Stephen M. Ayres

Metabolic responses of the heart in acute myocardial infarction in man

Abstract Acute myocardial infarction evokes a characteristic neurohumoral response: Catecholamine release is increased, plasma contents of free fatty acids and glucose are elevated and glucose tolerance is diminished. To what degree the myocardium participates in this stress response was evaluated by sampling coronary sinus and arterial blood in 50 patients with acute transmural infarction. Studies were initiated an average of 8 hours after the clinical onset of infarction and were continued for up to 60 hours. A total of 173 separate metabolic studies were analyzed. Forty-one percent exhibited a pattern of predominant myocardial free fatty acid uptake (mean extraction ratio 24 percent) in the presence of elevated plasma free fatty acid and glucose contents (respective means 1,181 μmol/liter and 210 mg/100 ml). Myocardial extraction ratios for glucose, lactate and pyruvate were low (respective means 1.1, 4 and 11 percent). Twenty-one percent of the studies revealed normal myocardial metabolism and 18 percent showed enhanced carbohydrate uptake, as evidenced by increased myocardial extractions of lactate and pyruvate (respective means 42 percent) and of glucose (mean 5 percent). Plasma contents of glucose and free fatty acids were lower than in the predominant free fatty acid group (respective means 156 mg/100 ml and 743 μmol/liter). The remaining 20 percent of studies showed high plasma substrate contents and low myocardial substrate uptake suggesting metabolic breakdown. The free fatty acid metabolic pattern was observed in more than 50 percent of the studies performed at the time of or close to the occurrence of important clinical complications. Propranolol, 0.1 mg/kg intravenously, shifted myocardial substrate utilization from free fatty acids toward carbohydrates. The myocardial respiratory quotient increased from an average of 0.79 to 0.88 ( P The study demonstrates that the metabolic patterns of the myocardium are influenced by the systemic response to stress. Beta adrenergic blockade changed substrate utilization of the myocardium, supporting the hypothesis that adrenergic activation plays an important role in these metabolic responses.

Enhanced transcardiac I-norepinephrine response during cold pressor test in obstructive coronary artery disease

Studies during the past decade have demonstrated that sympathetic nervous activity can play an important role in the regulation of coronary blood flow. It became apparent that alpha adrenergic mediated coronary vasoconstriction can compete with metabolically-induced coronary vasodilatation, particularly in myocardial regions with decreased coronary reserve [1–7]. Recent studies have also emphasized that increased sympathetic nervous activity enhanced ventricular irritability and lowers the threshold to ventricular fibrillation in the ischemic myocardium [8–11]. Since these observations suggest that increases in sympathetic nervous activity could place the patient with obstructive coronary artery disease at increased risk, we measured arterial and coronary sinus 1-norepinephrine contents during relatively mild sympathetic stress in this patient category and compared their response of transcardiac 1-norepinephrine pattern to that in patients with normal coronary arteries. We selected cold pressor stimulation because it is probably similar to the level of sympathetic stress experienced frequently during daily life. Our data indicate that there is a substantially greater increase in coronary sinus 1-norepinephrine concentrations in the patients with obstructive coronary artery disease compared to those without disease.

The prevalence of carboxyhemoglobinemia in New Yorkers and its effects on the coronary and systemic circulation.

Abstract Carboxyhemoglobin saturations ranging from 8.11 to 1.56% were found in a sample of more than 1,000 individuals engaged in various activities in New York City. The difference from lowest to highest carboxyhemoglobin in nonsmokers was 1.58%; in smokers it was as great as 5.0%. Experimental elevation of carboxyhemoglobin to levels similar to that seen in cigarette smokers produced a decrease in arterial and venous oxygen tensions and an increase in cardiac output and coronary blood flow. In contrast to the effect on the systemic vascular bed, carbon monoxide inhalation produced a decrease in myocardial oxygen extraction. These observations suggest that changes in coronary blood flow are a useful indicator of the effects of carbon monoxide when hemodynamically significant coronary artery disease prevents the expected increase in myocardial blood flow.

Identity of peroxy radicals produced from arachidonic acid in oxygenated solutions as studied by pulse radiolysis technique

Abstract The transient optical absorption spectra of the free and peroxy radicals of arachidonic acid were observed in aqueous solutions (and containing O2) using the fast reaction technique of pulse radiolysis and kinetic absorption spectrometry. From the change in absorbance of the transient spectra with pH, the ionization constants (pK) for these radicals were determined. The pK values for the free and peroxy radical adducts of AA were found to be 5.9 and 5.2 with t 1 2 of 14.6 and 6.0 μsec, respectively. The efficiency and rate of electron transfer from these peroxy radicals to p-benzoquinone (BQ) were determined. Electron transfer from the peroxy radical anion to BQ is efficient (48%) leading to the formation of •BQ−. The importance of production of peroxy radicals (in vitro) and their possible involvement as intermediates in the biosynthesis of prostaglandins (in vivo) are discussed.

Management of Acute Hypoxia and Hypercarbia in the Patient with Advanced Obstructive Airway Disease

The treatment of acute respiratory failure in advanced chronic airways obstruction is strikingly different from that where the lungs are relatively normal and failure develops following some acute nonspecific insult. It is now realized that the patient with underlying chronic airway obstruction rarely requires intubation and can usually be treated successfully with carefully controlled oxygen administration. In contrast, the patient with the “adult respiratory distress syndrome” usually requires early intubation with controlled ventilation. Various differences between these two types of acute respiratory failure are shown in Table 1.

Metabolic Causes of Arrhythmias in the Critically Ill Patient

Continuous electrocardiographic monitoring with prompt interpretation and therapeutic response remains one of the most important techniques in the care of the critically ill patient. Although originally recommended for patients with acute myocardial infarction, experience has shown that such monitoring is an effective and sensitive method for identifying abnormalities in a wide variety of clinical situations. A recent patient followed in our intensive care unit emphasizes the value of such monitoring.