Lecture 2. Respiratory Control & Adaptations

Greg Wells, Ph.D. The University of Toronto www.per4m.ca

All Slides © Greg D. Wells, Ph.D. (2009), All Rights Reserved Web: www.per4m.ca Email: [email protected] Tel: 416-710-4618

Part 1: The Ventilatory Response to Exercise

© Greg D. Wells, Ph.D. (2009)

Organization of the Control of Breathing Central Command

Afferent Feedback (Limbs)

Reticular Activating System (Reticular Formation & Raphe)

Respiratory Rhythm Generator (pre-Botz, VRG, NA)

Spinal Motoneurones (via VRG & DRG)

Respiratory Muscles

Feed Forward

Nucleus of the Solitary Tract

Central Chemoreflex

Peripheral Chemoreflexes & Lung / Airway Afferents

Lung (Pulmonary Ventilation)

Feed Back

© Greg D. Wells, Ph.D. (2009)

Drives to Ventilation Wakefulness drive cortex)

(cerebral

Movements signals (cerebellum)

Type III, IV afferents (MSNA hypothesis)

Central Command

Afferent Feedback (Limbs)

Cross-activation (neuronal network)

Reticular Activating System (Reticular Formation & Raphe)

Basal ventilation (medulla)

Respiratory Rhythm Generator (pre-Botz, VRG, NA)

Spinal Motoneurones (via VRG & DRG)

*

Nucleus of the Solitary Tract

H+, PCO2, SID (medullary surface) Central Chemoreflex

H+, PCO2, PO2, K+, La(carotid body)

*

Peripheral Chemoreflexes & Lung / Airway Afferents

Pulmonary stretch receptors Respiratory Muscles

*

Lung (Pulmonary Ventilation)

PCO2, PO2

* © Greg D. Wells, Ph.D. (2009)

Physiology During Incremental Exercise

© Greg D. Wells, Ph.D. (2009)

Ventilation During Constant Load Exercise * *

*

*

Mateika, J. H. and J. Duffin (1995). “A review of the control of breathing during exercise.” Eur J Appl Physiol 71(1): 1-27.

Drives to Ventilation Wakefulness drive cortex)

* Shows areas where training may have an effect.

(cerebral

Movements signals (cerebellum)

Type III, IV afferents (MSNA hypothesis)

Central Command

Afferent Feedback (Limbs)

Cross-activation (neuronal network)

Reticular Activating System (Reticular Formation & Raphe)

Basal ventilation (medulla)

Respiratory Rhythm Generator (pre-Botz, VRG, NA)

Spinal Motoneurones (via VRG & DRG)

*

Nucleus of the Solitary Tract

H+, PCO2, SID (medullary surface) Central Chemoreflex

H+, PCO2, PO2, K+, La(carotid body) Peripheral Chemoreflexes & Lung / Airway Afferents

*

Pulmonary stretch receptors Respiratory Muscles

*

Lung (Pulmonary Ventilation)

PCO2, PO2

* © Greg D. Wells, Ph.D. (2009)

Part 2: Adaptations of the Respiratory System to Training

© Greg D. Wells, Ph.D. (2009)

Adaptation #1: Peripheral Chemoreflex Organization of the Control of Breathing Central Command

Afferent Feedback (Limbs)

Reticular Activating System (Reticular Formation & Raphe)

Respiratory Rhythm Generator (pre-Botz, VRG, NA)

Spinal Motoneurones (via VRG & DRG)

Respiratory Muscles

Nucleus of the Solitary Tract

Central Chemoreflex

Peripheral Chemoreflexes & Lung / Airway Afferents

Lung (Pulmonary Ventilation)

© Greg D. Wells, Ph.D. (2009)

Ventilation vs. Predicted PCO2 80 2nd VE Threshold 70

Ventilation BTPS (L . min-1)

60 2nd VE Sensitivity 50 40 1st VE Threshold 30

1st VE Sensitivity

20 10

Basal Ventilation

0 30

35

40

45

50

55

60

Predicted PCO2 (mmHg) © Greg D. Wells, Ph.D. (2009)

Ventilation vs. End-Tidal PCO2 70

Ventilation BTPS (L . min-1)

60 50 40

Pre-training Pre-training fitted Post-training

30

Post-training fitted

20 10

Chemoreflex VEThresholds

0 30

35

40

45

50

55

End-Tidal PCO2 (mmHg)

Example of typical chemoreflex response pre- and post-training. The increase in © Greg D. Wells, Ph.D. (2009) chemoreflex threshold is indicated.

Adaptation #1: Peripheral Chemoreflex Central Command

Afferent Feedback (Limbs)

Reticular Activating System (Reticular Formation & Raphe)

Respiratory Rhythm Generator (pre-Botz, VRG, NA)

Spinal Motoneurones (via VRG & DRG)

Respiratory Muscles

Nucleus of the Solitary Tract

Central Chemoreflex

Peripheral Chemoreflexes & Lung / Airway Afferents

Lung (Pulmonary Ventilation)

Exercise Limiting Factors •  •  •  • 

Exercise induced arterial hypoxemia Increased work of breathing Respiratory muscle fatigue Dyspnoea © Greg D. Wells, Ph.D. (2009)

Adaptation #2: Pulmonary Function Organization of the Control of Breathing Central Command

Afferent Feedback (Limbs)

Reticular Activating System (Reticular Formation & Raphe)

Respiratory Rhythm Generator (pre-Botz, VRG, NA)

Spinal Motoneurones (via VRG & DRG)

Respiratory Muscles

Nucleus of the Solitary Tract

Central Chemoreflex

Peripheral Chemoreflexes & Lung / Airway Afferents

Lung (Pulmonary Ventilation)

© Greg D. Wells, Ph.D. (2009)

Results – Pulmonary Function FEV - 1

FIV - 1 4.4

4.2 F E: T2 - T3 *

4.2

F E: T2 - T4 *

4.0

4.0 *

3.8

Volume (L)

Volume (L)

3.8

3.6

3.6 3.4

3.4

3.2 F E: T2 - T4 *

3.2

3.0

F C: T2 - T3 * F C: T2 - T4 *

F E: T2 - T3 *

2.8

3.0 -1

0

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15 16 17 18 19

Time (wk)

-1

0

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15 16 17 18 19

Time (wk)

© Greg D. Wells, Ph.D. (2009)

Results – Pulmonary Function Forced Vital Capacity

5.1 F E: T2 - T4 *

4.9 F E: T2 - T3 *

Vital Capacity (L)

4.7 4.5 4.3 4.1 3.9 F C: T2 - T3 *

3.7 F C: T2 - T4 *

3.5 -1

0

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15 16 17 18 19

Time (wk)

Audrey Ferreras

© Greg D. Wells, Ph.D. (2009)

She reached a depth of 412.5 feet (125 meters) in 2 minutes, 3 seconds.

Adaptation #2: Pulmonary Function Central Command

Afferent Feedback (Limbs)

Reticular Activating System (Reticular Formation & Raphe)

Respiratory Rhythm Generator (pre-Botz, VRG, NA)

Spinal Motoneurones (via VRG & DRG)

Respiratory Muscles

Nucleus of the Solitary Tract

Central Chemoreflex

Peripheral Chemoreflexes & Lung / Airway Afferents

Lung (Pulmonary Ventilation)

Performance Limiting Factors •  •  •  • 

Exercise induced arterial hypoxemia Increased work of breathing Respiratory muscle fatigue Dyspnoea © Greg D. Wells, Ph.D. (2009)

Adaptation #3: Respiratory Muscle Function Organization of the Control of Breathing Central Command

Afferent Feedback (Limbs)

Reticular Activating System (Reticular Formation & Raphe)

Respiratory Rhythm Generator (pre-Botz, VRG, NA)

Spinal Motoneurones (via VRG & DRG)

Respiratory Muscles

Nucleus of the Solitary Tract

Central Chemoreflex

Peripheral Chemoreflexes & Lung / Airway Afferents

Lung (Pulmonary Ventilation)

© Greg D. Wells, Ph.D. (2009)

Back

Mechanics at Rest % VC 52

INSPIRATION thorax wall

lung

48

EXPIRATION thorax wall

lung

44 40 36 -10

-8

-6

-4

-2

0

32

-10

-8

-6

-4

-2

0

Intrapleural Pressure cm H 2O

© Greg D. Wells, Ph.D. (2009)

Mechanics During Exercise W to overcome ER Lungs

W to overcome L flow resist.

W to overcome ER CW

W to overcome FR CW

© Greg D. Wells, Ph.D. (2009)

RMT Mechanisms: Q Legs

Harms, C. A., M. A. Babcock, et al. (1997). “Respiratory muscle work compromises leg blood flow during maximal exercise.” J Appl Physiol 82(5): 1573-83.

Adaptation #3: Respiratory Muscle Function Central Command

Afferent Feedback (Limb & RM)

Reticular Activating System (Reticular Formation & Raphe)

Respiratory Rhythm Generator (pre-Botz, VRG, NA)

Spinal Motoneurones (via VRG & DRG)

Respiratory Muscles

Nucleus of the Solitary Tract

Central Chemoreflex

Peripheral Chemoreflexes & Lung / Airway Afferents

Lung (Pulmonary Ventilation)

Performance Limiting Factors •  •  •  • 

Exercise induced arterial hypoxemia Increased work of breathing Respiratory muscle fatigue Dyspnoea © Greg D. Wells, Ph.D. (2009)

Adaptation #4: Dyspnoea Central Command

Afferent Feedback (Limbs)

Reticular Activating System (Reticular Formation & Raphe)

Respiratory Rhythm Generator (pre-Botz, VRG, NA)

Spinal Motoneurones (via VRG & DRG)

Respiratory Muscles

Nucleus of the Solitary Tract

Central Chemoreflex

Peripheral Chemoreflexes & Lung / Airway Afferents

Lung (Pulmonary Ventilation)

Performance Limiting Factors •  •  •  • 

Exercise induced arterial hypoxemia Increased work of breathing Respiratory muscle fatigue Dyspnoea © Greg D. Wells, Ph.D. (2009)

Dyspnoea – Mechanisms

Central & peripheral chemoreceptors Type I afferents M+ spindles (length ~ volume) Type II afferents GTO (tension ~ pressure: Pdi / Pmax) Type III afferents M+ spindles (contraction ~ V, Fb, Ti:Te)

Pulmonary stretch receptors

Type IV afferents M+ spindles (metaboreceptors ~ H+, K+) © Greg D. Wells, Ph.D. (2009)

Dyspnoea – Typical Application

© Greg D. Wells, Ph.D. (2009)

Pathogenesis of Dyspnoea Type I afferents M+ spindles (length ~ volume) Dynamic hyperinflation Type II afferents GTO (tension ~ pressure: Pdi / Pmax) Dynamic hyperinflation (lose mechanical adv) RM weakness (Pmax) Type III afferents M+ spindles (contraction ~ V, Fb, Ti:Te) Hyperventilation

Hypoxia / hypercapnia Central & peripheral chemoreceptors

Dynamic hyperinflation Pulmonary stretch receptors

Type IV afferents M+ spindles (metaboreceptors ~ H+, K+) RM fatigue © Greg D. Wells, Ph.D. (2009)

RMT Effects: Dyspnoea

Volianitis, S., A. K. McConnell, et al. (2001). “Inspiratory muscle training improves rowing performance.” Med Sci Sports Exerc 33(5): 803-9.

© Greg D. Wells, Ph.D. (2009)

Summary Organization of the Control of Breathing Central Command

Afferent Feedback (Limbs)

Reticular Activating System (Reticular Formation & Raphe)

Respiratory Rhythm Generator (pre-Botz, VRG, NA)

Spinal Motoneurones (via VRG & DRG)

Respiratory Muscles

Nucleus of the Solitary Tract

Central Chemoreflex

Peripheral Chemoreflexes & Lung / Airway Afferents

Lung (Pulmonary Ventilation)

© Greg D. Wells, Ph.D. (2009)