Lecture 9 - Mechanics of Ventilation 1 Flashcards
what is the thoracic cavity lined by?
pleura
what is the thoracic cavity bound by?
- ribcage and intercostal muscles
- sternum
- thoracic vertebrae
- diaphragm
- thoracic inlet
how is the thoracic cavity flattened?
laterally
what is the pleura?
serous membranes covering all surfaces within the thoracic cavity, forms mediastinum between two plural cavities
what is the pulmonary or visceral plura?
covers surface of all organs and vessels in the thorax
what is the parietal plura?
lines inner walls of thoracic cavity
named according to region eg/ diaphragmatic plura
continuous with pulmonary plura
what is the sternopericardial ligament?
folds of pleura attaching heart to sternum
with is the place venue cavae?
fold of pleura suspending caudal vena cava
what are the pleural cavities?
two complete sacs (L and R)
airtight cavities containing small amount of fluid
what does the mediastinum enclose and what are the three devisions?
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
inspiration requires active muscular contraction, what is the principle muscle of inspiration (during normal breathing)
the diaphragm
what does the diaphragm seperate
the thoracic cavity from the abdomen
what are the three attachments of the diaphragm?
transverse processes of the first 2-3 lumbar vertebrae
internal aspect of ribs near coastal arch
caudal end of the sternum
what muscles are used for forced inspiration
the external intercostal and scalenus muscles
how do they external intercostal and scalenus muscles contribute to forced inspiration
draw rib cranially and laterally = expansion of the thorax
where do the external intercostal muscles run?
caudoventrally between adjacent ribs
where does the scalenus muscle originate and where does it insert?
on transverse process of cervical vertebrae and inserts on first few ribs
what muscles are required for normal expiration?
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.
what muscles are required for forced/active expiration
internal intercostal and abdominal muscles
when is active expiration required?
when the requirement for ventilation is elevated
how do the internal intercostal and abdominal muscles contribute to forced expiration
reduce the volume of the thorax below equilibrium volume
where do the internal intercostal muscles rn
caudodorsally between adjacent ribs and collapse thoracic cavity
what nerve innervates the diaphragm
the phrenic nerve, originates from spinal cord in 5th-7th cervical nerves
what does the intercostal nerve innervate
external and internal intercostal muscles
scalenus muscle
abdominal muscle
what is the alveolar pressure
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
what is the sub atmospheric pressure within intrathoracic/pleural pressure and how is it formed?
- parietal and visceral pleura adhere to each other due to fluid in film
- elastic recoil of lung and intercostal muscles appose each other
describe airflow during inspiration incl. the ventilation pressures
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.
describe airflow during inspiration incl. the ventilation pressures
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
what changes to normal inspiration occur with forced inspiration?
contraction of accessory muscles increases the thoracic pressure above resting inspiratory volume = greater pressure drop = greater pressure gradient
what changes to normal inspiration occur with forced expiration?
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
how does lung collapse occur?
via hole in thoracic wall or hole in lung leading to equalisation of atmospheric pressure within the lung, intrapleural (thoracic) space and the atmosphere
where is respiratory dead space, how can it be categorised?
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
what is anatomic dead space?
not anatomically adapted for gas exchange
eg/ all airways from nose to the terminal bronchi
what is physiological dead space?
total volume of air not participating in case exchange, includes any anatomical dead space plus any alveoli with inadequate circulation
what is tidal volume?
volume of air breathed in or out in a single breath in ml/breath
what is pulmonary minute ventilation?
tidal volume (ml/breath) x respiratory rate (breath/min)
what is alveolar ventilation?
(tidal volume - dead space volume) x resp rate
eg/ alveolar ventilation is volume of air entering alveoli in one minute
