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This study compared the dermal blood flow response to low levels of compressive pressure in healthy older and younger subjects. Dermal blood flow was measured over the left trochanter of 19 younger (21-45 yrs) and 22 older (> or = 60 yrs) subjects using a laser-Doppler velocitometer. Interface pressure, baseline flow, and flow during 60 minutes of left-side lying on an air mattress were measured. Baseline dermal blood flow did not differ significantly between the older and younger groups. Both groups showed a significant increase in blood flow over time during the 60 minutes of compression. The change in dermal blood flow over time was not significantly different between the two groups. This study demonstrated that healthy persons, regardless of their age, exhibited an increase in dermal blood flow over time at low levels of compressive pressure.

The time of appearance of the truncus arteriosus was studied in the chick embryo using an in ovo labeling technique. Three hundred embryos at stages 13-18 of Hamburger and Hamilton were selectively labeled at the distal end of the heart tube, using gelatine-india ink label; 122 of these embryos were reincubated and 111 of them reached stages 25-28. In these stages the final location of the label was determined. Only 95 of these embryos showed both a normal heart and a label located in it. The remaining embryos were discarded due to abnormal cardiac morphology or because the label was not found. Embryos labeled at stages 13-14 had label in the conus in 42.8% of the cases and in the boundary between the conus and the truncus arteriosus in 57.1% of the cases. Label placed at stages 15-16 was located in the conus in 6.1% of the cases, in the boundary between the conus and the truncus arteriosus in 44.8% of the cases, and in the truncus arteriosus in 48.9% of the cases. Finally, label placed at stages 17-18 was located in the boundary between the conus and the truncus arteriosus in 18.7% of the cases and in the truncus arteriosus in 81.2% of the cases. Our results permit us to conclude that the truncus arteriosus appears in the chick embryo as early as stages 15-16 of Hamburger and Hamilton (50-56 hours of incubation).