Closed-Chest Cardiopulmonary Bypass and Cardioplegia: Basis for Less Invasive Cardiac Surgery

Background. We developed a method of closed-chest cardiopulmonary bypass to arrest and protect the heart with cardioplegic solution. This method was used in 54 dogs and the results were retrospectively analyzed.

Methods. Bypass cannulas were placed in the right femoral vessels. A balloon occlusion catheter was passed via the left femoral artery and positioned in the ascending aorta. A pulmonary artery vent was placed via the jugular vein. In 17 of the dogs retrograde cardioplegia was provided with a percutaneous coronary sinus catheter.

Results. Cardiopulmonary bypass time was 111 ± 27 minutes (mean ± standard deviation) and cardiac arrest time was 66 ± 21 minutes. Preoperative cardiac outputs were 2.9 ± 0.70 L/min and postoperative outputs were 2.9 ± 0.65 L/min (p = not significant). Twenty-one-French and 23F femoral arterial cannulas that allowed coaxial placement of the ascending aortic balloon catheter were tested in 3 male calves. Line pressures were higher, but not clinically limiting, with the balloon catheter placed coaxially.

Conclusions. Adequate cardiopulmonary bypass and cardioplegia can be achieved in the dog without opening the chest, facilitating less invasive cardiac operations. A human clinical trial is in progress.     

Quantitation of T2′ anisotropic effects on magnetic resonance bone mineral density measurement

In this paper, the authors quantitate the anisotropy of susceptibility effects in an uniaxial trabecular bone model and show its relevance to clinical MR bone mineral density measurements. A physical model is described that quantitates the anisotropic MR behavior of uniaxial trabecular bone. To test the model, a phantom of parallel polyethylene filaments was scanned every 15° between 0° and 90° with respect to the system's main magnetic field (B₀). The distal radial metaphysis of a healthy female volunteer was scanned in orthogonal projections. The signal from each phantom image and each radial image was separated in a pixel-wise fashion into R₂ and R₂′ maps. As predicted, R₂′ relaxation showed anisotropic behavior and changed according to sin² (?), confirming that columnar structures parallel with B₀ will cause no MR susceptibility effects. Scans of the distal radius showed that R₂′ relaxation was twice as great with the forearm perpendicular to B₀ as when it was parallel to it, demonstrating different contributions from struts and columns. For both phantom and radial bone scans, R₂ relaxation was isotropic and did not change with object orientation.     

Time after excision and temperature alter ex vivo tissue relaxation time measurements

Previously unreported effects of tissue storage were recently observed in the authors' experimental magnetic resonance (MR) studies. To evaluate the effect of elapsed time after excision and storage temperature on tissue relaxation time measurements, tissue samples from the liver, pancreas, kidney, testis, spleen, and brain were obtained in rats. T1 and T2 were first measured within 5 minutes of excision, and between subsequent measurements, tubes were kept in a water bath at 40°C, at room temperature (28°C), or in an ice bath (4°C). Cellular and organellar integrity was assessed with electron microscopy and correlated with the MR findings. At 40°C (20-MHz spectrometer), the T1 of liver decreased from 280 msec ± 8 to 212 msec ± 10 during the first 60 minutes; the T1 of pancreas decreased from 276 msec ± 3 to 208 msec ± 2. Other tissues showed less than a 5% decrease in T1. T2 changes were smaller than T1 changes in all tissues. Electron microscopy of pancreatic acinar cells showed postmortem changes in mitochondria evolving over the first 60 minutes after death. Manganese loading experiments implicated mitochondrial manganese stores in the observed enhanced postmortem decrease in T1. This study calls into question reported relaxation time data for liver and pancreas. MR studies of excised tissues must account for time and temperature to prevent systematic experimental errors.     

Intravenous feeding with medium chain triglycerides. Effect on blood gases and the complement system in critically ill patients

Critically ill patients are usually in a catabolic state and may require total parenteral nutrition; this often includes lipid emulsions. Any adverse effects of constituents on pulmonary function, white cell function or the haemocoagulation system could have disastrous consequences in such patients. We have investigated the effects of a new intravenous lipid preparation containing medium chain triglycerides, which, in severely ill malnourished patients are theoretically a preferable energy source to conventional drug chain triglycerides. In a pilot study 17 critically ill patients whose lungs were artificially ventilated were given this lipid emulsion; no adverse effects were observed. Arterial oxygen and carbon dioxide tensions, ratio of inspired oxygen fractional concentration to arterial oxygen tension, platelet and white cell counts all remained constant and the complement system was not activated.     

Prolactin release induced by opiate agonists, effect of glucocorticoid pretreatment in intact and adrenalectomized rats

Cortisol administered at a dose of 25 mg/kg 24 h before measurements decreased the prolactin secretion induced by intraventricularly given opioids (dynorphin, beta-endorphin, Met-enkephalin or D-Met-Pro-enkephalinamide). The effect of cortisol was depressed by actinomycin D pretreatment. The cortisol-induced inhibition of the action of morphine was facilitated in adrenalectomized animals; measuring the effects of increasing doses of cortisol a maximal inhibition was obtained at a dose of 5 mg/kg. The opioid-induced corticosterone secretion was not affected 24 h after a single administration of cortisol. The present results show that the cortisol-induced inhibition of opioid-induced prolactin secretion is dependent on protein synthesis and independent of changes in drug metabolism, and of the type of opiate receptor preferentially affected by the opiate agonists employed.     

Response of lower esophageal contractility to changing concentrations of halothane or isoflurane: A multicenter study

A multiple-center study was performed to determine the relationship between lower esophageal contractility, clinical signs, and anesthetic concentration as expressed by minimum alveolar concentration (MAC). One hundred four American Society of Anesthesiologists Class I through III patients were exposed to isoflurane (with and without nitrous oxide) or halothane in concentrations of 0.5, 1.0, and 1.5 MAC. Heart rate and systolic blood pressure were continuously monitored. Both the amplitude and frequency of spontaneous and provoked lower esophageal contractions were measured in situ by using a 24-F probe equipped with provoking and measuring balloons. Combined results demonstrated statistically significant correlations (P<0.001) between lower esophageal contractility and MAC. Spontaneous lower esophageal contractions decreased from 1.10±0.12 (SEM) contractions per minute (0.5 MAC) to 0.42±0.05 (1 MAC) to 0.18±0.05 (1.5 MAC). Provoked lower esophageal contractility values decreased from 45±4 mm Hg (0.5 MAC) to 29±3 (1 MAC) to 19±2 (1.5 MAC). Heart rate changes did not correlate with MAC, and systolic blood pressure correlated in only one of three centers. Intracenter and intercenter analyses failed to demonstrate a significant relationship between lower esophageal contractility and heart rate or systolic blood pressure. No intracenter differences in either amplitude or frequency of lower esophageal contractions were observed, despite differences in volatile agents, induction techniques and agents, patient populations, and duration of anesthesia. Our studies indicate that lower esophageal contractility may be an indicator of anesthetic depth as reflected by MAC, but further studies are needed to quantify the effects of surgical stimulus, intravenous anesthetics, vasodilators, anticholinergics, calcium channel blockers, beta-adrenergic agonists, and the presence of a nasogastric tube.