Unit 4 - Dyspnea Flashcards
(39 cards)
what is the definition of dyspnea?
sensation of breathlessness or SOB experienced by both normal subjects and patients with diseases affecting respiratory system
what are components of dyspnea?
- increased work/effort
- unrewarded inspiration
- inspiratory difficulty
- shallow breathing
- rapid breathing
- tight chest
- suffocating feeling
what are psychometric measurements of dyspnea?
- MMRC (modified medical research council) dyspnea scale
- visual analogue scale
- modified Borg category scale
what is the modified Borg category scale to rate dyspnea?
scale from 0 (nothing at all) to 10 (maximal)
what is the modified medical research council scale?
Grade 0 (breathless with strenuous exercise) to Grade 4 (breathless when dressing, cannot leave house)
what is the mechanism of dyspnea?
- several sensory receptors located throughout respiratory system are responsible; no one is solely responsible
- afferent info from sensory receptors is processed at cortex along with respiratory motor command from cortex and brainstem
how are chemoreceptors involved in dyspnea?
induction of hypercapnia or severe hypoxemia causes dyspnea
-patients with the above aren’t invariably dyspneic
what do chest wall mechanoreceptors have to do with dyspnea?
located in muscle spindles and tendon organs in respiratory muscles
- innervated by anterior horn cells of spinal motor neurons
- project to somatosensory cortex
what are metaboreceptors? how are they involved in dyspnea?
- located in skeletal muscle
- respond to local changes in tissue environment with respect to by-products of metabolism
- source of afferent neurological signals that lead to perception of dyspnea during exercise w/o hypoxemia and hypercapnia
what are vagal receptors?
how are slowly adapting stretch receptors involved in dyspnea?
found in smooth muscle of larger airways
- correspond to myelinated afferent nerve fibers in vagus
- SARs activity is affected by:
- -inhalation of CO2 - inhibit activity
- -volatile anesthetics - may inhibit or stimulate receptors depending on concentration
- -furosemide - improve experimentally induced dyspnea
how are rapidly adapting stretch receptors involved in dyspnea?
receptors adapt rapidly to maintained inflation or deflation of the lungs
- AKA irritant receptors
- activated by mechanical and chemical irritant stimuli, inflammatory/immunological mediators, and by airway and lung pathological changes
- pneumothorax or other disease that distorts lung architecture can stimulate these receptors to cause dyspnea
how are C-fiber receptors involved in dyspnea?
juxta-pulmonary capillary receptors or J receptors
- localized close to alveolar capillaries in pulmonary and bronchial circulation
- respond to increased interstitial fluid outside capillaries
- pulmonary congestion is strong stimulator of C-fiber receptors
what receptors does hypercapnia act on? the quality of dyspnea?
acts on central chemoreceptors –> air hunger
what receptors does hypoxia act on? the quality of dyspnea?
acts on peripheral chemoreceptors –> air hunger
what receptors does respiratory motor command act on? the quality of dyspnea?
central corollary discharge, metaboreceptors –> work/effort
what receptors does bronchoconstriction act on? the quality of dyspnea?
RARs, C-fiber receptors –> chest tightness
what receptors does lung inflation act on? the quality of dyspnea?
SARs –> dyspnea relief
what is the systematic approach to dyspnea?
3 components
- controller - determines rate/depth of breathing
- ventilatory pump - facilitates movement of gas into and out of alveolus
- gas exchanger - consists of pulmonary vasculature and alveolus
dyspnea caused by ventilatory controller and gas exchanger problems is associated with what?
increased respiratory drive
- stimulation of chemoreceptors, pulmonary receptors (irritant, mechanical, vascular)
- behavioral factors
dyspnea caused by ventilatory pump problems is associated with what?
increased effort or work of breathing
- muscle weakness
- decreased compliance of chesst wall
- airflow obstruction (increased resistive load from narrowing of airways and increased elastic load from hyperinflation)
what are conditions that lead to acute hypoxemia?
- impaired gas exchange (asthma, pulmonary embolism, pneumonia, CHF)
- environmental hypoxia (altitude, fire)
what are conditions leading to increased dead space and/or acute hypercapnia?
- impaired gas exchange (acute, severe asthma; exacerbation of COPD; severe pulmonary edema)
- impaired ventilatory pump (muscle weakness, airflow obstruction)
what is metabolic acidosis-induced dyspnea caused by?
renal disease (renal failure, tubular acidosis)
