Breathlessness A Physiological Basis For Discussion

Heart aches, Lungs pant, The dry air Sorry, scant.. Heart aches, Lungs pant The dry air Sorry, scant Wilfrid Noyce, written at 21,100 feet on May 23 rd... Breathlessness is a group of se

Breathlessness-a physiological

basis for discussion

M.C.F.Pain

Heart aches,

Lungs pant,

The dry air

Sorry, scant.

Legs lift

And why at all?

Loose drift,

Heavy fall.

Prod the snow,

Its easiest way:

A flat step

Is holiday

**********

**********

One step

One heart-beat

Stone no nearer

Dragging feet.

Heart aches,

Lungs pant

The dry air

Sorry, scant

Wilfrid Noyce, written at 21,100 feet on May 23 rd

Breathlessness is a group of sensations with multiple

qualitative descriptors

described in terms of “how it is felt”

unconscious patient cannot be breathless

An all-embracing definition is difficult and usually involves a mechanistic approach

“Breathlessness arises when there is a recognition by the subject of an inappropriate relationship between respiratory work and total body work”

Four key words

Recognition Inappropriate Respiratory work Total body work

Some form of detector mechanism within the respiratory system which rises to a conscious level

Perception-some similarity to other sensory modalities

pain,sound,light

Area of psychophysics

2 questions Is it there?

How big is it?

Psychophysical experiments show a spectrum of perceptive ability in a normal population for most modalities

implies a bank of experience in which “appropriate”

information is stored

“We get used to things”

“inappropriate”, if a chronic state, becomes “acceptably” appropriate

temporal adaptation (nasal fatigue)

Respiratory work

= ventilatory work normally mostly inspiratory ventilation = breath size x frequency

breath size= inspiratory flow x duty cycle

= VT/Ti x Ti/T tot stretching work - Elastic airflow work - Resistive

work

VE=K

Load Drive

Work

Ventilation

Gas exchange

PO2

pH

Load Drive

Work

Higher centres (limbic system)

Mechanoreceptors Irritant receptors Chemoreceptors Baroreceptors Temperature

Stiff lungs

Narrow airways

Chest wall

Diaphragm

Threshold for work perception

range in normals modified by time drug modification

Carbon dioxide tension

Ventilation

1.5l/min/mmHg

40 60 80 10

20 30

L/min

mmHg Ventilatory response to carbon dioxide

A clinical analysis of breathlessness implies seeking answers to;

1 Clinical evidence of load or drive abnormality?

2 Appropriate investigations to confirm this

3 An explanation in terms of causation

A warning!

“A clinical physiologist offering a unifying hypothesis for breathlessness should be viewed with the same suspicion as a tattooed archbishop offering a free ticket to heaven”.

E.J.M.C