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Biomedical subjects

D R Leitch

Publications and source records attributed to D R Leitch.

36 records · Page 2Linked to original sources
PubMed1984

Cerebral arterial air embolism: II. Effect of pressure and time on cortical evoked potential recovery.

In a dog model of cerebral arterial gas embolism we studied the relative merits of several different treatments: air breathing at 2.8, 6, 8, and 10 bar (60, 165, 230, and 300 ft), and oxygen breathing at 2.8 bar. The study was confined to the recovery of cortical evoked potentials (CEP) while at pressure. It was confirmed that this was a very severe model; few dogs achieved full recovery and three failed to show any recovery. Injecting 0.4 ml of air into the right internal carotid artery was seen to be as effective in suppressing function in the left hemisphere as in the right. The level of recovery with compression treatment as a percentage of control was directly related to the level to which CEP was suppressed. No other physiological correlates were found with either the degree of CEP suppression or the degree of recovery. Nor was any improvement observed in the rate or maximum amount of recovery at any time out to 20 min as a result of pressures greater than 2.8 bar. Overall, no treatment surpassed oxygen at 2.8 bar.

Animals↗
PubMed1984

Cerebral arterial air embolism: III. Cerebral blood flow after decompression from various pressure treatments.

The effect of various combinations of time between 2 and 20 min and between pressures of 2.8 and 10 bar (60 and 300 ft) breathing air or oxygen at 2.8 bar (60 ft), on the continued recovery of cortical evoked potentials (CEP), cerebral blood flow (CBF), and water content of the brain were studied in the dog cerebral arterial air embolism model. It was found that the compression-decompression cycle alone resulted in a rise in cerebrospinal fluid pressure sustained for at least 20 min. The CBF study at 30 min showed an increased flow in dived, nonembolized animals. Water content of the brain was also significantly increased in these animals. The data suggest that the clearance of air is probably independent of pressure once past a threshold of 2.8 bar and is certainly hastened by oxygen. A time of around 8 min is probably required to clear the embolism. The evidence of gas bubble redistribution with recurrence and development of new sites of vascular obstruction in dogs exposed to significant inert gas uptake, however, suggests that a second problem of the clearance of recirculating gas exists. An incidental observation suggests that recently dived dogs may have been more prone to secondary deterioration. The results of these studies again suggest that there may be advantages to confining the treatment of arterial gas embolism to 2.8 bar breathing oxygen.

Animals↗
PubMed1984

Cerebral arterial air embolism: IV. Failure to recover with treatment, and secondary deterioration.

Cerebral arterial gas embolism was induced in 23 dogs that were then treated using one of six routines: no treatment; air at 2.8 bar (60 ft) for 2 min; air at 10 bar (300 ft) for 5 min; oxygen at 2.8 bar for 10 or 20 min; and air at 6 bar (165 ft) for 10 min. After decompression they were monitored for a total of 90 min after the time of embolization. The dogs then underwent an autoradiographic study of cerebral blood flow (CBF). A number of the air-treated dogs experienced a reduction in cortical evoked potential after decompression. Dogs in all groups, except the untreated group and the dog at 10 bar for 5 min, showed an improved CBF compared with their short-study counterparts. After compression treatment, CBF improved with time. Function in 7 dogs deteriorated to a variable small degree in the air-treated groups, while only 3 dogs in the group on oxygen for 10 min deteriorated by around 10%. The CBF of the oxygen groups was close to the undived control values, and their cerebrospinal fluid (CSF) pressures had returned to control levels. There was a dissociation between improving CBF and deteriorating function. It is evident that secondary deterioration is a random affair and therefore not easily studied. The results of the four-part series are summarized and discussed.

Animals↗
PubMed1984

Social desirability response bias and dietary inventory responses.

Royal Australian Air Force recruits completed a dietary frequency inventory (n = 309), a short social desirability inventory phrased in dietary terms (SDF, n = 309), and, in addition, a subsample answered the Marlow-Crowne social desirability scale (n = 96). Correlational and factor analyses showed that the SDF scores were related to the MC scale; and, the scores on the SDF scale were significantly related to the reported consumption of fresh fruit and vegetables and snack foods. In a further study, 20 lay persons were asked to sort the 66 foods listed in the dietary inventory into three categories: nutritionist-approved foods; nutritionist-disapproved foods; and, an 'uncertain' category. The results confirmed the finding that fresh fruit and vegetables were socially desirable foods, but sweet foods were not. It is concluded that social approval needs may influence the manner in which individuals report their consumption of these foods.

Adult↗
PubMed1983

An investigation of the effects of daily physical activity on the health of primary school students in South Australia.

Studies of the health effects of a daily physical activity programme have been carried out in 10-year-old school children in Adelaide, South Australia. In the first phase (1978) observations on endurance fitness, four skin folds, blood pressure and blood lipids were made before and after a randomized trial over a period of 14 weeks. Comparisons were made on over 500 children drawn from classes in seven Primary schools involved in an endurance fitness programme (1 1/4 hours per day), a skill programme and the previous physical education programme (controls). The fitness group experienced significant gains in physical work capacity (PWC) and showed significant decreases in body fat compared to the other two groups. No significant differences were observed in plasma cholesterol, triglycerides and HDL cholesterol. Subsequently in the second phase (1980) observations were made on a group of 216 10-year-old children who had already experienced two years of the physical activity programme adopted after phase one. Comparison with the observations in the 10-year-old children in 1978 made prior to the intervention revealed significantly smaller skin folds and greater PWC, with lower blood pressure reaching statistical significance for diastolic pressure in boys. The findings suggest beneficial effects on health of daily physical activity programmes within existing primary school curricula. There was no evidence of any loss of academic performance as measured by arithmetic and reading tests in spite of 45-60 minutes' loss of formal teaching time each day.

Australia↗
PubMed1983

A method for monitoring arterial blood gas and acid/base state during prolonged environmental studies.

The use of ear lobe arterialized capillary blood for monitoring blood gas tension and acid-base state is described. The method was validated against simultaneously taken arterial blood samples and separately against nasal end-tidal (ET) PCO2 and found to be an effective alternative to arterial puncture. Incidental observations showed that breathing through a mouthpiece caused the subjects to hypoventilate, as did the act of blood sampling with most subjects. Nasal ET gas monitoring was found to have less effect on a subject's breathing pattern and was used as the standard against which the effects of the other techniques were judged.

Blood Gas Analysis↗
PubMed1983

The effects of various gases on cortical and spinal somatosensory evoked potentials at pressures up to 10 bar.

The development of dog electrophysiological models for studying the treatment of cerebral arterial air embolism and spinal cord decompression sickness, required that the effects of the treatment gases on spinal and cortical somatosensory evoked potentials (SEP and CEP) be known. We found an inverse linear relationship between CEP amplitude and air pressure to 230 ft. An asymptote was approached when pressure was increased to 300 ft. This effect was not seen with 20% oxy-helium. The waves representing local cord events were depressed to a lesser extent than were the CEPs. We were able to detect an equilibration time in the EP suppression comparable to estimated inert gas wash-in time for the brain. A small depression of CEPs that did not reach significance was seen with exposure to 2.8 bar of oxygen and continuous exposure for up to 120 min caused no further diminution in amplitude than would be caused by time alone.

Air↗
PubMed1982

Prostaglandin I2, indomethacin, and heparin promote postischemic neuronal recovery in dogs.

Forty-five conditioned male mongrel dogs were exposed to multifocal ischemia sufficient to maintain suppression for 60 minutes of the P1-N1 amplitude of the cortical sensory evoked response (CSER), a quantifiable index of neuronal function. Ischemia was induced and regulated by successive embolization of 20 to 50 microliters increments of air via the right internal carotid artery. Subsequently, the P1-N1 amplitude recovery of the CSER was followed for an additional 15, 60, or 120 minutes while the dogs were treated or left untreated. The combination of prostaglandin I2 (PGI2), indomethacin, and heparin promoted a statistically significant augmentation of return of CSER amplitude relative to no treatment, PGI2 alone, indomethacin alone, PGI2 and heparin, indomethacin and heparin, or PGI2 and indomethacin. After 60 minutes of recovery, animals receiving combined PGI2, indomethacin, and heparin achieved a 57% recovery of P1-N1 amplitude relative to baseline, while the corresponding recoveries in all other groups clustered around 20%. By 120 minutes of postischemic follow-up, the CSER recovery induced by PGI2, indomethacin, and heparin was 80% compared to 17% in untreated animals. By 15 minutes into the recovery period, the combination of the three agents had eliminated very low flows in the "neuron-disabling" range (defined as 0 to 15 ml/100 gm/min for gray matter and 0 to 6 ml/100 gm/min for white matter) in contrast to the relative inefficacy of no treatment or treatment with other than the triple combination of drugs. The study lends some support to a planned clinical trial of PGI2, indomethacin, and heparin in acute occlusive stroke in humans.

Animals↗
PubMed1982

Observations on no-stop and repetitive air and oxynitrogen diving.

The historical origins of the respective air decompression schedules of the British and United States Navies are reviewed with particular reference to the repetitive diving rules. No-stop diving is also discussed. A series of single dive and repetitive dive trials of the Royal Navy Air Table is presented. U.S. Navy and Royal Naval Physiological Laboratory (RNPL) 1968 repetitive dive rules were also tested according to their respective tables on a selection of dives. Comparison of the two methods produce a remarkably similar outcome for dives to similar depths. For dives to very dissimilar depths there is no comparison. The RNPL system has commendable simplicity but lacks the flexibility of the U.S. Navy system for use with successive dives to different depths. Observations on the results of a triple no-stop repetitive dive experiment are presented. It is concluded that little would be gained by further practical investigation of no-stop diving times.

Air↗
PubMed1981

Diet, other lifestyle factors and HDL cholesterol in a population of Australian male service recruits.

The association between dietary and other factors and plasma high density lipoprotein (HDL) cholesterol concentration was examined cross-sectionally and longitudinally in a sample (n = 530) of Australian male service recruits (mean age 21 years) involved in a nine-week induction training program. The findings suggest that diet may make an independent contribution to HDL cholesterol, equal in importance to alcohol, smoking, fitness and obesity--previously identified as being important. Water and carbohydrate consumption showed a negative cross-sectional association with HDL cholesterol on multivariate analysis. The negative association for carbohydrates was also observed longitudinally. Less consistent associations for saturated fat and for total energy intake were also observed. When the relationship between dietary factors and the HDL cholesterol/cholesterol ratio was examined the most important dietary factor appeared to be saturated fat, which was negatively associated with this ratio. No consistent association was observed for any of the 67 individual foods examined.

Adult↗
PubMed1981

A study of unusual incidents in a well-documented series of dives.

We have analysed 43 unusual incidents, which occurred, during 1303 well-documented dives, according to the environmental factors involved. The objective was to find some indication of the causes of otherwise unexplained loss of consciousness in working divers. It was concluded that rapid compression may handicap divers if adequate time for recovery is not allowed in those adversely affected. Air diving deeper than 48 m (160 ft) appears to be unduly hazardous. A significant proportion of incidents studied may result from an interaction between the physiological effects of oxygen and carbon dioxide, especially in periods of hard work. The possibility was also raised that pressure alone might adversely lower acute oxygen toxicity thresholds. Diving with a Po2 below 1.3 bar prevents acute oxygen toxicity, while a Po2 exceeding 1.6 bar is potentially hazardous.

Air Pressure↗
PubMed1978

Decompression sickness or cold injury?

This paper reports two cases involving divers who presented with painful hands and were treated for decompression sickness. Although treatment was successful, their symptoms and diving history suggest non-freezing cold injury, the so-called immersion hand, rather than decompression sickness. For long exposures or cases where the diver may have inadequate insulation, thermal protection of hands is recommended even in water as warm as 16 degrees C.

Adult↗
PubMed1975

Effect of exercise and thermal stress on plasma volume.

Six male subjects exercised for 50 min at 25% (light exercise) and 55% (moderate exercise) of their estimated aerobic capacities in environments of 42 degrees C db, 35 degrees C wb and 30 degrees C db, 24 degrees C wb, respectively. Alterations in the hematocrit, hemoglobin, and plasma protein concentrations, and in the activity of an injected aliquot of isotopically labeled albumin were each used to calculate the percentage change in plasma volume occurring during exercise and recovery. Changes in each measure were consistent with a reduction in plasma volume during exercise and a return to preexercise levels during recovery. There was no significant difference between the measures when exercising in the heat, but during the more severe exercise in the cooler environment disproportional changes in protein, hematocrit, and hemoglobin were observed. Disproportional changes were also seen during the recovery phase, when the hematocrit and hemoglobin concentration indicated a more rapid return of the plasma volume to preexercise levels than did either the plasma protein concentration or albumin activity. During moderate exercise and recovery there was a 1% decrease in red cell volume. It is concluded that exercise accelerates the rate of protein movement from extravascular compartments to the intravascular compartment, leading to elevated plasma protein levels during recovery which favor the return of water to the intravascular space. Hemoglobin concentration is considered to be the most reliable measure of plasma volume change during exercise.

Adult↗
PubMedDate not supplied

The amount of circumscribed brain edema and the degree of post-ischemic neuronal recovery do not correlate well.

Fifty-four dogs were exposed to multi-focal ischemia sufficient to maintain suppression of the P1--N1 amplitude of the cortical sensory-evoked response (CSER) for 60 minutes. Subsequently, the P1--N1 amplitude recovery of the CSER was followed for an additional 15, 60, or 120 min while the dogs were treated or left untreated. The combination of PGI2, indomethacin, and heparin promoted a statistically significant augmentation of CSER amplitude return relative to: 1) no treatment; 2) PGI2 alone; 3) indomethacin alone; 4) PGI2 and heparin; 5) indomethacin and heparin; 6) PGI2 and indomethacin. Percentage gray matter water by the wet weight/dry weight technique was significantly elevated in all embolized groups compared to ten non-embolized controls, but the percentage recovery of the CSER did not correlate with the presence or degree of gray matter edema among embolized animals followed for 1 hour. Separation of embolized animals by the presence or absence of "neuron-disabling" flows (defined as 0-15 ml/100 gm/min for gray matter and 0-6 ml/100 gm/min for white matter) did produce significantly different mean CSER percentage recoveries but percentage gray matter water in the two groups was comparable. A proposed explanation of the data is that brain ischemia engenders two parallel processes which may become uncoupled. Ischemia creates metabolic conditions that lead to increased cellular imbibition of water and produces increased vascular leakiness. These perturbations increase brain water content. Concomitantly, there is an occurrence of further metabolic derangements and multifactorial interaction at the blood-endothelial interface which have a direct influence on neuronal function and recovery.

Animals↗