Effect of nitroglycerin on the coronary circulation in patients with coronary artery disease or increased left ventricular work

BIOKINETIC MODEL OF Tc-99m MIBI FOR EIGHT PATIENTS UNDERGONE MYOCARDIAL PERFUSION EXAMINATION via GAMMA CAMERA AND MATLAB PROGRAM: AN IN-VIVO STUDY

Biokinetic model of Tc-99m MIBI for eight patients undergone myocardial perfusion examination was studied using gamma camera and MATLAB program. A six-compartment model was adopted to interpret the metabolic mechanism of each patient. Within the model framework, the respective set of simultaneous differential equations was solved by a self-developed program run in MATLAB. The experimental results exhibited a good fit with the theoretical predictions via the model. The average biological half-lives of body fluid, heart, thyroid, liver, GI Tract and remainder were assessed as [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text][Formula: see text]h, respectively. A dimensionless AT index of disagreement between the experimental data and MATLAB optimal solution was proposed of validating the applied acquisition system and analytical method feasibility. An AT of zero implies a perfect agreement between the theoretical and empirical results, while averages of the derived AT were fluctuated from 3 [Formula: see text] 2 to [Formula: see text] for five compartments. The proposed refined equation estimated the internal dose from gamma-ray as [Formula: see text][Formula: see text]mSv for eight patients according to a fast screening method, which defined human body as a spherical ball to simplify the calculation in reality. The proposed MATLAB-based fitting of in-vivo data with the theoretical results was instrumental for assessing the radiation dose received by the Tc-99m MIBI scan participants.

Regulation of Coronary Blood Flow

The heart is uniquely responsible for providing its own blood supply through the coronary circulation. Regulation of coronary blood flow is quite complex and, after over 100 years of dedicated research, is understood to be dictated through multiple mechanisms that include extravascular compressive forces (tissue pressure), coronary perfusion pressure, myogenic, local metabolic, endothelial as well as neural and hormonal influences. While each of these determinants can have profound influence over myocardial perfusion, largely through effects on end-effector ion channels, these mechanisms collectively modulate coronary vascular resistance and act to ensure that the myocardial requirements for oxygen and substrates are adequately provided by the coronary circulation. The purpose of this series of Comprehensive Physiology is to highlight current knowledge regarding the physiologic regulation of coronary blood flow, with emphasis on functional anatomy and the interplay between the physical and biological determinants of myocardial oxygen delivery. © 2017 American Physiological Society. Compr Physiol 7:321-382, 2017.

Controllable NO release from Cu1.6S nanoparticle decomposition of S-nitrosoglutathiones following photothermal disintegration of polymersomes to elicit cerebral vasodilatory activity

Since the discovery of nitric oxide (NO) as a vasodilator, numerous NO therapies have been attempted to remedy disorders related to pathological vasoconstriction such as coronary artery disease. Despite the advances, clinical applications of NO therapies remain limited mainly because of the low stability of molecular NO donors (and NO molecules), and concerns about the increased oxidative stress and reduced arterial pressure associated with the systemic administration of NO. Here we design a photo-responsive polymersome with nitrosothiols and Cu_1.6S nanoparticles in its core and shell, respectively, and demonstrate the photo-triggered release of NO and its vasodilatory activity on zebrafish. Unlike conventional approaches, our design enhances the stability of NO donors and prospectively enables spatiotemporal regulation of NO release, thus minimizing the harmful effects associated with conventional NO therapies. We anticipate that such a strategy will open up new clinical applications of NO and help reveal the complex biological effects of NO in vivo.

Diagnostic value of myocardial SPECT to detect in-stent restenosis after drug-eluting stent implantation

Different angiographic patterns and restenosis rate may affect diagnostic value of single-photon emission computed tomography (SPECT) in the era of drug-eluting stents (DES). We aimed to determine the ability of myocardial SPECT to detect in-stent restenosis (ISR) in patients treated with DES compared to that of patients treated with bare metal stent (BMS). We evaluated 228 consecutive patients who underwent 6 months follow-up SPECT and coronary angiography (CAG) after stent implantation. In 228 patients, 354 vessels were treated with stent implantation (BMS, n = 105; DES, n = 249) and 65 (18.4%) vessels showed ISR (angiographic % diameter stenosis ≥ 50%) at the 6-month follow-up CAG. In patients with BMS-ISR (n = 37), restenosis was primarily diffuse (70.3%), whereas patients with DES-ISR (n = 28) exhibited more focal restenosis (53.6%, p = 0.028). The sensitivity and specificity of myocardial SPECT did not differ significantly between patients with BMS and those with DES (BMS vs. DES: sensitivity 56.8 vs. 39.3%, p = 0.163; specificity 72.1 vs. 76.5%, p = 0.460). Evaluation of 71 false positive and 33 false negative lesions showed that the most common cause of false-positive results in SPECT was the perfusion decrease which improved but not disappeared compared with the baseline (46 among 71 vascular territories). Despite different patterns of restenosis and ISR rates, the diagnostic value of SPECT did not differ between BMS and DES. Further study looking at ISR in larger number of patients and using other protocol such as Fleming-Harrington Redistribution Wash-in Washout may give additional information.

Nitroglycerin use in myocardial infarction patients

Acute myocardial infarction (MI) and its sequelae are leading causes of morbidity and mortality worldwide. Nitroglycerin (glyceryl trinitrate [GTN]) remains a first-line treatment for angina pectoris and acute MI. Nitroglycerin achieves its benefit by giving rise to nitric oxide (NO), which causes vasodilation and increases blood flow to the myocardium. However, continuous delivery of GTN results in tolerance, limiting the use of this drug. Nitroglycerin tolerance is caused, at least in part, by inactivation of aldehyde dehydrogenase 2 (ALDH2), an enzyme that converts GTN to the vasodilator, NO. We recently found that in a MI model in animals, in addition to GTN's effect on the vasculature, sustained treatment negatively affected cardiomyocyte viability following ischemia, thus resulting in increased infarct size. Coadministration of Alda-1, an activator of ALDH2, with GTN improves metabolism of reactive aldehyde adducts and prevents the GTN-induced increase in cardiac dysfunction following MI. In this review, we describe the molecular mechanisms associated with the benefits and risks of GTN administration in MI.

Nitrates and nitrites in the treatment of ischemic cardiac disease

The organic nitrite, amyl of nitrite, was initially used as a therapeutic agent in the treatment of angina pectoris, but was replaced over a decade later by the organic nitrate, nitroglycerin (NTG), due to the ease of administration and longer duration of action. The administration of organic nitrate esters, such as NTG, continues to be used in the treatment of angina pectoris and heart failure since the birth of modern pharmacology. Their clinical effectiveness is due to vasodilator activity in large veins and arteries through an as yet unidentified method of delivering nitric oxide (NO), or a NO-like compound. The major drawback is the development of tolerance with NTG, and the duration and route of administration with amyl of nitrite. Although the nitrites are no longer used in the treatment of hypertension or ischemic heart disease, the nitrite anion has recently been discovered to possess novel pharmacologic actions, such as modulating hypoxic vasodilation, and providing cytoprotection in ischemia-reperfusion injury. Although the actions of these 2 similar chemical classes (nitrites and organic nitrates) have often been considered to be alike, we still do not understand their mechanism of action. Finally, the nitrite anion, either from sodium nitrite or an intermediate NTG form, may act as a storage form for NO and provide support for investigating the use of these agents in the treatment of ischemic cardiovascular states. We review what is presently known about the use of nitrates and nitrites including the historical, current, and potential uses of these agents, and their mechanisms of action.

Efficacy of different forms of nitrates in angina pectoris

Nitroglycerin has maintained its position in the treatment of angina pectoris for more than a century. Efficacy of oral nitrates has been established and compares well with that of other anti-anginal drugs. New delivery systems are being developed for sustained systemic nitrate action. Beneficial action of nitrates in congestive heart failure and their crucial role in unstable angina and acute myocardial infarction has further widened their therapeutic use. A plausible hypothesis of the mechanism of nitrate-induced vasodilation has been presented, involving production of nitrosothiols and activation of guanylate cyclase in the vascular smooth muscle. Recent developments suggest that the rate degradation of nitrates and formation of nitrosothiols in the vascular smooth muscle are linked, offering an explanation to the relatively rapidly developing, but partial vascular tolerance during high-dose nitrate therapy.

THE EFFECT OF NITROGLYCERIN ON LEFT VENTRICULAR WALL TENSION IN FIXED ORIFICE AORTIC STENOSIS

Symptoms of myocardial ischemia occur in aortic stenosis in the absence of coronary artery disease. Increased left ventricular wall tension, a principal determinant of myocardial oxygen requirements, may contribute to these symptoms. This investigation was undertaken during the course of transseptal left heart catheterization in order to study the effect of nitroglycerin on left ventricular wall tension in eight patients with fixed orifice aortic stenosis. In seven of the subjects, nitroglycerin significantly reduced tension-time index per beat and per minute. In addition, left ventricular size may have diminished as a consequence of lower diastolic filling pressure. In view of the relationship between wall tension and myocardial oxygen consumption, these effects should favorably influence the balance between oxygen availability and oxygen requirements in patients with fixed obstruction to left ventricular outflow. The eighth patient experienced an appreciable increase in tension-time index, suggesting secondary hypertrophic subaortic stenosis.

Mechanisms responsible for the heterogeneous coronary microvascular response to nitroglycerin

Nitroglycerin dilates large (greater than or equal to 100 microns) but not small coronary arterial microvessels, and a putative metabolite of nitroglycerin, S-nitroso-L-cysteine, has been shown in vitro to dilate both large and small coronary microvessels. Based on this evidence, we tested the hypothesis that the lack of response of small coronary microvessels was due to an inability of small coronary microvessels to convert nitroglycerin into its vasoactive metabolite and examined possible explanations for this phenomenon. We studied left ventricular epicardial microvessels in vivo using video microscopy and stroboscopic epi-illumination in anesthetized, open-chest dogs. Diameters were determined while the epicardium was suffused with nitroglycerin, S-nitroso-L-cysteine, or S-nitroso-D-cysteine (all 10 microM) and nitroglycerin in the presence of L- or D-cysteine (100 microM). None of the agents affected systemic hemodynamics. Nitroglycerin dilated large arterioles (20 +/- 2%) but not small arterioles (1 +/- 1%). Both S-nitroso-L-cysteine and S-nitroso-D-cysteine were potent dilators of all size classes of microvessels. Concomitant application of L-cysteine and nitroglycerin evoked dilation in small microvessels (22 +/- 4%, p less than 0.5 versus nitroglycerin alone) and larger microvessels (27 +/- 6%, p = NS versus nitroglycerin alone). D-Cysteine did not alter the microvascular response to nitroglycerin in either small (7 +/- 4%, p = NS versus nitroglycerin alone) or large (18 +/- 3%, p = NS versus nitroglycerin alone) microvessels. Neither L-cysteine nor D-cysteine had a direct effect on microvascular diameter. These findings suggest that 1) sulfhydryl groups are required for the conversion of nitroglycerin to its vasoactive metabolite; 2) the interaction between nitroglycerin and sulfhydryl residues is a stereospecific process, indicating either an intracellular mechanism or a membrane-associated enzymatic reaction; and 3) a lack of available sulfhydryl groups may be responsible for the lack of response of small coronary arterioles to nitroglycerin.

Effects of nitroglycerin in patients with angina, normal coronary arteries, and left ventricular hypertrophy

The coronary hemodynamic and left ventricular mechanical responses to nitroglycerin were studied in eight patients with angina, normal coronary arteries, and pressure overload left ventricular hypertrophy (POLVH) and in five control subjects. Elevated mean and end-diastolic pressure and end-diastolic meridional stress characterized the POLVH group, although systolic meridional stresses were not significantly different from the control group. Thermodilution coronary sinus flow and estimated myocardial oxygen consumption declined significantly following nitroglycerin in both patient groups. Systolic and diastolic mechanical loads also decreased in both groups, although diastolic tone remained elevated in the patients with POLVH. The decrease in coronary sinus flow in the POLVH group was in excess of that expected from the decrease in systolic mechanical load, which suggests a combination of perfusion pressure-dependent decreases in coronary flow as well as an increased resistance to coronary inflow in these patients. The beneficial clinical response to nitroglycerin may reflect the lowered myocardial metabolic demand as well as the decrease in diastolic myocardial tensile and compressive forces.

Dose-related effects of intracoronary nitroglycerin on coronary hyperemia in patients with coronary artery disease

Although intracoronary nitroglycerin (NTG) is frequently required during percutaneous transluminal coronary angioplasty or thrombolysis, the dose-related hemodynamic effects and the extent to which intracoronary NTG--induced coronary hyperemia is limited in patients with coronary artery disease have not been defined. Therefore, we studied 19 patients with coronary artery disease (nine with no or minimal luminal narrowing of the left anterior descending coronary artery [group 1] and 10 with significant left anterior descending coronary stenosis [group 2]; mean arterial pressure and thermodilution coronary sinus and great cardiac vein blood flow were measured during bolus administrations of 50, 200, and 300 micrograms of intracoronary NTG. During the NTG-induced hyperemia, mean arterial pressure decreased 0%, 4% (both p = NS), and 6% (p less than 0.05) after 50, 200, and 300 micrograms doses, respectively. heart rate did not change. Global coronary hyperemia was greatest for 200 micrograms with coronary blood flow increasing (74 +/- 32% in group 1 and 53 +/- 25% for group 2) but was significantly different from 50 micrograms only in group 2 patients. Moreover, the regional coronary blood flow responses were attenuated in group 2 compared to group 1 for 50 micrograms, 18 +/- 13% vs 38 +/- 18%, and for 200 micrograms, 35 +/- 15% vs 72 +/- 34% (both p less than 0.05), with the reduction of regional coronary resistance in group 2 attenuated for all three doses of intracoronary NTG. The 300 micrograms dose did not provide further augmentation of either global or regional coronary blood flow or greater reduction in coronary resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in myocardial perfusion during exercise after isosorbide dinitrate infusion in patients with coronary disease: assessment by thallium-201 scintigraphy

We studied the effect of intravenous isosorbide dinitrate (ISDN) on myocardial perfusion of patients with coronary artery disease, by using exercise thallium-201 (TI-201) myocardial scintigraphy. A control study was conducted initially to assess regional myocardial perfusion rate. Left ventricular myocardium was divided into six parts: anterior, lateral, apical, inferior, posterior, and septal segments. The segmental myocardial perfusion was characterized according to TI-201 initial uptake index (IUI) of relative distribution and redistribution index (RDI) of TI-201 washout. The normal limit of IUI and RDI was established from the data of 17 persons with normal coronary arteries, and then the IUI less than or equal to 84% and the RDI greater than or equal to 1.12 was defined as abnormal. Based on IUI and RDI, each segment was characterized into three types: A type = IUI less than or equal to 84%, RDI greater than or equal to 1.12; B type = IUI less than or equal to 84%, RDI less than 1.12; and C type = IUI greater than 84%, RDI less than 1.12. ISDN was given as a dose of 0.1 mg/kg/hr, and then treadmill testing was repeated for the same duration of exercise time using the same protocol as in the control period. The segments of A type showed a significant improvement in IUI and RDI after receiving ISDN infusion, while the B and C type segments showed no change. It was also shown that the improvement of IUI and RDI of the A type segments was not as marked in multivessel disease as in cases of single-vessel disease.(ABSTRACT TRUNCATED AT 250 WORDS)

History of the synthesis and pharmacology of isosorbide dinitrate

A major research program in the University of Maryland School of Medicine, Department of Pharmacology, in the 1930s was the preparation of a large number of sugar alcohols and their anhydrides as substitute carbohydrates for diabetic diets. As an outgrowth of this work, many of these polyols were converted to their nitrate esters and investigated for their vasodilating properties. The organic nitrates that were synthesized were examined for their potency, duration of action, and possible therapeutic use. It was demonstrated that, contrary to prior belief, the depressor and vasodilating action was exhibited by their own molecular structure and not through hydrolysis and reduction to nitrite. The search for the finer mechanism(s) of action on the vascular musculature showed that these nitrated polyols and their anhydrides inhibited arterial adenosine triphosphatase, although this enzyme inhibition did not correlate with pharmacologic activity. Today the mechanism of action of these drugs is not clearly understood at the cellular level. The 1,4:3,6-dianhydrosorbitol 2,5-dinitrate (isosorbide dinitrate) was synthesized, studied, and reported in 1940. It appeared to be a useful drug because blood levels of the unhydrolyzed ester were found to persist for long periods of time. Subsequent clinical studies in the 1960s demonstrated its prophylactic value in angina pectoris and its prolonged action as a therapeutic asset. In 1967 the mononitrate was shown to be formed in vivo when the dinitrate was administered orally and has been studied as the possible pharmacodynamically active moiety.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional coronary vasoconstriction after combined beta-adrenergic and calcium channel blockade in patients with coronary artery disease

The beta-adrenergic and calcium channel blocking drugs, which individually and combined have proven efficacious in the treatment of angina pectoris, appear to have opposing effects on coronary artery vasomotion. Previous studies have shown that beta-adrenergic blockade may potentiate and calcium channel blockade reverse coronary vasoconstriction during adrenergic cold stimulation in patients with coronary artery disease. To assess the coronary hemodynamic effects of combined drug therapy, thermodilution coronary sinus and great cardiac vein flow and mean arterial pressure were measured during serial cold pressor testing, both before and after 0.1 mg/kg of intravenous propranolol and again after the addition of 10 mg of sublingual nifedipine in 21 patients (9 without [group A1] and 12 with [group A2] greater than 50% narrowing of the left anterior descending coronary artery). In an additional 15 patients (6 patients without [group B1] and 9 with [group B2] left anterior descending artery stenosis), serial cold pressor testing was performed reversing the drug order. Despite significant increases in mean arterial pressure (p less than 0.01) during cold pressor testing, coronary sinus resistance responses after propranolol plus nifedipine were not statistically significant for any group. However, regional coronary resistance responses differed between patients with and without left anterior descending artery stenosis. In group A1, great cardiac vein resistance was unchanged after propranolol plus nifedipine. In group A2, great cardiac vein flow decreased significantly after propranolol plus nifedipine from 8 +/- 17 to -4 +/- 12% (p less than 0.01 versus control), and great cardiac vein resistance increased from 4 +/- 21 to 15 +/- 19% (p less than 0.01 versus control). A similar significant response was observed for groups B1 and B2. Regional coronary vasoconstriction during adrenergic stimulation after combined drug therapy was only observed in patients with significant left anterior descending artery stenosis. These data suggest that in some patients with severe coronary artery disease, combined beta-adrenergic and calcium channel blockade modified regional coronary responses to adrenergic stimulation with an inhomogeneous distribution of blood flow to potentially ischemic regions without affecting total coronary blood flow. These data also imply that an improvement in anginal symptoms after combined drug therapy may be due primarily to mechanisms that reduce myocardial oxygen demand rather than to improved myocardial oxygen supply.

Paradoxical deterioration of left ventricular asynergy after administration of nitroglycerin

The effects of nitroglycerin on segmental asynergy were studied by 2-dimensional echocardiography. Forty-five patients with coronary artery disease and segmental wall motion abnormality at rest were examined, 31 with Q-wave and 14 with only ST-T abnormalities. Left ventricular (LV) echocardiograms were recorded from the LV apex in 4 planes, obtained by systematically rotating the transducer at 45 degrees intervals around the mitral office, using a mechanical device. Sixteen LV segments were analyzed in each patient on real-time display by 2 observers independently. The wall motion analysis was classified as normal, hypokinetic, akinetic or dyskinetic. Of 720 segments, 596 were agreed on by 2 observers in the assessment of wall motion before and after administration of nitroglycerin: 334 segments (56%) showed no change in wall motion, 206 (35%) showed improvement of wall motion and 56 (9%) showed worsening of myocardial asynergy after nitroglycerin. These data suggest that administration of nitroglycerin may result in unexpected worsening of segmental asynergy. This may be secondary to an adverse effect of a decrease in perfusion pressure in critically occluded arteries or may represent a coronary steal phenomenon.

Potential deleterious haemodynamic effects of glyceryl trinitrate on myocardial ischaemia in man

The potential adverse effects of glyceryl trinitrate on myocardial ischaemia were studied using low and high dose infusions in 10 patients with coronary heart disease. Cardiac venous flow was measured by the thermodilution technique and blood was sampled for metabolic studies. Angina pectoris was provoked by atrial pacing before drug infusion and the same heart rate was regained with low and high doses of glyceryl trinitrate. Both doses reduced myocardial ischaemia equally. The low dose of glyceryl trinitrate reduced mean systolic aortic pressure from 145(23) to 128(23) mm Hg and the high dose further to 103(9) mm Hg. Myocardial oxygen uptake decreased owing to a combined reduction in preload and afterload with the low dose and was substantially more reduced with the high dose owing to a further afterload reduction. Transmural perfusion gradient did not change with the low dose of glyceryl trinitrate but fell significantly with the high dose. This fall in myocardial perfusion probably accounts for the lack of further reduction in ischaemia with the high dose. Thus the adverse effects of glyceryl trinitrate infusion are small and do not increase myocardial ischaemia.

Myocardial exchange of metabolites after nitroglycerin in patients with coronary artery disease

We studied the effects of sublingual nitroglycerin (dose range 0.5-1.0 mg) on cardiac metabolism in the resting state in 12 patients with chronic coronary artery disease. Seven patients with chronic coronary artery disease served as a control group. No patient from either of the groups experienced angina pectoris during the study. Reduced heart work after nitroglycerin was evident from a 34% decrease of oxygen uptake (P less than 0.001) and a 35% fall in coronary sinus blood flow (P less than 0.01). Nitroglycerin decreased lactate extraction by 30% (P less than 0.05), lactate uptake by 58% (P less than 0.025); glucose uptake by 47% (P less than 0.01) while net exchange of free fatty acids did not change. The aorto-coronary sinus difference of plasma citrate became increasingly negative (from -4 +/- 3 mumol/l to -8 +/- 2 mumol/l) (P less than 0.02) after nitroglycerin. In the control group coronary sinus blood flow and myocardial exchange of oxygen and substrates remained unchanged. Our results suggest a relatively increased myocardial utilization of free fatty acids compared with that of carbohydrates after nitroglycerin. This may in part be explained as an inhibition of glycolysis due to citrate accumulation. The study indicates that myocardial lipid-carbohydrate metabolism is disturbed in chronic coronary artery disease even in patients without clinical evidence of ischaemia in resting state and that nitroglycerin reverses this condition towards the metabolism of the normal heart.

Radionuclide analysis of the forearm venous pressure-volume relationship: response to nitroglycerin

By means of equilibrium radionuclide forearm venous occlusion plethysmography, we studied 12 adult men without heart failure. By using stepwise increases in venous occlusion pressure (0, 10, 20, and 30 mm Hg), we found that the relationship between venous cuff pressure and forearm radionuclide volume was consistently linear (r greater than 0.985). When sublingual nitroglycerin (NTG) was administered (0.8 mg), the venous pressure-volume relationship was consistently shifted rightward (reducing the slope and increasing the intercept). This resulted in large increases in venous capacitance, as shown by other workers using alternative techniques. Increased venous distensibility due to NTG was caused by an entire shift of the venous pressure-volume relationship rather than increased capacitance at one occlusion pressure. Equilibrium radionuclide venous occlusion plethysmography is a sensitive way to characterize venous pressure-volume relations. In addition, by using radionuclide blood pool component imaging to evaluate venous compliance, concern over fluid transudation seen with standard strain gauge venous plethysmographic techniques can be ignored, particularly at higher occlusion pressures.

Pathogenesis of angina pectoris and role of nitrates in relief of myocardial ischemia

The pathophysiologic mechanism of angina of effort has been understood for one and three-quarter centuries. However, the mechanisms underlying angina at rest are still largely unknown. Coronary spasm, whatever its mechanism, clearly causes Prinzmetal's variant angina. However, evidence that spasm is the cause of all angina at rest is wanting. Rather than spasm, it is suggested that most attacks may be the result of normal fluctuations in the tone of conductive coronary arteries in the presence of critical levels of organic obstruction. The nitrates both relieve coronary spasm and diminish normal coronary tone. They also affect the systemic circulation, so as to favorably influence the level of energy demand.

Cutaneous administration of nitroglycerin: a review

Chronic administration of nitroglycerin may have important therapeutic effects in patients with angina, acute myocardial infarction, congestive heart failure and peripheral vascular disease. Because of unpredictable oral absorption and short duration of action, topical preparations provide an alternative mode of administration. New controlled release transdermal preparations appear to produce constant plasma nitroglycerin concentrations of 0.2-0.3 ng/ml that persist for up to 24 hours. Additional clinical trials of the therapeutic response to this drug form are necessary, particularly in regard to the relative hemodynamic efficacy and side-effect profile of sustained vs. fluctuating plasma nitroglycerin concentrations.

Effect of nitroglycerin on pulmonary perfusion distribution and gas exchange of normal subjects

In eight healthy subjects we assessed the effects of 3 mg sublingual nitroglycerin on lung distribution of ventilation and perfusion using 133Xe (sitting, supine and lateral decubitus) and on alveolo-arterial O2 and CO2 partial pressure differences [(PAO2-PaO2), (PaCO2-PACO2)] and physiological dead space to tidal volume ratio (VD/VT) (sitting). In all studied positions, nitroglycerin induced a significant decrease in uppermost perfusion indices, and a significant increase in dependent perfusion indices, without changing the distribution of ventilation. Significant increases in (PaCO2-PACO2) and VD/VT were observed up to 60 min after nitroglycerin. No changes in (PAO2-PaO2) occurred, except for a transient decrease due to transient hyperventilation following nitroglycerin. The redistribution of pulmonary perfusion after nitroglycerin may be attributed to the passive effects of lowered pulmonary vascular pressures, and to possible action on extra-alveolar vessels. The evolution of the indices of pulmonary gas exchange is compatible with the observed redistribution of ventilation/perfusion relationships.

Treatment of vasospastic angina pectoris at rest with nitroglycerin ointment: a short-term controlled study in the coronary care unit

The effectiveness of nitroglycerin ointment in vasospastic angina pectoris at rest was evaluated in 10 patients selected for study. The study was performed after a 24 hour control period, and a randomized single-blind crossover experimental design was followed. Two percent nitroglycerin ointment (15 mg) or placebo ointment was administered every 6 hours for a period of 48 hours each; the first treatment period was followed by a second in which each preparation was used for a 24 hour period. All patients were hospitalized in the coronary care unit; an objective evaluation was carried out using a multichannel electrocardiographic recording to assure recognition of the painless ischemic episodes. Coronary angiography showed critical stenosis of one or two vessels in 9 of the 10 patients; spasm was demonstrated in 3. Results of the ergonovine test were positive in nine of nine patients. Nitroglycerin ointment produced a significant reduction in the mean daily number of episodes during the first (12.5 +/- 3.9 versus 0.5 +/- 0.4, p less than 0.02) as well as the second treatment period (10.6 +/- 3.8 versus 0.6 +/- 0.4, p less than 0.02). These results demonstrate that nitroglycerin ointment provides effective, long-lasting protection against angina due to coronary spasm.

Pharmacologic intervention in cardiovascular nuclear medicine procedures

Relevant questions in ischemic heart disease are (1) what is the ischemic threat? (2) What is the extent of ventricular dysfunction? (3) Is the observed dysfunction reversible? Exercise testing can help to identify the ischemic threat. Catheterization studies have shown that resting ventricular dysfunction can be reversed in some patients through pharmacologic or surgical intervention. However, improved ventricular performance in ischemic heart disease may be achieved through a variety of mechanisms. Insight into all components of cardiac performance (regional and global contractillity, preload, afterload, and heart rate) and myocardial perfusion may be required to adequately describe the influence of intervention. Exercise radionuclide ventriculographic studies have demonstrated that stress-induced ventricular dysfunction can be reversed through surgical and pharmacologic intervention. Studies at rest have demonstrated that radionuclide techniques can detect drug-induced changes in ventricular performance in groups of patients. The challenge to cardiovascular nuclear medicine is the prospective identification of patients who would benefit most from aggressive intervention aimed at preventing or reversing ischemic ventricular dysfunction.

Coronary flow studies in patients with left ventricular hypertrophy of the hypertensive type. Evidence for an impaired coronary vascular reserve

Increased myocardial blood flow occurs in ventricular hypertrophy, but flow per 100 grams of myocardium remains normal. The increase in flow may be obtained at the expense of the existing coronary vascular reserve or by an increase in the vascular bed. The coronary vascular reserve was studied by analyzing the hyperemic reaction to selective injection of contrast agent into the coronary arteries in 25 patients: a control group (9 patients) with chest pain syndrome, normal coronary arteries and a normal left ventricle (Group I) and 16 patients with aortic stenosis, left ventricular hypertrophy and normal coronary arteries (Group II). The hyperemic response in Groups I and II was 73.3 +/- 2.2 and 65.8 +/- 9.1 percent, respectively (difference not significant). Group II was subdivided into two groups: Group IIA had five patients with a left ventricular mass of less than 200 g (mean 158.8 +/- 25.9); this group had a hyperemic response of 102.3 +/- 9.9 percent. Group IIB had 11 patients with a left ventricular mass of more than 200 g (mean 308.9 +/- 22.5) and a hyperemic response of 49.27 +/- 10.42 percent. The hyperemic response was correlated with the diastolic left ventricular-aortic gradient (r = +0.64, p less than 0.001), left ventricular mass (r = -0.51, p less than 0.01) and aortic diastolic pressure (r = +0.636, p less than 0.001). Group I had a left ventricular mass similar to that of Group IIA (124.9 +/- 9 and 158.8 +/- 26 g, respectively) but a lower hyperemic response (73.3 +/- 2 and 102.3 +/- 10 percent, respectively). These data suggest that severe left ventricular hypertrophy is associated with a reduction in coronary vascular reserve; it is speculated that this decrease in the vascular reserve capacity may be related to the ischemic component of hypertrophic heart disease.

Evaluation of the effects of systemic nitroglycerin on perfusion of ischemic myocardium in coronary heart disease assessed intraoperatively by antegrade blood flow through intact saphenous vein bypass grafts

To evaluate systemic nitroglycerin (NTG) effects on reduced perfusion of ischemic myocardium in coronary disease, intravenous NTG actions on coronary circulatory dynamics were directly assessed intraoperatively during aortocoronary bypass surgery in 24 patients. Thus metered antegrade blood flow was measured through 56 separate intack saphenous vein bypass grafts to analyze NTG perfusion response in the obstructed native coronary artery (CA). In 34 bypassed CA with proximal luminal diameter narrowing greater than 50% to 90%, NTG reduced (p less than 0.01) graft flow (GF) 82 to 63 cc/min, thereby indicating that NTG dilated proximal stenoses with resultant increased CA flow. In 11 bypassed CA obstructed greater than 90% to 100% with well developed collaterals distally, NTG decreased (p less than 0.05) GF 64 to 53 cc/min, thus indicating enhanced collateral flow. In contrast, in 11 bypassed CA obstructions greater than 90% to 100% without collaterals, that NTG increased (p less than 0.02) GF 91 to 100 cc/min indicated NTG nonresponsiveness of the severely diseased CA. Thus systemic NTG improves perfusion to ischemic myocardium subserved by diseased coronaries with less than 90% stenosis or by greater than 90% obstructed vessels with substantial collaterals distally.