Pregnancy attenuates activity of the baroreceptor reflex.

1. Pregnancy-induced changes in acute blood pressure regulation are reviewed. 2. Pregnant animals are less able to maintain arterial pressure during haemorrhage than non-pregnant animals. 3. Baroreceptor reflex-mediated increases in heart rate, renal sympathetic activity, vasopressin, ACTH and cortisol are reduced during pregnancy. Therefore, one explanation for the subnormal ability of pregnant animals to regulate arterial pressure during haemorrhage is that the baroreceptor reflex is not as effective. 4. Chronic increases in oestrogen levels in non-pregnant rabbits do not reduce the gain of baroreflex control of renal sympathetic activity. This and other findings suggest that oestrogen alone does not mediate the blunted baroreflex activity observed during pregnancy.

Cardiac loop ECG recording: a new noninvasive diagnostic test in recurrent syncope.

The most crucial step in diagnosing syncope is determining whether or not an arrhythmia is the cause. A new recording device, the continuous cardiac loop ECG recorder, affords prolonged ambulatory monitoring and can capture the rhythm at the time of syncope. To determine the impact of cardiac loop ECG recorders in diagnosing syncope, we reviewed the records of the first 48 patients referred for cardiac loop recording because of unexplained syncope or presyncope. Previous cardiac studies were nondiagnostic in all patients. In 36% of these patients, loop recording definitively determined whether an arrhythmia was the cause of symptoms. Median duration of monitoring was 28 days, with an average charge of $180 per month. Cardiac loop ECG recording is a convenient, safe, inexpensive, and potentially highly effective means of diagnosing unexplained syncope.