Transcript Positioning

V/Q relationships
Breathlessness
& Positioning
Week 11
Week 11 Tut 1 09-10
1
Session Plan
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Revisit Ventilation / Perfusion definitions and
relationships
Positioning for optimising V/Q
Definition of Work of Breathing
Dyspnoea
Week 11 Tut 1 09-10
2
Ventilation PerfusionDefinitions
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Alveolar ventilation (V)
Perfusion (Q – from German Quellen meaning to gush)
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V/Q matching: ideally = 1
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Week 11 Tut 1 09-10
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Factors affecting alveolar ventilation
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Intrapleural pressure affects ventilation
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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
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Decrease in O2 causes bronchodilation
Increase in CO2 causes bronchodilation
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Factors affecting perfusion
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Refer to physiology for the factors affecting blood flow
to the alveoli such as gravity, transmural pressures
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Deviations in the levels of O2 and CO2 in the alveoli
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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
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V/Q >1
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More air in the area relative to blood
↑ dead space
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NB physiological versus anatomical dead
space
refers to wasted ventilation e.g.
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PE
Pulmonary atherosclerosis
Capillary trauma
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V/Q < 1
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More perfusion than air called a shunt
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(NB - shunt can be referred to as
anatomical or physiological)
Definition of shunt
Refers to wasted perfusion e.g.
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Atelectasis
Consolidation
Tumour occluding main airway
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Diagnosis of V/Q mismatch
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V/Q scan
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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
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Normal V/Q Scan
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Adult pattern of V/Q matching
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Meaning of dependent
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Ventilation is better in the dependent area of lung – Why?
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Perfusion is better in the dependent area of lung – Why?
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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?
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The dependent lung
Week 11 Tut 1 09-10
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Paediatric pattern of V/Q matching
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Ventilation preferentially in the non-dependent area
of lung – Why?
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Perfusion preferentially in the dependent area of lung
– Why?
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Which lung has the best V/Q matching and hence gas
exchange ?
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The non- dependent lung
(This pattern is also seen in obese patients)
Week 11 Tut 1 09-10
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Dyspnoea and WOB
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Clinical term for breathlessness reported by the
patient:
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the sensation of unpleasant or uncomfortable respiration
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Results from an increase in the work of breathing
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Work of Breathing (WOB) definition
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The amount of muscle activity required to overcome the
elastic and resistive elements of the respiratory system
(Pryor and Prasad, 2008)
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In small groups what pathophysiological
changes may alter the WOB and
therefore likely to cause dyspnoea
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Pathophysiological changes
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Increased airways resistance
Decreased lung/chest wall compliance
Weakness of respiratory muscles
Increased metabolic rate
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Low cardiac output/ischaemia
Altered ABG’s
Deconditioning
Anaemia
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pyrexia
Reduces oxygen carrying capacity of the blood
Other pathologies
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e.g. pulmonary oedema
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Breathlessness/Dyspnoea
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In normal healthy individuals breathlessness is
a normal response to …
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Increased activity
Stress
In small groups think about what happens to
your biomechanics of ventilation when you get
breathless
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For a short period of time (acutely)
Over a long period of time (chronically)
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Biomechanical changes
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Accessory muscle use
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Cervical spine extension
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open airway and therefore reduce resistance
Shoulder elevation
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upper for inspiration facilitated by fixation of the upper
extremities
lower for expiration
Due to overuse of the accessory muscles
Audible breaths
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open mouth to increase volume of air
inspired/decrease airway resistance
Week 11 Tut 1 09-10
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Prior to Practical
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How will positioning impact upon normal V/Q in an
adult?
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How will positioning impact upon normal V/Q in an
infant?
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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
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Learning Outcomes
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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
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Bibliography
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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.
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