Mechanism of adenosine-induced elevation of pulmonary capillary wedge pressure in humans

An acute increase in Left Atrial volume and left ventricular filling pressure during Adenosine administered myocardial hyperaemia: CMR First-Pass Perfusion Study

OBJECTIVE

To investigate whether left atrial (LA) volume and left ventricular filling pressure (LVFP) assessed by cardiovascular magnetic resonance (CMR) change during adenosine delivered myocardial hyperaemia as part of a first-pass stress perfusion study.

METHODS AND RESULTS

We enrolled 33 patients who had stress CMR. These patients had a baseline four-chamber cine and stress four-chamber cine, which was done at peak myocardial hyperaemic state after administering adenosine. The left and right atria were segmented in the end ventricular diastolic and systolic phases. Short-axis cine stack was segmented for ventricular functional assessment. At peak hyperaemic state, left atrial end ventricular systolic volume just before mitral valve opening increased significantly from baseline in all (91 ± 35ml vs. 81 ± 33ml, P = 0.0002), in males only (99 ± 35ml vs. 88 ± 33ml, P = 0.002) and females only (70 ± 26ml vs. 62 ± 22ml, P = 0.02). The right atrial end ventricular systolic volume increased less significantly from baseline (68 ± 21ml vs. 63 ± 20ml, P = 0.0448). CMR-derived LVFP (equivalent to pulmonary capillary wedge pressure) increased significantly at the peak hyperaemic state in all (15.1 ± 2.9mmHg vs. 14.4 ± 2.8mmHg, P = 0.0002), females only (12.9 ± 2.1mmHg vs. 12.3 ± 1.9mmHg, P = 0.029) and males only (15.9 ± 2.8mmHg vs. 15.2 ± 2.7mmHg, P = 0.002) cohorts.

CONCLUSION

Left atrial volume assessment by CMR can measure acute and dynamic changes in preloading conditions on the left ventricle. During adenosine administered first-pass perfusion CMR, left atrial volume and LVFP rise significantly.

Changes in left ventricle myocardial volume during stress test using cadmium-zinc-telluride cardiac imaging: Implications in coronary artery disease

BACKGROUND

Cadmium-zinc-telluride (CZT) SPECT allows the estimation of left ventricle myocardial volume (LVMV). We tested the clinical relevance of rest-stress LVMV changes (Δ LVMV) in detecting coronary artery disease (CAD, coronary stenosis > 70%), using CZT-SPECT.

METHODS

We prospectively enrolled 512 consecutive patients with known or suspected CAD (mean age: 70.3 ± 9.2 years, 72% male) for stress-rest myocardial perfusion imaging (MPI, single-day stress-rest protocol). We quantified summed stress scores (SSS), summed rest scores, and summed difference scores, together with LVMV and ejection fraction (EF) after stress and at rest. All patients underwent coronary angiography within 30 days.

RESULTS

Two hundred seventy-two patients had CAD at coronary angiography. ΔLVMV ≤ 5 mL, corresponding to 6% of change from rest LVMV, was the best predictor of CAD (AUC = 0.831, 79% sensitivity, 82% specificity), irrespective of the stress protocol (dipyridamole or exercise stress) and independently of MPI-SSS, LV EF, and clinical history (P = 0.004). Integrated discrimination improvement (IDI) and net reclassification improvement (NRI) were significant for the addition of ΔLVMV ≤ 5 mL (IDI = 6.1%, P < 0.0001; NRI = 29.7%, P = 0.02) to MPI-SSS, whereas the other parameters were not.

CONCLUSIONS

The evaluation of ΔLVMV using CZT-SPECT can improve the diagnostic accuracy in predicting the presence of CAD when added to conventional MPI.

Purinergic receptor stimulation induces calcium oscillations and smooth muscle contraction in small pulmonary veins

KEY POINTS

We investigated the excitation-contraction coupling mechanisms in small pulmonary veins (SPVs) in rat precision-cut lung slices. We found that SPVs contract strongly and reversibly in response to extracellular ATP and other vasoconstrictors, including angiotensin-II and endothelin-1. ATP-induced vasoconstriction in SPVs was associated with the stimulation of purinergic P2Y2 receptors in vascular smooth muscle cell, activation of phospholipase C-β and the generation of intracellular Ca²⁺ oscillations mediated by cyclic Ca²⁺ release events via the inositol 1,4,5-trisphosphate receptor. Active constriction of SPVs may play an important role in the development of pulmonary hypertension and pulmonary oedema.

ABSTRACT

The small pulmonary veins (SPVs) may play a role in the development of pulmonary hypertension and pulmonary oedema via active changes in SPV diameter, mediated by vascular smooth muscle cell (VSMC) contraction. However, the excitation-contraction coupling mechanisms during vasoconstrictor stimulation remain poorly understood in these veins. We used rat precision-cut lung slices and phase-contrast and confocal microscopy to investigate dynamic changes in SPV cross-sectional luminal area and intracellular Ca²⁺ signalling in their VSMCs. We found that the SPV (∼150 μm in diameter) contract strongly in response to extracellular ATP and other vasoconstrictors, including angiotensin-II and endothelin-1. ATP-induced SPV contraction was fast, concentration-dependent, completely reversible upon ATP washout, and inhibited by purinergic receptor antagonists suramin and AR-C118925 but not by MRS2179. Immunofluorescence showed purinergic P2Y2 receptors expressed in SPV VSMCs. ATP-induced SPV contraction was inhibited by phospholipase Cβ inhibitor U73122 and accompanied by intracellular Ca²⁺ oscillations in the VSMCs. These Ca²⁺ oscillations and SPV contraction were inhibited by the inositol 1,4,5-trisphosphate receptor inhibitor 2-APB but not by ryanodine. The results of the present study suggest that ATP-induced vasoconstriction in SPVs is associated with the activation of purinergic P2Y2 receptors in VSMCs and the generation of Ca²⁺ oscillations.

Clinical value of hyperemic left ventricular systolic function in vasodilator stress testing

Exercise results in increased left ventricular contractility in normal individuals. Similar changes can also be seen with vasodilator stress. This article discusses the physiologic basis of these changes as well as reviews the clinical data supporting the use of these parameters for diagnostic and prognostic evaluation. Methodologic limitations as well as other concomitant pathologic processes which may confound interpretation of stress-induced changes in LVEF are also reviewed.

Differential effects comparing exercise and pharmacologic stress on left ventricular function using gated Tc-99m sestamibi SPECT

OBJECTIVE

Although post-ischemic stunning has emerged as an important marker for severe coronary artery disease (CAD), differences in stress methods may have different effects on left ventricular (LV) volumes and function.

METHODS

To assess differential effects comparing exercise and pharmacologic stress on the LV measurements, (99m)Tc-sestamibi gated single-photon emission computed tomography (SPECT) acquired more than 30 min after stress and at rest was evaluated in 38 patients undergoing adenosine triphosphate (ATP) stress (ATP group) and 38 age-and sex-matched patients subjected to exercise stress (Ex group) among 268 patients with normal SPECT findings.

RESULTS

Coronary risk factors and LV volumetric measurements at baseline were similar in the two groups. Compared with volumetric measurements at rest, end-diastolic volume (EDV) increased (72 +/- 21 ml to 74 +/- 21 ml; P = 0.01), end-systolic volume increased (25 +/- 12 ml to 28 +/- 13 ml; P = 0.001), and ejection fraction (EF) decreased after stress (66% +/- 8% to 63% +/- 9%; P < 0.002) in the ATP group. In the Ex group, by contrast, no such change was observed. In addition, changes in EDV (3 +/- 6 vs. -1 +/- 5 ml; P = 0.01) and the stress-to-rest ratio of EDV (1.04 +/- 0.09 vs. 0.99 +/- 0.08; P < 0.02) after stress were greater in the ATP than in the Ex group.

CONCLUSIONS

Differential effects of stress methods on LV volumes persist more than 30 min after the stress. These findings should be kept in mind when interpreting post-ischemic stunning.

Determinants of coronary microvascular dysfunction in symptomatic hypertrophic cardiomyopathy

Impaired hyperemic myocardial blood flow (MBF) in hypertrophic cardiomyopathy (HCM), despite normal epicardial coronary arteries, results in microvascular dysfunction. The aim of the present study was to determine the relative contribution of extravascular compressive forces to microvascular dysfunction in HCM. Eighteen patients with symptomatic HCM and normal coronary arteries and 10 age-matched healthy volunteers were studied with PET to quantify resting and hyperemic MBF at a subendocardial and subepicardial level. In HCM patients, MRI was performed to determine left ventricular (LV) mass index (LVMI) and volumes, echocardiography to assess diastolic perfusion time, heart catheterization to measure LV outflow tract gradient (LVOTG) and LV pressures, and serum NH(2)-terminal pro-brain natriuretic peptide (NT-proBNP) as a biochemical marker of LV wall stress. Hyperemic MBF was blunted in HCM vs. controls (2.26 +/- 0.97 vs. 2.93 +/- 0.64 ml min(-1) g(-1), P < 0.05). In contrast to controls (1.38 +/- 0.15 to 1.25 +/- 0.19, P = not significant), the endocardial-to-epicardial MBF ratio decreased significantly in HCM during hyperemia (1.20 +/- 0.11 to 0.88 +/- 0.18, P < 0.01). This pattern was similar for hypertrophied septum and lateral wall. Hyperemic MBF was inversely correlated with LVOTG, NT-proBNP, left atrial volume index, and LVMI (all P < 0.01). Multivariate regression analysis, however, revealed that only LVMI and NT-proBNP were independently related to hyperemic MBF, with greater impact at the subendocardial myocardial layer. Hyperemic MBF is more severely impaired at the subendocardial level in HCM patients. The level of impairment is related to markers of increased hemodynamic LV loading conditions and LV mass. These observations suggest that, in addition to reduced capillary density caused by hypertrophy, extravascular compressive forces contribute to microvascular dysfunction in HCM patients.

Evaluation of echocardiography indices of systolic function: a comparative study using pressure-volume loops in patients undergoing coronary artery bypass surgery

Transoesophageal echocardiography measures of systolic left ventricular function obtained during coronary artery bypass surgery are heavily influenced by alterations in loading conditions. No validation of these measurements against load independent indices obtained by pressure-volume loop analysis has been undertaken in humans. Ten patients undergoing coronary artery bypass surgery underwent simultaneous transoesophageal echocardiography and pressure-volume loop analysis of cardiac function at different loading conditions (reduced preload, increased afterload and atrial pacing). Fractional area change, afterload corrected fractional area change, and lateral basal wall peak systolic myocardial velocity, along with dP/dt, were compared to the preload recruitable stroke work relationship. There were no significant differences between the echocardiography measures when compared to the preload recruitable stroke work relationship; however, dP/dt varied significantly across loading conditions (p<0.001). Transoesophageal echocardiography adequately assesses systolic function across loading conditions commonly seen during coronary artery bypass surgery.

Dipyridamole-induced abnormal Tl-201 lung uptake in patients with normal myocardial perfusion: a marker of increased left ventricular filling pressures

BACKGROUND

The mechanism of dipyridamole-induced abnormal increased T1-201 lung uptake in patients without coronary artery disease is poorly understood. The purpose of this study was to evaluate the relation between dipyridamole-induced abnormal T1-201 lung uptake and left ventricular (LV) diastolic indexes using Doppler, color M-mode and Tissue Doppler modalities at rest, and at dipyridamole stress echocardiograpy (DSE) in patients with normal myocardial perfusion and LV function.

METHODS AND RESULTS

18 consecutive patients (mean age 64 +/- 7 years) with normal myocardial perfusion and increased lung T1-201 uptake on dipyridamole stress-redistribution single photon emission computed tomography (SPECT) were included in our study. These patients were compared with 18 age-matched control patients with normal perfusion and normal T1-201 lung uptake. All patients underwent DSE. A good correlation was found between the T-201 lung uptake, the peak early velocity of mitral inflow (E, r = 0.57) and estimated pulmonary capillary wedge pressure (PCWP = 1.24[E/Ea] + 1.9, r = 0.68). In patients with increased L/H ratio compared to control group, the E and the PCWP were significantly higher at baseline 81 +/- 18 vs 68 +/- 11 (cm/s) and 13 +/- 3 vs 10.2 +/- 2 (mmHg). An additional significant increase of E to 91 +/- 23 (cm/s (P = 0.001)) and PCWP to 14.8 +/- 3 (P = 0.005) after dipyridamole administration was seen; in contrast to a nonsignificant change observed in control group. For the detection of a dipyridamole induced PCWP >12 mmHg, a L/H ratio of >/=50% had a sensitivity of 72% and a specificity of 83%, resulting in a positive and a negative predictive value of 81% and 75%, respectively.

CONCLUSIONS

A dipyridamole-induced abnormal T1-201 lung uptake in patients with normal myocardial perfusion and systolic function is predictive of elevated filling pressures at rest and in response to dipyridamole administration, probably reflecting an intrinsic resting diastolic dysfunction and a further abnormal response to vasodilatation.

Effect of continuous ATP injection on human hemodynamics

Continuous ATP injection is used clinically for Tl imaging or coronary flow measurement and because the effect on human hemodynamics is unknown, the present study investigated it in 14 patients undergoing heart catheter examination. Continuous ATP injection induced chest symptoms in 13 of the patients and second-degree atrioventricular block in one, but these complications disappeared immediately after the end of ATP infusion. Continuous ATP injection decreased aortic pressure, but increased pulmonary artery pressure, right atrial pressure and pulmonary capillary wedge pressure. ATP increased heart rate, stroke volume and cardiac output, the latter the result of an increase in preload, a decrease in afterload, and the increase in heart rate.

Assessment of diastolic dysfunction. Invasive modalities

In this article, the author sought to review the two primary components of diastolic function that are most directly and accurately determined using invasive methodologies. For chamber relaxation this is optimally achieved using a micromanometer catheter, whereas for chamber compliance (or its inverse stiffness) this is best achieved by combining this catheter with a measure of instantaneous volume from a conductance catheter, using data from multiple cycles. Even with the ideal data set, the analysis of both properties involves physiologic and often mathematical assumptions, and the extent to which the data do not match these assumptions, the derived indexes may be misleading. Care in the data collection, and awareness of the various factors and pitfalls involved with their analysis can undoubtedly improve the interpretations. As advances in noninvasive methods continue to evolve, reliance on invasive methodologies will continue to fade into the background. At present, however, they remain the gold standard for the two primary diastolic properties described, and have clearly played a central role in the evolution of our understanding of cardiac diastolic disease and its treatment.

Cardiac afferents and neurohormonal activation in congestive heart failure

Cardiac chambers have afferent connections to the brainstem and to the spinal cord. Vagal afferents mediate depressor responses and become activated by volume expansion, increased myocardial contractility and atrial natriuretic factor. Sympathetic afferents, on the contrary, are activated by metabolic mediators, myocardial ischemia and cardiac enlargement. These opposite behaviors may lead to activation or suppression of the sympathetic nervous system and of the renin-angiotensin-aldosterone system. As cardiac diseases progress, the heart dilates, plasma norepinephrine increases, atrial natriuretic factor is released and the renin-angiotensin-aldosterone system is suppressed to maintain water and sodium excretion. This dissociation of the neurohormonal profile of cardiac patients, may be explained by coactivation of sympathetic afferents, by cardiac dilatation, and of vagal afferents by atrial natriuretic factor. In more advanced stages, atrial natriuretic factor suppression of the renin-angiotensin-aldosterone system is overridden by overt sympathetic activation and sodium and water retention ensues. Digitalis, angiotensin-converting enzyme inhibitors and beta-blockers selectively decrease cardiac adrenergic drive. A common mechanism of action, to all three groups of drugs, would be attenuation of sympathetic afferents and partial normalization of vagal afferents. Consequently, heart size and cardiac afferents emerge as the key factors to understand the pathophysiology and treatment of the syndrome of congestive heart failure.

Cardiac complications in the intensive care unit

Advances in the care of critically ill patients has been startling, especially in patients with acute coronary syndromes. With new therapies and procedures, however, have come new complications. On balance, our patients are better off, but the stakes are now higher and the complications more serious. The need for constant vigilance has never been greater.

Acute hemodynamic effects of endogenous adenosine in patients with chronic heart failure

OBJECTIVE

The objective of this study was to assess the acute hemodynamic effects of endogenous adenosine accumulation in patients with chronic heart failure. Exogenously administered adenosine has been shown to reduce pulmonary vascular resistance and to increase cardiac index in normal subjects and in patients with pulmonary hypertension or end-stage biventricular heart failure. Endogenous adenosine accumulation can be provoked by dipyridamole.

METHODS AND RESULTS

Ultra-low-dose dipyridamole (0.07 mg/kg/min for 4 minutes) was administered in 20 patients with either symptomatic idiopathic (n = 12) or ischemic (n = 8) dilated cardiomyopathy and reduced left ventricular ejection fraction (mean 25%+/-5%). Hemodynamic variables were measured before and within 1 minute from the end of dipyridamole infusion. After dipyridamole administration, a mild but significant increase in heart rate (4.5%; p = 0.03) and reduction in mean blood pressure (6.8%; p < 0.001) without changes in right atrial pressure (p = NS) were detected. Dipyridamole increased cardiac output by 26.6% (p < 0.001), cardiac index by 24% (p < 0.001), and stroke volume by 19.8% (p < 0.001), with concomitant 24.6% reduction of systemic vascular resistance (p < 0.001). Moreover, dipyridamole reduced mean pulmonary artery pressure by 8.3% (p < 0.01) and pulmonary vascular resistance by 33.3% (p = 0.001), without changes in pulmonary wedge pressure (p = NS). A significant correlation between percent decrease from baseline in pulmonary and systemic vascular resistance (r = 0.66; p = 0.002) was found after administration of dipyridamole.

CONCLUSIONS

Endogenous adenosine accumulation induced by ultra-low-dose dipyridamole infusion acutely improves the hemodynamic profile, decreasing pulmonary and, to a lower extent, systemic vascular resistance and increasing cardiac index in patients with severe chronic heart failure.

Effects of adenosine on left ventricular filling dynamics in patients with and without coronary artery disease: a Doppler echocardiographic study

OBJECTIVES

Adenosine, a potent coronary vasodilator is used as a pharmacologic stress agent for the assessment of coronary artery disease. A paucity of data exists on its effects on filling dynamics. Accordingly, this study was undertaken to evaluate the effects of adenosine on left ventricular filling as assessed by Doppler echocardiography.

METHODS AND RESULTS

We studied 69 patients (45 men, 24 women, aged 61+/-11 years) referred for evaluation of coronary artery disease. Two-dimensional echocardiography and pulsed-Doppler recordings at the mitral valve tips and annulus were performed at baseline and at maximal adenosine infusion of 140 microg/kg/min. During adenosine infusion, an increase in heart rate occurred (70+/-14 beats/min to 85+/-16 beats/min), with a mild decrease in blood pressure (130/75+/-26/13 mm Hg vs 119/66+/-25/13 mm Hg); both p < 0.02. Changes in filling dynamics included an increase in peak early inflow velocity, E/A ratio, and normalized peak filling rate. Of the patients investigated, 23 had one-vessel coronary artery disease, 29 had coronary disease in two vessels or more by angiography, and 17 had no significant disease. Patients without coronary artery disease (controls) had mild changes in E/A ratio (mean 7%). Patients with coronary artery disease had a more heterogeneous change in filling dynamics (range 43% to 369%, mean 26%), with a significant overlap with controls. However, changes in E/A ratio during adenosine infusion that exceeded the confidence limits of normal (-20% to +30%) were specific for coronary artery disease, with a positive predictive value of 84%.

CONCLUSIONS

Normally, adenosine induces significant increases in early filling as assessed by Doppler. The changes in patients with coronary stenosis are more variable. When these changes fall outside the confidence limits of normal, they are predictive of coronary artery disease.

Correlation between hemodynamic changes and tomographic sestamibi imaging during dipyridamole-induced coronary hyperemia

OBJECTIVES

The purposes of this study were to examine the effects of dipyridamole infusion on hemodynamic variables and to compare these changes with myocardial perfusion.

BACKGROUND

Dipyridamole stress testing with myocardial perfusion imaging is widely used in the assessment of patients with known or suspected coronary artery disease (CAD). Few studies, however, have correlated the hemodynamic effects of dipyridamole using invasive monitoring with perfusion patterns in patients with chest pain syndromes.

METHODS

Hemodynamic measurements were made in the cardiac catheterization laboratory with a Swan-Ganz thermodilution catheter before, during and after infusion of dipyridamole (142 microg/kg body weight per min for 4 min). Technetium-99m sestamibi was injected 3 min after the completion of the infusion.

RESULTS

There were 20 patients with and 6 without CAD, as demonstrated by angiography. Compared with baseline values, dipyridamole resulted in an increase in pulmonary capillary wedge pressure (54 +/- 78% vs. 32 +/- 26%, p = NS), cardiac index (36 +/- 21% vs. 40 +/- 18%, p = NS) and stroke volume index (16 +/- 18% vs. 40 +/- 18%, p = NS) and a decrease in systemic vascular resistance (22 +/- 13% vs. 24 +/- 11%, p = NS), aortic pressure (2 +/- 9% vs. 0 +/- 6%, p = NS) and pulmonary vascular resistance (19 +/- 25% vs. 11 +/- 32%, p = NS) in patients with and without CAD. The peak effect of dipyridamole on heart rate, systemic vascular resistance and pulmonary capillary wedge pressure was evident at 3 min after infusion in 70% of patients. Aminophylline, given to 20 patients, improved hemodynamic variables within 2 min. The single-photon emission computed tomographic sestamibi images were normal in the 6 patients without and abnormal in the 18 patients with CAD.

CONCLUSIONS

Dipyridamole-induced coronary hyperemia produces mild hemodynamic changes in patients with and without CAD; these changes are at or near peak effect at 3 min after infusion and are rapidly reversed by aminophylline.

Effect of inhaled nitric oxide on normal human left ventricular function

OBJECTIVES

This study determined the effects of inhaled nitric oxide (NO) on load-independent indexes of normal human left ventricular (LV) function.

BACKGROUND

Inhaled NO is a potent and selective pulmonary vasodilator. However, when it is used in patients with congestive heart failure, the decrease in pulmonary vascular resistance (PVR) is often associated with an increase in pulmonary capillary wedge pressure. NO has been shown to have a negative inotropic action, but it is not known whether it affects LV chamber function when delivered by inhalation.

METHODS

Eleven subjects (51 to 69 years old) with normal LV function (mean ejection fraction 72% [range 60% to 80%]) were studied. Four patients had concomitant coronary artery disease. Pressure-volume loop recordings were used to determine end-systolic and end-diastolic pressure-volume and preload recruitable stroke work relations. NO was delivered at 20 ppm for 10 min. In an additional group of patients with normal LV function, PVR (n = 5) and NO metabolites (n = 9) were measured.

RESULTS

There was no effect of inhaled NO on steady state LV pressures, volumes, contractility, contraction duration, active relaxation (time constant of relaxation, peak negative first derivative of left ventricular pressure), diastolic compliance or PVR. NO metabolites (methemoglobin and nitrate) were present in the LV cavity at the same concentration as right atrial venous blood, suggesting inactivation of free NO before arrival in the LV chamber. This study had a power of 0.995 to detect a 5% change in contractility (slope of preload recruitable stroke work relation) for alpha = 0.05, based on the multiple linear regression model used.

CONCLUSIONS

These results indicate that 20 ppm of inhaled NO does not have significant effects on normal LV function. This lack of effect may be due in part to rapid inactivation of free NO in transit to the heart.

Correlation of adenosine thallium 201 perfusion patterns with markers for inducible ischemia

To determine the frequency of true myocardial ischemia caused by hemodynamic, metabolic, and regional functional abnormalities after intravenous adenosine infusion in patients with coronary artery disease, 13 patients--11 with coronary artery disease--received intravenous adenosine and thallium 201 during cardiac catheterization. Intracoronary adenosine levels increased by an average of 9.4-fold over baseline. Of the 11 patients, all had > or = 70% stenoses with a mean number of redistribution defects per patient of 3.3 +/- 0.7. Only two (18%) patients had new wall motion abnormalities detected by echocardiography during adenosine infusion. Pulmonary capillary wedge pressure did not significantly rise (13 +/- 7 to 17 +/- 8 mm Hg, p= NS). Lactate production occurred in two patients. Coronary sinus oxygen saturation levels rose from 29% +/- 6% to 68% +/- 8%, consistent with less myocardial oxygen extraction. Thus, despite a high prevalence of defects detected by 201Tl, the prevalence of true myocardial ischemia in patients with coronary artery disease undergoing pharmacologic stress imaging with intravenous adenosine is low. Perfusion defects induced by vasodilator stress are predominantly caused by heterogeneity of flow reserve rather than true ischemia.

Inhaled nitric oxide: therapeutic applications in cardiothoracic surgery

Hypoxemia and increased pulmonary vascular resistance can greatly complicate the management of cardiothoracic surgical patients. These complications are commonly found in the setting of thoracic organ transplantation, adult and pediatric cardiac surgical procedures, and general thoracic surgical procedures. Inhaled nitric oxide is a new therapy that promises to be extremely valuable to the cardiothoracic surgeon. It has been shown to improve oxygenation in the setting of acute lung injury and to selectively lower pulmonary vascular resistance, without producing unwanted systemic vasodilation. The purpose of this review is to discuss the biochemistry, toxicity, experimental studies, and therapeutic applications of inhaled nitric oxide administration in cardiothoracic surgical patients.

Adenosine effectively controls pulmonary hypertension after cardiac operations

BACKGROUND

Pulmonary hypertension secondary to increased pulmonary vascular resistance may greatly complicate the perioperative management of patients having cardiac operations. Adenosine may have a therapeutic role as a selective pulmonary vasodilator. The purpose of this study was to examine the pulmonary hemodynamic effects of a central venous infusion of adenosine in cardiac operative patients with pulmonary hypertension.

METHODS

Ten cardiac patients with pulmonary hypertension (age, 62 +/- 6 years) were studied in the operating room under general anesthesia after weaning from cardiopulmonary bypass. Cardiac output, pulmonary vascular resistance, systemic vascular resistance, mean pulmonary arterial pressure, and mean systemic arterial pressure were determined before, during, and after central venous infusion of adenosine (50 micrograms x kg-1 x min -1) for 15 minutes. Statistical analysis was by analysis of variance, and significance was accepted at p < 0.05.

RESULTS

Adenosine produced significant pulmonary vasodilation. Mean pulmonary arterial pressure was lowered from 36 +/- 1 to 28 +/- 2 mm Hg (p < 0.05), and pulmonary vascular resistance was lowered from 560 +/- 30 to 260 +/- 30 dynes x s x cm-5 (p < 0.05) during adenosine administration. At the same time, cardiac output rose from 4.0 +/- 0.6 to 6.2 L/min (p < 0.05). Pulmonary vascular resistance, mean pulmonary arterial pressure, and cardiac output returned to baseline after the adenosine infusion was stopped. There was no change in systemic mean arterial pressure during adenosine infusion.

CONCLUSIONS

Adenosine may be used clinically as a selective pulmonary vasodilating agent to optimize pulmonary hemodynamic indices without adverse systemic hemodynamic effects in patients with pulmonary hypertension having cardiac operations. It may be particularly valuable in patients with right heart dysfunction by selectively lowering right ventricular afterload.