Thoracic duct lymph flow in fetal sheep with increased venous pressure from electrically induced tachycardia.

The intent of this study was to investigate thoracic duct lymph flow, as it is related to the development of hydrops fetalis during rapid atrial pacing. We studied 6 fetal sheep at 128 +/- 6 days of gestation who had chronically placed thoracic duct catheters, aortic and superior vena cava catheters, and atrial pacing electrodes. Atrial pacing at 317 beats/min caused an elevation in central venous pressure from a baseline value of 3 Torr to 7 Torr without affecting pH, arterial blood gas tensions, aortic blood pressure, total protein concentration, or colloid osmotic pressure, although there was a small rise in hematocrit. The thoracic duct lymph flow rate at baseline was 41 +/- 6 ml/h. After atrial pacing for 6 h, the lymph flow rate as measured over at least three consecutive 10-min intervals, and presumably the transvascular fluid filtration rate, increased to 67 +/- 7 ml/h if it was collected at an outflow pressure of 3 Torr, equal to the venous pressure prior to the onset of atrial pacing. However, if the lymph was collected instead at an outflow pressure of 7 Torr, equal to the actual venous pressure measured with rapid atrial pacing, then the lymph flow rate diminished to 48 +/- 5 ml/h. This difference in lymph flow secondary to the increase in venous pressure could account for a maximum of 19 ml/h of edema that accumulates in fetal interstitium and body cavities with atrial pacing.(ABSTRACT TRUNCATED AT 250 WORDS)