This chapter is not relevant to any specific Section from the 2017 CICM Primary Syllabus, because there is no specific entry which directs the candidates to learn extreme geriatric pulmonology, but the college has certainly snuck a section into their "important to note" section in the Learning Objectives, which solemnly warns that "for all sections of the Syllabus an understanding of normal physiology, and physiology at the extremes of age, obesity, pregnancy (including foetal) and disease (particularly critical illness) is expected". So far the extremes of age have been represented mainly by Question 19 from the first paper of 2019, which asked the candidates to "describe the effects of ageing on the respiratory system". Though many age-related changes are associated with the diseases we pick up in the course of our maturing, the college examiners warn us that the mention of any such diseases will earn no marks, and only "normal" age-associated changes are accepted.
The best article to offer as a peer-reviewed reference was Sharma & Goodwin (2006). One really has no need for anything else, but if one for some reason wants another recommendation, one would be well served by Janssens et al (1999) or Sprung et al (2006). All of these are freely available and in many ways superior to the offical textbooks (for one, their bibliography is better).
In summary:
Age-related changes | Effect of these changes |
Airway function and structure
|
|
Structural properties of the chest wall:
|
|
Function of respiratory muscles:
|
|
Structure of the lungs
|
|
Gas exchange
|
|
Control of ventilation
|
|
Immunological changes
|
|
Growing older is treacherous, and your own pharynx conspires to kill you in your sleep by growing lax and complacent. Once proud pharyngeal muscles find themselves less inclined to maintain their tone in old age, and upper airway reflexes are blunted. Malhotra et al (2006) found a significant decrease in the negative pressure reflex in the over-50s. To make matters worse, the soft palate lengthens, and the pharyngeal fat pad increases (which is not something associated with obesity, i.e. you can't diet-and-exercise away your pharyngeal fat pad).
Beyond the upper airway, the trachea and bronchi become more reactive, and more prone to spasm with slighter provocation. Using methacholine as the aforementioned provocation, Hopp et al (1985) found that the dose necessary to drop the FEV1/FVC by 20% changes significantly (exponentially decreases!) with age. As the age at which this really becomes a problem (70) is well beyond one's normal reproductive timeframe, one might expect that this is bug rather than a feature (i.e. it has no protective effect and is probably due to some sort of degenerative dysregulation of immune function).
Multiple age-related changes occur in the chest wall, all of which can be described as "normal" and age-related even though they might sound suspiciously like something disease-related:
All of that causes decreased chest wall compliance and increased chest wall resistance. Logically, it makes sense that it should take more effort to stretch open an old calcified ribcage, rather than a supple young ribcage. Mittman et al (1964) captured several elders and demonstrated experimentally that the lung compliance was exxentially halved between the ages of 20 and 70.
The many degenerative processes taking place in old age all conspire to produce the following changes to the lung volumes:
One might summarise these in the form of a graph (this one is from Stocks & Quanjer, 1995):
Decreased elastic fibre content in the lung needs to be emhasised. There is a gradual degradation in the elastin content of the lung parenchyma, which leads to the decrease of lung recoil. That recoil is the force which promotes a decrease in lung volume, and according to Turner et al (1968) it decreases at a rate of around 0.1 cm H2O every year, starting probably from the age of 50. The outcome of this is an increase in the FRC.
The increase of closing capacity with age also needs to be emphasised, as it has impact on the propensity of the elderly lung to collapse. Without revisiting the content of the chapter on closing capacity, it will suffice to say that closing capacity increases faster than the FRC (FRC also increases with age), such that the closing capacity exceeds supine FRC at around 44 years of age, and exceeds erect FRC at 66 years.
In summary, everything gets weaker and more intolerant of workload.
These are two major elements which conspire with malnutrition and increased work of breathing to make weaning from mechanical ventilation more difficult.
The changes in V/Q characteristics which one can expect in their old age can be summarised by this diagram from Wagner et al (1974), where a relatively young (44 year old) person already demonstrates V/Q mismatch in their MIGET traces:
Thus, in summary, there is:
In short, everything is the fault of a smaller surface area. The gas exchange membrane, presumably, remains as thin as ever, but there's just less of it. In summary, with age there is:
Sharma, Gulshan, and James Goodwin. "Effect of aging on respiratory system physiology and immunology." Clinical interventions in aging 1.3 (2006): 253.
Janssens, Jean-Paul, Jean-Claude Pache, and L. P. Nicod. "Physiological changes in respiratory function associated with ageing." European Respiratory Journal 13.1 (1999): 197-205.
Sprung, Juraj, Ognjen Gajic, and David O. Warner. "age related alterations in respiratory function—anesthetic considerations." Canadian journal of anesthesia 53.12 (2006): 1244.
Malhotra, Atul, et al. "Aging influences on pharyngeal anatomy and physiology: the predisposition to pharyngeal collapse." The American journal of medicine 119.1 (2006): 72-e9.
Hopp, Russell J., et al. "The effect of age on methacholine response." Journal of Allergy and Clinical Immunology 76.4 (1985): 609-613.
Turner, JAMES M., J. E. R. E. Mead, and MARY ELLEN Wohl. "Elasticity of human lungs in relation to age." Journal of applied physiology 25.6 (1968): 664-671.
Crapo, R. O. "The aging lung." Lung biology in health and disease 63 (1993): 1-25.
Polkey, Michael I., et al. "The contractile properties of the elderly human diaphragm." American journal of respiratory and critical care medicine 155.5 (1997): 1560-1564.
Mittman, Charles, et al. "Relationship between chest wall and pulmonary compliance and age." Journal of Applied Physiology 20.6 (1965): 1211-1216.
Tenney, S. M., and R. M. Miller. "Dead space ventilation in old age." Journal of applied physiology 9.3 (1956): 321-327.
Stam, H., et al. "Diffusing capacity dependent on lung volume and age in normal subjects." Journal of Applied Physiology 76.6 (1994): 2356-2363.