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Biomedical subjects

R M Wachter

Publications and source records attributed to R M Wachter.

At least 55 records · Page 3Linked to original sources
PubMed1997

Crystal structure and photodynamic behavior of the blue emission variant Y66H/Y145F of green fluorescent protein.

The crystal structure of a blue emission variant (Y66H/Y145F) of the Aequorea victoria green fluorescent protein has been determined by molecular replacement and the model refined. The crystallographic R-factor is 18.1% for all data from 20 to 2.1 A, and the model geometry is excellent. The chromophore is non-native and is autocatalytically generated from the internal tripeptide Ser65-His66-Gly67. The final electron density maps indicate that the formation of the chromophore is complete, including 1,2 dehydration of His66 as indicated by the planarity of the chromophore. The chromophore is in the cis conformation, with no evidence for any substantial fraction of the trans configuration or uncyclized apoprotein, and is well-shielded from bulk solvent by the folded protein. These characteristics indicate that the machinery for production of the chromophore from a buried tripeptide unit is not only intact but also highly efficient in spite of a major change in chromophore chemical structure. Nevertheless, there are significant rearrangements in the hydrogen bond configuration around the chromophore as compared to wild-type, indicating flexibility of the active site. pH titration of the intact protein and the chromopeptide (pKa1 = 4.9 +/- 0.1, pKa2 = 12.0 +/- 0.1) suggests that the predominant form of the chromophore in the intact protein is electrically neutral. In contrast to the wild-type protein [Chattoraj, M., King, B. A., Bublitz, G. U., & Boxer, S. G. (1996) Proc. Natl. Acad. Sci. U.S.A., 8362-8367], femtosecond fluorescence up-conversion spectroscopy of the intact protein and a partially deuterated form strongly suggests that excited-state proton transfer is not coupled to fluorescence emission.

Animals↗
PubMed1996

Thiols as mechanistic probes for catalysis by the free radical enzyme galactose oxidase.

Galactose oxidase, a mononuclear copper enzyme, oxidizes primary alcohols to aldehydes using molecular oxygen. A unique type of cross-link between tyrosine 272, an active-site copper ligand, and cysteine 228 provides a modified tyrosine radical site believed to act as a one-electron redox center. Substrate analogs incorporating a primary thiol group in place of the primary alcohol group in normal substrates (RCH2OH) have been studied as active-site mechanistic probes. Thiol sulfur coordinates to the active-site copper, leading to enzyme inactivation in a time- and concentration-dependent manner. The mechanism of inactivation involves redox chemistry related to the active-site redox centers, though inactivation does not proceed through the rate-determining hydrogen atom abstraction step that occurs in alcohol oxidation. Thiols are therefore classified as active-site-directed redox inactivators. The thiol analog of galactose, 6-Thio-Me-Gal, is also turned over by the enzyme, albeit at a much reduced rate, indicating that the energetics of turnover is changed significantly. Thiols constitute a particularly good model of the ground state enzyme-substrate complex. The Michaelis complex for thiol substrate analogs is stabilized at least 200-fold compared to the analogous alcohol substrates, whereas the transition state of H atom abstraction is destabilized, presumably due to a slight increase in distances of reacting atoms and weakening of hydrogen-bonding interactions due to the larger atomic radius of sulfur compared to that of oxygen.

Binding Sites↗
PubMed1995

Intensive care for patients with AIDS: clinical and ethical issues.

Pneumocystis carinii pneumonia (PCP) remains a common and morbid infection among patients with the acquired immunodeficiency syndrome (AIDS). Most patients who die of PCP do so because of respiratory failure. The survival after intubation and mechanical ventilation for PCP and respiratory failure has gone through three eras: Era I (1981-85), when the survival rate to hospital discharge was about 10%; Era II (1986-88), when the hospital survival rate rose to about 40%; and Era III (1989-present), when the hospital survival rate fell again to about 25%. Patients with CD4 counts of less than 50, patients who develop pneumothoraces while intubated, and patients spending more than 2 weeks in the ICU receiving mechanical ventilation appear to have very poor (< 10% survival) prognoses. As the survival rate has fallen in recent years, so too has the cost-effectiveness of ICU care for patients with severe PCP. It now costs about $200,000 (U.S.) to save a year of life through the use of the ICU in PCP, a relatively cost-ineffective intervention. Our present approach is to provide patients information about prognosis and options and allow them to make an informed choice about whether they would like ICU care should the medical need arise. Whether the high costs and low cost-effectiveness of intensive care should and will be factored into this decision are questions of great clinical and ethical importance for the future.

AIDS-Related Opportunistic Infections↗
PubMed1995

Cost and outcome of intensive care for patients with AIDS, Pneumocystis carinii pneumonia, and severe respiratory failure.

OBJECTIVE: To determine the costs and outcomes associated with intensive care unit (ICU) admission for patients with acquired immunodeficiency syndrome (AIDS)-related Pneumocystis carinii pneumonia (PCP), and severe respiratory failure. DESIGN: Survival and cost-effectiveness analysis. SETTING: A large municipal teaching hospital serving an indigent population. PATIENTS: Consecutive patients intubated and mechanically ventilated for AIDS, PCP, and respiratory failure from 1981 through 1991 (n = 113). The cohort was separated into three groups for analysis: patients admitted to the ICU in 1981 through 1985 (era I, n = 43), those admitted in 1986 through 1988 (era II, n = 33), and those admitted in 1989 through 1991 (era III, n = 37). MAIN OUTCOME MEASURES: Hospital charges and survival time; cost per year of life saved, using a zero-cost, zero-life assumption. RESULTS: Twenty-eight (25%) of the 113 patients mechanically ventilated for PCP and respiratory failure survived to hospital discharge: six (14%) of 43 in era I, 13 (39%) of 33 in era II, and nine (24%) of 37 in era III (P = .04). Post-ICU admission charges averaged $57,874 for the entire cohort, remaining relatively stable across the three eras. Cost of care for survivors was significantly more expensive than for those dying before discharge. The cost of ICU admission and subsequent hospitalization averaged $174,781 per year of life saved; $305,795 in era I, $94,528 in era II, and $215,233 in era III. Improved survival rates and shorter lengths of ICU stay led to the improved cost-effectiveness in era II, while the opposite trends resulted in worsening cost-effectiveness in recent years. The strongest predictors of hospital mortality in era III were low CD4 cell counts on hospital admission and the development of pneumothorax during mechanical ventilation. CONCLUSIONS: The cost-effectiveness of intensive care for patients with PCP and severe respiratory failure improved during the first 8 years of the AIDS epidemic but fell in recent years such that it is now below that of many accepted medical interventions.

AIDS-Related Opportunistic Infections↗
PubMed1995

Rationing health care: preparing for a new era.

As the American health care system struggles to provide universal access to quality care at an acceptable price, many planners focus on rationing as the only way to make available the necessary resources. I discuss some of the ethical, economic, and political issues that relate to health care rationing. The four important questions to consider when examining a rationing plan are: (1) Who acts as the gatekeeper? (2) What kinds of goods or services are rationed? (3) What happens to the money and resources that are saved by rationing? (4) Does the system provide a safety valve for the well-to-do? This article examines two prototypical rationing systems--the British system and the Oregon plan--and answers these four questions for both systems. Because of the absence of an efficient market economy in health care and the certainty of resource constraints, rationing is inevitable in American health care. The primary issues are whether rationing will be done implicitly or explicitly and whether it will be based primarily on ability to pay (as in the present system) or on comparative judgments about the costs and benefits of medical interventions.

Ethics, Medical↗
PubMed1994

The ethical appropriateness of using prognostic scoring systems in clinical management.

The four ethical principles of beneficence, nonmaleficence, autonomy, and social justice provide a framework for making medical decisions, including those that involve the administration of life-sustaining therapies. In recent years, a number of prognostic scoring systems, including the Acute Physiology Assessment and Chronic Health Evaluation (APACHE) system, have been developed to augment clinical judgment in determining which critically ill patients are likely to benefit from such therapies. Although these systems all have limitations, their use in decision making is as ethically appropriate as is the use of clinical judgment, which has its own limitations and has been used for years.

AIDS-Related Opportunistic Infections↗
PubMed1993

Advance directives for patients with human immunodeficiency virus infection.

A consensus has emerged in recent years that decisions about life-sustaining treatment made by informed, competent patients should be respected. Advance directives are expressions of a patient's preferences regarding life-sustaining treatments made while the patient is still competent, to be used if the patient loses competence. Patients infected with HIV have a high mortality rate and frequently lose competence as their disease progresses to AIDS. Therefore, the completion of advance directives in this patient group is vitally important.

Advance Directives↗
PubMed1992

Screening women of childbearing age for human immunodeficiency virus. A cost-benefit analysis.

In light of the increasing problem of perinatal human immunodeficiency virus (HIV) transmission, the issue of screening women for HIV is receiving considerable attention. We analyzed the costs and benefits of screening women of childbearing age for HIV. The analysis was based on a dynamic model of the HIV epidemic that incorporated disease transmission and progression, behavioral changes, and effects of screening and counseling. We found that the primary benefit of screening programs targeted to women of childbearing age lies not in the prevention of HIV infection in their newborns but in the prevention of infection in their adult contacts. Because of this benefit, screening medium- and high-risk women is likely to be cost-beneficial over a wide range of assumptions about program cost and behavioral changes in response to screening.

AIDS Serodiagnosis↗
PubMed1991

Pneumocystis carinii pneumonia and respiratory failure in AIDS. Improved outcomes and increased use of intensive care units.

To determine whether the outcome of intensive care for patients with AIDS, Pneumocystis carinii pneumonia (PCP), and respiratory failure has changed, we studied patients admitted to the intensive care units an San Francisco General Hospital from 1981 to 1988. We compared the course of patients with PCP and respiratory failure admitted to the intensive care unit from 1986 to 1988 with a similar cohort hospitalized from 1981 to 1985. The hospital survival rate for the 35 patients in the 1986 to 1988 cohort was 40%, compared with 14% for the 42 patients in the 1981 to 1985 cohort (p less than 0.01). Age, episode of PCP, time since AIDS diagnosis, anti-PCP therapy, and important clinical variables were similar in both cohorts. Corticosteroids were used commonly in the recent era. Patients who received steroids had an in-hospital survival rate of 46%, compared with 22% for those who did not receive steroids (p = NS). In a stepwise logistic regression model, ICU care in the recent era and higher serum albumin at the time of ICU admission were the only variables significantly associated with survival. The hospital survival of patients with PCP and respiratory failure has improved. The improvement could not be explained by patient selection or by better anti-PCP therapy. The apparent beneficial effect of corticosteroids deserves further study. The improvement in ICU outcome was reflected in increased ICU utilization by patients with AIDS, PCP, and respiratory failure.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Decisions about resuscitation: inequities among patients with different diseases but similar prognoses.

STUDY OBJECTIVE: To assess whether decisions about "do-not-resuscitate" (DNR) orders are made equitably in patients with different diseases but similar prognoses. DESIGN: Retrospective cohort study. SETTING: Three teaching hospitals: a university referral center, a county hospital serving a largely indigent population, and a Veterans Administration hospital. PATIENTS: Consecutive patients with any of the four following discharge diagnoses: the acquired immunodeficiency syndrome (AIDS) (100 patients); unresectable non-small-cell lung cancer (51 patients); cirrhosis with esophageal varices (51 patients); and severe congestive heart failure with coronary artery disease (115 patients). MEASUREMENTS AND MAIN RESULTS: Do-not-resuscitate orders were written for 52% of patients with AIDS and 47% of patients with cancer but for only 16% of patients with cirrhosis and 5% of patients with congestive heart failure (P less than 0.0001). Although DNR orders were associated with functional and mental status, reason for admission, and severity of illness, the strong association between DNR orders and disease category persisted after adjustment for these potential confounders by multiple logistic regression. A survey of housestaff showed that DNR orders were discussed more frequently with patients who had AIDS or lung cancer than with patients who had cirrhosis or heart failure, despite an accurate understanding of the generally similar prognoses among the four groups. CONCLUSIONS: Despite relatively similar prognoses, patients with AIDS or lung cancer are much more likely to receive DNR orders than patients with cirrhosis or severe congestive heart failure. This discrepancy cannot be explained by differences in severity of illness among patients or by misunderstandings of prognosis by clinicians. From our data, we cannot determine if patients with cirrhosis or heart failure receive too few DNR orders or if patients with AIDS or lung cancer receive too many. Our findings should encourage physicians to determine the preferences of patients about life-sustaining treatments more equitably.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Life-sustaining treatment for patients with AIDS.

Physicians increasingly are being called upon to make difficult decisions about intensive care for patients with the acquired immunodeficiency syndrome (AIDS). AIDS patients who require intensive care have a poor prognosis; the in-hospital mortality rate of those receiving mechanical ventilation for P carinii pneumonia is 86-100 percent in most studies. However, in the past year, two studies documenting improved outcome have been published. Physicians should understand these outcome data and use well-established ethical principles to allow informed competent patients with AIDS to express their preferences regarding intensive care. Patients should be encouraged to provide advanced directives regarding life-sustaining treatments or to designate surrogate decision-makers to be consulted should they lose mental competence. The health care system should provide alternatives to the ICU for compassionate terminal care. However, arbitrary policies denying intensive care to AIDS patients for whom it is medically indicated and desired are not warranted.

Acquired Immunodeficiency Syndrome↗