Chemical Factors: pCO₂, pO₂ and pH – Influence on Respiration (Nursing)

00:01 So as I said before, our respiration rates are going to be affected by multiple factors including chemical factors.

00:08 The influence of higher brain centers, pulmonary irritant reflexes and also inflation reflexes.

00:16 So, let's take a closer look at some of these things.

00:20 So the chemical factors are going to be the most important of all the factors that are going to affect our depth and rate of inspiration.

00:29 The partial pressures of carbon dioxide oxygen, as well as our H+ concentrations are pH are going to be the most important of these chemical factors.

00:41 Levels of these chemicals are sensed by central chemoreceptors found in the brain stem as well as peripheral chemoreceptors found in the aortic arch and the carotid arteries.

00:55 So taking a closer look at these peripheral chemoreceptors.

00:59 We find that sensory nerve fibers and cranial nerve lX or the pharyngeal branch of the glossopharyngeal cranial nerve are going to send impulses to the carotid bodies found on the carotid arteries.

01:15 From their central nerve fibers in the cranial nerve X are the vagus nerve are going to send signals to the aortic bodies found in the aortic arch of the heart.

01:28 So other influences are going to be things like the partial pressure of carbon dioxide.

01:35 So this is the most potent and closely controlled.

01:39 If our partial pressure of carbon dioxide levels rise or go up, which is known as hypercapnia.

01:47 The carbon dioxide will accumulate in our brain and join with water to become carbonic acid, and the carbonic acid will then dissociate leasing the H+ and causing a drop in our pH or increased acidity.

02:05 Increase H+ stimulates the central chemoreceptors of the brain stem which will then synapse with the respiratory regulatory centers that we talked about.

02:17 The respiratory centers will increase depth and rate of breathing which will act to lower our partial pressure of carbon dioxide by getting us to exhale more carbon dioxide and this will cause our pH levels to rise back to normal levels.

02:37 If blood partial pressure of carbon dioxide levels decreases.

02:41 Our respiration will become slow and shallow.

02:45 Also apnea or when you stop breathing or breathing cessation may occur when our carbon dioxide levels are extremely low.

02:57 Sometimes swimmers take advantage of this phenomena and voluntarily hyperventilate in order to enable them to hold their breath longer this works because as they hyperventilate it causes their carbon dioxide levels to drop because they're exhaling a lot more carbon dioxide than they're inhaling oxygen.

03:19 This causes a delay in respiration as the carbon dioxide levels need to build back up.

03:26 And so while they're holding their breath, they're able to hold it longer because their body wants to hold in more carbon dioxide.

03:36 However, by doing this they are counteracting the the need their body has four oxygen levels.

03:43 So this is still a dangerous practice to do.

03:48 So the changes in our partial pressure of carbon dioxide can regulate ventilation by a negative feedback mechanism.

03:57 So let's just take a look at how this negative feedback works.

04:02 First, let's start with a stimulus if that stimulus is the partial pressure of carbon dioxide decreasing the pH in the brains extracellular fluid, then the central chemoreceptors in the brain are going to respond to that lower pH.

04:21 As well are peripheral chemoreceptors found in our carotid and aortic bodies can also be stimulated when there is a decrease in the pH.

04:33 Both of these stimuli are going to send impulses to our medullary respiratory centers.

04:41 The medullary respiratory centers then send impulses to the respiratory muscles in our thoracic cavity and this is going to cause ventilation or more carbon dioxide to be exhaled.

04:55 So we already had too much acid or too much H+.

05:00 And so we need to get rid of carbon dioxide so we can shift that reaction away from H+.

05:09 And once this happens, the arterial partial pressure of carbon dioxide and the pH will return back to normal.

05:20 So hyperventilation is when we increase the depth and the rate of breathing and it exceeds our bodies need to remove carbon dioxide.

05:30 So we're breathing out so much that we're actually losing more carbon dioxide than our body should.

05:39 Usually hyperventilation can be caused by anxiety attacks.

05:43 Although there are other reasons why you might hyperventilate.

05:47 This hyperventilation leads to a decrease in our bloods carbon dioxide levels known as hypocapnia.

05:55 Hypocapnia can lead to cerebral vasoconstriction, which can lead to ischemia which can result in dizziness and sometimes fainting.

06:06 Usually you are able to know when your blood CO2 levels are starting to drop because the early symptoms include things like the tingling and involuntary muscle spasms in your hands and in your face.

06:20 The way we treat hyperventilation is by getting people to breathe into a bag.

06:26 So if a person is having an anxiety or panic attack and they're hyperventilating and removing too much carbon dioxide, we get them to breathe into a bag and by doing this, we're going to have them inhaling some of that carbon dioxide back into their body thus increasing our carbon dioxide levels and getting us back to normal CO2 levels.

06:54 So not only does CO2 or the partial pressure of CO2 have an effect but also the partial pressure of oxygen can have an effect.

07:04 Peripheral chemoreceptors and our aortic and carotid bodies can sense arterial oxygen levels.

07:12 If the partial pressure of oxygen begins to decline there's only a slight effect on ventilation because we have huge reservoirs of oxygen available in our hemoglobin.

07:26 It's going to require pretty substantial drop in arterial partial pressure of oxygen in order to increase ventilation.

07:35 So you would have to get really low oxygen levels in order for our body to respond by trying to breathe more.

07:44 When excited, the chemoreceptors will then cause the respiratory centers and our medullary and pontine areas to increase ventilation, but this again only happens when we drop really low.

08:01 So pH is another factor that influences our rate and depth of breathing and pH can modify respiratory rate and rhythm even if the carbon dioxide and the oxygen levels are normal.

08:15 This is going to be mediated by those peripheral chemoreceptors in the carotid and aortic bodies.

08:22 And a decrease in the pH can either reflect too much carbon dioxide in the body or carbon dioxide retention, but it can also reflect things an accumulation of lactic acid after a particularly anaerobic exercise activity like sprinting or lifting weights as well as excess ketone bodies, which are lot of times are acidic this can happen when people go on diets like a keto diet, where they're taking in more protein, beans and fats and less carbohydrates and so their body switches to ketosis.

08:59 The respiratory center can control attempts to raise the ph by increasing the respiratory rate and depth.

09:07 So if the pH drops too low, then the body can control by a causing you to exhale or breathe in and out a lot more often.

09:21 So to summarize because we've gone through a lot of these different factors.

09:27 Rising carbon dioxide levels are a powerful respiratory stimulant when the carbon dioxide levels go up or down our body is going to respond.

09:40 Normally our blood oxygen levels are going to affect breathing but only indirectly by influencing peripheral chemoreceptors and sensitivity to changes in the partial pressure of carbon dioxide.

09:56 If our arterial oxygen levels fall below a threshold of about 60.

10:03 That is when the partial pressure of oxygen will now become a major stimulus for respiration by way of those peripheral chemoreceptors.

10:14 When we have changes in our arterial pH, this can also affect our respiratory rate by resulting from carbon dioxide retention or metabolic factors, like something we ate or some type of disease and by this we're going to try to adjust our bloods pH by adjusting how much carbon dioxide is coming in and out of the body.

10:38 This too is also going to be influence by those peripheral chemoreceptors.