What happens during a Raynauds episode?
The Raynaud phenomenon is a recurrent vasospasm that is associated with cold temperatures and emotional stress [1]. Excessive vasoconstriction leads to hypoxia. The cause of vasoconstriction is a hyperactivation of the sympathetic nervous system [2] and probably the lack of parasympathetic response. The mechanism is thought to involve both central neural issues and peripheral impairment (subclinical polyneuropathy) [3]. The resulted chronic hypoxia leads to pain, atrophy and sometimes even ulceration [2].



References:


Bakst R, Merola JF, Franks AG, Sanchez M. Raynaud's phenomenon: pathogenesis and management. J. Am. Acad. Dermatol. 2008 Oct;59(4):633-53. doi: 10.1016/j.jaad.2008.06.004. PubMed PMID: 18656283. 
Wikipedia contributors, "Raynaud's phenomenon," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Raynaud%27s_phenomenon&amp;oldid=613954124 (accessed June 27, 2014).
Koszewicz M, Gosk-Bierska I, Jerzy G, Bilińska M, Podemski R, Budrewicz S, Adamiec R. Peripheral nerve changes assessed by conduction velocity distribution in patients with primary Raynaud's phenomenon and dysautonomia. Int Angiol. 2011 Aug;30(4):375-9. PubMed PMID: 21747356.