Lecture 2Lecture 2

Gas exchangeGas exchange

OO22 transport transport

COCO22 transport transport

Control of VEControl of VEVentilatory response to COVentilatory response to CO22

Ventilatory response to OVentilatory response to O22

Ventilatory response to pHVentilatory response to pH

Ventilatory response to exerciseVentilatory response to exercise

Gas ExchangeGas Exchange

It takes place at a respiratory It takes place at a respiratory surface. For unicellular organisms the surface. For unicellular organisms the RS is simply the cell membrane, but RS is simply the cell membrane, but for a large organisms it is the for a large organisms it is the respiratory system.respiratory system.

In humans, respiratory GE or VIn humans, respiratory GE or VEE is is carried out by mechanisms of the carried out by mechanisms of the lungs.lungs.

Alv are designed for rapid GE. While no GE occur in the heart, arteries and Alv are designed for rapid GE. While no GE occur in the heart, arteries and arterioles. arterioles.

Alv are found at the end of the branching bronchioles and so they have a Alv are found at the end of the branching bronchioles and so they have a good air supply.good air supply.The alv walls are very thin and have a moist surface. They are covered by a The alv walls are very thin and have a moist surface. They are covered by a network of capillaries which transport the gases. network of capillaries which transport the gases.

Blood takes about 1 sec to pass through the lung capillaries. In this time the Blood takes about 1 sec to pass through the lung capillaries. In this time the blood becomes nearly 100% saturated with Oblood becomes nearly 100% saturated with O22 and loses its excess of CO and loses its excess of CO22..

In pulmonary capillaries, OIn pulmonary capillaries, O22 diffuses into capillary blood, while CO diffuses into capillary blood, while CO22 diffuses into alveolar air.diffuses into alveolar air.

Blood returning to lungs is high in COBlood returning to lungs is high in CO22 and is low in O and is low in O22..Blood leaving lungs is enriched with OBlood leaving lungs is enriched with O22, low in CO, low in CO22..

The amount of air reaching the alv with each breath is equal to VThe amount of air reaching the alv with each breath is equal to VTT – V – VDD..

The ratio of COThe ratio of CO22 produced / O produced / O22 consumed is known as RQ. consumed is known as RQ.

OO22 transport transport

OO22 is carried in the blood in 2 forms; is carried in the blood in 2 forms;

1) bound to Hb (approx 98.5 %)1) bound to Hb (approx 98.5 %)2) dissolved in the plasma (approx 1.5 %).2) dissolved in the plasma (approx 1.5 %).

The amount of any gas that dissolves in blood is directly The amount of any gas that dissolves in blood is directly proportional to the partial pressure of the gas and the solubility proportional to the partial pressure of the gas and the solubility of the gas. Therefore, CO2 = SO2 * PO2 (Henry's law).of the gas. Therefore, CO2 = SO2 * PO2 (Henry's law).

Each molecule of Hb can carry 4 mol of OEach molecule of Hb can carry 4 mol of O22. Fully sat Hb can . Fully sat Hb can carry approx 1.36 ml Ocarry approx 1.36 ml O22 / g Hb, and normal human blood  / g Hb, and normal human blood contains about 15 g Hb / 100 ml blood. Multiplying these two contains about 15 g Hb / 100 ml blood. Multiplying these two constants yields 20.4 ml O2 / 100 ml blood. constants yields 20.4 ml O2 / 100 ml blood.

Hb is a protein in which a haem group is attached to Hb is a protein in which a haem group is attached to each of 4 subunit polypeptide chain (2 alpha & 2 beta). each of 4 subunit polypeptide chain (2 alpha & 2 beta). Hb contains 4 iron atoms (4 haem group). Each one Hb contains 4 iron atoms (4 haem group). Each one contain a Fecontain a Fe2+ 2+ within a haem group.within a haem group.

If 100 ml of plasma is exposed to an atmos with a POIf 100 ml of plasma is exposed to an atmos with a PO22 of 100 mmHg, only 0.3 ml of Oof 100 mmHg, only 0.3 ml of O22 would be absorbed. would be absorbed. However, if 100 ml of blood is exposed to the same However, if 100 ml of blood is exposed to the same atmos, about 19 ml of Oatmos, about 19 ml of O22 would be absorbed. WHY? would be absorbed. WHY?

The total quantity of OThe total quantity of O22 bound with Hb in normal bound with Hb in normal systemic arterial blood is about 19.4 ml /100 ml of systemic arterial blood is about 19.4 ml /100 ml of blood. On passing through the tissue capillaries, this blood. On passing through the tissue capillaries, this amount is reduced to approx 14.4 ml. Therefore, 5 ml is amount is reduced to approx 14.4 ml. Therefore, 5 ml is the quantity of O2 that are transported from the lungs the quantity of O2 that are transported from the lungs to the tissues by each 100 ml of BF.to the tissues by each 100 ml of BF.

During heavy exercise, there might be upto 20 times During heavy exercise, there might be upto 20 times ↑ ↑ in Oin O22 transport to the tissues compared to normal, transport to the tissues compared to normal,

Factors which affect the OFactors which affect the O22-Hb dissociation -Hb dissociation curve:curve:These factors may shift the curve to the right, These factors may shift the curve to the right, indicating lower affinity of Hb to Oindicating lower affinity of Hb to O22, or shift the , or shift the curve to the left, indicating an curve to the left, indicating an ↑↑ affinity of Hb to affinity of Hb to OO22. These factors includes;. These factors includes;1) 1) PCOPCO22::↑ PCO↑ PCO22 → ↓ affinity → ↓ affinity of Hb to Oof Hb to O22 → → shift the shift the curve to the right (this is called Bohr effect).curve to the right (this is called Bohr effect).2) 2) PHPH: : ↓ PH (or ↑ [H↓ PH (or ↑ [H++]) → ↓ affinity ]) → ↓ affinity of Hb to Oof Hb to O22 → → shift shift the curve to the right.the curve to the right.3) 3) TempTemp : : ↑↑ Temp Temp → → shift the curve to the right.shift the curve to the right.4) 4) 2,3- diphosphoglycerate2,3- diphosphoglycerate (2,3-DPG): : (2,3-DPG): :↑ ↑ 2,3-2,3-DPGDPG → ↓ affinity → ↓ affinity of Hb to Oof Hb to O22 → → shift the curve to the shift the curve to the right. right.

P50 is the pp of OP50 is the pp of O22 required to achieve 50% Hb required to achieve 50% Hb sat.sat.

COCO22 transport transport

COCO22 transported from the body cells back transported from the body cells back to the lungs in 3 forms;to the lungs in 3 forms;(1) Dissolved in the plasma (approx 7-(1) Dissolved in the plasma (approx 7-10%).10%).(2) Reacts with the amino group of plasma (2) Reacts with the amino group of plasma proteins to form carbamino proteins proteins to form carbamino proteins (carbaminohemoglobin) (approx 23-30%).(carbaminohemoglobin) (approx 23-30%).

(3) Reacts with H(3) Reacts with H22O to form HO to form H22COCO33 (approx (approx 60-70%)60-70%)

COCO22 + H + H22O ↔ HO ↔ H22COCO33 ↔ HCO ↔ HCO33-- + H + H++

COCO22 dissociation curve dissociation curve

The relationship of COThe relationship of CO22 content of blood to PCO content of blood to PCO22 is is known as COknown as CO22 dissociation curve. dissociation curve.

The volume of COThe volume of CO22 carried in the blood is carried in the blood is determined by PCOdetermined by PCO22. The dissolved form is . The dissolved form is directly proportionate to PCOdirectly proportionate to PCO22 (0.06 ml dissolved (0.06 ml dissolved in 100 ml of blood/1 mmHg PCOin 100 ml of blood/1 mmHg PCO22).).The curve is affected by the saturation of Hb with The curve is affected by the saturation of Hb with OO22 (Haldane effect). (Haldane effect).Oxyhemoglobin shifts the curve to the right, i.e. Oxyhemoglobin shifts the curve to the right, i.e. in the lungs COin the lungs CO22 is released from the blood. is released from the blood.Reduced Hb shifts the curve to the left, i.e. more Reduced Hb shifts the curve to the left, i.e. more COCO22 is taken up by the blood in the tissues. is taken up by the blood in the tissues.

Directional movement of CODirectional movement of CO22

All mov across membrane is by diffusion.All mov across membrane is by diffusion.

Note:Note: most of CO most of CO22 entering the blood in entering the blood in the tissues ultimately is converted to the tissues ultimately is converted to HCOHCO33--. This occurs almost entirely in the . This occurs almost entirely in the erythrocytes because the CA enzyme is erythrocytes because the CA enzyme is located there, but most of the HCOlocated there, but most of the HCO33-- then then moves out of the erythrocyte into the moves out of the erythrocyte into the plasma in exchange for chloride ions “ the plasma in exchange for chloride ions “ the chloride shift”. chloride shift”.

Chloride shiftChloride shift

The rise in the HCO3The rise in the HCO3-- content of red cell is much greater content of red cell is much greater than that in plasma as the blood passes through the than that in plasma as the blood passes through the capillaries. The excess of HCO3capillaries. The excess of HCO3-- leaves the red cell in leaves the red cell in exchange for clexchange for cl--. This change is called the chloride shift.. This change is called the chloride shift.

The chloride shift occurs rapidly and essentially complete The chloride shift occurs rapidly and essentially complete in 1 second.in 1 second.

The clThe cl-- content of the red cells in venous blood is content of the red cells in venous blood is therefore significantly greater than in arterial blood.therefore significantly greater than in arterial blood.

In pulmonary capillaries; clIn pulmonary capillaries; cl-- leaves the red cell and move leaves the red cell and move into the plasma in exchange for HCO3into the plasma in exchange for HCO3--; in systemic ; in systemic capillaries, the reverse occurs.capillaries, the reverse occurs.

The Haldane effectThe Haldane effect

It results from the simple fact that the It results from the simple fact that the combination of Ocombination of O22 with Hb in the lung causes the with Hb in the lung causes the Hb to become a stronger acid. This displaces COHb to become a stronger acid. This displaces CO22 from the blood and into the alveoli in 2 ways;from the blood and into the alveoli in 2 ways;(1) The more highly acidic Hb has less tendency (1) The more highly acidic Hb has less tendency to combine with COto combine with CO22 to form to form carbaminohemoglobin, thus displacing much of carbaminohemoglobin, thus displacing much of the COthe CO22 that is present in the carbamino form that is present in the carbamino form from the blood.from the blood.(2) The ↑ acidity of Hb also causes it to release (2) The ↑ acidity of Hb also causes it to release an excess of Han excess of H++, and these bind with HCO, and these bind with HCO33- to - to form Hform H22COCO33; this then dissociate into H; this then dissociate into H22O and COO and CO22, , and the COand the CO22 is released from the blood into the is released from the blood into the alveoli and, finally, into the air.alveoli and, finally, into the air.

Control of VControl of VEE

The 3 basic elements of the respiratory The 3 basic elements of the respiratory control system are: SENSORS, CENTRAL control system are: SENSORS, CENTRAL CONTROLLER and EFFECTORS.CONTROLLER and EFFECTORS.

1- SENSOR; which gather information and 1- SENSOR; which gather information and feed it to the feed it to the 2- CENTRAL CONTROLLER; in the brain, 2- CENTRAL CONTROLLER; in the brain, which coordinates the information and, in which coordinates the information and, in turn, sends impulses to the turn, sends impulses to the 3- EFFECTORS (respiratory muscles), 3- EFFECTORS (respiratory muscles), which cause Vwhich cause VEE..

Central controllerCentral controller

Central control of breathing is achieved at the Central control of breathing is achieved at the brainstem, specially the pons and midbrain brainstem, specially the pons and midbrain (responsible for involuntary breathing) and the (responsible for involuntary breathing) and the cerebral cortex (responsible for voluntary cerebral cortex (responsible for voluntary breathing).breathing).

The respiratory centre is divided into 4 groups of The respiratory centre is divided into 4 groups of neurones spread throughout the entire length of neurones spread throughout the entire length of the medulla and pons;the medulla and pons;(1) DRG:(1) DRG:- It is located in the entire length of the dorsal - It is located in the entire length of the dorsal aspect of the medulla.aspect of the medulla.- It lies in close relation to the NTS where visceral - It lies in close relation to the NTS where visceral afferents from cranial nerves IX and X terminate.afferents from cranial nerves IX and X terminate.- It comprises inspiratory neurons. Thus, they are - It comprises inspiratory neurons. Thus, they are almost entirely responsible for inspiration.almost entirely responsible for inspiration.

(2) VRG:(2) VRG:It is located in each side of the medulla, about 5 milliliters It is located in each side of the medulla, about 5 milliliters anterior and lateral to the DRG.anterior and lateral to the DRG.They are inactive during quiet breathing, but become They are inactive during quiet breathing, but become activated during increased pulmonary ventilation, as in activated during increased pulmonary ventilation, as in exercise.exercise.They are mainly expiratory neurons with some They are mainly expiratory neurons with some inspiratory neurons, both of which are activated when inspiratory neurons, both of which are activated when expiration becomes an active process.expiration becomes an active process.They are comprises 4 nuclei;They are comprises 4 nuclei;a) the nucleus retroambigualis (NR); which is a) the nucleus retroambigualis (NR); which is predominantly expiratory with upper motor neurons predominantly expiratory with upper motor neurons passing to the expiratory muscles of the other side.passing to the expiratory muscles of the other side.b) the nucleus ambiguous (NA); which controls the b) the nucleus ambiguous (NA); which controls the dilator function of larynx, pharynx and tongue.dilator function of larynx, pharynx and tongue.c) the nucleus para-ambigualis (NP); which is mainly c) the nucleus para-ambigualis (NP); which is mainly inspiratory and control the force of contraction of the inspiratory and control the force of contraction of the inspiratory muscles of the opposite side.inspiratory muscles of the opposite side.d) the Botzinger complex (BC); which has widespread d) the Botzinger complex (BC); which has widespread expiratory functions.expiratory functions.

(3) AC ???:(3) AC ???:It is located in the lower pons.It is located in the lower pons.They sends excitatory impulses to the DRG of neurons and They sends excitatory impulses to the DRG of neurons and potentiates the inspiratory drive.potentiates the inspiratory drive.It receives inhibiting impulses from the sensory vagal fibers It receives inhibiting impulses from the sensory vagal fibers of the Hering-Breuer inflation reflex and inhibiting fibers of the Hering-Breuer inflation reflex and inhibiting fibers from the pneumotaxic centre in the upper pons.from the pneumotaxic centre in the upper pons.

(4) PC;(4) PC;It is located dorsally in the upper pon.It is located dorsally in the upper pon.It transmits inhibitory impulses to the AC and to the It transmits inhibitory impulses to the AC and to the inspiratory areas to switch off inspiration.inspiratory areas to switch off inspiration.The function of this centre is primarily to limit inspiration. The function of this centre is primarily to limit inspiration. This has a secondary effect of increasing the rate of This has a secondary effect of increasing the rate of breathing.breathing.Some investigators believed that the role of this centre is Some investigators believed that the role of this centre is “fine tuning” of respiratory rhythm because a normal “fine tuning” of respiratory rhythm because a normal rhythm can exist in the absence of this centre. rhythm can exist in the absence of this centre.

2) Effectors2) Effectors

They are the muscles of respiration, including the They are the muscles of respiration, including the diaphragm, intercostal muscles, abdominal diaphragm, intercostal muscles, abdominal muscles and accessory muscles as muscles and accessory muscles as sternocleidomastoid.sternocleidomastoid.It is crucially important that these various muscle It is crucially important that these various muscle groups work in a coordinated manner, and this is groups work in a coordinated manner, and this is the responsibility of the central controller.the responsibility of the central controller.There is some evidence that some newborn There is some evidence that some newborn children, particularly those who are premature, children, particularly those who are premature, have uncoordinated respiratory muscle activity, have uncoordinated respiratory muscle activity, especially during sleep. For example, the thoracic especially during sleep. For example, the thoracic muscle may try to inspire while the abdominal muscle may try to inspire while the abdominal muscle expire. This may be a factor in the muscle expire. This may be a factor in the “sudden infant death syndrome” (SIDS).“sudden infant death syndrome” (SIDS).

3) Sensors3) Sensors

The sensors that contribute to the control of breathing The sensors that contribute to the control of breathing include lung stretch receptors in the smooth muscle of include lung stretch receptors in the smooth muscle of the airway, irritant receptors located between airway the airway, irritant receptors located between airway epithelial cells, joint and muscle receptors that epithelial cells, joint and muscle receptors that stimulate breathing in response to limb movement, stimulate breathing in response to limb movement, and juxtacapillary (or J) receptors located in alveolar and juxtacapillary (or J) receptors located in alveolar walls which sense engorgement of the pulmonary walls which sense engorgement of the pulmonary capillaries and cause rapid shallow breathing.  capillaries and cause rapid shallow breathing. 

The most important sensors are central The most important sensors are central chemoreceptors in the medulla as well as peripheral chemoreceptors in the medulla as well as peripheral chemoreceptors in the carotid and aortic bodies.  chemoreceptors in the carotid and aortic bodies.  

Central chemoreceptors (CC)Central chemoreceptors (CC)

They are most probably located on the ventrolateral They are most probably located on the ventrolateral surfaces of the medulla oblangato, which bathed surfaces of the medulla oblangato, which bathed CSF.CSF.The CCs in the medulla respond to changes in the The CCs in the medulla respond to changes in the pH of the CSF.  Decreases in CSF pH produce pH of the CSF.  Decreases in CSF pH produce ↑↑ in in breathing (hyperventilation) whereas breathing (hyperventilation) whereas ↑↑ in pH result in pH result in hypoventilation.in hypoventilation.They are highly sensitive to [HThey are highly sensitive to [H++] of the CSF evoked ] of the CSF evoked by PaCOby PaCO22, since CO, since CO22 can freely cross the blood- can freely cross the blood-brain barrier into the CSF while the barrier is brain barrier into the CSF while the barrier is relatively impermeable to Hrelatively impermeable to H++ and H and H22COCO33..

Stimulation of these receptors Stimulation of these receptors ↑↑ both the rate of rise both the rate of rise and the intensity of the inspiratory signals, thereby and the intensity of the inspiratory signals, thereby ↑↑ the frequency of the respiratory rhythm. the frequency of the respiratory rhythm.

Peripheral chemoreceptors (PC)Peripheral chemoreceptors (PC)They are located in the carotid bodies at the bifurcation of the They are located in the carotid bodies at the bifurcation of the common carotid arteries and in the aortic bodies above and common carotid arteries and in the aortic bodies above and below the aortic arch.below the aortic arch.They cause an They cause an ↑↑ in V in VEE in response to decreases in PaO2, in response to decreases in PaO2, increases in arterial PCOincreases in arterial PCO22 and increases in arterial hydrogen and increases in arterial hydrogen concentrations (decrease in pH).concentrations (decrease in pH).The carotid bodies are most important in humans. They The carotid bodies are most important in humans. They contain glomus cells of two or more types which show an contain glomus cells of two or more types which show an intense fluorescence staining because of their large content of intense fluorescence staining because of their large content of dapamine.dapamine.The mechanism of chemoreception is not yet understood. A The mechanism of chemoreception is not yet understood. A popular view has been that glomus cells themselves are popular view has been that glomus cells themselves are chemoreceptors.chemoreceptors.They are highly sensitive to changes in PaOThey are highly sensitive to changes in PaO22 and to a lesser and to a lesser extent to PaCOextent to PaCO22 and pH. They are also sensitive to temp. of and pH. They are also sensitive to temp. of the blood and BF.the blood and BF.The response of the PCs to PaCOThe response of the PCs to PaCO22 is much less important is much less important than that of the CCs.than that of the CCs.

Lung and airway receptorsLung and airway receptorsReceptors in the lung and airways are innervated by Receptors in the lung and airways are innervated by myelinated and unmyelinated vagal fibers. myelinated and unmyelinated vagal fibers. The unmyelinated fibers are C fibers.The unmyelinated fibers are C fibers.The myelinated fibers are commonly divided into SARs and The myelinated fibers are commonly divided into SARs and RARs on the basis of whether sustained stimulation leads to RARs on the basis of whether sustained stimulation leads to prolonged or transient discharge in their afferent fibers.prolonged or transient discharge in their afferent fibers.SARs are also known as pulmonary stretch receptors.They SARs are also known as pulmonary stretch receptors.They are thought to participate in ventilatory control by are thought to participate in ventilatory control by prolonged inspiration in conditions that reduce lung prolonged inspiration in conditions that reduce lung inflation.inflation. RARs are stimulated by chemicals such as histamine, dust, RARs are stimulated by chemicals such as histamine, dust, cigarette smoke. Therefore, they have been called irritant cigarette smoke. Therefore, they have been called irritant receptors.receptors.Activation of RARs in the lung may produce hyperpnea.Activation of RARs in the lung may produce hyperpnea.

J receptors are stimulated by hyperinflation of the lung. J receptors are stimulated by hyperinflation of the lung. They play a role in the dyspnea associated with left heart They play a role in the dyspnea associated with left heart failure, interstitial lung disease, pneumonia and failure, interstitial lung disease, pneumonia and microembolism. microembolism.

The Hering-Breuer reflexes thought to play a major role The Hering-Breuer reflexes thought to play a major role in VE by determining the rate and depth of breathing. in VE by determining the rate and depth of breathing. This can be done by using the information from the This can be done by using the information from the SARs to modulate the “switching off” mechanism in the SARs to modulate the “switching off” mechanism in the medulla. medulla.

The Hering-Breuer inflation reflex is an ↑ in the duration The Hering-Breuer inflation reflex is an ↑ in the duration of expiration produced by steady lung inflation, and the of expiration produced by steady lung inflation, and the Hering-Breuer deflation reflex is a ↓in the duration of Hering-Breuer deflation reflex is a ↓in the duration of expiration produced by marked deflation of the lung.expiration produced by marked deflation of the lung.

In human beings, the Hering-Breuer reflex probably is In human beings, the Hering-Breuer reflex probably is not activated until VT ↑ to more than three times normal not activated until VT ↑ to more than three times normal (i.e. < 1.5 l/breath). Therefore, this reflex appears to be (i.e. < 1.5 l/breath). Therefore, this reflex appears to be mainly a protective mechanism for preventing excess mainly a protective mechanism for preventing excess lung inflation rather than an important ingredient in lung inflation rather than an important ingredient in normal control of Vnormal control of VEE. .

Ventilatory response to COVentilatory response to CO22

The most important factor in the control of VThe most important factor in the control of VEE is is PaCOPaCO22..The VR to COThe VR to CO22 is normally measured by having is normally measured by having the subject inhale COthe subject inhale CO22 mixture or rebreathe from mixture or rebreathe from a bag so that the inspired PCOa bag so that the inspired PCO22 gradually ↑. gradually ↑.With a normal POWith a normal PO22 the VE ↑ by about 2-3 l/min the VE ↑ by about 2-3 l/min for each 1 mmHg rise in PCOfor each 1 mmHg rise in PCO22. Lowering the . Lowering the POPO22 produces 2 effects; produces 2 effects;1) there is a higher VE for a given PCO1) there is a higher VE for a given PCO22

2) the slope of the line becomes steeper.2) the slope of the line becomes steeper.The VR to COThe VR to CO22 is reduced by sleep, is reduced by sleep, ↑↑ age, and age, and genetic, racial and personality factors. It can genetic, racial and personality factors. It can also be reduced by if the work of breathing is ↑. also be reduced by if the work of breathing is ↑.

Ventilatory response to OVentilatory response to O22

The way in which a reduction of PaOThe way in which a reduction of PaO22 stimulates stimulates

VVEE can be studied by having the subject breathe can be studied by having the subject breathe hypoxic gas mixture.hypoxic gas mixture.

When the PCOWhen the PCO22 is ↑ a reduction in PO is ↑ a reduction in PO22 below below

100 mmHg causes some stimulation of V100 mmHg causes some stimulation of VEE..

Hypoxemia reflexly stimulates VHypoxemia reflexly stimulates VEE by its action on by its action on the carotid and aortic body chemoreceptors.the carotid and aortic body chemoreceptors.

Ventilatory response to pHVentilatory response to pH

A reduction in arterial blood pH stimulates VE.A reduction in arterial blood pH stimulates VE.

The chief site of action of a reduced arterial pH The chief site of action of a reduced arterial pH is the PCs, especially the carotid bodies in is the PCs, especially the carotid bodies in humans. It is also possible that the CCs itself is humans. It is also possible that the CCs itself is affected by a change in blood pH if it is large affected by a change in blood pH if it is large enough.enough.

Ventilatory response to exerciseVentilatory response to exerciseOn ex, VE ↑ promptly and, during strenuous ex, it may reach very On ex, VE ↑ promptly and, during strenuous ex, it may reach very high levels.high levels.

The ↑ in VE closely matches the ↑ in VOThe ↑ in VE closely matches the ↑ in VO22 and VCO and VCO22..

The PaCOThe PaCO22 does not ↑ during most form of ex, however, during does not ↑ during most form of ex, however, during sever ex it falls slightly.sever ex it falls slightly.The PaOThe PaO22 ↑ slightly, and it may fall at very high work levels. ↑ slightly, and it may fall at very high work levels.The arterial pH remains nearly constant for moderate ex, and falls The arterial pH remains nearly constant for moderate ex, and falls during heavy ex.during heavy ex.

Factors which play a role in the ↑ in VFactors which play a role in the ↑ in VEE during ex includes; during ex includes;- ↑ body temperature- ↑ body temperature- ↑plasma epinephrine conc- ↑plasma epinephrine conc- ↑plasma potassium conc- ↑plasma potassium conc- ↑ CO2 load to the lung- ↑ CO2 load to the lung- Passive movement of the limbs - Passive movement of the limbs