Reduced baroreflex sensitivity in elderly humans is not due to efferent autonomic dysfunction

A progressive decline in baroreflex sensitivity (BRS) is a characteristic f eature of human aging, the basis of which is poorly understood. The purpose of the present study was to determine whether alte rations in efferent bar oreflex function might contribute to the age-related decrease in BRS. We st udied 10 healthy young (mean age 30.5 years;age range 22-40 years; six male ) and 10 healthy elderly (mean age 70.7 years; age range 67-75 years; five male) volunteers. We tested efferent cardiac vagal function using the brady cardiac response to the cold face test, and efferent sym pathetic function using heart rate and blood pressure responses to four stress tests: (i) low -level cognitive stress, (ii) high-level cognitive stress, (iii) hand immer sion in ice water (cold presser test) and (iv) isometric sustained hand-gri p. Haemodynamic responses to these stresses are mediated via efferent baror eflex pathways, whereas the afferent components of each reflex response are independent of afferent baroreflex pathways. BRS was measured from simulta neous Finapres-derived continuous blood pressure and digital ECG R-R interv al data using the sequence analysis paradigm. As expected, BRS was signific antly reduced in the elderly group (7.29 +/- 0.74 ms/mmHg; mean +/- S.E.M.) compared with the young group (13.84 +/- 1.13 ms/mmHg; P < 0.001). However , neither the bradycardiac responses to the cold face test nor the efferent sympathetically mediated heart rate/blood pressure responses to the stress test battery were significantly different between the young and elderly gr oups. We conclude that the age-related decrease in BRS is not attributable to impairments in the efferent sympathetic or parasympathetic system compon ents of the baroreceptor reflex pathway.