Radiant heat is known to increase insensible water loss and, to a certain extent, oxygen consumption. Little is known about its cardiovascular effects. We measured cardiac output, stroke volume, heart rate, and lower limb and skin blood flow in 20 preterm newborn infants nursed in an incubator and under a radiant warmer at an abdominal skin temperature of 36.5°C. Mean (±SEM) birth weight was 1.57 (0.06) kg, gestational age 31.7 (0.4) weeks, and weight at examination 1.69 (0.02) kg; median postnatal age was 15 days. Skin and limb blood flow measurements increased by 44% to 55% with radiant heat ( P .001 and P .01, respectively). Cardiac output increased by 5.4% ( P .02) under the radiant warmer secondary to a small but significant ( P .05) increase in heart rate. The changes in cardiac output during radiant heat administration are comparable to those reported for oxygen consumption.
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