Surface tension of the respiratory tract fluid in fetal guinea pigs

A modification of the maximal bubble pressure method was used for surface tension determination of amniotic fluid and of liquid in various parts of the respiratory tract. Studies were done on guinea pig fetuses weighing from 29 to 113 grams. The value for amniotic fluid was 67.0 ± 4.4 dynes per centimeter, for the liquid in the upper trachea 63.8 ± 7.6 dynes per centimeter, and for that in the lower trachea 62.3 ± 9.3 dynes per centimeter. For that in the bronchii it was 44.2 ± 7.3 dynes per centimeter for fetuses weighing from 85 to 115 grams, and 65.8 ± 4.2 dynes per centimeter for fetuses from 25 to 55 grams. The bronchial values were significantly lower for fetuses of greater weight and significantly different from the surface tension of amniotic fluid. The significance of these findings is discussed.