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Biomedical subjects

W L Hunter

Publications and source records attributed to W L Hunter.

30 records · Page 2Linked to original sources
PubMed1990

Endothelial cell division in metaphyseal capillaries during endochondral bone formation in rats.

Endothelial cell division in the metaphyseal capillaries of growing rats was studied by serial sectioning and electron microscopic examination. The endothelium of these capillary sprouts forms a continuous attenuated squamous lining. During endochondral bone formation these growing vessels possess a region of endothelial cell division which is located behind the sprout tip in an area where the microvascular wall consists of an endothelium and a discontinuous layer of perivascular cells. Examination of this region has shown the presence of junctional attachments between daughter cells even before cell separation is complete. Thus, the integrity of the vascular wall is not compromised during cell division. Junctional complexes with adjacent endothelial cells are also formed along the cleavage plane prior to the completion of cytokinesis. Numerous microvilli and from both the daughter cells and adjacent endothelial cells often make contact and form junctions with the plasma membrane of the dividing cells. A model for endothelial junction formation between daughter cells during cytokinesis and the role that microvilli play in the process is proposed.

Animals↗
PubMed1983

Comparison of diving experience factors between divers classified as positive and negative for bone cysts.

Official U.S. Navy diving records for enlisted divers who were 35 years of age and older were examined for differences in diving experience between those who were classified as positive or negative for bone cysts. One-third of the divers (n = 31) were classified as positive, and two-thirds (n = 62) as negative, for bone cysts. Diving experience factors included total years of diving experience, frequency of dives between 15 and 31 m, frequency of dives deeper than 31 m, number of saturation dives, number of dives involving decompression, and number of cases of decompression sickness. None of these factors differed significantly between the two groups. While previous findings showed that bone cysts are twice as prevalent among divers as among a comparison group of Navy enlisted men matched to divers for age, rank, and occupational specialty, these results indicate that this high prevalence rate does not appear to be related to specific types of diving exposure. Other environmental factors such as long-bone injury, disease, or exposure to hazardous or toxic substances may account for differences in the prevalence of bone cysts between the two groups.

Adult↗
PubMed1982

Comparison of long-bone radiographs between U.S. Navy divers and matched controls.

The long-bone radiographs of a group of nondivers consisting of 177 U.S. Navy enlisted men were compared to the long-bone radiographs of 93 U.S. Navy enlisted divers who were 35 years of age and older. The nondiver control group was matched to the diver group for age, rank, and occupational specialty. Divers were found to have significantly more films classified as positive for aseptic bone necrosis (ABN) and bone cysts than nondivers, while the nondiver group had more films classified as doubtful for ABN than the diver group. The two groups were similar in the number of members classified as having bone islands and sclerotic areas. X-ray classifications by highly experienced radiologists were found to be only moderately reliable. These data indicate that diving as practiced by the U.S. Navy contributes independently to the development of ABN and bone cysts evidenced among divers in this age group. Some caution must be exercised in interpreting these findings, however, because of the larger number of doubtful films found for the nondiver group than for the diver group, the small number of positive and doubtful cases found in either group, the age of the samples used (35 years of age and older), and the substantial degree of unreliability demonstrated in classification of the films.

Adult↗
PubMed1979

Changes in serum ferritin and other factors associated with iron metabolism during chronic hyperbaric exposure.

Factors related to iron metabolism were determined in 20 United States Navy divers during 8 d of air saturation-excursion hyperbaric exposures. During these simulated dives progressive and correlated increases in serum ferritin and iron occurred. No significant changes were observed in bilirubin, hemoglobin, ceruloplasmin, transferrin, copper, or total iron binding capacity. The significance of the increased serum ferritin is discussed in relation to bone marrow damage and early detection of aseptic bone necrosis.

Air Pressure↗
PubMed1979

Effect of helium/nitrogen/oxygen mixtures on HPNS convulsion threshold in euthermic rats.

This study compares the effects of various so-called trimix mixtures (10, 20, and 40% N2 in He-O2) on the convulsion threshold pressure (Pc) and EEG activity in 60 adult male Wistar rats with chronically implanted electrodes with those in 20 rats in He-O2 only. Restrained animals were individually compressed with trimix mixtures at 80 or 160 atm per hour to a simulated depth of 138 ATA; colonic temperature was maintained at normal levels. Pc was defined as the initial occurrence of overt sustained generalized tonic-clonic seizures, accompanied by typical "spike and wave" patterns in all EEG leads. As in man, in rats trimix increased the depth of the onset of HPNS tremors and myoclonic jerks in all six groups of rats. However, the Pc of the trimix groups was no different from the Pc of the helium-oxygen group (113 ATA), and at 40% N2, rats showed EEG seizures but no overt convulsions. These results are discussed in relation to those of other studies showing the extension of Pc in mice and monkeys attained by adding narcotics to heliox; the paper also considers the relevance of method of compression, addition of nitrogen, core temperature, and species differences, as well as the need for EEG measurements and direct observation of overt convulsions as indicators of an effective antagonism of HPNS.

Animals↗
PubMed1978

Aseptic bone necrosis among U.S. Navy divers: survey of 934 nonrandomly selected personnel.

Nine hundred thirty-four U.S. Navy divers were selected and surveyed radiographically using standard techniques developed for detecting aseptic bone necrosis (ABN). X rays were read by qualified radiologists. A total of 16 positive cases was detected, and another 11 were interpreted as doubtful. ABN was found to be related to age and number of months in diving. After controlling for these factors, ABN could not be related to any of seven indices of diving activity. Divers with ABN did, however, have a history of more treatments for decompression sickness (DCS) than did divers without ABN. Implications of these findings are discussed, and the suggestion is made that ABN and DCS may not be related causally, but may be related to a third common factor. The need for controlled studies is discussed. The conclusion is made that the low prevalence rates of ABN among U.S. Navy divers cannot be related to any specific index of diving activity, and may not be causally related to DCS.

Adolescent↗
PubMed1978

Effect of long-term hyperbaric stress on ammonia metabolism in humans.

A significant increase in blood urea was found in 11 U.S. Navy divers during 8 d of air saturation hyperbaric exposure. Similar increases in blood urea have been found in animals that convulsed during hyperbaric oxygen exposure. Therefore, it is suggested that careful attention be given to blood ammonia and urea levels in humans during long-term hyperbaric exposure.

Adult↗
PubMed1977

Venous gas bubbles: production by transient, deep isobaric counterdiffusion of helium against nitrogen.

When awake goats were subjected to isobaric gas switching from saturation (17 hours) on 4.7 atmospheres of nitrogen (0.3 atmosphere of oxygen) to 4.7 atmospheres of helium (0.3 atmosphere of oxygen), bubbles detected by 5-megahertz Doppler ultrasound in the posterior vena cava 20 to 60 minutes after the switch continued for 4 hours. Similar experiments carried out at 6.7 atmospheres of inert gas and 0.3 atmosphere of oxygen produced more bubbles for as long as 12 hours after the gas switch. This is believed to be the first objective demonstration of the phenomenon of deep isobaric supersaturation under transient operational diving conditions at relatively shallow diving depths. Detection of bubbles by Doppler ultrasound confirms the potential importance of the phenomenon to shallow saturation diving and holds promise for better quantitification of its effects as well as those of its counterpart, isobaric undersaturation, which can confer a decompression advantage.

Animals↗
PubMed1977

Extension of pulmonary O2 tolerance in man at 2 ATA by intermittent O2 exposure.

To study extension of O2 tolerance by interruption of hyperoxic exposure, as compared to previous studies of continuous oxygen exposure, five healthy volunteers were exposed to oxygen at 2 ATA on an intermittent schedule of 20 min breathing O2, alternating with 5 min on a normoxic N2-O2 mixture. The cycle was repeated until symptoms or signs of O2 toxicity caused cessation of the experiment. Tracheal irritation and burning on inspiration occurred after 6-9 "oxygen hours" of exposure and progressed to severe tracheobronchial burning sensation, chest pain, and dyspnea after 11-15 h of O2. Average duration of exposure was 13.7 O2 h, inducing a mean vital capacity decrease of 10.3%. The decrease began soon after onset of symptoms. With intermittent O2 administration, nearly a doubling of the average duration of actual oxygen breathing was required to induce marked vital capacity change (greater than 10%) as compared to the previous studies of continuous O2 exposure. The increased duration of tolerable O2 exposure in man resembles the extension of O2 tolerance known to occur in animals exposed to intermittent hyperoxia.

Adult↗
PubMed1977

Effect of compression rate on HPNS convulsion threshold in the euthermic rat.

The modification of the development of the high pressure nervous syndrome (HPNS) has been demonstrated by varying the external environment (chamber temperature, compression rate) or the internal environment (core temperature, pharmacology, age). This study examined the effects of compression rate on the convulsion-threshold pressure and EEG activity in 68 adult male Wistar rats with chronically implanted electrodes. Restrained animals were individually compressed at a predetermined rate in helium-oxygen to a simulated depth of 4500 fsw (137 ATA), with colonic temperature maintained at normal levels. Six compression rates showed that convulsion-threshold pressure for euthermic rats did not significantly differ between any of the groups.

Animals↗
PubMed1976

Alteration of high pressure nervous syndrome in rats by alteration of colonic temperature.

The components of the high pressure nervous syndrome (HPNS) have been clearly described previously. Animal studies of HPNS, however, have been characterized by nonstandardized definitions of the various HPNS parameters, based on visual observations. Where EEG's have been used in HPNS studies, the frequent occurrence of movement-induced artifact has made much of the data difficult to interpret. Because of these limitations, efforts to clarify the influence of environmental variables on the syndrome have led to varying results, especially with respect to the influence of temperature. The technique used in this study consistently yielded artifact-free EEGs from unanesthetized, moving rats during simulated heliox dives. Typical seizure patterns in the EEG recordings were combined with clinical seizure activity to define HPNS convulsion-threshold pressure (Pc). By manipulating body temperature artificially, three groups of rats were investigated--hypothermic, euthermic, and hyperthermic animals. An inverse relationship between body temperature and HPNS convulsion-threshold pressure was demonstrated.

Animals↗