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Respiratory Physiology Flashcards

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1
Q

Inspiration Muscles

A

Diaphragm & external intercostals

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2
Q

Inspiration ACCESSORY Muscles

A

Sternocleidomastoid
Anterior/middle/posterior scalenes

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3
Q

What law applies to breathing & inspiration?

A

Boyle P1V1 = P2V2

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4
Q

Expiration Muscles

A

PASSIVE
Driven by chest wall recoil

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5
Q

Active Expiration Muscles

A

Transverse abdominis
Internal & external oblique
Internal intercostals

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6
Q

How many functional airway divisions are present?

A

23 divisions/generations

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7
Q

What are the 3 respiratory zones?

A

Conducting
Transitional
Respiratory (gas exchange)

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8
Q

Conducting Zone

A

Trachea, bronchi, & bronchioles
Ends w/ terminal bronchioles
Function to facilitate bulk gas movement
DEAD SPACE 150 mL or 2 mL/kg

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9
Q

Trachea

A

Conducting zone
Generation 0
Cilia present
Smooth muscle present
Cartilage present

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10
Q

Bronchi

A

Conducting zone
Generation 1-3
Cilia present
Smooth muscle present
Cartilage patchy

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11
Q

Bronchioles

A

Conducting zone
Generation 4
Cilia present
Smooth muscle present
NO cartilage

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12
Q

Transitional zone

A

Respiratory bronchioles
Duel function - air conduit & gas exchange

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13
Q

Respiratory Bronchioles

A

Transitional zone (sometimes noted as respiratory zone)
Generation 17
Some cilia & smooth muscle present
NO cartilage

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14
Q

Respiratory Zone

A

Gas exchange
Alveolar ducts & sacs

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15
Q

How does gas exchange occur?

A

Gas exchange occurs across the flat epithelium (type 1 pneumocytes) via diffusion

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16
Q

Alveolar Ducts

A

Generation 20
Some smooth muscle
NO cilia or cartilage

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17
Q

Alveolar Sacs

A

Generation 23
NO cilia, smooth muscle, or cartilage

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18
Q

What airway structures are susceptible to external compression?

A

Bronchioles & alveolar ducts
Do NOT contain cartilage

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19
Q

What keeps the airways open?

A

Positive (+) transpulmonary pressure Ptp

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20
Q

Minute ventilation

A

VE = Tidal volume (VT) x RR
Volume gas patient inhales & exhales over 1 minute
Inversely r/t PaCO2
Reference adult value = 4 L/min

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21
Q

Alveolar ventilation

A

VA = (Tidal volume - dead space) x RR
OR
= CO2 production / PaCO2

1° determinant CO2 elimination
Only measures VE available to participate in gas exchange

Directly proportional to CO2 production
Inversely proportional to PaCO2

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22
Q

Anatomic Dead Space

A

Air confined to the conducting airways

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23
Q

Alveolar Dead Space

A

Alveoli that are ventilated, but not perfused

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24
Q

Physiologic Dead Space

A

= Anatomic Vd + Alveolar Vd

Calculated w/ Bohr equation
Vd/Vt = (PaCO2 - PeCO2) / PaCO2

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25
Apparatus Dead Space
Vd added by equipment Facemask or HME Circle system
26
Dead Space to Tidal Volume Ratio
= Vd/Vt % Fraction tidal volume that contributes to dead space Reference adult value 33% during spontaneous ventilation Normal 150 mL / 450 mL = 0.33 50% during mechanical ventilation
27
↑Dead Space
Facemask, HME, PPV Atropine (anticholinergic) bronchodilation ↑conducting airway volume Old age Neck extension opens the hypopharynx HoTN, ↓CO, COPD, PE (thrombus, air, amniotic fluid) ↓pulmonary blood flow
28
↓Dead Space
- ETT, LMA, trach - Neck flexion - ↑CO - Position (supine or Trendelenburg)
29
Compliance
Compliance = ∆V / ∆P
30
Alveolar Compliance Curve Normal Upright Awake Adult
Non-dependent APEX ↑PAO2 ↓PACO2 ↑V/Q ratio (V>Q) ↓compliance ↓alveolar ventilation ↓pulmonary blood flow ↓alveolar perfusion Dependent BASE ↓PAO2 ↑PACO2 ↓V/Q ratio (V
31
Normal Va/Q Ratio
= 0.8 Ventilation = 4 L/min Perfusion = 5 L/min
32
Ventilation / Perfusion Mismatch
↑A-a gradient Bronchioles constrict to minimize zone 1 HPV minimizes shunt Blood passing through under ventilated alveoli tends to retain CO2
33
What is the most common cause of hypoxemia in the PACU?
Atelectasis Shunt V/Q = 0 Blood retains CO2 ↑PaCO2
34
What indicates severe V/Q mismatch?
Retained CO2 ↑PaCO2
35
Dead Space
Vd V/Q = ꝏ Ventilation but no perfusion Overventilated alveoli give off an excessive amount CO2 *CO2 diffuses 20x faster than oxygen* Apex V > Q Zone 1
36
Shunt
Shunt or venous admixture V/Q = 0 Perfusion but no ventilation Under-ventilated alveoli retains CO2 and unable to take in enough oxygen Base V < Q Zone 3
37
What law applies to alveolar surface tension?
Law of LaPlace P = (2 x T) / r P = pressure T = tension r = radius
38
What equalizes surface tension effects?
Surfactant ↓radius ↑surfactant concentration
39
When does surfactant production begin & peak?
Begins at 22-26 weeks gestation Peaks at 35-36 weeks
40
West Zones
1. Dead space 2. Ventilation matched to perfusion V/Q = 1 3. Shunt
41
West Zone 1
Alveolar pressure PA > arterial pressure Pa > venous pressure Pv Bronchioles constrict to minimize ventilation to poorly perfused alveoli
42
West Zone 1 Causes
HoTN, PE, excessive airway pressure (PPV or PEEP)
43
West Zone 2
Pa > PA > Pv Blood flow directly proportional to Pa-PA difference
44
West Zone 3
Pa > Pv > PA Any venous blood that empties directly into L side heart or bypasses the lungs HPV ↓pulmonary blood flow to poorly ventilated alveoli
45
Where to place the PA catheter tip?
West zone 3 Capillary pressure > alveolus Vessel always open & blood moving through
46
What are 3 anatomic shunt sites?
Thesbian, bronchiolar, & pleural veins
47
West Zone 4
Pa > Pis > Pv > PA Pulmonary edema
48
West Zone 4 Causes
↑capillary hydrostatic pressure - Fluid overload, mitral stenosis, and sever pulmonary vasoconstriction Profound reduction in pleural pressure - Laryngospasm or inhalation against closed glottis → negative pressure pulmonary edema
49
Alveolar Gas Equation
Used to estimate partial pressure O2 in the alveoli PAO2 = FiO2 x (PB − PH2O) − (PaCO2 / RQ)
50
Respiratory Quotient
= CO2 production / O2 consumption = 200 mL/min / 250 mL/min = 0.8
51
Hypoxemia
Low O2 concentration in the blood PaO2 < 80 mmHg
52
Hypoxia
Insufficient O2 to support the tissues
53
Hypoxemia Causes
1. Hypoxic mixture 2. Hypoventilation 3. Diffusion limitation 4. V/Q mismatch 5. Shunt
54
Hypoxic Mixture Causes
O2 pipeline failure High altitude
55
Hypoxic Mixture Presentation & Treatment
Normal A − a gradient Administer supplemental FiO2
56
Hypoventilation Causes
Opioid overdose Residual anesthetic agent Residual NMB Neuromuscular disease Obesity hypoventilation
57
Hypoventilation Presentation & Treatment
Normal A − a gradient Fix underlying cause - Narcan - Adequate NMB reversal Supportive ventilation CPAP/BiPAP Administer supplemental FiO2
58
V/Q Mismatch Causes
COPD One-lung ventilation Impaired HPV Embolism - air, gas, amniotic fluid
59
V/Q Mismatch Presentation & Treatment
↑A − a gradient Resume 2-lung ventilation Decrease/discontinue drugs that inhibit HPV Identify & treat embolism Administer supplemental FiO2
60
Diffusion Impairment Causes
Pulmonary fibrosis Emphysema Interstitial lung disease
61
Diffusion Impairment Presentation & Treatment
↑A − a gradient Administer supplemental FiO2
62
Shunt Causes
R→L shunt Atelectasis Pneumonia Bronchial intubation Intracardiac shunt
63
Shunt Presentation & Treatment
↑A − a gradient Supplemental FiO2 does NOT help
64
A − a Gradient
PAO2 − PaO2 Normal < 15 mmHg (physiologic shunt)
65
How much does shunt increase A − a gradient?
↑1% every 20 mmHg
66
Lung Volumes
IRV Vt ERV RV *Based on healthy 70 kg male
67
Lung Capacities
2+ lung volumes IC VC FRC TLC *Based on healthy 70 kg male
68
What are lung volumes & capacities based on?
IBW Healthy 70 kg male
69
How do lung volumes & capacities differ in females?
↓25%
70
IRV mL
3,000 mL
71
Tidal Volume mL
Vt = 500 mL OR 6-8 mL/kg IBW
72
ERV mL
1,100 mL
73
RV mL
Unable to measure 1,200 mL
74
Closing Volume
Variable Lung volume above RV when small airways begin to close/collapse
75
Closing Volume % TLC
30% TLC at 20 yo 55% TLC at 70 yo
76
IC mL
Inspiratory capacity IRV + Vt = 3,500 mL
77
Lung Capacities
2+ lung volumes = capacity
78
VC mL
Vital capacity IRV + Vt + ERV = 4,600 mL OR 65-75 mL/kg
79
FRC mL
Functional residual capacity ERV + RV = 2,300 mL OR 35 mL/kg Volume at end-expiration
80
TLC mL
IRV + Vt + ERV + RV = 5,800 mL
81
Closing Capacity
RV + CV = variable Absolute lung volume when small airways begin to close/collapse
82
What patients & scenarios does CC = FRC?
Neonate 30 yo under GA Supine 40 yo adult Standing or sitting 65 yo
83
What happens when CC ≥ FRC?
Airway closure during normal tidal volume breaths → intrapulmonary shunting & hypoxemia ↑WOB Unable to measure w/ spirometry
84
How to measure CV or CC?
Nitrogen or Xenon
85
Define FRC
Lung volume when inward elastic recoil (lung) balanced by the outward recoil (chest wall) = static equilibrium O2 reserve that prevents hypoxemia during apnea
86
What formula represents the time until an apneic patient desaturates?
= FRC / VO2 VO2 = oxygen consumption
87
↑FRC
COPD Advanced age elasticity ↑air trapping PEEP Position: - Sitting - Lateral - Prone
88
↓FRC
General anesthesia 50% reduction NMBs Obesity, pregnancy, and neonates Fluid overload or pulmonary edema ↑FiO2 → absorption atelectasis Position: - Supine - Lithotomy - Trendelenburg
89
Oxygen Content
CaO2 = (Hgb x SaO2 x 1.34) + (PaO2 x 0.003) O2 forms reversible bond w/ Hgb 97% O2 dissolved in the blood plasma 3%
90
Normal Hgb/Hct
Hgb 13-15 g/dL Hct 39-45%
91
What law applies to O2 dissolved in the blood plasma?
Henry's law = gas concentration in a solution α gas partial pressure above the solution Oxygen 20x less soluble than CO2
92
Normal CaO2
20.4 mL O2 per dL
93
Oxygen Delivery
DO2 = CaO2 x CO x 10 How fast O2 delivered to the tissues
94
What mechanism/factor drives O2 delivery?
Cardiac output
95
What converts dL → L?
Conversion factor = 10
96
Normal DO2
1,000 mL O2 per minute
97
Oxygen Consumption
VO2 = CO x (CaO2 − CvO2) x 10 Difference b/w O2 that leaves the lungs & O2 amount that returns
98
What law/principle applies to O2 consumption?
Fick
99
Normal VO2
250 mL/min OR 3.5 mL/kg
100
How does temperature affect VO2?
↓core body temp ↓O2 consumption VO2 ↓5-7% every 1°C
101
FICK PRINCIPLE
Vgas = [Diffision coefficient x (P1 − P2) x Surface area] / Membrane thickness Vgas = (D ∗ ∆P ∗ SA) / T ΔP = partial pressure gradient
102
Oxyhemoglobin Dissociation Curve P50
PaO2 when Hgb 50% saturated by O2 P50 = 26.5 mmHg
103
SpO2 90% : PaO2
90% = PaO2 60 mmHg 80% = PaO2 50 mmHg 75% = PaO2 40 mmHg 60% = PaO2 30 mmHg
104
What causes the carboxyhemoglobin dissociation curve to shift to the LEFT?
LEFT = LOVES - Alkalosis ↑pH ↓H+ - Hypocarbia ↓CO2 - Hypothermia - ↓2,3 DPG - Fetal hemoglobin FHgb α + γ - Benzocaine overdose → methemoglobin MetHgb - Carboyxhemoglobin (smoke inhalation) COHgb - Normal physiology = lungs
105
What causes the carboxyhemoglobin dissociation curve to shift to the RIGHT?
RIGHT = RELEASE - Acidosis ↓pH ↑H+ - Hypercarbia ↑CO2 - Hyperthermia (MH, neuroleptic malignant syndrome, or serotonin syndrome) - ↑2,3 DPG - Normal physiology = tissue level
106
Cellular Energy Currency
ATP Adenosine triphosphate
107
What is the 1° substrate used for ATP synthesis?
Glucose
108
Aerobic Metabolism
1. Glycolysis 2. Krebs cycle 3. Oxidative phosphorylation
109
Glycolysis
Convert 1 glucose to 2 pyruvic acid molecules Net gain 2 ATP
110
Krebs Cycle
Occurs in the mitochondria matrix Produces H+ ions as NADH to be used in the electron transport chain Net gain 2 ATP
111
Oxidative Phosphorylation
Electron transport chain Goal to produce ATP (energy) Net gain 34 ATP
112
Anaerobic Metabolism
Pyruvate acid → lactic acid → lactic acidosis Anion gap metabolic acidosis When oxygen supply reestablished intracellular lactate converted back to pyric acid inside the cell
113
What clears serum lactate?
Liver
114
CO2 Buffer System
H2O + CO2 ↔ H2CO3 (carbonic acid) ↔ H+ + HCO3¯ *Reaction requires carbonic anhydrase enzyme*
115
CO2 Transportation
Bicarbonate HCO3¯ 70% Hgb bound 23% Dissolved in plasma 7%`
116
Bohr Effect
O2 offloading from Hgb CO2 + ↓pH ↑H+ → erythrocyte releases O2 L shift at the tissue level
117
Haldane Effect
CO2 loading onto Hgb ↑O2 → erythrocyte releases CO2 R shift at the lungs
118
Hypercapnia Definition & Equation
Respiratory acidosis PaCO2 > 45 mmHg PaCO2 = (CO2 production) / (Alveolar ventilation)
119
Hypercapnia Causes
1. ↑CO2 production 2. ↓CO2 elimination 3. Rebreathing
120
What consequences are associated w/ hypercapnia?
↑CO2 displaces alveolar O2 → arterial hypoxemia ↓oxygen carrying capacity Oxyhemoglobin curve shifts R ↑P50 releases more O2 to the tissues Myocardial depressant & directly dilates the peripheral vasculature ↑HR ↑MVO2 ↑Pulmonary vascular resistance PVR Respiratory stimulant ↑minute + alveolar ventilation Hyperkalemia H+/K+ pump activation buffers CO2 Acidosis → plasma proteins buffer H+ & release Ca2+ → ↑Ca2+ ↑ICP CO2 freely diffuses across the blood-brain barrier ↓CSF pH ↓cerebrovascular resistance ↑CBF & volume
121
Acute Respiratory Acidosis Predicted pH
Every 10 mmHg > 40 mmHg → pH ↓0.08
122
Chronic Respiratory Acidosis Predicted pH
Every 10 mmHg > 40 mmHg → pH ↓0.03
123
CO2 Ventilatory Response Curve
Describes the relationship b/w PaCO2 & minute ventilation VE
124
What causes the CO2 ventilatory response curve to shift to the LEFT?
Respiratory center ↑sensitivity to CO2 Hypoxemia Metabolic acidosis Surgical stimulation Intracranial HTN ↑ICP Fear & anxiety Salicylates, Aminophylline, Doxapram, & NE
125
What causes the CO2 ventilatory response curve to shift to the RIGHT?
Respiratory center ↓sensitivity to CO2 Metabolic alkalosis Volatile anesthetics Opioids NMBs Post carotid endarterectomy Natural sleep
126
What receptors are the 1° PaCO2 monitor?
Central chemoreceptors in the medulla Respond INDIRECTLY to PaCO2
127
Where is the respiratory control center located?
Reticular activating system RAS in the medulla & pons
128
Respiratory Control Center 1° Function
1° job to determine how fast & deep patient breathes Regulate PaCO2 & PaO2
129
Where does the respiratory control center receive inputs from?
Central & peripheral chemoreceptors AND Stretch receptors in the lungs
130
Where are central chemoreceptors located?
Medulla
131
Where are peripheral chemoreceptors located?
Carotid bodies at the common carotid artery bifurcation AND Transverse aortic arch
132
Outline the central respiratory center
Medulla - DRG/VRG - Central chemoreceptors Pontine - Pneumotaxic (upper pons) - Apneustic (lower pons) Cerebral cortex - conscious breathing control able to modify responses
133
DRG
Dorsal respiratory group or center (DRC) Located in the nucleus tractus solitarius (medulla) Respiratory pacemaker Dorsal = inspiration
134
VRG
Ventral respiratory group or center (VRC) Located in the medulla 1° responsible for expiration Ventral = active expiration More important during exercise or stress
135
Pneumotaxic center
Located in the upper pons Inhibits the DRG (pacemaker) Triggers END inhalation
136
Apneustic Center
Located in the lower pons Stimulates the DRG (pacemaker) Triggers INhalation
137
Define Apneic Threshold
The highest PaCO2 where the patient will NOT breathe
138
How do central chemoreceptors respond to PaCO2?
INDIRECT response to PaCO2 Sends stimulatory impulses to the DRG
139
What 1° stimulates the central chemoreceptors?
CSF pH or H+ ion concentration
140
What receptors are the 1° PaO2 monitor?
Peripheral chemoreceptors Monitor hypoxemia PaO2 < 60 mmHg
141
What do peripheral chemoreceptors 2° monitor?
1° PaO2 2° PaCO2, H+, & perfusion pressure
142
What cells sense & transduce PaO2 into an AP?
Type 1 glomus cells Mediate hypoxic ventilatory drive
143
What serve as the peripheral chemoreceptors afferent limb?
Hering's nerve & glossopharyngeal nerve IX Terminates in the inspiratory center in the medulla
144
How does carotid endarterectomy impair peripheral chemoreceptors?
Severs the afferent limb on the surgical side
145
Pulmonary Reflexes
1. Hering-Breuer inflation reflex 2. Hering-Breuer deflation reflex 3. J receptors 4. Paradoxical head reflex
146
What transduces pulmonary reflexes?
Stretch receptors in the smooth airway muscle transduce pressure conditions in the airway Information transmits along the Vagus → DRG Efferent response via phrenic nerve
147
Hering-Breuer Reflex
INFLATION - When lung inflation > 1.5 L above FRC (3x Vt) reflex turns off the DRG - Stops further inspiration; helps to avoid overinflation - Reflex not active during normal inspiration DEFLATION - Stimulates patient to take a deep breath - Prevents atelectasis
148
J Receptors
Pulmonary C-fiber receptors Stimulation causes tachypnea in response to pulmonary embolism or CHF
149
Paradoxical Head Reflex
Newborn baby stimulus to take 1st breath
150
HPV
Hypoxic pulmonary vasoconstriction Local response to ↓alveolar oxygen tension PAO2 → minimizes shunt Pulmonary vascular bed the only region in the body that responds to hypoxia with vasoconstriction
151
How long to initiate the HPV response? When is the peak effect achieved?
Only seconds to initiate Achieves peak effect ≈ 15 minutes
152
What inhibits HPV?
Volatile anesthetics > 1.5 MAC Phosphodiesterase inhibitors Dobutamine Hypervolemia Excessive PEEP ↑Vt
153
How do volatile agents affect HPV?
Impair HPV ↑shunt fraction & ↓PaO2
154
What preserves HPV?
IV anesthetic agents - Ketamine - Propofol - Opioids

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