Hemodynamic effects of environmental hyperthermia in stage 18, 21, and 24 chick embryos.

Environmental hyperthermia is a hazard to the poikilothermic chick embryo. We studied effects of hyperthermia on mean vitelline arterial blood pressure and mean dorsal aortic blood flow in stage 18, 21, and 24 chick embryos. The pressure was measured with a servo-null micropressure system, and the blood flow was measured with a 20 MHz pulsed Doppler flowmeter. Temperature was monitored with a needle thermoprobe positioned adjacent to the embryo. Data were obtained at 37 degrees C, after warming to 40 degrees C, and then after cooling to 37 degrees C. At stage 21, the pressure increased from 0.96 +/- 0.05 (+/- SE) to 1.04 +/- 0.06 mm Hg on warming and returned from 1.05 +/- 0.04 to 0.87 +/- 0.04 mm Hg on cooling. Pressure measurements during warming and cooling were performed in two separate groups of embryos because of technical problems. The blood flow, studied using different groups of the embryo from the pressure study, also increased from 0.65 +/- 0.06 to 0.75 +/- 0.06 mm3/s on warming and returned to 0.56 +/- 0.05 mm3/s. The heart rate increased from 173 +/- 2 to 211 +/- 3 at 40 degrees C and returned to 170 +/- 3 at 37 degrees C. Stroke volume (flow/heart rate) did not change during the temperature variation. Vascular resistance, the quotient of pressure to blood flow obtained by a ratio analysis, changed from 1.53 +/- 0.33 (median +/- 95% confidence interval) to 1.42 +/- 0.29 mm Hg/mm3/s on warming and changed to 1.60 +/- 0.32 mm Hg/mm3/s on cooling. Similar results were obtained at stages 18 and 24.(ABSTRACT TRUNCATED AT 250 WORDS)