Respiratory Flashcards
Define hypoxia
Decrease in level of oxygen supplied to tissues
Define hypoxemia
Inadequate oxygenation of arterial blood and is defined as PaO2<80 mm Hg (at sea level)
DO2 =
CO x CaO2
List 5 causes of hypoxemia
Hypoventilation VQ mismatch Diffusion impairment Decreased FiO2 Intrapulmonary shunt
Which of the 5 causes of hypoxemia do not respond to oxygen supplementation?
Intrapulmonary shunt
When is supplemental oxygen indicated?
SpO2< 93%
Arterial oxygen content formula
[1.34 (ml O2/g) x SaO2 (%) x Hb (g/dL)] + [0.003 (ml O2/dl/mmHg) x PaO2 (mm Hg)]
Risks of using non-humidified oxygen:
- Drying and dehydration of nasal mucosa
- Respiratory epithelial degeneration
- Impaired mucociliary clearance
- Increased risk of infection
What is hyperbaric oxygen
100% oxygen under supraatmospheric pressures (>760 mm Hg) to increase the percent dissolved oxygen in bloodstream by 10-20%
Phases of oxygen toxicity
- Initiation: 24-72h of exposure to 100% O2; ROS damage
- Inflammatory phase: pulmonary epithelial lining destroyed and inflammatory cells recruited, massive release of inflammatory mediators results in increased tissue permeability and pulmonary edema
- Destruction: severe local destruction, many die
- Proliferation: type 2 pneumocytes and monocytes recruited
- Fibrosis: collagen deposition and interstitial fibrosis
Correlation b/t PaO2 and SaO2
PaO2 500 = 100% SaO2 PaO2 125 = 99% SaO2 PaO2 100 = 98% SaO2 PaO2 80 (hypoxemia) = <90%
P50 PaO2 29, SaO2 50
Primary physiologic cause of hypoxemia.
Low FiO2
Global hypoventilation
Venous admixture
Causes of venous admixture
Low V/Q region
Atelectasis (no V/Q)
Diffusion defects
Right to left shunts (PDA, VSD, intrapulmonary AV shunt)
Thickness of an alveolar wall
0.3 um
What is the smallest airway without aveoli?
terminal bronchioles
Conducting ariways end with…
terminal bronchioles
What is anatomic dead space?
Airway w/o alveoli - ends at terminal bronchioles
Define acinus
portion of lung distal to terminal bronchiole
External intercostal muscles aid in..
Inhalation
Internal intercostal muscles aid in…
Forced exhalation
Where does the velocity of gas decrease the most in the?
terminal bronchioles (so inhaled particles end up here most)
Weibel diagram
Conducting zone = trachea –> bronchi –> bronchioles –> terminal bronchioles
Transitional and respiratory zone –> respiratory bronchioles –> alevolar ducts –> alveolar sac
Respiratory capillary diameter
7-10 um
How long does an RBC spend in the capillary network?
0.75 s
Bronchial circulation supplies.
Conducting zone (trachea to terminal bronchioles)
Surface area of the lungs
50-100 meters squared
aveoli in lung
500 million
Alveoli diameter
0.3 mm
Function of surfactant
Decrease surface tension in alveoli
When oxygen moves from the thin side of the blood-gas barrier from the alveolar gas to hemoglobin of the RBC, it traverses the following layers in order:
Surfactant, epithelial cell, interstitium, endothelial cell, plasma, red cell membrane
What is the PO2 of inspired gas at Mt. Everest (barometric pressure of 247 mm Hg)?
247-47 (water vapor) x 0.21 = 42 mm Hg
What is the predominant mode of gas flow in the alveolar ducts?
Difffusion
Define tidal volume
volume inspired normally
Devine vital capacity
Max inspiration and max expiration = inspiratory reserve volume + tidal volume + expiratory reserve volume
Residual volume
gas that remained in lung after maximal expiration
Functional residual capacity
volume of gas in lung after a normal expiration = expiratory reserve volume + residual volume
Inspiratory capacity
Tidal volume + inspiratory reserve volume
What does Boyle’s law state?
Pressure x volume is constant (at constant temperature)
PV = K
What is alveolar ventilation?
Volume of fresh gas entering the respiratory zone each minute; (tidal volume - dead space) x resp freq
How can you increase alveolar ventilation?
increased tidal volume or respiratory frequency
Increasing tidal volume more effective b/c reduces proportion of each breath occupied by anatomic dead space
What is the alveolar ventilation equation?
VA = (VCO2/PCO2) x K
What is anatomic dead space?
Volume of the conducting airways
What is the Bohr equation?
VD/VT = (PACO2-PECO2)/PACO2
VD = dead space VT = tidal volume A = alveolar E = mixed expired
Bohr eqn: AEA (my initials:)
All of the expired CO2 comes from the alveolar gas and none from the dead space. MEASURES PHYSIOLOGIC DEAD SPACE
What is the normal ratio of dead space:tidal volume during resting breathing?
0.2-0.35
What is physiologic dead space?
Volume of gas that does not eliminate CO2
T/F. Anatomic dead space increases with many lung diseases
F - physiologic dead space increases
T/F. Upper regions of the lung ventilate better than lower regions.
F - Lower regions ventilate better than upper zones
What lung volumes cannot be measured with a simple spirometer?
total lung capacity, functional residual capacity, residual volume
They can be measured with helium dilution or body plethysomograph
T/F. The concentration of CO2 (and therefore its partial pressure) in alveolar gas and arterial blood is inversely related to the alveolar ventilation.
T
What does Fick’s law state regarding diffuson?
The rate of transfer of a gas through a sheet of tissue is proportional to the tissue area and the difference in gas partial pressure between the two sides, and inversely proportional to the tissue thickness
Diffusion rate proportional to partial pressure difference
Diffusion rate proportional to solubility of gas in tissue and inversely propotional to its molecular weight
CO2 diffuses ____ times more rapidly than O2 because it ha a higher _____
20 x
solubility
Transfer of carbon monoxide is….
diffusion limited b/t the amt of CO that gets into blood limited by diffusive properties and not amt of blood available
What gas is perfusion limited?
nitrous oxide (doesn’t bind with Hbg so partial pressure rises rapidly in blood, so blood flow depends on uptake)
T/F. Under resting conditions, the capillary PO2 virtually reaches that of alveolar gas when red cell is 1/3rd the way along the capillary.
T
Diffusion process challenged by:
exercise, alveolar hypoxia, thickening of the blood-gas barrier
Normal diffusing capacity
25 ml/min/mmHg
carbon monoxide used to determine
Formula = VCO2/PACO2
T/F. Oxygen transfer is normally diffusion limited.
F - Perfusion limited
Under what circumstances does oxygen transfer become diffusion limited?
Intense exercise, thickened blood-gas barrier, alveolar hypoxia
What is transmural pressure?
Pressure difference between the inside and outside of capillaries
What is normal pulmonary vascular resistance?
1.7 mm Hg/L/min
What are the two mechanisms for why an increase in pulmonary arterial venous or arterial pressure causes the pulmonary vascular resistance to fall?
Recruitment (opening of previously closed) and distension (increase caliber of vessels)
Recruitment more with increase in arterial pressure
Distention more with increase in venous pressure
What is hypoxic pulmonary vasoconstriction?
Contraction of smooth muscle in the walls of the small arterioles in the hypoxic region. PAO2 of pulmonary gas determines this reaction. When PAO2 < 70 mm Hg, marked vasoconstriction occurs.
What is the primary constituent of pulmonary surfactant?
dipamlitoyl phosphatidylcholine
Ratio of total systemic vascular resistance to pulmonary vascular resistance
10:1
What two wave wavelengths do pulse oximeters use?
660 and 940 mm
What are the 4 causes of venous admixture?
low VQ regions, small airway and alveolar collapse (atelectasis), diffusion defects, anatomic right to left shunts
T/F Cats have a right shift oxygemoglobin dissociation curve compared to dogs
T
What are examples of diffusion defects for venous admixture?
Oxygen toxicity, smoke inhalation, ARDS
T/F. Oxygen concentration is lower at higher altitudes
F - Still 21%, barometric pressure is lower so PatmO2 is lower
What gas is highest in the alveoli?
nitrogen (560 mm Hg)
T/F. Hypoventilation is a cause of hypoxemia in patients breathing room air but not in patients breathing enriched oxygen mixtures
T - With 100% oxygen, nitrogen is decreases to nearly 0 and oxygen increases to 665, alveolar CO2 could theoretically rise to 550 mm Hg before the alveolar oxygen decreased to a level that would lead to hypoxemia (PaO2 <80)
What is the difference between a physiologic shunt and a true or anatomic shunt?
physiologic: blood flowing past nonfxnal alveoli
true: blood completely bypasses alveoli (be they fxnal or not)
What cell proliferation is responsible for diffusion defect?
cuboidal, type 2 pneumocytes (normal is flat type 1)
What is the normal A-a gradient?
20 mm Hg = venous admixture
What is minute ventilation?
TV x RR
alveolar and dead space ventilation
What are causes of hypercapnia?
hypoventilation, increase in dead space ventilation, increased CO2 production, increased inspired CO2
Fowler’s method measures what?
Anatomic dead space
Measures concentration of a tracer gas (nitrogen) over time
Bohr’s method measures what?
Physiologic dead space
Volume of lung that does not eliminate CO2
What is the conclusion from the alveolar ventilation equation (VA = (VCO2/PaCO2) x K)
The only physiologic reason for increased PaCO2 is level of alveolar ventilation that is inadequate for the amount of CO2 produced by tissues
Normal dog PaCO2
30-42 mm Hg
Normal cat PaCO2
25-36 mm Hg
Venous CO2 is usually ___ higher than arterial CO2
3-6 mm Hg
What are the 3 neurons involved in the respiratory control center in medulla and pons?
- medullary respiratory center
- apneustic center
- pneumotaxic center
The medullary respiratory center is split into ….
Dorsal and ventral respiratory group
What is special about the dorsal respiratory group?
Located in region of nucleus tractus solitarius, where visceral afferents from cranial nerves IX and X terminate
responsible primarily for INSPIRATION (intrinsic periodic firing)
What are the 4 nuclei in the ventral respiratory group of the medullary resp center?
- Nucleus retrroambiguus
- Nucleus para-ambiguus
- Nucleus retrofacialis
- pre-Botzinger complex
What is the job of the ventral resp group of medullary resp center?
Controls voluntary forced exhalation and acts to increase the force of inspiration
What does the apneustic center do?
coordinates the speed of inhalation and exhalation; can be over ridden by pneumotaxic center
Where is the apneustic center?
lower (ventral) pons
Where is the pneumotaxic center and what does it do?
upper (dorsal) pons
Sends inhibitory impulses to the inspiratory center, terminating inspiration, and regulates inspiratory volume and RR
The descending automatic pathways (in anterolateral white matter of cord) are where…
paramedian reticular formation of the medullary and pontine tegmentum and laterally in the high cervical cord in close proximity with the spinothalamic tract
The descending voluntary pathways are where…
associated with the corticospinal tracts in brainstem and upper cervical cord
Phrenic motor neurons are where?
C3-C5
Intercostal motor neurons were where?
T2-12
Where are central chemoreceptors found?
medulla
Where are peripheral chemoreceptors found?
carotid and aortic bodies
Central chemoreceptors responsible for ___% of resp response to CO2
85%
What happens to CO2 that diffuses into brain?
Hydrated to carbonic acid –> dissociates to H+ and HCO3-; so the H+ is what actually stimulates respiration
Peripheral chemoreceptors respond to these 4 things to increase ventilation
Decreased pH, decreased PaO2, increased PaCO2, hypoperfusion
Peripheral chemoreceptors are exclusively responsible for the increased ventilation secondary to _____
hypoxemia
What is the Hering-Breuer inflation reflex?
pulmonary stretch receptors in SM respond to excessive stretch with large inspiration by sending action potentials thru large myelinated fibers of the vagus nerve to inspiratory area of medualla and apneustic center in pons; inhibits inspiratory discharge
main effect = slowing respiratory frequency by increasing expiratory time
Where are “irritant receptors” and what do they do?
Between airway epithelial cells, stimulated by noxious gases, cold, and inhaled dust; send AP via vagus causing BRONCHOCONSTRICTION AND INCREASED RR
What are “J” receptors and what do they do?
juxtacapillary receptors in alveolar walls close to capillaries
respond rapidly to chemicals in pulm circulation, distension of capillary walls, and accumulation of interstitial fluid to cause rapid, shallow breathing
How are arterial baroreceptors involved in ventilation?
Low blood pressure - hyperventilation
Large increase BP - hypoventilation
Strength of muscle contraction to inspire must overcome two main sources of impedance:
- elastic recoil of lungs and chest wall
2. resistance to gas flow (upper airways)
Carbon dioxide narcosis
PaCO2 > 90mmHg
What accounts for the normal v-a CO2 difference?
10% dissolved CO2 and 90% bound CO2 in RBC as bicarbonate from tissues back to lungs
What 3 things affect venous CO2?
PaCO2, de novo tissue CO2 production, tissue blood flow
What does Henry’s law say?
The amount of dissolved gas if proportional to the partial pressure
What is oxygen capacity?
Maximum number of O2 that can combine with Hb
Normal is 20.8 ml O2/dL blood
What is oxygen saturation?
Percentage of available binding sites that have oxygen attached.
O2 combined with Hb / O2 capacity x 100
What are the conformational changes to hemoglobin in respect to oxygenation of Hb?
R (relaxed) state with oxygenated
T (tense) state when deoxygenated
What shifts the oxygen dissociation curve to the right?
Increased temperature, 2,3-DPG, PCO2, hydrogen ions
Remember exercising muscle is hot, acidotic, hypercarbic and needs more oxygen in tissues
T/F. A right shift on the oxygen dissociation curve means the affinity of oxygen to hemoglobin is stronger.
F - means it is weaker so more O2 can be unloaded to tissues for the same given PO2
What is 2,3 DPG?
2,3-diphosphoglycerate = end product of red cell metabolism. This increased in chronic hypoxia and high altitudes. In stored RBC, 2,3-DPG reduced, so may not be that great at offloading oxygen.
A small addition of carbon monoxide to blood causes a left or right shift to O2 dissociation curve?
Left
Carbon monoxide affinity for Hb is ___ times greater than oxygen’s affinity for Hb
240
Means same amt of CO with bind with Hb when partial pressure of CO is 240 times lower than oxygen’s PP