Basics Of V\Q Matching - Part One

• About Part One
• Download Part One
• How to Pass
• How to Fail
• The SAQ
• The Viva
• Curriculum
• Research Methods and Statistics
  • Evidence-Based Medicine
  • Study Types
  • Clinical Trial Design
  • Data Types
  • Bias and Confounding
  • Frequency Distributions
  • Sample Size Calculation
  • Statistical Tests
  • Statistical Terms
  • Risk and Odds
  • Significance Testing
  • Drug Development
• Pharmacology
  • Pharmaceutics
    • Additives
    • Isomerism
  • Pharmacokinetics
    • Modeling
    • Absorption
    • Distribution
    • Metabolism and Clearance
    • Elimination
    • Bolus and Infusion Kinetics
    • Drug Monitoring
    • Epidural and Intrathecal
    • TIVA and TCI
  • Pharmacodynamics
    • Receptor Theory
    • Receptor Types
    • Dose-Response Curves
    • Mechanisms of Action
  • Variability in Drug Response
    • Adverse Effects
    • Drug Interactions
    • Alterations to Response
    • Pharmacogenetics
    • Drugs in Pregnancy
  • Toxicology
    • General Management
    • TCA Overdose
    • Organophosphates
• Cellular Physiology
  • The Cell Membrane
  • Organelles
  • Excitable Cells
  • Transport Across Membranes
  • Fluid Compartments
  • Cell Homeostasis
• Respiratory System
  • Respiratory Anatomy
    • Airway and Alveolus
    • Chest Wall and Diaphragm
    • Variations in Anatomy
  • Control of Breathing
  • Mechanics of Breathing
    • Respiration
    • Compliance
    • Time-Constants
    • Resistance
    • Surfactant
    • Volumes and Capacities
    • Spirometry
    • Work of Breathing
  • Diffusion of Gases
    • Oxygen Cascade
    • Diffusing Capacity and Limitation
  • V\Q Relationships
    • West's Zones
    • Basics of V\Q Matching
    • Dead Space
    • Shunt
  • Gas Transport
    • Oxygen Storage
    • Carbon Dioxide
  • Applied Respiratory Physiology
    • Positive Pressure Ventilation
    • Hypoxia
    • Hypo and Hypercapnea
    • Position and Ventilation
    • Humidification
    • Cough Reflex
    • Non-Respiratory Functions
    • Altitude Physiology
    • Respiratory Changes with Obesity
    • Neonates and Children
  • Respiratory Pharmacology
    • Anti-Asthma Drugs
• Cardiovascular System
  • Structure and Function
    • Cardiac Anatomy
    • Coronary Circulation
    • Cardiac Cycle
  • Electrical Properties
    • Cardiac Action Potential
  • Cardiac Output
    • Determinants of Cardiac Output
    • Venous Return
    • Myocardial Oxygen Supply and Demand
    • Pressure-Volume Relationships
    • Cardiac Reflexes
  • Peripheral Circulation
    • Starling Forces
    • Variations in Blood Pressure
    • Pulmonary Circulation
    • Cerebral Blood Flow
    • Hepatic Blood Flow
  • Circulatory Control
    • Baroreceptors
    • Valsalva Manoeuvre
    • CVS Changes with Obesity
    • CVS Effects of Ageing
  • Cardiovascular Pharmacology
    • Inotropes
    • Adrenoreceptors
    • Antiarrhythmics
• Renal System
  • Renal Physiology
    • Functional Anatomy and Control of Blood Flow
    • Glomerular Filtration and Tubular Function
    • Handling of Organic Substances
    • Measurement of GFR
    • Endocrine Functions of the Kidney
    • Acid-Base Balance
    • Dialysis
  • Fluids and Electrolytes
    • Sodium and Water
    • Potassium
• Acid-Base Physiology
  • Principles of Acid-Base Physiology
  • Compensation
  • Buffers
• Nervous System
  • Blood-Brain Barrier
  • CSF
  • Spinal Cord Anatomy
  • Intracranial Pressure
  • Intraocular Pressure
  • Sleep
  • Pain
  • Autonomic Nervous System
  • Neuropharmacology
    • Neurotransmitters
    • Anticonvulsants
    • Local Anaesthetics
    • Neuraxial Blockade
    • Acetylcholine Receptors
    • Opioids
    • Inhalational Anaesthetics
• Endocrine
  • A Brief Overview of Hormones
  • Insulin, Glucagon, and Somatostatin
  • Control of Blood Glucose
  • Hypothalamus and Pituitary
  • Thyroid
  • Adrenal Hormones
  • Calcium Homeostasis
  • Histamine
  • Prostanoids
• Musculoskeletal System
  • Skeletal Muscle Structure
  • Skeletal Muscle Innervation
  • Neuromuscular Blockers
• Nutrition & Metabolism
  • Basal Metabolic Rate
  • Fat Metabolism
  • Carbohydrate Metabolism
  • Protein Metabolism
  • Requirements and Starvation
  • Anaerobic Metabolism
• Thermoregulation
  • Regulation of Body Temperature
• Immunology
  • Inflammation
  • Innate Immunity
  • Adaptive Immunity
  • Hypersensitivity
• Microbiology
  • Classification of Microorganisms
  • Antimicrobial Resistance
  • Antiseptics
• Obstetrics & Neonates
  • Respiratory Changes
  • Cardiovascular Changes
  • Foetal Circulation
  • The Placenta
• Gastrointestinal System
  • Oesophagus
  • Gastric Secretions
  • Control of Gastric Emptying
  • Swallowing
  • Physiology of Vomiting
  • Liver Physiology
    • Functions of the Liver
    • Laboratory Assessment of Liver Function
    • Bile
• Haematology
  • Erythrocytes
  • Iron Homeostasis
  • Platelets
  • Transfusion
  • Haemostasis
  • Haemostatic Regulation
  • Coagulopathy Testing
• Equipment and Measurement
  • SI Units
  • Electrical Safety
  • Wheatstone Bridge
  • Neuromuscular Monitoring
  • Pressure Transduction
  • Pressure Waveform Analysis
  • Non-Invasive Blood Pressure
  • Cardiac Output Measurement
  • Pulse Oximetry
  • Oxygen Analysis
  • End-Tidal Gas Analysis
  • Blood Gas Analysis
  • Gas Flow
  • Principles of Ultrasound
  • Temperature and Humidity
  • Electrocardiography
  • Humidifiers
  • Supplemental Oxygen
  • Bispectral Index
  • Medical Gas Supply
  • Vapourisers
  • Breathing Systems
  • Bag-Valve-Mask
  • Circle System
  • Scavenging
  • Diathermy
  • Lasers
• Procedural Anatomy
  • Subclavian Vein
  • Internal Jugular Vein
  • Intercostal Catheter
  • Antecubital Fossa
  • Tracheostomy
  • Neuraxial
• Pharmacopoeia
• Toxicology
  • Recreational Drugs
    • Toxic Alcohols
  • Antidotes
    • Naloxone
    • Flumazenil
• Respiratory
  • Oxygen
  • Helium
  • Bronchodilators
    • Beta Agonists
    • Antimuscarinics
    • Phosphodiesterase Inhibitors
    • Leukotriene Antagonists
  • Corticosteroids
  • Pulmonary Vasodilators
• Cardiovascular Pharmacology
  • Adrenergic Vasoactives
  • Non-adrenergic Vasoactives
  • Antihypertensives
    • Centrally Acting Agents
    • Calcium Channel Blockers
    • Direct Vasodilators
    • ACE Inhibitors
    • Angiotensin Receptor Blockers
    • Neprilysin Inhibitors
    • Potassium Channel Activators
  • Antiarrhythmics
    • Sodium Channel Blockers
    • Beta-Blockers
    • Amiodarone
    • Sotalol
    • Digoxin
    • Adenosine
    • Magnesium
    • Atropine
• Renal
  • Diuretics
  • Intravenous Fluids
• Neuropharmacology
  • Propofol
  • Barbiturates
  • Ketamine
  • Dexmedetomidine
  • Local Anaesthetics
  • Benzodiazepines
  • Antidepressants
  • Antipsychotics
  • Anticonvulsants
  • GABA Analogues
  • Inhalational Anaesthetic Agents
  • Nitrous Oxide
• Analgesics
  • Opioids
  • COX Inhibitors
  • Tramadol
  • Paracetamol
• Autonomic
  • Anticholinesterases
  • Antimuscarinics
• Neuromuscular
  • Depolarising NMBs
  • Non-Depolarising NMBs
  • Dantrolene
  • Sugammadex
• Haematological
  • Anticoagulants
  • Direct Thrombin Inhibitors
  • Antifibrinolytics
  • Antiplatelets
• Antimicrobials
  • Penicillins
  • Glycopeptides
  • Aminoglycosides
  • Lincosamides
  • Metronidazole
  • Antifungals
• Endocrine
  • Hypoglycaemics
    • Insulin
    • Oral Hypoglycaemics
• Obstetric
  • Oxytocics
  • Tocolytics
• Gastrointestinal
  • Acid Suppression
  • Antiemetics
• Other Drugs
  • IV Contrast
• ANZCA Model Answers
• 2021
  • 2021A
    • 2021A Question 1
    • 2021A Question 2
    • 2021A Question 3
    • 2021A Question 4
    • 2021A Question 5
    • 2021A Question 6
    • 2021A Question 7
    • 2021A Question 8
    • 2021A Question 9
    • 2021A Question 10
    • 2021A Question 11
    • 2021A Question 12
    • 2021A Question 13
    • 2021A Question 14
    • 2021A Question 15
• 2020
  • 2020A
    • 2020A Question 1
    • 2020A Question 2
    • 2020A Question 3
    • 2020A Question 4
    • 2020A Question 5
    • 2020A Question 6
    • 2020A Question 7
    • 2020A Question 8
    • 2020A Question 9
    • 2020A Question 10
    • 2020A Question 11
    • 2020A Question 12
    • 2020A Question 13
    • 2020A Question 14
    • 2020A Question 15
  • 2020B
    • 2020B Question 1
    • 2020B Question 2
    • 2020B Question 3
    • 2020B Question 4
    • 2020B Question 5
    • 2020B Question 6
    • 2020B Question 7
    • 2020B Question 8
    • 2020B Question 9
    • 2020B Question 10
    • 2020B Question 11
    • 2020B Question 12
    • 2020B Question 13
    • 2020B Question 14
    • 2020B Question 15
• 2019
  • 2019A
    • 2019A Question 1
    • 2019A Question 2
    • 2019A Question 3
    • 2019A Question 5
    • 2019A Question 7
    • 2019A Question 8
    • 2019A Question 9
    • 2019A Question 10
    • 2019A Question 11
    • 2019A Question 12
    • 2019A Question 13
  • 2019B
    • 2019B Question 1
    • 2019B Question 2
    • 2019B Question 4
    • 2019B Question 5
    • 2019B Question 6
    • 2019B Question 7
    • 2019B Question 8
    • 2019B Question 9
    • 2019B Question 10
    • 2019B Question 11
    • 2019B Question 12
    • 2019B Question 13
    • 2019B Question 14
    • 2019B Question 15
• 2018
  • 2018A
    • 2018A Question 2
    • 2018A Question 4
    • 2018A Question 5
    • 2018A Question 6
    • 2018A Question 7
    • 2018A Question 8
    • 2018A Question 9
    • 2018A Question 12
    • 2018A Question 13
    • 2018A Question 14
    • 2018A Question 15
  • 2018B
    • 2018B Question 1
    • 2018B Question 2
    • 2018B Question 4
    • 2018B Question 5
    • 2018B Question 6
    • 2018B Question 8
    • 2018B Question 9
    • 2018B Question 10
    • 2018B Question 11
    • 2018B Question 12
    • 2018B Question 13
    • 2018B Question 14
    • 2018B Question 15
• 2017
  • 2017A
    • 2017A Question 2
    • 2017A Question 4
    • 2017A Question 8
    • 2017A Question 10
    • 2017A Question 11
    • 2017A Question 12
    • 2017A Question 14
    • 2017A Question 15
  • 2017B
    • 2017B Question 1
    • 2017B Question 2
    • 2017B Question 4
    • 2017B Question 5
    • 2017B Question 6
    • 2017B Question 7
    • 2017B Question 8
    • 2017B Question 10
    • 2017B Question 12
    • 2017B Question 14
    • 2017B Question 15
• 2016
  • 2016A
    • 2016A Question 1
    • 2016A Question 2
    • 2016A Question 4
    • 2016A Question 6
    • 2016A Question 8
    • 2016A Question 9
    • 2016A Question 13
  • 2016B
    • 2016B Question 1
    • 2016B Question 2
    • 2016B Question 4
    • 2016B Question 6
    • 2016B Question 8
    • 2016B Question 10
    • 2016B Question 11
    • 2016B Question 12
    • 2016B Question 15
• Appendices
• Definitions
• Key Graphs
• Laws and Equations
• Structures for SAQs
• Built on GitBook

Basics of V\Q Matching Basics of V/Q Matching

Optimal gas exchange occurs when regions of lung are ventilated in proportion to their perfusion, i.e. V/Q = 1

• Uneven distribution of ventilation and perfusion causes inefficient gas exchange:
  • Excessive ventilation causes excessive work
  • Inadequate ventilation causes inadequate gas exchange

Distribution of Ventilation

• The right lung is slightly better ventilated than the left
• In an erect patient the bases of the lung are better ventilatedThe weight of lung above compresses the lung below, improving the compliance of dependent lung whilst stretching the non-dependent lung.
  • This is only significant at low inspiratory flow rates
  • The V/Q ratio in the bases is ~0.6
  • The V/Q ratio in the apices is >3
• In a lateral position:
  • The dependent lung is better ventilated in a spontaneously breathing patient
  • The non-dependent lung is better ventilated in a ventilated patient

Distribution of Perfusion

• The pulmonary circulation is a low pressure circulation
• Gravity therefore has a substantial effect on fluid pressure
• Consequently, the distribution of blood throughout the lungs is uneven:
  • The bases perfused better than the apicesThis is affected by lung volume, with the effect:
    • Becoming more pronounced at TLC (with apical perfusion falling precipitously)
    • Reversing slightly at RV

V/Q Ratios

• The global V/Q ratio for normal resting lung is 0.9
• The global V/Q ratio improves to 1.0 during exercise

V/Q Mismatch and Etymology

• V/Q mismatch occurs when V/Q ≠ 1:
  • V/Q >1 (Dead Space)Ventilation in excess of perfusion.
    • However, pulmonary blood is passing ventilated alveoli and PaO2 is normal
  • V/Q 0 to 1 (V/Q scatter)Perfusion in excess of ventilation.
    • Increasing in PAO2 will increase PaO2
    • This is commonly referred to by the general term of V/Q mismatch
  • V/Q = 0 (Shunt)Mixed venous blood entering the systemic circulation without being oxygenated via passage through the lungs. PaO2 falls.

References

1. West J. Respiratory Physiology: The Essentials. 9th Edition. Lippincott Williams and Wilkins. 2011.
2. Lumb A. Nunn's Applied Respiratory Physiology. 7th Edition. Elsevier. 2010.

Last updated 2021-08-23 results matching "" No results matching ""