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What are the lung volumes as seen on spirometry?
- Tidal Volume (Vt): 500mL, normal amount of gas that enters or leaves in a single respiratory cycle
- Functional Residual Capacity (FRC): 2700mL, volume of gas left in lungs at end of Vt (passive expiration)
- Inspiratory capacity (IC): 4000mL, volume of gas that can be inspired from FRC
- Inspiratory Reserve Volume (IRV): 3500mL, volume of gas that can be additionaly inhaled after normal inspiration
- Expiratory Reserve Volume (ERV): 1500mL, volume of gas that can be additionaly exhaled after normal expiration
- Residual Volume (RV): 1200mL, amount of gas left in lungs after maximal expiration
- Vital Capacity (VC): 5500mL, maximal volume that can be expired after maximal inspiration
- Total Lung Capacity (TLC): 6700mL, total amount of gas in lungs after maximal inspiration.
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Draw a mental spirometry lung volume curve?
Do it.
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What cannot be measured using spirometry, what is used instead?
- Residual Volume (RV), or anything containing RV (TLC, FRC)
- Helium dilution
- plethysmography.
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What is total ventilation?
Total ventilation (ve)= Vt x RR.
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Where does anatomic dead space end, what is a good way to approximate anatomic dead space?
- Terminal bronchioles
- Persons weight in pounds (i.e. 150lbs = 150mL dead space).
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What constitutes alveolar dead space?
Alveoli containing air but without blood flow in surrounding capillaries.
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What is the physiologic dead space?
Total dead space: anatomical + alveolar dead space.
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What is alveolar ventilation?
- Alveolar ventilation (Va) = (Vt-Vd) x RR
- Vt: Tidal volume
- Vd: Dead space.
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What is the difference between increasing depth of breathing versus rate of breathing?
- Increasing depth: increases actual alveolar ventilation because dead space does not change
- Increasing rate: more ventilation of dead space.
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What is the major muscle of inspiration?
- Diaphragm
- Chest wall second.
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What is the major muscle of expiration?
- Resting conditions: passive process, relaxation of inspiratory muscles
- Active expiration: Abdominal muscles.
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What are the two main forces acting on the lung?
- Recoil: acts to collapse lung
- Intrapleural pressure: usually subatmospheric (negative pressure), acts to expand the lung (or collapse when positive pressure).
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What happens to systemic venous return and R ventricular output with inspiration?
Both are increased.
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What happens to venous return to L heart and L ventricular output in inspiration?
Both are decreased.
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What is the reflex increase in heart rate with inspiration (sinus arrythmia)?
Expansion of R atrium -> drop in BP -> reflex increase in HR.
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What does a valsalve maneuver do?
- Increase intrapleural pressure
- Increase central venous pressure
- Decrease venous return.
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What is the point of PEEP?
- PEEP: positive end expiratory pressure
- prevents collapse of small alveoli (atelectasis).
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What are the changes that occur with a simple pneumothorax?
- Intrapleural pressure increases
- Lung recoil decreses (lung collapses)
- Chest wall expands.
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Tension pneumothorax most commonly occurs in?
Patients on positive-pressure ventilator.
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What is compliance?
dP/dV.
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What happens to compliance as lungs inflate?
Decreases.
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Very compliant lungs have decreased?
Recoil.
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Stiff lungs have increased?
Recoil.
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What are the two components of lung recoil?
- Lung Tissue: collagen and elastin fibers, larger lungs have greater recoil
- Surface Tension: Greatest component of recoil.
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How does the law of LaPlace involve two different sized alveoli?
- If wall tension is the same in both alveoli, the smaller alveolus will have greater pressure
- i.e. more likely to collapse.
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What are the three main functions of surfactant?
- Lowers surface tension: lowers lung recoil, increases compliance
- Lowers surface tension more in smaller alveoli: decreases tendency for atelectasis
- Decreases capilllary filtration pressure: Decreases negative intrathoracic pressure.
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What is the cause of infant respiratory distress syndrome, another name?
- Deficiency of surfactant
- Hyaline Membrane Disease.
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What are the two main causes of adult respiratory distress syndrome (ARDS)?
- Sepsis: injury to endothelial capillary membrane by neutrophils
- Gastric Aspirations: direct injury to lung epithelium.
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What are the three main symptoms of ARDS?
- Increased lung recoil, decreased compliance
- Atelectasis
- Pulmonary edema.
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Resistance of an airway equals?
Resistance= 1/radius^4.
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What bronchi represent most of the airway resistance?
First and second.
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What produces bronchoconstriction?
Parasympathetic nerve stimulation.
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What produces bronchodilation?
Circulating catecholamines.
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What is normal FEV1/FVC?
80%.
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What characterizes obstructive pulmonary disease, what is it measured as?
- Increase in airway resistance
- Decreased expiratory flow rates
- FEV1/FVC: 50%.
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What characterizes restrictive pulmonary disease, what is it measured as?
- Inrease in lung recoil, decreased compliance
- Most lung volumes decreased, especially FRC, RV
- FEV1/FVC: 88%.
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How do you calculate the partial pressure of a gas?
- Pgas = Patm x Fgas
- Pgas: partial pressure of gas
- Fgas: concentration of gas
- Patm: atmospheric pressure.
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How do you calculate the partial pressure of an inspired gas?
PIgas= Fgas x (Patm-PH2O).
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What does partial pressure of water (PH2O) depend on?
- Temperature only
- at 37 C: 47 mm Hg.
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What is the normal Alveolar-arterial (A-a) gradient?
5-10 mm Hg.
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What two factors affect alveolar PCO2 (PACO2)?
- Metabolic production of CO2: constant under normal circumstances
- Alveolar ventilation: inversely related to PACO2.
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What is the equation showing factors that affect Alveolar PO2 (PAO2)?
- PAO2 = (Patm-47)FIO2 x PACO2/R
- R: Respiratory exchange ration = o.8.
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What factors affect diffusion of a gas between alveoli and capillaries (gas exchange)?
- Fick Law of Diffusion
- Vgas= A/T x D x (P1-P2)
- Vgas: rate of gas diffusion
- A: surface area of lung
- T: Thickness of membrane
- P1-P2: Pressure gradient.
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What are the two terms to describe dynamics of substance transfer b/w capillaries and interstitium?
- Perfusion-limited: the substance equalizes
- Diffision-limited: the substance does not equalize.
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What is a classic, always diffusion limited substance?
Carbon Monoxide (CO).
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What is a normal CO uptake?
25 mL/min.
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What is the normal carrying capacity for O2?
- 20% volume
- .2mL O2/1 mL blood.
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What shifts the O2-Hb curve to the left?
- Increased CO2 (Bohr Effect)
- Increased H+ (decreased pH)
- Increased 2,3-DPG
- Increased Temperature.
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What shifts the O2-Hb curve to the right?
- Everything opposite as left
- Fetal Hemoglobin (HbF)
- Stored blood (loss of 2,3-DPG).
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About 90% of CO2 is carried as?
Plasma Bicarbonate (H2CO3).
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What enzyme is needed to convert CO2 into bicarbonate, where is it found?
- Carbonic anhydrase
- Insede red cell
- CO2 + H2O -> H2CO3 -> H+ + HCO3-.
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What is the main drive for ventilation under normal conditions?
CO2 (H+) on central chemoreceptors.
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Where are the central chemoreceptors found, what do they sense?
- Close to surface of medulla
- CSF H+: CO2 freely crosses BBB, bicarbonate dissociates -> H+.
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What are the two peripheral receptors and afferent nerves?
- Carotid bodies: Carotid sinus, Glossopharyngeal nerve IX -- most important
- Aortic bodies: Aortic arch, Vagus nerve X.
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What do the peripheral receptors respond to?
PO2 in very hypoxic situations.
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Which receptors adapt, which do not?
- Central chemoreceptors adapt
- Peripheral do not.
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What nerve communicates the medulla (breathing center) to the diaphragm?
Phrenic nerve.
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A lesion at what levels would preveng diaphragmatic breathing?
Complete C1 or C2.
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What is Apneustic breathing?
- Prolonged inspiration with shortened expiration
- Lesion in caudal pons.
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What is Biot's breathing?
- Alternating apnea with periods of identical depth breaths
- Seen in increased intracranial pressure and midbrain lesions.
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What is Cheyne-Stokes breathing?
- Alternating apnea with periods of "crescendo-decrescendo" depth breaths
- Seen in infants and sleep, also some midbrain lesions.
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What are four causes of hypoxemia?
- Hypoventilation
- Diffusion Impairment
- Pulmonary (right to left) shunt
- Ventilation-perfusion mismatch.
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What happens to the A-a gradient with hypoventilation?
- No change
- Decrease of PO2 equal in all compartments (Alveolar, end capillary, systemic arterial).
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What does an A-a gradient greater than 10 usually signify?
Diffusion impairment.
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What is a clue of a pulmonary shunt?
Failure to correct hypoxemia with supplemental oxygen.
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Which alveoli recieve more ventilation, apex or base?
- Base: higher compliance (less inflated at rest)
- Apex have more negative pressure -> more inflated at rest -> lower compliance.
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What is the ideal ventilation/perfusion (V/Q) ratio, what does it mean when it is lower, higher?
- V/Q: 0.8, pH= 7.4
- V/Q < 0.8: underventilated, pH <7.4
- V/Q > 0.8: overventilated, pH > 7.4.
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