Charles Wildevuur

Pressure-diameter relationship in the human greater saphenous vein

BACKGROUNDnCompliance of artificial and autologous vascular grafts is related to future patency. We investigated whether differences in compliance exist between saphenous vein grafts derived from the upper or lower leg, which might indicate upper or lower leg saphenous vein preference in coronary artery bypass surgery. Furthermore, the effect of perivenous application of fibrin glue on mechanical vein wall properties was studied to evaluate its possible use as perivenous graft support.nnnMETHODSnVein segments (N = 10) from upper or lower leg saphenous vein grafts were collected for histopathologic examination and smooth muscle cell/extracellular matrix (SMC/ECM) ratio was calculated. This ratio is suggested to be related with vascular elastic compliance. In a second group vein graft segments (N = 6) from upper and lower leg were placed in an in vitro model generating stepwise increasing static pressure up to 150 cm H(2)O. Outer diameter was measured continuously with a video micrometer system. Distensibility was calculated from the pressure-diameter curves. A third group of vein graft segments (N = 7) was pressurized after fibrin glue application to prevent overdistension, and studied in the same setup.nnnRESULTSnVein segments from the lower leg demonstrated a consistent higher relative response compared with the upper leg saphenous vein graft (0.9176 +/- 0.03993 vs 0.5245 +/- 0.02512). Both reach a plateau in the high-pressure range (> 100 cm H(2)O). A significant difference in in vitro distensibility between upper and lower leg saphenous vein was only found at a pressure of 50 cm H(2)O (p < 0.05). With fibrin glue, support overdistension is prevented as revealed by the maximum relative response between fibrin glue supported upper and lower leg saphenous vein segments (0.4080 +/- 0.02464 vs 0.582 +/- 0.051), and no plateau is reached in the pressure range up to 150 cm H(2)O.nnnCONCLUSIONSnNo upper or lower leg saphenous vein preference could be deduced from the differences in pressure-diameter response due to loss of distensibility (and thus of compliance) in the high-pressure range. Fibrin glue effectively prevents overdistension and preserves some distensibility in the high-pressure range in both the upper and lower leg saphenous vein. This might provide a basis for clinical application of perivenous support.

IMPROVED TISSUE PERFUSION DURING PRESSURE REGULATED HYPERTHERMIC REGIONAL ISOLATED PERFUSION - A CLINICAL-STUDY

In previous studies on isolated hindlimb perfusions in dogs, the authors proved that the extracorporeal circuit should be regulated at a delta pressure (systemic mean arterial pressure minus hindlimb mean arterial pressure) of not more than 15 mmHg, to achieve adequate tissue perfusion. To confirm this in patients the authors performed clinical perfusions, divided into three groups. In group I and II the extracorporeal circuit was regulated at a delta pressure of 15 mmHg and 50 mmHg, respectively. In group III perfusions were performed using the common technique of a predetermined fixed flow. Tissue oxygenation, determined by means of a transcutaneous pO2 electrode, was adequate in group I and was severely impaired in group II and III. Although in group I high perfusion flows were needed, leakage was less than 10%. To achieve adequate tissue perfusion during clinical regional perfusions, the extracorporeal circuit must be regulated at a delta pressure of 15 mmHg.

Improved functional recovery of the isolated rat heart after 24 hours of hypothermic arrest with a stable prostacyclin analogue (ZK 36 374)

Prostacyclin (PGI2) can protect the heart against ischemia, i.e. it can reduce myocardial damage [9, 10]. PGI2 protects the myocardium in vivo by preventing platelets from clumping and by dispersing preformed platelet aggregates [1,14]. However, also in the absence of platelets, PGI2 was shown to protect the myocardium against ischemia at concentrations that did not affect smooth muscle tone in the vessel wall [2]. This protective effect of PGI2 in vitro might be related to a stabilization of cell membranes in adrenergic nerve endings and hence to the prevention of ischemia-induced catecholamine release [13]. The instability of PGI2, both in vitro and in vivo, limits its application during long ischemic periods. Recently, a stable prostacyclin analogue, ZK 36 374, was demonstrated to have several prostacyclin-mimetic activities, both in vitro and in vivo [11,12]. In this communication we report upon the beneficial effect of this stable prostacyclin analogue at a low concentration (4 nM) on the extent of ischemic damage, on the recovery of myocardial function and on the occurrence of arrhythmias in the isolated rat heart after 24 h hypothermic cardiac arrest.

Effects of artificial ventilation on surfactant phospholipid metabolism in rabbits

Surfactant phospholipid metabolism and lung stability were studied in mechanically ventilated and in spontaneously breathing rabbits (control group). During ventilation the dynamic lung-thorax compliance decreased to 79% after 6 h. Static compliance and amount and composition of surfactant phospholipids remained unaltered. These data indicate inactivation of alveolar surfactant during ventilation, which is reversible by a single large inflation. Incorporation of injected radioactively labeled palmitate into saturated phosphatidylcholine (SPC) of the lamellar body fraction increased significantly in the ventilated group; maximal specific activity increased from 20 dpm/nmol SPC at 6 h in the control group to 30 dpm/nmol SPC at 2 h in the ventilated group. The clearance of radioactivity from the lamellar bodies into the alveolar lumen was greatly enhanced in the ventilated group. The results are explained by assuming that as a result of the inactivation of alveolar surfactant, endocytosed surfactant is degraded in the type II cells instead of being recycled and that the degradation products are subsequently reutilized in surfactant synthesis. This interpretation is supported by computer simulations.

Surfactant replacement therapy in surfactant-deficient rabbits: Early effects on lung function and biochemical aspects

Lung-surfactant-deficient rabbits (n = 6) requiring artificial ventilation were subjected to a weaning-off regimen following surfactant replacement therapy. Surfactant-deficient rabbits (n = 6) that did not receive surfactant but underwent the same procedure served as controls. All surfactant-treated rabbits survived (i.e., reestablished spontaneous air breathing) whereas all the control animals died. In the surfactant-treated animals lung function improved in such a way that during the weaning period PaCO2 did not increase and the level of PaO2 remained significantly higher than in the control animals. The static lung compliance and the stability and expansion indices in vitro were significantly higher in the surfactant-treated rabbits. The lamellar body fraction of the lungs of surfactant-treated animals contained a significantly higher amount of surfactant phospholipids than those of the control animals.It is concluded that the animal model used in this study is an excellent tool for testing early effects of different surfactant preparations.

Platelet consumption during neonatal extracorporeal life support (ECLS)

This paper reports the results of a retrospective study of blood use and blood loss in 40 neonates during extracorporeal life support (ECLS). Immediately after onset of bypass 39±2.5ml platelets, 59.4±6.5ml packed red blood cells (PRBC) and 15.0±5.4ml fresh frozen plasma (FFP) per patient were needed. The average daily amount given per patient was 49.0±3.0ml of platelets and 48.0±3.4ml and 9.6±3.9ml of PRBC and FFP respectively. The 10 patients who had bleeding complications received 50.0±6.3ml/day of platelets compared to 49.0±3.4ml in the other patients. The majority of blood loss during the entire period of ECLS was from samples, averaging 43.0 ± 1.5ml/day. Neck wound drainage, 6.7±2.5ml/day per patient, lasted for the entire period.

Enhanced healing of 30 μm Gore-Tex PTFE microarterial prostheses by alcohol-pretreatment

Abstract Polytetrafluoroethylene (PTFE) microvascular prostheses with a fibril length of 30 μm were pretreated with alcohol (n = 18), implanted into the abdominal aorta of rats and were evaluated at 1 day (n = 3), 1 week (n = 3), 3 weeks (n = 6) and 6 weeks (n = 6) to determine whether alcohol-pretreatment might improve their healing. Untreated PTFE microvascular prostheses (n = 18) functioned as controls (all prostheses: length 10 mm, I.D. 1.5 mm). The alcohol-pretreated PTFE microarterial prostheses were initially completely filled and covered with clot and showed fast and complete healing within 6 weeks: endothelial cells and smooth muscle cells on the luminal surface, and the interstices filled with fibrous-like tissue. In contrast, the untreated PTFE prostheses were initially not filled or covered with clot and showed only healing near the anastomotic sites and scarce tissue ingrowth into the wall. These results demonstrate that alcohol-pretreatment improves the healing characteristics of PTFE microarterial prostheses with a fibril length of 30 μm. The alcohol-pretreatment renders the PTFE material more accessible to clot and subsequently to cells.

Captopril improves recovery of adenosine triphosphate during reperfusion of the ischemic isolated rat heart; a 31-phosphorus-nuclear magnetic resonance study

SummaryThe effect of captopril on energy-rich phosphates and pH during normothermic ischemic arrest, hypothermic cardioplegic arrest and subsequent reperfusion was investigated in the isolated rat heart using 31P-nuclear magnetic resonance. The hearts remained in the probe during all perfusion procedures and captopril (80 ml·l−1) treatment was started directly after cannulation.After normothermic ischemic arrest (15 min), the ATP content of captopril-treated hearts was not significantly different from that of untreated hearts (53±9% and 52±8%, respectively). Accumulation of inorganic phosphate at the end of ischemia was significantly less in treated hearts, suggesting a higher end-ischemic nucleotide content in treated hearts.Hypothermic cardioplegic arrest (St. Thomas Hospital solution, 4°C) lasted for 3 h at 10°C. Adenosine triphosphate in treated hearts was significantly lower at the end of ischemia; 36±6% compared to 53±9% for untreated hearts.Adenosine triphosphate in untreated hearts recovered to 76±9% after normothermic ischemia and to 72±7% after hypothermic ischemia at the end of 30 min reperfusion. Captopril significantly improved adenosine triphosphate recovery in both treated groups; 89±4% after normothermic and 83±4% hypothermic ischemia.We conclude that captopril has a beneficial effect on recovery of adenosine triphosphate both after normothermic and after hypothermic ischemia.

An Automatically Regulated Low Prime Heart-Lung Machine for Infants: A Rabbit Model

A new compact heart-lung machine for paediatric use was designed. The total volume of this system of only 90ml allows for priming without the use of donor blood. The priming volume could be kept small mainly by replacing gravity drainage with drainage by a negative pressure in the venous reservoir. To avoid volume shifts between the extracorporeal circuit and the infants circulation and to safely operate this minimal volume circuit, the heart-lung machine was automatically controlled. In this study we show that the miniaturized system functioned reliably under various conditions during cardiopulmonary bypass in rabbits.