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Airway, Lung, and Respiratory Muscle Function During Exercise

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Abstract

The sections in this article are:

1 Regulation of the Upper Airway During Exercise
1.1 Anatomy and Physiology of the Upper Airway
1.2 Contractile Properties and Endurance of Upper Airway Muscles
1.3 Changes in Upper Airway Flow Resistance During Exercise
1.4 Upper Airway Muscle Activities during Exercise
1.5 Oronasal Distribution of Respiratory Airflow
2 Effects of Exercise on Passive Respiratory Mechanics
2.1 Elastic Properties
2.2 Total Lung Capacity
2.3 Expiratory Flow Rates, Vital Capacity, and Residual Volume
3 Breathing Pattern During Exercise
3.1 Mechanical Breathing Pattern
3.2 Methods of Assessment of Respiratory Muscle Contraction
3.3 Pattern of Respiratory Muscle Contraction
3.4 Influence of Sensory Feedback on Breathing Pattern
3.5 Influence of Respiratory Mechanics on Breathing Pattern
3.6 Influence of Duration of Exercise on Breathing Pattern
3.7 Influence of Mode of Exercise on Breathing Pattern
3.8 Breathing Pattern during Recovery from Exercise
3.9 Physiological Implications of Exercise Breathing Pattern
4 Importance of Respiratory Load in Regulation of Exercise Hyperpnea
4.1 Helium‐Oxygen Unloading
4.2 Unloading with Pressure Assist
4.3 Conclusion
5 Locomotor‐Respiration Interdependence
5.1 Entrainment—the Most Obvious Locomotor‐Respiratory Interaction
5.2 How Does Entrainment Effect Ventilation?
5.3 Is there Stronger Evidence to Support a Significant Biomechanical Effect of Locomotion on Respiration in Dogs?
5.4 Are Biomechanical Effects Important in Entrainment in Humans?
5.5 Locomotory: Respiratory Interactions, Independent of Entrainment
5.6 Conclusion
6 Respiratory Muscle Perfusion and Energetics
6.1 Oxygen Cost of Hyperpnea
6.2 Respiratory Muscle Blood Flow
7 Exercise‐Induced Respiratory Muscle Fatigue
7.1 Respiratory System Design
8 Assessment of Diaphragm Fatigue in Animal Models
8.1 Glycogen Depletion
8.2 Fiber Type Recruitment
9 Definition of Fatigue
9.1 Task Failure vs. Objective Assessment of Fatigue
9.2 Contractile Changes with Fatigue
10 Predicting Respiratory Muscle Fatigue During Exercise
10.1 Application of Resting Tests to Respiratory Muscle Function During Exercise
11 Assessment of Respiratory Muscle Fatigue in Humans
11.1 Volitional Tests
11.2 Volitional Tests Applied to Exercise
11.3 Nonvolitional Tests
11.4 Bilateral Phrenic Nerve Stimulation (BPNS)
12 Characteristics of Diaphragm Fatigue
12.1 High‐ vs. Low‐Frequency Fatigue
12.2 Sites and Mechanisms of Respiratory Muscle Fatigue
12.3 Central Fatigue in Humans
12.4 Neurotransmission Fatigue
13 Bilateral Phrenic Nerve Stimulation Applied to Exercise
13.1 Short‐Term Exercise
13.2 Endurance Exercise
13.3 Factors Contributing to the Decline in Twitch Pdi Following Exercise
13.4 Role of Diaphragmatic Force Output in Fatigue
14 Consequences of Exercise‐Induced Diaphragmatic Fatigue
14.1 Fatigue vs. Task Failure
14.2 Does Training of Respiratory Muscles Affect Exercise Performance?
14.3 Altered Respiratory Muscle Recruitment with Fatigue
15 Physical Training Effects on Respiratory Muscles
15.1 Respiratory Muscle Morphology and Contractile Properties
15.2 Whole‐Body Training: Effects on Rodent Respiratory Muscles
15.3 Whole‐Body Exercise: Effects on Human Respiratory Muscle Performance
15.4 Specific Respiratory Muscle Training
16 Respiratory Sensation During Exertion
16.1 Mechanisms of Respiratory Sensations during Exercise
16.2 Methods of Assessing Respiratory Sensations
16.3 Respiratory Movements
16.4 An Urge to Breathe
16.5 A Sense of Respiratory Effort
16.6 Respiratory Sensation as a Respiratory Controller during Exercise
16.7 Respiratory Sensation as a Limiting Factor during Exercise
16.8 Conclusions
17 Summary—Pulmonary System Limitations and Their Effects on Exercise Performance
17.1 Absence of Pulmonary System Limitations in the Normally Fit
18 Contrasting Adaptabilities: Demand vs. Capacity
18.1 Alveolar Capillary Diffusion Surface of the Lung
18.2 Ventilatory Limitations/Constraints
18.3 Inadequate Alveolar Ventilation and V.O2max Limitations
18.4 Endurance Exercise Performance
19 Special Circumstances Favoring Pulmonary Limitations to Exercise Performance in Health
19.1 Hypoxia of High Altitudes
19.2 Aging Effects on Pulmonary Limitations
Figure 1. Figure 1.

a, Sagittal section of the human head and neck, showing the upper airways and some of the associated musculature. NC, nasal constrictor muscles; DN, dilator naris muscle; HP, hard palate; GG, genioglossus muscle; GH, geniohyoid muscle; H, hyoid bone; SH, sternohyoid muscle; SP, soft palate; EG, epiglottis. b, Section through the posterior pharynx showing some of the musculature acting on the soft palate and pharyngeal wall. TVP, tensor veli palatini muscle; LVP, levator veli palatini muscle; SC, superior pharyngeal constrictor muscles; SP, soft palate, c, Superior view of the larynx, showing the major laryngeal adductor and abductor muscles. TA, thyroarytenoid muscle; PCA, posterior cricoarytenoid muscle; TC, AC, and CC, thyroid, arytenoid and cricoid cartilages, respectively. See test for explanation of anatomy and muscular actions.

Parts b and c adapted from Bartlett and Warwick and Williams , respectively
Figure 2. Figure 2.

Top, Nasal airway pressure–flow relationships obtained during voluntary hyperpnea in a healthy subject. The tests were performed before (control) and after (exercise) exhausting cycle ergometer exercise. Note that the curves are nonlinear, showing the marked flow dependence of upper airway resistance. Also note that prior exercise shifts the pressure–flow curve to the right, indicating that exercise hyperpnea decreases resistance. Bottom, Log transformation of the data shown in the top panel, demonstrating the technique for determining the flow rate at the transition (tr) from laminar to turbulent flow. See text for detailed explanation of figure.

From Olson et al.
Figure 3. Figure 3.

Influence of exercise intensity on the integrated EMG activity of the nasal dilator muscles (AN EMG), mean inspiratory flow (VT/T1) and inspired pulmonary ventilation (V1). Values for both nasal and total VT/T1 and V1 are given, as indicated on the insets. Note that the plateau in both of these variables at exercise intensities exceeding 60% of the peak power coincides with the plateau in the AN EMG. * Significantly different than resting control value (P < 0.05); + significantly different than nasal V1 (P < 0.05).

From R. F. Fregosi and R. L. Lansing, unpublished observations
Figure 4. Figure 4.

Recordings showing changes in flow through the nose and mouth, and integrated EMG activity of the nasal dilator muscles (“alae nasi”) when a representative subject voluntarily changes the breathing route from nasal to oral during cycling exercise. Note that during nose breathing EMG activity is much higher, and the onset of the EMG burst precedes the onset of flow (vertical dashed lines). Also note that when the flow route changes from nasal to oral in midexpiration (A), the EMG amplitude is diminished but EMG onset no longer precedes the onset of flow. In contrast, when flow route changes at the end of expiration (B), EMG amplitude is diminished but onset time does not change. Thus, when the upper airway was configured for oral flow well before the next inspiration (A), the nervous system no longer had to activate the alae nasi musculature early and intensely in order to protect the nasal airway from collapse. In contrast, when the switch from nasal to oral flow was made at the very end of expiration (B), the system was still configured for a nasal breath, and the EMG burst preceded the onset of flow. However, the system soon sensed the absence of nasal flow and made appropriate adjustments during the breath, resulting in a reduced EMG amplitude. Taken together, these data suggest that (1) the configuration of the entire upper airway, presumably determined by a feedforward mechanism, is more important than local reflex mechanisms in determining the onset of upper airway muscle activities, and (2) local reflex mechanisms can alter burst amplitude during a breath (see text)

From Wheatley, Amis, and Engel
Figure 5. Figure 5.

Comparison of breathing pattern in normal humans during maximal incremental exercise and endurance exercise. The initial increase in minute ventilation is due to increases in both tidal volume and respiratory frequency. However, tidal volume stops increasing at high levels of ventilation and further increases in ventilation are due to increasing respiratory frequency alone. Tidal volume is less and respiratory frequency greater during endurance exercise at high levels of ventilation

Data obtained from Syabbalo et al. .] See text for details
Figure 6. Figure 6.

Young adult average tidal flow–volume and pressure–volume loops and minute ventilation (E) for eight athletes during rest and progressive exercise, which averaged 42%, 61%, 83%, 95%, and 100% of maximal oxygen uptake. Tidal flow–volume curves are shown plotted within preexercise (solid line) and postexercise (dashed line) maximum flow–volume curves. Tidal pressure–volume curves are shown also with constraints for effective pressure generation on expiration (Pmaxe) and the capacity for pressure generation on inspiration (Pcapi). Widths of Pmaxe and Pcapi at a given lung volume indicate 95% confidence intervals. The loops at a minute ventilation of 117 liter · min−1 represent the typical response to maximum short‐term exercise in an untrained young adult subject (maximum o2 40–50 ml · kg−1 · min−1). The E of 169 liters/min was the average response to maximum exercise in the trained subject (maximum o2 = 70–80 ml · kg−1 · min−1)

From Johnson, Saupe and Dempsey
Figure 7. Figure 7.

Time course of flow; lung volume; respiratory muscle pressure (Pmus); dynamic capacity of inspiratory muscles to generate pressure (Pcapi); and ratio of inspiratory Pmus to Pcapi before exercise, during light exercise, and during moderately heavy exercise. Data are the average from three subjects during cycle exercise. PIIA is postinspiratory muscle activity. Numbers in the bottom row are mean and peak Pmusl/PcapI. See text for details.

From B. Krishnan, T. Zintel, and C. G. Gallagher, unpublished data
Figure 8. Figure 8.

Equine costal diaphragmatic EMG (raw and moving time‐averaged); gastric, esophageal, and transdiaphragmatic pressure (PG, PE, and Pdi); and accelerometer tracing indicating left forelimb impact (arrows) during walking and during galloping (11 ms). Note that the foot plant activity does not occur during a consistent phase of the respiratory cycle when the horse is walking, whereas phase‐linking is apparent during the gallop.

From Ainsworth et al. (
Figure 9. Figure 9.

Canine breathing patterns are highly variable, as shown in this figure for one dog trotting on the treadmill while unencumbered by a breathing mask. The two types of patterns—high‐frequency type A (left panel), a pure high frequency oscillation in the esophageal pressure; and mixed‐frequency type B (right panel), a slower inherent breathing pattern with superimposed high‐frequency oscillations in the esophageal pressure—are apparent. Esophageal pressure (Pe), crural (CR), costal (CS), transverse abdominal (TA) EMG, and foot plant left hindlimb (FP) are shown. In type A and type B, decrements in esophageal pressure (and airflow) are always associated with electrical activation of the costal and crural diaphragm. In type B, oscillations in the esophageal pressure during expiration occur at intervals related to foot plant and hence TA activation.

From Ainsworth et al.
Figure 10. Figure 10.

Inspiratory flow (VI); electrical activity of the parasternal (PS, rib cage inspiratory), crural (CR), and costal (CS) diaphragm, and transverse abdominal (TA) muscles and sonomicrometry tracing of the costal diaphragm (SONO CS) in one dog at rest and during trotting. Note that either at rest or during exercise, phasic electrical activity of both inspiratory and expiratory muscles is evident and that phasic shortening of the costal diaphragm (downward displacement of SONO tracing) occurs only during electrical activation. This breathing pattern is representative of high‐frequency breathing with fb = 115 breaths · min−1

From Ainsworth et al.
Figure 11. Figure 11.

Inspiratory flow (VI) or tidal volume and gastric pressure (PG) traces from a human (left panel) and a dog (right panel). In the dog, note that at the onset of exercise, mean gastric pressure increases due to tonic increases in abdominal muscle activity.

From Ainsworth et al. .] In the human, gastric pressure increases during the transition from the walk to the jog. (From Henke et al. .] (Please note, in the dog an increased gastric pressure moves upward in the figure; whereas in the human the PG scales are reversed and increased PG moves down
Figure 12. Figure 12.

Oxygen cost of exercise hyperpnea. Right panel shows the effects of increasing ventilation on the per unit oxygen cost of breathing (mean values ±95% confidence interval). Left panel shows the effects of increasing ventilation on the total oxygen cost of breathing expressed as a percentage of the total body O2 (O2TOT) during moderate, heavy, and maximum progressive exercise. [Individual subject values (N = 9).] Values for the O2 cost of breathing were obtained in resting subjects from the measured increases in O2 that accompanied steady‐state mimicking of the pressure–volume loop, ∫ Pdi, ∫ Pg, fb, VT, and EELV obtained during various exercise intensities.

From Aaron et al.
Figure 13. Figure 13.

Example of bilateral phrenic nerve stimulation (BPNS) performed before and after exercise at 1 and 10 Hz. Both esophageal (Pe) and gastric (Pg) pressure fell following exercise, causing the reduction in the Pdi waveform amplitude. At 1 Hz stimulation, a prolongation in relaxation rate of the Pdi waveform was also observed. No changes were observed in the amplitude of the M‐waves from either the left or right hemidiaphragm.

From Johnson et al.
Figure 14. Figure 14.

Comparison of diaphragmatic fatigue produced by exercise vs. that produced by mimicking various levels of diaphragmatic force at rest. Plotted is the diaphragmatic force index (time integral for Pdi multiplied times breathing frequency) achieved during exercise in the studies by Johnson et al. (circles), Babcock et al. (triangles), and Mador et al. (squares) vs. the percentage fall in Pdi amplitude with supramaximal stimulation. This is shown relative to the force produced during resting hyperpnea vs. the fall in the Pdi waveform amplitude after this voluntary maneuver. Note that after performing the resting hyperpnea for the same time period as achieved during exercise (95% ), significant fatigue does not occur until a time integral of 600 cm H2 O s · min−1, whereas during exercise significant fatigue occurs at much lower levels of diaphragmatic work.

Figure 15. Figure 15.

Influence of fatigue on the dynamic capacity for pressure generation by the diaphragm. Note during heavy exercise (95% of ) that the peak diaphragmatic pressure produced during exercise (closed circles) approaches 70% of the dynamic capacity for producing transdiaphragmatic pressures (open circles). When a 20%–25% reduction in the maximal force‐generating capacity of the diaphragm is considered, peak Pdi produced during exercise approaches 90%–95% of this capacity (open circles).

Figure 16. Figure 16.

The fiber cross‐sectional area (μm2) to capillary number in three human respiratory muscles compared to a mixed fiber locomotor muscle.

Data are from Mizuno .] a, different (P < 0.05) from all other muscle; **, different (P < 0.05) from internal and external intercostals; *, different (P < 0.05) from internal intercostals
Figure 17. Figure 17.

Influence of exercise intensity and duration on the increase in citrate synthase (CS) activity in the costal diaphragm of rats following a 10‐week endurance running training program. Nine groups of animals trained at each of three exercise intensities (low = ∼55% VO2max; medium = ∼65% VO2max; high = 75%) and each of three exercise durations (30, 60, and 90 min · day−1).

Data are from Powers et al.
Figure 18. Figure 18.

Influence of exercise intensity and duration on the increase in citrate synthase (CS) activity in the crural diaphragm and parasternal intercostal muscles of rats following a 10‐week endurance running training program. Nine groups of animals trained at each of three exercise intensities (low = ∼55% VO2max; medium = ∼65% VO2max; high = 75%) and each of three exercise durations (30, 60, 90 min · day−1).

Data are from Powers et al.
Figure 19. Figure 19.

A schematic representation of known (solid lines) and putative (broken lines) neural pathways showing possible interactions between areas of respiratory control and respiratory‐related sensations during respiratory stimulation (e.g., exercise). The figure is intended to provide an “anatomical” basis to which the reader can refer, with respect to some of the research findings and ideas discussed in this review.

Figure 20. Figure 20.

Time course of end‐tidal PCO2 (PETCO2) and subjective ratings of air hunger (urge to breathe) in four subjects (RB, BL, DY, and SL) during complete neuromuscular paralysis. Subjects underwent fixed mechanical ventilation and made ratings (via a tourniqueted arm) as inspired CO2 concentration was surreptitiously increased; ratings were made using a seven‐point scale ranging from zero through slight (SLT) and moderate (MOD) to extreme (EXTR) with intermediate rating options. Nonparametric correlation coefficients (r) were calculated between ratings and the level of PETCO2 two min earlier (to allow for “equilibration” of medullary PCO2.

From Banzett et al.
Figure 21. Figure 21.

Relationship of alveolar ventilation (A) to arterial PCO2 () at various levels of maximum exercise (CO2) according to the alveolar air equation. Values shown for total minute ventilation (E) assume a VD/VT of 0.20 at maximum exercise. Note that to achieve a given level of hyperventilation at maximum exercise (e.g., a = 30 mm Hg), the ventilatory requirements are markedly different for the sedentary subject (CO2 = 3 liter · min−1, E ∼ 120 liter · min−1) vs. that achieved in the highly fit (CO2 = 6 liter · min−1; E > 190 liter · min−1). The shaded areas show the wide range of alveolar hyperventilation achieved at maximum exercise among healthy subjects across the fitness continuum with substantial overlap but a tendency for less hyperventilation at the higher maximum CO2 in the highly fit.



Figure 1.

a, Sagittal section of the human head and neck, showing the upper airways and some of the associated musculature. NC, nasal constrictor muscles; DN, dilator naris muscle; HP, hard palate; GG, genioglossus muscle; GH, geniohyoid muscle; H, hyoid bone; SH, sternohyoid muscle; SP, soft palate; EG, epiglottis. b, Section through the posterior pharynx showing some of the musculature acting on the soft palate and pharyngeal wall. TVP, tensor veli palatini muscle; LVP, levator veli palatini muscle; SC, superior pharyngeal constrictor muscles; SP, soft palate, c, Superior view of the larynx, showing the major laryngeal adductor and abductor muscles. TA, thyroarytenoid muscle; PCA, posterior cricoarytenoid muscle; TC, AC, and CC, thyroid, arytenoid and cricoid cartilages, respectively. See test for explanation of anatomy and muscular actions.

Parts b and c adapted from Bartlett and Warwick and Williams , respectively


Figure 2.

Top, Nasal airway pressure–flow relationships obtained during voluntary hyperpnea in a healthy subject. The tests were performed before (control) and after (exercise) exhausting cycle ergometer exercise. Note that the curves are nonlinear, showing the marked flow dependence of upper airway resistance. Also note that prior exercise shifts the pressure–flow curve to the right, indicating that exercise hyperpnea decreases resistance. Bottom, Log transformation of the data shown in the top panel, demonstrating the technique for determining the flow rate at the transition (tr) from laminar to turbulent flow. See text for detailed explanation of figure.

From Olson et al.


Figure 3.

Influence of exercise intensity on the integrated EMG activity of the nasal dilator muscles (AN EMG), mean inspiratory flow (VT/T1) and inspired pulmonary ventilation (V1). Values for both nasal and total VT/T1 and V1 are given, as indicated on the insets. Note that the plateau in both of these variables at exercise intensities exceeding 60% of the peak power coincides with the plateau in the AN EMG. * Significantly different than resting control value (P < 0.05); + significantly different than nasal V1 (P < 0.05).

From R. F. Fregosi and R. L. Lansing, unpublished observations


Figure 4.

Recordings showing changes in flow through the nose and mouth, and integrated EMG activity of the nasal dilator muscles (“alae nasi”) when a representative subject voluntarily changes the breathing route from nasal to oral during cycling exercise. Note that during nose breathing EMG activity is much higher, and the onset of the EMG burst precedes the onset of flow (vertical dashed lines). Also note that when the flow route changes from nasal to oral in midexpiration (A), the EMG amplitude is diminished but EMG onset no longer precedes the onset of flow. In contrast, when flow route changes at the end of expiration (B), EMG amplitude is diminished but onset time does not change. Thus, when the upper airway was configured for oral flow well before the next inspiration (A), the nervous system no longer had to activate the alae nasi musculature early and intensely in order to protect the nasal airway from collapse. In contrast, when the switch from nasal to oral flow was made at the very end of expiration (B), the system was still configured for a nasal breath, and the EMG burst preceded the onset of flow. However, the system soon sensed the absence of nasal flow and made appropriate adjustments during the breath, resulting in a reduced EMG amplitude. Taken together, these data suggest that (1) the configuration of the entire upper airway, presumably determined by a feedforward mechanism, is more important than local reflex mechanisms in determining the onset of upper airway muscle activities, and (2) local reflex mechanisms can alter burst amplitude during a breath (see text)

From Wheatley, Amis, and Engel


Figure 5.

Comparison of breathing pattern in normal humans during maximal incremental exercise and endurance exercise. The initial increase in minute ventilation is due to increases in both tidal volume and respiratory frequency. However, tidal volume stops increasing at high levels of ventilation and further increases in ventilation are due to increasing respiratory frequency alone. Tidal volume is less and respiratory frequency greater during endurance exercise at high levels of ventilation

Data obtained from Syabbalo et al. .] See text for details


Figure 6.

Young adult average tidal flow–volume and pressure–volume loops and minute ventilation (E) for eight athletes during rest and progressive exercise, which averaged 42%, 61%, 83%, 95%, and 100% of maximal oxygen uptake. Tidal flow–volume curves are shown plotted within preexercise (solid line) and postexercise (dashed line) maximum flow–volume curves. Tidal pressure–volume curves are shown also with constraints for effective pressure generation on expiration (Pmaxe) and the capacity for pressure generation on inspiration (Pcapi). Widths of Pmaxe and Pcapi at a given lung volume indicate 95% confidence intervals. The loops at a minute ventilation of 117 liter · min−1 represent the typical response to maximum short‐term exercise in an untrained young adult subject (maximum o2 40–50 ml · kg−1 · min−1). The E of 169 liters/min was the average response to maximum exercise in the trained subject (maximum o2 = 70–80 ml · kg−1 · min−1)

From Johnson, Saupe and Dempsey


Figure 7.

Time course of flow; lung volume; respiratory muscle pressure (Pmus); dynamic capacity of inspiratory muscles to generate pressure (Pcapi); and ratio of inspiratory Pmus to Pcapi before exercise, during light exercise, and during moderately heavy exercise. Data are the average from three subjects during cycle exercise. PIIA is postinspiratory muscle activity. Numbers in the bottom row are mean and peak Pmusl/PcapI. See text for details.

From B. Krishnan, T. Zintel, and C. G. Gallagher, unpublished data


Figure 8.

Equine costal diaphragmatic EMG (raw and moving time‐averaged); gastric, esophageal, and transdiaphragmatic pressure (PG, PE, and Pdi); and accelerometer tracing indicating left forelimb impact (arrows) during walking and during galloping (11 ms). Note that the foot plant activity does not occur during a consistent phase of the respiratory cycle when the horse is walking, whereas phase‐linking is apparent during the gallop.

From Ainsworth et al. (


Figure 9.

Canine breathing patterns are highly variable, as shown in this figure for one dog trotting on the treadmill while unencumbered by a breathing mask. The two types of patterns—high‐frequency type A (left panel), a pure high frequency oscillation in the esophageal pressure; and mixed‐frequency type B (right panel), a slower inherent breathing pattern with superimposed high‐frequency oscillations in the esophageal pressure—are apparent. Esophageal pressure (Pe), crural (CR), costal (CS), transverse abdominal (TA) EMG, and foot plant left hindlimb (FP) are shown. In type A and type B, decrements in esophageal pressure (and airflow) are always associated with electrical activation of the costal and crural diaphragm. In type B, oscillations in the esophageal pressure during expiration occur at intervals related to foot plant and hence TA activation.

From Ainsworth et al.


Figure 10.

Inspiratory flow (VI); electrical activity of the parasternal (PS, rib cage inspiratory), crural (CR), and costal (CS) diaphragm, and transverse abdominal (TA) muscles and sonomicrometry tracing of the costal diaphragm (SONO CS) in one dog at rest and during trotting. Note that either at rest or during exercise, phasic electrical activity of both inspiratory and expiratory muscles is evident and that phasic shortening of the costal diaphragm (downward displacement of SONO tracing) occurs only during electrical activation. This breathing pattern is representative of high‐frequency breathing with fb = 115 breaths · min−1

From Ainsworth et al.


Figure 11.

Inspiratory flow (VI) or tidal volume and gastric pressure (PG) traces from a human (left panel) and a dog (right panel). In the dog, note that at the onset of exercise, mean gastric pressure increases due to tonic increases in abdominal muscle activity.

From Ainsworth et al. .] In the human, gastric pressure increases during the transition from the walk to the jog. (From Henke et al. .] (Please note, in the dog an increased gastric pressure moves upward in the figure; whereas in the human the PG scales are reversed and increased PG moves down


Figure 12.

Oxygen cost of exercise hyperpnea. Right panel shows the effects of increasing ventilation on the per unit oxygen cost of breathing (mean values ±95% confidence interval). Left panel shows the effects of increasing ventilation on the total oxygen cost of breathing expressed as a percentage of the total body O2 (O2TOT) during moderate, heavy, and maximum progressive exercise. [Individual subject values (N = 9).] Values for the O2 cost of breathing were obtained in resting subjects from the measured increases in O2 that accompanied steady‐state mimicking of the pressure–volume loop, ∫ Pdi, ∫ Pg, fb, VT, and EELV obtained during various exercise intensities.

From Aaron et al.


Figure 13.

Example of bilateral phrenic nerve stimulation (BPNS) performed before and after exercise at 1 and 10 Hz. Both esophageal (Pe) and gastric (Pg) pressure fell following exercise, causing the reduction in the Pdi waveform amplitude. At 1 Hz stimulation, a prolongation in relaxation rate of the Pdi waveform was also observed. No changes were observed in the amplitude of the M‐waves from either the left or right hemidiaphragm.

From Johnson et al.


Figure 14.

Comparison of diaphragmatic fatigue produced by exercise vs. that produced by mimicking various levels of diaphragmatic force at rest. Plotted is the diaphragmatic force index (time integral for Pdi multiplied times breathing frequency) achieved during exercise in the studies by Johnson et al. (circles), Babcock et al. (triangles), and Mador et al. (squares) vs. the percentage fall in Pdi amplitude with supramaximal stimulation. This is shown relative to the force produced during resting hyperpnea vs. the fall in the Pdi waveform amplitude after this voluntary maneuver. Note that after performing the resting hyperpnea for the same time period as achieved during exercise (95% ), significant fatigue does not occur until a time integral of 600 cm H2 O s · min−1, whereas during exercise significant fatigue occurs at much lower levels of diaphragmatic work.



Figure 15.

Influence of fatigue on the dynamic capacity for pressure generation by the diaphragm. Note during heavy exercise (95% of ) that the peak diaphragmatic pressure produced during exercise (closed circles) approaches 70% of the dynamic capacity for producing transdiaphragmatic pressures (open circles). When a 20%–25% reduction in the maximal force‐generating capacity of the diaphragm is considered, peak Pdi produced during exercise approaches 90%–95% of this capacity (open circles).



Figure 16.

The fiber cross‐sectional area (μm2) to capillary number in three human respiratory muscles compared to a mixed fiber locomotor muscle.

Data are from Mizuno .] a, different (P < 0.05) from all other muscle; **, different (P < 0.05) from internal and external intercostals; *, different (P < 0.05) from internal intercostals


Figure 17.

Influence of exercise intensity and duration on the increase in citrate synthase (CS) activity in the costal diaphragm of rats following a 10‐week endurance running training program. Nine groups of animals trained at each of three exercise intensities (low = ∼55% VO2max; medium = ∼65% VO2max; high = 75%) and each of three exercise durations (30, 60, and 90 min · day−1).

Data are from Powers et al.


Figure 18.

Influence of exercise intensity and duration on the increase in citrate synthase (CS) activity in the crural diaphragm and parasternal intercostal muscles of rats following a 10‐week endurance running training program. Nine groups of animals trained at each of three exercise intensities (low = ∼55% VO2max; medium = ∼65% VO2max; high = 75%) and each of three exercise durations (30, 60, 90 min · day−1).

Data are from Powers et al.


Figure 19.

A schematic representation of known (solid lines) and putative (broken lines) neural pathways showing possible interactions between areas of respiratory control and respiratory‐related sensations during respiratory stimulation (e.g., exercise). The figure is intended to provide an “anatomical” basis to which the reader can refer, with respect to some of the research findings and ideas discussed in this review.



Figure 20.

Time course of end‐tidal PCO2 (PETCO2) and subjective ratings of air hunger (urge to breathe) in four subjects (RB, BL, DY, and SL) during complete neuromuscular paralysis. Subjects underwent fixed mechanical ventilation and made ratings (via a tourniqueted arm) as inspired CO2 concentration was surreptitiously increased; ratings were made using a seven‐point scale ranging from zero through slight (SLT) and moderate (MOD) to extreme (EXTR) with intermediate rating options. Nonparametric correlation coefficients (r) were calculated between ratings and the level of PETCO2 two min earlier (to allow for “equilibration” of medullary PCO2.

From Banzett et al.


Figure 21.

Relationship of alveolar ventilation (A) to arterial PCO2 () at various levels of maximum exercise (CO2) according to the alveolar air equation. Values shown for total minute ventilation (E) assume a VD/VT of 0.20 at maximum exercise. Note that to achieve a given level of hyperventilation at maximum exercise (e.g., a = 30 mm Hg), the ventilatory requirements are markedly different for the sedentary subject (CO2 = 3 liter · min−1, E ∼ 120 liter · min−1) vs. that achieved in the highly fit (CO2 = 6 liter · min−1; E > 190 liter · min−1). The shaded areas show the wide range of alveolar hyperventilation achieved at maximum exercise among healthy subjects across the fitness continuum with substantial overlap but a tendency for less hyperventilation at the higher maximum CO2 in the highly fit.

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Jerome A. Dempsey, Lewis Adams, Dorothy M. Ainsworth, Ralph F. Fregosi, Charles G. Gallagher, Abe Guz, Bruce D. Johnson, Scott K. Powers. Airway, Lung, and Respiratory Muscle Function During Exercise. Compr Physiol 2011, Supplement 29: Handbook of Physiology, Exercise: Regulation and Integration of Multiple Systems: 448-514. First published in print 1996. doi: 10.1002/cphy.cp120111