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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.
Draw a mental spirometry lung volume curve?
What cannot be measured using spirometry, what is used instead?
- Residual Volume (RV), or anything containing RV (TLC, FRC)
- Helium dilution
What is total ventilation?
Total ventilation (ve)= Vt x RR.
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).
What constitutes alveolar dead space?
Alveoli containing air but without blood flow in surrounding capillaries.
What is the physiologic dead space?
Total dead space: anatomical + alveolar dead space.
What is alveolar ventilation?
- Alveolar ventilation (Va) = (Vt-Vd) x RR
- Vt: Tidal volume
- Vd: Dead space.
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.
What is the major muscle of inspiration?
- Chest wall second.
What is the major muscle of expiration?
- Resting conditions: passive process, relaxation of inspiratory muscles
- Active expiration: Abdominal muscles.
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).
What happens to systemic venous return and R ventricular output with inspiration?
Both are increased.
What happens to venous return to L heart and L ventricular output in inspiration?
Both are decreased.
What is the reflex increase in heart rate with inspiration (sinus arrythmia)?
Expansion of R atrium -> drop in BP -> reflex increase in HR.
What does a valsalve maneuver do?
- Increase intrapleural pressure
- Increase central venous pressure
- Decrease venous return.
What is the point of PEEP?
- PEEP: positive end expiratory pressure
- prevents collapse of small alveoli (atelectasis).
What are the changes that occur with a simple pneumothorax?
- Intrapleural pressure increases
- Lung recoil decreses (lung collapses)
- Chest wall expands.
Tension pneumothorax most commonly occurs in?
Patients on positive-pressure ventilator.
What is compliance?
What happens to compliance as lungs inflate?
Very compliant lungs have decreased?
Stiff lungs have increased?
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.
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.
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.
What is the cause of infant respiratory distress syndrome, another name?
- Deficiency of surfactant
- Hyaline Membrane Disease.
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.
What are the three main symptoms of ARDS?
- Increased lung recoil, decreased compliance
- Pulmonary edema.
Resistance of an airway equals?
What bronchi represent most of the airway resistance?
First and second.
What produces bronchoconstriction?
Parasympathetic nerve stimulation.
What produces bronchodilation?
What is normal FEV1/FVC?
What characterizes obstructive pulmonary disease, what is it measured as?
- Increase in airway resistance
- Decreased expiratory flow rates
- FEV1/FVC: 50%.
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%.
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.
How do you calculate the partial pressure of an inspired gas?
PIgas= Fgas x (Patm-PH2O).
What does partial pressure of water (PH2O) depend on?
- Temperature only
- at 37 C: 47 mm Hg.
What is the normal Alveolar-arterial (A-a) gradient?
5-10 mm Hg.
What two factors affect alveolar PCO2 (PACO2)?
- Metabolic production of CO2: constant under normal circumstances
- Alveolar ventilation: inversely related to PACO2.
What is the equation showing factors that affect Alveolar PO2 (PAO2)?
- PAO2 = (Patm-47)FIO2 x PACO2/R
- R: Respiratory exchange ration = o.8.
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.
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.
What is a classic, always diffusion limited substance?
Carbon Monoxide (CO).
What is a normal CO uptake?
What is the normal carrying capacity for O2?
- 20% volume
- .2mL O2/1 mL blood.
What shifts the O2-Hb curve to the left?
- Increased CO2 (Bohr Effect)
- Increased H+ (decreased pH)
- Increased 2,3-DPG
- Increased Temperature.
What shifts the O2-Hb curve to the right?
- Everything opposite as left
- Fetal Hemoglobin (HbF)
- Stored blood (loss of 2,3-DPG).
About 90% of CO2 is carried as?
Plasma Bicarbonate (H2CO3).
What enzyme is needed to convert CO2 into bicarbonate, where is it found?
- Carbonic anhydrase
- Insede red cell
- CO2 + H2O -> H2CO3 -> H+ + HCO3-.
What is the main drive for ventilation under normal conditions?
CO2 (H+) on central chemoreceptors.
Where are the central chemoreceptors found, what do they sense?
- Close to surface of medulla
- CSF H+: CO2 freely crosses BBB, bicarbonate dissociates -> H+.
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.
What do the peripheral receptors respond to?
PO2 in very hypoxic situations.
Which receptors adapt, which do not?
- Central chemoreceptors adapt
- Peripheral do not.
What nerve communicates the medulla (breathing center) to the diaphragm?
A lesion at what levels would preveng diaphragmatic breathing?
Complete C1 or C2.
What is Apneustic breathing?
- Prolonged inspiration with shortened expiration
- Lesion in caudal pons.
What is Biot's breathing?
- Alternating apnea with periods of identical depth breaths
- Seen in increased intracranial pressure and midbrain lesions.
What is Cheyne-Stokes breathing?
- Alternating apnea with periods of "crescendo-decrescendo" depth breaths
- Seen in infants and sleep, also some midbrain lesions.
What are four causes of hypoxemia?
- Diffusion Impairment
- Pulmonary (right to left) shunt
- Ventilation-perfusion mismatch.
What happens to the A-a gradient with hypoventilation?
- No change
- Decrease of PO2 equal in all compartments (Alveolar, end capillary, systemic arterial).
What does an A-a gradient greater than 10 usually signify?
What is a clue of a pulmonary shunt?
Failure to correct hypoxemia with supplemental oxygen.
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.
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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