Breath Hold – Effect of Barometric Pressure on the Pulmonary System

by Thad Wilson, PhD

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    00:00 This particular table is going to go over an example of what can happen during breath hold-diving.

    00:08 We have O2 concentrations and CO2.

    00:11 Both in terms of percents and millimeters of mercury.

    00:15 During the resting condition, this is the alveolar gas, is around 14% or 100 millimeters of mercury.

    00:25 The carbon dioxide concentration is about 5.6% and that encompasses 40 millimeters of mercury.

    00:33 Now, right before descent, sometimes, people will hyperventilate a little bit.

    00:37 And they do that so that they’ll be able to hold their breath for a longer period of time.

    00:43 So just before the descent, the increase in O2 will go up to 16.7%.

    00:50 And the barometric pressure stays at 760, but the O2 pressure goes to 120.

    01:00 Carbon dioxide gets blown off a little bit so it went from 5.6 to 4, that decreased the partial pressure to 29.

    01:09 Now what a person does is they go underneath the water so this is after they have – right before they descended, they now are diving down deeper.

    01:19 At the apex of their dive, the oxygen concentration drops to 11%.

    01:24 However, look at the partial pressure of O2.

    01:29 It’s 149, more than what you started with.

    01:34 In terms of carbon dioxide concentration, it is at 3.2% or, in this case, about 42 millimeters of mercury.

    01:41 But it’s this oxygen that at the lowest portion of the dive at the apex, you don’t have a problem with O2.

    01:49 Why? Because barometric pressure’s so high.

    01:54 Where the clinical problem comes in with breath hold-diving is if someone goes to the surface too quickly after they’ve depleted their oxygen.

    02:04 So as they are starting to go towards the surface, oxygen concentration continues to decrease.

    02:09 Now, it’s only about 5.9%.

    02:13 But this is the very big problem, oxygen drops to about 41 millimeters of mercury.

    02:19 At this point, the person can black out.

    02:21 Blacking out while under the water is not good.

    02:24 This could involve a terminal condition or the person might die because they passed out underneath the water and will then of course drown.

    02:34 It’s interesting that barometric pressure makes such a difference in this case because notice that at the apex of the dive, partial pressures of O2 were so high, they were just high though artificially because of the high barometric pressure of the water.

    02:52 Okay.

    02:54 This is an example of someone who is holding their breath.

    02:58 This first part is the start of a breath hold.

    03:01 This is the start in which the body is really, really trying to breathe and then this is the end of the breath hold.

    03:11 So let’s look at the process the body does to try to hold their breath.

    03:16 This particular diagram shows a number of pressures.

    03:18 This interesophageal pressure or IEP being the most important.

    03:23 So if you look at interesophageal pressure, when you do a breath hold, it’s fairly stable until the point at which the body is really trying to breathe.

    03:34 And this forms a number of various portions that cause these Muller and Valsalva maneuvers.

    03:43 And you’ve all probably experienced this.

    03:45 And so after this particular lecture, I encourage you to take a breath hold.

    03:51 Take in as much air as you can, hold your breath for as long as you can.

    03:53 You’re eventually going to reach a point in which the body’s really trying to breathe.

    03:59 And that is the point in which these Muller and Valsalvas kick in.

    04:03 And then finally, you have the point at which you can no longer hold your breath and that’s when carbon dioxide levels get too high.

    04:13 So what kind of adaptations occur when someone is trying to do breath holds? And how can you improve someone’s breath hold time? Well, breathing faster is kind of interesting in that it blows off carbon dioxide so you can actually hold your breath longer if you hyperventilate before you breath hold.

    04:30 And it’s interesting that it’s not because you get more oxygen into your lungs.

    04:37 It’s because you’re blowing off more CO2.

    04:40 And CO2 is the stimulus to breathe.

    04:42 And so if you have less CO2 around, you’d be able to hold your breath for a longer of time.

    04:47 However, it’s not recommended when you’re doing breath hold-diving because of that blackout type of phenomenon.

    04:54 What other things affect breath hold time? One is what you’re doing underneath the water.

    04:59 So if you’re doing something like snorkling or taking pictures, the amount of energy you expend underneath the water will affect your breath hold time.

    05:10 Also, how much O2 you have in your lungs before you start.

    05:14 Finally, there’s a number of other items associated with psychological factors as well as some task and focus diversions that will increase your breath hold time.

    05:25 For example, if you’re diving off a coral reef and see a very pretty fish or trying to look at something, if you’re task is focused on that particular fish, you can hold your breath a little bit longer than you can if you were thinking about needing to come up to the surface to breathe.

    05:45 There are some chronic benefits of breath hold-diving.

    05:49 These include things like increasing in some pulmonary function values such as total lung capacity, vital capacity and inspiratory capacity.

    05:58 There’s also blunting or decrease sensitivity to carbon dioxide and oxygen.

    06:03 And what this does is make sure that you don’t have to breathe as often because you can hold your breath for a longer period of time before the stimulus to breathe hits.

    06:12 And there may even be some adaptation with things like diving bradycardia and some heightened peripheral vasoconstriction that sometimes happens.

    06:21 Now, that we’ve covered increases in barometric pressure, let’s go to decreases in barometric pressure.

    06:29 So usually the idea of decrease in barometric pressure is when a person goes to altitude or to high mountain environments.

    06:37 This particular diagram shows you that in terms of barometric pressures along the Y axis, these are the changes that occur as you increase height or elevation.

    06:52 I’ll point out a couple to you such as the summit of Mount Everest.

    06:58 There’s also places like Denver or Mexico City.

    07:03 So there are some of these areas that people live for full time throughout the whole year and other ones that you just might visit once.

    About the Lecture

    The lecture Breath Hold – Effect of Barometric Pressure on the Pulmonary System by Thad Wilson, PhD is from the course Respiratory Physiology.

    Included Quiz Questions

    1. At the apex of the dive
    2. When resting
    3. Before the descent
    4. During the ascent
    5. At the start of the descent
    1. Activity during breath-hold diving
    2. Hyperventilation
    3. Decreased oxygen demand
    4. Increased lung volume and oxygen content
    5. Focusing on a task
    1. An increased total lung capacity
    2. A decreased inspiratory capacity
    3. Diving tachycardia
    4. An increased ventilatory response to PaCO2
    5. An increased ventilatory response to PaO2
    1. It decreases CO2, which is the stimulus to breathe.
    2. It increases CO2, which is the stimulus to breathe.
    3. It increases CO2, which decreases the stimulus to breathe.
    4. It decreases PaO2, which decreases the stimulus to breathe.
    5. It increases hydrogen ions, which decrease the stimulus to breathe.

    Author of lecture Breath Hold – Effect of Barometric Pressure on the Pulmonary System

     Thad Wilson, PhD

    Thad Wilson, PhD

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