Respiratory Physiology Flashcards
Parietal Pleura
Membrane that lines the inner chest wall surface
Visceral Pleura
Membrane that lines the outer lung surface
Pleural Space
Potential space
Contains mucoid/serous fluid that allows the parietal & visceral pleura to slide easily ↓friction
Inspiratory Muscles
Diaphragm 1° ventilation muscle
External intercostals
Accessory muscles - sternocleidomastoid, trapezius, & scalene
Expiration
PASSIVE
Forced Expiration
Internal intercostals
Accessory muscles - internal/external obliques, transversus abdominus, & rectus abdominus
Alveolar Interdependence
Alveoli connected
Negative pressure gradient transfers from outer alveoli to innermost
Radial Traction
Outside airways are tethered to alveolar wall
↑Pel ↑radial traction ↑airway diameter ↓resistance
LaPlace
P = (surface tension x 2) / radius
Air-Liquid Interface
H2O molecules have mutual attraction
Surface tension b/w air & water
Surfactant
Amphipathic molecule (detergent) Polar & non-polar ↓Pel ↓WOB Prevents alveoli from emptying small → large Atelectasis ↓gas exchange
Deadspace
= VT [(PaCO2 - PeCO2) / PaCO2]
Over ventilation and/or under perfusion
Impaired gas exchange → V/Q mismatch ↑V/Q
Causes: PE, hypovolemia, cardiac arrest, shock, ↓pulmonary blood flow
Shunt
Ø alveolar ventilation d/t blockade or edema
Ø gas exchange → V/Q mismatch ↓V/Q
Absolute shunt V/Q = 0
Hypoxia unresponsive to supplemental oxygen
Causes: ETT mainstem, mucus plug, atelectasis, pneumonia, pulmonary edema, anything collapse alveoli
Oxyhemoglobin Dissociation Curve
Right Shift
↑CO2 hypercapnia
↓pH
↑H+ ion
↑temperature
↑BPG (2,3 diphosphoglycerate) ↑metabolism
Acidotic - oxygen more easily dissociates from hemoglobin
↓affinity
Oxyhemoglobin Dissociation Curve
Left Shift
↓CO2 hypocapnia ↑pH alkalosis ↓H+ ion ↓temperature ↓BPG Alkalotic - more difficult to unload oxygen ↑affinity
Fick’s Law
Gas diffusion across the alveolar-capillary membrane
= (area x diffusion coefficient x ΔP) / thickness
Air Components
79% nitrogen
21% oxygen
1% trace gases
Atmospheric Pressure
760mmHg
Upper Airway
Nose, mouth, pharynx, larynx, trachea
Nose
Filtration, smell, & air humidification
Larynx
Epiglottis, thyroid, & cricoid
Paired - arytenoid, corniculate, cuneiform
Motor Innervation
RLN motor all EXCEPT cricothyroid muscle
SLN external - cricothyroid muscle
Sensory Innervation
SLN internal - above & vocal cords
RLN - below the vocal cords
Posterior Cricoarytenoid
Please come apart
Vocal cord ABduction
Lateral Cricoarytenoid
Let’s close airway
Vocal cord ADduction
Cricothyroid
Cords tense
Vocal cord tension = laryngospasm
Thyroarytenoid
They relax
Vocal cord relaxation
Trachea
Incomplete cartilage rings - open posteriorly to prevent tracheal collapse
Transports gases b/w atmosphere & lung parenchyma
Begins at C6 (cricoid cartilage inferior border) & extends to carina
10-15cm
Cricoid = only complete ring
Bifurcates to R/L mainstem bronchus at T5
R Main Bronchus
T5
Shorter, wider, & more vertical
25-30° angle
R mainstem intubation
L Main Bronchus
T5
45° angle
R Lung
55% TLC
3 lobes
L Lung
45%
2 lobes
Diaphragm Innervation
C2-5
Phrenic nerve
Pneumocytes
Type 1 structural
Type 2 surfactant producing
Type 3 macrophages (alveolar)
Conducting Zone
NO gas exchange (anatomic dead-space)
Nose/mouth → terminal bronchioles
Pseudostratified ciliated epithelium transitions → ciliated columnar epithelium → cuboidal epithelium (terminal bronchioles) mucus-secreting goblet cells also present
Blood supply from thyroid, bronchial, & internal thoracic arteries (systemic circulation)
150mL
1/3 VT
2mL/kg IBW
Respiratory Zone
Gas exchange (diffusion) 350mL/500mL
Respiratory bronchioles, alveolar ducts, alveolar sacs, & alveoli
Cuboidal cells transitions → squamous epithelium
Blood supply from pulmonary circulation
Diameter 0.5mm & smaller
Average Adult CARINA
Front incisors to larynx = 13cm
Larynx to carina = 13cm
ETT ideal location 2cm above the carina
Transpulmonary Pressure
Difference b/w intrapleural & intra-alveolar pressures
*Determines lung size
Neuronal Control
Brainstem - medulla & pons
Medulla Control
Medulla control = DRG
Stimulates inspiration
“Pacemaker”
VRG helps w/ forced inspiration/expiration
Pons Control
Modifies medulla output
Pneumotaxic center located high in the pons ↓VT
Apneustic center located lower in the pons ↑VT
- Output limited by baroreflex input from the lung & input from the pneumotaxic center
Humoral Control
Central chemoreceptors response to hydrogen ion levels
Peripheral chemoreceptors respond to CO2, pH, & hypoxemia
Normal Stimulus to Breathe
Hypercapnia
Vagus
Cranial nerve X
Carries aortic arch & lung stretch signal to the DRG
Glossopharyngeal
Cranial nerve IX
Carries the carotid body signals to the DRG
Autonomic Control
PARASYMPATHETIC
Vagus
Mucus secretion, ↑vascular permeability, vasodilation, & bronchospasm
M3 receptor activation → bronchoconstriction
Autonomic Control
SYMPATHETIC
Inhibit mediator release from mast cells
↑mucociliary clearance
β2 exogenous activation → bronchodilation
FRC
Functional residual capacity
Point where lung elastic recoil = chest wall elastic recoil
Equilibrium point
Impacted by positioning, muscle relaxation, & insufflation
Normal Respiratory Quotient
0.8
200/250
CO2 diffuse 200mL from the pulmonary capillary blood into the alveoli
O2 diffuse 250mL from the alveoli into the pulmonary capillary blood
Compliance
Volume / Pressure
Static Compliance
= VT / (Pplat - PEEP)
Normal 60-100mL/cmH2O
Lung & chest wall compliance w/ NO air movement
↓static compliance
Fibrosis, obesity, edema, vascular engorgement, ARDS, external compression, & atelectasis
Set an inspiratory pause to measure Pplat (only available in volume control)
Dynamic Compliance
= VT / (peak pressure - PEEP)
Normal 50-100mL/cmH2O
Lung & chest wall compliance DURING a breath
↓dynamic compliance
Bronchospasm, tube kinking, mucous plug, external pressure, ↑RR, anything ↑airway resistance
Surface Tension
SURFACTANT = 2/3
Laminar Flow
Small airways ↓resistance
Reynold’s number <2,000
Turbulent Flow
Large airways
Reynold’s number >4,000
Medium-sized bronchi = highest airway resistance
Reynold’s Number
Indicates laminar or turbulent flow
2,000-4,000 considered transitional flow
Poiseuille’s Law
= [(π ∙ ∆P ∙ r^(4 )] / (8 η l)
West Zones
1 alveolar > arterial > venous pressure V/Q > 1
2 arterial > alveolar > venous pressure V/Q = 1
3 arterial > venous pressure > alveolar V/Q = 0.8
4 arterial > interstitial > venous pressure > alveolar V/Q < 1
Closing Volume
Volume above residual when small airways close
Closing Capacity
Absolute gas volume in the lung when small airways close
Factors that ↑closing capacity
- COPD, obesity, supine position, pregnancy, CHF, aging
Closing volume > FRC
Airway closure during normal tidal breathing → poorly or unventilated alveoli & intrapulmonary shunting
Haldane Effect
Blood oxygenation displaces CO2 from hemoglobin
Ability to carry CO2 in different oxygen environments
Occurs at alveolar-capillary membrane
Bohr Effect
Hemoglobin O2 affinity inversely proportional to CO2 levels
Acidic environment causes R shift
Occurs at the tissue level ↑CO2
P50
PaO2 26-28mmHg
50% Hgb saturated
SpO2:PaO2
90: 60
70: 40
60: 30
DLCO
Tests lungs capacity to diffuse carbon monoxide
Normal >75%
Mild 60-75%
Moderate 40-60%
Severe <40%
Intrinsic lung issue - tissue damage
Breathe in & hold 10 sec then exhale fully
CO2 Transportation
- Dissolved
- Chemically combined w/ amino acid proteins (bound to Hgb)
- Bicarbonate ions 80-90%
*Carbonic anhydrase assists reaction
Hypoxic Hypoxia
Issue w/in lungs ↓FiO2 Alveolar hypoventilation V/Q mismatch R → L shunt ***Supplemental FiO2*** Examples: COPD, overdose, high altitude, fibrosis, atelectasis, pulmonary embolism, congenital heart disease
Circulatory Hypoxia
↓CO
Severe heart failure, dehydration, sepsis, SIRS
Treat underlying problem
Hemic Hypoxia
↓hemoglobin content and/or function
Anemia, carboxyhemoglobin, methemoglobinemia
Treat underlying cause
Demand/Histoxic Hypoxia
↑O2 consumption or inability to utilize O2
Fever, seizures, cyanide toxicity
Supplemental FiO2
HPV
Hypoxic pulmonary vasoconstriction
↑PCO2 (acidosis) → vasoconstriction
↓PCO2 → vasodilation
Vasoconstriction in response to low regional PAO2
Diverts blood away from hypoxic → ventilated & oxygenated areas
Aims to optimize & correct V/Q mismatch
Anatomical Deadspace
Air present in the airway that never reaches the alveoli
Unable to participate in gas exchange
Alveolar Deadspace
Air w/in non-functional alveoli (disease or abnormal blood flow)
Unable to participate in gas exchange
Physiological Deadspace
= anatomical + alveolar deadspace
Upper Respiratory Infection
↑WBCs Inflamed & reddened mucosa Mucopurulent nasal secretions Congestion or rales > 37°C Tonsillitis Viral oropharynx ulcer Fatigue Laryngitis Sore throat
Allergies
HISTAMINE MEDIATED Sneezing Ash or boggy mucosa Itchy/running nose Conjunctivitis Wheezing Hives Swollen lips, tongue, eyes, or face Dry, red, & cracked skin
PAO2
(PB - PH2O) x FiO2 - (PaCO2/0.8)
A - a
PAO2 - PaO2
Normal 5-15mmHg
a/A Ratio
PaO2/PAO2
Normal >75%
Oxygen Content
CaO2 = (Hgb x 1.34 x SaO2) + (PaO2 x 0.003)
Normal 20.4mL per 100mL blood
Oxygen Delivery
DO2 = CO x CaO2
PaCO2
VCO2/VA
Total CO2 production / alveolar ventilation
PaO2/FiO2
P:F ratio PaO2/FiO2 Normal 400 <300 mild ARDS <200 moderate <100 severe
