In ESRD patients with LVH, ACE inhibition decreases LVM independently of its antihypertensive effect and of associated alterations in arterial hemodynamics. The decrease in LVM was due primarily to a decrease in LV volume, which may have resulted in these patients from chronic volume overload.
Physiol. 43): H1605-H1612, 1998.-To assess the contribution of the arterial and venous systems in the hemodynamic changes of normal pregnancy, we studied blood flow, vascular resistance, venous tone, and the viscoelastic properties (''creep'') of the upper and lower limbs (using plethysmography), aortic distensibility (using pulse wave velocity measurements), and cardiac dimensions (using echocardiography) in nine healthy women. Studies were longitudinally performed at the first (10-13 wk) and third (33-38 wk) trimesters of pregnancy in comparison with the period between the third and sixth month after delivery. From the first trimester, heart rate significantly increased while systemic blood pressure and limb vascular resistances did not change significantly and aortic distensibility increased (P Ͻ 0.05). Lower limb viscoelastic properties decreased at the third trimester (P Ͻ 0.05) and venous tone increased from the first trimester (P Ͻ 0.01), whereas little changes were observed at the site of upper limbs. The decrease in calf venous tone was significantly correlated with the increase in left ventricular diastolic diameter at the first (P Ͻ 0.001) and the third trimester (P Ͻ 0.05). The study provides evidence that during normal pregnancy, changes in the arterial and venous sides of the circulation occur independently of pressure alterations. The increase in venous tone, contributing to preload augmentation, and the decrease in aortic stiffness, reducing afterload, both optimize cardiac function until delivery. venous tone; aortic compliance; arterial distensibility; cardiac function IT IS WELL ACCEPTED that a normal pregnancy is characterized by a large increase in total blood volume and in cardiac output (31,32,48). Blood volume expansion appears early during the pregnancy and rises up to 50%. Cardiac output rises up to 40-50% above nonpregnant values, and the highest increase is reached halfway through gestation. Cardiac output is the product of heart rate and stroke volume. Heart rate is known to reach a 10-27% increase between weeks 4 and 36 of pregnancy (10). However, an increase in stroke volume might also play an important role at the early phase. Stroke volume appears elevated at least until weeks 28-32 (31). The mechanism(s) causing the increase in stroke volume are not yet well established. In pregnant rats and women, an increased cardiac contractility has been suggested (13,36,44), but the differentiation between the contractile properties of cardiac muscle itself and the contractile changes that result from altered preload and afterload is difficult to establish. The possibility should be considered that an increase in venous return also plays a major role. In the literature, numerous data indicate a significant increase in venous capacitance (11,17,18,28,35,47). However, significant discrepancies have also been reported, depending mainly on the site of measurement of venous variables (40, 46). Furthermore, the early venous changes could not be adequately detected because pregnant women were not ...
The aim of the present study as to investigate whether increased central hypervolemia induced by tail suspension (TS) in the rat is an appropriate model of cardiovascular deconditioning (CVD). First, the physiological relationship between central venous pressure (CVP) and extracellular fluid volume (ECFV) was studied. TS (20 degrees) increased CVP (5.8 +/- 0.7 vs. 2.8 +/- 0.8 mmHg; P < 0.01). After 24 h of TS, CVP had returned to control range while ECFV was reduced by 19%. CVP kinetics during 24 h of TS was not affected by either reduction (-20%) or augmentation (/35%) of the ECFV. The normalization of CVP is likely to be a consequence of ECFV reduction, which itself is reduced by increased urinary excretion of water and sodium. Second, recovery from TS was studied. Resumption of the horizontal position was shown to be associated with a significant increase of heart rate (HR) and a slight reduction of blood pressure (BP); there was an apparent delay between increased HR and reduced BP. This imbalance between HR and BP is compatible with CVD. A model of simulated orthostatism (SO) was developed to further investigate the responses of HR and BP. Interestingly, SO (90 degrees rotation) in the normal rat was associated with significant tachycardia and a slight increase of BP. This pattern remained stable for at least 3 h. In rats that were tail suspended for 48 h, episodes of hypotension and bradycardia (5 +/- 1 in 3 h) suggested a defect in adaptation to increased hydrostatic pressure. In conclusion, TS appears to be an appropriate model of CVD. Reduction process. Return to horizontal position in TS rats induced a tachycardia with minimal effects on BP; this pattern is close to that observed in humans assuming upright posture. SO in previously TS rats disclosed episodes of hypotension and bradycardia that deserve further investigation.
1. Pulsatile changes in the diameter of the common carotid artery were studied transcutaneously using an echo-tracking technique in 15 normal subjects: eight subjects before and during application of graded lower-body negative pressure from -5 to -15 mmHg, and seven subjects before and during weight-bearing head-up tilt at 30 and 60 degrees. 2. In concomitant studies of changes in forearm vascular resistance, it was seen that mild lower-body negative pressure produced deactivation of cardiopulmonary receptors without changes in systemic blood pressure or heart rate. 3. After lower-body negative pressure, a significant decrease in carotid arterial diastolic diameter [from 0.662 +/- 0.028 to 0.624 +/- 0.033 cm (lower-body negative pressure -10 mmHg) and 0.640 +/- 0.030 cm lower-body negative pressure -15 mmHg), P< 0.001 and < 0.05] was observed. 4. After head-up tilt, carotid arterial diameter was also significantly decreased at 30 and 60 degrees, whereas a significant increase in heart rate occurred only at 60 degrees and mean blood pressure did not change. 5. The study provides evidence that the geometry of the arterial wall is substantially modified by non-invasive manoeuvres such as head-up tilting and lower-body negative pressure. The latter is assumed to selectively deactivate human cardiopulmonary receptors, but the present data suggest that local changes may also influence carotid baroreceptors.
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