Phasic Pains Induced by Cold

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Abstract
From analyses of local vascular and sensory changes, 2 separate kinds of pain can be identified in a finger cooled in a water bath. The principal type, "first" pain, is properly termed "cold" pain. It is associated with a vasocon-striction which enhances cooling of the finger, but there is no evidence that the vasoconstriction is in itself a source of pain. The pain can be attributed to direct injury of the chilled tissues or nerves, and may be mediated by a metabolite locally released. In sustained exposure to cold, recurrent pains of the same type are noted. Another and separate type of pain from cooling, "second" pain, occurs only during the phase of recovery from the marked vasoconstrictive ischemia induced by intense cooling, as at bath temps, below 5oC. It is associated with reactive vasodilatation and consequent warming of the finger and return of function in sensory nerves earlier paralyzed by cold. A contribution of pain from dilatation of injured vessels is conjectured but is unproven. "After" pain, following soon upon withdrawal of the digit from the cold stimulus, is a subvariety of "second" pain; but return of sensibility in the part is here not a factor. These phenomena are relevant to the unusual susceptibility to cold pain commonly noted in 2 clinical syndromes: in injured tissues with deep hyperalgesia (sometimes accompanied by impairment of local circulation), and in the digits of patients with Raynaud''s disease.
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