Module 4: Respiratory function and regulation during exercise Flashcards
What is external respiration?
Pulmonary ventilation: air movement in and out of the lungs (breathing)
Pulmonary diffusion: gas exchange between the lungs and the blood
What is internal respiration?
Gas transport: movement of O2 and CO2 via the blood
Capillary diffusion: gas exchange between capillary blood and the tissues
What is the tidal volume (VT)?
The amount of air entering and leaving the lungs with every normal breath
mL
What is the alveolar volume (VA)?
The fresh air that reaches the alveoli
To calculate: VT - VD (dead space volume)
mL
What is the vital capacity (VC)?
The greatest amount of air that can be expired after a maximum inspiration
What is the residual volume (RV)?
The amount of air remaining in the lungs after maximal expiration
What is the functional residual capacity?
The amount of air remaining in the lungs after normal expiration
What is the total lung capacity (TLC)?
Sum of vital capacity and residual volume
What is minute ventilation (VĖ)?
The amount of air ventilated in and out of the lungs every minute
Equation: VE = VT X RR (Respiratory Rate)
Normative VT = 500 mL @ rest
Normative RR = 12 breaths/min @ rest
Normative VE = 500 x 12 = 6000 mL/min or 6 L/min @ rest
For an average untrained male during maximal exercise
Normative VT = 3000 mL
Normative RR = 40 breaths/min
Normative VE = 120 L/min -> x20 higher than rest
What is alveolar ventilation (VÅ)?
VÅ = VA X RR
VÅ = (VT-VD) X RR
Normative VT = 500 mL @ rest
Normative VD = 150 mL @ rest
Normative RR = 12 breaths/min @ rest
Normative VÅ = (500-150) X 12 = 4200 mL/min @ rest
For an average untrained male during maximal exercise
Normative VT = 3000 mL
Normative VD = 175 mL
Normative RR = 40
Normative VÅ = 113 L/min -> x27 higher than rest
How does minute ventilation change with exercise?
Proportional to metabolic demand - greater intensity = greater ventilation
Pulmonary ventilation during light exercise = 40 L/min - facilitated by higher tidal volume
Pulmonary ventilation during moderate exercise = 80 L/min - facilitated by higher tidal volume and RR
Pulmonary ventilation during maximal exercise = 120 L/min - facilitated by higher tidal volume and RR
What is the pathway in which gas exchange (pulmonary diffusion) occurs between the alveoli and capillaries?
Inspired air path: bronchial tree -> alveoli
blood path: right ventricle -> pulmonary arteries -> pulmonary capillaries
Alveoli are surrounded by these capillaries
What are the two major functions of gas exchange?
- Replenishing blood O2 supply
- Removing CO2 from blood
What are the factors that affect gas exchange?
- Partial pressure gradient across the barrier: high to low
- Diffusion capacity (solubility) of gas
- Characteristics of barrier
What is the nitrogen, oxygen, and carbon dioxide concentration in the atmospheric air?
These concentrations do not change
Nitrogen: 79.03%
O2: 20.93%
CO2: 0.03%
What is the definition of partial pressure?
The pressure of a single gas (attributes to total pressure)
What is the partial pressure (PO2) of dry atmospheric air at sea level?
PO2 = fraction x total pressure
Normative value for total pressure = 760 mmHg
PO2 = .2093 x 760 mmHg
PO2 = 159 mmHg
What is the partial pressure (PO2) of tracheal air at sea level?
Tracheal air contains water molecules which disperse the gas molecules. As a result, there is an increase in the total volume of air (water + gas) and thus a decrease in gas pressure for a given volume of air
PO2 = 149 mmHg
How does PO2 change throughout the body?
- Atmosphere: starting PO2 (159 mmHg)
- Trachea: small dip due to water vapour (149 mmHg)
- Alveoli: large dip due to mixing with venous blood (105 mmHg)
- Arterial blood: small dip (due to the fact that not all the deoxygenated blood coming from the right atrium and ventricle partakes in gas exchange), similar to alveoli (100 mmHg with a PCO2 of 40 mmHg)
^ PO2 here determines O2 bound to haemoglobin, and thus how much blood travels in the blood stream - Large decrease as O2 is used in the muscle
- Venous blood depends on muscle O2 use (O2 leftover)
How do PO2 and PCO2 in blood change with gas exchange at rest?
Alveoli at the level of the lungs: removing CO2 from the deoxygenated blood and bringing it into the alveoli, exchanging it for O2 which travels to the capillaries oxidizing the arterial blood.
PO2 = 105 mmHg, PCO2 = 40 mmHg
Blood is then pumped out by the pulmonary vein -> left atrium and ventricle -> systemic arteries
PO2 = 100 mmHg, PCO2 = 40 mmHg
Alveoli at the level of the muscles: skeletal muscle utilizes oxygen from the capillaries and CO2 enters the bloodstream
Blood is then pumped by the systemic veins -> right atrium and ventricle -> pulmonary artery -> lungs
PO2 = 40 mmHg, PCO2 = 46 mmHg
How do PO2 and PCO2 in blood change with gas exchange at heavy exercise?
PO2 = 15 mmHg
PCO2 = 60 mmHg
What happens to the PO2 of oxygen at high altitudes?
Decreases
Concentration or % of O2 in the air does not change
What is the bodies first response to buffer reduced PaO2 at high altitudes?
Increase pulmonary ventilation - breathing both deeper and more frequently
What is one example of a gas has a lower diffusion rate than oxygen?
Carbon dioxide
What is the difference between PaO2 and PAO2?
PaO2 = partial pressure of oxygen in arterial blood
PAO2 = partial pressure of oxygen in the alveoli
PAO2 (alveolar PO2) -> PaO2 (arterial PO2) -> SaO2 (arterial O2 saturation) -> CaO2 (arterial O2 content)
Big picture idea: pressure -> saturation -> content
How are we able to transport oxygen within our blood?
Haemoglobin - each carries 4 O2 molecules
Low pressure around haemoglobin - O2 is bounded loosely
High pressure around haemoglobin - O2 is bounded tightly
What is the equation to calculate blood O2 content?
Blood O2 content = [Hgb] x 1.34 mL O2 / g x % sat
Typical [Hgb] = 15 g % or 15g/100 mL (range of 13 to 18 - females tend to have a lower concentration)
1.34 mL of O2 binds to 1 Hgb when 100% saturation occurs
What is the typical % saturation that we see in arterial blood?
98%
What is the typical CaO2 that we see in arterial blood?
19.7 mL O2 / 100 mL blood, 197 mL/L
Plus there is a small amount of O2 that is dissolved in plasma (~3 mL/L)
~200 mL/L realistically
What is the typical CvO2 that we see in venous blood?
50 mL O2 / 100 mL blood, 150 mL/L
What is the PO2 in the arteries at rest?
100 mmHg
What is the PO2 in veins at rest?
40 mmHg
With regards to the oxyhemoglobin disassociation curve, describe the two sections of the graph:
- Loading portion: saturation stays high even with large changes in PO2 - meaning oxygen is tightly bound to haemoglobin
- Unloading portion: saturations changes quickly with even small changes in PO2, allows oxygen to unload into the tissues
What is the oxyhemoglobin saturation at the level of the veins at rest?
75%
What is the oxyhemoglobin saturation at the level of the arteries at rest?
98%
What is the oxyhemoglobin saturation at the level of the veins during exercise?
25%
What happens when we shift the oxyhemoglobin curve to the right and to the left?
Right = decreased affinity - oxygen is not tightly bound to haemoglobin
Left = increased affinity - oxygen is tightly bound to haemoglobin
During exercise, do we want the oxyhemoglobin curve shifting to the right or the left?
Right - promotes oxygen offloading which is what we want during exercise (O2 needs to be delivered to the active tissues)
What changes in temperature and pH induce the shifting of the oxyhemoglobin curve to the right and to the left?
Temperature and pH
Shifting to the right: increase in temperature (going from 37 degrees which is normal body temp. to 43 degrees), decrease in pH (going from a pH of 7.4 to 7.2)
What is the muscle A-VO2 difference at rest and during exercise?
Rest:
4-5 mL O2 / 100 mL blood
CaO2 = 20 mL O2 / 100 mL blood
CvO2 = 15-16 mL O2 / 100 mL blood
Exercise:
15 mL O2 / 100 mL blood
CaO2 = 20 mL O2 / 100 mL blood
CvO2 = 5 mL O2 / 100 mL blood
What is myoglobin?
A molecule similar to haemoglobin:
Composed of a globin and heme group, only found in muscle, and binds to O2 tighter than Hgb
The main job it performs is that it shuttles O2 into the mitochondria in muscle
What is the PO2 in the mitochondria?
PO2 = <5 mmHg so its easily offloaded
What are the changes in CaO2 and CvO2 during exercise?
CaO2 does not change, CvO2 decreases = greater A-VO2 difference (more O2 is being extracted and utilized by the SKM)
What are the minor and major ways we transport CO2 in the blood?
Minor: freely dissolved in plasma, carbaminohemoglobin - Hgb bounded to CO2
Major: CO2 within the bloodstream combines with water via the enzyme carbonic anhydrase to form carbonic acid, which immediately dissociates into a hydrogen and bicarbonate ion. Hydrogen is buffered by Hgb but blood pH still drops a little. Bicarbonate carries the CO2, travelling to the lungs for it to be expelled.
At the level of the tissues: forward process - increase in CO2 = increase in bicarbonate
At the level of the lungs: reverse process - decrease in bicarbonate = CO2 released
What is the mechanism that controls our ventilation rate?
Respiratory centres (inspiratory, expiratory) located in the brainstem (medulla oblongata, pons) - they work to maintain PaCO2 and PaO2
What structures send signals to the respiratory centers in order to control our ventilation?
Neural:
1. Central command from the brain
2. Signals from active muscle
Chemical:
3. Central chemoreceptors (brain) - stimulated by the increase of CO2 (H+) in cerebrospinal fluid and they work to increase the rate and depth of breathing in order to remove CO2
4. Peripheral chemoreceptors (aortic and carotid bodies) - sensitive to arterial blood PO2, PCO2, H+
- Mechanoreceptors/stretch receptors (lungs) - sense movement causing expiration
- Voluntary control (motor cortex)
What mechanisms can be associated with an anticipatory rise in ventilation prior to engaging in exercise?
Neural mechanisms
What mechanisms can be associated with an increase in ventilation during exercise?
Chemical mechanisms - fine-tune response
What mechanisms can be associated with a rapid decline in ventilation after exercise?
Neural mechanisms
What mechanisms can be associated with a slower decline in ventilation after exercise?
Chemical mechanisms
What is the ventilatory threshold?
VE or minute ventilation in exercise increases proportionally to exercise intensity until around 60% of VO2 max where it increases disproportionately this is known as the ventilatory threshold. This occurs as a result of higher PCO2 at higher exercise intensities. Above the VT, the increase in VE to remove CO2 is disproportionate to the body’s need for O2.
