Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School,...
-
Upload
jocelyn-holt -
Category
Documents
-
view
232 -
download
10
Transcript of Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School,...
![Page 1: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/1.jpg)
Respiratory Physiology: Gas ExchangeRespiratory Physiology: Gas Exchange
Dr Shihab Khogali
Ninewells Hospital & Medical School, University of Dundee
![Page 2: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/2.jpg)
Understand the difference between pulmonary ventilation and alveolar ventilation, and the significance of anatomical dead space
Understand the basic principles of ventilation perfusion matching
Understand the significance of alveolar dead space
Know that the physiological dead space = anatomical + alveolar dead space
Understand the four factors which influence the gas transfer across the alveolar membrane
Know the non-respiratory functions of the respiratory system
What is This LectureAbout?
See blackboard for detailed learning objectives
![Page 3: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/3.jpg)
The Dalton’s Law of partial pressures. Know that gases move across membranes by partial pressure gradient
The role of diffusion coefficient on gas transfer across membranes
The effect of membrane surface area and membrane thickness on gas transfer, with the Fick’s Law of diffusion
Understand the followings in relation to the four factors which influence gas transfer across membranes:
![Page 4: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/4.jpg)
![Page 5: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/5.jpg)
Some inspired air remains in the airways (anatomical dead space) where it is not available for gas exchange
Pulmonary Ventilation = tidal volume (ml/ breath) x Respiratory Rate (breath/min)
= 0.5 L X 12 breath/min = 6 L/min under resting conditions
Alveolar Ventilation is less than pulmonary ventilation because of the presence of anatomical dead space.
Alveolar Ventilation = (tidal volume – dead space volume) x Respiratory Rate = (0.5 – 0.15) x 12 = 4.2 L/min under resting conditions.
Pulmonary Ventilation & Alveolar Ventilation
Fresh airfrom inspiration
Airway dead-spacevolume (150 ml)
After inspiration,before expiration
Alveolar air
![Page 6: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/6.jpg)
Fig. 13-22, p. 472
![Page 7: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/7.jpg)
Pulmonary Ventilation: Is the volume of air breathed in and out per minute
Alveolar Ventilation:Is the volume of air exchanged between the atmosphere and alveoli per minute
This is more important as it represent new air available for gas exchange with blood.
![Page 8: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/8.jpg)
To increase pulmonary ventilation (e.g. during exercise) both the depth (tidal volume) and rate of breathing (RR) increase.
because of dead space:
It is more advantageous to increase the depth of breathing
Pulmonary Ventilation & Alveolar Ventilation
Fresh airfrom inspiration
Airway dead-spacevolume (150 ml)
After inspiration,before expiration
Alveolar air
![Page 9: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/9.jpg)
It is more advantageous to increase the Depth of Breathing
![Page 10: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/10.jpg)
Ventilation Perfusion
The transfer of gases between the body and atmosphere depends upon:Ventilation: the rate at which gas is passing through the
lungs.Perfusion: the rate at which blood is passing through
the lungs
![Page 11: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/11.jpg)
Ventilation Perfusion
Both blood flow and ventilation vary from bottom to top of the lung
Flow
Lung PositionBottom Top
Blood Flow
Ventilation
V/Q Ratio
1
2
The result is that the average arterial and alveolar partial pressures of O2 are not exactly the same. Normally this effect is not significant but it can be in disease.
![Page 12: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/12.jpg)
The match between air in the alveoli and the blood in the pulmonary capillaries is not always perfect
Ventilated alveoli which are not adequately perfused with blood are considered as alveolar dead space
In healthy people, the alveolar dead space is very small and of little importance (note: the physiological dead space = the anatomical dead space + the alveolar dead space)
The alveolar dead space could increase significantly in disease
Alveolar Dead Space
![Page 13: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/13.jpg)
Ventilation Perfusion Match in the Lungs
Local controls act on the smooth muscles of airways and arterioles to match airflow to blood flow
Accumulation of CO2 in alveoli as a result of increased perfusion decreases airway resistance leading to increased airflow
Increase in alveolar O2 concentration as a result of increased ventilation causes pulmonary vasodilation which increases blood flow to match larger airflow
![Page 14: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/14.jpg)
Area in which blood flow (perfusion)is greater than airflow (ventilation)
Helpsbalance
HelpsbalanceLarge blood flow
Small airflow
CO2 in area
Relaxation of local-airwaysmooth muscle
Dilation of local airways
Airway resistance
Airflow
O2 in area
Contraction of local pulmon-ary arteriolar smooth muscle
Constriction of local blood vessels
Vascular resistance
Blood flow
![Page 15: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/15.jpg)
Area in which airflow (ventilation)is greater than blood flow (perfusion)
Helpsbalance
HelpsbalanceLarge airflow
Small blood flow
CO2 in area
Contraction of local-airwaysmooth muscle
Constriction of local airways
Airway resistance
Airflow
O2 in area
Relaxation of local pulmonary arteriolar smooth muscle
Dilation of local blood vessels
Vascular resistance
Blood flow
![Page 16: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/16.jpg)
Note the Different Effects of O2
![Page 17: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/17.jpg)
1. Partial Pressure Gradient of O2 and CO2
2. Diffusion Coefficient for O2 and CO2
3. Surface Area of Alveolar Membrane
4. Thickness of Alveolar Membrane
Four Factors Influence The Rate of Gas Exchange Across
Alveolar Membrane
![Page 18: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/18.jpg)
Gases move across cell membranes etc by pressure gradient
The partial pressure of a gas determines the pressure gradient for that gas
The partial pressure of gas (1) in a mixture of gases that don’t react with each other is:
The pressure that gas (1) would exert if it occupied the total volume for the mixture in the absence of other components
Thus if the total pressure of the gas mixture is 100 kPa; and half of the mixture is gas (1): the partial pressure for gas (1) is 50 kPa
Ptotal =
P1 + P2 +…+ Pn
Dalton’s Law of Partial Pressures
The Total Pressure exerted by a gaseous mixture =
The sum of the partial pressures of each individual component in the gas mixture
What is Partial Pressure of Gas?
![Page 19: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/19.jpg)
The partial pressure of gas is:
The pressure that one gas in a mixture of gases would exert if it were the only gas present in the whole volume occupied by the mixture at a given temperature.
![Page 20: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/20.jpg)
![Page 21: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/21.jpg)
Overview of Respiration
Gases move from higher to lower partial pressures (partial pressure gradient)
Note units in the diagram (mmHg). Here in UK you we use kPa (kilopascals) but Americans and American texts use mmHg.
To convert divide mmHg by 7.5.
![Page 22: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/22.jpg)
Across Pulmonary Capillaries:O2 partial pressure gradientfrom alveoli toblood =
60 mm Hg (8 kP)100 – 40 mmHg i.e. (13.3- 5.3 kP)
CO2 partial pressure gradient from blood toalveoli =
6 mm Hg (0.8 kP)46 – 40 mmHg i.e. (6.1 – 5.3 kP)
Across Systemic Capillaries:O2 partial pressure gradientfrom blood totissue cell =
> 60 mm Hg (8 kP)100 – < 40 mmHg i.e. (13.3- < 5.3 kP)
CO2 partial pressure gradient from tissue cell toblood =
> 6 mm Hg (0.8 kP)> 46 – 40 mm Hg i.e. (> 6.1 – 5.3 kP)
Inspiration Expiration
Pulmonarycirculation
Systemiccirculation
Alveoli
Net diffusion gradientsfor O2 and CO2 betweenthe lungs and tissues
Tissues
Atmospheric air
![Page 23: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/23.jpg)
But the partial pressure gradient for CO2 is much smaller than the partial pressure gradient for O2???
CO2 is more soluble in membranes than O2. The solubility of gas in membranes is known as the Diffusion Coefficient for the gas.
The diffusion coefficient for CO2 is 20 times that of O2
What offset the difference in partial pressure gradient for CO2 and O2?
![Page 24: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/24.jpg)
The lungs provide a very large surface area with thin membranes to facilitate effective gas exchange
The airways divides repeatedly to increase the surface area for gas exchange
The small airways form outpockets (the alveoli). This help increase the surface area for gas exchange in the lungs
The lungs have a very extensive pulmonary capillary network
Remember: the pulmonary circulation receives the entire cardiac output
Effect of surface Area & Membrane Thickness on Gas Diffusion
Fick’s Law of diffusion
The amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the sheet but inversely proportional to its thickness
![Page 25: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/25.jpg)
The Respiratory Tree
![Page 26: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/26.jpg)
Alveoli: Thin-walled inflatable sacs
• Function in gas exchange
• Walls consist of a single layer of flattened Type I alveolar cells
Pulmonary capillaries encircle each alveolus
Narrow interstitial space
Respiratory Membranes
![Page 27: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/27.jpg)
Four Factors Influence the Rate of Gas Transfer Across The Alveolar Membrane
![Page 28: Respiratory Physiology: Gas Exchange Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.](https://reader033.fdocuments.in/reader033/viewer/2022061304/5513de7b5503466f748b532f/html5/thumbnails/28.jpg)
Nonrespiratory Functions of Respiratory System
Route for water loss and heat elimination
Enhances venous return (Cardiovascular Physiology)
Helps maintain normal acid-base balance (Respiratory and Renal Physiology)
Enables speech, singing, and other vocalizations
Defends against inhaled foreign matter
Removes, modifies, activates, or inactivates various materials passing through the pulmonary circulation
Nose serves as the organ of smell