Journal of Applied Physiology: Sex Differences in the Perceived Intensity of Breathlessness During Exercise with Advancing Age.

The prevalence of activity-related breathlessness increases with age, particularly in women, but the specific underlying mechanisms have not been studied. This novel cross-sectional study was undertaken to examine the effects of age and sex, and their interaction, on the perceptual and ventilatory responses to incremental treadmill exercise in 73 healthy participants (age range 40-80 yr old) with normal pulmonary function. Age-related changes at a standardized oxygen uptake (V[O.sub.2]) during exercise included significant increases in breathlessness ratings (Borg scale), ventilation ([V.sub.E]), ventilatory equivalent for carbon dioxide, and the ratio of tidal volume ([V.sub.T]) to dynamic inspiratory capacity (IC) (all P < 0.05). These changes were quantitatively similar in women (n = 39) and in men (n = 34). For the group as a whole, exertional breathlessness ratings increased as resting static inspiratory muscle strength diminished (P = 0.05), as exercise ventilation increased relative to capacity (P = 0.013) and as the [V.sub.T]/IC ratio increased (P = 0.003) during exercise. Older women (60-80 yr old, n = 23) reported greater (P < 0.05) intensity of exertional breathlessness at a standardized V[O.sub.2] and [V.sub.E] than age-matched men (n = 16), despite similar age-related changes in ventilatory demand and dynamic ventilatory mechanics. These increases in breathlessness ratings in older women disappeared when sex differences in baseline maximal ventilatory capacity were accounted for. In conclusion, although increased exertional breathlessness with advancing age is multi-factorial, contributory factors included higher ventilatory requirements during exercise, progressive inspiratory muscle weakness, and restrictive mechanical constraints on Vt expansion related to reduced IC. The sensory consequences of this age-related respiratory impairment were more pronounced in women, who, by nature, have relatively reduced maximal ventilatory reserve.

COMMENTARY

It is a common observation that healthy elderly women are more likely to report dyspnea as limiting their exercise capacity than healthy elderly men. They are also likely to report higher intensity of dyspnea at a given exercise level than men. This study sought to tease out effects of aging and gender on these observations. None of the subjects were ventilatory limited in their maximal exercise capacity, yet the older women reported higher dyspnea ratings than the men. The authors suggest smaller airways, dynamic hyperinflation, inspiratory muscle weakness, or increased stiffness in the lungs as potentials causes. However, they did not examine breathing pattern, beyond noting a higher breathing frequency in older women, as related to intensity of dyspnea. Perhaps older women also favor a breathing pattern that is less efficient and could cause greater dyspnea. This study remains to be performed. Any takers?

2008;104:1583-1593. [c] 2008 American Physiologic Society.