V q relationships breathlessness positioning
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V/Q relationships Breathlessness & Positioning. Week 11. Session Plan. Revisit Ventilation / Perfusion definitions and relationships Positioning for optimising V/Q Definition of Work of Breathing Dyspnoea. Ventilation Perfusion- Definitions. Alveolar ventilation (V)

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V/Q relationships Breathlessness & Positioning

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V q relationships breathlessness positioning

V/Q relationshipsBreathlessness & Positioning

Week 11

Week 11 Tut 1 09-10


Session plan

Session Plan

  • Revisit Ventilation / Perfusion definitions and relationships

  • Positioning for optimising V/Q

  • Definition of Work of Breathing

  • Dyspnoea

Week 11 Tut 1 09-10


Ventilation perfusion definitions

Ventilation Perfusion- Definitions

  • Alveolar ventilation (V)

  • Perfusion (Q – from German Quellen meaning to gush)

  • V/Q matching: ideally = 1

Week 11 Tut 1 09-10


Factors affecting alveolar ventilation

Factors affecting alveolar ventilation

  • Intrapleural pressure affects ventilation

    • The more negative it is the less capacity there is for it to become more negative and hence expand the lung

    • In adults more negative at the apices, less negative at the bases

    • (Overall more positive in paediatrics)

  • Lung compliance

  • Rib cage compliance (paediatrics)

  • Loading of the diaphragm

  • Lung pathology

  • Deviations gas levels in the alveoli

    • Decrease in O2 causes bronchodilation

    • Increase in CO2 causes bronchodilation

Week 11 Tut 1 09-10


Factors affecting perfusion

Factors affecting perfusion

  • Refer to physiology for the factors affecting blood flow to the alveoli such as gravity, transmural pressures

  • Deviations in the levels of O2 and CO2 in the alveoli

    • Hypoxaemia causes vasoconstriction

    • Hypercapnia causes vasoconstriction

    • SO blood is diverted away from under ventilated alveoli to alveoli that are better ventilated (sometimes confusingly referred to as the blood being shunted away from the under ventilated area)

    • (NB this is opposite to the systemic circulation)

Week 11 Tut 1 09-10


V q 1

V/Q >1

  • More air in the area relative to blood

  • ↑ dead space

    • NB physiological versus anatomical dead space

  • refers to wasted ventilation e.g.

    • PE

    • Pulmonary atherosclerosis

    • Capillary trauma

Week 11 Tut 1 09-10


V q 11

V/Q < 1

  • More perfusion than air called a shunt

    • (NB - shunt can be referred to as anatomical or physiological)

    • Definition of shunt

  • Refers to wasted perfusion e.g.

    • Atelectasis

    • Consolidation

    • Tumour occluding main airway

Week 11 Tut 1 09-10


Diagnosis of v q mismatch

Diagnosis of V/Q mismatch

  • V/Q scan

    • Usually to rule out a PE

    • Injection of radioactive particles to view perfusion

    • Inhalation of inert gases with radioactive tracer

    • Anterior, Posterior, Right lateral and Left lateral stills taken for ventilation and perfusion and compared

  • Now being replaced by helical CT scans

Week 11 Tut 1 09-10


Normal v q scan

Normal V/Q Scan

Week 11 Tut 1 09-10


Adult pattern of v q matching

Adult pattern of V/Q matching

  • Meaning of dependent

  • Ventilation is better in thedependent area of lung – Why?

  • Perfusion is better in the dependent area of lung – Why?

  • Which area of lung has the best V/Q match and hence gas exchange?

  • Which lung has the best V/Q match and hence gas exchange?

    • The dependent lung

Week 11 Tut 1 09-10


Paediatric pattern of v q matching

Paediatric pattern of V/Q matching

  • Ventilation preferentially in the non-dependent area of lung – Why?

  • Perfusion preferentially in the dependent area of lung – Why?

  • Which lung has the best V/Q matching and hence gas exchange ?

    • The non- dependent lung

  • (This pattern is also seen in obese patients)

Week 11 Tut 1 09-10


Dyspnoea and wob

Dyspnoea and WOB

  • Clinical term for breathlessness reported by the patient:

    • the sensation of unpleasant or uncomfortable respiration

  • Results from an increase in the work of breathing

  • Work of Breathing (WOB) definition

    • The amount of muscle activity required to overcome the elastic and resistive elements of the respiratory system

      (Pryor and Prasad, 2008)

Week 11 Tut 1 09-10


V q relationships breathlessness positioning

  • In small groups what pathophysiological changes may alter the WOB and therefore likely to cause dyspnoea

Week 11 Tut 1 09-10


Pathophysiological changes

Pathophysiological changes

  • Increased airways resistance

  • Decreased lung/chest wall compliance

  • Weakness of respiratory muscles

  • Increased metabolic rate

    • pyrexia

  • Low cardiac output/ischaemia

  • Altered ABG’s

  • Deconditioning

  • Anaemia

    • Reduces oxygen carrying capacity of the blood

  • Other pathologies

    • e.g. pulmonary oedema

Week 11 Tut 1 09-10


Breathlessness dyspnoea

Breathlessness/Dyspnoea

  • In normal healthy individuals breathlessness is a normal response to …

    • Increased activity

    • Stress

  • In small groups think about what happens to your biomechanics of ventilation when you get breathless

    • For a short period of time (acutely)

    • Over a long period of time (chronically)

Week 11 Tut 1 09-10


Biomechanical changes

Biomechanical changes

  • Accessory muscle use

    • upper for inspiration facilitated by fixation of the upper extremities

    • lower for expiration

  • Cervical spine extension

    • open airway and therefore reduce resistance

  • Shoulder elevation

    • Due to overuse of the accessory muscles

  • Audible breaths

    • open mouth to increase volume of air inspired/decrease airway resistance

Week 11 Tut 1 09-10


Prior to practical

Prior to Practical

  • How will positioning impact upon normal V/Q in an adult?

  • How will positioning impact upon normal V/Q in an infant?

  • How can positioning be used to assist V/Q matching in a patient with lung pathology and hence optimise oxygenation and removal of carbon dioxide

  • How can positioning reduce some of the biomechanical changes resulting from sustained breathlessness?

Week 11 Tut 1 09-10


Learning outcomes

Learning Outcomes

  • describe the relationship of ventilation and perfusion in the healthy adult

  • describe the relationship of ventilation and perfusion in the healthy child

  • identify common V/Q mismatches and their signs and symptoms

  • understand how breathlessness alters biomechanics

  • begin to understand the theory of positioning in relation to V/Q mismatch

  • begin to understand the theory of positioning in relation to breathlessness

Week 11 Tut 1 09-10


Bibliography

Bibliography

  • Davies, A. & Moores, C. (2003). The Respiratory System . Edinburgh: Churchill Livingstone

  • Hough, A. (2001). Physiotherapy in respiratory care. (3rd ed.). Cheltenham, Nelson Thornes.

  • Pryor, J. A. & Prasad, S. A. (Eds). (2008). Physiotherapy for respiratory and cardiac problems. (4th ed.). Edinburgh: Churchill Livingstone.

  • Wilkins, R. L., Sheldon, R. L. & Jones Krider, S. (2005). Clinical assessment in respiratory care. (5th ed.). St Louis: Mosby.

Week 11 Tut 1 09-10


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