SWG Resp Exam 1: Mechanisms of Breathing (SL/P900)

What are the two major effects of surface tension? $$$$$

1) DECREASES compliance of the lung 2) Maintains HYSTERESIS of the lung

List all the pertinent steps involved in *INSPIRATION* $$

1) Diaphragm contracts 2) Chest wall expand outwards 3) Increase in volume of pleural cavity Decrease in the intrapleural pressure 4) Increase in alveolar volume Decrease in alveolar pressure (Pi)

What are the two causes of the elastic forces of the lung? $$

1) Elastic TISSUE of the lung/thoracic wall 2) Surface tension of fluid that lines the inside walls of the alveoli

Airway resistance is primarily due to what two things?

1) Internal friction between gas molecules 2) Friction between the gas molecules and the WALLS of the airways

TEST: What are the three types of air flow?

1) Laminar 2) Transitional 3) Turbulent

RECAP: List some of the functions of surfactant $$$

1) Lowers surface tension of alveoli and lung, which increases lung compliance and DECREASES WORK of breathing 2) Promotes stability of alveoli so they don't COLLAPSE Also prevents transudation of fluid into alveoli

What is a diagnostic factor in a flow-volume curve for obstructive disease? Restrictive disease?

Both will have reduced airflow from normal but obstructive diseases will have a concave curve

What is the *equal pressure point* hypothesis? $$

*From Lange Pulmonary Physiology:* During forced expiration, there is a point along the airways where the pressure inside the airway is equal to the pressure outside. The transmural pressure gradient is 0 here (blue arrows). Above that point, the transmural pressure gradient is negative and the airway will collapse if cartilaginous support is insufficient to keep it open. As the forced expiratory effort continues, the equal pressure point will move down the airway toward the alveoli because, as the muscular effort increases, intrapleural pressure increases and because, as lung volume decreases, alveolar elastic recoil pressure decreases. *As the equal pressure point moves down the airway, dynamic compression increases and the airways ultimately begin to collapse*. *This airways closure can be demonstrated only at especially low lung volumes in healthy subjects, but the closing volume may occur at higher lung volumes in patients with emphysema.*

Answer the question in the image

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Answer the question in the image

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At the end of expiration, the muscles of respiration are (tense/relaxed). The lung has a natural (outward/inward) elastic recoil, while the chest wall has a natural (outward/inward) elastic recoil

At the end of expiration, the muscles of respiration are RELAXED. The lung has a natural INWARD elastic recoil, while the chest wall has a natural OUTWARD elastic recoil. These BALANCE each other out!

List all the pertinent steps involved in *EXPIRATION* $$

Basically opposite from inspiration 1) Diaphragm relaxes 2) Chest wall (CW) compresses inwards 3) Decrease in pleural cavity Increase in intrapleural pressure 4) Decrease in alveolar volume, increase alveolar pressure (Pi)

With the (lung/chest wall), as you increase in pressure you decrease in volume

CHEST WALL - Opposite for lung (increase in pressure, increase in volume)

Consider two elastic pipes in two separate chambers with different set pressures. You put water into those pipes with the same pressure. What will determine the flow in these situations: 1) Chamber pressure > pipe 2) Chamber pressure< pipe

Chamber pressure > airway pressure = flow will be determined by pressure difference (Transmural) between the tube and the chamber Chamber pressure <<< airway pressure = flow will only be determined by tube pressure

As surface tension increases, the size of the alveoli (increases/decreases), and the pressure (increases/decreases) $$$

DECREASES (because the fluid lining the walls of the alveoli is pulling and becoming tighter, drawing the alveolar walls inwards) - And as the alveoli get SMALLER, the pressure in the alveoli INCREASES! (assuming tension to be constant)

During dynamic compression of the airways which limits air flow during forced expiration, the flow is determined by ________ pressure $$$$$

DYNAMIC compression of the airways limits air flow during forced expiration, and the flow is determined by *TRANSPULMONARY/Transmural pressure* (alveolar - intrapleural) - This is different from normal breathing, which is driven by pressure gradient between alveoli and atmosphere

The pressure outside and the pressure inside the lungs are equal to zero during what parts of the respiratory cycle? RECAP: Pleural pressure increases on (inspiration/expiration) and decreases on (inspiration/expiration). It will always be less than ________ pressure. $$

END OF EXPIRATION and INSPIRATION (no air movement) Pleural pressure increases on EXPIRATION and decreases on INSPIRATION. It will always be less than ALVEOLAR pressure (so the lung doesn't collapse!)

TEST: What establishes the driving pressure in the airways and divides it into downstream and upstream segments? When is this established?

EQUAL PRESSURE POINT (EPP) - This is the point where the alveolar pressure is EQUAL to the pleural pressure - This is established at the PEAK EXPIRATORY flow when the pressure inside airway = pressure outside airway

What is the inverse of compliance?

Elastic recoil Compliance is the ease at which something can be stretched. Elastance is the force that opposes stretching or distortion.

Respiration can be divided into external and internal respiration. What does each exactly mean?

External: Gas exchange between air and blood - with the driving force being the pressure gradient generated via muscle contraction Internal: Gas exchange between blood and tissues

TRUE or FALSE: During expiration, the pleural pressure is positive so it can drive air out of the lungs Pleural pressure is always ___ than alveolar pressure $$$

FALSE! Pleural pressure is NEVER positive during the respiration cycle, or else the lungs will collapse! *Pleural pressure is always smaller than alveolar pressure, if not, the lung will be collapsed.* $$$

TRUE or FALSE: Since the functional division of bronchioles are very narrow collectively, they have very high resistance

FALSE, they actually have very LITTLE resistance because there are SO MANY of them in PARALLEL (much like capillaries) Medium-sized bronchi are where resistance occurs - Recall, in the cardio system, the arterioles are the resistance vessels too, not the capillaries

What happens with forced expiration in the airways?

Forced expiration will create positive intrapleural pressure causing transmural pressure (between the alveoli and the intrapleural space) to go down which means that parts of the airways will be compressed and there will be greater resistance to airflow. This increased resistance is called *dynamic compression*. This dynamic compression is further exacerbated during expiration because here, so very little air is left (lung volume decreased) in the alveoli to develop a larger alveolar pressure.

TEST: On inspiration, the pressure outside the lungs are (greater/lesser) than the pressure inside the lungs What happens at the end of inspiration to pressures? $

GREATER - And will move towards being equal with the pressure inside (max inspiration) - Diaphragm CONTRACTS, and both the PLEURAL CAVITY pressure and the pressure inside the LUNGS decrease (Pi) By the end of inspiration, the pressure outside and the pressure inside the lungs are equal to zero

TEST: Decreasing the radius of the tube will significantly (increase/decrease) the resistance of the tube to laminar flow *If airway radius is reduced by 50%, what would be the change in resistance?*

INCREASE! Resistance will increase to the 4th power or 16 fold

Emphysema (increases/decreases) lung compliance

INCREASES! Emphysema destroys the alveolar septal tissue that normally OPPOSES lung expansion, so it indeed does increase COMPLIANCE (distensibility) - Elderly folks also have increased compliance

What kind of airways do turbulent flow happen the most? TRUE or FALSE: Unlike turbulent flow, laminar flow can be heard with a stethoscope

In LARGER airways (nose, mouth, trachea) where there are HIGHER FLOW RATES FALSE, laminar flow = SILENT - Turbulent flow can be HEARD

Inspiration is a(n) (active/passive) process, while expiration is a(n) (active/passive) process The ________ is the most important muscle of inspiration, while the _______ muscles are the most important muscles of expiration

Inspiration: ACTIVE Expiration: PASSIVE (at REST, not during exercise or forced) Inspiration: DIAPHRAGM Expiration: ABDOMINAL muscles

Intrathoracic pressure refers to pressure within the ___________, which normally is slightly (more/less) than atmospheric pressure. This is what is known as _______ pressure and is what allows the lungs to (inflate/deflate) $$

Intrathoracic pressure refers to pressure within the *PLEURAL CAVITY* (also known as intraPLEURAL pressure) - This is normally slightly LESS than atmospheric pressure, aka *NEGATIVE pressure*, and is what allows the lungs to *INFLATE* (air goes into the lung down gradient)

What is Boyle's law and how does it pertain to breathing?

It states that within two closed but connected systems, changes in the pressure and volume in one chamber will affect the other in the following way: P1V1 = P2V2

AGAIN: The more compliant the lungs are, the (more/less) the alveolar elastic recoil

LESS (alveolar elastic recoil is OPPOSITE of lung compliance) - If the lungs could distend more and increase in volume, it would make sense that the elastic recoil of the alveoli, which wants to collapse, would be less so it can allow the lungs to stay inflated!

Airway resistance is very high at (low/high) lung volumes?

LOW

TEST: Surface tension can be described by using what law, which states what?

Law of LaPlace: - P(alveoli) = (2 x surface tension) / alveoli radius - P = (2 x T) / R *Pressure in the alveoli is directly proportional to surface tension and inversely proportional to alveolar radius)

What is pulmonary compliance a combination of?

Lung compliance + chest wall compliance - based on their elastic properties

TEST: Where is the major site of airway resistance? $$$$$

MEDIUM-SIZED BRONCHI!

TEST: Define compliance of the lung. What is it a reflection of? $$

Measure of the lung's ability to stretch and expand. - Compliance = Δ lung volume / Δ intrapleural pressure

TEST: In obstructive diseases, the ________ volume is greatly increased. In restrictive diseases, the peak _______ flow and total lung ________ are decreased.

Obstructive: RESIDUAL volume is greatly INCREASED (after expiration, because you have trouble getting air OUT) Restrictive: Peak EXPIRATORY flow and total lung CAPACITY are decreased - Restricts lung expansion (problem getting air IN)

Laminar flow is _______ streams of flow in the (small/large) airways, with the velocity at the (edge/center) twice as fast than at the (edge/center)

PARALLEL streams of flow in the SMALL airways, with the velocity at the CENTER twice as fast than at the edges (due to friction at the edges but not in the center)

When will the pressure of the chest wall be equal to the outside pressure P = 0? How much does the chest wall expand?

PNEUMOTHORAX - Chest wall expands at volume to take over about 75% of the total lung capacity

RECALL: What law describes resistance of laminar flow through a tube? What is the main relationship described by this law? $$$

POISEUILLE Law: R = 8nL / (pi * r^4) n = viscosity of fluid L = length of tube r = radius of tube R = Resistance *Resistance to flow is directly related to length and inversely (and exponentially) related to radius*

TEST: With a restrictive disorder, the (inspiratory/expiratory) phase of breathing requires more work With an obstructive disorder, the (inspiratory/expiratory) phase of breathing requires more work

Restrictive: INSPIRATORY phase requries more work Obstructive: EXPIRATORY phase requires more work

What is the effect of surface tension on alveoli if there was no surfactant? $

Smaller alveoli will develop greater pressure than larger ones when air fill and thus air will be shifted to large alveoli. This would be quite a bother.

Surfactant (increases/decreases) surface tension which (increases/decreases) lung compliance $$

Surfactant DECREASES surface tension which should INCREASES lung compliance!

A perterm infant has a surfactant deficiency, which of the following parameters are present in the preterm infant compared to the normal infant? Alveolar surface tension = (increased/decreased) Pulmonary compliance = (increased/decreased)

Surfactant deficiency Alveolar surface tension - increased Pulmonary compliance - decreased

TEST: What is surfactant? What kind of cells produce it, and what is it's function? $$$

Surfactant: Phospholipid Produced by: Alveolar Type II cells Function: *LOWER SURFACE TENSION* by becoming interspersed between H2O molecules (PREVENTS ALVEOLAR WALLS FROM STICKING TO EACH OTHER as they collapse!)

TRUE or FALSE: Longer distances increase flow resistance

TRUE, as distance and resistance are directly proportional

TEST: List whether the following increases or decreases in relation to INCREASED airway resistance: - Airway diameter - Turbulence - Rapid breathing - Lung volume - Bronchial smooth muscle contraction - Gas density $$$$

The following can cause an increase in airway resistance: - Airway diameter DECREASES - Turbulence INCREASES - Rapid breathing INCREASES (which increases turbulent flow) - Lung volume DECREASES - Bronchial smooth muscle contraction INCREASES - Gas density INCREASES Main point: *Any factor that decreases airway diameter, or increases turbulence will increase airway resistance*

The lung volume at any given pressure during (inspiration/expiration) is larger than that during (inspiration/expiration)

The lung volume at any given pressure during EXPIRATION is larger than that during inspiration - Even as you are exhaling, the pressure in the lungs is still greater than if you were inhaling

What is *hysteresis* in terms of pulmonary physiology? Why? $$

The phenomenon where inflation and deflation curves are not the same on a pressure-volume curve. Main reason: surface tension (though the mechanics are still unclear) Explanation provided by Lange Pulmonary Physiology: 1) The role of *surfactant film* - Surfactant effects on decreasing surface tension during inspiration is LESS than during expiration which could mean: - Inspiration = greater surface tension = a bit harder for air to fill - Expiration = less surface tension = less force pressuring air to leave so it stays in longer 2) Some alveoli or small airways may open on inspiration but close on expiration and this may be responsible for the lower inflection point seen on the pressure-volume curves

Define Functional Residual Capacity (FRC) At Functional Residual Capacity, the alveolar pressure is ______.

The volume of air present in the lungs at the end of passive expiration ZERO! (No air movement) - And since this is at the end of expiration, the inward pull of the lung is balanced by the outward pull of the chest wall

What happens to the equal pressure point in obstructive conditions such as emphysema?

There is LESS of a gradient, and then EPP occurs more or less throughout the entire airway so that air DOES NOT LEAVE the airway due to the lack of driving pressure (pleural pressure isn't higher than alveolar pressure to drive air out) - This is due to the lung parenchyma being weaker (loss of bronchiole elastic recoil) so when air leaves, it can drag the wall and collapse it. This combined with dynamic obstruction is problematic.

What is surface tension specifically in reference to the lungs? When would surface tension be theoretically eliminated?

Unbalanced forces by water molecules that are lined near a surface generate surface tension. Air is required for this to occur. Surface tension would be absent if the lungs were filled completely with fluids because then the fluid forces will be balanced out

Compliance of the lung is (volume/pressure) dependent. What happens to compliance at: - HIGH lung volume - LOW lung volume The (higher/lower) the compliance, the easier it is for lungs to INFLATE $$$

VOLUME dependent HIGH lung volume = LOW compliance LOW lung volume = HIGH compliance HIGHER (but it isn't necessarily a good thing as we see higher compliance in many pulmonary pathologies)

When the pleural cavity is ruptured/damaged, the intrapleural pressure (increases/decreases) and may exceed the ________ pressure, causing _______ on the lungs known as a ___________

When pleural cavity is ruptured/damaged, intrapleural pressure INCREASES and may exceed the ATMOSPHERIC pressure, causing COMPRESSION on the lungs known as a PNEUMOTHORAX