De. Manyari et al., ABNORMAL REFLEX VENOUS FUNCTION IN PATIENTS WITH NEUROMEDIATED SYNCOPE, Journal of the American College of Cardiology, 27(7), 1996, pp. 1730-1735
Objectives. We sought to compare the forearm reflex venous response to
mental arithmetic stress in patients with neuromediated syncope and i
n normal subjects. Background. Patients with neuromediated syncope hav
e a paradoxic arterial vasodilation in response to stressors that usua
lly provoke vasoconstriction. Given the postulated role of diminished
preload in provoking the reflex responses resulting in syncope, we hyp
othesized that mental stress might provoke paradoxic reflex venodilati
on in patients with neuromediated syncope. Methods. Twelve normal subj
ects (mean age [+/-SD] 47 +/- 9 years) and 27 patients with neuromedia
ted syncope (mean age 42 +/- 13 gears) were studied before and during
a mental arithmetic stress test. Forearm venous pressure-volume relati
ons were determined by using radionuclide plethysmography. Results. Du
ring mental arithmetic stress, heart rate and systolic and diastolic b
lood pressure increased significantly and similarly both in normal sub
jects and in patients with neuromediated syncope. The heart rate and b
lood pressure changes were qualitatively similar in both groups. Howev
er, with mental arithmetic stress, forearm venoconstriction of 13 +/-
2% (mean +/- SEM) was noted in normal subjects (p < 0.001) but not in
patients with neuromediated syncope (mean 2%, p = NS). This group resp
onse of patients with neuromediated syncope did not result from a lack
of individual responses but occurred because these patients had a wid
e range of responses. The normal physiologic and methodologic variabil
ity of the method was +/-4%. Thirteen of the 27 patients with neuromed
iated syncope had forearm venoconstriction of 14.5 +/- 6.8% during men
tal arithmetic stress,whereas 7 had paradoxic forearm venodilation of
14.6 +/- 8.8%, and 7 were considered nonresponders (-1.3 +/- 3.4%). Th
us, 14 (52%) of the 27 patients with syncope did not have normal vasoc
onstriction in response to mental stress. Conclusions. Patients with n
euromediated syncope have an abnormal range of forearm venomotor respo
nses to mental arithmetic stress. Reflex control of the veins may play
an important role in the pathogenesis of neuromediated syncope.