Failure of reflex venoconstriction during exercise in patients with vasovagal syncope.

Abstract

BACKGROUND:

In this study, we tested two hypotheses. First, we tested the hypothesis that reflex constriction of the venous capacitance beds in patients with vasovagal syncope is impaired during both subhypotensive lower-body negative pressure. Second, we proposed that splenic venoconstriction may be impaired during exercise in patients with vasovagal syncope.

METHODS AND RESULTS:

We evaluated 25 patients with vasovagal syncope (age, 45.0 +/- 15.9 years; 12 men, 13 women) and 24 control subjects (age, 41.3 +/- 13.7 years; 16 men, 8 women). A nuclear technique was used to assess changes in forearm venous tone during lower-body negative pressure and in splenic venous volume during cycle exercise. Changes in forearm vascular resistance (FVR) during cycle exercise were assessed with a strain-gauge plethysmography technique. The percentage reduction in unstressed forearm vascular volume during lower-body negative pressure was similar in patients and control subjects (9.0 +/- 8.0% versus 9.7 +/- 5.9%, P=NS). During exercise, splenic venous volume decreased less in patients than in control subjects (15.8 +/- 21.7% versus 42.6 +/- 12.6%, P < .0001). FVR decreased by 2 +/- 32% in patients but increased 108 +/- 90% in control subjects (P < .0001). There was no relation between percentage change in splenic volume and percentage change in FVR during exercise in either patients or control subjects (r= -.06, P=NS and r= -.18, P=NS, respectively).

CONCLUSIONS:

Patients with vasovagal syncope exhibit a failure of the normal increase in tone in the splenic capacitance bed and in forearm resistance vessels during dynamic exercise. Forearm venous tone increases normally during lower-body negative pressure.

• Authors: H L Thomson, J J Atherton, F A Khafagi, M P Frenneaux
• Journal: Circulation (Circulation) Vol. 93 Issue 5 Pg. 953-9 (Mar 01 1996) ISSN: 0009-7322 [Print] United States
• PMID: 8598086 (Publication Type: Clinical Trial, Journal Article, Research Support, Non-U.S. Gov't)

Topics

• Adult
• Aged
• Blood Pressure
• Exercise
• Female
• Humans
• Lower Body Negative Pressure
• Male
• Middle Aged
• Reflex (physiology)
• Spleen (blood supply)
• Syncope (physiopathology)
• Vascular Resistance (physiology)
• Vasoconstriction (physiology)
• Veins (physiopathology)