Medical College of Virginia, Virginia
Commonwealth University, and Hunter Holmes McGuire Department of Veterans Affairs Medical
Center, Richmond 23249, USA.
SOURCE:
Circulation 1997 Oct 21;96(8):2509-13
NLM CIT. ID:
98015963
ABSTRACT:
BACKGROUND: Autonomic and particularly
sympathetic mechanisms play a central role in the pathophysiology of vasovagal syncope. We
report direct measurements of muscle sympathetic nerve activity in patients with
orthostatic vasovagal syncope. METHODS AND RESULTS: We studied 53 otherwise healthy
patients with orthostatic syncope. We measured RR intervals and finger arterial pressures
and in 15 patients, peroneal nerve muscle sympathetic activity before and during passive
60 degree head-up tilt, with low-dose intravenous isoproterenol if presyncope did not
develop by 15 minutes. We measured baroreflex gain before tilt with regression of RR
intervals or sympathetic bursts on systolic or diastolic pressures after sequential
injections of nitroprusside and phenylephrine. Orthostatic vasovagal reactions occurred in
21 patients, including 7 microneurography patients. Presyncopal and nonsyncopal patients
had similar baseline RR intervals, arterial pressure, and muscle sympathetic nerve
activity. Vagal baroreflex responses were significantly impaired at arterial pressures
below (but not above) baseline levels in presyncopal patients. Initial responses to tilt
were comparable; however, during the final 200 seconds of tilt, presyncopal patients had
lower RR intervals and diastolic pressures than nonsyncopal patients and gradual reduction
of arterial pressure and sympathetic activity. Frank presyncope began abruptly with
precipitous reduction of arterial pressure, disappearance of muscle sympathetic nerve
activity, and RR interval lengthening. CONCLUSIONS: Patients with orthostatic vasovagal
reactions have impaired vagal baroreflex responses to arterial pressure changes below
resting levels but normal initial responses to upright tilt. Subtle vasovagal physiology
begins before overt presyncope. The final trigger of human orthostatic vasovagal reactions
appears to be the abrupt disappearance of muscle sympathetic nerve activity.
Adolescence
Adult
Aged
Aged, 80 and over
Baroreflex
Blood Pressure
Child
Electrocardiography
Female
Human
Male
Middle Age
Muscles/INNERVATION
Plethysmography
Support, U.S. Gov't, Non-P.H.S. Support, U.S. Gov't, P.H.S.
PUBLICATION TYPES:
JOURNAL ARTICLE
LANGUAGE:
Eng
On Sabbatical!
When my office
lease expired at the end of 2004, I decided to turn it into a
"sabbatical" from my private practice. Many years ago, in my
grandfather's 89th year of life, he told me, "John, it is important
to smell the roses while you can still smell them." His life
gave living a very good reputation. It is also true that the
pursuit of that philosophy required my grandfather to to re-open his
assay office/ore market in Wickenburg, Arizona as a 75-year-old because
he had run a little short of retirement money. Thus, if blessed with his
luck and health, I'll be back.. --jjh
