Vascular reactions correlated with pain due to cold

Psychophysical experiments with healthy volunteers were conducted to study the relationships between cold pain and blood perfusion of the skin. By means of a thermode the left middle finger was cooled to a constant temperature near 0 degrees C for 45 min. During this stimulation period, the subject regularly rated the pain on an electronically controlled visual analogue scale. Two variables of vascular reactions were measured: the finger photoplethysmogram of the cooled finger and the thermal flux at the skin surface of this finger. Cross correlograms computed between these noninvasive physiologic parameters of blood flow and the pain ratings revealed that pain intensity and degree of vasoconstriction were strongly correlated. The implications of these findings for the peripheral nociceptor mechanism of cold pain are discussed. We conclude that the nociceptors for this type of pain are most probably situated in deeper skin structures and that they are excited by temperatures ranging approximately from 3 to 20 degrees C.