Breathlessness-a physiological basis for discussion M.C.F.Pain Breathless 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 23rd. 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 Recognition 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. Inappropriate 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 E R work VE=K frequency Work Load Drive Ventilation Gas exchange PO2 PCO2 pH Stiff lungs Higher centres (limbic system) Narrow airways Chest wall Load Drive Diaphragm Work Threshold for work perception range in normals modified by time drug modification Mechanoreceptors Irritant receptors Chemoreceptors Baroreceptors Temperature Ventilatory response to carbon dioxide 1.5l/min/mmHg 30 20 Ventilation L/min 10 40 60 Carbon dioxide tension mmHg 80 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 [...]...Ventilatory response to carbon dioxide 1.5l/min/mmHg 30 20 Ventilation L/min 10 40 60 Carbon dioxide tension mmHg 80 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. .. 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 ... spectrum of perceptive ability in a normal population for most modalities Inappropriate implies a bank of experience in which “appropriate” information is stored “We get used to things” “inappropriate”,... work” Four key words Recognition Inappropriate Respiratory work Total body work Recognition Some form of detector mechanism within the respiratory system which rises to a conscious level Perception-some... lungs Higher centres (limbic system) Narrow airways Chest wall Load Drive Diaphragm Work Threshold for work perception range in normals modified by time drug modification Mechanoreceptors Irritant