Biomedical subjects

R M Harding

Publications and source records attributed to R M Harding.

At least 73 records · Page 4Linked to original sources

PubMed1991

Stability and extractability of double-stranded RNA of pangola stunt and sugarcane Fiji disease viruses in dried plant tissues.

When leaves infected with pangola stunt virus (PaSV) were dried at 23, 37, 50, 70 or 105 degrees C, the dsRNA was stable and could be extracted after aerobic storage at room temperature for 1 month, although at 105 degrees C the amount obtained was reduced. The dsRNA was also recovered after leaves were freeze dried and stored in vacuo at room temperature for 6 months, or were dried and stored aerobically at room temperature for 10.5 months. dsRNA of sugarcane Fiji disease virus (FDV) was also stable when infected leaves were dried at 23, 37, 50 or 105 degrees C and stored aerobically for 3 months or for at least 6 months when infected leaves were dried at 70 degrees C. The unexpected high stability and extractability of both PaSV and FDV dsRNA when dried in leaves at low or high temperatures and stored at room temperature indicate that these, and probably other plant-infecting reoviruses, can be transported readily in desiccated host tissue between different countries for later extraction and comparison of their dsRNAs.

Desiccation↗

PubMed1991

Virus-like particles associated with banana bunchy top disease contain small single-stranded DNA.

Virus-like particles were purified from banana plants with banana bunchy top disease. These particles were isometric with a diameter of 18 to 20 nm and a density of 1.28 to 1.30 g/ml in caesium sulphate. Associated with these particles were an ssDNA of about 1 kb and one major protein of Mr 20,100. DsDNA was synthesized from nucleic acid extracts from these particles and cloned. One clone, pBT338, hybridized specifically (i) with sap extracts from plants infected with banana bunchy top virus (BBTV) but not with sap extracts from healthy plants and (ii) with the small ssDNA in nucleic acid extracts from infected plants and virus-like particles. Banana bunchy top disease was transmitted from infected to healthy bananas by aphid inoculation and it was demonstrated that the small ssDNA was transmitted with the disease. It is probable that these particles represent the virions of BBTV containing small ssDNA and that the virus resembles subterranean clover stunt virus more than any other known virus.

Blotting, Southern↗

PubMed1991

Spatial differentiation of RH and GM haplotype frequencies in Sub-Saharan Africa and its relation to linguistic affinities.

This study analyzes patterns of variation in eight GM and seven Rhesus (RH) haplotypes across sub-Saharan Africa. We examine the concordance with genetic patterns of both geographic and language-family relationships by spatial analysis and ordination techniques. The genetic variation has significant spatial structure, but positive autocorrelation declines neither asymptotically nor proportionally with increasing distance. Evidently, neither isolation by distance with increasing distance. Evidently, neither isolation by distance nor clinical migration-selection models account for the observed genetic structure. Language-family relationship is the best predictor of genetic relationship and may reflect historic migrations and expansions of ethnically different peoples within sub-Saharan Africa. Yet the greatest part of the genetic variance remains unexplained by the models we have tested.

Africa, Central↗

PubMed1990

Peak expiratory flow at altitude.

The mini Wright peak flow meter is a useful, portable instrument for field studies but being sensitive to air density will under-read at altitude. True peak expiratory flow will increase at altitude, however, because of the decreased air density, given that dynamic resistance is unchanged. The effect of simulated altitude on peak expiratory flow (PEF) was determined in six subjects with both the mini Wright meter and a volumetric spirometer (which is unaffected by air density). With increasing altitude PEF as measured by the spirometer increased linearly with decreasing pressure, so that at a barometric pressure of 380 mm Hg* (half an atmosphere, corresponding to an altitude of 5455 m) there was a 20% increase over sea level values. The mini Wright flow meter gave readings 6% below sea level values for this altitude--that is, under-reading by 26%. Measurements of PEF made at altitude with the mini Wright meter should be corrected by adding 6.6% per 100 mm Hg drop in barometric pressure.

Altitude↗

PubMed1990

Rapid decompression to 50,000 feet: effect on heart rate response.

Interest in Molecular Sieve Oxygen Generation Systems (MSOGS) for use in military aircraft has demonstrated a need to study physiological effects of MSOGS product gas in the worst case scenario, a rapid decompression (RD). In this paper we report the heart rate (HR) response to positive pressure breathing (PPB) during and after RD from 6,096 to 15,239 m (20,000 to 50,000 ft) in a hypobaric chamber while breathing gas mixtures that simulate the product gas from MSOGS. Interbeat (R-R) intervals were recorded in 10 subjects while they breathed either Aviators' Breathing Oxygen (ABO), that is 99.5% oxygen, or 93% oxygen at two regulator settings: dilution and non-dilution. Additional experimental profiles on six subjects isolated the effects of hypoxia, anxiety, and PPB on HR changes after RD. Anxiety appeared to have the greatest effect. Most of the subjects showed increased HR and reduced HR variability after the onset of pressure breathing (immediately after decompression). As the exposure continued, HR variability increased as the HR began to decline. No consistent change in the HR response could be attributed to the modest increase in hypoxia produced by substitution of 93% oxygen for ABO.

Adult↗

PubMed1990

Positive pressure breathing for acceleration protection and its role in prevention of inflight G-induced loss of consciousness.

That pressure breathing for G protection (PBG) can improve both tolerance and endurance to high sustained +Gz acceleration is now well established. It is not surprising, therefore, that the undoubted potential benefits of PBG in an operational environment have been greeted with enthusiasm by aircrew and their commanders. In some quarters, the use of positive pressure breathing (PPB) during periods of high sustained +Gz acceleration is being hailed as a potential cure for the problem of G-induced loss of consciousness (G-LOC). We believe, however, that confidence in the technique for this purpose in modern, highly agile fighter aircraft is misplaced. This article reviews PPB's background and present use as protection against +Gz acceleration, and summarizes the physiologic basis for its effectiveness, before relating it to its undoubted role in support of other anti-G strategies. From theoretical considerations supported by published evidence, we conclude that while PPB, if used correctly and when combined with other strategies, can enhance tolerance to +Gz acceleration, its principal influence on the occurrence of G-LOC will be by virtue of its ability to increase endurance by decreasing aircrew fatigue.

Acceleration↗

PubMed1990

Modern European cranial variables and blood polymorphisms show comparable spatial patterns.

Spatial patterns in cranial traits for modern European populations are compared with patterns described by Sokal et al. (1989) for blood polymorphisms. Spatial patterns in these variables are described from both one-dimensional and directional autocorrelation correlograms. Manhattan distances computed among one-dimensional correlograms are used (1) to cluster variables with similar patterns and (2) to test the hypothesis that these clusters are to some extent accounted for by the type of variable. The one-dimensional correlograms for cranial traits do not show a significant contrast with either red cell antigens or the set of blood polymorphisms that excludes HLA. The only contrast that accounts for any of the cluster structure among one-dimensional correlograms is that between HLA and non-HLA variables. A cluster analysis of the directional correlograms demonstrates that cranial traits reflect patterns comparable to those for blood polymorphisms. This finding implies that patterns in cranial variables can be accounted for by the same, or similar, population processes as those inferred from patterns in blood polymorphisms. The implications of this finding for the likely origin of the northwest-southeast cline seen in some modern blood polymorphisms and modern cranial variables, but not in Neolithic cranial variables, are discussed.

Antigens↗

PubMed1989

Spatial patterns of human gene frequencies in Europe.

The aims of this study of spatial patterns of human gene frequencies in Europe are twofold. One is to present new methodology developed for the analysis of such data. The other is to report on the diversity of spatial patterns observed in Europe and their interpretation as evidence of population processes. Spatial variation in 59 allele and haplotype frequencies (26 genetic systems) for polymorphisms in blood antigens, enzymes, and proteins is analyzed for an aggregate of 3,384 localities, using homogeneity tests, one-dimensional and directional spatial correlograms, and SYMAP interpolated surfaces. The data matrices are reduced to reveal the principal patterns by clustering techniques. The findings of this study can be summarized as follows: 1) There is significant heterogeneity in allele frequencies among the localities for all but one genetic system. 2) There are significant spatial patterns for most allele frequencies. 3) There is a substantial minority of clinal patterns in these populations. Clinal trends are found more frequently in HLA alleles than for other variables. North-south and northwest-southwest gradients predominate. 4) There is a strong decline in overall genetic similarity with geographic distance for most variables. 5) There are few, if any, appreciable correlations in pairs of allele frequencies over the continent, and there is little interesting correlation structure in the resulting correlation matrix. 6) Few spatial correlograms are markedly similar to each other, yet they form well-defined clusters. Spatial variation patterns, therefore, differ among allele frequencies. Patterns of human gene frequencies in modern Europe are diverse and complex. No single model suffices for interpretation of the observed genetic structure. Some clinal patterns reported here support the Neolithic demic-expansion hypothesis, others suggest latitudinal selection. Most of the clinal patterns are in HLA alleles, but there is also evidence from ABO for east-west migration diffusion. The majority of patterns are patchy, consistent with hypotheses of isolation by distance or of settlement of genetically differing, subsequently expanding ethnic groups. While undoubtedly there has been an ongoing stochastic process of differentiation consistent with the isolation-by-distance model, this has not obscured the directional patterns caused by migration (demic diffusion), and has perhaps only reinforced the contribution from settlement of ethnic units to patterns of genetic variation. However, the impact of the latter is most difficult to discern and requires further methodological developments.

ABO Blood-Group System↗

PubMed1988

Classification of the European language families by genetic distance.

Genetic distances among speakers of the European language families were computed by using gene-frequency data for human blood group antigens, enzymes, and proteins of 26 genetic systems. Each system was represented by a different subset of 3369 localities across Europe. By subjecting the matrix of distances to numerical taxonomic procedures, we obtained a grouping of the language families of Europe by their genetic distances as contrasted with their linguistic relationships. The resulting classification largely reflects geographic propinquity rather than linguistic origins. This is evidence for the primary importance of short-range interdemic gene flow in shaping the modern gene pools of Europe. Yet, some language families--i.e., Basque, Finnic (including Lappish), and Semitic (Maltese)--have distant genetic relationships with their geographic neighbors. These results indicate that European gene pools still reflect the remote origins of some ethnic units subsumed by these major linguistic groups.

Ethnicity↗

PubMed1985