mechanics of breathing Flashcards
how does the pleural membrane surround the lungs
on both sides but the two sides arent connected
cover the lungs and interior of the thorax
what is between the pleural membranes
an extremely thin layer of intrapleural fluid
what is the role of intrapleural fluid
allows the membranes to glide across each other and reduces friction
the lungs are effectively stuck to the rib cage and diaphragm due to the cohesive force of the pleural fluid on the membranes, even though they are trying to pull apart from each other
what are the 2 parts that make up the pleural membranes
visceral: coats the outer surface of the lungs
parietal: coats the inner surface of the ribs
what is pleurisy
inflammation of the pleura
increased friction
breathing is difficult
pneumothorax
air enters the pleural cavity and the 2 membranes are forced apart as air enters down a pressure gradient
the relationship between the 2 pleural membranes is lost and the affected lung becomes useless and collapses due to the elastic recoil of the lung and chest wall in opposite directions
which muscles are involved in inspiration
external intercostals and the diaphragm
also the sternocleidomastoids and scalenes
what muscles are involved in expiration
expiration is passive at rest
internal intercostals and abdominal muscles during severe respiratory load
describe the changes in pressure in the thoracic cavity related to the diaphragm
diaphragm is dome shaped at rest
flattens when it contracts which decreases the thoracic pressure by increasing the volume - air moves into the lungs
vice versa on expiration
how are the intercostal muscles involved in changing the dimensions of the rib cage
internal intercostals:
pump-handle motion - increases anterior-posterior dimension
bucket handle motion - increases the lateral dimension
external intercostals:
elevate the ribs and increase the lateral dimensions
Asthma and smooth muscle
over-reactive constriction of bronchial smooth muscle
increases resistance
expiration phase is most affects as the airways are compressed by the physical forces of expiration
Boyle’s law
pressure exerted by a gas is inversely proportional to its volume
gases also move from areas of high pressure to areas of low pressure
define ventilation
the physical act of getting air in and out of the lungs
intra-thoracic (alveolar) pressure
PA
pressure inside the thoracic cavoty
may be -ve or +ve compared to atmospheric pressure
intra pleural pressure
Pip
pressure inside the pleural cavity
always -ve
transpulmonary pressure
PT
difference between alveolar and intra pleural pressure
always +ve
PA - Pip
Bulk flow of air relationships
bulk flow of air between the atmosphere and the alveoli is proportional to the difference between atmospheric and alveolar pressures and inversely proportional to the airway resistance
F = (Patm - PA)/R
when is atmospheric pressure equal to alveolar pressure
between breaths at the end of an unforced expiration
no air is flowing
the dimensions of the lungs and thoracic cage are stable as a result of opposing elastic forces - lungs are stretched and attempting to recoil and the chest wall is compressed and attempting to move outwards
intrapleural pressure is subatmospheric and transpulmonary pressure opposes the forces of elastic recoil
what does airway resistance determine
how much air flows into the lungs at any given pressure difference between atmosphere and alveoli
what is the major determinant of airway resistance
the radii of the airways
what are the 2 mechanical factors that affect respiratory minute volume
difference between alveolar and atmospheric pressures
airway resistance
define respiratory minute volume
Respiratory minute volume is the volume of gas inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from a person’s lungs per minute
what are the 2 compartments in the thoracic cavity
alveolar and intra-pleural
why is intrapleural pressure always less than alveolar pressure
alveolar pressure can be +ve or -ve
intrapleural pressure is always -ve as there is no air in the pleural cavity (normally)
transpulmonary pressure is the difference between alveolar and intrapleural pressure , it is always +ve because intrapleural pressure is always -ve
