MODULE SUPPLEMENT: NEUROLOGICAL SYSTEM
What Are The Clinical Implications Of These Changes?

Decreased beta adrenergic receptor responsivity is important in terms of the changes that occur with age in cardiac function. These are discussed in the module on the cardiovascular system (see Response to Stress in the Cardiovascular Module--Note: this link will open in a new browser window). As noted previously in this module, this change is implicated in the development of a tendency toward a more vasoconstrictive state. This, however, can be modified by exercise.

Theoretically, these changes may make older adults less responsive to beta blockers, but empirically this hasn’t been shown to be true, at least as related to cardiovascular function. Note has been made, however, that the bronchodilator response to beta2 agonists may be attenuated so that other bronchodilators should be considered in the treatment of asthma in older adults (Resnick & Connolly, 1999).

The data on the influence of beta adrenergic stimulation on metabolic rate are interesting in light of the decline in metabolic rate that occurs with age. Much of this decline is attributed to loss of lean body mass, but this may be an additional factor that could influence this change. More data are needed in this area to determine its clinical implications.

Additional findings that are often attributed, at least partially, to alterations in the PNS include:

1. Increased vulnerability to orthostatic hypotension because of decreased baroreceptor sensitivity. This can be minimized through exercise and maintenance of a healthy cardiovascular system.
2. Decreased peripheral reflexes because of alterations in nerve conduction velocity. As noted above, loss of the Achilles tendon reflex is noted to occur in a fairly large number of individuals who are at an advanced old age, although others feel that, with excellent technique, it can be obtained in healthy persons. Other reflexes may be less predictably related to aging per se, and minimal data are available in this area. Thus an underlying cause for any alteration should be explored.
3. Diminished or absent vibratory sensation below the knees which has been attributed to changes in the small vessels feeding the posterior columns of the spinal cord (Williams, 2001). At the same time, proprioception, as assessed through joint position sense, is noted not to change even though it uses a similar pathway to vibratory sensation (Williams, 2001).
4. Altered thermoregulatory mechanisms. This is really multifactorial, involving not only changes in the skin and its vasculature but also changes in fat distribution, loss of lean body mass, and alterations in central mechanisms.