Factors responsible for lymph flow include inherent lymphatic contractions, interstitial fluid pressure, and skeletal muscle contraction. We have found that fetal lymph vessels lack a well developed smooth muscle layer and we have not detected spontaneous lymphatic contractions. Others have shown that the fetal interstitial space is more compliant than that of the adult. In the absence of spontaneous lymph vessel contractions and in the presence of a more compliant interstitial space, fetal skeletal muscle contraction may be of major importance for generating lymph flow. We hypothesized that skeletal muscle paralysis would lead to a decrease in fetal lymph flow. We studied 7 fetal sheep with chronically placed thoracic duct catheters. We measured the lymph flow rate at various outflow pressures, stop flow pressure (the pressure at which lymph flow stopped), heart rate, and vascular pressures at baseline and then after administering pancuronium bromide at a dose sufficient to inhibit fetal movement. Table

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Neuromuscular blockade not only caused an 18% decrease in lymph flow rate but also decreased stop flow pressure by 27%. Heart rate and vascular pressures did not change. Although skeletal muscle contractions contribute to fetal lymph flow and to stop flow pressures, other factors must be responsible for the majority of the flow.