what happens to breathing rate after you hold your breath

respiratory physiology is a complex topic, which comprises both voluntary and involuntary components equally well as underlying reflexes. Still, jiff property is a simple and intuitive activeness that tin be used to highlight differing aspects of respiratory physiology and can be adjusted for various educational and outreach settings, such as lectures, tutorials, and laboratories. Here, we outline a number of elementary jiff-concord demonstrations and interventions that target specific elements of respiratory command to lengthen and shorten jiff-hold duration. Nosotros also incorporate tools and data, which can facilitate skills such as protocol design and implementation, data collection, analysis, and interpretation in small-grouping settings.

Groundwork

Concepts associated with the control of breathing can finer exist taught with simple laboratory demonstrations. Breath holding can be used in a fun, interactive, and thought-provoking fashion to demonstrate many of the physiological concepts and principles underlying the control of breathing. The individual factors contributing to volitional breath-hold elapsing are relatively well known. Nonetheless, agreement how these mechanisms interact to determine the intermission point of a breath hold remains a challenging area of integrative physiology (three, 12, 25).

The break point of a maximal breath hold is determined by the complex interactions of multiple factors including 1) chemical (i.e., chemostimuli), 2) mechanical (i.e., lung stretch), 3) descending cortical "bulldoze," and 4) cerebral factors (e.yard., volition, practise, and expectation; meet Fig. ane) (2, 12). To meliorate empathize the limiting factors that determine breath-hold duration, it is important to understand the physiology involved in normal respiration.

Fig. 1.Schematic of factors affecting the control of breath-hold duration. Many factors contribute to changes in ventilation, some of which are voluntary (descending control from higher encephalon centers) and some of which are involuntary (i.due east., changes in O_ii and CO₂ or lung stretch). These factors act on the respiratory centers in the brain stem and can increase or decrease ventilation appropriately. Increases in lung stretch will subtract the drive to breathe, whereas chemoreceptor stimulation (decreased O₂ or increased CO_two) will increase the bulldoze to breathe. It is of import to annotation that this is a simplified schematic of respiratory control, and there are many other factors that tin can bear on ventilation.

The basic breathing rhythm and pattern is set through a number of interacting nuclei within the brain stem and pons (dorsal, pontine, and ventral respiratory groups) (for a review, see Ref. 22). Respiration is so coordinated through the diverse inputs impinging upon the respiratory controller. These inputs include descending drive from the cortex (7), chemoreceptors (thirteen, 21), and pulmonary stretch receptors (e.thousand., Hering-Breuer reflex (meet Ref. 16)), to proper name a few (come across Fig. 1).

Fundamental (brain stem) and peripheral (carotid bodies) respiratory chemoreceptors contribute to the maintenance of relatively stable blood gases through distinct but interacting chemoreflexes. The central chemoreceptors detect accumulating brain tissue Pco ₂/H⁺ concentration, increasing respiration as CO_two levels in brain tissue ascension above a threshold (i.e., central chemoreflex). The peripheral chemoreceptors detect increases in arterial Pco _ii/H⁺ concentration (reductions in arterial pH) and decreases in arterial Pa_O2 , increasing animate in response to either stimuli through an O_ii-CO₂ stimulus interaction (i.due east., peripheral chemoreflex) (5, 8, nine, 18, 20, 23).

Mechanical factors that contribute to breathing include tedious adapting pulmonary stretch receptors that fire in response to stretch or inflation of the lungs. When activated, these receptors send inhibitory signals to the respiratory centers in the encephalon stalk to decrease the drive to exhale and inhibit inspiratory drive (e.g., Hering-Breuer reflex). This allows for relaxation and recoil of lungs and chest wall to occur, initiating expiration, protecting against overstretch (14, sixteen). A number of descending drives originating from higher encephalon centers besides affect breathing. Starting time, in that location is a naturally higher bulldoze to breathe during wakefulness that is a event of cortical input into the respiratory controller. The removal of this drive to breathe during sleep or anesthesia reduces breathing and leaves its regulation solely reliant on the "chemical pilot" (i.e., chemoreflexes) (seven). In addition, will allows for voluntary alteration of the breathing blueprint in response to various stressors (e.yard, practise, Valsalva maneuver, and breath holding). With high extreme volition an private can maintain a closed airway even as descending drive starts to contract the respiratory muscles (east.g., involuntary diaphragmatic contractions). These responses can likewise exhibit a learning effect. For example, in breath holding, cognitive and psychomotor tasks, such equally mental arithmetic or squeezing a ball, can divert attention away from the desire to exhale that is experienced during breath holding and increase its time (1). Additionally, successive breath holding attempts produce improvements in breath-agree time, suggesting a practice effect and habituation to the sensation of dyspnea (1).

Maneuvers that affect any of these mechanisms outlined above may improve breath-hold duration. Trained divers or other breath-holding specialists may optimize all of these contributing factors to greatly prolong breath-hold fourth dimension. In this commodity, nosotros outline a set of elementary demonstrations, designed with the flexibility to be adopted as a complete laboratory or series of lecture or tutorial-based demonstrations. Importantly, nosotros aim to narrate factors contributing to breath-agree duration. In this series of activities, students volition perform a serial of maximal breath-belongings experiments to tease apart private factors contributing to breath-concur duration.

Learning Objectives

After the completion of this activity, students should be able to do the post-obit:

• 1. Explicate the individual physiological mechanisms (and their relative importance) involved in the command of breath property.

• two. Explain the integrative physiology that allows for humans to voluntarily perform extreme breath property.

• 3. Develop a hypothesis regarding integrative respiratory physiology and design an experiment to test information technology using man participants.

• 4. Safely collect and analyze data and draw appropriate conclusions.

• 5. Using the information, discuss the possible contributions of various physiological feedback loops that affect breath-hold duration.

• half dozen. Critique experimental pattern to improve future explorations.

Action Level

Based on the availability of supplies and the simplicity of the procedures outlined here, this action would be suitable for utilise in a variety of high school or undergraduate course settings. These demonstrations can be adapted to laboratory sessions, in-grade tutorials, or in-course lectures. These activities have been designed for courses addressing integrative physiology and may be suitable for utilize in senior high schoolhouse through to upper-year undergraduate university curricula.

Prerequisite Student Cognition

Before doing this activity, students should have a basic understanding of the following:

• one. Pulmonary structure and office (inspiratory muscles, pressure gradients, and lung volumes) likewise as factors involved in the chemoreceptor control of breathing.

• 2. Basic reflex physiology, including various types of receptors (east.g., chemoreceptors and stretch receptors) and effectors (eastward.g., respiratory muscles), and how physiological feedback mechanisms work to maintain homeostasis.

• iii. The effects of changes in blood gases (high or low CO₂ and O_ii) on ventilation.

In addition, students should know how to do the following:

• 1. Follow basic laboratory instructions and work efficiently in a team.

• 2. Record data in a data table.

• 3. If collecting a larger data set, students should be able to calculate basic descriptive statistics (e.g., mean and SD/SE) and plot graphs (e.g., bar graphs).

Time Required

A breath hold performed past untrained individuals can range from 30 s to 2 min. If students are performing these activities as part of a complete laboratory, our experience suggests that at to the lowest degree two h is required for the completion, recording of data, and discussion of experimental results. Still, adoption of individual demonstrations included hither for apply in a classroom or tutorial session may be easily accommodated. A laboratory study or manuscript could besides be assigned to develop literature review and data analysis skills.

METHODS

Equipment and Supplies

The post-obit basic equipment is required per grouping for this activity (suggested iv–6 students/grouping):

One chair

One stopwatch

Nose clips (participant tin can agree their ain nose if olfactory organ clips are unavailable)

One plastic bag (5–8 liters, easily obtained at a grocery store)

One record canvas or laboratory notebook (see Table i for an example)

Table 1. Data collection table for breath-agree activities

Role A: sit-in of the chemoreflex control of breathing

Activeness ane: rebreathing from a closed circuit

Clarification: animate in and out of a bag until the limit of tolerance is reached by participant or depth of breathing increases to the bespeak where the bag is collapsed during inspiration. O2 is decreasing and CO2 is increasing with every breath.

Observations:

Office B: establishing a baseline breath-concord elapsing

Activeness 2: terminate-inspiratory breath agree

Description: taking a total breath in and and so performing a breath concord for as long as possible. Lung volume is maximized, and the air in the lungs is room air.

Hypothesis:

Breath-hold fourth dimension:

Other observations:

Office C: chemoreflex interventions

Activeness 3: end-inspiratory jiff hold with prior hyperventilation

Description: hyperventilating for 30 south before an end-inspiratory breath hold. CO2 levels in the blood are decreased.

Hypothesis:

Jiff-hold time:

Other observations:

Activeness 4: stop-inspiratory breath agree with prior hyperoxia

Description: taking v breaths of 100% O2 before an stop-inspiratory breath hold. O2 levels in the blood are increased.

Hypothesis:

Jiff-hold time:

Other observations:

Activity 5: rebreathing followed by a jiff hold

Description: rebreathing from a closed excursion for ane min before completing an end-inspiratory breath concord. O2 is decreased, and CO2 is increased.

Hypothesis:

Jiff-hold time:

Other observations:

Office D: assessing the role of lung stretch

Activity 6: cease-expiratory breath hold

Description: taking a normal breath out and and so completing a breath hold for as long as possible. Lung volume is minimized, and the air in the lungs is room air.

Hypothesis:

Breath hold time:

Other observations:

Activity vii: repeated rebreathing after a jiff hold

Description: completing an end-inspiratory breath hold followed by 2 breaths from a closed circuit (handbag) and then attempting to consummate a second breath hold. This is repeated for three breath holds, if possible. Holding your breath increases COtwo and decreases O2; lung stretch receptors are activated while rebreathing.

Hypothesis:

Jiff-hold fourth dimension:

Other observations:

If available, the following optional equipment tin can be used to farther certificate physiological responses:

Supplemental 100% O₂

One center charge per unit monitor

One finger pulse oximeter [oxyhemoglobin saturation (Sp_O2 ), e.one thousand., Nonin Onyx; can also be used to make up one's mind centre rate]

A capnograph (cease-tidal CO_two sensor, e.g., Masimo EMMA)

Ethical Approval for Working With Human Participants

Adopters of this activity are responsible for obtaining informed consent and/or ethics clearance to piece of work with human participants at their home institution. In Canada, research activities must be cleared past a local Research Ideals Board and accommodate to the Tri-Council Policy Statement on enquiry ethics (TCPS2), which is consistent with the Declaration of Helsinki. For a summary of the American Physiological Club's "Guiding Principles for Research Involving Animals and Man Beings," please encounter www.the-aps.org/mm/Publications/Ethical-Policies/Beast-and-Human-Research. If this action is used equally a sit-in only, informed consent must still be obtained from participants. The sample traces included in this article (Figs. 2 and 3) were obtained in the laboratory of C. D. Steinback (Ethics Protocol ID 00048741) afterward written informed consent by participants.

Instructions

In groups of 4 to six, accept one student participant sit comfortably in a chair and ensure that they are comfortable with holding their jiff. Accept a second pupil lead the demonstration past giving instructions and observing the participant. A tertiary student can act as the timer, recording the duration of each jiff hold to the nearest second. Additional students can tape and/or use the boosted optional equipment listed in a higher place, if available. Students can rotate through responsibilities as well as acting as a participant to obtain a consummate data set. Students can work through each of the seven activities described below.

Part A: Demonstration of Chemoreflex Command of Breathing

Activity 1: rebreathing from a closed circuit.

Rebreathing from a closed system will crusade an increase in arterial CO_two and decrease in arterial O₂ equally a part of metabolic rate. In this observational action, students will visualize the progressive increment in the charge per unit and depth of breathing as the participant rebreathes from a bag. This is an important theoretical concept when discussing the chemical drive to breathe, which increases progressively throughout a jiff hold. Students should be able to use this sit-in to develop a hypothesis regarding the outcomes (with respect to breath-concur duration) in subsequent activities. Figure two shows representative physiological information from a typical rebreathe. In improver, students may be directed to primary literature discussing this topic in more detail (4, six, 17, 26).

Fig. 2.An example of the changes in expired O₂, CO₂, and ventilation during rebreathing. During normal breathing (A; shaded region), end-tidal O_two was 94 mmHg, stop-tidal CO_two was 39 mmHg, and infinitesimal ventilation was 11.5 l/min. The participant subsequently breathed in and out of a grocery produce purse (B) to gradually increase arterial CO₂ and decrease arterial O₂, triggering increases in ventilatory charge per unit and depth (demonstrated in the respiratory flow channel). In this example, ∼3.5 min of rebreathing decreased end-tidal O₂ to 45 mmHg, increased end-tidal CO₂ to 57 mHg, and increased infinitesimal ventilation to 64.half-dozen l/min (C; shaded region). This protocol demonstrates the powerful increase in the bulldoze to exhale during reduced O₂ or increased CO₂.

Directions.

I: Fill THE BAG.

With a nose clip in place, have the participant take a large breath of room air and then breathe into a previously empty plastic bag, closing the bag so that information technology stays total.

Two: REBREATHE.

Once the bag is total of expired air, take the participant resume normal breathing in and out of the closed bag. Have the fourth dimension recorder showtime the stopwatch when the participant begins to rebreathe. The participant should continue to rebreathe until their depth of breathing causes the bag to collapse or until the participant reaches their limit of tolerance. The observer should stop the test if the participant exhibits whatever signs or symptoms of discomfort or dizziness. In our experience, rebreathing should exist limited to no longer than ii min. Rebreathing for longer than 2 min may cause dizziness, with longer periods of rebreathing conveying an increased take chances of syncope. If you are able to measure CO_two using a capnograph, ensure to non exceed 50 mmHg of end-tidal CO_ii. The duration of rebreathing should exist recorded in the data collection sheet, along with whatsoever observations of changes in rate and depth of breathing. After the test, the participant should describe the awareness during rebreathing to the observers.

Part B: Establishing a Baseline Breath-Hold Elapsing (Control)

Activity 2: end-inspiratory breath agree.

This baseline breath-holding activity establishes the typical breath-agree duration as a command and familiarizes the participant to the discomfort of breath belongings and the type of protocol they will undergo. The investigators will need a stopwatch (and a finger pulse oximeter to track heart rate and Sp_O2 , if available).

Directions.

I: BASELINE VALUES.

Start by having the participant sitting comfortably, and take a timer and reader nearby. Record the resting center rate and O₂ saturation, and if you lot take a capnograph and oximeter, also record the resting CO_two and Sp_Otwo .

2: PERFORM A BREATH HOLD FROM A MAXIMAL Finish INSPIRATION.

Instruct the participant to accept a full breath in and concur as long as they can. The fourth dimension recorder should apply a stopwatch to record the breath-hold duration in a data table (see Tabular array 1 for an example). If you lot have an oximeter, have an observer call out and record the heart rate and O₂ saturation every xv s for recording. If y'all have a capnograph, you can measure out the CO₂ before starting and of the first expired breath later the pause signal, thus giving an indication of arterial CO₂ accumulation during the breath concur.

With all jiff holds, the participant should exist instructed non to "bear downwardly" (i.e., no Valsalva maneuver) during the breath hold, and the observer should watch for any signs of dizziness and note the time of onset of whatsoever involuntary diaphragmatic contractions should they occur.

Role C: Chemoreflex Interventions

Activity 3: stop-inspiratory breath concur with prior hyperventilation.

Hyperventilation (defined equally an increase in alveolar ventilation in excess of metabolic demands) reduces the Pco ₂ in the blood. Through the removal of CO₂, this activity is designed to identify the role of CO₂ in determining breath-hold fourth dimension. Based on the results of part A, activity 1, of this laboratory, students should be able to hypothesize what event prior hyperventilation would have on breath-hold duration. Students tin can use a capnograph to mensurate the cease-tidal CO_two earlier hyperventilating, afterwards hyperventilation, and at the stop of breath holding (i.e., break bespeak).

Directions.

I: HYPERVENTILATION.

Instruct the participant to breathe deep and fast for 30 s. Extreme and prolonged hyperventilation can cause dizziness and lightheadedness, so the observer should be monitoring the participants for whatsoever signs of dizziness. Monitor end-tidal CO_two if possible, and limit the hypocapnia to 25 Torr CO₂ to minimize the chances of dizziness and discomfort.

II: PERFORM A Jiff HOLD FROM A MAXIMAL Finish INSPIRATION.

After 30 s of hyperventilation, accept the participant perform a maximal inspiration (like to part B, activity 2) and then instruct them to perform a maximal jiff hold. If a pulse oximeter is bachelor, the participant should exist stopped from property their breath if Sp_Otwo reaches 85%. If a pulse oximeter is non available, the breath hold should be stopped at 3 min.

Activeness 4: end-inspiratory breath concur with prior hyperoxia.

In much the aforementioned way that hyperventilation removes CO₂ as a chemostimuli and increases the elapsing of a jiff hold, animate 100% O_ii (hyperoxia) increases the capacity for jiff-hold duration by prolonging the time before peripheral chemoreceptors are stimulated past hypoxia/hypercapnia during breath hold. If available, supplemental O₂ tin exist used to perform this demonstration. Based on the results of function A, activity ane, of this laboratory, students should be able to hypothesize what effect breathing 100% O_two would take on breath-hold duration. Students can apply a pulse oximeter if they wish to have a measure of starting Sp_O2 (in %) before and during breath holding.

Directions.

I: PREBREATHE 100% O₂.

Fill a bag with 100% O₂ and instruct the participant to breathe 100% O₂ from a bag for v normal breaths. Later the fifth breath, instruct the participant to commencement a breath concur afterwards a full inspiration, equally described above.

Two: PERFORM A Jiff-HOLD FROM A MAXIMAL Cease INSPIRATION.

Have the participant perform a maximal inspiration (similar to part B, activity 2).

Activity 5: breath hold later on rebreathing.

Rebreathing from a closed circuit (e.g., part A, activity i) does not let metabolically derived CO_ii to be cleared from the claret or for atmospheric O₂ to enter the blood. Thus, the accumulation of CO₂ stimulates key and peripheral chemoreceptors and the reduction in O₂ also stimulates peripheral chemoreceptors. In the contrary way that activities three and iv prolong breath-concord duration, performing a breath concur after 60 south of rebreathing volition demonstrate the function that chemoreceptor activation plays in reducing jiff-hold duration.

Directions.

I: REBREATHE.

Instruct the participant to rebreathe from a closed circuit in a similar fashion to office A, activity 1, for 60 south or until chemoreflex activation is apparent through increased in rate and depth of breathing.

Two: PERFORM A Jiff-Concord FROM A MAXIMAL END-INSPIRATION.

Later 60 southward of rebreathing, have the participant perform a maximal inspiration breath concord for equally long equally possible (similar to part B, action 2).

Part D: Assessing the Role of Lung Stretch

Activity 6: end-expiratory breath agree.

Maximal inspiration activates slow-adapting pulmonary stretch receptors, preventing overinflation past initiating expiration and/or reducing the bulldoze to breathe. Expiration reduces lung stretch and the activity of these receptors. This activity is designed to illustrate the role of lung stretch in regulating jiff-hold duration.

Directions.

I: PERFORM A BREATH HOLD FROM A NORMAL Finish EXPIRATION.

At the end of a normal expiration, have the participant perform a maximal breath concur. The recorder should time the breath agree and tape the duration of the breath hold on the data collection sail for comparing with other breath-agree durations.

Activeness seven: repeated rebreathing after jiff belongings.

After activities 1–half dozen of this laboratory, students should take an understanding of private mechanisms that may influence jiff-holding duration (e.thousand., levels of O₂ and CO_ii; lung stretch). Earlier this activeness, students should be encouraged to hypothesize which contributing factor, chemic drive or lung stretch inhibition, is more stiff with respect to influencing breath-agree elapsing. As classically described by Fowler (xi), past interspersing successive breath holds with periods of rebreathing, this activeness is designed to demonstrate the powerful influence of lung stretch during the human activity of breathing on breath-property duration, even in the confront of increases in blood gas chemostimuli.

Directions.

I: INITIAL Jiff HOLD Afterward MAXIMAL Cease INSPIRATION.

Instruct the participant to take a total breath in and hold it every bit long every bit they can.

II: REBREATHING.

Once the participant can no longer hold their breath, have them breathe out into a previously empty pocketbook, rebreathing for two breaths. They should then be encouraged to inspire the full volume of gas from the same bag and attempt to agree their breath again. Repeat this process of intermittent breath hold and rebreathing until the participant tin can no longer hold their breath or until they have held their jiff three times (for a representative tracing, see Fig. iii). If the participant is feeling dizzy or experiencing any sign of dizziness equally noted by the observer, this protocol should be stopped immediately.

Fig. 3.Sample repeated breath hold and rebreathing tracing. A: repeated rebreathe protocol. Later a menses normal animate, the participant holds their jiff. At the end of the first breath hold, the participant breathes in and out of a bag twice and holds their breath again. This procedure is repeated twice. B: changes in the force per unit area of terminate-tidal O_two (Pet _O2 ; solid bars) and terminate-tidal CO_ii (Pet _COii ; shaded confined). During normal breathing, end-tidal O₂ is 95 mmHg and cease-tidal CO₂ is 38 mmHg. The cease-tidal gases immediately afterward the first breath concur are xc and 47 mmHg of O₂ and CO₂, respectively; 78 and 50 mmHg of O₂ and CO₂, respectively, later on the second jiff hold; and 62 and 51 mmHg of O₂ and CO₂, respectively, after the third jiff hold. C: respiratory flow tracing (from spirometry) demonstrating the breathing pattern during the repeated rebreathing protocol. This protocol demonstrates the importance of lung stretch in depressing the drive to exhale, axiomatic past the power to hold ane's breath despite decreasing O₂ and increasing CO₂ levels during the breath-holds.

Troubleshooting

There is limited equipment required for this simple laboratory sit-in. Brusk of making certain that the disposable bags accept no leaks, and that the participant makes a complete seal on the bag, very fiddling technical difficulty is expected. Brand sure the stopwatch, pulse oximeter, and capnograph have new batteries. In some cases, participants may require a number of practise trials to follow directions accurately. Information technology is oftentimes helpful to give the participants five min between trials to recover earlier beginning another breath hold.

Prophylactic Considerations

Students with any of the following atmospheric condition/states should not serve as the participants: known cardiovascular disease (eastward.g., diagnosed hypertension or cardiac arrhythmias), known respiratory disease (e.g., asthma), or if they are a regular smoker.

Jiff holding for prolonged time can cause dizziness, lightheadedness, and possible fainting. If at whatever fourth dimension during any jiff hold the participant feels dizzy, they should begin breathing again immediately. One person should be observing the participant during every jiff hold and watching for signs of dizziness. The signs of dizziness (and fainting) include face flushing, sweating, shaking, or loss of rest. If any of these signs are observed, the participant should exist instructed to breathe again. The participant should perform all breath holds in the seated position, and the observer should also be standing close enough to support them should they need information technology. Brand sure the participant is always observed, and communicate with the participant during and after each exercise.

Of particular note, activities that include rebreathing or hyperventilation are more likely to result in lightheadedness or dizziness, and extra precautions should exist taken to eliminate the risks of fainting. The hyperventilation elapsing should non exceed lx s before the breath-concord test in part C, activity 3. In addition, if you are able to measure out CO₂ (e.one thousand., an EMMA capnograph or Advertizement Instruments gas analyzer), limit the level of hypocapnia during the hyperventilation period to a minimum of 25 Torr end-tidal Pco ₂. Hyperventilation-induced hypocapnia causes cerebral vasoconstriction, causing some individuals to feel transient dizziness. Interestingly, the fastest manner to increment CO_two and ameliorate these symptoms is to perform a breath hold to retain metabolically derived CO_ii.

RESULTS AND Give-and-take

Expected Results

Students should collect their own data (recorded in Tabular array 1). After a review of bones underlying physiology and factors that bear on breath-agree duration (eastward.g., Fig. 1), students should exist able to hypothesize how breath-hold elapsing volition exist affected during each activity. Expected results from each activity are shown in Figs. 2–4. Specifically, expected breath-agree durations for activities two–6 are shown in Fig. 4 (hateful data nerveless from twenty participants). Expected results are briefly outlined below.

Fig. 4.Data summary of sample breath-agree duration data. Representative data for mean breath-hold times (north = 20; error confined represent SE) were collected in the laboratory of C. D. Steinback. Using the breath hold afterward the inspiration time (96 s) every bit the command, hyperventilation increased breath-hold duration to 138 southward past lowering the arterial Pco ₂ before the start of the jiff hold. Hyperoxia increased breath-hold fourth dimension to 157 s by increasing the arterial Po ₂ before the start of the breath hold. Conversely, rebreathing for 1 min before the start of a breath hold decreased the time from 96 to 42 s by increasing the Pco _ii and decreasing the Po _two before the start of the breath hold. Each of these demonstrates the function of chemoreceptor pathways in the command of breathing. The function of the lung stretch receptors is shown past comparison the breath concord after inspiration (control; 96 s) to the breath hold after expiration (37 s).

Activity 1: rebreathing from a closed circuit (2 min).

Given the increase in metabolically derived CO₂ and a reduction in arterial O₂, experimenters will detect an increase in the rate and depth of animate. Meet Fig. two for a representative tracing. This sit-in illustrates the chemoreflex control of breathing.

Activeness 2: end-inspiratory jiff hold.

This is the "control" demonstration that other breath-hold durations can exist compared with. This activeness will event in an intermediate breath-hold duration.

Action 3: end-inspiratory breath hold with prior hyperventilation.

Given the reduction in arterial CO₂ that results from prior hyperventilation, breath-hold duration should be longer than the command breath hold, as it will take longer for the threshold for chemoreceptor activation to exist reached.

Activity 4: finish-inspiratory breath hold with prior hyperoxia.

Similar to activeness 3 above, a breath agree afterwards prior hyperoxia will result in a longer breath-hold duration than the control.

Activity 5: breath hold subsequently rebreathing.

Due to the aggregating of chemostimuli (i.e., high CO_two and low O_two), performing a breath hold after 60 s of rebreathing will result in a shorter duration than the command.

Activity 6: end-expiratory breath concord.

Due to both the lack of inhibitory lung stretch and a smaller lung volume reservoir to mix atmospheric air with arterial blood, this breath-hold elapsing will likely be the shortest compared with the control.

Activity seven: repeated rebreathing afterwards jiff holding.

Despite the fact that chemostimuli are not being relieved subsequently the first breath concur, the act of breathing itself relieves the sensation of dyspnea, allowing the participant to perform another jiff hold. Each successive jiff hold will become shorter in elapsing as chemostimuli proceed to accumulate.

Discussion/Misconceptions

In that location are a number of misconceptions that can be addressed with these demonstrations. Starting time, it is common for people to assume that breath-concord duration is dictated primarily past lowered O_two levels. That is to say, that O_ii is reduced during a breath concur, and the chemoreceptor drive to breath is responsible for the awareness of dyspnea and contributes to break point. If you were to notice Sp_O2 using a pulse oximeter in part B, activity 2, you lot would find that although Po ₂ is probable reduced, Sp_O2 is maintained at high levels, fifty-fifty afterward a few minutes of breath belongings. Indeed, to actuate the peripheral chemoreceptors in the absence of any changes in CO₂, one would need to reduce arterial O₂ to ∼60 mmHg. If you take a capnograph available, measuring the CO₂ of the first jiff afterwards break betoken after the breath concord would have demonstrated higher levels of CO₂ (hypercapnia). These two observations illustrate that CO₂ accumulation acting on key and peripheral chemoreceptors makes larger contributions to the urge to breathe compared with the relatively modest reduction in O₂ during brusque-duration breath hold. The rebreathing test (part A, activity ane), which could too exist performed in a background of 100% O_ii, illustrates the powerful urge to exhale driven by increasing CO₂ levels. Similarly, the breath-hold duration after prior hyperventilation where hypocapnia is induced, also illustrates the relationship between CO_ii and breath-hold duration, admitting in the opposite direction.

Second, fifty-fifty if someone is enlightened of the role of chemoreceptors in respiratory control, these explanations may as well exist partly misleading with respect to jiff-agree elapsing, every bit they are an incomplete caption of the factors that affect breath-concur elapsing and break point. Every bit the activity in function D, activity 7, illustrates, increases in chemostimuli may not be equally important as the absence of the physical act of breathing (i.e., lung stretch) in driving the urge to exhale. In this activity, despite the fact that blood gases are not corrected by the act of breathing, the participant is yet able to jiff hold for more time after a few respiratory cycles. This confirms that there are other factors at play during the respiratory cycle (east.thou., transient lung stretch), independent of blood gas levels.

As such, students should be encouraged to identify multiple mechanisms at play during jiff holding at varied lung volumes. In particular, it is important to note that inspiration (i.e., larger lung book) may activate lung stretch receptors but also increases the corporeality of O_ii bachelor in the lungs, which can diffuse into the blood and increases the "sink" into which CO₂ can diffuse as it leaves the lungs. Conversely, expiration decreases the volume of O_two in the lungs and reduces the sink into which CO₂ can enter (27). In addition, students may be directed to primary literature discussing this topic in more particular (x).

Evaluation of Student Work

Students should collect data for each activity listed above on multiple participants (if time permits) or puddle the data from each individual group. Students can then plot the mean data of the breath-concur duration from each activity and present the data in bar graphs (similar to Fig. four) with SDs using any data assay and graphing software program (east.one thousand., Microsoft Excel). In this mode, data can exist compared betwixt trials, and the variability present in any population of participants tin can exist illustrated. If the course includes statistical analysis, take students perform either paired t-tests (when comparing any ane jiff-hold duration with the control action) or use repeated-measures ANOVAs to compare the data beyond all activities, using an appropriate mail service hoc test for pair-wise comparisons.

Critical Thinking Questions

Question 1.

Explicate how arterial blood gas limerick changes when performing a jiff concur at rest and the effects on drive to breathe of both CO₂ and O₂. Include references where necessary.

ANSWER.

When a jiff hold is performed at rest, arterial O₂ levels begin to drib and arterial CO₂ begins to ascent (pH levels drop) as a function of metabolism (fifteen, 19). The rise in CO₂ and drib in pH stimulate both peripheral and key chemoreceptors, and the decrease in O₂ (if reduced significantly) stimulates the peripheral chemoreceptors. The chemoreceptors then relay this information to the medullary respiratory eye of the brain stalk, eliciting an increase in the drive to exhale. During voluntary breath holding, you may find involuntary respiratory movements (diaphragmatic contractions) when this occurs.

Question 2.

Describe a feedback loop of the chemical control of breath holding.

Respond.

Draw-in sequence: 1) homeostasis, 2) breath agree, 3) consecutive increase in arterial CO_ii, decrease in pH, and decreases in arterial O₂ concentrations, 4) increment in chemoreceptor activity, v) convergence of afferent sensory data at the medullary respiratory center, half-dozen) increase drive to exhale, 7) suspension point or end of breath concord, and 8) back to homeostasis. Run across Fig. one for components to include.

Question iii.

Provide an explanation every bit to why a breath concord after a full inspiration produces longer breath-hold duration than a breath concord after expiration. Use results nerveless from the activities yous performed and relevant references to back up your answer.

Answer.

During a maximal inspiratory breath hold, you activate the pulmonary stretch receptors, which send signals to the brain to decrease the drive to breathe (10, 24). If you hold your jiff after an expiration, you volition have decreased the stimulus to the stretch receptors, making the drive to breathe more prominent sooner. Additionally, the corporeality of bachelor O₂ is inverse with changing lung volumes. Larger lung volumes let for a greater volume of gas to aid dilute the increase in metabolically derived CO_ii levels.

Question 4.

Place and explain one technique not demonstrated in the aforementioned activities that may subtract breath-property time. Justify your answer past proposing the machinery involved and use the results collected from this laboratory to back up your answer.

ANSWER.

Jiff-property fourth dimension can be increased/decreased by manipulating 1 of the factors involved in the control of breath-holding (shown in Fig. i). Any technique that 1) decreases O₂, 2) increases CO₂, or three) decreases lung book/lung stretch will suffice. For case, if a volunteer were to exercise for ane min before holding their breath (maximal inspiration), they would have increased their metabolism thereby increasing the rate at which O₂ is consumed and CO_ii is produced. This would decrease jiff-hold fourth dimension by activating both primal and peripheral chemoreceptors earlier.

Inquiry Applications

These simple breath-hold activities can exist a valuable tool for undergraduate students to utilise their knowledge of physiology in an integrative setting. To increase the inquiry level, the instructor can let students to decide what activities are to be included earlier the breath hold (e.g., full inspiration, expiration, and exercise), what level of body position or activity (east.g., lying, sitting, standing, eyes open up or airtight, or walking on a treadmill), what students direct their attention to during the breath hold (eastward.grand., environmental distraction), and what additional equipment and measurements to make (eastward.g., Sp_O2 or terminate-tidal CO₂).

Students can use the experiments from this laboratory exercise to further explore and understand extreme sports, environments, and pathophysiological conditions that compromise respiratory physiology. Examples of topics that students can study include free diving, jiff-hold records, the mammalian diving reflex, synchronized swimming, underwater hockey, loftier-altitude physiology, sleep apnea, and chronic obstructive pulmonary affliction. To do this, they must search the published scientific literature using PubMed (www.pubmed.com) and read, summarize, and reference published articles on their chosen topic. Within these reports, students are required to compare the physiology of their selected topic to healthy normal individuals animate room air at i temper at sea level.

Wider Educational Applications

This action can be adapted to laboratory, classroom, or tutorial settings, both in pocket-size and large groups, to lower-level to higher-level students of physiology. In addition, these activities tin can be used in public outreach activities (eastward.g., high schoolhouse and public talks) to engage nonspecialists in the importance and relevance of agreement the physiology of everyday life.

DISCLOSURES

No conflicts of interest, financial or otherwise, are alleged by the author(s).

AUTHOR CONTRIBUTIONS

Author contributions: R.J.S., T.A.D., J.E.F., C.D.B., and C.D.S. conception and blueprint of inquiry; R.J.S., T.A.D., J.E.F., C.D.B., and C.D.S. performed experiments; R.J.S., T.A.D., J.E.F., C.D.B., and C.D.S. analyzed information; R.J.South., T.A.D., C.D.B., and C.D.S. interpreted results of experiments; R.J.S. and C.D.South. prepared figures; R.J.S., T.A.D., J.Eastward.F., C.D.B., and C.D.S. drafted manuscript; R.J.Southward., T.A.D., J.Eastward.F., C.D.B., and C.D.S. edited and revised manuscript; R.J.S., T.A.D., J.Eastward.F., C.D.B., and C.D.Southward. approved final version of manuscript.

ACKNOWLEDGMENTS

The authors thank Dr. Charlotte Usselman, Christina MacKay, Jeff Vela, Sydney Schmidt, Maria Abrosimova, and Jamie Pfoh for the aid in collecting the information set presented as office of this article.

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Source: https://journals.physiology.org/doi/full/10.1152/advan.00030.2015

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