Key result
Head-up tilt and active standing reduce augmentation index ~18% by lowering central blood volume.
Why the study?
Does altering preload via postural changes, thigh cuff, or phlebotomy affect central pressure augmentation index in healthy volunteers and patients?
Does altering preload via postural changes, thigh cuff, or phlebotomy affect central pressure augmentation index in healthy volunteers and patients?
p-value: p=<0.05
Preload significantly alters the augmentation index through changes in the forward pressure wave, challenging the traditional view that AIx is solely determined by wave reflection.
Preload reduction may lower AIx beyond wave reflection; challenges traditional interpretation but remains hypothesis-generating in level-4 data.
OBJECTIVE: Augmentation index (AIx) is often used to quantify the contribution of wave reflection to central pulse pressure. Recent studies have challenged this view by showing how contractility-induced changes in the forward pressure wave can markedly impact AIx. We hypothesized that changes in preload will also affect AIx through changes in the forward wave and studied this in two experiments. METHODS: Noninvasively obtained aortic pressure was used to study central haemodynamics and wave morphology. In the first experiment, we examined the effects of head-up tilt with and without unilateral thigh cuff in 12 young healthy volunteers (mean age 26 years, 50% men). In the second experiment, we examined the effects of active standing in 31 middle-aged patients (mean age 57 years, 65% men) before and after phlebotomy. RESULTS: Head-up tilt or active standing significantly decreased AIx [-17.7 ± 10.4 percentage point (pp) in the young population, -4.7 ± 12.3 pp in the middle-aged population, both P < 0.05]. The fall in AIx was associated with increases in HR, diastolic pressure and systemic vascular resistance and a decrease in stroke volume (all P < 0.05). Inflation of a unilateral thigh cuff reduced the decrease in AIx by 10.7 pp, whereas 500 ml of blood loss augmented the fall in AIx by 5.9 pp (both P < 0.05). The changes in AIx were related to a preload-induced change in forward pressure wave shape (earlier peaking and steeper downstroke). CONCLUSION: Next to inotropic and chronotropic effects, preload emerges as another myocardial factor that obscures the relation between wave reflection and AIx.
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Velde et al. (2017) studied Healthy volunteers and patients planned for regular phlebotomy (n=43). Preload-modifying interventions (head-up tilt, active standing, thigh cuff, phlebotomy) vs. Supine position was evaluated on Change in Augmentation index (AIx) during head-up tilt in the young population (p=<0.05). Head-up tilt and active standing significantly decreased the augmentation index by reducing central blood volume, an effect that was attenuated by a thigh cuff and exacerbated by phlebotomy.
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