Abstract
In previous studies, Flow Mediated Dilation (FMD) was used to study the effect of cardiac surgery on endothelial function. This study investigated the effect of on‐pump cardiac surgery on FMD and reactive hyperemia. The FMD‐response and reactive hyperemia were measured in 25 patients the morning before‐ and the first morning after cardiac surgery. Brachial artery diameter and blood flow were measured with ultrasound at baseline before 5 min occlusion of the blood flow to the forearm, and continuously for 3 min after release of the occlusion. An exponential wash‐out model was fitted to the blood flow over time. Nineteen patients remained for final data analysis. Data are mean ± SEM. The FMD response was reduced after surgery from 3.3 ± 0.5% to 1.4 ± 0.6% (P = 0.02). Max blood flow after cuff release was reduced from 342 ± 30 mL preoperatively to 305 ± 30 mL postoperatively (P < 0.00) and fell toward baseline significantly quicker; preoperative half‐life was 36 ± 2.4 sec. versus 29 ± 1.9 sec postoperatively (P < 0.00). Resting blood flow was reduced from 84 ± 9 mL/min to 66 ± 9 mL/min, (P < 0.00). Brachial artery baseline diameter was unaffected by coronary artery bypass surgery (P = 0.3). The observed reduction in brachial artery FMD after surgery, by previous authors taken to represent endothelial dysfunction, may at least partly be due to reduced hyperemic flow postoperatively. In studies where FMD is measured on multiple occasions, flow data should also be included. Reduced postoperative blood flow to the arm may indicate regional differences in vascular resistance after cardiac surgery.
Highlights
The vascular endothelium participates in the regulation of vascular tone and tissue perfusion
All patients had severe coronary artery disease verified by angiogram and underwent coronary artery bypass grafting with cardiopulmonary bypass (CPB) (Table 2)
In agreement with other results cited by Ruel et al we found that the ratio between resting blood flow and reactive hyperemia was similar in pre- and postoperative tests
Summary
The vascular endothelium participates in the regulation of vascular tone and tissue perfusion. It is suspected that surgical trauma and “stress” may cause a transient deterioration in endothelial function, which in turn may contribute to postoperative vascular dysfunction (Celermajer et al 1992; Ruel et al 2004; Hu et al 2013; Sondergaard et al 2015). Several methods are used to assess vascular endothelial function. Flow-mediated dilatation (FMD) is currently considered to be the gold standard. FMD is noninvasive, safe, and feasible for clinical use. FMD uses ultrasound imaging to measure the dilation of the brachial artery during reactive hyperemia. Reactive hyperemia occurs when a five minutes occlusion of forearm blood flow is released and is due to vasodilatation caused by local metabolites affecting arterioles in the occluded forearm
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