Lecture 21: Pulmonary Ventillation And Gas Laws Flashcards Preview

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1

Describe the nasal cavity

* Respiratory epithelium
- Pseudostratified ciliated columnar epithelium with goblet cells
* Nasal cavity
- Conchae (turbinates)
* Nasopharynx
- Uvula
* Larynx
- Glottis

2

Describe the tracheobronchial tree

* Trachea:
- Pseudostratified ciliated columnar epithelium
- With goblet cells
- Incomplete cartilaginous rings
- Trachealis muscle
* Carina:
- Inside trachea at point of branching of primary bronchi
- Sensitive to irritation
- Produces cough reflex
* Bronchi:
- Anatomy: Pseudostratified ciliated columnar epithelium and Numerous cartilaginous plates
- Branchings:
--Primary: Supply lungs
-- Secondary: Supply lobes
-- Tertiary: Supply lobules
* Bronchioles:
- Anatomy: Devoid of cartilage, 1 mm or less in diameter
-- Ciliated columnar epithelium → simple cuboidal
-- Simple squamous in smaller branches
-- Much smooth muscle but no cartilage
- Branchings:
-- Terminal
-- Respiratory

* Alveolar ducts
* Alveoli

- See slide 8-9

3

Describe the two types of respiratory muscles

* Inspiratory muscles:
- Respiratory diaphragm
- External intercostal muscles (limited)
- Sternomastoids
- Serratus anterior muscles
- Scalene muscles
* Expiratory muscles:
- Note that expiration is passive at rest
- Forceful expiration:
-- Abdominal muscles
-- Internal intercostals

-- See slide 14

4

Describe Total Lung Capacity

Total lung capacity =
- The maximum volume of gas the lungs can hold.
- Total lung capacity is made up of distinct, non-overlapping sub-compartments referred to as lung volumes.
- Combinations of lung volumes form lung capacities

5

Describe the Four types of Pulmonary Volumes

* Tidal volume
- 500 ml
- Volume of air that is inspired or expired with each breath at rest
* Inspiratory reserve volume
- 3000 ml
- Volume of air that can be inspired in addition to tidal volume with forceful inspiration
- Volumes and capacities are based on average young adult male; reduce by about 20-25% for female; increase for larger individual or athlete
* Expiratory reserve volume
- 1100 ml
- Additional volume of air that can be expired at end of tidal volume by forceful expiration
* Residual volume
- 1200 ml
- Volume of air remaining in lungs after forceful expiration

- See Slide 19

6

Describe the four types of pulmonary capacities

* Vital capacity
- 4600 ml
- The sum of all the volumes that can be inspired or exhaled
- Inspiration to the maximum extent plus expiration to the maximum extent
* Total lung capacity
- 5800 ml
- The sum of all the volumes = vital capacity plus residual volume
* Inspiratory capacity
- 3500 ml
- The sum of volumes above resting capacity = tidal volume plus inspiratory reserve volume
* Functional residual capacity
- 2300 ml
- The sum of volumes below resting capacity = expiratory reserve volume + residual volume

- See Slide 22

7

What is Minute Ventilation?

* Total volume of gases moved into or out of the lungs per minute = minute ventilation (VE).
- Calculated as: (Breaths per minute) x (tidal volume)
- i.e.: 16 breaths/minute x 500 ml/breath
= 8000 ml/minute (or 8 L per minute)

8

Describe Alveolar Ventilation

* Total volume of gases that enter spaces participating in gas exchange per minute = alveolar ventilation (VA).
- Calculated as:
(Breaths per minute) x (Tidal Volume ─ Dead space)
i.e.: 16 breaths/minute x (500 ml/breath –150 ml/breath)
= 5600 ml/minute (or 5.6 L per minute)
* Dead space:
- Anatomic dead space: Trachea, bronchi, bronchioles
- Physiological dead space: = Anatomic dead space + ventilated alveoli with poor or absent perfusion
- Total dead space in a normal individual: 0.15 liters
* Respiratory bronchioles + perfused alveoli: .35 liters
- Note that tidal volume = .5 liters

9

Compare alveolar to minute ventilation

* Minute ventilation:
=.5 x breathing rate
* Alveolar ventilation:
= (tidal volume –dead space) x breathing rate
= .35 x breathing rate

10

How does one calculate Dead Space volume?

* Observations:
- Dead space does not participate in ventilation and contains negligible CO2.
- Amount of CO2in regions of lungs involved in gas exchange = that of arterial blood (PaCO2).
- Therefore: VD = VTot * X * (PaCO2─ PECO2)/PaCO2

* Note:
- Dead space does not participate in gas exchange and, therefore, contains negligible carbon dioxide.
- Amount of carbon dioxide originating from regions of lungs involved in gas exchange equals that of arterial blood because blood gases equilibrate with alveolar gases during transit through the pulmonary circulation.

Pa = arterial pressure, Pe = expired pressure

11

Describe transpulmonary pressure

* Pressures resulting in the movement of air in and out of the lungs:
- Pleural pressure: Pressure of the fluid between parietal pleura and the visceral pleura
- Alveolar pressure: Pressure of the air inside the alveoli
- Transpulmonary pressure: Difference between the alveolar pressure and the pleural pressure

Difference in pressure between pleural and alveolar pressures during any point in the inspiration or expiration cycles.
- Measured in centimeters of water

- See slide 31-33

12

Describe the average pleural pressure range

* Pressure of fluid in the space between the visceral and parietal pleura
Measured in centimeters of water
- During inspiration: -5 to -7.5 cm H2O
- During expiration: -7.5 to -5 cm H2O

13

Describe alveolar pressure ranges

* Pressure of air inside the alveoli
Measured in centimeters of water
- During inspiration: 0 to -1 cm H2O
- During expiration: 0 to +1 cm H2O

14

Define and describe Compliance

* The extent (volume) to which lungs will expand for each unit increase in the transpulmonary pressure
* Remember:
- Transpulmonary pressure is the difference in pressure between the alveolar pressure and the pleural pressure.
- Alveolar pressure is the pressure of the air inside the alveoli.
- Pleural pressure is the pressure of the fluid in the space between the pleural and parietal pleura.
* Expressed in liters (volume of air) per centimeter of water (pressure).
- Normal: 200 ml air per centimeter of water
* Compliance is a measure of the expansibility of the lungs and trachea.

* Compliance (capacitance) = Increase in volume/Increase in pressure:
* Calculating compliance:
- Compliance is equal to distensibility X volume.
- Distensibility = Vinc/Pinc x Vorig
- Distensibility x Vorig = Vinc/Pinc = Compliance

- See Slide 39-40

15

Compare Compliance to Elastance

* Compliance is a measure of the ease with which a hollow viscus may be distended; i.e., the volume change resulting from the application of a unit pressure differential between the inside and outside of the viscus; the reciprocal of elastance.
* Elastance is a measure of the tendency of a hollow viscus to recoil toward its original dimensions upon removal of a distending or collapsing force.

16

Describe Surface Tension

* When water forms a surface with air, the water molecules on the surface of the water have an especially strong attraction for one another. As a result, the water surface is always attempting to contract. In lungs, this would cause the alveoli to try to collapse.
* The most important components of surfactant are:
- Dipalmitoylphosphatidylcholine (a phospholipid)
- Surfactant apoproteins
- Calcium ions
* Surfactant is produced by type II alveolar cells.
* Part of the molecule dissolves, while the rest of it spreads over the surface of the water in the alveoli.
* If air passages leading from the alveoli are blocked, the surface tension in the alveoli collapses the alveoli. This creates positive pressure in the alveoli:
- Pressure = 2 x surface tension / radius of the alveolus
* For an average size alveolus with a radius of about 100 micrometers and lined with normal surfactant:
- The pressure is about 4 cm of water pressure (3 mm Hg).
* If there is no surfactant, the pressure would calculate to about 18 cm of water pressure; about 4.5 times as great.

17

What are the approximate components of air at atmospheric pressure and at saturated alveoli pressure

* Atmospheric pressure:
- 78.09% N
- 20.95% O2
- .93% Ar
- 0.03% CO2
* At alveoli saturated with 6.18% water vapor:
- 73.26% N
- 19.65% O2
- .87% Ar 47
- 0.03% CO2

18

Describe the Three Gas Laws

* Dalton’s Law:
- The total pressure exerted by the mixture of non-reactive gasses is equal to the sum of the partial pressures of individual gasses.
* Boyle’s Law:
- For a fixed amount of an ideal gas kept at a fixed temperature, P (pressure) and V (volume) are inversely proportional.
* Henry’s Law:
- At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.

19

Describe the Ideal Gas Law

P = nRT / V
- P = pressure
- n = number of molecules
- R = universal gas constant
- T = temperature
- V = volume of container

20

Describe the Laws of Partial Pressures

* Partial pressure of O2 at alveolar membrane:
= 760 x 0.197 = 150 mm Hg
* Partial pressure of CO2 at alveolar membrane
= 0.21 mm Hg
* Pressure is directly proportional to the concentration of the gas molecules.
* Rate of diffusion is directly proportional to pressure caused by that gas alone.
* A gas dissolved in a fluid also exerts its own partial pressure against a cell membrane.
* The partial pressure of a gas in solution is determined not only by its concentration but also by the solubility coefficient of the gas. This is Henry’s law.
Partial pressure = [dissolved gas] / sol. Coefficient
- Solubility of oxygen = 0.024
- Solubility of carbon dioxide = 0.57
* Because carbon dioxide is more soluble in water than oxygen, It will exert a partial pressure (for a given concentration) that is less than 1/20th that of oxygen.

21

Describe Vapor Pressure of Water

* Vapor pressure of water is the partial pressure exerted to escape from the liquid phase to the gas phase.
* At normal body temperature (37° C) this vapor pressure is 47 mm Hg.
* Vapor pressure of water depends on the temperature of the water:

Temperature of 0 °C: Vapor Pressure = 5 mmHg
Temperature of 37 °C: Vapor Pressure = 47 mmHg
Temperature of 100 °C: Vapor Pressure = 760 mmHg

22

Describe Factors that affect rate of gas diffusion in a fluid

* Solubility of gas in the fluid
* Cross-sectional area of the fluid
* Distance through which the gas must diffuse
* Molecular weight of gas
* Temperature of fluid (remains reasonably constant)