A Bundle of the Top 10 OPAT Publications in 2022

Outpatient parenteral antimicrobial therapy (OPAT) has become more common in clinical settings. Correspondingly, OPAT-related publications have also increased; the objective of this article was to summarize clinically meaningful OPAT-related publications in 2022. Seventy-five articles were initially identified, with 54 being scored. The top 20 OPAT articles published in 2022 were reviewed by a group of multidisciplinary OPAT clinicians. This article provides a summary of the "top 10" OPAT publications of 2022.

A review of evidence, antimicrobial stability, and feasibility considerations for OPAT continuous infusion

Outpatient parenteral antimicrobial therapy (OPAT) has been widely used in clinical practice for many decades because of its associated cost savings, reductions in inpatient hospital days, and decreases in hospital-associated infections. Despite this long history, evolving practice patterns and new drug delivery devices continue to present challenges as well as opportunities for clinicians when designing appropriate outpatient antimicrobial regimens. One such change is the increasing use of extended and continuous infusion (CI) of antimicrobials to optimize the achievement of pharmacokinetic and pharmacodynamic targets. Elastomeric devices are also becoming increasingly popular in OPAT, including for the delivery of CI. In this article, we review the clinical evidence for CI in OPAT, as well as practical considerations of patient preferences, cost, and antimicrobial stability.

Facilitating OPAT in rural areas

A sizable portion of the United States' population lives in a rural setting. Coupled with a limited number of infectious diseases providers, this has created a need for innovative practice models to deliver outpatient antimicrobial therapy and clinical monitoring in rural settings. This article reviews existing literature regarding outpatient parenteral antimicrobial therapy in rural settings and explores existing barriers and potential solutions that may be of assistance to providers looking to provide these services.

A Bundle of the Top 10 OPAT Publications in 2021

As outpatient parenteral antimicrobial therapy (OPAT) becomes more common, it may be difficult to stay current with recent related publications. A group of multidisciplinary OPAT clinicians reviewed and ranked all OPAT publications published in 2021. This article provides a high-level summary of the OPAT manuscripts that were voted the “top 10” publications of 2021.

Survey of pharmacists on their roles and perceptions of outpatient parenteral antimicrobial therapy in the United States

OBJECTIVES

To define outpatient parenteral antimicrobial therapy (OPAT) clinical pharmacy practice across the United States, specifically pharmacist functions, design of pharmacist involvement, and to compare pharmacist training of those who practice in OPAT to infectious diseases pharmacists who do not.

METHODS

A survey of a possible 32 questions was emailed to the American College of Clinical Pharmacists (ACCP) Infectious Diseases Practice and Research Network (PRN) e-mail list. Results were focused on US-based respondents.

PARTICIPANTS

In total, 87 pharmacists responded; 27 of these pharmacists (31%) practiced in OPAT.

RESULTS

Training background did not differ between groups. Programs with an OPAT pharmacist were more likely to have a formal OPAT team compared to those without an OPAT pharmacist (P < .001). OPAT pharmacists were early in their careers with 66.7% practicing <5 years in OPAT. Most OPAT pharmacists (66.7%) practiced at an academic medical center with a median full-time equivalent (FTE) of 0.6. Moreover, 63% utilized a collaborative practice agreement and 81.5% shared job functions with other pharmacist roles, most commonly antimicrobial stewardship. Few OPAT programs involved a dispensing component (28%). The median daily census was 43 patients followed by an OPAT pharmacist. Pharmacists performed a variety of tasks in OPAT.

CONCLUSION

Pharmacist nondispensing involvement in OPAT is an emerging trend in the United States with wide variability in program structure and pharmacist tasks. A ratio of 1 OPAT pharmacist for every 45-70 OPAT patients is proposed to facilitate expansion of pharmacist clinical practice in OPAT.

619. Current State of Infectious Diseases Pharmacist OPAT/COpAT Practice in the United States

Background

Outpatient parenteral antimicrobial therapy (OPAT) is the process of administering intravenous (IV) antimicrobials outside the acute inpatient setting. Oral antimicrobials for complex infections are referred to as complex outpatient antimicrobial therapy (COpAT). OPAT/COpAT programs are expanding, as are the opportunities for clinical Infectious Diseases (ID) pharmacists (RPHs) involvement. The current state of clinical (non-dispensing) role and the functions being performed by RPHs in OPAT/COpAT is unknown.

Methods

To define the current state of OPAT/COpAT pharmacy practice across the United States (US), specifically the clinical functions performed by RPHs, design of RPH involved OPAT/COpAT clinics, and compare training of RPHs who practice in OPAT/COpAT to ID RPHs who do not, a survey of a possible 31 questions was emailed to the American College of Clinical Pharmacists (ACCP) Infectious Diseases Practice and Research Network (PRN) email list. Results were focused on US-based respondents.

Results

Eighty-seven RPHs responded with 27 practicing in OPAT/COpAT. Training background did not differ between groups. Programs with an OPAT/COpAT RPH were more likely to have a formal OPAT team compared to those without an OPAT/COpAT RPH (p &lt; 0.001). OPAT/COpAT RPHs were early in their careers, with roughly half practicing &lt; 5 years in ID, and 66.7% practicing &lt; 5 years in OPAT/COpAT. Most OPAT/COpAT RPHs (66.7%) practiced at an academic medical center with a median full time equivalent (FTE) of 1 RPH. Most (63%) utilized a collaborative practice agreement and 81.5% shared job functions with other ID RPH roles, most commonly antimicrobial stewardship. Few (28%) OPAT/COpAT programs involved a dispensing component. The average daily census was 42 patients followed by an OPAT/COpAT RPH. There was wide variability in the types of tasks ID RPH performed in OPAT/COpAT, the three most important tasks are listed in Figure 1.

OPAT Pharmacists Task Ranking by Importance

Conclusion

This is the largest known survey of OPAT/COpAT RPHs. RPH involvement in OPAT/COpAT in the US is an emerging trend with wide variability in program structure. Tasks performed by OPAT/COpAT RPHs varied significantly; however, OPAT/COpAT RPH respondents’ functions are largely clinical in nature.

Disclosures

All Authors: No reported disclosures

Call to Pharmacists: End Use of "Red Man Syndrome"

Red Man Syndrome is a term used for an adverse event attributed to vancomycin infusion. Based on the presentation within white patients, the term is imprecise at best and can lead to suboptimal classification and management. Recent calls have advocated for the discontinuation of the use of this terminology. Pharmacists should take the lead in advocating for this change.

Emergence of Resistance in Klebsiella aerogenes to Piperacillin-Tazobactam and Ceftriaxone

We examined the effects of piperacillin-tazobactam (TZP) concentration and bacterial inoculum on in vitro killing and the emergence of resistance in Klebsiella aerogenes The MICs for 15 clinical respiratory isolates were determined by broth microdilution for TZP and by Etest for ceftriaxone (CRO) and cefepime (FEP). The presence of resistance in TZP-susceptible isolates (n = 10) was determined by serial passes over increasing concentrations of TZP-containing and CRO-containing agar plates. Isolates with growth on TZP 16/4-μg/ml and CRO 8-μg/ml plates (n = 5) were tested in high-inoculum (HI; 7.0 log10 CFU/ml) and low-inoculum (LI; 5.0 log10 CFU/ml) time-kill studies. Antibiotic concentrations were selected to approximate TZP 3.375 g every 8 h (q8h) via a 4-h prolonged-infusion free peak concentration (40 μg/ml [TZP40]), peak epithelial lining fluid (ELF) concentrations, and average AUC0-24 values for TZP (20 μg/ml [TZP20] and 10 μg/ml [TZP10], respectively), the ELF FEP concentration (14 μg/ml), and the average AUC0-24 CRO concentration (6 μg/ml). For HI, FEP exposure significantly reduced 24-h inocula against all comparators (P ≤ 0.05) with a reduction of 4.93 ± 0.64 log10 CFU/ml. Exposure to TZP40, TZP20, and TZP10 reduced inocula by 0.81 ± 0.43, 0.21 ± 0.18, and 0.05 ± 0.16 log10 CFU/ml, respectively. CRO-exposed isolates demonstrated an increase of 0.42 ± 0.39 log10 CFU/ml compared to the starting inocula, with four of five CRO-exposed isolates demonstrating TZP-nonsusceptibility. At LI after 24 h of exposure to TZP20 and TZP10, the starting inoculum decreased by averages of 2.24 ± 1.98 and 2.91 ± 0.50 log10 CFU/ml, respectively. TZP demonstrated significant inoculum-dependent killing, warranting dose optimization studies.

925. Adverse Events Due to Inappropriate Prescribing in Older Adults Living with HIV

Background

People living with HIV (PLWH) are aging and experience age-related comorbidities as well as physiological changes leading to a higher risk for polypharmacy, drug-drug interactions, inappropriate prescribing and related adverse events (AE). Prior studies have highlighted a growing concern for inappropriate prescribing in older PLWH. The objective of this study was to examine the prevalence of AEs resulting from inappropriate prescribing in PLWH > 65 years of age.

Methods

This was a retrospective chart review. PLWH followed-up at the outpatient HIV clinic at the University Hospital in New Mexico between 01/01/2015 and 08/21/ 2018 were eligible if they were > 65 years of age and had >1 potentially inappropriate prescriptions (PIP). PIP were identified using the Beers and STOPP/START criteria for inappropriate mediations in elderly, as well as drugs incorrectly dosed, and potentially deleterious drug-drug interactions (DDI). The University of Liverpool’s HIV interaction checker and Lexicomp’s interaction checker were used to screen for DDI between HIV and non-HIV drugs, and between non-HIV drugs. AEs related to PIPs were collected and their severity was classified using the WHO scale for grading of AEs.

Results

A total of 104 PLWH >65 years of age fulfilled the eligibility criteria. Most patients were male (88.5%) with an average age of 69 years. The majority of patients were virologically suppressed (89%), with an average CD4 cell count of 650 cells/µL. Polypharmacy (>5 non-HIV medications) was identified in all 104 patients; average number of non-HIV medications was 9.4 + 4.8. 30 (28.8%) patients experienced >1 AE, with a total of 53 AEs identified. Of those, 20 (67%) presented with a serious AE. 14 patients (47%) had to seek treatment at an emergency department and 2 patients (7%) had to be hospitalized. The most common AEs included falls (27/53 events; 51%), bleeds (7/53 events; 13%), fractures (4/53 events; 8%). Risk for an AE was significantly associated with increasing number of medications (OR 1.16; 95% CI 1.05-1.29).

Conclusion

PIP and related AEs are common in older PLWH. Interventions to prevent harm including medication reconciliation, medication review, and medication prioritization according to the risks/benefits of individual patients are warranted.

Disclosures

Keenan L. Ryan, PharmD, PhC, Theravance (Advisor or Review Panel member)

296. IV-to-PO Antibiotic Step-down Therapy for Treatment of Uncomplicated Streptococcal Bloodstream Infections

Background

Beta-lactams are the drug of choice for uncomplicated Streptococcal bloodstream infections (BSIs). However, due to the low bioavailability of oral beta-lactams, it’s unclear whether de-escalation from IV to PO therapy is safe and effective. Our objective was to compare the efficacy and safety of step-down IV-to-PO antibiotic therapy to IV-only treatment of uncomplicated Streptococcal BSIs.

Methods

This was a retrospective study at a level-1, academic medical center in New Mexico of patients ≥ 18 years of age treated for uncomplicated Streptococcal BSI between January 2017 and December 2019. The primary outcome was clinical failure in patients receiving IV-only therapy compared to IV-to-PO step-down therapy. Clinical failure was defined as having at least one of the following: persistent bacteremia, 30-day reinfection at any site or new-onset sepsis, 30-day BSI recurrence, or 30-day all-cause mortality. Secondary outcomes include 30-day all-cause readmission, 30-day antibiotic-related side effects, 30-day C. difficile-associated diarrhea and hospital length of stay (HLOS).

Results

A total of 98 patients were included: 51 in the IV-to-PO group and 47 in the IV-only therapy group. The median age for both groups was 61 years; 65% patients were male, and 72% were Caucasian. BSIs were predominantly associated with respiratory infections (24.5%). Streptococcus pneumoniae (29.6%) was the most common pathogen. Nine patients (19.1%) in the IV-only group and none in the IV-to PO group experienced a clinical failure. 30-day reinfection at any site or new-onset sepsis (88.9%) was the primary cause of clinical failures. Fourteen patients (14.3%) were readmitted due to any cause within 30 days, 6 patients (11.8%) from the IV-to-PO and 8 (17%) from the IV-only group. Patients in the IV-to-PO group had a shorter duration of therapy than patients in the IV-only group (13 vs. 15 days, p=0.001), and decreased HLOS (5 vs. 12 days, p&lt; 0.001). Clinical failure was not statistically different when assessed for co-morbidities, source of infection, Pitt bacteremia score, documented BSI clearance, ICU admission or pathogen.

Conclusion

IV-to-PO step-down therapy appears to be a safe and effective alternative for treating uncomplicated Streptococcal BSIs in patients who are otherwise clinical stable.

Disclosures

Keenan L. Ryan, PharmD, PhC, Theravance (Advisor or Review Panel member)

Anatomic accuracy of airway training manikins compared with humans

Airway simulators, or training manikins, are frequently used in research studies for device development and training purposes. This study was designed to determine the anatomic accuracy of the most frequently used low-fidelity airway training manikins. Computerised tomography scans and ruler measurements were taken of the SynDaver^® , Laerdal^® and AirSim^® manikins. These measurements were compared with human computerised tomography (CT) scans (n = 33) from patients at the University of Michigan Medical Center or previously published values. Manikin measurements were scored as a percentile among the distribution of the same measurements in the human population and 10 out of 27 manikin measurements (nine measurements each in three manikins) were outside of two standard deviations from the mean in the participants. All three manikins were visually identifiable as outliers when plotting the first two dimensions from multidimensional scaling. In particular, the airway space between the epiglottis and posterior pharyngeal wall, through which airway devices must pass, was too large in all three manikins. SynDaver, Laerdal and AirSim manikins do not have anatomically correct static dimensions in relation to humans and these inaccuracies may lead to imprecise airway device development, negatively affect training and cause over-confidence in users.

Treatment of patients with HIV or hepatitis C by pharmacist clinicians in a patient-centered medical home

PURPOSE

This report describes an innovative pharmacy practice model assisting in the care of patients living with or at risk of acquiring human immunodeficiency virus (HIV) and/or hepatitis C virus (HCV).

SUMMARY

In the state of New Mexico, pharmacists can obtain prescribing privileges through a Pharmacist Clinician (PhC) license. The license allows PhCs to assess patients, order laboratory/diagnostic tests, prescribe medication, and bill select insurances. PhCs have developed a practice model for patients living with or at risk of HIV and/or HCV at a Level 3 National Committee for Quality Assurance Patient-Centered Medical Home in Albuquerque, New Mexico. In 2015, 5 PhCs, employed part time, were involved with 8 different clinics: (1) HIV Adherence and Complex Care, (2) HIV Transitions of Care, (3) HCV Mono- and Co-Infection, (4) HIV Pre-Exposure Prophylaxis (PrEP), (5) HIV Primary Care and Cardiovascular Risk Reduction, (6) Young Adult Clinic, (7) Perinatal HIV, and (8) Pediatric HIV. In 2015, PhCs at the clinic billed for 774 direct patient encounters.

CONCLUSION

Pharmacists with the PhC license are able to provide high-quality medical care to patients living with or at risk of HIV and/or HCV infections within an interprofessional medical home model.

Using spectral reflectance to distinguish between tracheal and oesophageal tissue: applications for airway management

Proper placement of the tracheal tube requires confirmation, and the predominant method in addition to clinical signs is the presence of end-tidal carbon dioxide. Such is the importance of confirmation that novel methods may also have a place. We previously demonstrated using ex-vivo swine tissue a unique spectral reflectance characteristic of tracheal tissue that differs from oesophageal tissue. We hypothesised that this characteristic would be present in living swine tissue and human cadavers. Reflectance spectra in the range 500-650 nm were captured using a customised fibreoptic probe, compact spectrometer and white light source from both the trachea and the oesophagus in anesthetised living swine and in human cadavers. A tracheal detection algorithm using ratio comparisons of reflectance was developed. The existence of the unique tracheal characteristic in both in-vivo swine and cadaver models was confirmed (p < 0.0001 for all comparisons between tracheal and oesophageal tissue at all target wavelengths in both species). Furthermore, our proposed tracheal detection algorithm exhibited a 100% positive predictive value in both models. This has potential utility for incorporation into airway management devices.

Predictors of Clostridium difficile infection and predictive impact of probiotic use in a diverse hospital-wide cohort

BACKGROUND

Hospital-based predictive models for Clostridium difficile infection (CDI) may aid with surveillance efforts.

METHODS

A retrospective cohort of adult hospitalized patients who were tested for CDI between May 1, 2011, and August 31, 2016, was formed. Proposed clinical and sociodemographic predictors of CDI were evaluated using multivariable predictive logistic regression modeling.

RESULTS

In a cohort of 5,209 patients, including 1,092 CDI cases, emergency department location (adjusted odds ratio [aOR], 1.91; 95% confidence interval [CI], 1.51, 2.41; compared with an intensive care unit reference category, which had the lowest observed odds in the study) and prior exposure to a statin (aOR, 1.26, 95% CI, 1.06, 1.51), probiotic (aOR, 1.39; 95% CI, 1.08, 1.80), or high-risk antibiotic (aOR, 1.54; 95% CI, 1.29, 1.84), such as a cephalosporin, a quinolone, or clindamycin, were independent predictors of CDI. Probiotic use did not appear to attenuate the odds of CDI in patients exposed to high-risk antibiotics, but moderate-risk antibiotics appeared to significantly attenuate the odds of CDI in patients who received probiotics.

CONCLUSIONS

Emergency department location, high-risk antibiotics, probiotics, and statins were independently predictive of CDI. Further exploration of the relationship between probiotics and CDI, especially in diverse patient populations, is warranted.

Monitoring non-invasive cardiac output and stroke volume during experimental human hypovolaemia and resuscitation

BACKGROUND

Multiple methods for non-invasive measurement of cardiac output (CO) and stroke volume (SV) exist. Their comparative capabilities are not clearly established.

METHODS

Healthy human subjects (n=21) underwent central hypovolaemia through progressive lower body negative pressure (LBNP) until the onset of presyncope, followed by termination of LBNP, to simulate complete resuscitation. Measurement methods were electrical bioimpedance (EBI) of the thorax and three measurements of CO and SV derived from the arterial blood pressure (ABP) waveform: the Modelflow (MF) method, the long-time interval (LTI) method, and pulse pressure (PP). We computed areas under receiver-operating characteristic curves (ROC AUCs) for the investigational metrics, to determine how well they discriminated between every combination of LBNP levels.

RESULTS

LTI and EBI yielded similar reductions in SV during progressive hypovolaemia and resuscitation (correlation coefficient 0.83) with ROC AUCs for distinguishing major LBNP (-60 mm Hg) vs resuscitation (0 mm Hg) of 0.98 and 0.99, respectively. MF yielded very similar reductions and ROC AUCs during progressive hypovolaemia, but after resuscitation, MF-CO did not return to baseline, yielding lower ROC AUCs (ΔROC AUC range, -0.18 to -0.26, P < 0.01). PP declined during hypovolaemia but tended to be an inferior indicator of specific LBNP levels, and PP did not recover during resuscitation, yielding lower ROC curves (P < 0.01).

CONCLUSIONS

LTI, EBI, and MF were able to track progressive hypovolaemia. PP decreased during hypovolaemia but its magnitude of reduction underestimated reductions in SV. PP and MF were inferior for the identification of resuscitation.

Comparison of cardiac output monitoring methods for detecting central hypovolemia due to lower body negative pressure

Reduction in mean arterial pressure (MAP) is a late indictor of progressive circulatory pathology. Non-invasive monitoring methods that are superior indicators of circulatory compromise would be clinically valuable. With IRB approval, 21 healthy volunteers were subjected to progressive lower body negative pressure (LBNP) until the onset of presyncopal symptoms. We evaluated the usefulness of four investigational methods of arterial blood pressure waveform analysis during progressive hypovolemia: mean arterial pressure (MAP); the ModelFlow cardiac output algorithm (MF); the long time interval method (LTI); and the product of pulse pressure and heart rate (PP*HR). Electrical bioimpedance measurement of cardiac output (EBI) provided a reference. When results were analyzed, we found significant differences between the methods. MF, LTI, and EBI all corresponded with LBNP severity, while MAP and PP*HR did not. In terms of discriminating between (a) decompression to -45 mmHg; versus (b) recovery five minutes after LBNP cessation, there was a significant difference between MF and LTI: the receiver operating characteristic area-under-the-curve (ROC AUC) for MF was 0.57 and for LTI was 0.76. In terms of discriminating between (a) the 11 subjects who tolerated the protocol (i.e., tolerated higher levels of LBNP); versus (b) the 10 non-tolerant subjects, there was also a significant difference between MF and LTI: the ROC AUC for MF was 0.40 and for LTI was 0.66. There were no significant differences between MF nor EBI, however. In conclusion, LTI is notable as the only method which (a) correlated with decompression: (b) distinguished between decompression to -45 mmHg versus recovery; and (c) distinguished between those subjects who adequately compensated for central hypovolemia (tolerant) and those who did not have such robust physiologic compensation (non-tolerant).

Effects of histamine receptor blockade on cardiovascular changes induced by 35 GHz radio frequency radiation heating

1. The role of histamine in heat-induced cardiovascular changes is uncertain. The purpose of this study was to examine effects of histamine H-1- and H-2-antagonism on heart rate, mean arterial blood pressure (MAP), localized body temperature changes, survival times, and lethal body temperatures that occur during the exposure of anaesthetized rats to 35 GHz radio frequency radiation (RFR). 2. Forty-eight ketamine-anaesthetized Sprague-Dawley rats were exposed, in several different treatment groups (n = 8 in each), to 35 GHz RFR at a level that resulted in significant body heating and subsequent death. During irradiation, a continuous increase in heart rate and a biphasic response in blood pressure (initial increase followed by a decrease) were observed in all groups of animals. 3. An H-1-antagonist, diphenhydramine (1 mg kg(-1) body wt) and an H-2-antagonist, cimetidine (5 mg kg(-1)), administered after sustained RFR exposure, failed to reverse the RFR-induced hypotension. High doses of the drugs (5 and 10 mg kg(-1), respectively) also did not alter the response. Post-RFR survival time was significantly decreased in the high-dose drug-treated group, compared with vehicle-treated (0.9% NaCl, 50% ethanol and 50% D5W) controls. 4. In experiments in which the two drugs were administered prior to RFR exposure, MAP in animals receiving high-dose antihistamines was significantly depressed compared with that of vehicle-treated animals during the first 35 min of RFR exposure. Antihistamine pretreatment, however, did not alter the total RFR exposure time required for death to occur. 5. In summary, pharmacological blockade of H-1 and H-2 receptors is not beneficial in anaesthetized rats made hypotensive by RFR exposure. This indicates that activation of H-1 and H-2 receptors by histamine does not occur to any significant extent and does not mediate the hypotensive response developed in this model of hyperthermia.

Inter-species extrapolation of skin heating resulting from millimeter wave irradiation: modeling and experimental results

This study reports measurements of the skin surface temperature elevations during localized irradiation (94 GHz) of three species: rat (irradiated on lower abdomen), rhesus monkey (posterior forelimb), and human (posterior forearm). Two exposure conditions were examined: prolonged, low power density microwaves (LPM) and short-term, high power density microwaves (HPM). Temperature histories were compared with calculations from a bio-heat transfer model. The mean peak surface temperature increase was approximately 7.0 degrees C for the short-term HPM exposures for all three species/locations, and 8.5 degrees C (monkey, human) to 10.5 degrees C (rat) for the longer-duration LPM exposures. The HPM temperature histories are in close agreement with a one-dimensional conduction heat transfer model with negligible blood flow. The LPM temperature histories were compared with calculations from the bio-heat model, evaluated for various (constant) blood flow rates. Results suggest a variable blood flow model, reflecting a dynamic thermoregulatory response, may be more suited to describing skin surface temperature response under long-duration MMW irradiation.

Platelet-activating factor does not mediate circulatory failure induced by 35-GHz microwave heating

Sustained whole-body exposure of anesthetized rats to 35-GHz radiofrequency radiation produces localized hyperthermia and hypotension, leading to circulatory failure and death. The physiological mechanism underlying the induction of circulatory failure by 35-GHz microwave (MW) heating is currently unknown. The purpose of this study was to determine whether platelet-activating factor (PAF) contributes to the hypotensive state induced by MW heating. Ketamine-anesthetized rats were instrumented for the measurement of arterial blood pressure, ECG and temperature at five sites. Administration of the PAF-receptor antagonist WEB 2086 (0.5 or 5 mg/kg) following the induction of circulatory failure (defined as a decrease in mean arterial blood pressure to 75 mmHg) failed to reverse the hypotension induced by MW heating and consequently did not alter the subsequent survival time. Furthermore, pretreatment with WEB 2086 at either dose did not alter subsequent mean arterial blood pressure, temperature responses to MW heating or survival time. Finally, MW heating did not alter either blood PAF levels or serum or lung PAF acetylhydrolase levels. Taken together, these results demonstrate that PAF does not mediate the hypotension induced by 35-GHz MW heating.

Lack of effect of 94 GHz radio frequency radiation exposure in an animal model of skin carcinogenesis

Although there is no evidence that electromagnetic energy in the radio frequency radiation (RFR) band is mutagenic, there have been suggestions that RFR energy might serve as either a promoter or co-promoter in some animal models of carcinogenesis. Recent developments in electromagnetic technology have resulted in the manufacture of RFR sources capable of generating frequencies in the millimeter wavelength (MMW) range (30-300 GHz). Because absorption of MMW energy occurs in the skin, it is to be expected that long-term detrimental health effects, if any, would most likely be manifest in the skin. In this study we investigated whether a single (1.0 W/cm(2) for 10 s) or repeated (2 exposures/week for 12 weeks, 333 mW/cm(2) for 10 s) exposure to 94 GHz RFR serves as a promoter or co-promoter in the 7,12-dimethylbenz[a]anthracene (DMBA)-induced SENCAR mouse model of skin carcinogenesis. Neither paradigm of MMW exposure significantly affected papilloma development, as evidenced by a lack of effect on tumor incidence and multiplicity. There was also no evidence that MMW exposure served as a co-promoter in DMBA-induced animals repeatedly treated with 12-O-tetradecanoylphorbol 13-acetate. Therefore, we conclude that exposure to 94 GHz RFR under these conditions does not promote or co-promote papilloma development in this animal model of skin carcinogenesis.

Regional distribution of Hsp70 in the CNS of young and old food-restricted rats following hyperthermia

We examined the effect of aging on the capacity of the brain to produce heat shock protein (Hsp70) in response to heat stress, using high-powered microwaves (HPM, 2.06 GHz, 2.2 W/cm(2)) to induce hyperthermia for periods so brief that thermoregulatory factors were functionally eliminated as confounding variables. Unanesthetized young (6 months) and old (25 months) male, food-restricted Sprague-Dawley rats were exposed to HPM to induce a mean peak tympanic temperature (T(ty)) of 42.2 degrees C within 30 s. T(ty) returned to <40.0 degrees C within 6 min post-exposure in both age groups. Rats were euthanized 6 or 24 h later for immunohistochemical determination of Hsp70 accumulation in 10 brain regions. HPM exposure induced significant increases in 7 of the 10 regions. There were no significant differences observed in the pattern or density of Hsp70 accumulation between the young and old rats at 6 h post-HPM exposure, with the exception of the medial vestibular nucleus, which demonstrated significantly greater Hsp70 accumulation in the old rats. There were significant differences between the age groups at 24 h post-exposure, however, there was no general pattern; i.e., depending on the brain region, aged rats displayed significantly greater, lesser, or similar increases in Hsp70 expression compared with young. Taken together, these results demonstrate that the brain of aged, food-restricted rats does not display a loss of capacity to accumulate Hsp70 in response to heat stress.

Nitric oxide does not contribute to the hypotension of heatstroke

The purpose of this study was to determine whether nitric oxide (NO) contributes to the hypotensive state induced by prolonged environmental heat (EH) stress. Ketamine-anesthetized rats were instrumented for the measurement of arterial blood pressure, electrocardiogram, and temperature at four sites. Rats were exposed to EH (ambient temperature, 40 +/- 1 degrees C) until mean arterial blood pressure (MAP) decreased to 75 mmHg, which was arbitrarily defined as the induction of heatstroke. In addition to cardiovascular and temperature measurements, the time required to reach this MAP end point and the subsequent survival time were measured. In three separate experimental series, the competitive NO synthesis inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) was administered (0, 10, or 100 mg/kg) either before, during (30 min after initiation of EH), or immediately after EH. L-NAME administered at any of these times transiently increased MAP. L-NAME infusion either before or during EH did not alter the EH time required to decrease MAP to 75 mmHg, but L-NAME pretreatment did decrease the colonic temperature at which this MAP end point was reached. L-NAME infusion before or after EH did not affect subsequent survival time, but L-NAME administered during EH significantly decreased survival time. The administration of L-NAME at any time point, therefore, did not prove beneficial in either preventing or reversing heatstroke. Taken together, these data suggest that NO does not mediate the hypotension associated with heatstroke.

Repeated exposure of C3H/HeJ mice to ultra-wideband electromagnetic pulses: lack of effects on mammary tumors

It has been suggested that chronic, low-level exposure to radiofrequency (RF) radiation may promote the formation of tumors. Previous studies, however, showed that low-level, long-term exposure of mammary tumor-prone mice to 435 MHz or 2450 MHz RF radiation did not affect the incidence of mammary tumors. In this study, we investigated the effects of exposure to a unique type of electromagnetic energy: pulses composed of an ultra-wideband (UWB) of frequencies, including those in the RF range. One hundred C3H/HeJ mice were exposed to UWB pulses (rise time 176 ps, fall time 3.5 ns, pulse width 1.9 ns, peak E-field 40 kV/m, repetition rate 1 kHz). Each animal was exposed for 2 min once a week for 12 weeks. One hundred mice were used as sham controls. There were no significant differences between groups with respect to incidence of palpated mammary tumors, latency to tumor onset, rate of tumor growth, or animal survival. Histopathological evaluations revealed no significant differences between the two groups in numbers of neoplasms in all tissues studied (lymphoreticular tissue, thymus, respiratory, digestive and urinary tracts, reproductive, mammary and endocrine systems, and skin). Our major finding was the lack of effects of UWB-pulse exposure on promotion of mammary tumors in a well-established animal model of mammary cancer.

Exercise in the heat is limited by a critical internal temperature

We examined whether fatigue during exertional heat stress occurred at a critical internal temperature independent of the initial temperature at the start of exercise. Microwaves (2.1 GHz; 100 mW/cm(2)) were used to rapidly (3-8 min) heat rats before treadmill exercise to exhaustion. In a repeated-measures design, food-restricted male Sprague-Dawley rats (n = 11) were preheated to three levels (low, medium, and high). In addition, two sham exposures, Sham 1 and Sham 2, were administered at the beginning and end of the study, respectively. At the initiation of exercise, hypothalamic (T(hyp)) and rectal (T(rec)) temperatures ranged from 39.0 degrees C to 42.8 degrees C (T(hyp)) and 42.1 degrees C (T(rec)). The treadmill speed was 17 m/min (8 degrees grade), and the ambient temperature during exercise was 35 degrees C. Each treatment was separated by 3 wk. Run time to exhaustion was significantly reduced after preheating. There was a significant negative correlation between run time and initial T(hyp) and T(rec) (r = 0.73 and 0.74, respectively). The temperatures at exhaustion were not significantly different across treatments, with a range of 41.9-42.2 degrees C (T(hyp)) and 42.2-42.5 degrees C (T(rec)). There were no significant differences in run time in the sham runs administered at the start and end of the investigation. No rats died as a result of exposure to any of the treatments, and body weight the day after each treatment was unaffected. These results support the concept that a critical temperature exists that limits exercise in the heat.

Ultra-wideband electromagnetic pulses: lack of effects on heart rate and blood pressure during two-minute exposures of rats

Exposure to fast-rise-time ultra-wideband (UWB) electromagnetic pulses has been postulated to result in effects on biological tissue (including the cardiovascular system). In the current study, 10 anesthetized Sprague-Dawley rats were exposed to pulses produced by a Sandia UWB pulse generator (average values of exposures over three different pulse repetition rates: rise time, 174-218 ps; peak E field, 87-104 kV/m; pulse duration, 0.97-0.99 ns). Exposures to 50, 500 and 1000 pulses/s resulted in no significant changes in heart rate or mean arterial blood pressure measured every 30 s during 2 min of exposure and for 2 min after the exposure. The results suggest that acute UWB whole-body exposure under these conditions does not have an immediate detrimental effect on these cardiovascular system variables in anesthetized rats.

Regional brain heating during microwave exposure (2.06 GHz), warm-water immersion, environmental heating and exercise

Nonuniform heating may result from microwave (MW) irradiation of tissues and is therefore important to investigate in terms of health and safety issues. Hypothalamic (Thyp), cortical (Tctx), tympanic (Tty), and rectal (Tre) temperatures were measured in rats exposed in the far field, k-polarization (i.e., head pointed toward the transmitter horn and E-field in vertical direction) to two power densities of 2.06 GHz irradiation. The high-power density (HPM) was 1700 mW/cm2 [specific absorption rate (SAR): hypothalamus 1224 W/kg; cortex 493 W/kg]; the low-power density (LPM) was 170 mW/cm2 (SAR: hypothalamus 122.4 W/kg; cortex 49.3 W/kg). The increase (rate-of-rise, in degrees C/s) in Thyp was significantly greater than those in Tctx or Tre when rats were exposed to HPM. LPM produced more homogeneous heating. Quantitatively similar results were observed whether rats were implanted with probes in two brain sites or a single probe in one or the other of the two sites. The qualitative difference between regional brain heating was maintained during unrestrained exposure to HPM in the h-polarization (i.e., body parallel to magnetic field). To compare the temperature changes during MW irradiation with those produced by other modalities of heating, rats were immersed in warm water (44 degrees C, WWI); exposed to a warm ambient environment (50 degrees C, WSED); or exercised on a treadmill (17 m/min 8% grade) in a warm ambient environment (35 degrees C, WEX). WWI produced uniform heating in the regions measured. Similar rates-of-rise occurred among regions following WSED or WEX, thus maintaining the pre-existing gradient between Thyp and Tctx These data indicate that HPM produced a 2-2.5-fold difference in the rate-of-heating within brain regions that were separated by only a few millimeters. In contrast, more homogeneous heating was recorded during LPM or nonmicrowave modalities of heating.

Cardiovascular and thermal responses in rats during 94 GHz irradiation

We investigated the thermal distribution and cardiovascular effects produced by sustained exposure of rats to 94 GHz radio-frequency electromagnetic radiation (RFR). Sixteen ketamine-anesthetized Sprague-Dawley rats were exposed individually at a power density of 75 mW/cm2 under far-field conditions in E orientation. Irradiation began when colonic temperature was 37 degrees C and continued until death. Large, immediate increases in subcutaneous temperature on the irradiated side were accompanied by more moderate, delayed increases in colonic temperature. These body-temperature responses were similar to previous results obtained during 35 GHz RFR exposure. During irradiation, arterial blood pressure initially increased and then precipitously decreased until death. The heart rate increased throughout the exposure period. When comparing the results of these 94 GHz exposures with those in previous studies of lower RFR frequencies, it appears that the patterns of heart-rate and blood-pressure changes that occur before death are similar. We conclude that exposure to 94 GHz RFR produces extreme peripheral heating without similar levels of core heating and that this pattern of heat deposition is sufficient to produce circulatory failure and subsequent death.

Cardiovascular and thermal effects of microwave irradiation at 1 and/or 10 GHz in anesthetized rats

Relatively large thermal gradients may exist during exposure of an animal to microwaves (MWs), particularly at high frequencies. Differences in thermal gradients within the body may lead to noticeable differences in the magnitude of cardiovascular changes resulting from MW exposure. This study compares the thermal distribution and cardiovascular effects of exposure to a single MW frequency with effects of simultaneous exposure to two frequencies. Ketamine-anesthetized male Sprague-Dawley rats (n = 58) were exposed individually to one of three conditions: 1-GHz, 10-GHz, or combined 1- and 10-GHz MWs at an equivalent whole-body specific absorption rate of 12 W/kg. The continuous-wave irradiation was conducted under far-field conditions with animals in E orientation (left lateral exposure, long axis parallel to the electric field) or in H orientation (left lateral exposure, long axis perpendicular to the electric field). Irradiation was started when colonic temperature was 37.5 degrees C and was continued until lethal temperatures were attained. Colonic, tympanic, left and right subcutaneous, and tail temperatures, and arterial blood pressure, heart rate, and respiratory rate were continuously recorded. In both E and H orientations, survival time (i.e., time from colonic temperature of 37.5 degrees C until death) was lowest in animals exposed at 1-GHz, intermediate in those exposed at 1- and 10-GHz combined, and greatest in the 10-GHz group (most differences statistically significant). At all sites (with the exception of right subcutaneous), temperature values in the 1- and 10-GHz combined group were between those of the single-frequency exposure groups in both E and H orientations. During irradiation, arterial blood pressure initially increased and then decreased until death. Heart rate increased throughout the exposure period. The general, overall patterns of these changes were similar in all groups. The results indicate that no unusual physiological responses occur during multi-frequency MW exposure, when compared with results of single-frequency exposure. Bioelectromagnetics 21:159-166, 2000. Published 2000 Wiley-Liss, Inc.

Radio frequency radiation of millimeter wave length: potential occupational safety issues relating to surface heating

Currently, technology is being developed that makes use of the millimeter wave (MMW) range (30-300 GHz) of the radio frequency region of the electromagnetic spectrum. As more and more systems come on line and are used in everyday applications, the possibility of inadvertent exposure of personnel to MMWs increases. To date, there has been no published discussion regarding the health effects of MMWs; this review attempts to fill that void. Because of the shallow depth of penetration, the energy and, therefore, heat associated with MMWs will be deposited within the first 1-2 mm of human skin. MMWs have been used in states of the former Soviet Union to provide therapeutic benefit in a number of diverse disease states, including skin disorders, gastric ulcers, heart disease and cancer. Conversely, the possibility exists that hazards might be associated with accidental overexposure to MMWs. This review attempts to critically analyze the likelihood of such acute effects as burn and eye damage, as well as potential long-term effects, including cancer.

Oxidative stress precedes circulatory failure induced by 35-GHz microwave heating

Sustained whole-body exposure of anesthetized rats to 35-GHz radio frequency radiation produces localized hyperthermia and hypotension, leading to circulatory failure and death. The physiological mechanism underlying the induction of circulatory failure by 35-GHz microwave (MW) heating is currently unknown. We hypothesized that oxidative stress may play a role in the pathophysiology of MW-induced circulatory failure and examined this question by probing organs for 3-nitrotyrosine (3-NT), a marker of oxidative stress. Animals exposed to low durations of MW that increased colonic temperature but were insufficient to produce hypotension showed a 5- to 12-fold increase in 3-NT accumulation in lung, liver, and plasma proteins relative to the levels observed in control rats that were not exposed to MW. 3-NT accumulation in rats exposed to MW of sufficient duration to induce circulatory shock returned to low, baseline levels. Leukocytes obtained from peripheral blood showed significant accumulation of 3-NT only at exposure levels associated with circulatory shock. 3-NT was also found in the villus tips and vasculature of intestine and within the distal tubule of the kidney but not in the irradiated skin of rats with MW-induced circulatory failure. The relationship between accumulation in liver, lung, and plasma proteins and exposure duration suggests either that nitro adducts are formed in the first 20 min of exposure and are then cleared or that synthesis of nitro adducts decreases after the first 20 min of exposure. Taken together, these findings suggest that oxidative stress occurs in many organs during MW heating. Because nitration occurs after microwave exposures that are not associated with circulatory collapse, systemic oxidative stress, as evidenced by tissue accumulation of 3-NT, is not correlated with circulatory failure in this model of shock.

Lack of effects on heart rate and blood pressure in ketamine-anesthetized rats briefly exposed to ultra-wideband electromagnetic pulses

Fourteen Sprague-Dawley rats were exposed to pulses produced by a Bournlea ultra-wideband (UWB) pulse generator (rise time, 318-337 ps; maximum E field, 19-21 kV/m). Exposures at a repetition frequency of 1 kHz for 0.5 s or to repetitive pulse trains (2-s exposure periods alternating with 2 s of no exposure, for a total of 2 min) resulted in no significant changes in heart rate or mean arterial blood pressure. These results suggest that acute whole-body exposure to UWB pulses does not have a detrimental effect on the cardiovascular system.

HSP70 expression in the CNS in response to exercise and heat stress in rats

We have previously documented the regional distribution of 70-kDa heat shock protein (HSP70) in brains of rats made hyperthermic by brief exposure to high-powered microwaves (HPM; 2.06 GHz). We now compare HSP70 expression induced by HPM exposure to that induced by exertional and/or environmental heat stress. Rats were chronically implanted with a temperature probe guide in the hypothalamic region of the brain (Tbr). After recovery, the following treatment groups were examined: HPM; sham exposed; treadmill exercise at room temperature (24 degreesC; Ex-1); treadmill exercise in a warm environment (34 degreesC; Ex-2); and sedentary groups (Sed-1 and Sed-2), in which ambient temperature was adjusted so that the Tbr mimicked the Tbr in the corresponding exercise groups. Significant HSP70 expression occurred only in the hyperthermic (Ex-2, Sed-2, and HPM) groups. The pattern of HSP70 expression was similar among Ex-2 and Sed-2 rats but differed from that in HPM rats. We conclude that 1) the pattern of HSP70 expression differs between HPM and nonmicrowave heating, and 2) exercise alone was not sufficient to induce central HSP70 expression.

Arterial baroreflex modulation of heat-induced vasodilation in the rabbit ear

The purpose of this study was to determine whether nonthermal baroreflexes arising from cardiopulmonary and/or arterial baroreceptors modulate rabbit ear blood flow (EBF) during hyperthermia. Intact and sinoaortic-denervated (SAD) rabbits were chronically instrumented with a Doppler ultrasonic flow probe for measurement of EBF velocity (kHz). During whole body heating in conscious rabbits, EBF and ear vascular conductance (EVC) increased as core temperature increased until maximal plateau levels of EBF and EVC were reached. The maximal plateau level of EVC attained during heat stress was lower in SAD than in intact rabbits. Subsequent intrapericardial administration of procaine at maximal EBF blocked cardiac afferents but did not alter EVC in either animal group. In a second experiment, ramp decreases in mean arterial pressure were produced by vena caval occlusion at maximal EBF. In intact rabbits, EBF and EVC decreased linearly as mean arterial pressure fell, but EBF and EVC did not decrease during vena caval occlusion in SAD rabbits. Thus neither pharmacological nor mechanical unloading of cardiac baroreceptors results in reflex vasoconstriction in the heat-stressed rabbit ear. However, baroreflexes arising from arterial baroreceptors may modulate EBF in heat-stressed rabbits.

Administration of a nitric oxide donor does not affect hypotension induced by 35-GHz microwave heating

Sustained whole body exposure to 35-GHz radiofrequency radiation produces localized hyperthermia and hypotension, leading to circulatory failure and death. We previously demonstrated that pressor responses to nitric oxide (NO) synthesis inhibition are reduced following 35-GHz microwave (MMW) heating, implying that NO levels might also be reduced. This study therefore sought to determine whether administration of S-nitroso-N-acetylpenicillamine (SNAP), a NO donor, influences MMW-induced hypotension in ketamine-anesthetized rats. First, rats were exposed to MMW until mean arterial pressure (MAP) fell to 75 mmHg. MMW exposure was then discontinued and either SNAP (300 micrograms/kg/h) or saline was infused. SNAP infusion affected neither the hypotension nor the survival time following MMW exposure. In a second protocol, SNAP (300 micrograms/kg/h) or saline was infused prior to and throughout MMW exposure, which was continued until death. SNAP infusion did not alter either the onset or the magnitude of terminal hypotension. Therefore, we conclude that exogenous NO does not affect cardiovascular responses to 35-GHz MMW heating.

Age does not affect thermal and cardiorespiratory responses to microwave heating in calorically restricted rats

This study sought to determine whether age influences the thermal distribution and cardiorespiratory responses to 35 GHz microwave (MW) heating. Male Sprague-Dawley rats (n = 8/group) 3 to 4 mo old (young), 15 to 16 mo old (middle-aged), and 24 to 25 mo old (old) were used. All animals were restricted to 63% of ad libitum feed. Rats were anesthetized (ketamine) and a catheter was placed into a carotid artery for measurement of mean arterial blood pressure (MAP). Anesthetized rats were then exposed to MWs until death, while measuring MAP, heart rate and temperatures at five sites (colonic, left and right tympanic, subcutaneous, and tail). Before MW exposure, there were no significant (p < .05) differences among age groups in measured parameters. MW produced increases in temperature at each of the measured sites; temperatures at death did not differ between groups. Heart rate increased throughout MW exposure, in a statistically identical manner in all age groups. MAP was initially well maintained and then, in the latter phases of heating, precipitously declined until death, with no discernible age-related difference. Respiration rate was not altered by MW exposure in any group. Finally, there were no group differences in the MW exposure time required to induce death. Thus, age does not alter thermal and cardiorespiratory responses to 35 GHz MW heating in food-restricted rats.

Effects of esmolol on 35 GHz microwave-induced lethal heat stress

1. The purpose of this study was to examine effects of the beta(1)-adrenoreceptor antagonist esmolol (infused at 2 or 4 mg kg-1 body wt min-1) on heart rate, blood pressure, respiratory rate, localized body temperature changes, survival times, and lethal body temperatures that occur during the exposure of anaesthetized rats to 35 GHz microwaves. 2. Forty Sprague-Dawley rats, anaesthetized with ketamine, were exposed to 35 GHz microwaves at a level that resulted in heating and death. During irradiation, a continuous increase in heart rate and a biphasic response in blood pressure (initial increase followed by a decrease) were observed in all groups of animals. 3. Esmolol caused a significant dose-dependent decrease in blood pressure, relative to saline-treated animals, but only a small attenuation of the heat-induced rise in heart rate. In experiments in which esmolol was infused and microwave exposure was continued until death, drug-treated animals survived for significantly shorter periods and died at significantly lower body temperatures. The change in survival may have been related to the lower blood pressure due to esmolol treatment.

Circulatory failure induced by 35 GHz microwave heating: effects of chronic nitric oxide synthesis inhibition

Sustained exposure to radiofrequency radiation of millimeter wave (MMW) length produces hyperthermia and subsequent circulatory failure. This study sought to determine whether this phenomenon is altered by chronic pretreatment with the nitric oxide (NO) synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME). Rats drank either 1) water, 2) water + L-NAME, or 3) water + L-NAME + L-arginine (at 20 and 50 times the dose of L-NAME) for 14 days. Ketamine-anesthetized rats were exposed to MMW until mean arterial blood pressure (MAP) fell to 75 mmHg, at which point MMW exposure was discontinued. MAP initially increased during exposure in all groups; the pressor response in L-NAME-treated rats was greater than that in water-drinking rats. Subsequently, MAP fell in all groups. The MMW exposure time required to reach MAP = 75 mmHg was significantly reduced in L-NAME-treated rats, although survival times (post-MMW) of L-NAME-treated and control rats were not statistically different. Coadministration of L-arginine abolished the enhanced pressor response produced by L-NAME, but did not completely reverse the shortened MMW exposure time in L-NAME-treated rats. Thus, chronic NO synthesis inhibition with L-NAME reduces the ability of rats to withstand 35 GHz microwave heating, suggesting that NO does not mediate the hypotension produced by this form of hyperthermia.

Does nitric oxide mediate circulatory failure induced by 35-GHz microwave heating?

The purpose of this study was to determine whether nitric oxide (NO) contributes to the hypotensive state induced by exposure to radiofrequency radiation of millimeter-wavelength (MMW). This was accomplished using a synthetic analogue of L-arginine, N omega-nitro-L-arginine methyl ester (L-NAME), to competitively inhibit NO synthesis. Ketamine-anesthetized rats were instrumented for the measurement of arterial blood pressure, ECG, and temperature at five sites. Animals were exposed to 35-GHz radiofrequency radiation until mean arterial pressure (MAP) decreased to 75 mmHg. MMW exposure was then halted and either saline or L-NAME (1, 2.5, 5, or 10 mg/kg) was administered; each rat received only one dose. Following irradiation, L-NAME at each dose produced a peak increase in MAP that was smaller than that produced by the same dose of L-NAME in nonirradiated rats. There was no difference in post-MMW survival times between L-NAME-and saline-treated rats. These results indicate that bolus administration of L-NAME does not reverse hypotension induced by 35-GHz microwave heating, suggesting that excess levels of NO do not mediate this form of circulatory failure.

Angiotensin II modulates arterial baroreflex function via a central alpha 1-adrenoceptor mechanism in rabbits

To test the hypothesis that angiotensin II (ANG II) modulates arterial baroreflex function via a central alpha 1-adrenoceptor mechanism, we examined the effects of intravertebral infusion of ANG II on baroreflex function curves before and after intravertebral administration of the alpha 1-adrenoreceptor antagonist prazosin. Rabbits were chronically instrumented with subclavian and vertebral arterial catheters, venous catheters, and aortic and vena caval occludes. Baroreflex curves were obtained by relating heart rate (HR) to mean arterial pressure during increases and decreases in arterial pressure. Intravertebral infusions of ANG II (5, 10, and 20 ng.kg-1.min-1) produced a dose-dependent shift of the midrange of the curve toward higher pressures (64 +/- 1 to 68 +/- 1, 76 +/- 1, and 85 +/- 2 mmHg, respectively). Pretreatment with prazosin (10 micrograms/kg) via the vertebral artery markedly reduced the shift in the baroreflex curve induced by the highest dose of ANG II (64 +/- 2 to 70 +/- 2 mmHg). These data suggest that ANG II resets the operating point of the HR baroreflex curve to a higher blood pressure and that this effect is mediated via a central alpha 1 mechanism. When the effects of vertebral ANG II on the baroreflex control of renal sympathetic nerve activity (RSNA) were examined, intravertebral administration of ANG II, while reducing the gain and the maximum RSNA, did not reset the RSNA baroreflex curve. These data suggest that ANG II acutely resets the HR baroreflex but not the RSNA baroreflex and that the resetting involves an alpha 1-adrenergic mechanism.

Sustained 35-GHz radiofrequency irradiation induces circulatory failure

The objective of this study was to determine the thermal distribution and concomitant cardiovascular changes produced by whole-body exposure of ketamine-anesthetized rats to radiofrequency radiation of millimeter wave (MMW) length. Rats (n = 13) were implanted with a flow probe on the superior mesenteric artery and with a catheter in the carotid artery for the measurement of arterial blood pressure. Temperature was measured at five sites: left (Tsl) and right subcutaneous (sides toward and away From the MMW source, respectively), colonic (Tc), tympanic, and tail. The animals were exposed until death to MMW (35 GHz) at a power density that resulted in a whole-body specific absorption rate of 13 W/kg. During irradiation, the Tsl increase was significantly greater than the Tc increase. Heart rate increased throughout irradiation. Mean arterial pressure (MAP) as well maintained until Tsl reached 42 degrees C, at which point MAP declined until death. Mesenteric vascular resistance tended to increase during the early stages of irradiation but began to decrease at Tsl > or = 41 degrees C. The declines in both mesenteric vascular resistance and MAP began at Tc < 37.5 degrees C; death occurred at Tc = 40.3 +/- .3 degrees C and Tsl = 48.0 +/- .4 degrees C. These data indicate that circulatory failure and subsequent death may occur when skin temperature is rapidly elevated, even in the presence of relatively normal Tc.

Chronic administration of L-NAME in drinking water alters working memory in rats

To examine the role of nitric oxide (NO) in the maintenance of working memory of rats, the effects of chronic administration (in drinking water) of the NO synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME), on this behavior was examined with a simple test of remembering recently explored objects. Unlike other working memory tasks that require a subject to perform for a reward such as food or water or to avoid shock, our task measured spontaneous exploration of novel and familiar objects and has been described as a "pure" working memory task [9]. Normal subjects spend significantly more time in contact with new environmental components and less time with familiar objects. A subject that extensively reexplores a stimulus with which it has previous experience is presumed to exhibit some memory loss associated with the object. Memory changes were evaluated by measuring the relative time subjects explored familiar versus new stimulus objects. Rats (n = 15) that chronically drank L-NAME (approximately 90 mg/kg/day) for 14 days spent significantly less time exploring a novel object than did rats (n = 13) that drank only tap water (p < .05). This effect of L-NAME was abolished by concurrent administration of L-Arginine (approximately 4.5 g/kg/day). Total object exploration was not affected by our drug treatments, suggesting that our object discrimination task is not activity dependent. These data are consistent with the hypothesis that NO is required for some forms of working memory.

Effects of compartmental fluid repletion on heat-induced limb vasodilation in dehydrated baboons

Dehydration attenuates the increase in hindlimb blood flow produced by environmental heating (EH) in baboons. This study explored whether intravascular volume repletion alone was sufficient to remove this dehydration-induced attenuation. In six unanesthetized, chronically instrumented baboons, the increases in hindlimb blood flow during EH were measured under these conditions: euhydrated, dehydrated (64-68 h of water deprivation) without fluid replenishment, and dehydrated with intravenous fluid replenishment by either 6% high-molecular-weight dextran solution (to replenish vascular volume) or hyperosmotic saline (to replenish vascular and interstitial fluid volumes). EH consisted of acute exposure to ambient temperatures of 38-42 degrees C until core temperature (Tc) reached 39.5 degrees C. During dehydration without fluid replenishment the increments in mean iliac artery blood flow (MIBF) and iliac vascular conductance (IVC) produced by EH (i.e., value at Tc = 39.5 degrees C - pre-EH value) were reduced by 39 and 44%, respectively. After infusion of a volume of dextran solution equal to blood volume lost during dehydration, the increment in MIBF during EH was partially restored to the euhydrated level, but the increment in IVC remained at the dehydrated level. Infusion of hyperosmotic saline during dehydration completely restored the increases in MIBF and IVC during EH to euhydrated levels. Thus restoration of normal blood volume alone in dehydrated baboons does not completely restore normal hindlimb vasodilation during EH.

Effect of water or saline intake on heat-induced limb vasodilation in dehydrated baboons

Dehydration markedly attenuates the increase in hindlimb blood flow elicited by environmental heating (EH) in baboons. This study sought to determine the importance of gradually produced increases in body fluid osmolality and decreases in body fluid volume in producing this attenuation. The hindlimb blood flow increases during EH of seven unanesthetized chronically instrumented baboons were examined during euhydration, dehydration (64-68 h of water deprivation), and after ad libitum oral rehydration with either water or a hyperosmotic saline solution. EH consisted of acute exposure to ambient temperatures of 38-42 degrees C until internal temperature reached 39.5 degrees C. Dehydration depressed the maximal external iliac artery blood flow (MIBF) and iliac vascular conductance (IVC) attained during EH in the euhydrated state by 37 and 43%, respectively. Rehydration with either water or saline solution, however, restored maximal MIBF and IVC to euhydrated levels. Because plasma osmolality remained at dehydrated levels after rehydration with saline, hyperosmolality does not produce the dehydration-induced attenuation in hindlimb blood flow.

Vasopressin contributes to maintenance of arterial blood pressure in dehydrated baboons

This study primarily sought to determine whether the role of vasopressin (VP) in maintenance of arterial blood pressure is enhanced in awake, chronically instrumented baboons after 68-72 h of dehydration. This question was approached by pharmacologically blocking vasopressin V1-receptors in euhydrated and dehydrated baboons with or without a normally functioning renin-angiotensin system (RAS). VP blockade during dehydration produced a rapidly occurring (within 5 min), statistically significant (P less than 0.05) decrease in mean arterial pressure (MAP) of 5 +/- 1 mmHg in the RAS-intact condition and an identical decline in MAP (5 +/- 1 mmHg) during blockade of the RAS by captopril, an angiotensin I-converting enzyme inhibitor. At 15 min after induction of VP blockade, heart rate was elevated by 9 +/- 2 beats/min in the RAS-intact condition and by 20 +/- 5 beats/min in the RAS-blocked condition. In addition, VP blockade in the dehydrated state produced small and equal increases in hindlimb vascular conductance in RAS-intact and RAS-blocked conditions. None of these cardiovascular changes were produced by VP blockade in the euhydrated state. RAS blockade produced modest declines in MAP in both hydration states, but the fall was larger by 7 +/- 4 mmHg in the dehydrated state. Thus both VP and the RAS contribute to the maintenance of arterial blood pressure during dehydration in the conscious baboon.

Perfusion scan findings understate the severity of angiographic and hemodynamic compromise in chronic thromboembolic pulmonary hypertension

Major vessel chronic thromboembolic pulmonary hypertension is potentially remediable by thromboendarterectomy. The diagnosis often has been delayed because a lung perfusion scan demonstrated modest defects thought to be incompatible with severe vascular obstruction. To define the relationships between perfusion scan abnormalities, angiographic findings, and hemodynamic data, we analyzed 25 consecutive patients with chronic major vessel thromboembolic pulmonary hypertension who subsequently underwent thromboendarterectomy. We found that the perfusion lung scan consistently caused us to underestimate the severity of pulmonary arterial obstruction as defined by pulmonary angiography. Furthermore, there was no significant correlation between the severity of hemodynamic compromise and the extent of obstruction defined by perfusion scan or angiogram. These findings suggest that, when pulmonary hypertension is known or suspected, the diagnosis of correctable, chronic major vessel obstruction should be pursued by angiography and hemodynamic assessment even though the perfusion scan may demonstrate only two segmental defects.