L9 Mechanics of Ventilation Flashcards
describe the position of the Thoracic inlet
bounded by 1st ribs, 1st sterner and 1st thoracic vertebra
the pleura forms how many cavities
2, mediastinal pleura meet at midline
how does the pleura attache to the sternum
via the sternopericardial ligament
how does the pleura enclose the vena cava
plica venae cavae (fold of pleura)
which regions of the pleura enclose the heart
cranial and caudal and middle regions
what is the pleura called on the lateral aspects of the thoracic cavity
costal pleura
what is the pleura called most near to the lungs
visceral pleura
what is the most caudal pleura called
diaphragmatic pleura
during inspiration the diaphragm….
contracts (to form a larger space in the thoracic cavity)
what is the diaphragm made from
tendinous sheet of collagen and muscle
where does the diaphragm attach
transverse processes of first 2-3 lumbar vertebrae, lateral at costal arches and ventrally at the sternum
which muscles are used for forced inspiration
external intercostal and scalenus muscles
Describe the fibre position of the external intercostal and scalenus muscles
External intercostal runs caudoventrally between the ribs.
Scalenus originates on the transverse process of the cervical vertebrae and inserts on the first few ribs to draw cranial and laterally for expansion
what does the diaphragm do during expiration
relaxes passively due to elastic recoil of lungs
Air expulsion from the lungs continues until …
the thorax reaches a point of equilibration b/w the elastic recoil of the lungs and resistance to the stretching associated with inspiration
Which muscles are used for forced expiration
internal intercostal and abdominal muscles contract to reduce the volume of the thorax below equilibration volume
which nerve innervates the diaphragm
phrenic nerve
what is atmospheric pressure?
760mm Hg
what is intrapleural/ intrathoracic pressure?
~756mm Hg (lower than that inside a relaxed lung)
What is alveolar pressure?
~760mm Hg as per atmospheric pressure. Changes during inspiration (decreases) and expiration (increases)
what is the transmural pressure gradient?
difference b/w alveolar and intrapleural pressure
describe what determines airflow during inspiration
diaphragm contracts > thorax expands > drop in pressure in pleural cavity > expansion of lungs > drop in intra-alveolar pressure > airflow down pressure gradient until pressure equal to atmospheric
Describe what determines airflow during expiration
relaxation inspiratory muscles > decrease in thoracic and lung volumes > increase intra-alveolar pressure > airflow down pressure gradient out of lungs
What is pneumothorax?
entry of air into the pleural space, leading to partial loss of vacuum and therefore lung collapse.
Either through hole in lung or thoracic wall
If the mediastinum is broken, will both lungs collapse?
no, most species have two separate pleural cavities joined at the midline by mediastinum.
What is respiratory dead space ?
the volume of gas in airways not involved in gas exchange. Both anatomical and physiological.
anatomical= areas not adapted for gas exchange e.g. nose to the terminal bronchioles
physiological= total vol gas not participating due to anatomy or alveoli without adequate circulation
if the aim of an animal is to increase O2, it is more efficient for an animal to increase ____ rather than _____
better to increase tidal volume rather than respiratory rate. Because all additional air taken in will be available for gas exchange.
What is the pulmonary minute equation
pulmonary minute ventilation (ml/ min) = Tidal volume (ml/ breath) x Respiratory rate (breaths/ min)
Define tidal volume
volume air breathed in or out in a breath
What is the equation to describe alveolar ventilation
= (tidal volume - dead space volume) x RR
therefore the volume of gas entering and leaving alveoli in one minute
