Developing and implementing core competencies in children's environmental health for students, trainees and healthcare providers: a narrative review

Knowledge of the health impacts of environmental exposures (such as pollution disasters, poor air quality, water contamination, climate change) on children's health has dramatically increased in the past 40 years. The World Health Organization (WHO) estimated that 23% of all deaths worldwide were attributable to the environment, and 26% of deaths in children less than 5 years old could be prevented with removal of environmental risks factors. Yet, little has permeated medical education, leaving pediatric providers ill equipped to address these issues. To address this gap, members from the Pediatric Environmental Health Specialty Units, a United States nationwide network of academically affiliated experts who have created numerous environmental health educational materials and programs, have identified fifteen core environmental health (EH) competencies needed by health care providers to enable them to effectively address environmental health concerns. These competencies can serve as the foundation for the development and implementation of relevant educational programs. The core EH competencies are based upon these foundational elements: 1) Definition of "children's environmental health" that describes how environmental exposures (positive and negative) in early life influence the health and development in childhood and across the entire human life span 2) Children are not "little adults" and so have unique vulnerabilities to environmental hazards; 3) Environmental health inequities exist, causing some children to have a disproportionate amount of unhealthy exposures and consequently a greater risk of adverse effects; 4) Climate change will translate to numerous adverse health effects that will particularly affect children worldwide. In this article, the authors describe the core environmental health competencies and provide resources, online tools, strategies, and examples targeted to all levels of training and practice to better enable leaders and educators to bring this important content to the forefront.

Are women with obesity and infertility willing to attempt weight loss prior to fertility treatment?

OBJECTIVE

To assess attitudes towards weight loss interventions in patients seeking infertility treatment.

METHODS

We evaluated prior weight loss experiences, attitudes towards future interventions by body mass index (BMI), and willingness to delay fertility treatment for weight loss interventions stratified by BMI using logistic regression amongst women ≤45years old with infertility over three months or recurrent pregnancy loss.

RESULTS

The average age of our convenience sample of respondents (148 of 794 eligible women, 19%) was 34.5 years old, with a mean BMI of 26.7±7.4kg/m², including 37 with a BMI >30kg/m² (25%). Most women had attempted conception over 1year. The majority of women with overweight or obesity were attempting weight loss at the time of survey completion (69%). While 47% of these women reported interest in a supervised medical weight loss program, 92% of overweight women and 84% of women with obesity were not willing to delay fertility treatment more than 3 months to attempt weight loss.

CONCLUSION

Most women with obesity and infertility in our population are unwilling to postpone fertility treatment for weight loss interventions.

Building a model to increase live birth rate through patient-specific optimization of embryo transfer day

PURPOSE

Many practices are moving away from cleavage-stage transfer in favor of blastocyst transfer. The purpose of this study is to evaluate how the overall live birth rate for fresh IVF cycles may increase by optimizing the day of transfer for each patient.

METHODS

This is a retrospective cohort study of 1225 first fresh autologous IVF cycles performed between May 2012 and November 2013. Stepwise logistic regression was used to determine characteristics associated with live birth following cleavage-stage versus blastocyst transfer. The optimal transfer day (i.e., the day that maximized the odds of live birth) was determined for each patient, and the actual live birth rate was compared with the projected rate had each patient undergone transfer on her optimal day.

RESULTS

With transfer on the optimal day for each patient, the overall birth rate would have increased from its actual value of 34.8 % to a projected 43.0 %, a 24 % increase. The majority of this increase (21 %) was due to optimization of patients who underwent cleavage-stage transfer but had a higher projected birth rate from blastocyst transfer. These patients were older (37.8 versus 36.0 years, p < 0.01) and had more follicles ≥18 mm than patients who should have remained with a cleavage-stage transfer.

CONCLUSIONS

A model can be built enabling patient-specific identification of optimal transfer day; within this discovery cohort, such optimization was estimated to increase live birth following a fresh transfer by 24 %. This study suggests blastocyst transfer should be more widely offered; however, there remain patients for whom a cleavage-stage transfer may yield better outcomes.

Taiwan food scandal: the illegal use of phthalates as a clouding agent and their contribution to maternal exposure

In 2011 the Taiwan Food and Drug Administration reported that plasticizers di(2-ethylhexyl) phthalate (DEHP) and di-iso-nonyl phthalate (DiNP), endocrine disruptors, were illegally added to clouding agents used in foods and beverages. 965 products were found contaminated, of which 206 were exported to 22 countries. This study's purpose was to obtain English names for 28 contaminated products for which DEHP levels were reported, calculate estimated average daily intake (mg/kg/day) for a 50 kg woman consuming one portion, and compare to U.S. and E.U. guidelines for daily intake. We found that drinking just one bottle (500 ml) of sports drinks would result in an average DEHP intake of 0.14 mg/kg bw/day (range 0.091-0.341), which exceeds by several fold government guidelines (0.02-0.06 mg/kg bw/day). One (2 g) serving from 4/14 samples of contaminated dietary supplements exceeds the guideline of 0.02 mg/kg bw/day. In conclusion, consuming even one portion of tainted drinks and some powders would lead to daily intake of DEHP that greatly exceeds established safety guidelines, raising concerns about potential adverse effects, particularly reproductive tract development in the male fetus. Global distribution of DEHP-contaminated and other adulterated products should prompt governments to become proactive in food safety regulations and chemical testing.

Use of a job-exposure matrix to assess occupational exposures in relation to birth defects

Accurate exposure assessment remains a challenge in occupational epidemiology. We evaluated one approach, use of a job-exposure matrix (JEM), by applying the National Institute for Occupational Safety and Health (NIOSH) JEM to a large case-control birth defects study that included parental occupation information. We investigated the JEM exposure predictions in several ways and found that for a substantial proportion of the parents in the birth defects study, the JEM yielded either no exposure data or nonsense predictions. Among exposure predictions that were plausible, most were of low probability. The high probability exposure predictions were statistically unstable, and neither low nor high probability exposure predictions were reliable. There was considerable discrepancy between the JEM predictions and expert assessments for five exposures of interest. Application of the NIOSH JEM to the birth defects study database (and probably other databases as well) does not provide a useful means of assessing occupational exposures.

Prioritizing back injury risk in hospital employees: application and comparison of different injury rates

To identify high risk areas for back injury in a large teaching hospital, we calculated standard injury rates and newly developed composite statistics for nursing and non-nursing work groups. Data were extracted from the hospital's workers' compensation database. The hospital-wide total injury rate was 4.6 reports per 100 full-time equivalents (FTE); Compensation Case Rate, 1.4 cases per 100 FTE; Compensation Severity Rate, 76 days lost per 100 FTE; and the Cost Rate, $3742 per 100 FTE. The Total Injury Reports Rate for nursing varied from 14.2 per 100 FTE for Intensive Care Unit (ICU) Nursing to 3.8 per 100 FTE for Pediatric Nursing. Non-nursing areas also demonstrated increased rates for back injury. Individual statistical rates ranked areas differently in risk, whereas composite statistical measures consistently ranked ICU Nursing, Buildings and Grounds, and Orthopedics/Neurological Nursing as the top three. Patient handling was the precipitating event in the majority of nursing back injuries, indicating the need for ergonomic intervention. The use of combined statistical measures provided a more integrative measure for describing and following back injury risk over time.

Incorporating an environmental/occupational medicine theme into the medical school curriculum

Medical schools have been slow in teaching students how to recognize and intervene in occupationally and environmentally related illnesses. In this article, we report on the efforts at one medical school, in which an occupational medicine physician teamed with medical school educators developed, implemented, and evaluated an environmental/occupational medicine (EOM) curriculum that was introduced in several locations, using a thematic approach. This effort resulted in new EOM content being added to eight core courses in a developmental sequence and the creation of several elective experiences. We describe techniques and strategies that might be useful at other institutions in promoting the EOM theme and improving communication. Occupational/environmental physicians and educators can play leadership roles in raising interest in EOM within the medical school setting and in developing and implementing an EOM curriculum.

Injuries caused by hazardous materials accidents

STUDY OBJECTIVE

To describe exposures that prehospital and ED personnel may encounter as a result of hazardous material incidents.

METHODS

Retrospective analysis of hazardous material incident reports from six district hazardous material teams in Massachusetts from their inception through May 1996.

RESULTS

The chemicals most frequently involved were various hydrocarbons and corrosive materials. Chlorine derivatives were involved in 18% of all incidents and 23% of all incidents resulting in victims. Victims were produced by 47 of 162 (29%) incidents. Respiratory exposures were the most frequent type of exposure and resulted in the largest number of victims transported to a hospital. Overall 24 of 26 (92%) incidents with chemical exposures resulted in symptomatic victims and 33 of 35 (94%) incidents produced victims requiring hospital transport. Respiratory symptoms were the most frequent, both in the number of incidents where they were observed and the total number of victims with symptoms.

CONCLUSION

Multiple victim transport to EDs from a single hazardous material incident is most likely to result from an inhalation exposure to a respiratory irritant. Information from descriptive studies should allow improved preparation for potential hazardous material victims.

Methods of prioritizing and measuring occupational health risks utilizing hospital back injury data. Development of composite comparative statistics

The employee health service of a Boston hospital wanted a method to prioritize the risk of occupational injury or illness among its employees as the first step in developing a comprehensive ergonomics program. Data from the safety office and workers' compensation third-party administrator (TPA) was combined with hospital payroll data to create rates that compared all work areas based on the common denominator of 100 full-time equivalents (FTE). Rates for four different aspects of injury experience were calculated: incidence of total reported injuries, incidence of serious injuries, level of severity of injuries, and cost. The use of these simple rates alone was inadequate to accurately prioritize risk. Because most work areas ranked differently from one rate scale to the next, it was unclear which, if any, single rate most accurately defined risk. Composite statistics that combined all of the rates were needed. The Composite Risk Indicator (CRI), the Average Relative Risk (ARR), and the Justified Average Relative Risk (JARR) were developed and examined for their utility. The JARR emerged as the best choice in this setting because it captured all available information about injury or illness experience and provided a meaningful single indicator of risk that could be followed over time.

Mechanisms of and facility types involved in hazardous materials incidents

The purpose of this study was to systematically investigate hazardous materials (hazmat) releases and determine the mechanisms of these accidents, and the industries/activities and chemicals involved. We analyzed responses by Massachusetts' six district hazmat teams from their inception through May 1996. Information from incident reports was extracted onto standard coding sheets. The majority of hazardous materials incidents were caused by spills, leaks, or escapes of hazardous materials (76%) and occurred at fixed facilities (80%). Transportation-related accidents accounted for 20% of incidents. Eleven percent of hazardous materials incidents were at schools or health care facilities. Petroleum-derived fuels were involved in over half of transportation-related accidents, and these accounted for the majority of petroleum fuel releases. Chlorine derivatives were involved in 18% of all accidents and were associated with a wide variety of facility types and activities. In conclusion, systematic study of hazardous materials incidents allows the identification of preventable causes of these incidents.

Are reference intervals for carboxyhemoglobin appropriate? A survey of Boston area laboratories

CO is a leading cause of poisoning deaths in the US today. Treating physicians use the carboxyhemoglobin (COHb) % saturation to guide the diagnosis and treatment of CO intoxication. We conducted a telephone survey of hospitals and laboratories in the Boston area, focusing on methodology for COHb determination and accompanying COHb reference intervals. Among 130 facilities, 23 (18%) provide COHb analysis. All facilities that perform the COHb test utilize dedicated multiwave-length photometry. Reference intervals for COHb varied widely among facilities. Eight of 21 (38%) facilities give unacceptably high "normal intervals" for nonsmokers when compared with values available in the literature. Thirteen of 20 (65%) use reference intervals for smokers that are too low, and 3 of 20 (15%) use values that are too high. These reference values provided by the testing facilities may be misleading to the ordering physicians unfamiliar with background COHb saturations. This may lead to misdiagnoses, false reassurances, and perhaps less aggressive treatment than might be warranted. The results of this study argue for wider adoption of COHb reference intervals supported by the current literature.

Are reference intervals for carboxyhemoglobin appropriate? A survey of Boston area laboratories

CO is a leading cause of poisoning deaths in the US today. Treating physicians use the carboxyhemoglobin (COHb) % saturation to guide the diagnosis and treatment of CO intoxication. We conducted a telephone survey of hospitals and laboratories in the Boston area, focusing on methodology for COHb determination and accompanying COHb reference intervals. Among 130 facilities, 23 (18%) provide COHb analysis. All facilities that perform the COHb test utilize dedicated multiwave-length photometry. Reference intervals for COHb varied widely among facilities. Eight of 21 (38%) facilities give unacceptably high "normal intervals" for nonsmokers when compared with values available in the literature. Thirteen of 20 (65%) use reference intervals for smokers that are too low, and 3 of 20 (15%) use values that are too high. These reference values provided by the testing facilities may be misleading to the ordering physicians unfamiliar with background COHb saturations. This may lead to misdiagnoses, false reassurances, and perhaps less aggressive treatment than might be warranted. The results of this study argue for wider adoption of COHb reference intervals supported by the current literature.

Lead poisoning from mobilization of bone stores during thyrotoxicosis

We describe a case of thyrotoxicosis accompanied by markedly elevated blood lead levels (initially 53 micrograms/dl) in a 37-year-old woman. No current source of lead exposure was found; the woman gave a history indicative of lead exposure as a child and as an adult 7 years previously, however. In addition, she was found to have markedly elevated bone lead levels, as measured by K-x-ray fluorescence (154 +/- 5 in the mid-tibia and 253 +/- 6 micrograms/g bone mineral in the patella), and an increased serum osteocalcin level (2.76 nmol/l), reflecting the increased bone turnover that often accompanies hyperthyroidism. During treatment with propylthiouracil, serial observations demonstrated a decline in serum osteocalcin that paralleled a decline in blood lead levels. Bone lead levels did not change appreciably. The patient also continued to have lingering neuropsychological symptoms consistent with chronic lead effects. We suggest that increased bone turnover accompanying thyrotoxicosis led to clinically significant lead poisoning in this patient, due to mobilization of accumulated bone lead stores acquired many years earlier. This phenomenon raises the general issue of more subtle forms of lead exposure from increased bone turnover states (e.g., osteoporosis).

Medical surveillance in the biotechnology industry

A medical program appropriate for employees in biomedical laboratories should be based upon specific understanding of the risks and hazards associated with the work activities. Components of a medical program might include: preplacement examinations, periodic monitoring evaluations, tracking of prolonged or unusual illness, specific illness or exposure-related evaluations, epidemiological studies, immunization programs, and exit (or termination) evaluations.

Lead poisoning in automobile radiator mechanics

Exposure to lead occurs during automobile radiator repair when soldered joints are heated, but this relatively common hazard has received little public recognition. We therefore studied lead exposure among automobile radiator mechanics in the Boston area. Twenty-seven shops were surveyed, and most were found to be small and poorly ventilated. Seventy-five workers were interviewed and tested for blood lead and free erythrocyte protoporphyrin levels. Fifty-six of the 75 actually repaired radiators, and they had a mean blood lead level of 37.1 micrograms per deciliter (range, 16 to 73). Thirty-nine percent of these mechanics had levels higher than 40 micrograms per deciliter; hematologic, neurologic, and renal effects are known to develop at or above this blood lead level. Multiple regression analysis showed that the number of radiator repair work stations (an index of exposure) was the variable most significantly associated with increased blood lead levels. We conclude that excessive exposure to lead occurs frequently among radiator repair workers and should be prevented by improved ventilation, engineering controls, and the use of respirators (if indicated) while working.

General occupational health history and examination

This paper presents a method for developing occupational medical examinations using the preplacement examination (PPE) and the periodic monitoring examination (PME). The steps for developing an appropriate PPE include goal definition, analysis of job requirements and potential exposures, an occupational and medical history, and a targeted physical examination derived from the preceding steps. The PPE should result in the proper placement of the worker. It also serves as a baseline for comparison to future testing or health-related developments. The PME checks the effectiveness of more primary preventive measures such as plant engineering controls and personal protection. The contents and frequency of the PME depend on the pathophysiology and toxicology of the hazardous exposures, the interval exposure and medical history, and legal requirements. Individual and group results should be assessed periodically for trends suggesting work-related problems that would need further evaluation.

Italian occupational health: concepts, conflicts, implications

This paper examines Italy's worker-based model for occupational health, especially its key concepts and its relation to social conflict. It briefly reviews the history of three approaches to occupational health in Italy: university-based, industry-based, and government-based. It then analyzes the worker-based approach, which emerged in the late 1960s and early 1970s as worker groups and trade unions mobilized around new concepts of occupational health. Five key concepts are discussed: the workers' homogeneous group; workers' subjectivity; the use of contract language; the development of local occupational health institutions; and the use of occupational hazard risk maps. The analysis illustrates how the social processes of mobilization and institutionalization affected the ideas and structures of Italian occupational health. Worker mobilization in Italy produced ideological changes in the nation's occupational health system, institutional changes in universities and governments, and legislative changes at national and local levels. The institutionalization of reforms, however, created new conflicts and problems and tended to restrict worker participation and promote expert intervention. The paper concludes with a brief outline of the history of occupational health approaches in the United States and then discusses the implications of the five Italian concepts for US occupational health policy.

The occupational and environmental health history

Occupational and environmental diseases frequently masquerade as routine medical disorders. Yet environmental factors rarely enter into the clinician's differential diagnosis. This article provides a sequence of steps that can be used by the practicing physician for detecting occupational diseases: Step 1: Routine screening questions for all patients (List of job titles? Exposure to fumes, dusts, chemicals, loud noise, or radiation? Temporal relationship of the chief complaint to activities at work or at home?). Step 2: Consideration of sources of exposure (workplace or home surroundings). Step 3: Identification and handling of the hazardous agent. Step 4: Follow-up, consultation, and resolution of the problem. Equipped with this approach, the clinician can play an important role in the detection and prevention of occupational- and environmental-related diseases.

Effect of chronic potassium depletion on digitalis-induced inotropy and arrhythmias

The arrhythmogenic and inotropic effects of digoxin were studied in normokalemic controls, chronically hypokalaemic, and potassium-repleted dogs instrumented to maintain heart rate, mean aortic pressure, mean left atrial pressure and autonomic tone constant. The duration of digoxin infusion needed to produce ventricular tachycardia (VT) was 56.7 +/- 3.6 min in depleted dogs, 69.0 +/- 2.7 min in controls (P less than 0.005 compared with depleted dogs), and 60.5 +/- 3.0 min in repleted dogs. Baseline left ventricular dP/dt (LV dP/dt) was similar in all groups. After digoxin, LV dP/dt increased more in controls and repleted dogs than in chronically hypokalaemic dogs; eg, after 45 min of digoxin infusion LV dP/dt increased 12.7 +/- 4.4% in hypokalaemic dogs; eg, after 45 min of digoxin infusion LV dP/dt increased 12.7 +/- 4.4% in hypokalaemic dogs, 43.8 +/- 3.3% in controls (P less than 0.025) and 39.3 +/- 8.5% in repleted dogs (P less than 0.025). The inotropic response to isoprenaline was also attenuated in the chronically hypokalaemic dogs. Plasma digoxin was similar in all groups. LV digoxin was also similar in control and depleted dogs. Although inhibition of Na+, K+-ATPase and the initial velocity of 3[H]-ouabain specific binding was less in depleted dogs at VT than in controls (P less than 0.05), the magnitude of this difference was not sufficient to explain the attenuated inotropic response. No histological abnormalities were seen on light or electron microscopy in any of the groups. Therefore chronic hypokalaemia has two deleterous effects. It increases sensitivity to the arrhythmogenic effects of digoxin and impairs the inotropic response to digoxin, and isoprenaline.

The family and home hemodialysis: adolescents' reactions to a father on home dialysis

Quality of life is the most controversial issue surrounding home hemodialysis. We examined how sixteen adolescents and their six families reacted to having a father on home hemodialysis, exploring the interplay between adolescent developmental conflicts and family stresses. Family members underwent role changes to adjust to alterations imposed by hemodialysis. Some adolescents helped relieve family stresses by taking an active role in dialysis. These eight adolescents developed greater self-esteem which enhanced identity growth and facilitated separation. Psychological responses were observed that resembled the "death guilt," "psychic numbing," and "invisible contamination" described in Hiroshima survivors. Adolescent developmental problems can be dwarfed by family conflicts around chronic illness and dialysis. Families adjusted to home hemodialysis showing new growth, managing with a barely workable arrangement, or adapting unsuccessfully. Understanding more about how home hemodialysis can influence family interactions can enable the medical staff to facilitate beneficial changes, and thereby improve the quality of life for patient and family.

Effects of digitalis on normal and abnormal left ventricular segmental dynamics

To study the effects of digoxin on regional left ventricular performance, continuous ventricular dynamics were assessed in nine patients with stable coronary disease. Computer-assisted analysis of the fluoroscopic motion of surgically implanted mid wall myocardial markers was used. The markers define six minor ventricular radii and outline the left ventricle. One and one-half hours after administration of 1 mg of intravenous digoxin, mean velocity of circumferential fiber shortening for all segments increased 19 percent, from 0.67 +/- 0.06 to 0.78 +/- 0.06 circumference/sec (P less than 0.01) and ejection fraction increased 4.5 percent, from 0.50 +/- 0.03 to 0.53 +/- 0.03 (P less than 0.05). Segmental velocity of circumferential fiber shortening, total segmental shortening and early segmental systolic shrtening increased in 83 percent to 91 percent of normal segments, depending on which index was used. Only 45 to 55 percent of initially abnormal segments benefited from digoxin. In general, segmental dyssynergy increased even when net ventricular function was enhanced. These results suggest that in pateints with chronic left ventricular contraction abnormalities due to coronary disease, deterioration of performance in abnormal regions after administration of digoxin may result from increased stress imposed by increased afterload and by improved segmental dynamics in more normal areas.

Correlation between microsomal (Na+ + K+)-ATPase activity and [3H]ouabain binding to heart tissue homogenates

ATP plus Mg2+ plus Na+ supported [3H]ouabain binding to canine left ventricular tissue homogenates and microsomal (Na+ + K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) activity from the same tissue were measured. A linear relationship was found between the initial velocity of [3H]ouabain binding to tissue homogenates and microsomal (Na+ + K+)-ATPase activity from the same tissue in the presence and absence of in vivo bound digoxin. In vivo bound digoxin reduced both measurements. With tissue from digoxin-free hearts, a linear relationship was also obtained between the initial velocity and the maximum level of [3H]ouabain binding to tissue homogenate. Binding of [3H]ouabain to whole tissue homogenate is a convenient method for estimating (Na+ + K+)-ATPase activity in small left ventricular biopsy samples.

Age-related changes in ouabain pharmacology. Ouabain exhibits a different volume of distribution in adult and young dogs

To better understand why one must administer much higher doeses of digitalis glycosides to immature than to mature humans and animals, we studied ouabain pharmacokinetics in adult and young dogs. Consistent with reported observations that ouabain-binding, metabolism, and excretion do not change with age, we found no significant differences in the transfer coefficients in a linear two-compartment open model for ouabain pharmacokinetics following a bolus of 0.05 mg/kg. We did find, however, that young dogs had nearly twice the ouabain volumes of distribution per kilogram of body weight as adults (155.4 +/- 1.2 (SE) ml/kg vs. 80 +/- 0.6, P less than 0.0005) and that one could account for this difference with the fact that young dogs had nearly twice the plasma volume 108 +/- 9.8, vs. 68 +/- 7.3, P = 0.001) and interstitial fluid space (318 +/- 35 vs. 190 +/- 6.5, P = 0.006) as the adults. For the same dose per kilogram, left and right ventricular ouabain concentrations were inversely related to the volume of distribution, with the adults having significantly higher tissue levels and incidence of arrhythmias. One must give more ouabain to a young dog to get the same plasma concentration as in an adult because the mass of ouabain in rapid equilibrium with the plasma is diluted in a larger volume of distribution.

Investigation of the safe withdrawal period for propranolol in patients scheduled for open heart surgery

The time necessary for dissipation of radioactive labelled propranolol and its metabolites and the cardiac effects of this agent in the hearts of patients undergoing open-heart surgery were studied. Isoprenaline produced chronotropic and inotropic responses in atrial muscle in tissue bath studies which were normal 8 to 12 hours after withdrawing propranolol. After the administration of either 25 or 75 muCi of 14C-labelled propranolol, the myocardial tissue concentration declined to insignificant levels between 24 and 28 hours. We conclude that withdrawal of propranolol therapy 24 to 48 hours before cardiac surgery should be acceptable.

Studies on magnesium's mechanism of action in digitalis-induced arrhythmias

The mechanism by which magnesium affects digitalis-induced arrhythmias was studied in dogs with and without beta-receptor blockade. Digoxin was infused at a rate of 2.5mug/kg/min until ventricular tachycardia developed, then half the animals were given MgSO4, the other half saline. In animals given MgSO4, sinus rhythm was immediately re-established; in animals given saline, ventricular tachycardia persisted. In animals with beta-receptor blockade, MgSO4 was as effective in abolishing ventricular tachycardia as in those without beta-receptor blockade. We found no evidence that magnesium re-activated digoxin-inhibited (Na+, K+)-ATPase, altered myocardial or microsomal digoxin binding, or acted via the autonomic nervous system. Magnesium's direct effect on calcium and potassium fluxes across the myocardial cell membrane may be the mechanism of its antiarrhythmic action in digitalis-toxic arrhythmias.

Hemodynamics, renal function, plasma renin, and aldosterone in man after 5 to 14 days of bedrest

Continous bedrest for 5 to 14 days had no significant effect on resting heart rate, blood pressure or cardiac output in six normal men. Head-up tilt induced greater tachycardia in 5 of 6 patients after bed rest than in the control period. Propranolol diminished both the tachycardia and the incidence of hypotension and faintness in upright posture. Body weight, serum electrolytes and resting renal plasma flow, and glomerular filtration rate were unchanged by bedrest. Plasma volume fell, extracellular fluid volume increased, and plasma renin activity was significantly elevated following bedrest. Unusually large increases in plasma renin followed head-up tilt or administration of isoproterenol during bedrest, and after resuming normal activity. During bedrest, plasma aldosterone was often increased in the early morning. We conclude that after bedrest, upright posture evokes strong beta-adrenergic activity, with exaggerated metabolic and circulatory responses which can be reduced or abolished by the beta-adrenergic blocker, propranolol.

Dose response in vivo to digoxin in normo-and hyperkalaemia: associated biochemical changes

The effect of digoxin, at two different inotropic levels, was examined in normo- and hyperkalaemic dogs. For similar inotropic responses, normo- and hyperkalaemic dogs had similar levels of (Na+, K+)-ATPase inhibition and microsomal-bound digoxin.

Physiological distribution of digoxin in human heart

Using the recipient's human heart removed at cardiac transplantation, the distribution of digoxin at both the cellular and subcellular level has been studied. In the presence of diffuse histological myocardial abnormalities tissue digoxin is decreased, but the subcellular distribution, presumably reflecting binding to a possible receptor site, is uniform. When the histological abnormality is focal then digoxin distribution is uniform.These results suggest that in the presence of myocardial ischaemia plasma digoxin concentrations may not reflect total myocardial levels accurately.

The inotropic effects of digoxin in hyperkalemia. Relation to (Na+,K+)-ATPase inhibition in the intact animal

The effects of hyperkalemia on the inotropic properties of digoxin were studied in anesthetized mongrel dogs. With preload, afterload and heart rate maintained constant in dogs who received atropine and practolol to block cardiac reflexes, 0.08 mg/kg digoxin increased the first derivative of the left ventricular pressure curve (LV dp/dt) 53.1 ± 8.3% (SEM) in normokalemic animals but only 9.5 ± 2.5% in hyperkalemic animals at 60 min. This decrease in the inotropic effects of digoxin by hyperkalemia was accompanied by significant decreases in both total left ventricular digoxin concentration and microsomal-bound digoxin. (Na + , K + )-ATPase was inhibited 43.3 ± 2.4% in normokalemic animals but only 27.4 ± 2.5% in hyperkalemic animals ( P < 0.01), while (Mg ++ )-ATPase levels were similar in normokalemia and hyperkalemia. In animals not given digoxin, hyperkalemia had no effect on either LV dp/dt or (Na + , K + )-ATPase. There was a good correlation between the positive inotropic effects of digoxin and percent inhibition of (Na + , K + )-ATPase.

These studies provide further support for the importance of (Na + , K + )-ATPase inhibition and microsomal-bound digoxin in determining the inotropic effects of digoxin. Hyperkalemia alters the inotropic effects of digoxin by decreasing binding of digoxin to a microsomal cell fraction containing (Na + , K + )-ATPase activity.

These studies also provide support for the importance of reflex withdrawal of sympathetic tone in modifying the inotropic properties of digoxin in normokalemic and hyperkalemic animals.

Measurement of central venous oxygen saturation in patients with myocarial infarction

Central venous oxygen saturation (CVSO 2 ) was measured in 31 patients with myocardial infarction. CVSO 2 correlated well with the patients' clinical course. In those patients not in heart failure, mean ± sem for CVSO 2 was 70 ± 1%. When heart failure was present, CVSO 2 averaged 56 ± 1%. When both heart failure and shock were present, CVSO 2 averaged 43 ± 1%. In nine patients, serial determinations of arterial oxygen saturation and CVSO 2 were made. In 22 of 26 instances, either a fall in CVSO 2 was accompanied by an increase in the arteriovenous oxygen saturation difference or an increase in CVSO 2 was accompanied by a decrease in arteriovenous oxygen saturation difference. Serial measurements of CVSO 2 appear to be a useful method of monitoring changes in myocardial function in patients with myocardial infarction.