Inter-relations among declines in arterial distensibility, baroreflex function and respiratory sinus arrhythmia.

OBJECTIVES

We hypothesized that structural and neural cardiovascular (CV) deficits may be intimately linked. Specifically, decreased carotid distensibility with age may blunt the arterial baroreflex, thereby reducing resting cardiac vagal tone.

BACKGROUND

Increased CV risk is associated with lower carotid distensibility, impaired baroreflex function and reduced respiratory sinus arrhythmia (RSA), possibly representing a direct path between structural and neural CV deficits.

METHODS

We estimated the mechanostructural and neural components of baroreflex function and examined their relation to RSA in young (20 to 31 years) and older (59 to 71 years) subjects rigorously screened for CV and autonomic diseases.

RESULTS

In the older subjects, RSA was < 20% of that in the younger subjects. Moreover, mechanical transduction of pressure into barosensory vessel stretch was approximately 40% lower (p < 0.05) and arterial baroreflex gain more than 60% lower (p < 0.05) in the older group. Although neural transduction of stretch into vagal outflow only tended to be less (p < 0.08), it was an important determinant of baroreflex function. A path analysis model showed comparable contributions of both the mechanical and neural components to baroreflex gain; however, lower overall baroreflex gain in the older group did not relate to lower RSA.

CONCLUSIONS

These data suggest that decreased carotid distensibility does reduce baroreflex function with age, but this does not lead to reduced resting vagal outflow.