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Biomedical subjects

R E Moon

Publications and source records attributed to R E Moon.

At least 55 records · Page 3Linked to original sources
PubMed1990

Cerebral oxygen availability by NIR spectroscopy during transient hypoxia in humans.

The effects of mild hypoxia on brain oxyhemoglobin, cytochrome a,a3 redox status, and cerebral blood volume were studied using near-infrared spectroscopy in eight healthy volunteers. Incremental hypoxia reaching 70% arterial O2 saturation was produced in normocapnia [end-tidal PCO2 (PETCO2) 36.9 +/- 2.6 to 34.9 +/- 3.4 Torr] or hypocapnia (PETCO2 32.8 +/- 0.6 to 23.7 +/- 0.6 Torr) by an 8-min rebreathing technique and regulation of inspired CO2. Normocapnic hypoxia was characterized by progressive reductions in arterial PO2 (PaO2, 89.1 +/- 3.5 to 34.1 +/- 0.1 Torr) with stable PETCO2, arterial PCO2 (PaCO2), and arterial pH and resulted in increases in heart rate (35%) systolic blood pressure (14%), and minute ventilation (5-fold). Hypocapnic hypoxia resulted in progressively decreasing PaO2 (100.2 +/- 3.6 to 28.9 +/- 0.1 Torr), with progressive reduction in PaCO2 (39.0 +/- 1.6 to 27.3 +/- 1.9 Torr), and an increase in arterial pH (7.41 +/- 0.02 to 7.53 +/- 0.03), heart rate (61%), and ventilation (3-fold). In the brain, hypoxia resulted in a steady decline of cerebral oxyhemoglobin content and a decrease in oxidized cytochrome a,a3. Significantly greater loss of oxidized cytochrome a,a3 occurred for a given decrease in oxyhemoglobin during hypocapnic hypoxia relative to normocapnic hypoxia. Total blood volume response during hypoxia also was significantly attenuated by hypocapnia, because the increase in volume was only half that of normocapnic subjects. We conclude that cytochrome a,a3 oxidation level in vivo decreases at mild levels of hypoxia. PaCO is an important determinant of brain oxygenation, because it modulates ventilatory, cardiovascular, and cerebral O2 delivery responses to hypoxia.

Adult↗
PubMed1990

Initial table treatment of decompression sickness and arterial gas embolism.

This descriptive, nonrandomized, multicenter-based study compares the treatment outcomes of two major categories of recompression treatment tables for recreational sport SCUBA divers suffering from decompression sickness and/or arterial gas embolism. Stratified and logistic regression analyses were used to compare the enhanced tables, which use pressures of 165 fsw (feet of salt water) or 60 fsw with extended recompression time, to the regular tables, which use pressures of 60 fsw or less without extended recompression time. A total of 113 cases were treated with enhanced tables, 54 being successes. A total of 214 cases were treated with regular tables, 135 being successes. The final logistic statistical model after adjusting for confounding factors found a significant improvement in successful treatment outcomes for divers treated with tables that use pressures of 60 fsw or less without extended recompression time (OR = 0.47, 95% CI = 0.28-0.78).

Adult↗
PubMed1990

Hyperbaric medicine: an integral part of trauma care.

In conclusion, HBO constitutes an important therapeutic tool in managing a variety of syndromes associated with trauma and is thought to possess potential benefits for the management of others. Because its therapeutic efficacy and limitations are as yet incompletely understood and appreciated, continuing research is warranted. This article provides a discussion of these conditions and applications as well as descriptions of the basic physics of gas behavior, the principle of the physiologic basis of HM, the general manner of clinical application of pressure and oxygen, and the special set of problems encountered when providing sophisticated medical care in the hyperbaric environment. Ultimately, this article encourages the highly motivated trauma anesthesiologist to enhance his or her contribution to and active participation in the field of HM.

Anesthesia↗
PubMed1989

Patent foramen ovale and decompression sickness in divers.

30 patients with a history of decompression sickness were examined for the presence of patent foramen ovale by bubble contrast, two-dimensional echocardiography and colour flow doppler imaging. With bubble contrast, 11 (37%) of the patients had right-to-left shunting through a patent foramen ovale during spontaneous breathing. 61% of a subset of 18 patients with serious signs and symptoms had shunting. This number was significantly higher than the 5% prevalence seen with the same diagnostic technique in 176 healthy volunteers. The presence of patent foramen ovale seems to be a risk factor for the development of decompression sickness in divers.

Acute Disease↗
PubMed1989

Should hyperbaric oxygen be used to treat the pregnant patient for acute carbon monoxide poisoning? A case report and literature review.

Carbon monoxide (CO) is the leading cause of death due to poisoning. Although uncommon, CO poisoning does occur during pregnancy and can result in fetal mortality and neurological malformations in fetuses who survive to term. Uncertainty arises regarding the use of hyperbaric oxygen (HBO) as a treatment for the pregnant patient because of possible adverse effects on the fetus that could be induced by oxygen at high partial pressures. While the dangers of hyperoxia to the fetus have been demonstrated in animal models, careful review of animal studies and human clinical experience indicates that the short duration of hyperoxic exposure attained during HBO therapy for CO poisoning can be tolerated by the fetus in all stages of pregnancy and reduces the risk of death or deformity to the mother and fetus. A case is presented of acute CO poisoning during pregnancy that was successfully treated with HBO. Recommendations are suggested for the use of HBO during pregnancy.

Adolescent↗
PubMed1989

Effect of epidural lidocaine on spinal cord blood flow.

The effect of epidural lidocaine on spinal cord blood flow (SCBF) was measured in mongrel dogs. Spinal evoked potentials were used to measure spinal cord conduction and enabled us to time the measurement of SCBF associated with maximum reduction in latency and amplitude of spinal evoked potentials produced by instillation of 5 ml of 2% lidocaine in the epidural space. We used the radioactive microsphere technique to quantitate SCBF in the cervical, upper thoracic, lower thoracic, and lumbar regions of the spinal cord. A narcotic/relaxant technique was used to eliminate SCBF changes associated with other anesthetic agents. Other parameters known to affect SCBF were kept constant and within normal physiologic values. As compared with saline solution controls, there were significant decreases in SCBF in all the four areas of spinal cord in animals given epidural lidocaine, most marked in the lumbar area.

Anesthesia, Epidural↗
PubMed1988

Neuroimaging of scuba diving injuries to the CNS.

Diving accidents related to barotrauma constitute a unique subset of ischemic insults to the CNS. Victims may demonstrate components of arterial gas embolism, which has a propensity for cerebral involvement, and/or decompression sickness, with primarily spinal cord involvement. Fourteen patients with diving-related barotrauma were studied with MR imaging of the brain and spinal cord and with CT of the brain. In four patients with presumed cerebral gas embolism, cranial MR was abnormal in three patients while CT was abnormal in only one. Twelve patients had decompression sickness and spinal cord symptoms. MR documented spinal cord abnormalities in three patients. However, scans obtained early in our study were frequently limited by technical constraints. MR of the brain is more sensitive than conventional CT scanning techniques in detecting and characterizing foci of cerebral ischemia caused by embolic barotrauma to the CNS. Although spinal MR may be less successful in the localization of spinal cord lesions related to decompression sickness, these lesions were previously undetectable by other neuroimaging methods.

Adolescent↗
PubMed1986

Pulmonary gas exchange in humans exercising at sea level and simulated altitude.

In a previous study of normal subjects exercising at sea level and simulated altitude, ventilation-perfusion (VA/Q) inequality and alveolar-end-capillary O2 diffusion limitation (DIFF) were found to increase on exercise at altitude, but at sea level the changes did not reach statistical significance. This paper reports additional measurements of VA/Q inequality and DIFF (at sea level and altitude) and also of pulmonary arterial pressure. This was to examine the hypothesis that VA/Q inequality is related to increased pulmonary arterial pressure. In a hypobaric chamber, eight normal subjects were exposed to barometric pressures of 752, 523, and 429 Torr (sea level, 10,000 ft, and 15,000 ft) in random order. At each altitude, inert and respiratory gas exchange and hemodynamic variables were studied at rest and during several levels of steady-state bicycle exercise. Multiple inert gas data from the previous and current studies were combined (after demonstrating no statistical difference between them) and showed increasing VA/Q inequality with sea level exercise (P = 0.02). Breathing 100% O2 did not reverse this increase. When O2 consumption exceeded about 2.7 1/min, evidence for DIFF at sea level was present (P = 0.01). VA/Q inequality and DIFF increased with exercise at altitude as found previously and was reversed by 100% O2 breathing. Indexes of VA/Q dispersion correlated well with mean pulmonary arterial pressure and also with minute ventilation. This study confirms the development of both VA/Q mismatch and DIFF in normal subjects during heavy exercise at sea level. However, the mechanism of increased VA/Q mismatch on exercise remains unclear due to the correlation with both ventilatory and circulatory variables and will require further study.

Adult↗
PubMed1986

Monaghan 225 ventilator use under hyperbaric conditions.

The Monaghan 225 ventilator was tested to ambient pressures of 6 atmospheres absolute (ATA) in a hyperbaric chamber. The ventilator would function with delivered tidal volume which was independent of ambient pressure. Ventilatory rate declined in an exponential fashion. At 6 ATA, the ventilatory rate was 45 percent of the preset rate at 1 ATA. By decreasing the circuit resistance and increasing the inspiratory flow rate, the 6 ATA rate could be increased to 72 percent of the 1 ATA value. The maximum minute ventilation of the ventilator at 1 ATA was approximately 48 L/min; at 6 ATA, its maximum was 18 L/min. Synchronized intermittent mandatory ventilation, assist/control, and PEEP functions were satisfactory at 6 ATA. While using 100 percent O2 to power the ventilator at 2.82 ATA, the oxygen leakage was 57.7 L/min (converted to 1 ATA pressure, 20 degrees C), of which 33.7 L/min was successfully scavenged using simple techniques. A minor modification was made to the ventilator, allowing it to be driven by compressed air while maintaining complete flexibility in setting the FIo2. The ventilator has proven stable and reliable in clinical use at ambient pressures up to 6 ATA.

Equipment Design↗
PubMed1985

Ventilation-perfusion inequality in normal humans during exercise at sea level and simulated altitude.

To investigate the effects of both exercise and acute exposure to high altitude on ventilation-perfusion (VA/Q) relationships in the lungs, nine young men were studied at rest and at up to three different levels of exercise on a bicycle ergometer. Altitude was simulated in a hypobaric chamber with measurements made at sea level (mean barometric pressure = 755 Torr) and at simulated altitudes of 5,000 (632 Torr), 10,000 (523 Torr), and 15,000 ft (429 Torr). VA/Q distributions were estimated using the multiple inert gas elimination technique. Dispersion of the distributions of blood flow and ventilation were evaluated by both loge standard deviations (derived from the VA/Q 50-compartment lung model) and three new indices of dispersion that are derived directly from inert gas data. Both methods indicated a broadening of the distributions of blood flow and ventilation with increasing exercise at sea level, but the trend was of borderline statistical significance. There was no change in the resting distributions with altitude. However, with exercise at high altitude (10,000 and 15,000 ft) there was a significant increase in dispersion of blood flow (P less than 0.05) which implies an increase in intraregional inhomogeneity that more than counteracts the more uniform topographical distribution that occurs. Since breathing 100% O2 at 15,000 ft abolished the increased dispersion, the greater VA/Q mismatching seen during exercise at altitude may be related to pulmonary hypertension.

Acclimatization↗
PubMed1985

Diffusion limitation in normal humans during exercise at sea level and simulated altitude.

The relative roles of ventilation-perfusion (VA/Q) inequality, alveolar-capillary diffusion resistance, postpulmonary shunt, and gas phase diffusion limitation in determining arterial PO2 (PaO2) were assessed in nine normal unacclimatized men at rest and during bicycle exercise at sea level and three simulated altitudes (5,000, 10,000, and 15,000 ft; barometric pressures = 632, 523, and 429 Torr). We measured mixed expired and arterial inert and respiratory gases, minute ventilation, and cardiac output. Using the multiple inert gas elimination technique, PaO2 and the arterial O2 concentration expected from VA/Q inequality alone were compared with actual values, lower measured PaO2 indicating alveolar-capillary diffusion disequilibrium for O2. At sea level, alveolar-arterial PO2 differences were approximately 10 Torr at rest, increasing to approximately 20 Torr at a metabolic consumption of O2 (VO2) of 3 l/min. There was no evidence for diffusion disequilibrium, similar results being obtained at 5,000 ft. At 10 and 15,000 ft, resting alveolar-arterial PO2 difference was less than at sea level with no diffusion disequilibrium. During exercise, alveolar-arterial PO2 difference increased considerably more than expected from VA/Q mismatch alone. For example, at VO2 of 2.5 l/min at 10,000 ft, total alveolar-arterial PO2 difference was 30 Torr and that due to VA/Q mismatch alone was 15 Torr. At 15,000 ft and VO2 of 1.5 l/min, these values were 25 and 10 Torr, respectively. Expected and actual PaO2 agreed during 100% O2 breathing at 15,000 ft, excluding postpulmonary shunt as a cause of the larger alveolar-arterial O2 difference than accountable by inert gas exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Physiological responses to exercise at 47 and 66 ATA.

Five male volunteers served as subjects for exercise studies during three dives to pressures of 47 and 66 ATA while breathing gases containing 0.5 ATA PO2 and varying amounts of N2 and He. The inspired gas density ranged from 1.1 g/l (BTPS) at the surface to 17.1 g/l at the highest pressure. Dyspnea at rest and during exercise was evident in all divers and was predominantly inspiratory in nature. Despite the dyspnea, divers were able to perform work requiring an O2 consumption larger than 2 l/min STPD at each depth. Compared with surface measurements, moderate work at depth was associated with alveolar hypoventilation, arterial hypercapnia, very large physiological dead space, and higher levels of arterial lactate and signs of simultaneous respiratory and metabolic acidosis. The increase of ventilation that accompanies the onset of acidemia at the surface was not present at depth. Acidemia at depth was more severe, and its onset occurred at lesser work rates than at 1 ATA. No large differences could be ascertained when a variety of responses obtained with inspired gas having a density of 7.9 g/l at 47 ATA were compared with those obtained with an inspired gas density of 17.1 g/l at 66 ATA. It appears that the major impact of the environment on the physiological responses to work was almost fully manifested at a pressure of 47 ATA with a He-O2 gas mixture. It is cautioned that maximum work tolerance may be an insufficient assessment of the physiological condition of a diver exposed to these high pressures.

Acid-Base Equilibrium↗
PubMed1981

Endotracheal artificial larynx -- preliminary report.

In experimental animals a one stage surgical procedure has been developed which at laryngectomy allows for the creation of a wide and patent tracheopharyngeal fistula. An endotracheal artificial larynx has been developed which has been found effective in prevention of aspiration in experimental animals. Bench studies indicate that an adequate voice probably can be obtained with this device.

Animals↗
PubMed1980

Application of queueing theory to pharmacokinetics.

This paper considers the steady-state plasma drug concentration in a one-compartment, open pharmacokinetic model with multiple doses and first-order kinetics using a classical deterministic technique as well as a queueing theoretical stochastic analysis. The stochastic analysis employs a new method for obtaining the steady-state probability distribution of the content of a dam with compound Poisson input and a general release rule. It is shown that if the deterministic steady-state average concentration exists, it is equal to the mean value of the steady-state concentration, the probability distribution of which is obtained using the stochastic model. Moreover, the steady-state probability distribution of the concentration and its mean always exist in the stochastic model. Ramifications of the stochastic method of analysis are discussed.

Absorption↗