resp part2 - previous semester *GOOD REVIEW FOR RESP* Flashcards
lung compliance
Shows “distensibility” of lungs and chest wall
Is inversely related to elastance, which depends on the amount of elastic tissue
Is inversely related to stiffness
In middle range of pressure describe compliance
compliance is greatest and the lungs are most distensible
middle range is most compliant
At high expanding pressure describe compliance
compliance is lowest, the lungs are least distensible , and the curve flattens.
Compliance=
change in volume of lung (change ofV) for each unit change in pressure (change ofP). Pressure refers to transpulmonary pressure
Changes in lung compliance
In patient with emphysema
lung compliance is increased and the tendency of the lung to collapse is decreased. Therefore , at original FRC, the tendency of lungs to collapse is less than the tendency of chest wall to expand. The lung-chest wall system will seek a new, higher FRC so that the two opposing forces can be balanced; the patient’s chest becomes barrel-shaped, reflecting higher volume.
pneumothorax
If air is introduced into the pleural space (pneumothorax), the intrapleural pressure becomes equal to atmospheric pressure. The lung will collapse (its natural tendency ) and chest wall will spring outward (its natural tendency)
fibrosis and lung compliance
In a patient with fibrosis , lung compliance is decreased and the tendency of lungs to collapse is increased. Therefore, at the original FRC, the tendency of the lungs to collapse is greater than the tendency of the chest wall to expand. The lung-chest wall system will seek a new lower FRC so that the two opposing forces can be balanced.
Pleural space is a relative
vacuum
The negative force always required to keep the lungs open.
-5cmH2O
Alveolar Pressure
It is the air pressure in alveoli
Normally = 0 cmH2O
decrease in inspiration, increase in expiration
During normal quiet inspiration ,it is the major driving force for air flow into the lungs
Transpulmonary Pressure =?
= Alveolar Pressure minus Pleural Pressure
Transpulmonary Pressure -neonates first breath
First breath of neonates generates transpulmonary pressure of 40 to 80 cmH2O
Pleural Pressures
Resting ?
Inspiration?
Resting -5 cm H20
Inspiration -8 cm H20
Alveolar Pressure at:
Resting
Inspiration
Expiration
Alveolar Pressure at:
Resting 0 cm H20
Inspiration -1 cm H20
Expiration +1 cm H20
Alveolar pressure equals atmospheric pressure and is said to be ?
Alveolar pressure equals atmospheric pressure and is said to be zero (no flow)
Pleural pressure ?
is always negative
what is lung volume
FRC
how do we measure pleural pressure?
by a balloon catheter in the esophagus
how does the negative pressure get created in the intrapleural space
Elastic recoil of lungs trying to collapse and the chest wall trying to expand, creates a negative pressure in the intrapleural space
as lung volume increases alveolar pressure becomes what?
alveolar pressure decreases to less than atmospheric pressure (becomes negative -1cmh20
during inspiration pleural pressures becomes??
more negative than it was at rest -5- -8cmh20
during expiration alveolar pressure
alveolar pressure becomes greater becomes positive +1cmh20 than atm pressure.
Intrapleural pressure returns to its resting value during
Intrapleural pressure returns to its resting value during a normal (passive ) expiration. However, during a forced expiration, intrapleural pressure actually becomes positive. This positive intrapleural pressure compresses the airways and makes expiration more difficult
SURFACTANT is secreted by?
type II alveolar cells
surfactant is composed of?
phospholipid, proteins, and ca++
how does surfactant work
Lines the alveoli, act as surface tension ‘reducer’ by disrupting the intermolecular forces (hydrogen bond) between the water molecules of liquid-act like “detergent”
This reduction in surface tension prevents small alveoli from collapsing and increases compliance, decrease work of inspiration allowing the lungs to inflate much more easily
surfactant Synthesis starts week
24 week of gestation
Almost always present at week 35
how do we check to see if surfactant is present for fetal lung maturity.
Lecithin-to- Sphingomyelin (L/S) ratio of > 2:1 in amniotic fluid is indicative of fetal lung maturity
Neonatal respiratory distress syndrome: S&S?
Occurs in premature infants because of lack of surfactant. The infant shows atelectasis (lung collapse), difficulty reinflatting the lungs( as a result of decreased compliance) and hypoxemia because of V/Q
neonatal treatment for prematurity
Treatment
Maternal steroid shots before birth. This speeds up formation of surfactant in the fetus.
Artificial surfactant to infants by inhalation
airflow equation
q=change p/R
q=airflow
change p= pressure gradient
r= air way resistant
resistance to flow
R= resistance
= viscosity of the inspired gas
l = length of airway
r = radius of airway
Notice the powerful inverse fourth-power relationship between resistance and size ( radius) of airways.
If airway radius decreases by a factor of 4, then resistance will increase by a factor of 256(44) and air flow will decrease by a factor of 256
R= 8nl/PIEr4
Contraction and relaxation of bronchial smooth muscles
Parasympathetic stimulation
irritants, slow reacting substance of anaphylaxis-A (asthma) constrict the airways, the radius and the resistance to airflow
Contraction and relaxation of bronchial smooth muscles
Sympathetic stimulation
and sympathetic agonist dilate the airways , increase radius and decrease resistance to airflow via 2 receptor
Low lung volumes
are associated with less radial traction and increased airway resistance