Interprofessional Simulation Learning Game Increases Socialization and Teamwork Among Students of Health Professions Programs

BACKGROUND

Interprofessional (IP) socialization is important to develop early in the training of health professions students.

PURPOSE

This study compared changes in health professions students' IP socialization and readiness to function in IP teams and sought to understand students' participation experiences using a simulation learning game ( Friday Night at the ER [FNER]).

METHODS

The single-center study targeted students in 13 health professions programs using a mixed-methods design. Student teams engaged in open discussion, played the game, and participated in team debriefing.

RESULTS

IP socialization increased from fairly great to great extent among all students. Qualitative analyses revealed 3 overarching themes supporting the development of IP communication and systems-based thinking. Program evaluation data revealed that students highly valued this experience as being effective and important to their professional development.

CONCLUSIONS

An IP experience consisting of FNER gameplay and structured debriefing can improve IP socialization and lay the foundation for the development of IP skills among early health professions students.

Utilizing an Ecomap to Visualize the Impact of Social Determinants of Health in an Interprofessional Forum

INTRODUCTION

Graphical representations of a case study can help learners recognize how systems and institutions impact health. The impact of the social determinants of health (SDoH) on individual and community health is well established, yet it may be challenging for students to visualize the impact of these components within a case study.

PURPOSE

This study explored the use of ecomaps in an interprofessional forum and examined the perceptions from students and faculty regarding use of this educational tool.

METHODS

This tool was assessed over two semesters, Fall 2021 (n=968) and Fall 2022 (n= 835) to evaluate student and faculty perceptions of the use of the tool along with faculty's assessment of student completion of the tool within a rubric.

RESULTS

Nearly all students (99%) came prepared to the forum and presented their ecomaps to others during the small group discussion to facilitate conversation as they explored the role of SDoH related to the case study. Both students and faculty rated the use of this tool favorably.

DISCUSSION

In conclusion, ecomaps were viewed favorably by both students and faculty. This visual exploration of SDoH helps students to visualize both positive and negative factors that impact a patient's experience.

Virtual escape room paired with simulation improves health professions students' readiness to function in interprofessional teams

BACKGROUND

This project investigated the change in nursing, pharmacy, and physical therapy students' interprofessional socialization after participation in a virtual interprofessional escape room and case conference simulation.

INTERPROFESSIONAL EDUCATION ACTIVITY

Interprofessional teams of nursing (n = 93), pharmacy (n = 75) and physical therapy (n = 33) students completed asynchronous, online learning (sepsis recognition and total hip replacement post-operative precautions) followed by a virtual escape room and a virtual simulated patient case conference. During the case conference, interprofessional student teams developed a discharge plan for an individual after a hip replacement complicated by post-operative sepsis. Before and after the experience, students completed a knowledge test and a validated survey instrument that assessed their interprofessional socialization (Interprofessional Socialization and Valuing Scale-21). During the simulated patient case conference, faculty assessed student performance using a standardized rubric. After the experience students completed a program evaluation.

DISCUSSION

Interprofessional socialization significantly increased (5.5 ± 0.9 vs. 6.0 ± 0.9) among all students with a medium effect size (Cohen's d = 0.56). Faculty assessment of individual student's team performance during the virtual simulation revealed a moderate rate meeting competency, with good interrater reliability. Students highly valued this learning experience as being both effective and important to their professional development, as indicated on the program evaluation.

IMPLICATIONS

A virtual interprofessional experience consisting of asynchronous online learning, a virtual escape room, and a virtual case conference positively influenced students' interprofessional socialization. Students valued the experience and recognized its importance in their development as student health professionals.

Validation of the Interprofessional Collaborative Competency Attainment Survey (ICCAS) retrospective pre-test measures

Establishing the effectiveness of IPE experiences is essential, and current assessment measures may be subject to various types of bias. The Interprofessional Collaborative Competency Attainment Survey (ICCAS) is administered after the learning experience as retrospective pretest and posttest measures of perceived collaborative practice skills. Because the ICCAS does not have an actual pretest, there are potential risks of recall bias and social desirability bias. To address these concerns, Jackson (2017) proposed conducting a true ICCAS pretest before the learning experience and examining the differences between the true and retrospective pretest scores and the differences between these pretest and posttest scores. This study design was implemented for two in-person Interprofessional forums conducted in the Fall (N = 745) and following Spring (N = 599) semesters. Students from 11 (Fall) and 12 (Spring) health professions education programs were included. True ICCAS pretest scores did not significantly differ from the retrospective pretest scores in either sample, although the effect sizes for pretest to posttest gains were slightly smaller for the true pretest scores. These results support and provide confidence for using the standard ICCAS administration methodology by demonstrating the administration methodology is not adversely impacted by recall or social desirability biases.

An Interprofessional Escape Room Experience to Improve Knowledge and Collaboration Among Health Professions Students

Objective. The purpose of this study was to extend our understanding of escape room pedagogical design by investigating the impact of escape room puzzle content on changes in students' immediate recall knowledge and demonstration of interprofessional skills during a subsequent simulation.Methods. Students from nursing, pharmacy, and physical therapy programs were randomized to complete an escape room themed around acute management of sepsis (intervention group; n=133) or general acute care (control group; n=129) prior to participating in a simulated patient discharge case conference. Students completed a knowledge assessment before the escape room, immediately after the escape room, and immediately after the simulation. Additionally, students completed the Interprofessional Socialization and Valuing Scale (ISVS-21) before and after the experience along with a post-program evaluation. Faculty rated student achievement of interprofessional learning objectives during the simulation using a standardized rubric.Results. Students in the intervention group had higher scores on the knowledge test administered immediately after the escape room. All participants' ISVS-21 scores increased from before to after the activity. Interprofessional learning objectives, as evaluated by faculty, were met by 248 (94.7%) students.Conclusion. Participating in an interprofessional escape room activity with specific puzzle content improved students' immediate recall knowledge. In both groups, self-assessed interprofessional socialization improved, and a high percentage of students achieved the interprofessional learning objectives in a subsequent simulation. Escape rooms can be an innovative pedagogical tool that can positively impact immediate recall knowledge and interprofessional collaborative skills of health professions students.

Evaluating the impact of interprofessional forums on dental medicine students' collaborative practice skill perception

PURPOSE

This study evaluates third-year dental medicine students' perceived competencies related to interprofessional collaborative practice (IPCP) after completing two exposure level experiences with students from other professions across a large academic health center.

METHODS

Two cohorts of D3 dental medicine students (2018-2019 and 2019-2020) completed the Interprofessional Collaborative Competencies Attainment Survey (ICCAS) after participating in in-person 2.5-h Interprofessional (IP) Forums in the Fall and Spring semesters. Self-reported competencies were compared between pre-and post-IP Forum ratings and between Fall and Spring.

RESULTS

Prior to the IP Forums, dental medicine students (n = 185) reported perceived skill in the interprofessional competencies to be from Good to Very Good using the ICCAS. After participation in the Fall IP Forum, students' ICCAS scores increased in all ICCAS subscales with large effect sizes. Students reported a perceived decline in these skills in the four months between Fall and Spring IP Forums and restoration of IP skill levels after participating in a second IP Forum (Spring).

CONCLUSIONS

Participation in IP Forums has a positive impact on students' IPCP skill perception. Our data suggest that perceived skill level requires repeated IP learning experiences. If dental medicine students are expected to embrace collaborative practice to enhance patient outcomes, then dental school educators must provide opportunities for students to engage in collaborative practice experiences at all levels of their training.

Assessing the assessment: a comparison of the IPASS and ICCAS to measure change in interprofessional competencies following a large-scale interprofessional forum

Measuring the effectiveness of interprofessional education (IPE) experiences is essential but challenging. Surveying learners before (pretest) and after (posttest) an IPE experience may result in minimal change due to response shift bias. Retrospective pretest/posttest assessment may ameliorate response shift bias but may also result in inflated change scores due to social desirability bias. We studied a cohort of 675 students from 12 health professions who completed the Interprofessional Attitudes Scale (IPAS) within the 4 weeks before (pretest) and the 3 weeks after (posttest) an IPE forum and completed the Interprofessional Collaborative Competency Attainment Survey (ICCAS) within the 3 weeks after the forum as a retrospective pretest/posttest. We found higher scores on the pretest IPAS than the retrospective pretest ICCAS and greater change in scores on the ICCAS than the IPAS, indicating potential response shift and social desirability biases. Furthermore, we found few significant correlations between change scores in subscales of the two tests, but a high number of strong and significant correlation among the ICCAS subscale change scores. Our results indicate the timing of pretest administration may impact change scores or that subscales of IPAS may be more unique than those of ICCAS. These findings suggest that educators should consider the potential impact of response shift and social desirability biases when interpreting results of the IPAS and ICCAS in response to an IPE learning experience.

COVID-19 and Post-intensive Care Syndrome: Community-Based Care for ICU Survivors

Survivors of critical illness, including those with COVID-19, are likely to experience post-intensive care syndrome (PICS). PICS involves a constellation of physical, cognitive, and mental health problems that can occur following hospitalization in an intensive care unit (ICU). This focused review describes the impact of PICS on an individual’s function, societal participation, and family. Specific evidence-based screening tools for in-home identification of the deficits associated with PICS are recommended. Recognition of PICS through early screening by home health care providers is crucial in order to assemble the physical rehabilitation, mental health, and community resources needed to mitigate the long-term effects of COVID-19 and other critical illnesses. This review concludes with further PICS resources for community-based providers to enhance their knowledge and expertise and to prepare them for caring for COVID-19 and other critical illness survivors.

Home and Community-Based Physical Therapist Management of Adults With Post-Intensive Care Syndrome

More than 4 million adults survive a stay in the intensive care unit each year, with many experiencing new or worsening physical disability, mental health problems, and/or cognitive impairments, known as post-intensive care syndrome (PICS). Given the prevalence and magnitude of physical impairments after critical illness, many survivors, including those recovering from COVID-19, could benefit from physical therapist services after hospital discharge. However, due to the relatively recent recognition and characterization of PICS, there may be limited awareness and understanding of PICS among physical therapists practicing in home health care and community-based settings. This lack of awareness may lead to inappropriate and/or inadequate rehabilitation service provision. While this perspective article provides information relevant to all physical therapists, it is aimed toward those providing rehabilitation services outside of the acute and postacute inpatient settings. This article reports the prevalence and clinical presentation of PICS and provides recommendations for physical examination and outcomes measures, plan of care, and intervention strategies. The importance of providing patient and family education, coordinating community resources including referring to other health care team members, and community-based rehabilitation service options is emphasized. Finally, this perspective article discusses current challenges for optimizing outcomes for people with PICS and suggests future directions for research and practice.

Creating a Film to Teach Health Professions Students the Importance of Interprofessional Collaboration

Objective. To produce, implement, and evaluate the effectiveness of a film to develop the foundational knowledge and skills of health professions students and teach them the importance of interprofessional collaboration. Methods. An existing interprofessional case study about a Hispanic man suffering from multiple chronic health conditions and the impact his health had on his family served as the basis for the film. To ensure a high-quality production, faculty members partnered with a local theatre company to produce the film. Upon completion, the film was integrated into an annual interprofessional forum and evaluated by both students and faculty members in 2016, 2017, and 2018. Results. The 22-minute film, entitled Meet Fred Santiago: Improving Care Through Interprofessional Collaboration, was shown to 1921 students and 250 faculty members who participated in the interprofessional forum over the three years. Of these, 1858 students and 174 faculty members completed a program evaluation following the forum. The majority (>86%) of student and faculty respondents agreed or strongly agreed that the film presented a realistic view of the challenges faced by people with multiple chronic health problems. The majority of students (>85%) agreed or strongly agreed that the film helped them appreciate the breadth of issues confronting individuals with multiple chronic health problems. Conclusion. The film, Meet Fred Santiago, is an effective tool for introducing health professions students to the complex interrelationship of medical, psychological, and social issues experienced by individuals with chronic health conditions.

Training the trainers: A preceptor development program targeting interprofessional collaboration competencies

INTRODUCTION

Faculty and preceptor development have been noted to be areas of need within the expansion of interprofessional education (IPE). The primary objective of this pilot study was to evaluate the impact of a preceptor development program on pharmacy preceptors' self-reported competence toward interprofessional collaboration.

METHODS

Pharmacy preceptors were invited to participate in a two-hour preceptor development program followed by a brief survey. Preceptor development program objectives were to: define IPE and interprofessional collaborative practice (IPCP); describe the benefits of IPCP for patients/clients, healthcare providers, and health systems; discuss the four Interprofessional Education Collaborative (IPEC) Core Competencies; and describe IPE student experiences aimed at increasing collaborative practice. The Interprofessional Collaborative Competencies Attainment Survey (ICCAS) was administered after the preceptor development program. Descriptive statistics were used to characterize the data and paired t-tests were used to analyze pre-/post-program scores.

RESULTS

Thirty (35%) preceptors completed the survey. Mean scores for all twenty items in the ICCAS instrument increased from pre- to post-(p < 0.05). The mean total ICCAS score pre- was 5.28 ± 1.12 and post- was 6.17 ± 1.11 (p < 0.01) out of a possible total score of seven.

CONCLUSIONS

A preceptor development program targeting IPE and IPCP increased pharmacy preceptors' self-reported competence toward interprofessional collaboration.

Improving Pharmacy Students' Attitudes Toward Collaborative Practice Through a Large-scale Interprofessional Forum Targeting Opioid Dependence

Objective. To evaluate the impact of a large-scale interprofessional forum on pharmacy students' attitudes toward interprofessional collaborative practice. Methods. Pharmacy students were asked to complete the Interprofessional Attitudes Scale (IPAS) prior to and after completing a three-hour interprofessional forum. Scores for the total IPAS and each of the subscales were computed using the mean of students' responses to the items for each. Results. Of the 133 pharmacy students who participated in the forum, there were valid pre- and post-intervention matched IPAS data for 124 (93.2%). In general, prior to the forum, students reported positive attitudes toward interprofessional collaborative practice as demonstrated by mean scores greater than 4.0 (agree) on the total IPAS scale and on all of the IPAS subscales except the Interprofessional Biases subscale). There was a significant increase from pre- to post-intervention scores on all the subscales except Patient-Centeredness. Based on the Cohen d measure of effect size, the greatest changes were in the Teamwork, Roles and Responsibilities and Community-Centeredness subscales, followed by the Interprofessional Biases subscale and Diversity and Ethics subscale. Conclusion. Prior to participating in an interprofessional student forum, pharmacy students generally had positive attitudes toward interprofessional collaborative practice. After participating in the forum, these attitudes become even more positive. Interprofessional education interventions, such as the forum, play an important role in shaping student's attitudes toward interprofessional collaboration.

Physical Impairments Associated With Post-Intensive Care Syndrome: Systematic Review Based on the World Health Organization's International Classification of Functioning, Disability and Health Framework

BACKGROUND

Post-intensive care syndrome (PICS) is a constellation of new or worsening impairments in physical, mental, or cognitive abilities or a combination of these in individuals who have survived critical illness requiring intensive care.

PURPOSE

The 2 purposes of this systematic review were to identify the scope and magnitude of physical problems associated with PICS during the first year after critical illness and to use the World Health Organization's International Classification of Functioning, Disability and Health (ICF) framework to elucidate impairments of body functions and structures, activity limitations, and participation restrictions associated with PICS.

DATA SOURCES

Ovid MEDLINE, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials (CENTRAL), PubMed, CINAHL Plus with Full Text (EBSCO), Web of Science, and Embase were searched from inception until March 7, 2017.

STUDY SELECTION

Two reviewers screened titles, abstracts, and full text to independently determine study eligibility based on inclusion and exclusion criteria.

DATA EXTRACTION

Study methodological quality was assessed using the Newcastle-Ottawa Scale. Data describing study methods, design, and participant outcomes were extracted.

DATA SYNTHESIS

Fifteen studies were eligible for review. Within the first year following critical illness, people who had received intensive care experienced impairments in all 3 domains of the ICF (body functions and structures, activity limitations, and participation restrictions). These impairments included decreased pulmonary function, reduced strength of respiratory and limb muscles, reduced 6-minute walk test distance, reduced ability to perform activities of daily living and instrumental activities of daily living, and reduced ability to return to driving and paid employment.

LIMITATIONS

The inclusion of only 15 observational studies in this review may limit the generalizability of the findings.

CONCLUSIONS

During the first year following critical illness, individuals with PICS experienced physical impairments in all 3 domains of the ICF.

Teaching evidence-based practice principles to prepare health professions students for an interprofessional learning experience

OBJECTIVE

The research assessed online learning modules designed to teach health professions students evidence-based practice (EBP) principles in an interprofessional context across two institutions.

METHODS

Students from nine health professions at two institutions were recruited to participate in this pilot project consisting of two online learning modules designed to prepare students for an in-person case-based interprofessional activity. Librarians and an instructional designer created two EBP modules. Students' competence in EBP was assessed before and after the modules as well as after the in-person activity. Students evaluated the online learning modules and their impact on the students' learning after the in-person session.

RESULTS

A total of 39 students from 8 health professions programs participated in the project. Average quiz scores for online EBP module 1 and module 2 were 83% and 76%, respectively. Following completion of the learning modules, adapted Fresno test of competence in EBP scores increased (p=0.001), indicating that the modules improved EBP skill competence. Student evaluations of the learning modules were positive. Students indicated that they acquired new information skills that contributed to their ability to develop a patient care plan and that they would use these information skills in their future clinical practice.

CONCLUSIONS

Online EBP learning modules were effective in developing EBP knowledge and skills for health professions students. Using the same modules ensured that students from different health professions at different stages of their professional programs had consistent knowledge and enabled each student to fully engage in an interprofessional evidence-based activity. Student feedback indicated the modules were valued and beneficial.

Impairments, activity limitations and participation restrictions experienced in the first year following a critical illness: protocol for a systematic review

INTRODUCTION

Critical illness requiring intensive care unit (ICU) management is a life-altering event with ∼25% of ICU survivors experiencing persistent reductions in physical functioning, impairments in mental health, cognitive dysfunction and decreased quality of life. This constellation of problems is known as 'postintensive care syndrome' (PICS) and may persist for months and/or years. The purpose of this systematic review is to identify the scope and magnitude of physical problems associated with PICS during the first year after discharge from ICU, using the International Classification of Functioning, Disability and Health framework to elucidate the impairments of body functions and structures, activity limitations and participation restrictions.

METHODS AND ANALYSIS

Medline (Ovid), Cochrane Database of Systematic Reviews (Ovid), Cochrane Central Register of Controlled Trials (Ovid), PubMed, CINAHL (EBSCO), Web of Science and EMBASE will be systematically searched for observational studies reporting the physical impairments of body functions and structures, activity limitations and participation restrictions associated with PICS. Two reviewers will assess the articles for eligibility according to prespecified selection criteria, after which an independent reviewer will perform data extraction which will be validated by a second independent reviewer. Quality appraisal will be performed by two independent reviewers. Outcomes of the included studies will be summarised in tables and in narrative format and meta-analyses will be conducted where appropriate.

ETHICS AND DISSEMINATION

Formal ethical approval is not required as no primary data is collected. This systematic review will identify the scope and magnitude of physical problems associated with PICS during the first year after discharge from ICU and will be disseminated through a peer-reviewed publication and at conference meetings, to inform practice and future research on the physical problems associated with PICS.

TRIAL REGISTRATION NUMBER

CRD42015023520.

Integrating public health and allied health education through a core curriculum: an action research approach

This paper describes the use of an action research model to effect curricular change--specifically, to develop a core curriculum that prepares public health and health professions students to meet emerging needs in today's health care environment. The action research process is based on a series of steps wherein the problem is identified, data are collected and interpreted, action is taken, and action is reflected upon. These steps are then repeated. Consensus building proceeds as participants engage in continual analysis and implementation of changes, followed by more analysis. This process led to the emergence of three core content focus areas: Population, Wellness and Disability; Evidence-Based Practice; and Communication and Professionalism. "Focus Area Working Groups" were established to further delineate each content area. These groups initially developed 62 learning objectives across the three focus areas. Those objectives were subsequently distilled and refined, resulting in 25 "Core Essentials" that now define the core curriculum and serve as content guides rather than prescriptive learning objectives. The action research model proved to be beneficial in helping faculty from diverse health disciplines build consensus as they identified common professional and interprofessional learning needs.

Tissue inhibitor of metalloproteinase-1 modulates allergic lung inflammation in murine asthma

Matrix metalloproteinases (MMPs) modulate development, inflammation, and repair in lungs. Tissue inhibitors of MMPs (TIMPs) interact with MMPs, controlling the intensity and nature of the response to injury. Absence of MMP-9, -2, and -8 activities is associated with altered lung inflammation during allergic sensitization. To test the hypothesis that the absence of TIMP-1 enhances allergic lung inflammation, airway hyperreactivity (AHR), and lung remodeling in asthma, we studied TIMP-1 null (TIMP-1 KO) mice and their WT controls using an ovalbumin (OVA) asthma model. TIMP-1 KO mice, compared to WT controls, developed an asthma phenotype characterized by AHR, pronounced cellular lung infiltrates, greater reduction in lung compliance, enhanced Th2 cytokine mRNA and protein expression, and altered collagen lung content associated with enhanced MMP-9 activity. Our findings support the hypothesis that TIMP-1 plays a protective role by preventing AHR and modulating inflammation, remodeling, and cytokine expression in an animal model of asthma.

Physiologic evidence for high-frequency chest wall oscillation and positive expiratory pressure breathing in hospitalized subjects with cystic fibrosis

BACKGROUND AND PURPOSE

This investigation identified ventilation distribution, gas mixing, lung function, and arterial blood oxyhemoglobin saturation (SpO2) physiologic responses to 2 independent airway clearance treatments, high-frequency chest wall oscillation (HFCWO) and low positive expiratory pressure (PEP) breathing, for subjects who had cystic fibrosis (CF) and who were hospitalized during acute and subacute phases of a pulmonary exacerbation.

SUBJECTS

Fifteen subjects with moderate to severe CF were included in this study.

METHODS

Subjects performed single-breath inert gas tests and spirometry before and immediately after HFCWO and PEP breathing at admission and discharge. Arterial blood oxyhemoglobin saturation was monitored throughout each treatment.

RESULTS

At admission and discharge, PEP breathing increased SpO2 during treatment, whereas HFCWO decreased SpO2 during treatment. Ventilation distribution, gas mixing, and lung function improved after HFCWO or PEP breathing.

DISCUSSION AND CONCLUSION

High-frequency chest wall oscillation and PEP breathing are similarly efficacious in improving ventilation distribution, gas mixing, and pulmonary function in hospitalized people with CF. Because SpO2 decreases during HFCWO, people who have moderate to severe CF and who use HFCWO should have SpO2 monitored during an acute exacerbation.

Physiologic evidence for the efficacy of positive expiratory pressure as an airway clearance technique in patients with cystic fibrosis

BACKGROUND AND PURPOSE

Individuals with cystic fibrosis (CF) have large amounts of infected mucus in their lungs, which causes irreversible lung tissue damage. Although patient-administered positive expiratory pressure (PEP) breathing has been promoted as an effective therapeutic modality for removing mucus and improving ventilation distribution in these patients, the effects of PEP on ventilation distribution and gas mixing have not been documented. Therefore, this preliminary investigation described responses in distribution of ventilation and gas mixing to PEP breathing for patients with moderate to severe CF lung disease.

SUBJECTS AND METHODS

The effects of PEP breathing on ventilation distribution, gas mixing, lung volumes, expiratory airflow, percentage of arterial blood oxyhemoglobin saturation (SpO(2)), and sputum volume were studied in 5 patients with CF (mean age=18 years, SD=4, range=13-22) after no-PEP, low-PEP (10-20 cm H(2)O), and high-PEP (>20 cm H(2)O) breathing conditions. Single-breath inert gas studies and lung function tests were performed before, immediately after, and 45 minutes after intervention. Single-breath tests assess ventilation distribution homogeneity and gas mixing by observing the extent to which an inspired test gas mixes with gas already residing in the lung.

RESULTS

Improvements in gas mixing were observed in all PEP conditions. By 45 minutes after intervention, the no-PEP group improved by 5%, the low-PEP group improved by 15%, and the high-PEP group improved by 23%. Slow vital capacity increased by 1% for no PEP, by 9% for low PEP, and by 13% for high PEP 45 minutes after intervention. Residual volume decreased by 13% after no PEP, by 20% after low PEP, and by 30% after high PEP. Immediate improvements in forced expiratory flow during the middle half of the forced vital capacity maneuver (FEF(25%-75%)) were sustained following high PEP but not following low PEP.

DISCUSSION AND CONCLUSION

This study demonstrated the physiologic basis for the efficacy of PEP therapy. The results confirm that low PEP and high PEP improve gas mixing in individuals with CF, and these improvements were associated with increased lung function, sputum expectoration, and SpO(2). The authors propose that improvements in gas mixing may lead to increases in oxygenation and thus functional exercise capacity.

Pulmonary pathologies in pallid mice result from nonhematopoietic defects

Several single gene pigment mutants of inbred C57BL/6J mice display a triad of subcellular granule-associated defects: oculocutaneous pigment dilution, prolonged bleeding due to defects in platelet dense granules, and abnormal lysosomes. These features also characterize Hermansky-Pudlak Syndrome (HPS), making these mice relevant animal models for HPS. Mice of one mutant strain, pallid, in addition to the hallmark triad of signs, also exhibit age-dependent lung pathology. Respiratory system mechanics showed that the age-dependent histopathology of pallid mice was accompanied by a decrease in lung reactance. Furthermore, the possibility that pallid pulmonary pathology may result from persistent inflammation due to microhemorrhage owing to the platelet defect was examined. Hematopoietic reconstitution of pallid mice with marrow from normal C57BL/6J donors did not prevent the development of the pulmonary histopathology or respiratory system mechanics characteristic of the pallid genotype. Similarly, wild-type mice 12 months after engraftment with pallid marrow did not develop pallid-like pulmonary histopathology or respiratory system mechanics. Thus, pallid-associated pulmonary functional and structural pathologies are not linked to the marrow (bleeding) genotype, but instead are the result of an age-dependent process resulting from a defect(s) in one or more nonhematopoietic cell types.

Relationships between the anxiety sensitivity index, the suffocation fear scale, and responses to CO2 inhalation

Interest in documenting ways to predict anxious responding in panic disorder (PD) patients has proliferated recently in the literature. In the current study, two self-report measures were assessed to determine their relative utility in predicting responses to a panicogenic challenge. The Anxiety Sensitivity Index (ASI) and the Suffocation Fear Scale (SFS) were evaluated by correlating scores on these measures with reactions to inhalation of 35% carbon dioxide (CO2), assessed via anxiety ratings, panic symptom intensity, tidal volume (VT) and respiratory rate (RR). A sample of 14 PD patients and 14 matched control (MC) participants demonstrated that the relationship between ASI scores and responses to 35% CO2 were stronger than the relationship between SFS scores and responses to CO2. Specifically, both respiratory responses (VT and RR) and self-reported reactions (anxiety and symptom intensity) were significantly correlated with scores on the ASI. In contrast, scores on the SFS were significantly correlated with only one measure of respiratory change (VT). Although preliminary, these data indicate that the ASI may be a more useful tool than the SFS in predicting self-reported and respiratory responses to CO2 challenges.

N-Methyl-D-aspartate receptor expression in the nucleus tractus solitarii and maturation of hypoxic ventilatory response in the rat

Ventilatory responses to hypoxia are critically dependent on the activation of N-methyl-D-aspartate (NMDA) glutamate receptors in adult rats. To investigate the role of NMDA receptors during development, we measured minute ventilation (V E) in 5-d, 10-d, and 15-d-old intact, freely behaving rat pups, using whole-body plethysmography during breathing of room air (RA), during hypoxia (10% O(2)), and during hypercapnia (5% CO(2)), both before and after administration of the NMDA receptor antagonist MK-801 (1 mg/kg intraperitoneally). MK-801 did not affect V E in RA in the younger animals, but increased both V E and respiratory frequency in the 15-d- old rats. Similarly, V E responses to hypoxia were unchanged from control values in young animals, whereas V E respones in 15-d-old rats showed significant attenuation under hypoxic conditions. In contrast, hypercapnic ventilatory responses were not altered by administration of MK-801 to rats at any age. To further examine the topographic distribution patterns of NMDA receptor-positive neurons in the caudal brainstem and their recruitment during hypoxia, we performed immunostaining for NMDA receptor subunit NR1 and c-fos after exposing rat pups at postnatal ages of 2 d, 5 d, 10 d, and 20 d and adult rats to either RA or 10% O(2) for 3 h. With advancing postnatal age, NR1 expression increased in the nucleus tractus solitarii (nTS), whereas it decreased in the hypoglossal nucleus. Hypoxic exposure was associated with increased c-fos expression in the nTS at all postnatal ages, with a marked increase occurring in >/= 10-d-old animals. Similarly, the density of c-fos-NR1 double-labeled neurons during hypoxia progressively increased with maturation. We conclude that NMDA glutamate receptor expression in the caudal brainstem undergoes postnatal maturation that closely parallels the development of the hypoxic ventilatory response in the rat.

AMPA glutamate receptors and respiratory control in the developing rat: anatomic and pharmacological aspects

The developmental role of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) glutamate receptors in respiratory regulation remains undefined. To study this issue, minute ventilation (V(E)) was measured in 5-, 10-, and 15-day-old intact freely behaving rat pups using whole body plethysmography during room air (RA), hypercapnic (5% CO(2)), and hypoxic (10% O(2)) conditions, both before and after administration of the non-N-methyl-D-aspartate (NMDA) receptor antagonist 1,2,3, 4-tetrahydro-6-nitro-2,3-dioxobenzo[f]quinoxaline-7-sulfonamide disodium (NBQX; 10 mg/kg ip). In all age groups, V(E) during RA was unaffected by NBQX, despite reductions in breathing frequency (f) induced by increases in both inspiratory and expiratory duration. During hypoxia and hypercapnia, V(E) increases were similar in both NBQX and control conditions in all age groups. However, tidal volume was greater and f lower after NBQX. To determine if AMPA receptor-positive neurons are recruited during hypoxia, immunostaining for AMPA receptor (GluR2/3) and c-fos colabeling was performed in caudal brain stem sections after exposing rat pups at postnatal ages 2, 5, 10, and 20 days, and adult rats to room air or 10% O(2) for 3 h. GluR2/3 expression increased with postnatal age in the nucleus of the solitary tract (NTS) and hypoglossal nucleus, whereas a biphasic pattern emerged for the nucleus ambiguus (NA). c-fos expression was enhanced by hypoxia at all postnatal ages in the NTS and NA and also demonstrated a clear maturational pattern. However, colocalization of GluR2/3 and c-fos was not affected by hypoxia. We conclude that AMPA glutamate receptor expression in the caudal brain stem is developmentally regulated. Furthermore, the role of non-NMDA receptors in respiratory control of conscious neonatal rats appears to be limited to modest, albeit significant, regulation of breathing pattern.

Exaggerated anxiety is not unique to CO2 in panic disorder: a comparison of hypercapnic and hypoxic challenges

Current biological models of panic disorder (PD) assert that this disorder is maintained by hypersensitivity to carbon dioxide (CO2) and related asphyxia cues, which is manifested as an exaggerated suffocation alarm (D. Klein, 1993). Because suffocation can result from both increased CO2 (hypercapnia) and decreased oxygen (O2; hypoxia), this study examined respiratory responding and anxiety during 5% CO2 (a hypercapnic challenge) and 12% O2 (a hypoxic challenge) in 14 PD patients and 14 matched controls (MC). Results demonstrate that irrespective of the source of suffocation, PD patients respond with increased anxiety relative to MC participants. Significant group differences were observed in respiratory functioning, with the PD patients showing higher respiratory rates in response to both challenges. The MC sample demonstrated the expected respiratory responses to both hypercapnia and hypoxia. The findings indicate that PD patients are hypersensitive to alterations in breathing and that this reactivity is not specific to CO2.

An anatomic atlas of the medulla oblongata of the adult goat

An anatomic atlas of the goat brain stem was developed for use in studies that analyze medullary neuronal groups, and factors that influence variability in the location of neuronal groups were determined. The medullas of 31 adult goats (weight, 17-88 kg) were fixed, harvested, frozen, serially sectioned, stained with 0.5% neutral red, and examined with a light microscope. Obex, the point at which the central canal opens into the fourth ventricle, was taken as the zero reference point from which the rostrocaudal and mediolateral coordinates of medullary neuronal groups were determined, whereas dorsoventral coordinates were calculated from the medullary surface. Histological variations with goat body weight were quantified, and linear regression analysis provided adjustment factors for weight in all three dimensions. Similar analysis of percentage of shrinkage on fixation and processing provided adjustment factors for precise coordinates of medullary neuronal groups. For accurate location of neuronal groups, body weight and histological procedure should be taken into account. The present study provided adjustment factors for body weight and standard histological processing to locate most major medullary neuronal groups in the adult goat.

Exaggerated anxiety is not unique to CO2 in panic disorder: a comparison of hypercapnic and hypoxic challenges

Current biological models of panic disorder (PD) assert that this disorder is maintained by hypersensitivity to carbon dioxide (CO2) and related asphyxia cues, which is manifested as an exaggerated suffocation alarm (D. Klein, 1993). Because suffocation can result from both increased CO2 (hypercapnia) and decreased oxygen (O2; hypoxia), this study examined respiratory responding and anxiety during 5% CO2 (a hypercapnic challenge) and 12% O2 (a hypoxic challenge) in 14 PD patients and 14 matched controls (MC). Results demonstrate that irrespective of the source of suffocation, PD patients respond with increased anxiety relative to MC participants. Significant group differences were observed in respiratory functioning, with the PD patients showing higher respiratory rates in response to both challenges. The MC sample demonstrated the expected respiratory responses to both hypercapnia and hypoxia. The findings indicate that PD patients are hypersensitive to alterations in breathing and that this reactivity is not specific to CO2.

Acid-base regulation and control of ventilation in human pregnancy

The purposes of this review were twofold: to apply modern physicochemical principles to explain changes in acid-base regulation and the control of ventilation in human pregnancy; and to demonstrate the value of pregnancy as a model for the study of endocrine effects on physiological control systems. Application of P.A. Stewart's approach (P.A. Stewart. Can. J. Physiol. Pharmacol. 61: 1444-1461, 1983) shows that lower values of plasma hydrogen ion concentration ([H+]) observed at rest and in association with exercise in pregnancy are the result of lower values for carbon dioxide tension (PCO2) and total weak acid ([Atot]). This effect is partly offset by a lower strong ion difference ([SID]). The ability to predict plasma [H+] at rest and following strenuous exercise in pregnancy (J.G. Kemp, F.A. Greer, and L.A. Wolfe. J. Appl. Physiol. 83: 644-651, 1997) supports the validity of Stewart's approach. Jennings and associates (D.B. Jennings. Can. J. Physiol. Pharmacol. 72: 1499-1512, 1994) have further demonstrated in animal models the involvement of plasma osmolality and circulating levels of angiotensin II (ANG II) and arginine vasopressin (AVP) in the chemical control of ventilation. We hypothesize that pregnancy-induced increases in respiratory sensitivity to carbon dioxide are the combined result of reduced plasma osmolality, reduced cerebrospinal fluid [SID], and augmented circulating levels of progesterone, ANG II, and AVP.Key words: human gestation, hydrogen ion concentration, strong ion difference, osmolality, angiotensin II, arginine vasopressin, progesterone.

Acid-base regulation and control of ventilation in human pregnancy

The purposes of this review were twofold: to apply modern physicochemical principles to explain changes in acid-base regulation and the control of ventilation in human pregnancy; and to demonstrate the value of pregnancy as a model for the study of endocrine effects on physiological control systems. Application of P.A. Stewart's approach (P.A. Stewart. Can. J. Physiol. Pharmacol. 61: 1444-1461, 1983) shows that lower values of plasma hydrogen ion concentration ([H+]) observed at rest and in association with exercise in pregnancy are the result of lower values for carbon dioxide tension (Pco2) and total weak acid ([A(tot)]). This effect is partly offset by a lower strong ion difference ([SID]). The ability to predict plasma [H+] at rest and following strenuous exercise in pregnancy (J.G. Kemp, F.A. Greer, and L.A. Wolfe. J. Appl. Physiol. 83: 644-651, 1997) supports the validity of Stewart's approach. Jennings and associates (D.B. Jennings. Can. J. Physiol. Pharmacol. 72: 1499-1512, 1994) have further demonstrated in animal models the involvement of plasma osmolality and circulating levels of angiotensin II (ANG II) and arginine vasopressin (AVP) in the chemical control of ventilation. We hypothesize that pregnancy-induced increases in respiratory sensitivity to carbon dioxide are the combined result of reduced plasma osmolality, reduced cerebrospinal fluid [SID], and augmented circulating levels of progesterone, ANG II, and AVP.

NMDA receptors mediate peripheral chemoreceptor afferent input in the conscious rat

N-methyl-D-aspartate (NMDA) glutamate receptors mediate critical components of cardiorespiratory control in anesthetized animals. The role of NMDA receptors in the ventilatory responses to peripheral and central chemoreceptor stimulation was investigated in conscious, freely behaving rats. Minute ventilation (VE) responses to 10% O2, 5% CO2, and increasing intravenous doses of sodium cyanide were measured in intact rats before and after intravenous administration of the NMDA receptor antagonist MK-801 (3 mg/kg). After MK-801, eupcapnic tidal volume (VT) decreased while frequency increased, resulting in a modest reduction in VE. Inspiratory time (TI) decreased, whereas expiratory time remained unchanged. The VE responses to hypercapnia were qualitatively similar in control and MK-801 conditions, with slight reductions in respiratory drive (VT/TI) after MK-801. In contrast, responses to hypoxia were markedly attenuated after MK-801 and were primarily due to reduced frequency changes, whereas VT was unaffected. Sodium cyanide doses associated with significant VE increases were 5 and 50 microg/kg before and after MK-801, respectively. Thus 1-log shift to the right of individual dose-response curves occurred with MK-801. Selective carotid body denervation reduced VE during hypoxia by 70%, and residual hypoxic ventilatory responses were abolished after MK-801. These findings suggest that, in conscious rats, carotid and other peripheral chemoreceptor-mediated hypoxic ventilatory responses are critically dependent on NMDA receptor activation and that NMDA receptor mechanisms are only modestly involved during hypercapnia.

Physical conditioning attenuates respiratory responses to steady-state exercise in late gestation

PURPOSE

To study the ventilatory effects of closely monitored cycle ergometer conditioning (HR target, 145-150 beats x min(-1); 25 min/session; three sessions per week) during the second and third pregnancy trimesters (TMs) in healthy human pregnancy.

METHODS

Subjects were 27 previously sedentary pregnant women (exercised group, EG). A sedentary control group (CG, N = 20) was also studied. Subjects were tested at rest and during upright cycle ergometry at three steady-state power outputs (approximately 20, 45, and 65 W) at the start of the second TM (ENTRY), at the end of the second and third TMs (post-training), and 3 months postpartum (PP, nonpregnant control).

RESULTS

Significant reductions in exercise HR were observed in the EG at each exercise level, confirming achievement of an aerobic conditioning effect. In both groups the ventilatory equivalent for oxygen (VE/O2) was significantly higher at all work rates during pregnancy compared with that during PP. This effect was caused by significantly higher exercise tidal volumes (VT) at each work rate in both groups during pregnancy versus PP. Respiratory sensitivity as reflected by the ventilatory equivalent for carbon dioxide (E/VECO2) and calculated arterial carbon dioxide tension (PaCO2) was significantly increased at all three work rates in late gestation versus PP and increased slightly with advancing gestational age in both groups. The main effects of physical conditioning were attenuation of increases in VE/VO2 observed at all exercise levels between the end of TM2 and TM3 and reductions in respiratory perception of effort (RPEr) between ENTRY and the end of TM3. Attenuation of increases in VE/VO2 during TM3 in the EG was attributed to the combined effects of enhanced fat versus carbohydrate utilization (resulting in reduced CO2 output and drive to ventilate) and attenuation of pregnancy-induced increases in dead space ventilation in late gestation.

CONCLUSION

The study results support the hypothesis that physical conditioning reduces both ventilatory demand and respiratory perception of effort in late gestation.

Effect on breathing of surface ventrolateral medullary cooling in awake, anesthetized and asleep goats

In adult and neonatal goats, we chronically implanted thermodes on the ventrolateral (VLM) medullary surface to create reversible neuronal dysfunction and thereby gain insight into the role of superficial VLM neurons in control of breathing in anesthetized, awake and asleep states. Consistent with data of others, cooling caudal area M and rostral area S caused sustained apnea under anesthesia. However, in the awake and NREM sleep states, cooling at this site caused only a modest reduction in breathing, indicating that neurons at this site are not critical for respiratory rhythm in these states. Moreover, data in the awake state over multiple conditions suggest neurons at this site do not integrate all intracranial and carotid chemoreception. The data suggest though that neurons at this site have a facilitatory-like effect on breathing both unrelated and related to intracranial chemoreception. We believe that this facilitation serves a function similar to the facilitation provided by the carotid chemoreceptors and by sources associated with wakefulness. Accordingly, elimination/attenuation of any one of these three influences (caudal M rostral S VLM, wakefulness, carotid chemoreception) results in a slight decrease in breathing, removal of two of the three results in a greater decrease in breathing, and removal of all three results in sustained apnea.

Effects of cooling the ventrolateral medulla on diaphragm activity during NREM sleep

Dysfunction through cooling of neurons near the ventrolateral medullary (VLM) surface results in apnea in the anesthetized state, whereas similar neuronal dysfunction in the awake state only modestly decreases breathing. The purpose of this study was to investigate effects on breathing, as measured by diaphragm electromyogram (EMGdi), of VLM neuronal dysfunction during NREM sleep, a naturally occurring change in state. In six goats, thermodes for cooling were chronically implanted between the first hypoglossal rootlet and the pontomedullary junction (area M and area S). During wakefulness and NREM sleep, bilateral VLM cooling (thermode temp = 20 degrees C) for 30 sec decreased EMGdi mean activity and minute EMGdi (p < 0.05) and lengthened the time between diaphragm contractions. During NREM sleep, reductions in mean and minute EMGdi during cooling tended to be greater than during waking, but not significantly. However, following carotid body denervation. VLM cooling caused prolonged apnea during NREM sleep but only a brief apnea in the awake state. The data suggest that either intact VLM neuronal mechanisms or intact carotid afferents are necessary for sustained EMGdi activity during NREM sleep.

Effect on breathing of ventral medullary surface cooling in neonatal goats

The present study was designed to determine whether neurons near the ventral medullary surface (VMS) that are important to control of breathing in adult mammals are also important to control of breathing in neonates. In 7-day-old goats (n = 22), the VMS was surgically exposed under halothane anesthesia. Stainless steel thermodes (2 x 2 mm) were used to cool (20 degrees C) and thereby create neuronal dysfunction of discrete VMS sites. Bilateral cooling under anesthesia 0-2 or 2-4 mm lateral to the midline between the exit of cranial nerves VI and XII resulted in a reduction (P < 0.05) of breathing and most often in apnea. Cooling caudal or rostral to this area did not have a consistent effect on breathing. In 7-day-old goats (n = 8), 3 x 3-mm thermodes were chronically implanted bilaterally on the VMS surface between the exit of cranial nerves VI and XII. The goats recovered and were studied over several days thereafter. VMS cooling while the goats were awake caused breathing to decrease (P < 0.05), but apnea was never observed. The decrease was less (P < 0.05) than while the goats were anesthetized. After 10 s of cooling, the hypopnea while the goats were awake was uniform during eupnea, hypercapnia, hyperoxia, and hypoxia, but after 10 s of cooling, the decrease was relatively greater (P < 0.05) during hyperoxia and hypercapnia. These effects of VMS cooling are qualitatively the same as in adult goats; thus the data are consistent with mature VMS contribution to the control of breathing in neonatal goats.

Imaging of VMS activity during blood pressure challenges in awake and anesthetized goats

We examined scattered-light changes in a rostral ventral medullary surface (VMS) area from five goats after blood pressure challenges during waking and halothane anesthesia. Reflected 660-nm images were digitized at 1/s after baseline; intravenous saline; 5, 10, or 15 micrograms/kg phenylephrine administration; or sodium nitroprusside infusion sufficient to lower blood pressure by 50%. Phenylephrine elicited a dose-dependent, blood pressure elevation during both states and a substantial transient reflectance increase (interpreted as activity decline) during anesthesia, but only a minimal, long-latency, slow-reflectance decrease activity increase) during waking. Sodium nitroprusside elicited lowering of blood pressure and decreased reflectance in the rostral site during anesthesia. The magnitude of the reflectance change to depressor challenge increased 30%, and the onset latency shortened during waking. Isolated regions of enhanced reflectance changes appeared during both challenges. Activity in this rostral VMS site differentially responds to blood pressure elevation or lowering, and state markedly alters the responses. We speculate that VMS responses to depressor challenge represent reflex activation of respiratory regions.

Effect of dichloroacetate on PaCO2 responses to hypoxia in awake goats

To gain insight into the role of cerebral lactic acidosis in the hypoxic ventilatory response, we administered dichloroacetate (DCA) intravenously to inhibit lactic acid production in 7 awake goats (40-70 kg) during 0.5 h of normoxia (inspired O2 fraction = 0.209) and 5 h of poikilocapnic hypoxia (inspired O2 fraction = 0.125). On separate days, these goats were also studied with a continuous saline infusion (18 ml/h iv) during 5 h of normoxia and hypoxia. Arterial PCO2 (PaCO2) did not change during the 5-h normoxic period. During hypoxia, arterial PO2 fell significantly (P < 0.05) with both saline (from 111.3 to 39.0 Torr) and DCA (from 111.8 to 42.0 Torr) infusions. PaCO2 decreased (P < 0.05) during the first 0.5 h of both the saline and DCA hypoxia protocols. The decrease was greater (P < 0.05) during DCA (from 36.5 to 33.5 Torr) than during saline infusion (from 37.7 to 36.3 Torr). With saline infusion, PaCO2 decreased (P < 0.05) by 4.9 Torr between 0.5 and 5.0 h of hypoxia. However, over this period of DCA hypoxia, PaCO2 did not significantly decrease (P > 0.05). We conclude that the enhanced hyperventilation with DCA during acute hypoxia is consistent with brain lactic acidosis depressing breathing. Absence of additional significant hyperventilation after 0.5 h of DCA hypoxia suggests that a time-dependent alleviation of brain lactic acidosis might normally contribute to ventilatory acclimatization to hypoxia.

Ventral medullary surface activity during hypoxia in awake and anesthetized goats

The rostral ventrolateral medullary surface (VMS) plays a major state-dependent role in the control of breathing; its role during hypoxia remains speculative. We therefore assessed activity within the rostral VMS by measuring reflectance of scattered light in 5 goats during normoxia, hypoxia, and hyperoxia in awake and halothane anesthetic states. Within the first minute of hypoxia, light reflectance began to decrease in the awake state; reflectance reached a stable nadir within 30 min about 10 and 17% below control values (P < 0.01), at 12 and 10% inspired O2, respectively. In the anesthetized state, reflectance decreased (P < 0.01) by 6% at 10% inspired O2. After 30 min in the awake state, reflectance returned (P < 0.01) toward control values, reaching a stable level at 7 and 11% below control at 12 and 10% inspired O2, respectively (P < 0.05). Hyperoxia resulted in a 1% increase (P < 0.05) in reflectance. Changes in reflectance during hypoxia did not consistently parallel changes in breathing, heart rate, or arterial blood pressure. We conclude that, a) decreased reflectance during hypoxia results, in part, from increased neural activity, and b) state exerts a substantial effect on the response of VMS areas to hypoxia.

Effect on breathing of neuronal dysfunction in the caudal ventral medulla of goats

It has been reported that the caudal ventrolateral medulla (VLM) is important in central chemoreception and the control of breathing. The objective of this study was to determine in adult goats the effects on breathing of neuronal dysfunction of this caudal VLM region (area L; caudal to rostral hypoglossal nerve rootlet). Thermodes were chronically implanted on the VLM to cool neurons and thereby cause neuronal dysfunction. During awake and (halothane) anesthetized states, cooling the caudal VLM for 20 s to 20 degrees C did not alter breathing (P > 0.10). However, between 20 and 30 s of cooling and during recovery from cooling 0-4 mm caudal to the rostral hypoglossal rootlet, there was a 12 (awake) to 25% (anesthetized) increase (P < 0.05) in breathing. This tachypneic hyperpnea was uniform over conditions of eucapnia, hypercapnia, and hypoxia and resulted from reduced inspiratory time that increased frequency. We conclude that in goats inhibitory neurons are located in area L and the lateral caudal ventral medulla.

Effect of carotid chemoreceptor denervation on breathing during ventrolateral medullary cooling in goats

It has been postulated that the so-called area S of the ventrolateral medulla (VLM) integrates peripheral chemoreceptor activity; thus cooling-induced dysfunction of neurons in this VLM area should functionally eliminate carotid chemoreceptor stimulation of breathing. Accordingly, carotid chemoreceptor denervation (CBD) should not alter the breathing effects of VLM neuronal dysfunction. To test this hypothesis in awake goats, chronically implanted thermodes were used to cool the VLM and thereby cause reversible neuronal dysfunction in all or portions of VLM areas M and S. Within 5 s after initiation of cooling approximately 60-100% of areas M and S in (P < 0.05) uniformly over conditions of eupnea, hypercapnia, and hypoxia. Between 10 and 20 s of cooling, the reduction in VI was approximately 10% greater (P < 0.05) during hypercapnia than during eupnea and hypoxia. For the remaining 10 s of cooling and for approximately 1 min after cooling, VI increased to and above control for all conditions. For all conditions, CBD accentuated the depression of VI during cooling, causing VI to decrease (P < 0.05) 10-40% more than before CBD. After CBD, the greatest effect on VI of cooling was again during hypercapnia. Thus the carotid bodies in intact goats appear to sense blood gas errors caused during VLM cooling to minimize the decreases in VI. We conclude that the data from this study do not support the concept that the VLM integrates carotid chemoreceptor activity.

Rostral ventral medullary surface activity during hypercapnic challenges in awake and anesthetized goats

Regions within the rostral ventral medullary surface (RVMS) play an important role in cardiorespiratory responses to CO2 during anesthesia. Activity within a RVMS area, in which local cooling elicited marked ventilatory and blood pressure reductions, was measured as 660 nm scattered light changes in 5 goats following 5% CO2 challenges during waking and anesthetic states. During wakefulness, hypercapnia elicited a substantial, short latency transient (1-1.5 min) activity increase, followed by a sustained decrease. Stimulus cessation elicited a large and rapid off-transient activity increase which persisted for approximately 20 min. In contrast, during halothane anesthesia, the initial activation was absent, and the later activity decline and off-response were much reduced. We conclude that biphasic RVMS activity responses emerge to CO2 stimulation, and are state-dependent.

Differential effect of ventrolateral medullary cooling on respiratory muscles of goats

The objective was to determine whether there is an inhomogeneous response of respiratory muscles during cooling-induced ventrolateral medullary (VLM) neuronal dysfunction in anesthetized and awake goats. Thermodes for cooling were chronically implanted on all or portions of rostral, intermediate, and caudal areas of the VLM of 16 adult goats. Electromyograms (EMGs) were obtained from chronically implanted wires in the diaphragm (di), transversus abdominis (TA), and triangularis sterni (TS) muscles. During some periods of cooling in 9 of 16 anesthetized airway-intubated goats, complete cessation of EMGdi coincided with a reduced yet sustained inspiratory flow. In six awake tracheotomized goats, VLM cooling decreased (P < 0.05) EMGdi duration and minute activity more than inspiratory duration and minute ventilation. Cooling thus decreased activation of the diaphragm more than activation of other respiratory muscles. On the other hand, during VLM cooling in 3 of 10 airway-intact awake goats, cessation of inspiratory flow coincided with sustained EMGdi, suggesting that cooling decreased stimulation of the upper airway muscles more than stimulation of the diaphragm. Finally, VLM cooling in a majority of goats decreased EMGTA and EMGTS more than EMGdi. We conclude that VLM neuronal dysfunction has a differential effect on respiratory muscles of adult anesthetized and awake goats.

Effects on breathing of ventrolateral medullary cooling in awake goats

Our objective was to investigate the role of the ventrolateral medulla (VLM) in the control of breathing during the awake state. In 17 awake adult goats, chronically implanted thermodes were used to cool the VLM and thereby cause reversible neuronal dysfunction in all or portions of the area between the first hypoglossal rootlet and the ponto-medullary junction (so-called area M (rostral) and area S). Within 5 s after the initiation of cooling, 60-100% of areas M and S, pulmonary ventilation (VE) decreased uniformly over conditions of eucapnia, hypercapnia, hypoxia, and exercise (P < 0.05). Between 10 and 20 s of cooling, the reduction in VE was approximately 10% greater during eucapnia and hypercapnia than during hypoxia and exercise (P < 0.05). For the remaining 10 s of cooling and for about 1 min after cooling, VE increased to and above control level. Cooling only rostral area M or only caudal area M-rostral area S affected breathing qualitatively in the same manner as when 60-100% of areas M and S were cooled. However, cooling caudal area S had effects that differed significantly (P < 0.05) from more rostral cooling in that the initial decrease in VE was attenuated and the subsequent increase was accentuated. The initial uniform decreased VE during cooling suggests that superficial VLM nonchemoreceptor neurons facilitate breathing. The subsequent relatively greater effect of cooling during eucapnia and hypercapnia probably reflects dysfunction of chemoreceptor-related neurons that normally stimulate breathing. The stimulation of breathing during the later stages and after cooling may suggest that some VLM neurons inhibit breathing.

Ventilatory responses to cooling the ventrolateral medullary surface of awake and anesthetized goats

The ventrolateral medulla (VLM) has been reported to be important as a source of tonic facilitation of dorsal respiratory neurons and as a site critical for respiratory rhythmogenesis. We investigated these theories in awake and anesthetized goats (n = 13) by using chronically implanted thermodes to create reversible neuronal dysfunction at superficial VLM sites between the first hypoglossal rootlet and the pontomedullary junction (area M (rostral) and area S). During halothane anesthesia (arterial PCO2 = 57.4 +/- 4.5 Torr), bilateral cooling (thermode temperature = 20 degrees C) of 60-100% of areas M and S for 30 s produced a sustained apnea (46 +/- 4 s) that lasted beyond the period of cooling. While the animals were awake (arterial PCO2 = 36.0 +/- 1.9 Torr), cooling the identical region in the same goats resulted in a decrease (approximately 50%) in pulmonary ventilation, with a brief apnea seen only in one goat. Reductions in both tidal volume and frequency were observed. Qualitatively similar responses were obtained when cooling caudal area M-rostral area S and rostral area M, but the responses were less pronounced. Minimal effects were seen in response to cooling caudal area S. During anesthesia, breathing is critically dependent on superficial VLM neurons, whereas in the awake state these neurons are not essential for the maintenance of respiratory rhythm. Our data are consistent with these superficial VLM neuronal regions providing tonic facilitation to more dorsal respiratory neurons in both the anesthetized and awake states.

Ventral medullary surface activity during sleep, waking, and anesthetic states in the goat

We examined activity, measured as changes in reflected light, from the surface of a rostral ventral medullary area that is involved in cardiorespiratory control. We collected images during sleep and waking states and during halothane anesthesia in five adult unrestrained goats. During quiet sleep, overall activity increased and overall variability decreased compared with waking levels, whereas rapid eye movement sleep increased variability, and average activity decreased to near-waking levels. Distinct regions of activation and suppression appeared during sleep states. Deep anesthesia decreased activity and minimized variation. We speculate that alterations in rostral ventral medullary surface activity may play a role in state-dependent changes in cardiorespiratory control mechanisms.

Effect of metabolic rate on ventilatory roll-off during hypoxia

This study was done to determine 1) whether goats demonstrate the roll-off phenomenon, i.e., a secondary decrease in minute ventilation (VE), after an initial hyperventilation during various levels of hypoxia and, if so, 2) whether roll-off could be due to changes in metabolic rate. We hypothesized that roll-off occurs in the goat during hypoxia but is not due to hypometabolism. To answer question 1, eight unanesthetized adult goats were exposed to 15-20 min of hypoxia at 0.15, 0.12, and 0.09 inspired O2 fraction (FIO2), resulting in 60, 40, and 30 Torr arterial PO2, respectively. Goats were fitted with a face mask connected to a spirometer to measure VE, and arterial blood gas samples were obtained via carotid arterial catheters. Roll-off was seen with 0.15 and 0.12 FIO2, whereas VE steadily increased with 0.09 FIO2. During hypoxia, arterial PCO2 fell 2, 3, and 7 Torr at 0.15, 0.12, and 0.09 FIO2, respectively. In the second series of experiments, nine different goats were exposed to 30 min of 0.12 FIO2. O2 consumption and CO2 production were measured five times during baseline and hypoxia. VE increased to 32% above baseline values after 2 min of hypoxia and then gradually decreased by 18%. Changes in breathing frequency and tidal volume contributed to the roll-off. O2 consumption decreased (P = 0.0029, analysis of variance) and CO2 production increased (P = 0.0027) during hypoxia, although both changes were small (< 7%) compared with the eventual 18% decrease in VE. We conclude that the adult goat demonstrates the roll-off phenomenon during moderate levels of hypoxia. (ABSTRACT TRUNCATED AT 250 WORDS)

Circulatory and metabolic responses in awake dogs to infusion of iso-rANP/(rBNP)

We reported that a second rat atrial peptide, iso-atrial natriuretic peptide (iso-rANP(1-45)) and a potential putative homologue, iso-rANP(17-45) (identical with rat brain natriuretic peptide except for one amino acid) elicited circulatory and renal responses in anesthetized rats. In the present studies, low-dose intravenous infusions of iso-rANP(1-45) (6.3-25 pmol kg-1 min-1) and iso-rANP(17-45) (12.5-50 pmol kg-1 min-1) into conscious dogs produced subtle circulatory effects compared to control studies. Relative to oxygen consumption, cardiac output was lower and total peripheral resistance higher with both iso-rANP(1-45) and iso-rANP(17-45). Heart rate tended to be slightly lower relative to control studies during peptide infusions, and the highest infusion doses caused a decrease in mean arterial pressure. Plasma protein increased and plasma osmolality decreased with iso-rANP(1-45); infusion of iso-rANP(17-45) caused a decrease in the respiratory exchange ratio. The mechanism of action of iso-rANP may have been direct, via an active receptor. However, we previously reported for these same experiments that infusion of iso-rANP(1-45) and iso-rANP(17-45) increased plasma ANP and decreased plasma renin activity. Thus, circulatory changes during infusion of iso-rANP were consistent with an indirect mechanism related to increased endogenous ANP.