Blood storage XXII. Improvement in red blood cell 2,3-DPG levels at six weeks by 20 mM PO4 in CPD-adenine-inosine

Inorganic phosphate has been known to assist red blood cell maintenance of ATP and in the presence of inosine to assist in the maintenance of 2,3-DPG. High concentrations of phosphate, while helping ATP maintenance, were found to be deleterious to 2,3-DPG maintenance in CPD- adenine preservatives. However, in the presence of inosine, concentrations of phosphate as high as 10 mM were advantageous to 2,3- DPG maintenance. The present study extends the observations on ATP and 2,3-DPG maintenance in CPD-adenine-inosine preservatives from the previous 10 mM to 20 mM phosphate. A high phosphate (20 mM) effect has been seen as improved maintenance of 2,3-DPG levels during the fifth and sixth weeks of storage of whole blood at 4C. This supports the previously reported observation of improved maintenance of 2,3-DPG in a 10 mM phosphate preservative. This is ten times the 2 mM phosphate concentration in CPD-adenine. In the low phosphate preservative (2 mM), 2,3-DPG maintenance is less than that in all of the higher phosphate preservatives after the second week of storage. ATP concentrations in this experiment show good maintenance throughout six weeks of storage.     

Student reflective groups at a Scottish College of Nursing

In this paper student views on reflective groups, set up as an important element of the new Project 2000 course in a Scottish College of Nursing, are reported. A random sample of 19 students were interviewed. While the reflective groups were very popular with students because they provided support, there was little evidence of a linkage between theory and practice. It was clear that the ambitious objective of stimulating reflection-on-action was not attained. Practice certainly was discussed, but it tended to be dominated by dramatic and emotionally charged aspects of care rather than the more frequent routine concerns. There were, however, indications that the original aim of the reflective groups could be achieved if tutors could establish a common understanding of the purpose of the groups and of reflection, and if the practices on which students reflected consisted less of single day visits where the students saw themselves as non-participant outsiders.     

Treatment of defects of the anterior abdominal wall in newborns

Primary closure of an omphalocele or gastroschisis may cause respiratory compromise in the neonate. Some authors recommend primary closure of the defect with prolonged respiratory support because of dissatisfaction with staged visceral reduction and use of a Silastic pouch. Our experience with use of a Silastic pouch from 1975 to 1982 was reviewed. Twenty-three newborns with major defects of the abdominal wall (14 omphaloceles and 9 gastroschisis anomalies) were surgically treated, and only one death occurred. The mean birth weight of the infants was 2,927 g; nine of them were premature. Seven infants had major associated anomalies. The goal of the surgical procedure was closure of the abdominal wall without compromise of the cardiorespiratory status. During the operation, muscle relaxants were avoided and the infants breathed spontaneously. If progressive visceral reduction caused tachypnea (rate of more than 70/min) or hemodynamic instability, a Silastic pouch was constructed. Ten patients were treated with primary fascial closure, and 13 were treated with a Silastic prosthesis. The neonates with the prostheses required three to eight reductions, and the prostheses were in place for 4 to 22 days. No patient had wound dehiscence, wound infection, or an intestinal fistula. The one death occurred in an infant with trisomy 18 syndrome and multiple anomalies. Thus, the Silastic pouch was effective when the defect could not be closed primarily without respiratory compromise.     

Evaluation of collateral circulation of the hand

In 1929, Edgar V. Allen described a noninvasive evaluation of the patency of the arterial supply to the hand of patients with thromboangitis obliterans (Am J Med Sci 1929;178:237). In the early 1950s, Allen's test was modified (Wright I. Vascular diseases in clinical practice. Chicago: Year Book Medical Publishers, 1952) for use as a test of collateral circulation prior to arterial cannulation. This test involves the examiner occluding the patient's ulnar and radial arteries while the patient makes a fist, causing the hand to blanch. The patient is then asked to extend the fingers. After the hand is open, the examiner releases the ulnar artery while continuing to maintain pressure on the radial artery. Adequate collateral circulation is felt to be indicated by return of normal color to the hand. The patient is instructed not to hyperextend the fingers when opening the hand. Hyperextension may cause a decrease in perfusion to the arch, possibly resulting in a false interpretation of the Allen test (Anesthesiology 1972;37:356). The modified Allen's test can be performed quickly and easily, but it is susceptible to error. (With Allen's original test, both hands were tested simultaneously. The patient clenched both fists tightly for 1 minute while the examiner compressed one artery of each hand. This method helps diagnose complete occlusion, just as Allen intended. The test was later modified, however, to evaluate the adequacy of collateral circulation. To perform the modified Allen's test, the examiner compresses both arteries while the patient's fists are clenched. The patient then opens the hand, and the adequacy of circulation is evaluated when the examiner releases one of the arteries.) This study was designed to combine the modified Allen's test with the sensitivity of oximetry and plethysmography to provide a quantifiable and reproducible evaluation of the palmar collateral circulation with or without the subject's cooperation. Superficial palmar arches of 90 normal volunteers (aged 22–45 years) were evaluated with the modified Allen's test. These results were compared with the flow patterns demonstrated by plethysmography and pulse oximetry. All of the modified Allen's tests were normal, with the palmar blush occurring in an average of 2.3 seconds (range, 2–5 s). Results were recorded independently by two observers, with agreement in all cases. Four of the 90 (4.4%) palmar arches were found to have abnormal circulatory patterns. Plethysmography clearly demonstrated the dominant arterial supply to the hand and, in appropriate cases, indicated the existence of an incomplete arch. The four abnormal circulatory patterns (two incomplete palmar arches and two other aberrant arterial communications) were clearly shown by plethysmography. Pulse oximetry was found to be too sensitive. Significant changes in flow did not result in a decrease in saturation. Only the incomplete superficial palmar arches resulted in a change in saturation. The two abnormal arterial communications were not detected by pulse oximetry. Pulse oximetry also could not show dominant flow patterns. Our findings indicate that plethysmography can be used to demonstrate palmar collateral circulation, but that pulse oximetry cannot.This work was funded by the Anesthesiology Research Foundation and the Samuel J. Roessler Research Scholarship.This paper was presented at the Society of Critical Care Medicine's 19th Annual Education and Scientific Symposium, San Francisco, California, May, 1990.     

Encapsulated bacteria deform lipid vesicles into flagellated swimmers

We study a synthetic system of motile Escherichia coli bacteria encapsulated inside giant lipid vesicles. Forces exerted by the bacteria on the inner side of the membrane are sufficient to extrude membrane tubes filled with one or several bacteria. We show that a physical coupling between the membrane tube and the flagella of the enclosed cells transforms the tube into an effective helical flagellum propelling the vesicle. We develop a simple theoretical model to estimate the propulsive force from the speed of the vesicles and demonstrate the good efficiency of this coupling mechanism. Together, these results point to design principles for conferring motility to synthetic cells.

The interaction of active and passive matter lies at the heart of biology. Active matter (1) consists of collections of entities that consume energy from their environment to generate mechanical forces, which often result in motion. Thus, the cell membrane, whose essential component is a passive lipid bilayer, can actively remodel during cell growth; motility; and, ultimately, cell evolution, under the forces exerted by a host of active agents. For example, continuous polymerization–depolymerization of actin in the cytoskeleton deforms the eukaryotic cell membrane into two- and one-dimensional protrusions (lamellipodia and filopodia) that can move the whole cell (2, 3). Similar actin-supported membrane protrusions are thought to have facilitated the accidental engulfment of bacteria that led to the emergence of eukaryotic cells (4). The biophysics of active membranes has therefore been subjected to interdisciplinary scrutiny (5). More recently, learning how to create active membranes systems that deform, divide, and propel has become a priority area in the drive to synthesize life ab initio (6).Lipid vesicles enclosing natural or artificial microswimmers are becoming a model system for studying active membranes in vitro (7–15). Such composites have also direct biological relevance. For instance, from inside their eukaryotic hosts, bacterial pathogens such as Rickettsia rickettsii or Listeria monocytogenes (16, 17) continue their life cycles by hijacking the actin polymerization–depolymerization apparatus of their hosts and pushing out a tube-like protuberance from the plasma membrane. The pathogens then contact other host cells or escape into the surrounding medium by means of these membrane tubes (18).To date, research in coupling swimmers with membranes has mostly been theoretical and numerical. Such models have predicted a range of interfacial morphological changes and, in some cases, net motion of the interface (7–13). The experimental realization of these systems was only recently achieved by encapsulating swimming Bacillus subtilis bacteria (14) and synthetic Janus particles (15) in giant lipid vesicles. Both experiments reported nonequilibrium membrane fluctuations and vesicle deformations, ranging from tubular protrusions to dendritic shapes. However, net motion of the vesicles was not observed in either case.Here we present a similar experimental design but with markedly different outcome. Escherichia coli, another common motile bacterium, also extrudes membrane tubes but in addition sets the whole vesicle into motion. We demonstrate that such motion is due to a physical coupling between the flagella bundle of the enclosed cells and the tubes. The tube–flagella composite functions as a helical propeller for the entire vesicle.In biology, the specificity of interactions between bacteria and the membranes of eukaryotic hosts underlies the plethora of parasitic and symbiotic relations that have emerged between cells (18–20). Likewise, our observations illustrate the importance of small details in the design of active matter systems (21). Encapsulated bacteria propelled by a single bundle of helical flagella can generate net motion of the vesicles, whereas encapsulated swimmers propelled at similar speeds by phoresis fail to do so (15). These observations illustrate the fact that it is dangerous to proceed from coarse-grained simulations or theory that neglect such details to predict the behavior of particular systems. At the same time, our results point to a design principle for conferring motility to artificial cell models.