[Vena cava occlusion syndrome. Cardiovascular parameters and uterine blood supply]

In late pregnancy about 10% of the patients suffer from dizziness and a shock symptomatic if placed in a supine position. These symptoms are reversible if the patient turns to the lateral position. In the present paper experiments in human and sheep are reviewed. The cause for this disease is the occlusion of the inferior vena cava by the gravid uterus. The venous backflow to the maternal heart is reduced and the cardiac output decreased by about 1 1/min. The total peripheral resistance (TPR) is increased (Lees et al. 1967b). The increase in TPR is due to the compression of the vena cava by the uterus and not related to an increased arterial tone during the first time course. The fall in mean arterial blood pressure is of varying degree and paralleled by an increase of the blood pressure in the vena cava below the compression and the uterine vein. The fall of the mean arterial blood pressure war related to the decrease of the perfusion pressure. The fall in arterial blood pressure and most important the rise of the uterine vein blood pressure led to a decrease of the perfusion pressure across the uterus. The uterine blood flow fell proportional to the drop of perfusion pressure. The uterine vasculare resistance remained unchanged. The fall of uterine blood flow was associated with a fall of fetal heart rate.