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We have studied the effect of active and passive smoking during pregnancy on post-ischemic vascular reactivity in 40 mother-infant pairs (table). 10 mothers (controls) did not smoke and were not exposed to involuntary smoking; 20 mothers (active smokers) had smoked at least 10 cigarettes/day during pregnancy; and 10 mothers (passive smokers) had been exposed to tobacco smoke from their husbands who smoked more than 10 cigarettes/day. The mothers and the infants were healthy and no complications were recorded during pregnancy delivery or the 1st 5 days after birth. Post-ischemic vascular reactivity was evaluated during the 2nd day after birth. Transcutaneous PO2 (cPO2) was monitored with an Oxymonitor" (Hellige); the skin electrode (Transoxode) was fixed on the forearm and set at 37 degrees Celsius; a pneumatic cuff was applied to the upper arm and inflated to 50 mm Hg above systolic pressure to occlude forearm circulation for 4 minutes. The post-occlusive peak tcPO2 was taken as a measure of post-ischemic reactive hyperemia. This technique has proven useful for evaluating vascular abnormalities in diabetic children. A significant reduction in tcPO2 was found for both the smoking mothers and their infants for mothers indirectly exposed to tobacco smoke and their infants (table). Reactive hyperemia in response to arterial occlusion lasting more than 3 minutes is due to a fall in vessel wall PO2 to O causing direct vascular smooth-muscle relaxation by reduction in oxidative phosphorylation and the local production of vasodilator metabolites such as adenosine histamine or prostaglandins. The reduction in reductive hyperemia in mothers exposed to tobacco smoke and in their infants may therefore be partly related to impairment of prostacyclin production by endothelial cells. The vascular alterations caused by smoke can produce a dysfunction of placental blood flow similar to that observed in the chronic placental insufficiency syndromes; this may explain the reduction of birthweight observed in infants of mothers exposed to active or involuntary tobacco smoking. (full text)