Panting, Starved for Air, and Wheezing

July 17th, 2013 by Phil Weiser Leave a reply »

Student: Is the “Clustering of Dyspnea Symptoms” done statistically or phenomenologically?

Professor: Both!

According to Lansing, Gracely, and Banzett (2009),

“There are at least three separable ‘qualities’ of uncomfortable breathing sensations”:

    • ‘Work’,
    • ‘Air hunger’, and
    • ‘Tightness’.

“The division into different kinds of sensation classification is not based on perceptual quality alone. To be classed as distinct, the perception must have a different afferent source; this is most easily demonstrated by applying stimulus combinations that excite different afferents demonstrating that the sensations can vary independently.”

Sense of Work / Effort
Student: I can sense that this is like, “Breathing is hard work.” Or, “I am huffing and puffing to get up this hill.”

Professor: Try up a moderate hill in the mile-high city of Denver.

  • No change in work capacity, said the classical physiologists.
  • However, for me, all of a sudden part way up that hill, I was shocked with having to breathe harder than I would at sea level.

Professor: Lansing et al. (2009) state:

“‘Work’ of breathing is perceived as uncomfortable when the work of breathing or the required motor command:

    • is increased by high minute ventilation (rate or tidal volume),
    • by increasing impedance to inspiration,
    • by weakness of respiratory muscles, or
    • by placing inspiratory muscles at a disadvantageous length.

“Subjects and patients choose descriptors such as ‘my breathing requires more work’, ‘my breathing requires more effort than usual‘.”

Professor: Banzett (2007) summed up the mechanism for panting:

  • “The neural pathways proposed for these sensations include corollary discharge from motor cortical centers that drive voluntary breathing.
  • “Muscle mechanoreceptors and metaboreceptors are probably also involved, while corollary discharge from the brainstem is probably not (Figure 4).”

Banzett 2007 Fig 4 work effort

Figure 4. Neural pathways underlying work/effort sensation.

Professor: Hey, I found a preliminary figure for the Pulmonary Rehab book chapter (1993), and it looks very similar to Banzett (2007) Figure 4:

Weiser Mahler etal Dyspnea model 1992

Figure: Schematic diagram of the mechanism for dyspnea, demonstrating the interrelationships among ventilatory muscle activity, pulmonary mechanics, breathing effort, and breathing discomfort.

Student: Wow! They are very similar, and yours was done 14 years earlier.

Air Hunger

Professor: Well, let’s move on to symptoms like, “I cannot get in enough air”. Or, “I’m starved for air.” Just picture a runner at the finish line, gasping for breath.

Professor: Moreover, Lansing et al. (2009) state:

  • “‘Air hunger’ is the conscious perception of the urge to breathe, a fundamental biological drive. This sensation arises when pulmonary ventilation is insufficient.
  • “It is described as ‘cannot get enough air’, ‘uncomfortable urge to breathe’, ‘starved for air’ and is the sensation felt at the end of a long breath hold.”

Professor: Banzett (2007) summed up the mechanism for not enough air:

  • “The most likely afferent stimulus for air hunger is corollary discharge conveying a copy of the medullary respiratory center discharge to the sensory areas of the forebrain, although a role for direct projection of chemoreceptors to the forebrain  has not been disproved.
  • “We conclude that pulmonary stretch receptor information is capable of relieving air hunger; chest wall afferent information probably has a weaker effect. There is some information from animal experiments that suggests this inhibition takes place at a level above the medullary respiratory centers, but below the cortex (Figure 3).”

Banzett 2007 Fig 3 air hunger

Figure 3. Neural pathways underlying air hunger. Proposed pathways for relief of air hunger by tidal inflation are shown by right hand arrows.

Professor: Please note that Air Hunger symptoms can be experimentally dissociated from reports of uncomfortable respiratory Work or Effort.

Chest Tightness

Student: And I have exercise-induced asthma that really makes me fight for breath.

Professor: Lansing et al. (2009) state:

  • “‘Tightness’ appears to be specific to bronchoconstriction and is the earliest symptom of asthma.
  • “Asthmatics report descriptors such as ‘my chest feels tight’ or ‘my chest is constricted’ localized to the chest or lungs.
  • “Tightness is not the only sensation reported in asthma; asthmatics also report work and air hunger during severe attacks.”

Professor: Banzett (2007) summed up the possible bronchoconstrictor mechanism for chest tightness:

“That the pathway for tightness [may also well be] vagal in origin (Figure 5).”

Banzett 2007 Fig 5 tightness

Figure 5. Neural pathways underlying tightness.

 

Student: Look at the three Figures from Lansing et al. (2009). They indicate feedback going to the forebrain sensory areas.

Professor: Very interesting! Let’s look into the studies of “corollary discharge conveying a copy of the medullary respiratory center discharge to the sensory areas of the forebrain.

Student: How about the emotional dimension of chest tightness and other breathing symptoms?

Professor: Okay.

Take Home Message:  Uncomfortable breathing is reported as a mismatching of signals from ventilatory drive or airway with the resulting ventilation or discomfort memory,

Next: Cortical and subcortical central neural pathways in respiratory sensations (Davenport & Vovk (2009) Resp Physiol Neurobiol 167: 72–86).

References

Banzett RB. (2007) The peripheral mechanisms of dyspnea. pp 150-151, In: O’Donnell DE, Banzett RB, Carrieri-Kohlman V, Casaburi R, Davenport PW, Gandevia SC, Gelb AF, Mahler DA, Webb KA. (2007) Pathophysiology of Dyspnea in Chronic Obstructive Pulmonary Disease: A Roundtable. Proc Am Thorac Soc 4: 145–168.

Davenport FW, Vovk A. (2009) Cortical and subcortical central neural pathways in respiratory sensations. Resp Physiol Neurobiol 167: 72–86.

Lansing RW, Gracely RH, Banzett, RB. (2009) The Multiple Dimensions of Dyspnea: Review and Hypotheses. Respir Physiol Neurobiol 30: 53–60.

Parshall MB, Manning HL, Bourbeau J, Calverley PM, Gift AG, Harver A, Lareau SC, Mahler DA, Meek PM, O’Donnell DE. (2012) An official American Thoracic Society statement: Update on the mechanisms, assessment, and management of dyspnea. Am J Resp Crit Care 185: 435-452.

Weiser PC, Mahler DA, Ryan KP, Hill KL, Greenspon LW. (1993) Clinical assessment and management of dyspnea. In: Pulmonary rehabilitation: Guidelines to success. 2nd edition. Hodgkin, J, Bell CW, eds. Philadelphia: Lippincott, 478-511.

 

Be Sociable, Share!
    Advertisement

    Comments are closed.