Skip to main content
SpringerLink
Log in

Pathophysiology of syncope

  • Published:
Clinical Autonomic Research Aims and scope Submit manuscript

Abstract.

Syncope or near-syncope is a not uncommon effect of gravitational or other stresses and it occurs when cerebral blood flow falls to below about half the normal value. It is not necessarily abnormal, and individuals who are usually asymptomatic show the same reaction if a stress is sufficiently great to result in hypotension. Blood pressure is regulated mainly by baroreceptor reflexes by their control of vascular resistance and heart rate. The ability to vasoconstrict powerfully is important in resisting syncope; heart rate responses are of much less physiological significance. The intriguing unanswered question is what suddenly changes vasoconstriction and tachycardia to vasodilatation and bradycardia. It is now known not to be due to stimulation of cardiac receptors and some cerebral signal is more probable. People are more likely to faint when upright, motionless, warm, following meals, dehydrated or emotionally stressed, and these factors may be involved in some reflex syncopes including micturition and defaecation syncopes. Plasma volume is of considerable importance and increasing this by interventions such as salt loading, exercise training, and even sleeping with the bed head raised can often be of clinical benefit.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Similar content being viewed by others

References

  1. Barcroft H, Edholm OG (1945) On the vasodilation in human skeletal muscle during post-haemorrhagic fainting. J Physiol 104:161–175

    Google Scholar 

  2. Bishop VS, Hayworth JR (1991) Hormonal control of cardiovascular reflexes. In: Zucker IH, Gilmore JP (eds) Reflex Control of the Circulation. CRC Press, Boca Raton, pp 253–271

  3. Blair DA, Glover WE, Greenfield ADM, Roddie IS (1959) Excitation of cholinergic vasodilator nerves to human skeletal muscles during emotional stress. J Physiol 148:633–647

    PubMed  Google Scholar 

  4. Brown CM, Hainsworth R (1999) Assessment of capillary fluid shifts during orthostatic stress in normal subjects and subjects with orthostatic intolerance. Clin Auton Res 9:66–73

    Google Scholar 

  5. Brown CM, Hainsworth R (2000) Forearm vascular responses during orthostatic stress in control subjects and patients with posturally related syncope. Clin Auton Res 10:57–61

    PubMed  Google Scholar 

  6. Carey BJ, Eanes PJ, Panerai RB, Potter JF (2001) Carbon dioxide, critical closing pressure and cerebral haemodynamics prior to vasovagal syncope in humans. Clin Sci 101:351–358

    Article  CAS  PubMed  Google Scholar 

  7. Cooper VL, Hainsworth R (2001) Carotid baroreceptor reflexes in humans during orthostatic stress. Exp Physiol 86:677–681

    Article  CAS  PubMed  Google Scholar 

  8. Cooper VL, Hainsworth R (2002) Effects of head-up tilting on baroreceptor control in subjects with different tolerances to orthostatic stress. Clin Sci 103:221–226

    PubMed  Google Scholar 

  9. Daly MdeB, Hazzledine JL, Ungar A (1967) The reflex affects of alterations in lung volume on systemic vascular resistance in the dog. J Physiol 188:331–351

    PubMed  Google Scholar 

  10. Doe CPA, Drinkhill MJ, Myers DS, Self DA, Hainsworth R (1996) Reflex vascular responses to abdominal venous distension in anesthetized dogs. Am J Physiol 271:H1049–1056

    CAS  PubMed  Google Scholar 

  11. Eckberg DL, Sleight P (1992) Human baroreflexes in health and disease. Oxford. Clarendon Press

  12. El-Bedawi KM, Hainsworth R (1994) Combined head-up tilt and lower body suction: a test of orthostatic tolerance. Clin Auton Res 4:41–47

    CAS  PubMed  Google Scholar 

  13. El-Bedawi KM, Wahbha MMAE, Hainsworth R (1994) Cardiac pacing does not improve orthostatic tolerance in patients with vasovagal syncope. Clin Auton Res 4:233–237

    CAS  PubMed  Google Scholar 

  14. El-Sayed H, Hainsworth R (1995) Relationship between plasma volume, carotid baroreceptor sensitivity and orthostatic tolerance. Clin Sci 88:463–470

    PubMed  Google Scholar 

  15. El-Sayed H, Hainsworth R (1996) Salt supplement increases plasma volume and orthostatic tolerance in patients with unexplained syncope. Heart 75:134–140

    CAS  PubMed  Google Scholar 

  16. Fitzpatrick AP, Banner N, Cheng A, Yacoub M, Sutton R (1993) Vasovagal reactions may occur after orthotopic heart transplantation. J Am Coll Cardiol 21:1132–1137

    CAS  PubMed  Google Scholar 

  17. Grubb BP, Gerard G, Rousk K (1991) Cerebral vasoconstriction during head-upright tilt-induced vasovagal syncope: a paradoxic and unexpected response. Circulation 84:1157–1164

    CAS  PubMed  Google Scholar 

  18. Hainsworth R (1991) Reflexes from the heart. Physiol Rev 71:617–658

    CAS  Google Scholar 

  19. Hainsworth R (1999) Syncope and fainting: classification and pathophysiological basis. In Mathias C, Bannister R Autonomic Failure 4th ed. University Press Oxford 428–436

    Google Scholar 

  20. Hainsworth R (2000) Head-up sleeping for posturally related syncope. Clin Auton Res 10:225–226

    Google Scholar 

  21. Hainsworth R (2000) Heart rate and orthostatic stress. Clin Auton Res 10:323–326

    CAS  PubMed  Google Scholar 

  22. Hainsworth R (2002) Syncope: what is the trigger? Heart 88:123–124

    Google Scholar 

  23. Hainsworth R, Karim F, McGregor KH, Wood LM (1983) Hind-limb vascular capacitance responses in anaesthetized dogs. J Physiol 337:417–428

    CAS  PubMed  Google Scholar 

  24. Heistad DD, Kontos HA (1983) Cerebral Circulation. In: Handbook of Physiology. Sect 2 eds Shepherd JT, Abboud FM. Vol III, pp 137–182

  25. Jordan J, Shannon JR, Black BK (2000) The pressor response to water drinking in humans: a sympathetic reflex? Circulation 101:504–509

    CAS  PubMed  Google Scholar 

  26. Julu POO, Cooper VL, Hansen S, Hainsworth R (2003) Cardiovascular regulation in the period preceding vasovagal syncope in conscious humans. J Physiol 549:299–311

    Article  CAS  PubMed  Google Scholar 

  27. Koizumi K, Kollai M (1981) Control of reciprocal and non-reciprocal action of vagal and sympathetic efferents: study of centrally induced reactions. J Auton Nerv Syst 3:483–501

    Article  CAS  PubMed  Google Scholar 

  28. Kosinski DJ, Grubb BP, Wolfe DA (2003) Permanent cardiac pacing as therapy for neurocardiogenic syncope. Clin Auton Res. This supplement

  29. Lassen NA (1959) Cerebral blood flow and oxygen consumption in man. Physiol Rev 29:183–238

    Google Scholar 

  30. Lewis T (1932) Vasovagal syncope and the carotid sinus mechanism. Brit Med J 1:873–876

    Google Scholar 

  31. Liu JE, Hahn RT, Stein KM, Markowitz SM ,Okin PM, Devereux RB, Lerman BB (2000) Left ventricular geometry and function preceding neurally mediated syncope. Circulation 101:777–791

    CAS  PubMed  Google Scholar 

  32. Ludbrook J (1993) Haemorrhage and shock. In: Hainsworth R, Mark AL (eds) Cardiovascular reflex control in health and disease. London: Saunders, pp 463–490

  33. Mary DASG (1989) The urinary bladder and cardiovascular reflexes. Int J Cardiol 23:11–17

    Article  CAS  PubMed  Google Scholar 

  34. Mercarder MA, Varghese PJ, Potolicchio SJ, Venkatraman GK, Lee SW (2002) New insights into the mechanism of neurally mediated syncope. Heart 88:217–225

    Article  PubMed  Google Scholar 

  35. Morita H, Vatner SF (1985) Effects of hemorrhage on renal nerve activity. Circ Res 57:788–793

    CAS  PubMed  Google Scholar 

  36. Mtinangi BL, Hainsworth R (1998) Increased orthostatic tolerance following moderate exercise training in patients with unexplained syncope. Heart 80:596–600

    CAS  PubMed  Google Scholar 

  37. Norcliffe LJ, Bush V Hainsworth R (2002) Patients with posturally-related syncope have increased responsiveness of the cerebral circulation in carbon dioxide. Clin Auton Res 12:316

    Google Scholar 

  38. Novak V, Honos G, Schondorf R (1996) Is the heart empty at syncope? J Auton Nerv Syst 60:83–92

    Article  CAS  PubMed  Google Scholar 

  39. Oberg B, Thoren P (1972) Increased activity in left ventricular receptors during haemorrhage or occlusion of the caval veins in the cat. Acta Physiol Scand 85:164–173

    CAS  PubMed  Google Scholar 

  40. Schroeder C, Bush VE, Norcliffe LJ, Luft FC, Tank J, Jordan J, Hainsworth R (2002) Water drinking acutely improves orthostatic tolerance in healthy subjects. Circulation 106:2806–2811

    Article  PubMed  Google Scholar 

  41. Scott EM, Greenwood JP, Gilbey SG, Stoker JB, Mary DASG (2001) Water ingestion increases sympathetic vasoconstrictor discharge in normal human subjects. Clin Sci 100:335–342

    Article  CAS  Google Scholar 

  42. Sneddon JF, Counihan PJ, Bashir Y, Haywood GA, Ward DE, Camm AJ (1993) Impaired immediate vasoconstrictor responses in patients with recurrent neurally mediated syncope. Am J Cardiol 71:72–76

    Article  CAS  PubMed  Google Scholar 

  43. Stevens PM (1996) Cardiovascular dynamics during orthostasis and influence of intravascular instrumentation. Am J Cardiol 17:211–218

    Article  Google Scholar 

  44. Uvnas B (1966) Cholinergic vasodilator nerves. Fed Proc 25:1618–1622

    CAS  PubMed  Google Scholar 

  45. Wallin BG, Sundlof G (1982) Sympathetic outflow to muscle during vasovagal syncope. J Auton Nerv Syst 6:287–291

    Article  CAS  PubMed  Google Scholar 

  46. Wright CI, Drinkhill MJ, Hainsworth R (2000) Reflex effects of independent stimulation of coronary and left ventricular mechanoreceptors in anaesthetized dogs. J Physiol 528:349–358

    Article  CAS  PubMed  Google Scholar 

Download references

Author information

Authors and Affiliations

  1. Institute for Cardiovascular Research, University of Leeds, Leeds, LS2 9JT, UK

    Roger Hainsworth

Authors
  1. Roger Hainsworth
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Roger Hainsworth.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Hainsworth, R. Pathophysiology of syncope. Clin Auton Res 14 (Suppl 1), i18–i24 (2004). https://doi.org/10.1007/s10286-004-1004-2

Download citation

  • Issue Date:

  • DOI: https://doi.org/10.1007/s10286-004-1004-2

Key words

Search

Navigation