart rate and arousal of the autonomic sympathetic nervous system may make people feel less anxious. People who have panic attacks often say that they feel like they can’t breathe and are suffocating. When the diving response is turned on, on the other hand, it has an oxygen-saving effect that makes it possible to hold your breath for longer, which helps the organism stay alive. So, CFI may be a good way to treat panic disorder and other types of anxiety disorders. Also, the diving response is easy to trigger with cold moisture (like ice packs), which makes it an easy treatment to give. More research needs to be done to learn more about how activating the diving response makes people feel less anxious.
The Possible Mechanism
Immersion of the face in cold water slows the heart rate more than immersion of other body parts. The difference between the air temperature and the water temperature has a big effect on the DR. Since there are more receptors in the eyes, forehead, and nose, which are part of the ophthalmic region of the trigeminal nerve, the face is more sensitive to cold water when it is fully submerged in water.
When fear is triggered, one of the most important signs of PD is a dysregulated autonomic nervous system (ANS), which is marked by sympathetic nervous system (SNS) arousal. It has been shown that slowing down the heart rate can help people with panic attacks feel better quickly. PD treatments are often ineffective and expensive, so we need to know more about the underlying pathophysiology of the disease to help us make better ones. Patients with PD may benefit from simple, easy-to-use treatments that try to control the ANS and turn off the fear response. So, the purpose of this study is to find out if the DR, which is activated by holding your breath and the resulting slowing of your heart rate, is able to reduce the physiological fear response that comes with panic.
How to activate the dive reflex yourself?
First, you’ll need a big bowl, or you may use your sink. Fill it with frigid water next; the water must be colder than 50 degrees for this process to work. However, freezing water has shown to be the most effective in my experience! Next, for 30 seconds, immerse your face in water while holding your breath. Remove your head from the water and repeat the dipping technique. If this isn’t possible or you’re not comfortable underwater, there are a couple more methods to elicit the same reaction.
Some alternative ways include filling a ziplock bag with ice, using a cold cloth or frozen veggies, pouring cold water on your face, rubbing cold water on your wrists, having a cold shower, and swimming.