Prolonged pulmonary vascular hyperreactivity in conscious dogs after cardiopulmonary bypass

Pulmonary hypertension associated with cardiopulmonary bypass and cardiac surgery

BACKGROUND AND AIM

Pulmonary hypertension (PH) is frequently associated with cardiovascular surgery and is a common complication that has been observed after surgery utilizing cardiopulmonary bypass (CPB). The purpose of this review is to explain the characteristics of PH, the mechanisms of PH induced by cardiac surgery and CPB, treatments for postoperative PH, and future directions in treating PH induced by cardiac surgery and CPB using up-to-date findings.

METHODS

The PubMed database was utilized to find published articles.

RESULTS

There are many mechanisms that contribute to PH after cardiac surgery and CPB which involve pulmonary vasomotor dysfunction, cyclooxygenase, the thromboxane A2 and prostacyclin pathway, the nitric oxide pathway, inflammation, and oxidative stress. Furthermore, there are several effective treatments for postoperative PH within different types of cardiac surgery.

CONCLUSIONS

By possessing a deep understanding of the mechanisms that contribute to PH after cardiac surgery and CPB, researchers can develop treatments for clinicians to use which target the mechanisms of PH and ultimately reduce and/or eliminate postoperative PH. Additionally, learning about the most up-to-date studies regarding treatments can allow clinicians to choose the best treatments for patients who are undergoing cardiac surgery and CPB.

Dominance of free wall radial motion in global right ventricular function of heart transplant recipients

Assessment of right ventricular (RV) function using conventional echocardiography might be inadequate as the radial motion of the RV free wall is often neglected. Our aim was to quantify the longitudinal and the radial components of RV function using three-dimensional (3D) echocardiography in heart transplant (HTX) recipients. Fifty-one HTX patients in stable cardiovascular condition without history of relevant rejection episode or chronic allograft vasculopathy and 30 healthy volunteers were enrolled. RV end-diastolic (EDV) volume and total ejection fraction (TEF) were measured by 3D echocardiography. Furthermore, we quantified longitudinal (LEF) and radial ejection fraction (REF) by decomposing the motion of the RV using the ReVISION method. RV EDV did not differ between groups (HTX vs control; 96 ± 27 vs 97 ± 2 mL). In HTX patients, TEF was lower, however, tricuspid annular plane systolic excursion (TAPSE) decreased to a greater extent (TEF: 47 ± 7 vs 54 ± 4% [-13%], TAPSE: 11 ± 5 vs 21 ± 4 mm [-48%], P < .0001). In HTX patients, REF/TEF ratio was significantly higher compared to LEF/TEF (REF/TEF vs LEF/TEF: 0.58 ± 0.10 vs 0.27 ± 0.08, P < .0001), while in controls the REF/TEF and LEF/TEF ratio was similar (0.45 ± 0.07 vs 0.47 ± 0.07). Current results confirm the superiority of radial motion in determining RV function in HTX patients. Parameters incorporating the radial motion are recommended to assess RV function in HTX recipients.

Cyclohexanone contamination from extracorporeal circuits impairs cardiovascular function

Extracorporeal circulation provides critical life support in the face of cardiopulmonary or renal failure, but it also introduces a host of unique morbidities characterized by edema formation, cardiac insufficiency, autonomic dysfunction, and altered vasomotor function. We tested the hypothesis that cyclohexanone (CHX), a solvent used in production of extracorporeal circuits and intravenous (IV) bags, leaches into the contained fluids and can replicate these clinical morbidities. Crystalloid fluid samples from circuits and IV bags were analyzed by gas chromatography-mass spectrometry to provide a range of clinical CHX exposure levels, revealing CHX contamination of sampled fluids (9.63-3,694 microg/l). In vivo rat studies were conducted (n = 49) to investigate the effects of a bolus IV infusion of CHX vs. saline alone on cardiovascular function, baroreflex responsiveness, and edema formation. Cardiovascular function was evaluated by cardiac output, heart rate, stroke volume, vascular resistance, arterial pressure, and ventricular contractility. Baroreflex function was assessed by mean femoral arterial pressure responses to bilateral carotid occlusion. Edema formation was assessed by the ratio of wet to dry organ weights for lungs, liver, kidneys, and skin. CHX infusion led to systemic hypotension; pulmonary hypertension; depressed contractility, heart rate, stroke volume, and cardiac output; and elevated vascular resistance (P < 0.05). Mean arterial pressure responsiveness to carotid occlusion was dampened after CHX infusion (from +17.25 +/- 1.8 to +5.61 +/- 3.2 mmHg; P < 0.05). CHX infusion led to significantly higher wet-to-dry weight ratios vs. saline only (3.8 +/- 0.06 vs. 3.5 +/- 0.05; P < 0.05). CHX can reproduce clinical cardiovascular, neurological, and edema morbidities associated with extracorporeal circulatory treatment.

Factors contributing to successful discontinuation from inhaled nitric oxide therapy in pediatric patients after congenital cardiac surgery

OBJECTIVE

To investigate variables that contribute to successful discontinuation from inhaled nitric oxide (iNO) therapy in children after surgical repair of congenital heart disease.

DESIGN

Analysis of retrospectively collected data.

SETTING

The pediatric intensive care unit of a university hospital.

PATIENTS

A total of 65 pediatric patients receiving iNO therapy for the purpose of pulmonary circulation control after cardiac surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients were classified into two groups: those successfully weaned from iNO therapy on the initial attempt (group A, n = 45) and those for whom the initial attempt at weaning failed (group B, n = 20). Variables including intraoperative findings, postoperative hemodynamic and ventilatory variables, medication profiles, and dose and duration of iNO therapy were compared between groups. Using a multivariate logistic regression model, iNO therapy of >72 hrs (odds ratio, 5.6) and NO dose at discontinuation of <2 ppm (odds ratio, 4.1) were found to be significantly associated with successful weaning. Those results could be emphasized in a subgroup of left-to-right shunt cardiac anomaly.

CONCLUSIONS

Longer continuation (>72 hrs) and lower final concentration (<2 ppm) represent factors contributing to successful discontinuation of iNO therapy in pediatric patients after cardiac surgery, specifically for children with left-to-right shunt correction.

Pulmonary vascular endothelial responses are differentially modulated after cardiopulmonary bypass

The aim of this study was to characterize the mechanisms underlying pulmonary vascular dysfunction after cardiopulmonary bypass (CPB) by examining responses of isolated pulmonary arteries to selective endothelium-dependent and -independent activators in control and post-CPB dogs. Adult male mongrel dogs were placed on closed-chest, hypothermic CPB for 2.5 h, and then allowed to recover. Anatomically matched pulmonary arterial rings were isolated and suspended for isometric tension recording. Contractile responses to the alpha1-adrenergic agonist phenylephrine were similar in endothelium-containing arteries from control and CPB animals. Endothelium denudation increased contractions to phenylephrine to a similar extent in both groups. Endothelium-dependent relaxation to acetylcholine was decreased 4 days after CPB compared with controls. In contrast to acetylcholine, endothelium-dependent relaxation to bradykinin or to A23187 were not impaired 4 days after CPB. Inhibition of nitric oxide synthase (NOS) with L-NAME depressed the response to acetylcholine in control vessels, confirming that a component of the response to acetylcholine was nitric oxide (NO) dependent. At lower concentrations of acetylcholine, this component of the response was abolished after CPB. The residual relaxation evoked by acetylcholine in the presence of L-NAME also was impaired in CPB compared with control arteries. This suggests that the CPB-induced impairment of acetylcholine-evoked relaxation may not involve both an NO-mediated and an NO-independent component. L-NAME depressed the response to bradykinin to a similar degree in control and CPB arteries. Vascular smooth-muscle dilatation to the NO donor, SIN-1, or to the K+ATP-channel opener, cromakalim, were similar in endothelium-denuded arteries from CPB and control animals. These results suggest that CPB causes a selective impairment in endothelial dilator function without changing the vascular smooth-muscle response to vasodilator or vasoconstrictor stimuli.

L-arginine and substance P reverse the pulmonary endothelial dysfunction caused by congenital heart surgery

BACKGROUND

The increase in pulmonary vascular resistance (PVR) seen in children after cardiopulmonary bypass has been attributed to transient pulmonary endothelial dysfunction (PED). We therefore examined PED in children with congenital heart disease by assessing the L-arginine-nitric oxide (NO) pathway in terms of substrate supplementation (L-arginine [L-Arg]), stimulation of endogenous NO release (substance P [Sub-P]), and end-product provision (inhaled NO) before and after open heart surgery.

METHODS AND RESULTS

Ten patients (aged 0.62+/-0.27 years) with pulmonary hypertension undergoing cardiac catheterization who had not had surgery and 10 patients (aged 0.65+/-0.73 years) who had recently undergone cardiopulmonary bypass were examined. All were sedated and paralyzed and received positive-pressure ventilation. Blood samples and pressure measurements were taken from catheters in the pulmonary artery and the pulmonary vein or left atrium. Respiratory mass spectrometry was used to measure oxygen uptake, and cardiac output was determined by the direct Fick method. PVR was calculated during steady state at ventilation with room air, during FIO(2) of 0.65, then during additional intravenous infusion of L-Arg (15 mg. kg(-1). min(-1)) and Sub-P (1 pmol. kg(-1). min(-1)), and finally during inhalation of NO (20 ppm). In preoperative patients, the lack of an additional significant change of PVR with L-Arg, Sub-P, and inhaled NO suggests little preexisting PED. Postoperative PVR was higher, with an additional pulmonary endothelial contribution that was restorable with L-Arg and Sub-P.

CONCLUSIONS

Postoperatively, the rise in PVR suggested PED, which was restorable by L-Arg and Sub-P, with no additional effect of inhaled NO. These results may indicate important new treatment strategies for these patients.

Superoxide anion scavengers restore NO-mediated pulmonary vasodilation after lung transplantation

Left lung autotransplantation (LLA) results in a chronic attenuation in endothelium-dependent, nitric oxide (NO)-mediated pulmonary vasodilation. We tested the hypothesis that this abnormality involves a decrease in the effective concentration of NO due to inactivation by superoxide anion. Size- and position-matched pulmonary arterial rings were isolated from the right (control) and left (LLA) lungs of seven dogs 1-5 mo post-LLA. The rings were suspended for isometric tension recording and contracted with phenylephrine, and cumulative dose-response curves for ACh or calcium ionophore (A-23187) were generated. Endothelium-dependent relaxation to ACh was inhibited post-LLA, with the maximum vasorelaxation response reduced from 88 +/- 5 to 63 +/- 5% (P < 0. 01) post-LLA. In contrast, after pretreatment with the superoxide anion scavengers tiron or superoxide dismutase (SOD), the dose-response relationships for ACh were similar in control and LLA rings. Oxypurinol, which inhibits superoxide anion production by endothelial xanthine oxidase, also restored the vasorelaxation response to ACh in LLA rings. The pulmonary vasorelaxant response to A-23187 was also attenuated (P < 0.01) post-LLA, and this effect was entirely reversed by pretreatment with tiron, SOD, or oxypurinol. These results indicate that the attenuated responses to these pulmonary vasorelaxants post-LLA involve inactivation of NO by superoxide anion generated by endothelial xanthine oxidase.

Alteration of the neonatal pulmonary physiology after total cardiopulmonary bypass

OBJECTIVES

The purpose of this study was to analyze the mechanisms associated with lung injury after cardiopulmonary bypass and to propose strategies of prevention.

METHODS

Thirty-two neonatal piglets underwent 90 minutes of hypothermic cardiopulmonary bypass without aortic cross-clamping. Five experimental groups were defined: group I had standard cardiopulmonary bypass (control), group II received continuous low-flow lung perfusion during cardiopulmonary bypass, group III treatment was similar to that of group I with maintenance of ventilation, group IV received pneumoplegia, and group V received nitric oxide ventilation (30 ppm) after cardiopulmonary bypass. Data drawn from hemodynamic and gas exchange values and muscular and pulmonary tissular levels of adenosine triphosphate (in micromoles per gram) and myeloperoxidase (in international units per 100 mg) were used for comparisons before and 30 and 60 minutes after cardiopulmonary bypass. Pulmonary and systemic vascular endothelial functions were assessed in vitro after cardiopulmonary bypass on isolated rings of pulmonary and iliac arteries.

RESULTS

Pulmonary vascular resistance index, cardiac index, and oxygen tension were better preserved in groups II, IV, and V. All groups disclosed a significant decrease in lung adenosine triphosphate levels and an increase in myeloperoxidase activity whereas these levels stayed within pre-cardiopulmonary bypass ranges in muscular beds. Endothelium-dependent relaxation was preserved in systemic arteries but was strongly affected in pulmonary arteries after cardiopulmonary bypass. None of the methods that aimed to protect the pulmonary vascular bed demonstrated any preservation of pulmonary endothelial function.

CONCLUSION

Cardiopulmonary bypass results in ischemia-reperfusion injury of the pulmonary vascular bed. Lung protection by continuous perfusion, pneumoplegia, or nitric oxide ventilation can prevent hemodynamic alterations after cardiopulmonary bypass but failed to prevent any of the biochemical disturbances.

Selective endothelial dysfunction in conscious dogs after cardiopulmonary bypass

It has previously been demonstrated that cardiopulmonary bypass (CPB) causes prolonged pulmonary vascular hyperreactivity (D.P. Nyhan, J.M. Redmond, A.M. Gillinov, K. Nishiwaki, and P.A. Murray. J. Appl. Physiol. 77: 1584-1590, 1994). This study investigated the effects of CPB on endothelium-dependent (acetylcholine and bradykinin) and endothelium-independent (sodium nitroprusside) pulmonary vasodilation in conscious dogs. Continuous left pulmonary vascular pressure-flow (LP-Q) plots were generated in conscious dogs before CPB and again in the same animals 3-4 days post-CPB. The dose of U-46619 used to acutely preconstrict the pulmonary circulation to similar levels pre- and post-CPB was decreased (0.13 +/- 0.01 vs. 0.10 +/- 0.01 mg.kg-1.min-1, P < 0.01) after CPB. Acetylcholine, bradykinin, and sodium nitroprusside all caused dose-dependent pulmonary vasodilation pre-CPB. The pulmonary vasodilator response to acetylcholine was completely abolished post-CPB. For example, at left pulmonary blood flow of 80 ml.kg-1.min-1 acetylcholine (10 micrograms.kg-1.min-1) resulted in 72 +/- 15% reversal (P < 0.01) of U-46619 preconstriction pre-CPB but caused no change post-CPB. However, the responses to bradykinin and sodium nitroprusside were unchanged post-CPB. The impaired pulmonary vasodilator response to acetylcholine, but not to bradykinin, suggests a selective endothelial defect post-CPB. The normal response to sodium nitroprusside indicates that cGMP-mediated vasodilation is unchanged post-CPB.

Post-cardiopulmonary bypass pulmonary hypertension in lambs with increased pulmonary blood flow. A role for endothelin 1

BACKGROUND

After cardiopulmonary bypass (CPB), pulmonary hypertension and its associated increased vascular reactivity are a major source of morbidity, particularly for children with increased pulmonary blood flow. Although post-CPB pulmonary hypertension is well described, its mechanisms remain incompletely understood. Plasma levels of endothelin 1. a potent vasoactive substance implicated in pulmonary hypertension, are increased after CPB. The purpose of the present study was threefold: to characterize the changes in pulmonary vascular resistance and vascular reactivity induced by hypothermic CPB; to investigate the effects of preexisting increased pulmonary blood flow on these changes; and to better define the role of endothelin 1 in the pathogenesis of post-CPB pulmonary hypertension.

METHODS AND RESULTS

Vascular pressures and blood flows were monitored in 14 1-month-old lambs with increased pulmonary blood flow (after in utero placement of an aortopulmonary shunt) and 6 age-matched control lambs. During the 2-hour study period after 105.3 +/- 20.6 minutes of hypothermic CPB the increase in pulmonary vascular resistance was significantly augmented in lambs with increased pulmonary blood flow compared with control lambs (P < .05). Pretreatment with PD 145065 (a nonselective endothelin receptor blocker; 50 micrograms.kg-1.min-1) completely blocked this increase in pulmonary vascular resistance and blocked the increase in pulmonary vascular resistance in response to acute alveolar hypoxia after CPB (96.3 +/- 88.5% versus -9.7 +/- 16.4%; P < .05). Plasma endothelin 1 levels increased after CPB in all lambs.

CONCLUSIONS

Preexisting increased pulmonary blood flow alters the response of the pulmonary circulation to hypothermic CPB; the increase in pulmonary vascular resistance induced by CPB is augmented in lambs with increased pulmonary blood flow. Pretreatment with endothelin 1 receptor blockers eliminated the increase in pulmonary vascular resistance and the pulmonary vasoconstricting response to alveolar hypoxia, suggesting a role for endothelin 1 in post-CPB pulmonary hypertension. Endothelin 1 receptor blockers may decrease morbidity in children at risk for pulmonary hypertension after surgical repair with CPB and warrants further study.