THE EFFECT OF RAPID LOCAL COOLING ON HUMAN FINGER NAILFOLD CAPILLARY BLOOD-PRESSURE AND BLOOD-CELL VELOCITY

1. The effect of a rapid local reduction in finger temperature on finger nailfold capillary blood pressure and blood cell velocity was investigated in healthy subjects. 2. Cooling was achieved by placing the finger into an adjustable copper cylindrical finger holder, which incorporated a Peltier element within its base; thus the entire finger from just distal to the nailfold to the interphalangeal joint was cooled. The Peltier element was cooled to 8 degrees C for 5 min. 3. Finger tip temperature was reduced to 76+/-12% of its resting value during cooling (28.8+/-4.8 degrees C (mean+/-S.D.) baseline versus 22.1+/-6.4 degrees C in the fifth minute of cooling, P = 0.012); this was accompanied by a reduction in capillary blood cell velocity similar to that described previously in cooling experiments using cold air (baseline median, 671 mu m s(-1) (range, 29-4421 mu m s(-1)) versus median during cooling, 221 mu m s(-1) (range, 6.7-2579 mu m s(-1)), P = 0.012). 4. The magnitude and timing of the capillary pressure response to cooling and recovery varied between individuals. In the group as a whole, there was no significant fall in capillary pressure during cooling (basal before cooling, 16.7+/-3.7 mmHg versus minimum during cooling, 15.1+/-3.5 mmHg, P = 0.12), whereas capillary pulse pressure amplitude was reduced (basal before cooling, 5.3+/-3.1 mmHg versus minimum during cooling, 3.7+/-2.6 mmHg, P = 0.028). 5. During the recovery phase, post cooling, both capillary pressure and capillary pulse pressure amplitude were markedly elevated compared to baseline or the cooling phase. Capillary pressure increased from a minimum of 15.1+/-3.5 mmHg during cooling to a maximum of 20.9+/-4.0 mmHg in the recovery phase (P = 0.028) and capillary pulse pressure amplitude increased from a minimum of 3.7+/-2.6 mmHg during cooling to a maximum of 7.7+/-4.2 mmHg during the recovery phase, P = 0.028. 6. These data demonstrate that the Peltier-controlled finger holder provides an effective way of rapidly cooling the finger. Although cooling reduced capillary blood cell velocity, capillary pressure did not change significantly. Such findings suggest that the ratio of precapillary: postcapillary resistance is maintained during cooling. In contrast, the marked increases of capillary blood cell velocity, capillary pressure and capillary pulse pressure amplitude in the recovery phase suggests that a reduction in precapillary resistance may play a role.