Lecture 9 - Mechanics of Ventilation 1

Question 1

what is the thoracic cavity lined by?

Answer 1

pleura

Question 2

what is the thoracic cavity bound by?

Answer 2

• ribcage and intercostal muscles
• sternum
• thoracic vertebrae
• diaphragm
• thoracic inlet

Question 3

how is the thoracic cavity flattened?

Answer 3

laterally

Question 4

what is the pleura?

Answer 4

serous membranes covering all surfaces within the thoracic cavity, forms mediastinum between two plural cavities

Question 5

what is the pulmonary or visceral plura?

Answer 5

covers surface of all organs and vessels in the thorax

Question 6

what is the parietal plura?

Answer 6

lines inner walls of thoracic cavity
named according to region eg/ diaphragmatic plura
continuous with pulmonary plura

Question 7

what is the sternopericardial ligament?

Answer 7

folds of pleura attaching heart to sternum

Question 8

with is the place venue cavae?

Answer 8

fold of pleura suspending caudal vena cava

Question 9

what are the pleural cavities?

Answer 9

two complete sacs (L and R)

airtight cavities containing small amount of fluid

Question 10

what does the mediastinum enclose and what are the three devisions?

Answer 10

mediastinum encloses thymus, heart, trachea, oesophagus, major thoracic vessels and nerves.
the three divisions are:
- cranial mediastinum = cranial to the heart
- middle mediastinum = containing heart
- caudal mediastinum = caudal to the heart

Question 11

inspiration requires active muscular contraction, what is the principle muscle of inspiration (during normal breathing)

Answer 11

the diaphragm

Question 12

what does the diaphragm seperate

Answer 12

the thoracic cavity from the abdomen

Question 13

what are the three attachments of the diaphragm?

Answer 13

transverse processes of the first 2-3 lumbar vertebrae
internal aspect of ribs near coastal arch
caudal end of the sternum

Question 14

what muscles are used for forced inspiration

Answer 14

the external intercostal and scalenus muscles

Question 15

how do they external intercostal and scalenus muscles contribute to forced inspiration

Answer 15

draw rib cranially and laterally = expansion of the thorax

Question 16

where do the external intercostal muscles run?

Answer 16

caudoventrally between adjacent ribs

Question 17

where does the scalenus muscle originate and where does it insert?

Answer 17

on transverse process of cervical vertebrae and inserts on first few ribs

Question 18

what muscles are required for normal expiration?

Answer 18

NONE = normal expiration is PASSIVE
utilises elastic recoil of the lung
expulsion of air until contraction of thorax reaches equilibrium between elastic recoil and resistance to stretch of insp muscles.

Question 19

what muscles are required for forced/active expiration

Answer 19

internal intercostal and abdominal muscles

Question 20

when is active expiration required?

Answer 20

when the requirement for ventilation is elevated

Question 21

how do the internal intercostal and abdominal muscles contribute to forced expiration

Answer 21

reduce the volume of the thorax below equilibrium volume

Question 22

where do the internal intercostal muscles rn

Answer 22

caudodorsally between adjacent ribs and collapse thoracic cavity

Question 23

what nerve innervates the diaphragm

Answer 23

the phrenic nerve, originates from spinal cord in 5th-7th cervical nerves

Question 24

what does the intercostal nerve innervate

Answer 24

external and internal intercostal muscles
scalenus muscle
abdominal muscle

Question 25

what is the alveolar pressure

Answer 25

760mmHg (Same as atmospheric) when the muscles of ventilation are relaxed or fixed and the glottis is open. transient changes: decreases w/ insp, increases with/ exp

Question 26

what is the sub atmospheric pressure within intrathoracic/pleural pressure and how is it formed?

Answer 26

- parietal and visceral pleura adhere to each other due to fluid in film - elastic recoil of lung and intercostal muscles appose each other

Question 27

describe airflow during inspiration incl. the ventilation pressures

Answer 27

contraction of the diaphragm --> expansion of thorax --> DROP in pressure of thoracic cavity (754mmHg) , expansion of lungs drop in alveolar pressure (759mmHg) --> airflow DOWN pressure gradient into lungs.

Question 28

describe airflow during inspiration incl. the ventilation pressures

Answer 28

relaxation of inspiratory muscles --> decrease in lung and thoracic volume = thoracic pressure goes back to 756 --> increased alveolar pressure (761mmHg) --> airflow DOWN pressure gradient OUT of lungs

Question 29

what changes to normal inspiration occur with forced inspiration?

Answer 29

contraction of accessory muscles increases the thoracic pressure above resting inspiratory volume = greater pressure drop = greater pressure gradient

Question 30

what changes to normal inspiration occur with forced expiration?

Answer 30

reduction in thoracic volume and lung volume below resting volume = greater increase in intralveolar pressure = greater pressure gradient = faster and more complete emptying of lung

Question 31

how does lung collapse occur?

Answer 31

via hole in thoracic wall or hole in lung leading to equalisation of atmospheric pressure within the lung, intrapleural (thoracic) space and the atmosphere

Question 32

where is respiratory dead space, how can it be categorised?

Answer 32

volume of airways that does not participate in gas exchange can be anatomical or physiological due to existence of dead space not all air breathed in is available for ventilation

Question 33

what is anatomic dead space?

Answer 33

not anatomically adapted for gas exchange | eg/ all airways from nose to the terminal bronchi

Question 34

what is physiological dead space?

Answer 34

total volume of air not participating in case exchange, includes any anatomical dead space plus any alveoli with inadequate circulation

Question 35

what is tidal volume?

Answer 35

volume of air breathed in or out in a single breath in ml/breath

Question 36

what is pulmonary minute ventilation?

Answer 36

tidal volume (ml/breath) x respiratory rate (breath/min)

Question 37

what is alveolar ventilation?

Answer 37

(tidal volume - dead space volume) x resp rate | eg/ alveolar ventilation is volume of air entering alveoli in one minute