1 - Repiratory Mechanics ( I )

Question 1

Objective: Define lung compliance

Answer 1

Math: Slope of PV Curve

Word: “Softness”

C = ΔV / ΔP

Inverse of elastance

Question 2

Objective: Define elastic recoil of lung and chest wall

What is defined at equilibrium?

Answer 2

Chest - Elastic recoil = expand

Lung - Elastic recoil = collapse

At equilibrium, these two forces are equal and no air is moving in or out; defines the Functional Resdiual Capacity (FRC)

Question 3

Objective: What is the role of surface tension and surfactant in the lung?

Answer 3

• Inserts between water molecules along surface (like cholesterol in a membrane) lowering the surface tension
  
  • Primary molecule is DPPC
• [Surfactant] α 1 / Surface Tension
• Small Molecules have high [Surfactant] due to small surface area; thus will have the most reduced surface tension

Question 4

Objective: How does lung volume and pressure change during inhalation?

Answer 4

Start of Inhalation: Balanced; Transmural Pressure (P_TM) = Elastic Recoil of Lungs; FRC, mouth open and all muscles relaxed

Begin Inhalation: Addition force is added as diaphragm contracts (volume increases); pressure lowers; P_TM > P_{Elastic Lung}; Lungs fill will air and expand

During Inhalation: Lung volume increases, pressure in alveoli decreases to negative

End Inhalation: Lungs stretched, elastic recoil force increased to balance with P_TM; air no longer enters lung

Question 5

Objective: How does pressure change during inhalation?

Answer 5

Before: P_Alv = P_Atmosphere (0)

Start/During: Volume Increase, P_Tm > P_{Lung Recoil} ; Air enters lung

End: P_{Lung Recoil} Increases, until = P_Tm; Air no longer flows due to lack of gradient

Question 6

Objective: What is a pneumothorax (two types)

What is atelectasis?

Answer 6

1. Tension: Air accumulates in pleural cavity; sharp pleuritical pain; increasing; mediastinum shift away; medical emergency
2. Non-Tension: Air in pleural cavity, does not increase.

Atelectasis = Partial/Total Collapse of Lung; mediastinum shift towards collapse

Question 7

What is the innervation difference of the visceral and parietal pleura?

Answer 7

Visceral Pleura is insensitive to pain

Pareital pleura inflammation = pleurisy (pleuritis); sharp pain, can spread to shoulder

Question 8

What areas of the airway does gas exchange take place?

Answer 8

The last four layers (the smallest)

Question 9

Define:

Apnea

Eupnea

Dyspnea

Hyperpnea

Bradypnea

Tachypnea

Orthopnea

Answer 9

Apnea - Absence of spontaneous ventilation

Eupnea - Normal spontanteous breathing

Dyspnea - Difficulty breathing

Hyperpnea - Increased volume of breathing (with or w/out increased frequency)

Bradypnea - Decrease in rr

Tachypnea - Increase in rr

Orthopnea - Dyspnea which occurs when lying flat (person will sleep propped up, or in chair)

Question 10

Define: Functional Residual Capacity (FRC)

Answer 10

Amount of gas present in lunch when mount oppen, and respiratory muscles are relaxed

Question 11

What two factors result in lung recoil?

What has the largest affect?

Answer 11

1. Lung tissue elastic recoil (think balloon); act to collapse the lung
2. Surface Tension forces; act to collapse the lung

- - - -

Surface Tensionis the main contributor

Question 12

Laplace’s Law?

Small vs Large Alveolus

Answer 12

P = T / (r/2)

P = Pressure

T = Surface Tension

R = Radius

P α T

P α 1 / r

In the absence of surfactant–small alveoli would want to collapse (higher P, smaller r – air would flow down gradient to larger alveoli).This would create a gas-exchangeright-to-left shunt

Question 13

Is normal inhalation and exhalation an active or a passive process?

What role to accessory muscles play? (clinical presentation)

What about forced exhalation?

Answer 13

Inhalation: Active, Diaphragm contacts and flattens–volume of thorax increases

Clinical: During exercise, coughing, sneezing–COPD–patients breath in “tripod” position to optimize use of accessory muscles in shoulder girdle

Exhalation: Passive, diaphragm relaxes, volume decreases; driven by elastic recoil of the lung and surface tension

Forced Exhalation: Active process used during exercise o hyperventilation; uses abdominals / internal intercostals

Question 14

Boyle’s Law

Answer 14

At constant temperature, pressure of gas is inversely proportional to volume

P α 1 / V

This makes practical sense–small volume, large pressure;

Question 15

Types of Pneumothorax:

Spontaneous

Non-Spontaneous

Primary Spontaneous

Secondary Spontaneous

Traumatic

Iatrogenic

Answer 15

Spontaneous - Without any trauma/medical procedure

Non-Spontaneous - Due to trauma/medical procedure

Primary Spontaneous - W/out any existing pathology

Secondary Spontaneous - Arising due to lung disease (COPD)

Traumatic - Trauma, stab, shot

Iatrogenic - Trauma from medical procedure; pacemaker, etc