Breathing and Exercise

Breathing and Exercise

Ventilation (1)

Gas Exchange (2)

Gas Transport (3)

Gas Exchange (4)

Cell Respiration (5)

Respiration Requires the Interaction of Physiological Systems

Respiration Requires the Interaction of Physiological Systems

Conducting Zone: Structure-FunctionConducting Zone: Structure-Function

• Nasal Cavity is rich in blood supply which warms inspired air.

• Moist lining humidifies.• Upper airways are mainly cartilaginous plates

that are ‘stiff’ and conduct air efficiently.• Lower airways contain more smooth muscle

which can regulate airflow by relaxing and expanding.

• Mucociliary ‘elevator’ filters.

Respiratory Zone - Structure-FunctionRespiratory Zone - Structure-Function

• Type 1 epithelial cells are thin (0.1 to 0.5 µm) making gas exchange with blood efficient.

• Type 2 epithelial cells make surfactant which keep alveoli ‘open’.

• Alveolar macrophages remove bacteria and other contaminants.

• Highly branched allows for great surface area for gas exchange.

(Patm - Palv)

Airway ResistanceFlow =

End-Expiration

(Patm - Palv)

Airway ResistanceFlow =

Inspiration

(Patm - Palv)

Airway ResistanceFlow =

Expiration

InspirationInspiration

Inspiratory Muscle Action

Expiration

Expiration

Vol

ume

(lit

ers)

0

2

4

6

Time

Lung Volumes and Capacities in Healthy Subjects

Males Females

Measures (20-30 yrs) (20-30 yrs)

VC 4800 3200

RV 1200 1000

FRC 2400 1800

TLC 6000 4200

RV/TLC x 100 20% 24%

Measurements are in ml except where indicated.

Lung Volumes and Capacities in Healthy Subjects

Males Females Males

Measures (20-30 yrs) (20-30 yrs) (50 to 60 yrs)

VC 4800 3200 3600

RV 1200 1000 2400

FRC 2400 1800 3400

TLC 6000 4200 6000

RV/TLC x 100 20% 24% 40%

Measurements are in ml except where indicated.

Dead Space

• Anatomical Dead Space (ADS) is the volume of air needed to fill the conducting zone.

• Physiological Dead Space (PDS) is ADS + nonfunctional alveoli.

• Healthy people: ADS = PDS• Some pulmonary diseases: ADS < PDS

Ventilation of Dead Space and Alveoli

VT is volume required to fill dead space (VD) + alveoli (VA).

In healthy subjects:

VT = ~500 ml

VD = ~150 ml

VA = ~350 ml

Ventilatory Adjustments and Respiratory Efficiency

• Increase tidal volume– alveolar ventilation increases– dead space ventilation is unchanged

• Increase respiratory frequency– alveolar ventilation increases– dead space ventilation increases

• Increasing tidal volume more efficient!!!

What Determines the Work of

Breathing?

• Lung and Chest Wall Compliance

• Tissue and Airway Resistance

Elastic Properties of the Lung are a Determinant of Compliance

Elastic Properties of the Lung are a Determinant of Compliance

Lung Volume

Transpulmonary Pressure

Compliance = y/x

Lung Volume is a Determinant of ComplianceLung Volume is a Determinant of Compliance

Lung Volume(% Total Lung Capacity)

Transpulmonary Pressure (cm H2O)

Total Lung Capacity (elastic elements

are stretched)

Functional Residual Capacity

Residual Volume(airways are compressed)

Resistance

• Tissue resistance (~20% of total resistance)

• Airway resistance (~80% of total resistance)

– Airway dimensions

– Smooth muscle contraction

– Intrapleural pressure

Regulation of Airway Smooth Muscle

Airways constricted by:Parasympathetic

stimulationAcetylcholineHistamineLeukotrienesThromboxane A2Serotonin-adrenergic agonists

Decreased PCO2

Airways dilated by:Sympathetic stimulation

(2 receptors)

Circulating 2 agonists

Nitric oxide

Increased PCO2 in small airways

Decreased PO2 in small airways

Lung Volume is Invesrsely related to Airway Resistance

Lung Volume

AirwayResistance

High Intrapleural PressuresCompress Airways

Low Intrapleural PressuresDistend Airways

Airway Compression and Intrapleural Pressure

Ventilation (1)

Gas Exchange (2)

Gas Transport (3)

Gas Exchange (4)

Cell Respiration (5)

Respiration Requires the Interaction of Physiological Systems

Respiration Requires the Interaction of Physiological Systems

Regulation of Pulmonary Vascular Blood Flow

• Pulmonary artery pressure• Extravascular events• Chemical regulation of pulmonary vascular

smooth muscle• Gravity

Pulmonary Vascular Resistance

Mean Pulmonary Artery Pressure (mmHg)

Increased Pressure decreases Vascular Resistance in the Pulmonary Circulation

Recruitment Distension

Ventilation-Perfusion Matching

• Regional Ventilation– Increased by high

CO2

• Regional Circulation– Decreased by low O2

Ensures regions of the lung that are well ventilated are also well perfused

Ventilation (1)

Gas Exchange (2)

Gas Transport (3)

Gas Exchange (4)

Cell Respiration (5)

Respiration Requires the Interaction of Physiological Systems

Diffusion of Gases

O2

CO2

T

P1

P2

A

( )VA DT

P Pgas 1 2

Surface Area for Pulmonary Gas Exchange is Influenced by:

• Body position• Body size

• Exercise• Some pulmonary diseases

Atmospheric

Air

(mmHg)

Humidified

Air

(mmHg)

Alveolar

Air

(mmHg)

Expired

Air

(mmHg)

N2 597.0 (78.6%) 563.4 (74.1%) 569.0 (74.9%) 566.0 (74.5%)

O2 159.0 (20.8%) 149.3 (19.7%) 104.0 (13.6%) 120.0 (15.7%)

CO2 0.3 (0.04%) 0.3 (0.04%) 40.0 (5.3%) 27.0 (3.6%)

H2O 3.7 (0.5%) 47.0 (6.2%) 47.0 (6.2%) 47.0 (6.2%)

Total 760 (100.0%) 760 (100.0%) 760 (100.0%) 760 (100.0%)

Partial Pressures of Respiratory Gases as they Enterand Leave the Lungs at Sea Level

Partial Pressures of Respiratory Gases as they Enterand Leave the Lungs at Sea Level

Gas Pressure Gradients in the LungGas Pressure Gradients in the Lung

Values are PO2 and PCO2 in mmHg

PulmonaryCapillary

AlveoliEnvironment

TissueMetabolism

Air-Blood Barrier

Artery

Vein

O2

CO2

0.03159

40104

40104

45 40

Gas Pressure Gradients in the Lung:Light to Moderate Exercise

Gas Pressure Gradients in the Lung:Light to Moderate Exercise

Values are PO2 and PCO2 in mmHg

PulmonaryCapillary

AlveoliEnvironment

TissueMetabolism

Air-Blood Barrier

Artery

Vein

O2

CO2

0.03159

40104

40104

6025

5 O2 molecules are dissolved in solution on both sides of the semi-permeable membrane (no net movement).

DissolvedO2 = 5

DissolvedO2 = 5

Hemoglobin as an O2 Carrier

Hemoglobin now binds 4 O2 molecules, leaving only one in solution. There is now a 5:1 dissolved O2 ratio (O2 now moves from left to right).

Hb

DissolvedO2 = 5

DissolvedO2 = 1

Hemoglobin as an O2 Carrier

5 O2 molecules are dissolved in solution on both sides of the semi-permeable membrane (no net movement).

DissolvedO2 = 5

DissolvedO2 = 5

Hemoglobin as an O2 Carrier

RBC transit in pulmonary capillary at rest is 1.0 sec

RBC transit in pulmonary capillary during exercise is as little as 0.5 sec

RBC transit in pulmonary capillary at rest is 1.0 sec

RBC transit in pulmonary capillary during exercise is as little as 0.5 sec

Diffusion - Limited Transfer in the Lung

Presence of an end capillary to alveolus partial pressure difference

Perfusion-Limited Transfer in the Lung

• Absence of an end capillary partial pressure difference

• An increase in blood flow increases gas exchange with air by sending more blood through pulmonary capillaries.

Diffusion of O2 to TissuesDiffusion of O2 to Tissues

Diffusion-Limited

Diffusion of CO2 from TissuesDiffusion of CO2 from Tissues

Perfusion-Limited

Transport of O2 in the Blood

O2 Carrying Capacity of Blood

Capacity of Blood to Transport O2 is determined byCharacteristics of the Hb-O2 Dissociation Cure

Capacity of Blood to Transport O2 is determined byCharacteristics of the Hb-O2 Dissociation Cure

‘S’ Shape of Hb-O2 Dissociation Curve‘S’ Shape of Hb-O2 Dissociation Curve

• Caused by interaction of 4 Hb subunits as they bind O2.

• Hb subunits associate with O2 sequentially with each successive binding facilitating the next.

• Flat upper portion insures consistent and adequate O2 delivery over a broad range of alveolar and arterial PO2.

• Steep portion permits rapid unloading of O2 from Hb during times of need, when PO2 is low.

Hb-O2 Binding Affinity is Influenced by Many Factors

Hb-O2 Binding Affinity is Influenced by Many Factors

Venous Blood has a Decreased O2 Carrying Capacity

Venous Blood has a Decreased O2 Carrying Capacity

Bohr EffectBohr Effect

Tissues:

High CO2 or reduced pH decrease Hb affinity for O2 and facilitates O2 unloading from blood.

Lungs:

Reduced CO2 or increased pH increase Hb affinity for O2 and facilitate O2 uptake by the blood.

Transport of CO2 in the Blood

Blood CO2 Transport

• CO2 ~ 7%

• HbCO2 ~ 23%

• HCO3- ~ 70%

Haldane Effect describes the Reduced Capacityof Arterial Blood to Transport CO2

Haldane Effect describes the Reduced Capacityof Arterial Blood to Transport CO2

Blood CO2

(ml/dl)

Blood PCO2 (mmHg)

Haldane Effect

Tissues:Deoxygenated Hb affinity for CO2 is higher than Hb-O2

affinity for CO2. This results in an increased capacity of blood to carry CO2.

Lungs:Hb-O2 has decreased affinity for CO2 and is more acidic than deoxygenated Hb. This facilitates CO2 removal from the pulmonary capillaries.

Control of Breathing Requires Three Elements:One that Senses the 'Internal Climate',One that Integrates Sensory Info and Central Commands,One that Carries Out the Order

Central Controller

pons, medulla,other parts of brain

Sensors EffectorsNegative Feedback

chemical, mechanical,and other receptors

inspiratory andexpiratory muscles

Input Output

Medullary Respiratory Centers

Figure 22.25

Depth and Rate of Breathing: PCO2

Peripheral and Central Chemoreceptors have different Response Characteristics

Breathing is stimulated by:

• Peripheral - PCO2, pH, PO2

• Central - pH, PCO2 (indirect)

Central response to arterial PCO2 is of greater magnitude.

Peripheral response to arterial PCO2 is faster.

Ventilation(liters/min)

Time (sec)

Sole Source of Ventilatory Drive to Hypoxia Comes from Peripheral Chemoreceptors

Sole Source of Ventilatory Drive to Hypoxia Comes from Peripheral Chemoreceptors

Hypoxia

Peripheral Chemoreceptorafferent nerves intactor denervated

• Respiratory adjustments are geared to both the intensity and duration of exercise

• During vigorous exercise:

– Ventilation can increase 20 fold

– Breathing becomes deeper and more vigorous, but respiratory rate may not be significantly changed (hyperpnea)

• Exercise-enhanced breathing is not prompted by an increase in PCO2 or a decrease in PO2 or pH

– These levels remain surprisingly constant during exercise

Respiratory Adjustments: Exercise

• As exercise begins:– Ventilation increases abruptly, rises slowly, and

reaches a steady state• When exercise stops:

– Ventilation declines suddenly, then gradually decreases to normal

Respiratory Adjustments: Exercise

Pulmonary Response to Constant Load Exercise

Exercise-Induced Lactic Acidosis

H20 + C02 H2C03 H+ + HC03

-

CA

Incremental Exercise Test

• Acclimatization – respiratory and hematopoietic adjustments to altitude include:– Increased ventilation – 2-3 L/min higher than at

sea level– Chemoreceptors become more responsive to

PCO2

– Substantial decline in PO2 stimulates peripheral chemoreceptors

Respiratory Adjustments: High Altitude