ventilation perfusion gas exchange l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
VENTILATION/PERFUSION & GAS EXCHANGE PowerPoint Presentation
Download Presentation
VENTILATION/PERFUSION & GAS EXCHANGE

Loading in 2 Seconds...

play fullscreen
1 / 15

VENTILATION/PERFUSION & GAS EXCHANGE - PowerPoint PPT Presentation


  • 723 Views
  • Uploaded on

VENTILATION/PERFUSION & GAS EXCHANGE. AIMS. What factors are important in gas exchange?. What factors affect gas transfer?. What is the ventilation/perfusion ratio?. GAS EXCHANGE. ADEQUATE ALVEOLAR VENTILATION (V A ) TRANSFER OF GAS ACROSS ALVEOLAR-CAPILLARY MEMBRANE

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'VENTILATION/PERFUSION & GAS EXCHANGE' - keladry


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
ventilation perfusion gas exchange
VENTILATION/PERFUSION & GAS EXCHANGE

AIMS

  • What factors are important in gas exchange?
  • What factors affect gas transfer?
  • What is the ventilation/perfusion ratio?
gas exchange
GAS EXCHANGE
  • ADEQUATE ALVEOLAR VENTILATION(VA)
  • TRANSFER OF GAS ACROSS ALVEOLAR-CAPILLARY MEMBRANE
  • ADEQUATE PERFUSION
  • MATCHING OF VENTILATION AND PERFUSION
pulmonary blood flow
Pulmonary blood flow
  • PULMONARY CIRCULATION
    • Small, supply- deoxygenated blood by pulmonary artery, drained by pulmonary veins to left atrium
    • low arterial pressures (mean=15mmHg, SP=25,DP=8),
    • capillaries -vulnerable to stretch and collapse,
      • pressures 7-12 mmHg
      • radial traction opens blood vessels as lung expands
    • low resistance- tenth of systemic
    • large surface area,
    • cardiac output- 5 L/min
distribution of blood flow in lung
Distribution of blood flow in lung
  • Unequal
  • upright lung - from base to apex
  • supine lung- higher blood flow in apex, base unchanged
  • blood flow in dependent region is greater
  • differences due to changes in pressures in pulmonary artery i.e P=hqg, i.e P increases by 1cmH20 for every cm down the lung
transfer of gases
TRANSFER OF GASES
  • FICK’S LAW
    • GAS FLOW=PAS/ TMw

Where, P= pressure gradient

A= surface area

S= solubility

T= thickness

Mw= molecular weight

  • Diffusion- THIN MEMBRANE(0.2-1m); LARGE SURFACE AREA (50-70 m2)
  • Measurement of gas transfer- transfer factor, use CO (0.3%)-(KCO)
ventilation perfusion
VENTILATION/PERFUSION
  • VENTILATION- VT & f; PERFUSION- cardiac output
  • RATIO OF VENTILATION TO PERFUSION
    • efficiency of gas transfer by alveoli
    • ratios= 0.5-3.0, mean = 0.8
    • extreme situations
      • diffusion limitation
      • perfusion limitation
      • limitations in both
    • Posture (gravity) - affects ratios
      • P= hg - pressure 1cmH2O /cm of lung
      • standing BF from base to apex, VAfrom base to apex, ratios from base to apex
      • top of lung not very important
conclusions
CONCLUSIONS
  • 1. Factors important for gas exchange - VA, gas transfer, perfusion and matching.
  • 2.
  • 3.

Gas transfer is directly proportional to pressure difference, surface area, & inversely to thickness- Fick’s law.

Efficiency of gas exchange is increased if ventilation and perfusion are matched.

o 2 transport
O2 TRANSPORT
  • Solubility- small (0.3 ml O2/100 ml blood),bound to Haemoglobin (Hb)
  • Hb (heme +globin)
    • each Hb can bind 4 O2
    • 15g of Hb/100 ml blood
    • 1.34ml O2/g Hb
    • SaO2= 97%
  • Oxygen dissociation curve
    • sigmoid, plateau at 100 mmHg
    • steep at 50 mmHg (in the tissues),thus unloading of O2,
    • curve shift to the right (Bohr shift)

CO2, T, 2,3 DPG, pH

    • shift to left, Hb more saturated
co 2 transport
CO2 TRANSPORT
  • 1/ PHYSICALLY DISSOLVED- (5% )
    • 20x >soluble than O2
  • 2/ BICARBONATE (HCO3-)- 70%
    • Small amount produced in plasma
    • Maj. prod. in RBC
    • Requires carbonic anhydrase,
    • CO2+H2O H2CO3 H+ + HCO3-
    • Chloride shift
  • 3/Carbamino compounds- 5-10%; amine groups in Hb combine with CO2
  • CO2 dissociation curve
    • Almost linear in physiological range
    • Haldane effect, shift to the right, easier to lose CO2 at lungs, and release O2 to tissues
acid base balance
ACID-BASE BALANCE
  • AIMS:
    • What are acids and bases?
    • What is pH?
    • Why does pH vary?
    • How do you regulate pH?
acids bases
ACIDS & BASES
  • Acids- release H+ ions
  • Bases- release OH- ions
    • In body fluids at low concentrations
    • thus pH scale (1-14) to represent [H+] and [OH-]
  • pH scale
    • used to represent [H+] in body,
    • = - log10 [H+]
    • blood= 7.40.02
    • gastric acid= 1, urine= 6
    • pH>7 is basic, pH<7 is acidic
variation of ph
VARIATION OF pH
  • IMPORTANCE
    • Death if pH remains < 6.8 or >8 for less than a day
    • Metabolic enzymes stop working, depression of CNS
  • Changes in pH
    • due mainly to [ H+] produced by the body
    • Acid production- H2CO3, H2PO4, H2SO4, Lactic, Pyruvic acids
    • Vomiting, diarrhoea, dehydration
regulation of acid base
REGULATION OF ACID BASE
  • DIRECT BUFFERING IN BLOOD
    • seconds
    • proteins, phosphates, Hb, HCO3-
  • INDIRECT BY LUNGS
    • minutes
    • increase or decrease breathing
  • INDIRECT BY KIDNEYS
    • slow, hours & days
    • excreting excess base or acid
  • HENDERSON-HASSELBALCH EQUATION
    • defines the relationship between pH and the concentration of a salt and its corresponding acid
conclusions15
CONCLUSIONS
  • 1. Acids are substances release H+ ions, Bases release OH- ions
  • 2.pH scale (1-14) is a measure of the acidity and alkalinity
  • 3. pH varies due to internal & external changes of acids & bases (range=7.35-7.45)
  • 4. pH regulated by, blood buffering, lungs & kidney