Continuous measurements of oxygen saturation during haemodialysis

A new technique for recording and analysing continuous measurements of oxygen saturation (SpO2) by pulse oximeter during haemodialysis was used to compare changes in SpO2 in eight patients during two 4 h periods of dialysis using a cuprophane membrane, once using an acetate dialysate, and once using bicarbonate. The computer-derived patterns of SpO2 show whether hypoxaemia was caused mainly by extrapulmonary abnormalities (ventilatory control) or intrapulmonary abnormalities (V/Q distribution). The patterns of oxygen saturation were analysed for (i) stability, (ii) the lower median 20th centile of SpO2, and (iii) time below a SpO2 of 90%. Not all patients had reduced oxygenation during acetate dialysis. Three of eight patients had a stable pattern with acetate dialysis and six of eight were stable with bicarbonate. Five of eight patients had a lower SpO2 with acetate but one patient had a lower SpO2 with bicarbonate. Four patients had prolonged, clinically significant periods of oxygen desaturation with SpO2 less than 90%; two of these had particularly prolonged periods during acetate (62 min and 12 min), but one patient showed a longer period during bicarbonate than acetate dialysis (7 min). In two patients the SpO2 declined to less than 84%. The patterns of SpO2 suggested that the decrease in oxygen saturation was due more to extrapulmonary abnormalities causing an instability in ventilatory control rather than to venous admixture. It is recommended that pulse oximetry is used to identify patients at risk of hypoxaemia, to monitor these patients during haemodialysis, and to administer oxygen to those whose SpO2 falls below 90%, particularly if they have anaemia or cardiovascular disease.

Altered consciousness: pharmacology and phenomenology BAP Summer Meeting, York, July 1991: Sleep and general anaesthesia as altered states of consciousness

In this article parallels are drawn between sleep and anaesthesia. Both can be described as 'behavioural states' in which stimulation and inhibition of certain neuronal groups will give rise to specific psychological states. The neuronal mechanisms leading to these states are reviewed and compared. Sensory information flow through the thalamus is reduced in sleep and anaesthesia, the thalamic gating being controlled by other areas of the brain including the sensory cortex. Thus a feedback loop may exist with the brain determining its own level of arousal. Anaesthesia increases gating at the thalamus and thus specifically reduces arousal. Consciousness is a specific attribute of the brain and is not required for the processing of sensory stimuli and learning, both of which have been shown to occur during sleep and anaesthesia. The implications of these findings for monitoring awareness during anaesthesia are discussed.

Clinical features of giant cell arteritis

The clinical features of GCA can be classified into: (1) the systemic manifestations of malaise, weight loss, fever, night sweats and depression; (2) the proximal muscle pain and stiffness of polymyalgia rheumatica; (3) arteritic manifestations of pain or tenderness due to local inflammation; and (4) arteritic manifestations of ischaemia due to narrowing or occlusion of vessels. These may occur singly or in any combination and may come and go with the passage of time. Thus GCA can result in many different clinical signs and symptoms. The feared ocular and cerebrovascular complications of the condition can be prevented by the early institution of corticosteroid treatment. Early diagnosis is therefore vital. This is a simple matter when GCA presents in the classical textbook manner, but in atypical cases diagnosis can be exceedingly difficult. The absence of a reliable way of excluding the disease means that diagnosis is often a clinical exercise. A sound knowledge of the many and varied clinical manifestations of GCA is therefore required if the physician is going to prevent the ocular and cerebrovascular complications of GCA by early diagnosis and treatment.

Methanol oxidation and assimilation in Hansenula polymorpha. An analysis by 13C n.m.r. in vivo

The metabolism of methanol was monitored in whole cells of the methylotrophic yeast Hansenula polymorpha by using [13C]methanol and n.m.r. in vivo. The main products observed under normal conditions were trehalose and glycerol, whereas cells that were starved before exposure to [13C]methanol also accumulated glutamate, glutamine and alanine; formate was also more prominent in spectra from starved cells. Cells exposed to high methanol concentration together with high oxygenation oxidized methanol extensively, leading to formaldehyde accumulation; label was not found in any subsequent metabolic products, indicating possible cell inactivation. [13C]Formate was incorporated into metabolic products in glucose-grown cells exposed to 150 mM-methanol for 3 h, but not in cells starved for 3 h, in which it was oxidized. At 21 degrees C such 3 h-starved cells showed a slower metabolism of [13C]methanol compared with those at 37 degrees C, and also converted methanol into formate rather than into assimilation products. The labelling pattern in trehalose from starved cells at 37 degrees C was consistent with methanol assimilation via the pentose phosphate pathway. Lack of appearance of labelled formaldehyde and formate during metabolism under normal conditions suggests that the linear oxidation pathway is not a major contributor to methanol oxidation; their appearance in extreme conditions suggests instead a more likely role in detoxification.

Patterns of oxygenation after thoracotomy

We have studied patterns of oxygen saturation (SpO2) before and after thoracotomy in 20 patients monitored nightly from the preoperative night to the fourth postoperative night. After operation, 10 patients received paravertebral bupivacaine (PVB) infusion and 10 received paravertebral saline (PVS) infusion. Papaveretum was given as required. Before operation the SpO2 profiles formed two groups: stable with SpO2 greater than 94% and stable with a median SpO2 less than 94% (hypoxaemia). During the first night after operation SpO2 profiles formed four groups: stable, not hypoxaemic (2/20); stable, hypoxaemic but improving (8/20); stable and constant hypoxaemia (5/20); unstable, hypoxaemic and deteriorating (5/20). Eleven patients remained hypoxaemic as late as the fourth night after operation. All patients who were hypoxaemic before operation were hypoxaemic after operation. Postoperative hypoxaemia was predicted in only 50% of cases. Papaveretum requirement was reduced in the PVB group, but regional analgesia did not affect the proportion of patients showing each SpO2 profile. Papaveretum caused a decrease in SpO2 in both analgesic groups.

Changes in amplitude and latency of the P300 component of the auditory evoked potential with sedative and anaesthetic concentrations of nitrous oxide

The P300 component of the auditory evoked response was recorded from six subjects whilst they listened via headphones to a series of clicks which were interrupted unpredictably by a tone burst. They were instructed to press a button as quickly as possible after hearing the tone whilst breathing first air and then a series of increasing concentrations of nitrous oxide. Both the amplitude and the latency of the P300 changed in a dose-dependent manner with nitrous oxide, as did minimum reaction time. At nitrous oxide concentrations which prevented recall of any events that occurred whilst breathing the gas, four subjects continued to respond to the tone by pressing the button. In three subjects, the P300 wave was still detectable with a nitrous oxide concentration at which the task was no longer performed. These results show that there is retention of the ability to perform a reaction time task when there is a complete loss of recall of the task. There may be some recognition of an auditory stimulus, as manifest by a P300 wave, albeit reduced greatly in amplitude, in the absence of a motor response to it. The P300, therefore, merits investigation as a tool for studying conscious awareness under anaesthesia.

Adjuvant therapy for neuroendocrine small cell carcinoma of the cervix: review of the literature

Neuroendocrine cell carcinoma of the cervix is a virulent tumor associated with an extremely poor prognosis. Even in clinical Stage I disease, there may be subclinical hematogenous and lymphatic metastases with frequent recurrences. Adjuvant postoperative external pelvic radiotherapy has been reported to offer some degree of local control; however, most patients succumb to distant disease. Following radical abdominal hysterectomy and pelvic lymphadenectomy, with confirmation of the neuroendocrine tumor by electron microscopy and immunohistochemical staining, two patients were given adjuvant systemic chemotherapy with concurrent pelvic radiotherapy, employing regimens with documented activity against small cell carcinoma of the lung of neuroendocrine origin. Despite severe myelotoxicity and persistent neuropathy, both patients are alive without clinical evidence of disease at 28+ and 47+ months.

Driving and arthritis

In a 3-year period, 94 patients with driving difficulties due to a variety of musculoskeletal disorders were assessed by the occupational therapy department of a rheumatology unit. The individual's ability to carry out each part of the driving process was recorded and the patients were classified into six broad categories. While some parts of the driving process often proved difficult, patterns of disability were found with different musculoskeletal disorders. Almost all of these difficulties could be overcome by simple modifications to vehicle or driving technique. Only one severely disabled individual required referral to a specialized mobility unit, while two individuals were found to be unsafe. Thus, almost all arthritic individuals are able to continue driving with the help of simple modifications. By providing an unsophisticated driving assessment service, a rheumatology unit can enable patients to continue driving and so maintain independence.

In vitro microleakage associated with posterior composite restorations used with different base/bonding system combinations

The study aimed to determine the base/restoration combination which allowed the least microleakage in Class II cavities. One hundred premolar teeth were prepared with a standardized, minimal two-surface cavity and randomly ascribed to ten equal groups. The cavities were restored by use of one of ten different material/technique combinations. Restored teeth were sealed to within 1 mm of the restoration margins with nail varnish prior to the immersion of the crowns in 5% (buffered) eosin for 48 h. The teeth were then hemisected longitudinally, in a mesio-distal plane, through the midline of the restoration by means of a diamond disc with water coolant, and one half of each tooth was then photographed. The transparencies were examined by image analysis programmed to facilitate calculation of the percentage of the tooth/restoration interface and of the crown dentin exhibiting dye penetration. Light- and chemically-cured glass-ionomer-based restorations showed similar amounts of leakage when expressed as a percentage area of crown dentin. This was significantly (p less than 0.05) less than that shown by cavities both etched and bonded. Cavities restored without enamel etching or involving the use of a bonding system exhibited significantly (p less than 0.05) greatest leakage.

Ulnar tunnel syndrome

The ulnar tunnel syndrome is a relatively uncommon condition resulting from compression of the ulnar nerve as it passes through the loge de Guyon, or ulnar tunnel, in the wrist. The syndrome may cause weakness and atrophy of the intrinsic hand muscles and loss of sensation in the ulnar nerve distribution of the hand. The most common cause of ulnar tunnel syndrome is chronic occupational trauma, either from pressure exerted over the hypothenar eminence by a tool or from the use of the heel of the hand as a hammer. Nonoccupational etiologies include congenital, inflammatory, neoplastic, vascular, metabolic, degenerative and traumatic disorders. Diagnosis often requires neurophysiologic evaluation, in addition to a careful history and physical examination. Conservative treatment aimed at protecting the ulnar tunnel from trauma frequently is effective. Occasionally, surgical decompression of the ulnar tunnel is required.

Methylamine metabolism in Hansenula polymorpha: an in vivo 13C and 31P nuclear magnetic resonance study

Methylamine uptake, oxidation, and assimilation were studied in Hansenula polymorpha, a methylotrophic yeast. The constitutive ammonia transport system was shown to be effective at accumulating methylamine within cells cultured with methylamine or ammonia as a nitrogen source. [13C]methylamine oxidation rates were measured in vivo in methylamine-adapted cells by 13C nuclear magnetic resonance and were found to be lower than its uptake rate into the cells. The 13C label of methylamine was found exclusively in trehalose and glycerol, and [13C]formaldehyde was also extensively assimilated, indicating the presence of an assimilation pathway for the methylamine carbon. In vivo 31P nuclear magnetic resonance analysis showed major differences in the endogenous polyphosphate levels and mean chain length during adaptation of the cells from ammonia to methylamine, indicating that methylamine accumulated in the vacuole in the same manner as basic amino acids and purines. [13C]glucose metabolism was drastically altered during adaptation of the cells from ammonia to methylamine as a nitrogen source. The total rate of glucose utilization and the rate of ethanol production fell. Direct trehalose synthesis from glucose increased, indicating a switch from carbon utilization for growth to that for storage. The rate of methylamine oxidation was sufficient to support a much higher flow of carbon into central biosynthetic pathways. These results suggest that this reduction in biosynthetic carbon flow, rather than nitrogen availability, was the main factor responsible for reducing the growth rate of the yeast when ammonia was replaced by methylamine as the nitrogen source.

Nitrous oxide sedation causes post-hyperventilation apnoea

We have studied, in six normal subjects, the effect of nitrous oxide sedation on the ventilatory pattern and oxygen saturation using pulse oximetry (SpO2) after hyperventilation to an end-tidal carbon dioxide partial pressure (PE'CO2) of 3 kPa. This value of PE'CO2 was shown to be less than the apnoeic threshold of all these subjects when their ventilation vs PE'CO2 response curves were plotted. All subjects became apnoeic when told to relax following hyperventilation while breathing 75% nitrous oxide for 90 s. Apnoea was defined as cessation of breathing for 20 s or more. The mean duration of apnoea was 78 s (range 29-130 s). All subjects demonstrated arterial desaturation (mean SpO2 75%, range 44-87%). In contrast, following hyperventilation with air, no apnoea was seen in any subject, although there was some evidence of desaturation (mean SpO2 92.5%, range 88-98%). It was concluded that subjects who are sedated with nitrous oxide behave similarly to those who are anaesthetized rather than to those who were fully conscious, in that they become apnoeic below the apnoeic threshold point. The reduction in SpO2 after hyperventilation was explained almost entirely by apnoea and may explain abnormalities of respiratory control and hypoxaemia in patients recovering from general anaesthesia or sedation accompanied by hypocapnia. This mechanism may be of importance in obstetric patients after breathing Entonox, when apnoea and hypoxaemia may reduce oxygen delivery to the fetus.

In vivo 13C and 15N NMR studies of methylamine metabolism in Pseudomonas species MA

Pseudomonas species MA was grown with methylamine as a sole source of carbon and nitrogen enabling the total flow of carbon and nitrogen into this organism to be simultaneously monitored in vivo using 13C and 15N NMR. [13C]Methylamine was rapidly and extensively incorporated into the methyl group of N-methylglutamate during high oxygenation of the cell suspension, but when the oxygenation rate was lower, a significant portion was also found in the methyl group of gamma-glutamylmethylamide. At later times the carbon label was found in intermediates of the serine assimilation pathway, with glutamate derived from the tricarboxylic acid cycle being the most abundant product. Incorporation of [15N]methylamine was only detected as N-methyl[15N]glutamate, but when protein synthesis was inhibited, the label was also detected in the amino nitrogen of glutamate. When oxygenation rates were lower, the 15N-labeled methylamine was found in the methylamide group of gamma-glutamylmethylamide in addition to being incorporated into N-methylglutamate. gamma-Glutamylmethylamide formation was linked to the overall energy state of the cell and was not affected by inhibition of the carbon assimilation pathway. Neither 5-hydroxy-N-methylpyroglutamate nor N-methyl-alpha-ketoglutaramate were detected to any significant extent. A mechanism was proposed for the role of gamma-glutamylmethylamide in the regulation of endogenous nitrogen supplies in this organism.

Structure and organization of the gas vesicle gene cluster on the Halobacterium halobium plasmid pNRC100

Halobacterium halobium strain NRC-1 contains intracellular gas-filled vesicles (GVs) that confer buoyancy to the cells. Cloning of the major GV protein (GvpA)-encoding gene, gvpA, and analysis of GV-deficient mutants (Vac-) of H. halobium led to the identification of a region of a 200-kb plasmid, pNRC100, important for GV synthesis. We report here the nucleotide sequence of an 8520-bp region which, including gvpA, contains twelve open reading frames (ORFs) that are organized into two divergent transcription units, gvpAC oriented rightward, and gvpD, E, F, G, H, I, J, K, L, and M located upstream from gvpAC and oriented leftward. Insertions into the gvpA promoter and gvpD and E resulted in the Vac- phenotype. The overall gene organization is highly compact with the end of one ORF overlapping with the beginning of the next in most cases. The gene cluster is bracketed by two ISH8 element copies in inverted orientation, an organization suggestive of a composite transposon. Comparison of predicted amino acid sequences showed homology between GvpA, and the gvpJ and gvpM putative gene products. The putative gvpC gene product contains eight copies of an imperfectly repeated sequence with similarity to repeats in a cyanobacterial GvpC plus a highly acidic C-terminal region not found in the cyanobacterial homologue.

The physiological cost of wearing a disposable respirator

In order to gain an understanding of the physiological stresses imposed by the wearing of a single-use disposable respirator, a series of experiments was done to measure the cardiopulmonary effects of wearing the respirator (heart rate, respiratory rate, and blood pressure); resistance to breathing while wearing a respirator; and heat stress imposed by the use of a respirator (changes in inspired and expired air temperature). Ten men, ages 24 to 35, of varying fitness levels, served as volunteers in the studies. All the men exercised on a treadmill both with and without 3M Model 8715 disposable respirators. Workloads corresponding to light, moderate, and heavy levels were calculated for each volunteer based on his maximal oxygen uptake. As work intensity increased, an increase in breathing resistance was found. Peak resistances were in the range of +/- 2 cm water. Work-intensity level increases in respiratory rates were found with and without the respirators, but the respirator use trial had a significantly increased respiratory rate. Heart rate also showed a dose-related increase as work intensity increased and was significantly greater in the respirator trials at heavy levels of work and during recovery. Systolic blood pressure showed a biphasic response to respirator use, being significantly lower at rest and higher at high levels of work. Diastolic blood pressure changes were less dramatic but were elevated in the respirator trials. Clinically important increases in blood pressure were found in two volunteers when respirators were worn. Air temperatures immediately anterior to the face were, on average, 7.5 degrees C higher in the respirator trials.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct detection of free radical generation in an in vivo model of acute lung injury

Electron spin resonance (ESR) spectroscopy has been used to provide direct evidence that free radical production occurs in an in vivo model of acute lung injury. Two experimental groups of rabbits were given the spin trap alpha-phenyl N-tert.-butyl nitrone (PBN), together with endotoxin in the test group, and saline in the control group. Both groups were subsequently briefly ventilated with air containing cigarette smoke. Plasma samples from the endotoxin pretreated group showed a sudden burst of radical formation, detected as PBN spin adduct, which peaked in the first ten minutes after smoke exposure. No signals were detected in the control group. Permeability of the alveolar capillary barrier of the lung, measured by the clearance of 99mTc-DTPA, demonstrated significantly greater damage following smoke in the endotoxin primed animals than in the controls. Temporal studies suggest that this increase in permeability occurred after a burst of radical production. These studies provide supportive evidence for the hypothesis that endotoxin promotes the accumulation of a population of primed white cells within the lung, which when triggered by cigarette smoke, are able to generate a burst of free radicals which produce tissue damage and acute lung injury.

Molecular analysis of amoeboid chemotaxis: parallel observations in amoeboid phagocytes and metastatic tumor cells

Metastasis is a multistep process in which amoeboid chemotaxis plays a key role in the movement of tumor cells into and out of vessels. On a molecular level, much of what is known about amoeboid chemotaxis has been learned through work with Dictyostelium discoideum, a lower eukaryotic amoeboid phagocyte. One of the first and most crucial events to occur in the actin cytoskeleton following chemotactic stimulation is activation of actin nucleation. This is followed by incorporation of specific actin cross-linking proteins into the cytoskeleton, proteins which are implicated in the extension of pseudopods and filopods. Together, these events have been termed the Cortical Expansion Model for amoeboid chemotaxis. Detailed biochemical analysis has implicated a new actin-capping protein and has shown that one of the cross-linking proteins is Elongation Factor 1a, suggesting a link between chemotaxis and growth control. Preliminary data from parallel studies on neoplastic cells are presented.

Effects of a clinically detectable PDA on pulmonary mechanics measures in VLBW infants with RDS

We examined the effect of a clinically detectable patent ductus arteriosus (PDA) and its successful treatment with indomethacin on serial measures of pulmonary mechanics in 10 very-low-birthweight (VLBW) intubated infants with respiratory distress syndrome (RDS). Pulmonary mechanics were measured by the passive expiratory flow technique. Total respiratory system compliance (Crs) gradually improved as RDS resolved. However, a significant decrease in mean Crs was associated with the development of a clinically detectable PDA, ranging from 1.51 +/- 0.21 to 0.90 +/- 0.08 mL/cmH2O/m (P less than 0.05). We also noted an increase in mean Crs, from 0.90 +/- 0.08 to 1.49 +/- 0.21 mL/cmH2O/m (P less than 0.05), after successful treatment of a PDA with indomethacin. Total respiratory system resistance (Rrs) did not change. We conclude that a clinically significant PDA is associated with a decreased Crs and that successful treatment of a PDA with indomethacin is associated with an improvement in lung compliance. These findings imply that the development of a clinically detectable PDA and its subsequent treatment complicates the interpretation of pulmonary mechanics data in VLBW infants with RDS.