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Biomedical subjects

N J Clark

Publications and source records attributed to N J Clark.

18 recordsLinked to original sources
PubMed1993

Reducing exposures during the pouring operations of a brass foundry.

The focus of this exposure assessment and control technology study was a brass foundry and the lead exposures of workers involved in the transportation and pouring of metal. Controls in place at the foundry included ventilation systems at the furnace and along the continuous and stationary pouring lines. Real-time measurements were made to determine which tasks were the primary exposure sources, and a hand-held aerosol monitor was used to measure real-time aerosol exposures (as a surrogate for lead) in the workers' breathing zones. Data were collected over two 30-min sampling periods while worker activities were monitored using a video camera. Analysis of the data showed that the greatest aerosol exposures occurred during the transportation of an unventilated, full ladle, resulting in an average concentration of at least twice that of the other tasks. The study concluded that the addition of exhaust ventilation such as a moveable hood and duct system during the ladle transport and pouring tasks, and the implementation of a side draft hood at the pigging area, could result in a reduction of worker exposure to aerosols during the continuous pouring operation by up to 40%. The controls and techniques suggested in this study could be applied to pouring operations throughout the industry to reduce worker exposure to metal fumes.

Humans↗
PubMed1992

Silica exposure in hand grinding steel castings.

Exposure to silica dust was studied in the grinding of castings in a steel foundry that used conventional personal sampling methods and new real-time sampling techniques developed for the identification of high-exposure tasks and tools. Approximately one-third of the personal samples exceeded the National Institute for Occupational Safety and Health recommended exposure limit for crystalline silica, a fraction similar to that identified in other studies of casting cleaning. Of five tools used to clean the castings, the tools with the largest wheels, a 6-in. grinder and a 4-in. cutoff wheel, were shown to be the major sources of dust exposure. Existing dust control consisted of the use of downdraft grinding benches. The size of the casting precluded working at a distance close enough to the grates of the downdraft benches for efficient capture of the grinding dust. In addition, measurements of air recirculated from the downdraft benches indicated that less than one-half of the respirable particles were removed from the contaminated airstream. Previous studies have shown that silica exposures in the cleaning of castings can be reduced or eliminated through the use of mold coatings, which minimize sand burn-in on the casting surface; by application of high-velocity, low-volume exhaust hoods; and by the use of a nonsilica molding aggregate such as olivine. This study concluded that all these methods would be appropriate control options.

Air Pollutants, Occupational↗
PubMed1988

Preservation of the ischemic canine myocardium: a comparison of hypothermia, lidoflazine, and ketanserin.

The purpose of this study was to determine whether ketanserin protects the globally ischemic canine heart and whether such protection, if present, is independent of that provided by hypothermia or calcium channel blockade with lidoflazine. Forty mongrel dogs, anesthetized with halothane, were divided into eight groups of five and subjected to one hour of global myocardial ischemia during hypothermic (30 degrees C; groups 1 to 4) or normothermic (37 degrees C; groups 5 to 8) cardiopulmonary bypass (CPB). Dogs in groups 1 and 5 served as controls with respect to prebypass myocardial protective therapy, and received only placebo (a normal saline bolus) prior to CPB. Before bypass, dogs in groups 2 and 6 received lidoflazine, 1.25 mg/kg intravenously (IV); those in groups 3 and 7 received ketanserin, 5 mg IV bolus, followed by a continuous infusion at 33 microg/min during bypass. Animals in groups 4 and 8 were given both lidoflazine and ketanserin according to the dosing schedules above. No type of pharmacologic or mechanical cardiovascular support was provided after termination of CPB. Postbypass hemodynamic performance and survival of the unsupported animal were assumed to reflect the degree of myocardial protection during CPB. One minute after bypass, mean arterial pressure and cardiac output were decreased in all groups. Cardiac output was lower in groups 5 to 8 (normothermic CPB) than in groups 1 to 4 (hypothermic CPB). After CPB, left ventricular filling pressures were elevated in all groups kept normothermic and in group 3 (hypothermic CPB plus ketanserin). By 15 minutes after CPB, there were no survivors in groups 5, 7, and 8. Sixty percent of animals in group 6 (normothermic CPB plus lidoflazine) survived to the end of the study. Relative odds of survival were increased 110-fold by hypothermia and sevenfold by lidoflazine. Conversely, treatment with ketanserin was associated with an increased likelihood of nonsurvival. It is concluded that, at the doses studied, ketanserin does not protect the canine myocardium against ischemic injury and may exert a detrimental effect when combined with calcium channel blockade in this setting.

Animals↗
PubMed1987

Comparison of sufentanil-N2O and fentanyl-N2O in patients without cardiac disease undergoing general surgery.

Sufentanil (mean total dose 2 micrograms/kg) was compared with fentanyl (mean total dose 15 micrograms/kg) as a supplement to 60% N2O anesthesia in 30 adult patients undergoing general surgical procedures. Comparisons were made with respect to stability of hemodynamic variables (heart rate and systolic and diastolic blood pressure), changes in stress hormones (cortisol, antidiuretic hormone, epinephrine, norepinephrine, and dopamine), recovery of alertness and orientation, time to extubation, postoperative analgesia, and measures of respiratory depression (resting end-tidal carbon dioxide tension [PETCO2], CO2 response curve for minute ventilation [delta VE/delta PETCO2]). Hemodynamic variables remained stable and similar in both groups throughout the study. Plasma hormone levels remained similar to baseline in both groups until 1 h postoperatively when epinephrine levels were significantly elevated in both groups (P less than 0.05). Recovery times, including time to extubation, were similar in both groups. Patients given sufentanil had less pain 30 min postoperatively than those given fentanyl, although at 60 min postoperatively pain levels were similar in both groups. Small but significant elevations in resting PETCO2 were seen in both groups postoperatively (P less than 0.05), but postoperative delta VE/delta PETCO2 responses were significantly depressed only in patients receiving fentanyl (P less than 0.05). The results of this study demonstrate that sufentanil-N2O anesthesia is as effective as fentanyl-N2O in attenuating the hemodynamic and hormonal responses to the stress of general surgery. Because continuous intraoperative PETCO2 monitoring was not employed in this study, intraoperative hypocapnea cannot be strictly excluded as a possible influence on the postoperative measures of ventilatory drive.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Antagonism of postoperative opioid-induced respiratory depression: nalbuphine versus naloxone.

The authors compared naloxone and nalbuphine as antagonists of opioid-induced respiratory depression to determine the relative efficacies and safety of the two agents. In a double-blind, randomized fashion, 90 anesthetized patients received a mean dose of 25 micrograms/kg fentanyl during surgery. Inadequate spontaneous respirations at the end of anesthesia were treated with either naloxone 0.08 mg or nalbuphine 2.5 mg IV every 2 min while heart rate (HR), systolic and diastolic blood pressures (SBP, DBP), respiratory rate (RR), and tidal volume (TV) were measured at 2-min intervals. Arterial blood samples for analysis of PaCO2, PaO2, and pH were drawn when spontaneous ventilation resumed, and 30 and 60 min later. Narcotic antagonism and respiration were deemed adequate when TV was greater than or equal to 4 ml/kg and RR greater than or equal to 8 breaths/min. Heart rate, SBP, DBP, TV and RR were recorded, as were the occurrence of renarcotization (RR less than 8) and analgesic requirements every 5 min during the recovery room stay. Sixty of 90 patients required narcotic antagonism at the end of surgery. No patient required more than three doses (0.24 mg) of naloxone or four doses (10 mg) of nalbuphine. Both antagonists produced similar and moderate increases in SBP and HR while restoring adequate spontaneous ventilation. There were no significant differences in TV, RR, or arterial blood gases (ABGS) between the two groups after narcotic reversal.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Failure of nalbuphine to antagonize morphine: a double-blind comparison with naloxone.

The authors studied the respiratory and analgesic effects of nalbuphine (0.21 mg/kg, intravenous), naloxone (0.014 mg/kg, intravenous), and placebo (normal saline) when given after morphine (0.21 mg/kg, intravenous) in a double-blind, randomized fashion. Resting end-tidal CO2 (PETCO2), ventilatory and occlusion pressure responses to CO2 rebreathing, and pain threshold were measured in 12 healthy adult volunteers before, 5 min, and 30 min after morphine. Nalbuphine, naloxone, or saline were administered 55 min after morphine, and the above measurements were repeated 5 min later (60 min after morphine) as well as 90, 120, 180, and 240 min after morphine. Whereas naloxone reversed respiratory depression as measured by all three respiratory parameters, nalbuphine either further depressed (resting PETCO2) or did not affect (ventilatory and occlusion pressure responses to CO2 rebreathing) respiratory drive. Morphine produced a significant elevation of the pain threshold. Significant decreases in the pain threshold were seen only after naloxone. Saline and nalbuphine did not significantly alter the pain threshold. The data indicate that nalbuphine may not reliably antagonize moderate doses of morphine.

Adult↗
PubMed1985

Pulmonary arterial catheterization before anesthesia in patients undergoing cardiac surgery. Placement of the pulmonary arterial catheter before anesthesia for cardiac surgery: safe, intelligent, and appropriate use of invasive hemodynamic monitoring.

Should one catheterize the pulmonary artery (PA) for cardiac surgery before or after induction of anesthesia? Issues of central importance to this question include (1) the patient's preexisting hemodynamic abnormalities, (2) cardiovascular effects of anesthetic induction drugs, and (3) hemodynamic stress caused by laryngoscopy, endotracheal intubation, and PA catheter insertion. Some clinicians use the PA catheter immediately before anesthetic induction to detect and correct acute abnormalities in preload and ventricular function. This approach has been described as being partially responsible for decreased morbidity and mortality in patients with cardiovascular disease. Hemodynamic instability during induction has been reported with many of the common anesthetic induction agents, especially in patients with poor ventricular function. Since blood pressure is the product of cardiac output and systemic vascular resistance, accurate interpretation and treatment of hypotension are possible only when these variables are provided by vigorous use of the PA catheter. Early detection of myocardial ischemia is possible with examination of acute changes in the pulmonary capillary wedge pressure tracing. However, the lack of such information can restrict even the best anesthetist. Insertion of the PA catheter in the awake patient can be accomplished effectively and with minimal risk, so long as good patient rapport, adequate premedication, and continuation of antianginal medication until the time of surgery are assured. Preinduction placement of the PA catheter provides valuable, objective information for the cardiac anesthesiologist without incurring significant risk to the patient.

Anesthesia↗
PubMed1980

The pathology and mineral content of lungs in cases of mesothelioma in the United Kingdom in 1976.

A study was made of 93 cases of mesothelioma who died in 1976 in the United Kingdom. Lung tissue was available for mineral fibre analysis from 86 of these cases, and also from 29 cases of cerebrovascular disease and 27 cases of bronchial carcinoma, matched for place of death, age and sex with the mesothelioma cases. It was observed that: (1) mesothelioma patients had more amphibole fibres in their lungs than did control cases; (2) chrysotile fibres were not present in greater numbers in the mesothelioma patients than in the control cases; (3) four of the mesothelioma cases had no amphibole fibres in their lungs; two of these had chrysotile fibres, and the other two had no asbestos fibres; and (4) 30 cases of mesothelioma had no chrysotile fibres in their lungs.

Adult↗
PubMed1980

Identification and quantification of asbestos fibres in human tissues.

The examination of three dust preparations by two independent laboratories using analytical transmission microscopic techniques has shown that comparable results can be produced. Further interlaboratory collaboration is required, however, to clarify and improve the results that can be obtained. Those areas that require further investigation are data interpretation from energy-dispersive X-ray analysis equipment and counting procedures. The results that have been obtained so far by interlaboratory collaboration are very encouraging, and it is hoped that such joint efforts will be expanded in the future.

Asbestos↗
PubMedDate not supplied

Can NCAST and HOME Assessment Scales be used with Hmong refugees?

This descriptive study of a convenience sample of 32 recently settled, preliterate Hmong families tested the applicability of the NCAST and HOME assessment tools in the Hmong refugee population. The sample means on the Nursing Child Assessment Feeding Scale (NCAFS), Nursing Child Assessment Teaching Scale (NCATS), and the Home Observation for Measurement of the Environment (HOME) were compared to a randomly selected sample of white (n = 60), African American (n = 60), and Hispanic (n = 60) families from the University of Washington NCAST (Nursing Child Assessment Satellite Training) normative data bank. The NCAFS and NCATS Hmong total means were not significantly different when compared to the combined normative sample total means. However, when the ethnic groups were compared using ANCOVA with ethnicity and education as covariates, the parent, child, and scale total means were found to be significantly different (p < .05). Hmong HOME total means were significantly lower when compared to the combined normative sample (p < .05) and with separate ethnic group comparisons (p < .05). Although lower for this population lacking formal education, scores were not significantly different when compared to the combined normative sample means. Findings suggest that the NCAST tools should be used with respect for the impact of ethnicity and education on total scores. Findings do not support the use of the HOME scale with this population except as a teaching guide.

Adolescent↗