resp part2 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
High lung volumes
are associated with greater radial traction and decrease airway resistance. In asthma, pt “learn” to breath at higher lung volumes to offset the high airway resistance associated with their disease.
Site of airway resistance
The major site of airway resistance in the medium-sized bronchi.
The smallest airways would seems to offer the highest resistance, but they do not, because of their parallel arrangement.
“Work” of Breathing
During normal quiet condition, respiratory muscles ‘work’ only during inspiration and NOT during expiration.
Work of inspiration:
3 things
Compliance work
Tissue Resistance Work
Airway Resistance Work
Tidal Volume:
Tidal Volume: is the volume inspired or expired with each normal breath
Inspiratory Reserve Volume
Inspiratory Reserve Volume: is the volume that can be inspired over and above the tidal volume. It is used during exercise
Expiratory Reserve Volume
Expiratory Reserve Volume: is the volume that can be expired after the expiration of tidal volume
Residual Volume
is the volume that remains in the lungs after a maximum expiration. It cannot be measured by spirometry
Helium Dilution Method.
Pulmonary Volumes are recorded by Spirometer except Residual Volume which is measured by Helium Dilution Method.
Vital Capacity (VC)
Is the sum of TV, IRV and ERV.
How is pulmonary capacity determined
Pulmonary Capacity is combination of two or more pulmonary volumes
Inspiratory Capacity
TV+IRV
Functional Residual Capacity
ERV+ Residual Volume
Volume remaining in the lungs after a tidal volume is expired
Total Lung Capacity
Is the sum of all four volumes.
It is the volume in lungs after a maximum inspiration
“Vital Capacity is everything but the residual volume”
Functional Residual Capacity - FRC
Volume of air remaining in lung after normal tidal exhalation
Acts as RESERVIOR for O2 during airways obstruction or apnea
Prevents large SWINGS of PO2 by acting as buffer
FRC=?
ERV+RV
FRC is reduced by
Supine position
Obesity
Pregnancy
Anesthesia
decreased from what 4 things will decrease FRC and predispose a patient to what?
Therefore, all these things predispose to HYPOXEMIA
Implication: preoxygenation/denitorgenation does what to FRC?
PREOXYGENATION / DENITORGENATION before anesthetic induction is very important providing reservoir of O2, as this “fills” the FRC with 100% O2, allowing more time (upto10 min.) for airways manipulation, breath holding episodes etc.
FRC Increases by:
PEEP , CPAP
Increase airway resistant – asthma
Forced vital capacity (FVC)
Is the volume of air that can be forcibly expired as hard and as rapid possible, after taking maximum inspiration
FORCED EXPIRATORY VOLUME IN 1ST SECOND ( FEV1)
Is the volume of air that can be expired in the first second of a forced maximal expiration as hard and as rapid possible
Is normally 80% of the forced vital capacity (FVC)
FEV1/FVC ratio = 4/5= 0.80 (80%)
FEV1 is low in both obstructive and restrictive diseases (trouble is blowing air out
obstructive lung diseases what happens in FVC and FEV
In obstructive lung diseases such as asthma and COPD, FEV1 is reduced more than FVC so that FEV1/FVC is decreased (hallmark)
restrictive lung disease what happens to FVC and FEV
In restrictive lung disease such as pulmonary fibrosis, pneumothorax, scoliosis, myasthenia gravis or ALS, both FEV1 and FVC are reduced and FEV1/FVC is either normal or is increased
Forced expiratory flow (FEF 25-75) or Midmaximal expiratory flow
Is best of accessing small airway disease
Obstructive Lung Disease ‘increase resistance to flow’
Obstruction of air flow, resulting in air trapping in the lung.
Emptying impaired-high RV , low VC
FEV1/FVC ratio decreases (hallmark)
4 Types of Obstructive lung disease :
Bronchiectasis
Chronic Bronchitis
Emphysema
Asthma
Restrictive Lung Disease ‘stiff lungs, decrease expansion’
Restricted lung expansion causes decreased all lung volumes ( VC and TLC), PFTs: FEV1/FVC ratio >80%
Poor breathing mechanics (extrapulmonary)
Poor muscular effort: polio, M gravis
Poor apparatus: scoliosis
Poor lung expansion (pulmonary)
Lungs are restricted; cannot expand
Defective alveolar filling: pneumonia, ARDS, pulmonary edema
Interstitial fibrosis: causes increased recoil (decrease compliance), thereby limiting alveolar expansion. Complications include cor pulmonale. Can be seen in diffuse interstitial pulmonary fibrosis and bleomycin toxicity. Symptoms include gradual progressive dyspnea and cough
slide 47
slide 48
PCWP
is an indirect measure of ‘left atrial pressure’
normally 10mmhg
how do we measure right sided heart catheterization
Measure by Right Sided Heart Catheterization (SWAN-GANZ)
PWP
is used in CHF to study pressure changes in left atrium
decrease BP decrease PCWP = Hypovolemic shock, give fluid
decrease BP increase PCWP = Failing heart, give inotrops
Right atrium pressure
<5mmhg
Right ventricle pressure
<25/<5mmhg
Left atrium pressure
< 12mmhg
Left ventricle pressure
<150/10mmhg
Pulmonary trunk pressure
<25/10mmhg
Aorta pressure
<150/90mmhg
PCWP pressure
<12mmhg
What is PCWP measuring?
PCWP (mmHg) is a good approximation of left atrial pressure. Measured with Swan
Pulmonary artery Pressures
Systolic= 25 mmHg Diastolic= 8 mmHg Mean= 15 mmHg Capillary= 7 mmHg
Pressure and Cardiac output in the pulmonary circulation
Pressure
Are much lower in pulmonary circulation (15mmHg) than in the systemic circulation (100mmHg)
Pressure and Cardiac output in the pulmonary circulation
Compliance
Is much higher
Pressure and Cardiac output in the pulmonary circulation
Resistance
is much lower
Pressure and Cardiac output in the pulmonary circulation
Cardiac output of the right ventricle
Is pulmonary blood flow
Is equal to CO of the left ventricle
In lungs, alveolar hypoxia causes
In lungs, alveolar hypoxia causes vasoconstriction
This diverts blood away from poorly ventilated, hypoxic regions towards well-ventilated regions of lung leads to?
decrease shunting of blood (protective)
Fetal pulmonary vascular resistance is very high due to hypoxic vasoconstriction
decrease blood flow
Oxygenation with first breath decreases pulmonary vascular resistance
increase blood flow
Global hypoxia (breathing in thin air at high altitude)
vasoconstriction of entire lungs leads to pulmonary HTN leads to RVF
Pulmonary vascular resistance (PVR)
PVR= P pul artery-P l atrium/C0 x 80
SVR
SVR= MAP-CVP/CO x 80
normal value 900-1200