Respiratory Pathophysiology Flashcards
Purpose of the pulmonary system
supply oxygen from the atmosphere to the blood and remove CO2, maintain acid base balance, phonation, pulmonary defense, oxygen for metabolism
Partial pressure of gases in air
79% Nitrogen, 600 mmHg
21% Oxygen 159.6 mmHg
1% Carbon Dioxide and other gases
Glycolysis in anaerobic metabolism
not sustainable for life
inefficient because it only yields 2 ATP
happens in the cytoplasm
Byproducts of the Aerobic metabolism
CO2, H2O, heat
Anaerobic metabolism
glycolysis –> 2 ATP and goes thru fermentation turning pyruvate into lactate
Purpose of the nose
used for filtration, smell, and humidification of incoming air
3 paired cartilages of the larynx
corniculate, arytenoid, and cuneiform
3 unpaired cartilages of the larynx
epiglottis, thyroid, cricoid
Why is the right mainstem bronchus more likely to be intubated over the left?
shorter, wider, and more vertical (25 degree angle)
the right lung makes up ____ TLC and is divided into ___ lobes
55%; 3
the left lung makes up ___ TLC and is divided into ___ lobes
45%; 2
Conducting zones of the airway
trachea –> bronchi –> bronchioles
No gas exchange occurs - anatomic dead space
has goblet cells- secrete mucus
the terminal bronchioles measure 1mm in diameter and lose cartilaginous plates
Resiratory/Transitional zones of the airway
terminal bronchioles –> alveolar ducts –> alveolar sacs
where gas exchange occurs - gas moves by diffusion
no goblet cells
respiratory bronchioles have diameter of 0.5 mm
What is the primary muscle of ventilation?
the diaphragm
What innervates the diaphragm?
C-3-4-5 roots to the phrenic nerve
When are intercostal muscles primarily used?
exertion
external - forced inhalation
internal - forced expiration
What the 3 types of pneumocytes in the lungs?
type 1 - structural
type 2 - surfactant producing
type 3 - macrophages
The distance from front incisors to carina is
26 cm
front incisors to larynx - 13 cm
larynx to carina - 13 cm
Blood supply to the conducting zone
from systemic circulation
from thyroid, bronchial, and internal arteries
Blood supply to the respiratory/transitional zone
from the pulmonary circulation
Anatomic dead space can be estimated by:
150 mLs (for a 70kg 6’0” man)
1/3 of tidal volume
1 mL/lb. or 2 mLs/kg of body weight (IBW)
Mechanics of inspiration
phrenic nerve innervates diaphragm to contract
drop in intrathoracic pressure - air pulls in
external intercostal help lift sternum and elevate ribs (increases AP diameter)
Does loss of intercostal function have an effect on ventilation?
not really
Mechanics of expiration
passive
increase in intrathoracic pressure - push air out
the elastic forces of the lung, chest wall, and abdomen compress the lungs
internal intercostals help with forceful expiration
What are the inspiratory accessory muscles?
sternocleidomastoid
scalene
What are the expiratory accessory muscles?
rectus, internal/external obliques, transversus abdominus
Transpulmonary pressure is the difference
between intrapleural and intra-alveolar pressures
What does the transpulmonary pressure determine?
the size of the lungs
a higher pressure = larger lung
Components of WOB
elastic and resistance forces of the lung and chest wall
Dorsal respiratory group stimulates
inspiration
Ventral respiratory group stimulates
inspiration/expiration (helps with forced inspiration/expiration)
the pneumotaxic center control of the lungs
decreases tidal volume
where is the pneumotaxic center located?
higher region of the pons
the apneustic center controls
increases in tidal volume for long and deep breathing
output is limited by baroreflex input from the lung and pneumotaxic center
where is the apneustic center located?
lower region of the pons
what do central chemoreceptors respond to?
hydrogen ion levels
what do peripheral chemoreceptors respond to?
CO2, pH, hypoxemia
What is the normal stimulus to breathe?
Hypercapnia
Which cranial nerve carries the aortic arch and lung stretch signals to the DRG?
CN X (vagus)
Which cranial nerve carries the carotid body signals to the DRG?
CN IX (glossopharyngeal)
Parasympathetic influence on the airway
causes mucus secretion, increased vascular permeability, vasodilation, bronchospasm
Activation of which receptors causes bronchoconstriction?
M3
Sympathetic influence on airway
inhibit mediator release from mast cells, increase mucociliary clearance
Activation of which receptors causes bronchodilation?
Beta 2
Which weight should we use for setting a Vt?
always IBW!
What are the 4 lung volumes?
residual
expiratory reserve
tidal
inspiratory reserve
Which volume cannot be measured by spirometry?
residual volume
What are the 4 lung capacities?
inspiratory = IRV + Vt
vital = IRV + Vt + ERV
functional residual = RV + ERV
total lung = IRV + Vt + ERV + RV
FRC definition
represents the point where elastic recoil of the lung is in equilibrium with the elastic recoil of the chest wall
“oxygen reserve”
Factors that affect FRC
upright and prone position = increases FRC
supine position = decreases FRC
muscle relaxation = decreases FRC
insufflation = decreases FRC
What is the respiratory quotient?
0.8
Which pleura covers the lung and which pleura covers the chest wall?
lung: visceral pleura
chest wall: parietal pleura
What is the space between the visceral and the parietal pleura called?
pleural cavity
Compliance =
change in volume / change in pressure
static compliance definition
compliance of the lung and chest wall WITH NO AIR MOVEMENT
don’t consider airway resistance*
What causes decreased static compliance?
fibrosis, obesity, edema, vascular engorgement, ARDS, external compression, atelectasis
What is the equation to calculate static compliance?
Tidal volume / (plateau pressure - PEEP)
ex. 500 / (12-5) = 71
normal value 60-100 mL/cmH2O
How do we measure plateau pressure?
have to set an inspiratory pause on the vent
usually can only do in volume control mode
dynamic compliance definition
compliance of the lung and chest wall during a breath
airway resistance plays a large role!
What causes decreased dynamic compliance?
bronchospasm, tube kinking, mucous plugs, increased RR
really anything that increases airway resistance…
How to calculate dynamic compliance
tidal volume / (peak pressure - PEEP)
ex. 500 / (20-5) = 33
normal 50-100mL/cmH2O
Where are elastic forces greatest?
in collapsed and hyperinflated alveoli
require a greater change in pressure to achieve a set increase in volume
What plays the largest role in reducing surface tension
?
surfactant
Laminar flow is mostly
in small airways
Turbulent flow is mostly
in large airways
Where is the greatest airway resistance?
in the medium sized bronchi
What does the Reynolds number predict?
when flow will be laminar or turbulent
What has the biggest impact on the Reynolds number?
diameter of the vessel
Which west zone should a PA catheter tip be placed in?
zone 3
Zone 1 pressure in order of greatest to least
alveolar > arterial > venous
V/Q >1
Zone 2 pressure in order of greatest to least
arterial > alveolar > venous
V/Q = 1
Zone 3 pressure in order of greatest to least
arterial > venous > alveolar
V/Q = 0.8
Zone 4 pressure in order of greatest to least
arterial > interstitial > venous > alveolar
V/Q < 1
Denitrogenation always causes some degree of ___
atelectasis
Closing volume definition
is the volume above residual volume where small airways close
closing capacity definition
absolute volume of gas in the lung when small airways close (CV + RV)
increases from 30% of TLC at age 20 to 55% by age 70
increased by supine position, pregnancy, obesity, COPd, CHF, aging
If closing volume is greater than FRC
airway closure occurs during tidal breathing leading to poorly ventilated alveoli and shunting
oxygen in the blood is carried in two ways
- physical - dissolved in blood
- chemical - bound to Hgb
Hgb rapidly and reversibly binds oxygen, allowing oxygen to be released into the tissues
Each Hgb molecule binds up to ___ oxygen molecules
4
Each gram of Hgb binds ____ mL of oxygen
1.34
Right shift on oxy/hgb dissociation curve
lower affinity at tissue level (increase CO2, increase temp, decreased pH, decreased O2, increased 2,3 DPG)
Left shift on oxy/hgb dissociation curve
higher affinity at lungs (decrease CO2, decreased temp, decrease 2,3 DPG, increase pH)
Haldane effect
in the lung
oxygenation of blood displaces carbon dioxide from hemoglobin
shows relationship for blood’s ability to carry CO2 in different oxygen environments
curve shifts up and left when PO2 decreases
Bohr effect
in the tissue
hemoglobin’s affinity for o2 is inversely related to CO2 levels
SaO2 50% … PaO2 =
27
SaO2 70% … PaO2 =
40
SaO2 90% … PaO2 =
60
CO2 is transported in the blood by
- physical solution 5-10% (dissolved in blood)
- chemically combined with amino acids of blood proteins 5-10% (bound to Hgb)
- bicarbonate ions 80-90%***
What is the equation for rapid conversion of CO2 into bicarb?
CO2 + H2O –> carbonic anhydrase –> HCO3- + H+
What is the chloride shift?
HCO2 leaves the RBCs, chloride enters to maintain electrical neutrality in the tissue capillaries
What is the quickest compensation for acid base imbalances?
serum buffers
Hypoxic hypoxia caused
from: decrease FiO2 <0.21 alveolar hypoventilation V/Q mismatch R --> L shunt
Clinical examples of hypoxic hypoxia
high altitude, O2 equipment error, drug overdose, COPD, pulmonary fibrosis, PE, atelectasis, congenital heart disease
Examples of circulatory hypoxia
reduced cardiac output
severe HF, dehydration, sepsis, SIRS
Clinical examples of hemic hypoxia
reduced Hgb content/function
anemias, carboxyhemoglobinemia, methemoglobinemia
Which hypoxia would supplemental oxygen be helpful?
hypoxic hypoxia* and demand/histotoxic hypoxia
Clinical examples of demand/histotoxic hypoxia
increased O2 consumption or inability to utilize O2
fever, seizures, cyanide toxicity
Hypoxic pulmonary vasoconstriction definition
reflex contraction of pulmonary vasculature in response to a low regional partial pressure of oxygen
intended to match regional perfusion to ventilation in the lungs
how does the HPV response work
diverts blood away from hypoxic areas of the lungs to areas with better ventilation and oxygenation
What does pulmonary circulation do in a hypoxic environment (acidic) ?
vasoconstrict
How is HPV reduced/eliminated?
elevated FiO2, volatile anesthetics above 1 MAC
Which disease has constant HPV if not treated and what can it lead to?
OSA, can lead to pulmonary HTN
causes of deadspace
PE, hypovolemia, cardiac arrest, shock
anything that decreases pulmonary blood flow
causes of shunts
mucus plugging, right mainstem intubation, atelectasis, pneumonia, pulmonary edema
anything that causes alveoli to collapse or fill
difference between anatomic and alveolar dead space
anatomical - air in the airway that never reaches the alveoli and does not participate in gas exchange
alveolar - air in nonfunctioning alveoli (disease or abnormal blood flow)
physiologic dead space =
alveolar + anatomic dead space
represents all of the air that is not being used for gas exchange
Bohr’s Equation in terms of dead space
deadspace = Vt [(PaCO2 - PeCO2) / PaCO2]
ex. 55 x [(45 - 32) / 45] = 144 mL
PeCO2 is normally ____ less than PaCO2
2-5 mmHg
due to mixing with anatomic deadspace during exhalation
venous admixture is the result of
mixing of non-oxygenated blood with oxygenated blood distal to the alveoli
mixed venous oxygen tension (PVO2) represents
overall balance between O2 consumption and o2 delivery
factors that lower PVO2
decreased CO, increase O2 consumption, decreased Hgb concentration
absolute shunt
V/Q = 0
hypoxia unresponsive to supplemental oxygen
Shunt
wasted perfusion - airway obstruction, pneumonia
low V/Q
Dead space
wasted ventilation - pulmonary embolism, cardiogenic shock
high V/Q
Shunt like alveoli have ___ PO2 and ___ PCO2
low PO2 and high PCO2
deadspace like alveoli have ___ PO2 and ___ PCO2
high PO2 and low PCO2
Symptoms of URI
elevated WBC, mucopurulent nasal secretions, inflamed and reddened mucosa, congestion/rales, temp >37, tonsillitis, viral ulcer, fatigue, laryngitis, sore throat
Histamine related allergy symptoms
sneezing, ash or boggy mucosa, itchy/runny nose, conjunctivitis, wheezing, hives, facial swelling, dry,red and cracked skin
Fick’s Law of Diffusion
Rate of gas diffusion = D x A x deltaP / T
D = diffusion coefficient of gas
A = surface Area
deltaP = difference in partial pressure of gas across membrane
T = thicc ness ;-)
Alveolar gas equation
PAO2 = (PB - PH2O) x FiO2 - (PACO2 / 0.8)
ex. (760 - 47) x .21 - (40 /0.8) = 100
PB = barometric pressure
A-a Gradient
PAO2 - PaO2
ex. 100-92 = 8
normal 5-15
increases with age, obesity, supine position, heavy exercise
What equation is a good indicator of overall gas exchange?
A/a ratio
PAO2 / PaO2
normal >75%
Oxygen content equation
CaO2 = (HB x 1.34 x SaO2) + (PaO2 x 0.003)
CaO2 = 20.4
CvO2 = 15 mL o2/100mL blood
CaO2 - CvO2 = 5 mL O2/100 mL blood (consumption)
Oxygen delivery
= CO x CaO2
ex. 5 x 200 = 1000mL/min
Fick Equation/Oxygen consumption
VO2 = CO x (CaO2 - CvO2)
ex.. 5 x (200-150) = 250mL/min
CO2/Alveolar ventilation equation
PaCO2 = VCO2 / VA
shows that PACO2 levels are inversely proportional to alveolar ventilation
PaO2/FiO2 ratio (P/F ratio)
= PaO2 / FiO2
ex. 100 / .21 = 476
normal 400-500
P/F ratio <300 indicates
mild ARDS
P/F ratio <200 indicates
moderate ARDS
P/F ratio < 100 indicates
severe ARDS
