The oscillating ‘vena cava syndrome’ during quiet standing—an unexpected observation in late pregnancy

Abstract

Summary. While studying the lung function of pregnant women at term in four different postures, we were surprised to note marked cyclic accelerations in the heart rate in two‐thirds of the women when in a standing position. The mean cycle length was 105 s (range: 1–4 min) and the amplitude had a mean of 27 beats/min (range: 9–51). Blood flow velocity measurements with ultrasound Doppler over the femoral vein showed that there was an intermittent reduction of flow during quiet standing. When the venous return ceased, maternal heart rate increased, cardiac output decreased and blood pressure fell. After the venous blood flow was restored, maternal heart rate, cardiac output and blood pressure returned to normal until the cycle started again. Concomitant with these maternal heart rate changes, different patterns of fetal heart rate were observed. About 70% of the fetuses showed reduction in the long‐term variability, increase in fetal heart rate or periodic accelerations. Although no woman fainted during quiet standing, the maternal circulatory changes were consistent with those seen in the classical vena cava syndrome.

Premature Contractions: Are They Caused by Maternal Standing?

“…The venous flow velocity decreased remarkably coinciding with each phase of tachycardia; in contrast, with each increase of the venous flow, maternal heart rate returned to normal level [6]. In addition, the plethysmogram showed a continuous venous pooling in the leg with a periodic release of venous blood coinciding with the onset of maternal heart rate renormalisation.…”

“…The same reaction was seen when the woman was leaning forward, or when the uterus was lifted upwards by the investigator. In the 19 postpartum controls, the cyclical tachycardia at standing was not present, although in some cases the interval between the pre-and postpartum measurements amounted to only a few hours [6].…”

“…In women who did not have tachycardia in the standing posture, the venous flow and the other parameters were unrestricted [6].…”

“…the tracing had a spindle-shaped form with an increase of the breathing movements during the increase in heart rate [6].…”

“…Since we have systematically studied cardiopulmonary functions of pregnant women [5], our attention was focused on this possibility as a result of an upright posture [6].…”