Lung (3) Flashcards
O2 consumption
240 - 280 ml/min
Co2 Production
190 - 220 ml/min
Overall water loss per day from breathing
250 ml/day
Layers of Mucous
- Inner Sol layer (Cilia)
- Outer gel layer
Clearance of particles
- Impaction: Nasal cavity
- Sedimentation: lower airways
- Diffusion: alveoli (macrophage clearance)
Lung metabolic function
- Renin: Angiotensinogen to Ang1
- ACE: Ang1 to Ang 2
- ACE2: Ang2 to Ang 1-7
(viruses use ACE2 to enter)
Dichotomic divisions
- Conducting zone (1-16) : Dead space
- Respiratory zone (17-23) : alveolar space
Physiological Dead space
Sum of anatomical dead space (150ml) and Functional/Alveolar dead space (negligible)
Functional Dead space
Space of the ventilated alveoli that does not participate in gas exchange
Alveolar cells
- Type-1: Squamous for gas exchange
- Type-2: Smaller, produce surfactant
Alveolar Ventilation
4900 ml/min
Dynamic lung volumes
Related to rate at which air flows in/out of lungs
Static lung volumes
Not affected by the rate of air in/out of lungs
Tidal Volume (TV)
500 ml
Amount of air entering/leaving the lungs without extra effort
Inspiratory Reserve Volume (IRV)
3100 ml (1900 ml F)
Max inspiration above tidal volume
Expiratory Reserve Volume (ERV)
1200 ml (800 ml F)
Volume exhaled above tidal volume
Residual Volume (RV)
1200 ml (1000 ml F)
Air remaining in the lungs after complete exhalation
Inspiratory Capacity (IC)
3600ml (2400 ml F)
Largest amount that can be inhaled
(TV+IRV)
Functional Residual Capacity (FRC)
2400 ml (1800 ml F)
Volume after normal expiration
Vital Capacity (VC)
4800 ml (3200 ml F)
Entire volume that can be maximally inhaled and exhaled
Total Lung capacity (TLC)
6000 ml (4200 ml F)
All of the lung volume
(VC + RV)
How do we determine FRC
- Helium Dilution method
- Plethysmography
- Spiroscope
- Clinical spirogram
Helium Dilution method
Closed circuit with spirometer and patient asked to breathe until helium is equilibrated
c1 * v1 = c2 * (v1+v2)
v2 = FRC
Plethysmography
Air tight cabin with shutter, after expiration patient is asked to do a forceful inspiration while shutter is closed. Chest extends and pressure is measured.
Spiroscope
Measures gas flow
V = Q * T
Clinical Spirogram
To measure forced expiratory volume in 1 second
- Ask patient for max inh & ex. (VC)
- Tiffeneau-index: FEV / VC
How much of the VC can be exhaled in 1 second, should be 80% normally
How to determine Dead space
- O2 inh & N2 exh.
- pCO2 measurement
Dead space, O2 inh & N2 exh.
1) Patient inhales pure oxygen
2) During exhalation N2 conc is detected
3) As long as person is exhaling from dead space no N2 is detected
4) If volume where N2 appears is known, V of dead space can be calculated
Relationship bw Alveolar ventilation and pCO2
Inverse hyperbolic
PaCO2
40 mmHg
Effects of ventilation on PaCO2
- Hyperventilation: PaCO2 < 40 mmHg (hypocapnia)
- Hypoventilation: PaCO2 > 40 mmHg (hypercapnia)
What keeps alveoli open in resting position?
Negative pressure of intrapleural space counteracts retraction tendency
Ppl = - 5 cmH2O
Transmural Pressure (Ptm)
Pressure difference bw Pa and Ppl
Ptm = Pa - Ppl
= 0 - (-5) = + 5 cmH2O
Surfactant
- Composed of lipids and proteins
- Reduces surface tension
- Reduces cohesion force of H2O
Surfactant and Work of breathing
Reduced work
- W = P * V
- Surfactant lowers retraction tendency
- Less work needed
Surfactant and Alveoli collapse
- Smaller radius, higher pressure (Laplace law)
- More surfactant in smaller alveoli to reduce pressure by surface tension
Surfactant and Pulmonary Edema
- Retraction tend. in alveoli creates suction force on capillaries causing fluid movement from cap to interstitium. (Pulmonary edema)
- Surfactant reduces retraction tend., less suction force, no edema
Hysteresis
- Difference in curves of expiration and inspiration
- Caused by surfactant, less compliance on inspiration since more surface tension due to smaller alveoli
Compliance
How volume changes as a result of pressure change
C = V / P
- Compliance of the lung is high