Physiology: Mechanics of Breathing

TEST: 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 3) Prevents transudation of fluid into alveoli

Give the regular RR range at rest and during exercise

At rest: 10-20 times/min During exercise: 40-45 times/min

TEST: 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!

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)

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

DECREASES (because the fluid lining the walls of the alveoli is pulling and becoming tighter, drawing the alveolar walls inwards)

TEST: Surface tension (increases/decreases) the compliance of the lung and maintains ________ of the lung

DECREASES compliance of the lung and maintains HYSTERESIS of the lung

_______ compression of the airways limits air flow during forced expiration, and the flow is determined by ________ pressure

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

TEST: During inspiration, the diaphragm (relaxes/contracts) and both the ______ _____ pressure and the pressure inside the ______ decrease

Diaphragm CONTRACTS, and both the PLEURAL CAVITY pressure and the pressure inside the LUNGS decrease (Pi)

TEST: The pressure outside and the pressure inside the lungs are equal to zero during what parts of the respiratory cycle?

END OF EXPIRATION and INSPIRATION (no air movement)

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

TEST: During expiration, the diaphragm (relaxes/contracts), the rib cage volume (increases/decreases) and both the ______ _____ pressure and the pressure inside the ______ increase

Expiration: - Diaphragm RELAXES - Rib cage volume DECREASES - Both the PLEURAL CAVITY and pressure inside the LUNGS INCREASE

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

External: Gas exchange between air and blood 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

FALSE! Pleural pressure is NEVER positive during the respiration cycle, or else the lungs will collapse!

AGAIN: At rest, there is (positive/negative) intrapleural pressure, allowing _______ of the lungs

NEGATIVE intrapleural pressure, allowing EXPANSION of the lungs

TRUE or FALSE: Balanced forces at the surface generate surface tension

FALSE, UNBALANCED forces generate surface tension

TRUE or FALSE: Unlike turbulent flow, laminar flow can be heard with a stethoscope

FALSE, laminar flow = SILENT - Turbulent flow can be HEARD

TEST/TRUE or FALSE: Surfactant decreases lung compliance

FALSE, surfactant decreases surface tension which should INCREASE lung compliance!

TRUE or FALSE: The intrapleural pressure at the end of expiration is more negative than during inspiration

FALSE, the intrapleural pressure is more negative DURING INSPIRATION so air can flow IN to the alveoli - At the end of expiration, intrapleural pressure is still negative but not as much

TRUE or FALSE: Since bronchioles are very small, they have very high resistance

FALSE, they actually have very LITTLE resistance because there is SO MANY of them in PARALLEL (much like capillaries)

TEST: On inspiration, the pressure outside the lungs are (greater/lesser) than the pressure inside the lungs

GREATER - And will move towards being equal with the pressure inside (max inspiration)

What is the phenomenon called that describes why the inflation and deflation curves are not the same on a pressure-volume curve?

HYSTERESIS

TEST: Decreasing the radius of the tube will significantly (increase/decrease) the resistance of the tube to laminar flow

INCREASE!

What kind of airways do turbulent flow happen the most?

In LARGER airways (nose, mouth, trachea) where there are HIGHER FLOW RATES

Inspiration is a(n) (active/passive) process, while expiration is a(n) (active/passive) process

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

RECAP: Describe the progression of alveolar pressure through one cycle of respiration

Inspiration: Alveolar pressure slightly decreases as you're breathing in, and as you reach max inhalation and can't breath in anymore does the alveolar pressure start increasing Expiration: Alveolar pressure continues to increase until you start running out of breath to exhale, in which it starts decreasing

The ________ is the most important muscle of inspiration, while the _______ muscles are the most important muscles of expiration

Inspiration: DIAPHRAGM Expiration: ABDOMINAL muscles

TEST: 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)

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!

TEST: Surface tension can be described by using the Law of _______, which states what?

Law of LaPlace: - P(alveoli) = (2 x surface tension) / alveoli radius - P = (2 x T) / R As surface tension increases, so does the pressure in the alveoli! - And as the alveoli get SMALLER, the pressure in the alveoli increases! (assuming tension to be constant)

TEST: Where is the major site of airway resistance?

MEDIUM-SIZED BRONCHI!

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)

RECALL: What law describes resistance of laminar flow through a tube?

POISEUILLE Law: R = 8nL / (pi * r^4) n = viscosity of fluid L = length of tube r = radius of tube R = Resistance

RECAP: Pleural pressure increases on (inspiration/expiration) and decreases on (inspiration/expiration). It will always be less than ________ pressure.

Pleural pressure increases on EXPIRATION and decreases on INSPIRATION. It will always be less than ALVEOLAR pressure (so the lung doesn't collapse!)

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

Reflection of the DISTENSIBILITY of the lungs - Compliance = change in lung volume / change in intrapleural pressure

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

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: REDUCE alveolar SUFACE TENSION by becoming interspersed between H2O molecules (PREVENTS ALVEOLAR WALLS FROM STICKING TO EACH OTHER as they collapse!)

TRUE or FALSE: By the end of inspiration, the pressure outside and the pressure inside the lungs are equal to zero

TRUE!

TRUE or FALSE: Emphysema increases lung compliance

TRUE! Emphysema destroys the alveolar septal tissue that normally OPPOSES lung expansion, so it indeed does increase COMPLIANCE (distensibility)

TEST/TRUE or FALSE: Pleural pressure is always smaller than alveolar pressure

TRUE! If not, the lung will collapse!

TRUE or FALSE: Longer distances increase flow resistance

TRUE, as distance and resistance are directly proportional

TRUE or FALSE: At the end of expiration, atmospheric pressure is equal to alveolar pressure

TRUE, both are 0 cm H2O

TRUE or FALSE: Pressure is greater inside the lungs during exhalation

TRUE, so air flows down its pressure gradient and moves OUT of the lungs

TEST: List whether the following increases or decreases to cause an INCREASE 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

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

TEST: Define Functional Residual Capacity (FRC)

The volume of air present in the lungs at the of passive expiration

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)

Complaince of the lung is (volume/pressure) dependent and it is the inverse of ______ _____ of the lung

VOLUME dependent - Greater compliance at low lung volume Inverse of the ELASTIC RECOIL of the lung

Define alveolar pressure (Palv)

Water pressure (cm H2O) held within the alveoli

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

At Functional Residual Capacity, the alveolar pressure is ___

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