Respiratory Physiology: Mechanisms II

Question 1

What three opposing force must be overcome for inspiration to occur?

Answer 1

• Elastic recoil
• Inertance or impedance of acceleration of the respiratory system
• Frictional resistance

Question 2

_______________ is determined by airflow and not by a change in lung volume.

Answer 2

Frictional resistance

Question 3

The average velocity of air is equal to

Answer 3

Overall flow rate/ Cross-sectional area

Question 4

Which type of airflow is being described below?

Airflow occurs at low flow rates and in a pattern that is parallel to the walls of the cylinder.

Answer 4

Laminar

Question 5

Which type of airflow is being described below?

Velocity of airflow increases at points of bronchial division- the flow stream becomes unstable and eddy currents cause distibances in flow.

Answer 5

Transitional flow

Question 6

Which type of airflow is being described below?

Increased flow rates; currents parallel and perpendicular to the walls of the tube

Answer 6

Turbulent flow

Question 7

A reynolds number greater than _______ results in turbulent flow.

Answer 7

2000

Question 8

Which regions are more likey to experience turbulent flow?

Answer 8

Conducting zone larger airways

Example: Nose, trachea, bronchi

NOTE: Small airways of gas exhange have laminar flow

Question 9

How is turbelent flow produced?

Answer 9

By the friction between moving air and the wall of the tube. As flow increases the eddy currents occur at transitional points

Question 10

What is the relationship of gas viscocity and driving pressure in cases of laminar flow, turbelent flow, and transitional flow, respectively?

Answer 10

Laminar Flow

• Driving pressure is directly proportional to gas viscocity

Turbulent flow

• Driving pressure is proportional to square of flow and is dependent of gas density

​Transitional flow

• Driving pressure is proportional to both gas density and gas viscocity

Question 11

How is reynold number calculated?

Answer 11

r= radius

v= average velocity

d=density

η= viscosity

Question 12

Flow is mostly ___________throughout the bronchial tree

Answer 12

transitional

Question 13

What is one reason why identifying small airway disease is challenging?

Answer 13

Laminar flow, which is present in small airways, is silent.

NOTE: Breathing sounds heard with a stethoscope are due to turbulent flow

Question 14

Stridor

Answer 14

Noisy breathing with high-pitched crowning sound

Question 15

What is the cause for stridor?

Answer 15

Turbelent air currents attempt to force their way through narrow breathing passages

Question 16

Laryngomalacia

Answer 16

Soft, immature catilage of the upper larynz collapses inward during inhalation, causing airway obstruction

NOTE: Laryngomalacia is one of the most common causes of chronic stridor

Question 17

How is resistance calculated?

Answer 17

Question 18

Airway resistance

Answer 18

Frictional resistance of the entire airway from the tip of the nose (or mouth) to the alveoli

Question 19

Pulmonary Resistance

Answer 19

Frictional resistance afforded by the lungs and airways combined

Question 20

Chest Wall Resistance

Answer 20

Frictional resistance of the chest wall and abdominal structures

Question 21

Are bronchioles in parallel or series?

Answer 21

Parallel

Question 22

How can resistance of a lower airway be calculated?

Answer 22

R= R_large + R_medium + R_small

NOTE: The 1st eight genetations of the conductin system (trachea, bronchi) provide the majority of resitance in the airways. Small airway DO NOT make a significant contribution

Question 24

Do small airways make a significant contribution to the overall total airway resistance of the bronchial tree?

Answer 24

No because the airflow velocity is very low due to the increased cross-sectional area. Also, because bronchioles are in parallel not in series.

NOTE: An individual bronchiole has a high resistance but in total the resistance is small.

Question 25

Which component of the lower airway provides the greatest resistance?

Answer 25

Bronchi

Question 26

What factors increase airway resistance?

Answer 26

Airway mucus Edema Contraction of the bronchiole smooth muscle Density and viscosity of the moving gas **NOTE:** There is a slightly higher airway resistance during exhalation, than during inhalation, because the flow rate is slightly slower.

Question 27

Airways lengthen during _________ (inspiration/expiration) and shorten during ______ (inspiration/ expiration) with the phases of respiration.

Answer 27

Lengthen; Shorten

Question 28

What factors contribute to airway resistance?

Answer 28

Number, length, and cross-sectional area **NOTE:** Of these factors, cross-sectional area is the most important because resistance is inversely proportional to the 4th power of the radius.

Question 29

What are the two opposing forces that control airway size?

Answer 29

* Smooth muscle and elastic forces * Tend to constrict airways and decrease the cross-sectional area * Outward traction of the airway * Due to the interdependence of alveoli and terminal bronchioles and because of **positive transpulmonary pressure**

Question 30

Conductance

Answer 30

1/ Airway resistance

Question 31

\_\_\_\_\_\_\_\_\_\_\_\_\_ (increased/decreased) gas density increases airway resistance.

Answer 31

Increased

Question 32

Status Asthmaticus

Answer 32

A clinical condition characterized by bronchospasm, edema, and mucus in the airway resulting in increased airway resistance

Question 33

Treatment for Status Asthmaticus

Answer 33

O2-He low density gas mixture

Question 34

How does elastic recoil affect the caliber of the airway?

Answer 34

* Direct traction on small intapulmonary airways * Effects on intrapleural pressure

Question 35

At FRC, what is the normal airway resistance?

Answer 35

1-3 c, H2O/ L.sec **NOTE:** Airway resistance is higher in children due to small overall airway size

Question 36

Which neurohumoral molecules cause vasoconstriction of the airway smooth muscles?

Answer 36

Histamine Ach Leukotrienes **NOTE:** These molecules are released from mast/epithelial cells

Question 37

\_\_\_\_\_\_\_\_\_\_\_\_\_ (parasympathetic/sympathetic) nervous system causes constriction of airways, while __________ nervous system causes dilation of airways.

Answer 37

Parasympathetic; sympathetic

Question 38

What drug can be used to access airway hyperresponsiveness?

Answer 38

Metacholine (a histamine-like compound)

Question 39

Parasympathetic leads to airway __________ (**constriction/relaxation**), blood vessel _________ (**dilation/ constriction**) and __________ (**increased/decreased**) glandular secretion.

Answer 39

constriction; dilation; increased

Question 40

Sympathetic leads to airway __________ (constriction/relaxation), blood vessel _________ (dilation/ constriction) and __________ (increased/decreased) glandular secretion.

Answer 40

Relaxation; constriction, decreased

Question 41

Which factors can lead to constriction of airways?

Answer 41

Parasympathetic stimulation Acetylcholine Histamine Leukotrienes Thromboxane A2 Serotonin a-adrenergic agonists Decreased PCO2 in small airways

Question 42

Which factors can lead to dilation of airways?

Answer 42

Sympathetic stimulation B2 receptors Circulating B2 agonists NO Increased PCO2 in small airways Decreased PCO2 in small airways

Question 43

Dynamic compliance

Answer 43

The change in volume of the lungs divided by the distending pressure during the course of a breath.

Question 44

How is surface tension related to compliance?

Answer 44

An increase in surface tension results in a decrease in compliance. This is because an increase in surface tension leads to an increase in pressure. Rememeber, pressure and compliance are inversely proportional, so an increase in pressure would result in a decrease in compliance.

Question 45

Is surfactant more available at larger volumes or lower volumes?

Answer 45

**Larger.** This facilitates expansion of the lungs. Less surfactant is available during tidal volume. **REMEMBER:** Tidal volume is the lung volume representing the normal volume of air displaced between normal inhalation and exhalation when extra effort is not applied.

Question 46

What is the relationship between compliance, resistance, and volume?

Answer 46

* If two tubes have the same compliance but a different resistance, the **volume does not change,** if both are given sufficient time to fill * If two tubes have difference compliances, the volume will change **NOTE:** Increased respiratory frequency in patients with small airway obstruction do not allow insufficient time to fill and will not contribute to dynamic compliance

Question 47

How do sighs and yawns help to increase dynamic compliance?

Answer 47

By restoring the surfactant layer during the increase tidal breath

Question 48

Explain expiratory flow limitations.

Answer 48

During expiration, as the lung volume decreases so does the flow rate.

Question 49

Why is expiratory flow limited?

Answer 49

This occurs when the floppy distensible tubes become compressed during normal expiration. Pressure outside the airway exceeds to pressure inside the airway

Question 50

How and when expiratory flow limitation occurs is important in various disease states, such as Chronic Obstructive Pulmonary Disease. Why?

Answer 50

* During normal conditions, collapse near tubes **with cartilage**; dynamic airway compression * In disease state, collapse occurs near small airways devoid of cartilage, leading to **premature airway closure**

Question 51

The cross-sectional area of the airways decreases toward the trachea and the velocity _________ (increases/decreases)

Answer 51

Increase

Question 52

What happens to tracheal dimensions and air velocity during cough?

Answer 52

1. At start of a cough, subject takes a deep breath ~1.5 time VT 2. Causing an **increase in elastic recoil**; the glottis closes and chest wall muscle contract causing an **increase in pleural pressure**. 3. The glottis opens and **air is forcefully expelled.** 4. During cough, the non-cartilaginous posterior membranous region of the trachea is compressed causing **tracheal diameter to narrow.** 5. The **turbulent airflow** at the site of compression is the sound that we refer to as “cough”.

Question 53

How does the relationship between airway closure and volume levels differ between healthy subjects and subects with COPD?

Answer 53

In healthy subjects, airway closure occurs at low volumes. In subjects with COPD, airway closure occurs at much higher volumes.

Question 54

What are the two components that contribute to the work of breathing?

Answer 54

* **Elastic component** * **​**Overcoming the recoil of the chest wall and lung parenchyma * Work to overcome the surface tension * **Resistive component** * **​**Tissue (lung) and airway resistance

Question 55

How is work of breathing calculated?

Answer 55

W= Pressure x Change in volume * **Pressure** is the change in transpulmonary pressure required to overcome the elastic and resistance work of breathing * **Volume** the volume of gas moving into and out of the lung

Question 56

Mechanical work of a normal lung

Answer 56

Question 57

Mechanical work in a lung with reduced compliance

Answer 57

Question 58

Mechanical work associated with increased airway resistance

Answer 58

Question 59

Breathing pattern associated with pulmonary fibrosis?

Answer 59

Shallow/rapid pattern

Question 60

Breathing pattern associated with obstructive pulmonary disease

Answer 60

Breath more deeply and slowly

Question 61

Normal respiratory rate

Answer 61

breaths/min-