Journal of Applied Physiology, Vol 62, Issue 1 34-38, Copyright © 1987 by American Physiological Society
State-related changes in lung liquid secretion and tracheal flow rate in fetal lambs
K. A. Dickson, J. E. Maloney and P. J. Berger
The volume of liquid in the fetal lungs depends on the rate of liquid
secretion (Vs) across the pulmonary epithelium and the rate of flow out of
the trachea (Vtr). We measured Vs, by an isotope-dilution technique, and
Vtr, with a bubble flowmeter, during low-voltage (LV) and high-voltage (HV)
electrocortical activity. In nine chronically instrumented fetal lambs, Vtr
was greater during the transition to and at LV (16.98 +/- 1.98 ml/h, mean
+/- SE, n = 23) than values during the transition to and at HV (8.69 +/-
0.8 ml/h). A pronounced peak in Vtr of 22.3 +/- 1.8 ml/h (n = 197) occurred
at the transition to LV and early in the LV state. Ten minutes or more into
LV, Vtr had declined to 10.3 +/- 1.8 ml/h (n = 235). Vtr remained low
throughout the HV state. Vs values were not significantly different
throughout the LV (11.83 +/- 1.34 ml/h, n = 216) and the HV (13.61 +/- 2.34
ml/h, n = 174) states. Diaphragmatic burst rate during LV (146.9 +/- 6.7
bursts/5 min, n = 432) was greater than during HV (26.5 +/- 4.6 bursts/5
min, n = 348), but burst rate was not correlated with Vtr. In summary, Vtr
reaches a peak during the early part of LV when breathing commences and Vs
remains constant throughout the behavioral cycle. As a result, lung liquid
volume increases slightly during HV and decreases by a similar amount in
the early part of LV.
