Compliance of Cardio-Respiratory Systems

Question 1

Transmural Pressure

Answer 1

Pressure inside - pressure outside

So, a P_TM > 0 means that a fluid will flow out or expand the vessel

and a P_TM < 0 means that a fluid will flow in or compress the vessel

Question 2

As an elastic vessel stretches, . . .

Answer 2

. . . the recoil force increases and opposes the pressure inside of the vessel.

Question 3

Compliance

Answer 3

ΔP / ΔV

A characteristic of a closed, elastic structure that relates the change in volume of the structure to the change in pressure within the structure, i.e., the stiffness of the system.

Question 4

Transmural pressure determines the final volume of a vessel given its ___.

Answer 4

Transmural pressure determines the final volume of a vessel given its compliance.

Question 5

The stiffer or more rigid a structure, the more it resists. . .

Answer 5

being moved from its resting position

Question 6

The pressure inside of a vessel is equal to. . .

Answer 6

. . . the sum of the pressure outside the vessel (P_o) and the recoil pressure of the vessel (P_el).

Question 7

When we discuss the alveolus in the lung, the external pressure is the. . .

Answer 7

. . . pressure of the pleural space.

Question 8

When we discuss the alveolus in the lung, the elastic pressure is the. . .

Answer 8

. . . pressure generated by the elastic recoil of the lung tissue that has expanded.

Question 9

Left ventricles of different compliance on a LV pressure / LV volume curve

Answer 9

The way this graph is drawn, the slope of the curve is ΔP/ΔV, which is 1 / compliance

Question 10

Potential causes of reduced ventricular compliance

Answer 10

• Change in the structure of the ventricular tissue
• Energy required to pump calcium out of the cells is impaired

Question 11

Reduced ventricular compliance leads to . . .

Answer 11

. . . higher pressures in the ventricle (and consequently in the pulmonary veins and capillaries, which empty into the ventricle) for any given filling volume, and reduced filling of the ventricle, which can compromise the stroke volume

This higher pressure in the ventricle during diastole may cause fluid to leak into the lungs

Question 12

since relaxation of the ventricle is energy dependent, . . .

Answer 12

since relaxation of the ventricle is energy dependent, conditions that reduce oxygen supply to the ventricle can be associated with reduced compliance

Question 13

Structural states that may reduce ventricular compliance

Answer 13

• Fibrosis
• Endocarditis
• Bacterial plaques
• Amyloid deposits
• Hypertrophy of cardac muscle

Question 14

In respiratory physiology, forces are typically expressed as

Answer 14

In respiratory physiology, forces are typically expressed as the pressure generated by the height of column of water (in centimeters H2O)

Question 15

In cardiovascular physiology, forces are typically expressed as . . .

Answer 15

In cardiovascular physiology, forces are typically expressed as the pressure generated by the height of a column of mercury (in mm of Hg).

Question 16

Mercury is approximately ___ times as dense as water

Answer 16

Mercury is approximately 13 times as dense as water

Question 17

The volume of our respiratory system reflects the interaction between the actions of the ___ and ___.

Answer 17

The volume of our respiratory system reflects the interaction between the actions of the chest wall and lungs (as linked by the pleural space which separates them).

Muscles generated a negative pressure in the chest which acts against the elastic recoil of the lung tissue.

Question 18

Resting position

Answer 18

The volume occurring when there are no external forces acting on the structure. The resting position of the lungs and chest wall can only be determined in vitro

Question 19

The resting position of the chest wall alone is about ___

Answer 19

The resting position of the chest wall alone is about 75-80% of vital capacity

Question 20

Vital capacity

Answer 20

Difference between maximal inspiration and maximal expiration

Question 21

The resting position of the lung is ___

Answer 21

The resting position of the lung is below residual volume

Question 22

The pressure-volume relationships of the isolated lung, isolated chest wall and the respiratory system

Answer 22

Question 23

At the resting volume of the respiratory system, i.e., the point at which the transmural pressure is zero, . . .

Answer 23

At the resting volume of the respiratory system, i.e., the point at which the transmural pressure is zero, the tendency of the lung to collapse is offset by the tendency of the chest wall to spring out

Question 24

The volume of the respiratory system at which the transmural pressure is zero

Answer 24

functional residual capacity (FRC)

At volumes above FRC, the balance of forces is such that the respiratory system wants to get smaller; at volumes below FRC, the balance of forces pushes the system toward a higher volume

Question 25

The longer a muscle (up to certain limits) at the time that it is stimulated by a given neurological impulse, . . .

Answer 25

The longer a muscle (up to certain limits) at the time that it is stimulated by a given neurological impulse, the greater the tension generated

Same logic as the heart’s stretch/contractility relationship

Question 26

At low thoracic volumes, the inspiratory muscles are ___

At high thoracic volumes, the inspiratory muscles are ___

Answer 26

At low thoracic volumes, the inspiratory muscles are relatively long and thus generate a high tension when stimulated by a neurological impulse (end of expiration)

At high thoracic volumes, the inspiratory muscles are shortened and are less effective at generating tension for a given neural stimulus (end of inspiration)

Question 27

Gas trapping

Answer 27

As lung volume becomes smaller, some airways narrow (and resistance increases) to the point that expiratory flow is extremely low. Since you cannot exhale indefinitely, you may not be able to empty all of the air out of the lung that you would expect if end-expiratory volume were always determined merely by the balance of forces between lung and chest wall. Thus, some gas is effectively trapped in this base region of the lung,

Question 28

End expiratory lung volume

Answer 28

Generic term for the volume of the lung at the end of exhalation.

In healthy, resting individuals, EELV is equal to FRC. But, exercising individuals or individuals with a lung condition (emphysema, obesity, etc), where volume is not being determined solely by the elastic properties of the lungs and chest wall, they may be different.

Question 29

Pressure by Vital capacity curves for various lung conditions

Answer 29

Question 30

Total Lung Capacity

Answer 30

Volume of gas in the lung at maximal inspiration

Determinants: recoil of the chest wall, recoil of the lung, stiffness of the lung and chest wall, inspiratory muscle strength.

Making the respiratory system bigger – force generated by the inspiratory muscles

Making the respiratory system smaller – recoil force of the chest wall; recoil force of the lungs

Question 31

If you are using your expiratory muscles, the ___ and the ___ will not be the same.

Answer 31

If you are using your expiratory muscles, the EELV and the FRC will not be the same.

Question 32

Residual Volume

Answer 32

volume of gas in the lung at the end of a maximal expiratory maneuver

Determinants: tendency of the chest wall to spring outward, elastic recoil of the lung inward, airway narrowing (which prevents some of the gas in the small airways from exiting the lung), expiratory muscle strength to overcome the tendency of the chest wall to spring outward at low lung volumes.

Question 33

In individuals over age ___, dynamic considerations come into play in determining residual volume

Answer 33

In individuals over age 40, dynamic considerations come into play in determining residual volume

Question 34

Basic spirogram

Answer 34

Question 35

Surface tension is produced at. . .

Answer 35

an air-liquid interface

Question 36

Liquids with more surface tension / cohesion tend to. . .

Answer 36

. . . arrange in a shape that minimizes their surface area, resulting in a vector force inwards that creates a pressure according to Laplace’s Law.

Question 37

Laplace’s law for surface tension

Answer 37

P = 2T / r

Question 38

Alveolar size and position

Answer 38

Alveoli in the bottom of the lung are smaller than those at the top, due to their compression by the weight of the lung tissue.

Question 39

The alveolar surface tension problem

Answer 39

By Laplace’s law, left to their own devices, the alveoli would all collapse into one larger alveolus. In order to prevent this, and do reduce the surface tension of each alveolus proportional to its radius (to keep pressure constant, P = 2 T / r), type I pneumocytes produce a detergent, surfactant. Surfactant reduces the cohesion of the liquid, thus reducing its tension. As the radius of the alveoli increase, the density of the surfactant becomes greater.

Question 40

Major causes of changed lung compliance

Answer 40

• Change in elastic forces
• Change in surface tension

Question 41

Endless flow through an infinitely flexible tube

Answer 41

Question 42

Why might a patient with high thoracic pressure have a low blood pressure?

Answer 42

Because the heart cannot expand, meaning that its preload will be low, and therefore it is far to the left on a Starling curve.

Question 43

Under conditions of flow limitation, ___ is increased.

Answer 43

Under conditions of flow limitation, residual volume is increased.

Question 44

In severely obese patients, residual volume is. . .

Answer 44

. . . normal. Weirdly. It is normal because of two opposing pathologies.

1. From a fluid statics perspective, having an increased force from the chest wall should greatly reduce its ability to recoil outward, reducing the residual volume.
2. From a fluid dynamics perspective, increased chest wall weight translates to increased pleural pressure and thus a negative transmural pressure, causing heightened airway resistance to the point of decreased flow and exhalatory volume, increasing residual volume.

There is still increased work of breathing felt by the patient, because they must overcome a pressure barrier in order to breathe. But once they overcome that barrier, the compliance curve is the same.

Question 45

Mr. Jones is diagnosed with Amyloidosis in which the heart muscle is infiltrated with an abnormal material that reduces the compliance of the heart. You predict his blood pressure will. . .

Answer 45

increase / be higher than normal

It now takes a higher pressure to fill the heart to the same volume

Question 46

Ms. Smith is a long-time smoker, which has caused her to develop emphysema, which decreases the elastic recoil of the lung tissue. You predict that her FRC will . . .

Answer 46

increase / be higher than normal

The functional residual capacity is determined by the balance of forces between lung recoil inward, chest recoil inward, and the inspiratory muscles pulling the chest wall outward. With reduced elastic recoil of the lungs, the balance of forces is shifted such that lung volume is greater at TLC.

Question 47

Systolic vs Diastolic Failure

Answer 47

Question 48

Preload and Afterload on cardiac PV cycle

Answer 48