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Physiology of ventilation &
work of breathing

Puneet Malhotra
Dept. of Pulmonary Med, PGIMER
20.03.04
Goals of respiration
1.Ventilation
2.Diffusion of O2 & CO2
3.Transport of O2 & CO2
4.Regulation of respiration
Ventilation
• Movement of air in & out of lungs
the airways
respiratory muscles
dead space ventilation
• Measurement of ve...
Movement of air in & out of lungs
The airways

Anatomic dead space
Respiratory Muscles
quadriplegics

COPD

Inspiration

Expiration
The diaphragm

Hoover’s sign
Effect of posture on respiratory muscles
Upright: FRC

Supine: FRC

Lateral:
The pressures
• Pressure differences > airflow
• Ppl precede Palv
• Palv and air flow in phase
• At points of no flow Palv...
Dead space ventilation
• 3 types
• Anatomic dead space
1ml/lb ideal body wt., 150 ml/500ml VT
VT- anat dead space/VT ratio...
Yes:
high freq
ventilation

VA = f x [VT - VD]
• Alveolar dead space
V/Q = Infinity
PTE, Pulm vasoc, CO
• Physiologic dead space (VD)
anat + alveolar dead space
Normally...
Measurement of ventilatory capacity
• MIP, MEP
• FVC (FEVC, FIVC)

depend on a
single maneuver

• FEV1
• PEFR
• MBC/MVV

d...
Work of breathing
• Work to overcome “afterload” on resp system
• Spont ventilation: resp muscles
Controlled ventilation: ...
Normally work is performed only for inspiration
Divided into 2 fractions

0.5L

E

Rel

v

I

5

TranspulmP

Raw

10cm H2O
“minimal” work of breathing
Actual work performed by resp m. in health is minimal
VO2R = 3ml/min (<5% of total VO2)
Inters...
Importance in the ICU
• Measurement of WOB in ICU not routine
• Until recently performed by physiologists>clinicians
• Mos...
Measurement of WOB in ICU
2 ways:
a) Determination of O2 cost of breathing
b) Measurement of mechanical WOB
a) O2 cost of ...
b) Measurement of mechanical WOB
• 2 ways
a) Graphics
Paw tracings
P/V curves
b) Pressure time product
Paw tracings
P/V curves
Example 1
P/V curves Example 2

E

E
I

Normal PV loop

I

PV loop in COPD
P/V curves Example 3

E
Pt. effort to trigger
ventilator

Solution: increase
trigger sensitivity

I
Pressure time product
Pressure time product (contd.)
• Work = P.dV
• Underestimates isometric work i.e. resp m. work
which consumes O2 but doesn...
WOB measurement at the bedside
• Bicore CP-100 Pulmonary Monitor
• Automated measurement of
VA, Pulm mechanics
WOBv and WO...
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Pneumology - Ventilation physiology-and-work-of-breathing

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Transcript of "Pneumology - Ventilation physiology-and-work-of-breathing"

  1. 1. Physiology of ventilation & work of breathing Puneet Malhotra Dept. of Pulmonary Med, PGIMER 20.03.04
  2. 2. Goals of respiration 1.Ventilation 2.Diffusion of O2 & CO2 3.Transport of O2 & CO2 4.Regulation of respiration
  3. 3. Ventilation • Movement of air in & out of lungs the airways respiratory muscles dead space ventilation • Measurement of ventilation • The work of breathing • Importance in the ICU
  4. 4. Movement of air in & out of lungs The airways Anatomic dead space
  5. 5. Respiratory Muscles quadriplegics COPD Inspiration Expiration
  6. 6. The diaphragm Hoover’s sign
  7. 7. Effect of posture on respiratory muscles Upright: FRC Supine: FRC Lateral:
  8. 8. The pressures • Pressure differences > airflow • Ppl precede Palv • Palv and air flow in phase • At points of no flow Palv = 0
  9. 9. Dead space ventilation • 3 types • Anatomic dead space 1ml/lb ideal body wt., 150 ml/500ml VT VT- anat dead space/VT ratio e.g.150/500=30%, 150/300=50% can gas exchange occur if pt. is ventilated with VT< anat dead space?
  10. 10. Yes: high freq ventilation VA = f x [VT - VD]
  11. 11. • Alveolar dead space V/Q = Infinity PTE, Pulm vasoc, CO • Physiologic dead space (VD) anat + alveolar dead space Normally VD = anat dead space VD/VT = (PaCO2-PECO2) / PaCO2 <30% normal <60%=> successful weaning ratio: VT or alv dead space
  12. 12. Measurement of ventilatory capacity • MIP, MEP • FVC (FEVC, FIVC) depend on a single maneuver • FEV1 • PEFR • MBC/MVV depends on continued maximal effort
  13. 13. Work of breathing • Work to overcome “afterload” on resp system • Spont ventilation: resp muscles Controlled ventilation: ventilator Partial support: both • Work = Force x Distance = Pressure x Volume • SI unit = Joule/L
  14. 14. Normally work is performed only for inspiration Divided into 2 fractions 0.5L E Rel v I 5 TranspulmP Raw 10cm H2O
  15. 15. “minimal” work of breathing Actual work performed by resp m. in health is minimal VO2R = 3ml/min (<5% of total VO2) Interstitial lung disease: rapid shallow breathing Increased effort reqd. to expand lungs pts. breath at a lower FRC COPD: pts. Breath slow & deep i.e. at higher FRC to prevent airway collapse at low lung volumes
  16. 16. Importance in the ICU • Measurement of WOB in ICU not routine • Until recently performed by physiologists>clinicians • Most ICU pts. are extubated < 96 hrs using standard weaning criteria • “advantages” of measuring WOB ensure pt.-vent synchrony aid to weaning comparison of diff. modes of MV
  17. 17. Measurement of WOB in ICU 2 ways: a) Determination of O2 cost of breathing b) Measurement of mechanical WOB a) O2 cost of breathing Total VO2 – VO2 during spont breathing [ VO2 = CO X (CaO2-CVO2) ] drawbacks: in ICU O2 COB may represent small % of VO2 VO2 itself influenced by many other factors
  18. 18. b) Measurement of mechanical WOB • 2 ways a) Graphics Paw tracings P/V curves b) Pressure time product
  19. 19. Paw tracings
  20. 20. P/V curves Example 1
  21. 21. P/V curves Example 2 E E I Normal PV loop I PV loop in COPD
  22. 22. P/V curves Example 3 E Pt. effort to trigger ventilator Solution: increase trigger sensitivity I
  23. 23. Pressure time product
  24. 24. Pressure time product (contd.) • Work = P.dV • Underestimates isometric work i.e. resp m. work which consumes O2 but doesn’t result in dV e.g. against PEEPi • Under heavy loading conditions e.g. ARDS PTP correlates better with fatigue potential • Pressure time index = P/Pmax x Ti/Ttot >0.15 => fatigue
  25. 25. WOB measurement at the bedside • Bicore CP-100 Pulmonary Monitor • Automated measurement of VA, Pulm mechanics WOBv and WOBp Respiratory drive • Oesophageal balloon, pnemotachograph
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