Blood pressure variation over 24 h was studied in twelve subjects with suspected or established autonomic failure using ambulatory intra-arterial monitoring. Three subjects who had been previously diagnosed as having orthostatic hypotension due to autonomic failure were found to have normal circulatory reflexes. A generally consistent circadian variation of blood pressure was seen in the other nine subjects, pressure rising gradually from its lowest point early in the morning to a peak during the early part of the night; this pattern was also found during bed rest in four subjects. Supine hypertension (an hourly mean blood pressure of greater than 170/90 mmHg) not suspected from sphygmomanometric readings was observed in four subjects, generally during the night. Heart rate variability was reduced in six subjects while short-term blood pressure variability was markedly increased.
Cardiovascular adaptations to the circulatory and volume changes of pregnancy have been studied in late normal and hypertensive pregnancy and postpartum. There has been evidence of a marked plasma volume expansion in normal pregnancy, blunted in preeclampsia; an increased capillary permeability during normal pregnancy; augmented left ventricular mass, which is increased in mild preeclampsia; and similar increases in peripheral venous distensibility during normal and preeclamptic pregnancy. In mild preeclampsia the enlarged ventricle has been shown to be capable of maintaining a normal cardiac output despite elevated afterload. The forearm vascular bed appears to play little part in these adjustments, because forearm venous distensibility has been shown to be higher during normal pregnancy than during postpartum; in hypertensive individuals there was no difference during pregnancy and postpartum. It is evident from this brief review that it is too early to draw clear-cut conclusions regarding the vascular, volume, and cardiac response to normal and hypertensive pregnancy. Research in this field, including two-dimensional echocardiography and plethysmography in larger homogeneous groups, will probably lead to a better understanding of the pathophysiological mechanism of pregnancy hypertension.
1. Venous compliance and plasma volume were measured in thirty-one continuously normotensive women early (11-20 weeks) and late (31-40 weeks) in pregnancy and following delivery. 2. Mathematically fitted pressure/volume curves, obtained by venous occlusion plethysmography, were analysed according to two describing functions (i) the peak of the first derivative dv/dp max and (ii) a work index, integral of 25 (10) p dv. 3. The relationship between venous/volume factors seen after delivery, was disturbed during pregnancy, at which time the work index provided evidence for decreased venous compliance. 4. Pregnancy could be regarded as a potentially hypertensive state, brought about by a vascular/volume mismatch.
Capillary permeability (CP) is elevated in late normal pregnancy, when compared to postpartum values. In women with pregnancy associated hypertension (PAH), pregnancy CP levels are not different from postpartum and are less than in normal pregnancy. These changes in capillary permeability are not explained by alterations in serum albumin.
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