METABOLIC CONSEQUENCES OF CHRONIC HYPOXIA

CT contrast predicts pancreatic cancer treatment response to verteporfin-based photodynamic therapy

The goal of this study was to determine dominant factors affecting treatment response in pancreatic cancer photodynamic therapy (PDT), based on clinically available information in the VERTPAC-01 trial. This trial investigated the safety and efficacy of verteporfin PDT in 15 patients with locally advanced pancreatic adenocarcinoma. CT scans before and after contrast enhancement from the 15 patients in the VERTPAC-01 trial were used to determine venous-phase blood contrast enhancement and this was correlated with necrotic volume determined from post-treatment CT scans, along with estimation of optical absorption in the pancreas for use in light modeling of the PDT treatment. Energy threshold contours yielded estimates for necrotic volume based on this light modeling. Both contrast-derived venous blood content and necrotic volume from light modeling yielded strong correlations with observed necrotic volume (R² = 0.85 and 0.91, respectively). These correlations were much stronger than those obtained by correlating energy delivered versus necrotic volume in the VERTPAC-01 study and in retrospective analysis from a prior clinical study. This demonstrates that contrast CT can provide key surrogate dosimetry information to assess treatment response. It also implies that light attenuation is likely the dominant factor in the VERTPAC treatment response, as opposed to other factors such as drug distribution. This study is the first to show that contrast CT provides needed surrogate dosimetry information to predict treatment response in a manner which uses standard-of-care clinical images, rather than invasive dosimetry methods.

Effect of clamping of the renal vein in dogs on certain biochemical and histopathological changes

Experimental investigations were carried out on dogs in which the renal vein was clamped for a period of 15 min, 30, and 60 min consecutively. It has been found that clamping of the renal vein for 15 min results in tissue anoxia and degeneration of the epithelium of the renal tubules. Clamping for 60 min causes cellular acidosis and necrosis of the tubules. It can therefore be said that clamping of the renal vein for even a short time is highly dangerous.

Approach to acid-base problems in the critically ill and injured

The use of the Henderson-Hasselbalch equation and the relationships between bicarbonate levels and the pCO2 or carbonic acid concentration in evaluating acid-base abnormalities are explained. The etiology, pathophysiology, diagnosis and treatment of respiratory alkalosis and acidosis and metabolic alkalosis and acidosis are discussed. The results of laboratory tests should be examined in relation to the patient's condition and consistency with other laboratory tests. Therapy is directed at correcting the underlying problems and, secondarily, at correcting the numbers. Patients respond primarily to rate of change and not absolute numbers. Therefore, problems should be corrected at approximately the rate they develop. Treatment should be guided by continued patient observation and serial laboratory studies.

Effect of decreased O2 supply to tissue on the lactate: pyruvate ratio in blood

Experiments were performed with trained conscious dogs with permanently implanted intravascular catheters. With the dogs in a basal resting state, the concentrations of lactate (L) and pyruvate (P) in arterial blood fluctuated widely from day to day, whereas their concentration ratio (L/P) remained relatively constant. By contrast, decrease in tissue O(2) supply induced by severe chronic anemia increased the arterial blood L/P, specifically, with only random accompanying changes in the lactate or pyruvate concentrations themselves. When systemic O(2) consumption was increased acutely by muscular exercise, cardiac output increased, and the changes in blood L/P were small and not consistent between different dogs. But when O(2) supply to the tissues was simultaneously limited by anemia, L/P increased during exercise, and the magnitude of the increase was proportional to the severity of the anemia. These results suggest that changes in blood L/P during exercise are related specifically to tissue O(2) supply.

The effects of chronic hypoxemia on electrolyte and acid-base equilibrium: an examination of normocapneic hypoxemia and of the influence of hypoxemia on the adaptation to chronic hypercapnia

We have carried out balance studies in normal dogs in order to appraise the effects of chronic hypoxemia on acid-base and electrolyte equilibrium. During the first phase of observation we produced a state of "pure" hypoxemia by reducing the oxygen concentration (utilizing nitrogen as a diluent) and by adding carbon dioxide to the environment in a concentration sufficient to keep arterial CO(2) tension (PCO(2)) within normal limits. The data demonstrate that such a 9-day period of normocapneic hypoxemia has no effect on electrolyte excretion and is virtually without effect on plasma composition. During the second phase of observation we subjected the hypoxemic dogs to stepwise increments in arterial carbon dioxide tension in order to evaluate the effects of the low oxygen tension on the acid-base adjustments to a chronic state of hypercapnia. At least 6 days was allowed for extracellular composition to reach a new steady state at each level of inspired carbon dioxide. The data demonstrate a rise in both plasma bicarbonate concentration and renal acid excretion that was not significantly different from that which has been described previously for hypercapnia without hypoxemia. Just as in these earlier studies, plasma hydrogen ion concentration rose with each increment in carbon dioxide tension, each millimeter Hg increment in PCO(2) leading to an increase in hydrogen ion concentration of 0.32 nmole per L. It thus appears that the chronic"carbon dioxide response curve" is not significantly influenced by moderately severe hypoxemia.

Blood lactate and pyruvate in pulmonary insufficiency

Blood lactate and pyruvate levels and lactate-pyruvate ratios were determined in 20 patients with severe hypoxemia due to pulmonary insufficiency, 18 patients having arterial oxygen tensions (pO2) lower than 50 mm. of mercury, and 8 having tensions lower than 40 mm. of mercury. Most of the patients had normal lactate levels and lactate-pyruvate ratios in spite of severe hypoxemia, and there was no correlation between pO2 or oxygen content and raised levels. All but 1 patient with an elevated lactate level and lactate-pyruvate ratio had a disorder of systemic circulation with hypotension. On the other hand, failure of the right side of the heart with cor pulmonale did not lead to hyperlactatemia. In the resting state generalized tissue hypoxia and increased anaerobic metabolism are seldom due to clinical hypoxemia per se. When present, increased anaerobic metabolism is related to a systemic circulatory disorder, with resultant inadequate tissue perfusion.