Estimation of pulmonary blood flow from sinusoidal gas exchange during anaesthesia: a theoretical study.

We simulated the use of simultaneous sinusoidal changes of inspired O2 and N2O (Williams et al., J Appl Physiol, 1994; 76: 2130-9) at fractional concentrations up to 0.3 and 0.7, respectively, to estimate FRC and pulmonary blood flow (PBF) during anaesthesia, using O2 as an insoluble indicator. Hahn's approximate equations, which neglect the effect of pulmonary uptake and excretion on expiratory flow, estimate dead space and alveolar volume (VA) with systematic errors less than 10%, but yield systematic errors in PBF which are approximately proportional to FIN2O in magnitude. A correction factor (1 - P)-1 for Hahn's equations for PBF (where P is the mean partial pressure of the soluble indicator) reduces the dependence of PBF estimates of FIN2O, and the solution of equations describing the simultaneous mass balance of both indicators yields accurate results for a wide range of mean FIN2O. However, PBF estimates are sensitive to measurement errors and a third gas must be present to ensure that the indicator gases behave independently.

Technology in health care--blessing or curse?

This paper looks at technology and health care in terms of processes (here defined as goal-related, autonomous and self-regulated arrangement of actions) and their interactions. Using this approach, technology is considered to be the quality of the processes we are trying to achieve. However, health care and the life around it is a complex network of closely interacting processes, and through their interactions, processes can influence each other in various ways. In many cases such interactions can result in unwanted, inappropriate interference and the implementation of unsatisfactory health care technologies.

Diagnostic accuracy of organ electrodermal diagnostics. A pilot study.

OBJECTIVE: To estimate the diagnostic accuracy as well as the scope of utilisation of a new bio-electronic method of organ diagnostics. DESIGN: Double-blind comparative study of the diagnostic results obtained by means of organ electrodermal diagnostics (OED) and clinical diagnoses, as a criterion standard. SETTING: Department of Surgery, Helen Joseph Hospital, Johannesburg. PATIENTS: 70 pre-selected inpatients of mean age 36 (SD = 7) years with suspected pathology of one (or more) of the following organs: oesophagus, stomach, duodenum, biliary tract, pancreas, colon, kidneys and urinary tract. In total, 276 of the abovementioned internal organs were selected for statistical consideration. MAIN OUTCOME MEASURES: The difference between the so-called basic electrical impedance of the skin and the impedance value established for a particular organ projection area (the skin zone corresponding to a particular internal organ). RESULTS: In total 250 true OED results were obtained from the 276 subjects considered: detection rate 90.6% (95% CI 87.1-94.1%). Established OED sensitivity was 91.8% (95% CI 88.6-95.0%) and OED specificity equalled 89.9% (95% CI 86.4-93.4%). The predictive value for positive OED results was 83.3% (95% CI 78.9-87.7%) and for negative OED results 95.2% (95% CI 92.0-98.4%). The OED results were affected neither by the type nor the aetiology of disease, i.e. OED estimates the actual extent of the pathological process within particular organs but does not explain the cause of pathology directly. No side-effects of the OED examinations were observed. CONCLUSIONS: So-called organ projection areas do exist on the skin surface. The electrical impedance of the projection areas corresponding to diseased organs is increased, relative to that of healthy organ-related skin zones. The difference in impedance is proportional to the intensity of the pathological process. OED, which utilises these electrical phenomena of the skin, may detect diseased organs and estimate the extent of pathological process activity within these organs.

Localisation of myocardial ischaemia from the magnetocardiogram using current density reconstruction method: computer simulation study.

A computer simulation study is performed to investigate the method of current density reconstruction to localise myocardial ischaemia. A computer model of the entire human heart is used to simulate the excitation and repolarisation process in eight topographically different cases of myocardial ischaemia. The associated magnetocardiogram is calculated at 37 positions of the KRENIKON biomagnetic measurement equipment. The method of current density reconstruction is applied at the S-point (the last discernible deviation from the ST-segment at the end of the QRS-complex) of the MCG to find characteristics of the myocardial ischaemia simulated by the model. The results show that it is possible to determine the location of the ischaemia. The current density distribution may be interpreted physiologically in terms of the so-called 'injury-current'. This indicates that magnetocardiography might be a suitable method for noninvasive ischaemia diagnosis, and further investigations of the current density reconstruction method for the injury current should be performed on patients with ischaemic heart disease.

The 'economics' of medical technology.

The word 'economics' is used in this paper in its widest sense, referring to issues that 'influence the management, regulation and government of an enterprise'. In addition to the obvious monetary issues in health-care technology, social, ethical, legal and cultural issues are also discussed. The eventual, generally high cost of health care is definitely influenced to a greater or lesser extent by these factors. It is suggested that proper evaluation during the planning stage could lead to the development and introduction of technologies into health care in a more cost-effective way.

Cost escalation in health-care technology--possible solutions.

Solutions to cost escalation due to health-care technology are proposed. It is argued that proper systems analysis, technology assessment, and planning would result in net savings and improved cost-benefits. Identification of needs early in the technological life cycle can positively influence the final form of the chosen technology. A national centre for technology assessment is proposed. Arguments in favour of a local medical equipment manufacturing industry, emulating overseas examples, are advanced, appropriateness being the main criterion. Analysis of the cost breakdown of imported technology suggests ways of reducing costs considerably, while stimulating the local economy. Digital telecommunications technology and its application to rural health care is cited as an example of a potentially worthwhile investment in making overall coverage more equitable.

Cycling device powered by the electrically stimulated muscles of paraplegics.

The paper describes a device (Paracycle), that uses functional neuromuscular stimulation to exercise subjects, explore FNS technology and provide paraplegics with locomotion. The Paracycle is a four-wheeled cycling vehicle that may be used as a stationary exercise device or for locomotion. It incorporates a fully adjustable seat and an electric motor to assist or retard the cycling motion, as well as speed and direction controls. Furthermore, it has braces to fasten the feet to the pedals and to stabilise the ankle, as well as gearing to enable subjects with very small forces to move the vehicle forward. Results are presented for two cases studies. Good stability of the leg was achieved during the cycling motion and this would appear to be a major advantage of functional neuromuscular stimulation cycling over functional neuromuscular stimulation gait. Important areas for future research include a better understanding of the biomechanics of functional neuromuscular stimulation cycling and the development of Paracycle-like devices that can be used independently by paraplegics.

Acute calcium homeostasis in MHS swine.

To elucidate a pathogenesis for the reduction in bone calcium content observed in MHS individuals, we studied the acute calcium homeostasis of MHS swine. This was achieved by the serial measurement, with a calcium selective electrode, of calcium transients in Landrace MHS (five) and control Landrace/large white cross MH negative (five) swine following IV bolus injection of calcium gluconate 0.1 mmol X kg-1--a dose which induced an acute 45 per cent increase in plasma ionised calcium. Experimental animals were anaesthetised with ketamine 10 mg X kg-1 IM, thiopentone (intermittent divided doses) 15-25 mg X kg-1 (total) IV and N2O/O2 (FIO2 0.3) by IPPV to maintain a normal blood gas, acid/base state. The plasma ionised calcium decay curve observed in MHS swine did not differ from that of control normal swine. Further it was noted that the induced acute rise in plasma ionised calcium failed to trigger the MH syndrome in any MHS swine. It is concluded that the mechanisms of acute calcium homeostasis in MHS swine are normal. An explanation for the reduction in bone calcium content observed in MHS individuals must be sought, therefore, through study of the slow long-term component of the calcium regulatory process. In addition, the conventional strictures placed on the use, in MHS patients, of calcium gluconate are called in question.

The cost and appropriateness of health care technology in South Africa. A plea for the development of a local medical equipment industry.

Some of the main reasons for the increase in the cost of health care technology are summarized. Local problems in the health care delivery system are not being solved effectively by imported medical equipment. The expertise required for the local solution of problems is available in the RSA and should be developed further. A private-sector consortium with matching funding from the State should serve as a clearing house for developing and evaluating assessment criteria, promoting the use of existing cost-efficient medical technologies, and identifying obsolete and inappropriate ones. The formation of a local health care technology corporation should be considered seriously.

Effects of an intravenous bolus calcium injection on glomerular filtration rate and electrolyte excretion in the kidney in conscious pigs.

This paper reports the changes observed in the concentration of various constituents of plasma and in their excretion in the urine after a bolus intravenous injection of 2,2 mM calcium gluconate into conscious pigs weighing 20 kg. In the plasma, both ionic and total calcium concentrations increased but returned to normal within 35 minutes, while sodium, potassium and inorganic phosphate did not change significantly. In the kidney, the urine volume, glomerular filtration rate (GFR) and fractional sodium excretion increased slightly during the first 10 minutes but became significantly depressed later. Potassium and phosphate levels decreased, the latter significantly, while the calcium concentration increased significantly and only returned to normal after 70 minutes. These results suggest that since the disturbances in urinary volume, GFR and fractional phosphate excretion persist after both the plasma calcium and urinary calcium levels have returned to normal, factors other than these calcium values may be responsible for changes in the former measurements.

Calcium supplementation during cardiopulmonary bypass in paediatric surgery.

This paper reports on the monitoring of plasma ionized calcium (Ca++) levels in children undergoing cardiopulmonary bypass (CPB) for open-heart surgery. The pump was primed with blood treated with either heparin or citrate-phosphate-dextrose (CPD). In certain cases calcium supplementation was used. In all cases a sudden drop in Ca++ levels took place at the start of CPB, followed by a slow recovery. In the patients who received heparinized blood the drop was slight (14%) and recovery fast (10 minutes), but in those who received CPD the drop was excessive (58%) and recovery was still incomplete after 1 hour despite supplementation with 0,5 g calcium gluconate per unit of whole blood. Different supplementation regimens were tried and the optimum was achieved by using 1 g calcium gluconate per unit of whole blood. This limited the drop in the Ca++ level to 42%, and recovery to prebypass levels took place within 45 minutes.

Transient response of the calcium homeostatic system: effect of calcitonin.

With the use of an intravenous step load of calcium, a rapid (less than 30 min) process that helps regulate plasma calcium has been identified in pigs. The process appears to be calcitonin dependent, may not involve simple equilibration, and varies inversely with age, as it is virtually absent in old sheep compared with its intensity in young sheep. Based on these findings and a general model of calcium homeostasis, five classes of regulatory processes are proposed. Grade I (half time, t1/2, congruent to 15 min) is a transient and saturable response present only in young individuals and is calcitonin dependent. Grade II (1/2 congruent to 60-90 min) is parathyroid hormone and possibly calcitonin dependent. Grade III (t1/2 = 3-4 h) is parathyroid hormone dependent and probably renal in nature. Grade IV (t1/2, several hours) is vitamin D dependent and intestinal in nature. Grade V (t1/2, hours or days) is parathyroid hormone and calcitonin dependent and skeletal in nature.

Transient response of thyroidectomized pigs to bolus calcium injections and the effect of salmon calcitonin and parathyroid hormone.

The intravenous injection of calcium gluconate (0.11 mM/kg body weight) into conscious thyroidectomized pigs elicits a 30% rise in both ionized and total calcium concentrations of plasma, which return to basal levels within 180 min. The administration of calcitonin (2.5-10 MRC U/kg body weight) reduces this time to 30 to 40 min which is similar to the time obtained in thyroid intact animals. These results suggest that calcitonin may be involved in the fast calcium removal processes and thus in the short-term regulating system of calcium homeostasis. Neither parathyroidectomy nor the administration of parathyroid hormone affected the time for recovery in thyroidectomized pigs, suggesting that the short-term regulation is independent on the parathyroid gland and its hormone.

A report on the safety of an intravenous compound calcium solution and the levels of plasma total and ionized calcium following injection.

An intravenous compound 5% calcium solution was subjected to three trials in S.A. Mutton Merino X Merino ewes to establish its safety and also to resultant levels of blood total and particularly ionized calcium. In the first trial, 10 animals each received 20 ml of the compound but the administration time progressively decreased from 90 seconds in the first to only 15 seconds in the last ewe. Plasma total calcium levels more than doubled in all the animals and, except for transient disorientation in the last ewe, nothing untoward was noted. In the second trial 4 ewes again received 20 ml of the compound while in the third trial 5 ewes received the compound at the rate of 0,5 ml/kg. In both trials the administration time was about 30 seconds. Plasma total and ionized calcium levels more than doubled initially and, while there was a steady and parallel decline in both, they were still more than 60% higher than pre-injection levels after as long as 2 hours.

Transient response of the calcium homeostatic system of the conscious pig to bolus calcium injections.

Calcium injection in the pig elicits a fast transient response which reinstates the calcium concentration to within normal limits between 30 and 40 min after injection. Although the fate of the calcium that disappeared is not known, the present experiments eliminate the kidneys and the bone remodeling cells as the main short-term regulators. The fast response is independent of parathyroid hormone but is greatly dependent of calcitonin. Further experiments are being performed to discover the nature and site of the regulating mechanisms.