Ventilation and Lung mechanics

Question 1

what is ventilation?

Answer 1

process of inspiration and expiration.

Question 2

Neurones in the _______________generate automatic rhythmic impulses which are responsible for the normal involuntary rhythmic breathing pattern.

Answer 2

respiratory center in the medulla of the brain

Question 3

describe the different lung volumes!

Answer 3

ur notes

Question 4

what r pulmonary capacities?

Answer 4

when describing events int he pulmonary cycle, it is sometimes desirable to consider 2 or more of the volumes together>> pulmonary capacities

Question 5

anatomical dead space? value?

Answer 5

Only part of the tidal volume is available for gas exchange.

The rest fills the conducting airways, which extend from the nostrils to the terminal bronchioles.

The volume of the conducting airways is known as anatomical dead space bc no gas exchange occurs there

150ml

Question 6

what is the alveolar dead space?

Answer 6

those alveoli which r not perfused or r damged, dont take place in gas exchange! & ventelation in those parts r wasted!

Question 7

what is the total dead space?

Answer 7

total of all dead spaces !

Total dead space = Anatomical dead space + alveolar dead space.

Question 8

what is minute ventilation? how much is it?

Answer 8

amount of air flows in or out of the tract in 1 min!

500ml or 6L

Question 9

what is minute repiratory volume? how do we calculate it?

Answer 9

total amount of new air moved into the respiratory passages each minute

Tidal volume x respiratory rate

normal TV is 500ml

normal RR is 12 breaths per min

500x12= 6L/min

Question 10

what is alveolar ventilation? equation

what is its signficance?

Answer 10

total volume of NEW air entering the alveoli & adjacent gas areas each min.

OR

The RATE at which air reaches those areas is Alveolar ventilation

AV = (TV – Ads) x RR

(look at ex in ur book)

it is one of the mafor factors determining the concentrations of O2 and Co2 int he alveoli

Question 11

“At rest, (at the end of quiet expiration, when the respiratory muscles are relaxed)

the lung is subject to 2 equal and opposing forces.

One is directed inwards and the other outwards.

Explain this concept and what happens in change of pressures

Answer 11

 Inward: the lung’s elasticity and ST generate an inwardly directed force that favours small lung volumes.

 Outward: The muscles and various connective tissues associated with the rib cage also have elasticity, these elastic elements favour outward movement of the chest wall



Net effect: At rest the two opposing forces balance each other, and also creates a negative pressure within the intrapleural space relative to atmospheric pressure. “

Question 12

describe the mechanism of normal quiet inspiration and the role of inspiratory muscles

Answer 12

diaphragm and external intercostal contract>> causes thoracic cavity to be large and rib cage rises>> causing LARGE VOLUME and LOW pressure (cuz u got more space)

This low P. in lungs will cause influx of air from out to in!

vise versa with expiration

Question 13

Describe the mechanism of quiet expiration and the role of elastic recoil

Answer 13

In quiet expiration, when the muscle contraction ceases, the elastic recoil of the lung results in the thoracic cavity and lung returning to the original equilibrium position.

Thus quiet expiration is a passive process.

Question 14

in quiet inspiration, how many % is the diaphragm involved?

what about the muscles in quiet expiration

Answer 14

70%

tricked you! quiet expiration is a PASSIVE process! no muscles used!

Question 15

describe the mechanism of forced inspiration and forced expiration and the accessory muscles of inspiration and expiration

Answer 15

Forced inspiration (during excersize)>>

1. sternocleidomastoid & scalene of neck
2. serratus anterior & pectoralis major of chest wall

Forced expiration

1. internal intercostal muscles
2. abdominal wall muscles (ex & in oblique & rectus abdominus)

Question 16

what does the pleural space contain?

Explain the importance of the pleural seal in respiration

Answer 16

10 ml of pleural fluid spread as a thin film over the visceral and parietal pleural surfaces

the 2 pleural membranes contribute to the pleural seal

The ST between the molecules of this fluid forms a seal, holding the outer surface of the lungs to the inner surface of the chest wall.

It is this seal which ensures that the chest wall and lungs move together.

Just like if there was a little bit of watter btw ur cup and coaster, its gets stuck to gther and when u life the cup the coaster is stuck to it

Question 17

Explain why the pressure within the pleural cavity is lower than atmospheric p. at rest and changes in pleural pressure during respiratory cycle.

Answer 17

****continual suction of excess fluid into lymphathic channels maintains a slight suction in the pleural cavity. therefore the lungs r held to the thoracic wall and glued there!****

sooooo. ..
* the pleural pressure is always in (slight suction) meaning a slightly negative p.,*

the normal pleural pressure at beginning of inspiration is -5 cm of water, which is required to keep the lung open to their resting levels!

in inspiration>expansion of chest cage pull lungs outwards

creating a MORE negative p. of -7.5cm of water

Question 18

define elastic recoil

Answer 18

tendency of BOTH elastin and collagen fibres to return to their original size when stretched)

Question 19

define Radial traction

Answer 19

Question 20

Pressure changes in the pleural cavity & alveoli during inspiration & expiration

Answer 20

intraplural presure

inspiration: -4 becomes -6 decreases
expiration: -6 becomes -4 increases

intrapulmonary pressure

inspiration: 0 becomes -1 decreases
expiration: 0 becomes +1 increases

Question 21

Explain how a pneumothorax occurs and why this results in collapse of the lung

Answer 21

.At rest, (i.e. the end of a quiet expiration), the intra-pleural pressure is slightly below atmospheric pressure, and the ST of the small amount of pleural fluid creates a seal which keeps the lung adherent to the chest wall.

If an opening is created which allows the pleural cavity to communicate with the air outside, air will flow into the pleural cavity down the pressure gradient until the pressure in the pleural cavity reaches atmospheric pressure.

When the pleural seal is broken, and the elastic recoil of the lung causes it to collapse towards the hilum, as the negative pleural pressure and outward recoil of the chest wall can no longer counteract it.

Question 22

Define the term ‘compliance’ of the lungs

in order to acheive complience of the lungs, what must happen?

Answer 22

• stretchiness of the lungs*
• To stretch the lungs the elastic recoil of the lung must be overcome.*

The elastic properties of the lungs arise from two sources:

1.  Elastic tissue in the lungs
2.  ST of the fluid lining the alveoli

Question 23

what is surfactant? what is its role?

Answer 23

Surfactant, is secreted by type II pneumocytes in the lung.

It is a complex mixture of phospholipids & proteins with detergent properties.

The hydrophilic ends of these molecules lie in the alveolar fluid with their hydrophobic ends projecting into the alveolar gas.

As a result, they float on the surface of the lining fluid

ROLE: the surfactant molecules, which are interspersed between the fluid molecules, disrupt the interaction between fluid molecules on the surface thereby reducing the surface tension.

Question 24

surfactant is absent in fetuses younger than_______

Answer 24

25 wks

Question 25

Explain the effect of ST relation to the alveoli SIZE and the role surfactant in this case.

Answer 25

As an alveolus expands, surfactant molecules are spread further apart, making them less efficient. Hence, as the alveolus expands the ST increases.

As an alveolus shrinks, the surfactant molecules come closer together increasing their concentration on the surface & act more efficiently to reduce the ST. Hence, surfactant reduces ST as area of the alveolus decreases.

The force required to expand smaller alveoli is therefore less than that required to expand large ones.

Question 26

what if the ST was constant in both sized alveoli? what would happen

Answer 26

if the ST was constant in all alveoli, smaller alveoli would have higher pressures w/in it. Therefore, if 2 unequal sized alveoli were connected by an airway,….

t

The effect of this would be that the smaller alveoli (w/ higher pressure) would collapse into larger alveoli (w/ less pressure) to form a few huge air-filled spaces (known as bullae).

Question 27

complience vs elasticity

Answer 27

,

Question 28

Describe the factors which influence airway resistance in the normal lung & how airway resistance changes over the breathing cycle.

Question 29

define functional residual capacity

how does this change in older people?

Answer 29

is the volume of air in the lungs at the end of a quiet expiration, basically as u get older you lose elasticity of ur lung (ur lung’s ability to recoil)

therefore their expiration sucks and they end up not expiring as much, leaving MORE air in their lungs after their expiration

so FRC increases!

Functional residual capacity is the volume of air in the lungs at the end of a quiet expiration

Question 30

what prevents the smaller alveoli form emptying into large ones?

Answer 30

lalllsss…

it depends on the size (radius) of the alveoli!

basically,

if u have large alveoli, the surfactant molecules are spread further apart, making them less efficient. Hence, as the alveolus _expands_ the ST _increases_.

if u have small alveoli the surfactant molecules come closer together increasing their concentration on the surface and act more efficiently to reduce the ST. Hence, as the alveolus shrinks the ST de**creases**.

Therefore, different sized alveoli can have the same pressure within them. This stabilizes the lungs by preventing small alveoli collapsing into big ones.

Question 31

what is transpulmonary pressure

Answer 31

the pressure difference btw the alveoli & pleaural pressure

it is a measure of the elastic forces in the lungs that tend to collapse the lungs at each instant of respiration called recoil pressure

Question 32

Where in the bronchial tree is the main site of airways resistance?

why is there not much resistence in the airwyas!

Answer 32

Resistance of a single tube increases sharply with falling radius.

However, the combined resistance of the small airways is normally low because they are connected over a branching structure.

Most of the resistance to breathing therefore resides in the _upper respiratory tract,_ except when the small airways are compressed during forced expiration.

Question 33

Increased airways resistance (obstruction) – name 3 different mechanisms and the disease name

Answer 33

Question 34

Airways resistance ________ as lung volume ________

Answer 34

Airways resistance increases as lung volume decreases

Question 35

label interstium

Answer 35

Question 36

What is the resting expiratory level?

Question 37

Why is intrapleural pressure always slightly negative (relative to atm pressure?)

Answer 37