Biomedical subjects
Publications and source records attributed to N Willis.
Blood gas variables produced from a computed in vivo oxygen dissociation curve, PaeO2, P95 and C(a-x)O2, were introduced in the University Hospital of Wales in 1986. Some recently obtained results are described.
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The volume of discard for valid blood sampling from indwelling femoral (leader cath) and radial (Venflon) arterial cannulae (with internal volume of cannula plus connecting tubing of approximately 2 ml) was investigated by analysing sequential 2-ml aliquots of 10-ml samples. The aliquots were analysed for pH, carbon dioxide tension, oxygen tension, standard bicarbonate, haemoglobin concentration, haemoglobin oxygen saturation and potassium concentration. Analysis of variance showed that, for these variables and these catheters, a valid blood sample was obtained after discarding 4 ml, but not after only 2 ml. The haemoglobin concentration, as measured by a Corning oximeter, provided good warning of inadequate discard.
When a sample of arterial blood is analysed for oxygen tension and, using a modern oximeter, for haemoglobin concentration and saturation, it is possible to calculate the position of the oxygen dissociation curve and two new variables: "P95" and "C(a-x)O2". P95 is the tension at which the haemoglobin would be 95% saturated and can, therefore, constitute a target tension for near-maximum arterial content of oxygen. C(a-x)O2 (the "conditional extraction" of oxygen) is the amount of oxygen, in ml/dl blood, which can be extracted from the arterial blood for a hypothetical mixed-venous oxygen tension PxO2. It is explained how it is possible to estimate the adequacy of tissue oxygenation by comparing any available estimate of the required extraction (normally about 5 ml dl-1) with conditional extractions calculated for three hypothetical values of PxO2 covering the clinical range. Methods of calculation are given. For accurate results at high arterial saturations, a peripheral venous sample may be required in addition to the arterial sample.
Blood oxygen content calculated from haemoglobin concentration, measured haemoglobin oxygen saturation and measured oxygen tension was compared with three other methods of estimating oxygen content. These other methods were those of Van Slyke and Zander, which are direct methods, and a method using Kelman's equation to estimate the saturation from measured oxygen tension and hence content. The coefficients of correlation (corr coeff) (r) were 0.9050 (n = 22), 0.9919 (n = 24) and 0.9862 (n = 25) for the respective methods when compared with oxygen content calculated using measured saturation. The Van Slyke method proved to be imprecise in our hands. The direct measurement using the oxygen cuvette of Zander gave oxygen content values similar to those estimated from measured saturation. The oxygen content calculated from pO2 alone when compared to that derived from measured saturation had a corr coeff (r) of 0.9862 (n = 25), but the high residual standard deviation (So) of 6.939 ml/l indicates that the practice of calculating oxygen content from oxygen tension alone is imprecise. We conclude that oxygen content may be satisfactorily estimated by the Zander method when it becomes generally available, but until then the measurement of oxygen saturation is a necessary prerequisite to the estimation of blood oxygen content.
Serum creatine kinase levels in 39 control females and 59 obligate carriers of Becker muscular dystrophy (BMD) have been used to construct likelihood ratios for carrier detection. In 24 possible carriers of BMD, analysis of DNA with X chromosome specific DNA probes linked to the dystrophy gene, has been used in conjunction with creatine kinase measurement to calculate final risk estimates of carrier status. Incorporation of information from probe genotype into the Bayesian calculation, enables a substantially lower risk to be deliniated for some possible carriers of the BMD gene. Thus, although the existing DNA probes are not sufficiently closely linked to BMD to be used in prenatal diagnosis, they can make a major contribution to genetic counseling by refining the estimated probability of carrier status.
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Plasma pyruvate kinase (PK) and creatine kinase (CK) were measured in healthy subjects engaging in (a) mild exercise, 30 min on an exercise cycle maintaining a pulse rate of 150/min, (b) moderate exercise, squeezing a ball until exhaustion with a sphygmomanometer cuff inflated above systolic pressure around the arm (max. 2 min) and (c) severe exercise, completing a marathon race. Mild exercise resulted in no change in enzyme levels over 24 h. Moderate exercise produced a small increase in PK but no change in CK. PK activity rose from 35.3 +/- 10 U/l pre-exercise to 41.3 +/- 13 U/l 15 min post-exercise (n = 8, p less than 0.025). Severe exercise (completing a marathon race) resulted in a 3-fold increase in PK from 26 (4-87) U/l pre-race to 69 (21-156) U/l immediately post-race, and also, as expected, an increase in CK from 60 (15-164) U/l to 257 (72-1535) U/l (results are means and ranges, n = 69, p less than 0.001 for both enzymes). Runners showed parallel increases in PK and CK (p less than 0.05 by Spearman rank correlation). The mean post-race activity of CK-MB was less than 5% of total CK but 18 runners had values greater than 6% (mean 4.8, range 1-18). We conclude that PK, like CK, is increased following exercise due to liberation of muscle enzyme. However, only severe exercise is likely to lead to a substantial increase in plasma PK activity and therefore prejudice its clinical usefulness as a diagnostic test.
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Seventeen of 24 RNA viruses and eight of nine DNA viruses replicated in a cell line derived from a pig fallopian tube. The following RNA viruses grew poorly in it: the virus of transmissible gastroenteritis of pig and the swine-influenza, Sendai and bovine para-influenza type 3 viruses. Among other RNA viruses an untyped swine para-myxovirus and some picornaviruses, rhabdoviruses and togaviruses attained high titers and produced an extensive cytopathic effect. Among the DNA viruses a porcine adeno, equine rhinopneumonitis, infectious bovine rhinotraceheitis, pseudorabies and porcine cytomegalo viruses replicated in pig fallopian tube cells as well as in other cells generally used to grow them.
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