Jonathan N. Myers

Bio: Jonathan N. Myers is an academic researcher from Stanford University. The author has contributed to research in topics: Body mass index & Cardiorespiratory fitness. The author has an hindex of 15, co-authored 27 publications receiving 3882 citations. Previous affiliations of Jonathan N. Myers include Veterans Health Administration & VA Palo Alto Healthcare System.

Clinician’s Guide to Cardiopulmonary Exercise Testing in Adults A Scientific Statement From the American Heart Association

Abstract: Exercise testing remains a remarkably durable and versatile tool that provides valuable diagnostic and prognostic information regarding patients with cardiovascular and pulmonary disease. Exercise testing has been available for more than a half century and, like many other cardiovascular procedures, has evolved in its technology and scope. When combined with exercise testing, adjunctive imaging modalities offer greater diagnostic accuracy, additional information regarding cardiac structure and function, and additional prognostic information. Similarly, the addition of ventilatory gas exchange measurements during exercise testing provides a wide array of unique and clinically useful incremental information that heretofore has been poorly understood and underutilized by the practicing clinician. The reasons for this are many and include the requirement for additional equipment (cardiopulmonary exercise testing [CPX] systems), personnel who are proficient in the administration and interpretation of these tests, limited or absence of training of cardiovascular specialists and limited training by pulmonary specialists in this technique, and the lack of understanding of the value of CPX by practicing clinicians. Modern CPX systems allow for the analysis of gas exchange at rest, during exercise, and during recovery and yield breath-by-breath measures of oxygen uptake (Vo2), carbon dioxide output (Vco2), and ventilation (Ve). These advanced computerized systems provide both simple and complex analyses of these data that are easy to retrieve and store, which makes CPX available for widespread use. These data can be readily integrated with standard variables measured during exercise testing, including heart rate, blood pressure, work rate, electrocardiography findings, and symptoms, to provide a comprehensive assessment of exercise tolerance and exercise responses. CPX can even be performed with adjunctive imaging modalities for additional diagnostic assessment. Hence, CPX offers the clinician the ability to obtain a wealth of information beyond standard exercise electrocardiography testing that when appropriately applied and interpreted …

Exercise and Heart Failure A Statement From the American Heart Association Committee on Exercise, Rehabilitation, and Prevention

Abstract: Heart failure (HF) may be defined as the inability of the heart to meet the demands of the tissues, which results in symptoms of fatigue or dyspnea on exertion progressing to dyspnea at rest. The inability to perform exercise without discomfort may be one of the first symptoms experienced by patients with HF and is often the principal reason for seeking medical care. Therefore, exercise intolerance is inextricably linked to the diagnosis of HF. It might be expected that a tight relationship would exist between indices of resting ventricular function and exercise capacity. Data indicate, however, that indices of resting ventricular function (such as ejection fraction [EF]) are only weakly correlated to exercise tolerance.1 Exercise intolerance is defined as the reduced ability to perform activities that involve dynamic movement of large skeletal muscles because of symptoms of dyspnea or fatigue. Many investigators have sought mechanisms to explain the source of exercise intolerance. The aims of this position statement are to review (1) factors that affect exercise tolerance, with specific emphasis on chronic HF due to systolic dysfunction; (2) data that support the role of exercise training in chronic systolic HF, including the risks and benefits; (3) data on exercise training in patients with HF due to diastolic dysfunction; and finally (4) the subgroups of patients with HF for which data are lacking, and (5) the subgroups of patients who should not be included in exercise training programs. We anticipate this report will stimulate appropriate use of exercise training in patients with HF when indicated and encourage further studies in those areas in which data are lacking. ### Cardiovascular The capacity for performing aerobic exercise depends on the ability of the heart to augment its output to the exercising muscles and the ability of these muscles to utilize oxygen from the delivered …

Assessment of Functional Capacity in Clinical and Research Settings A Scientific Statement From the American Heart Association Committee on Exercise, Rehabilitation, and Prevention of the Council on Clinical Cardiology and the Council on Cardiovascular Nursing

Abstract: The assessment of functional capacity reflects the ability to perform activities of daily living that require sustained aerobic metabolism. The integrated efforts and health of the pulmonary, cardiovascular, and skeletal muscle systems dictate an individual’s functional capacity. Numerous investigations have demonstrated that the assessment of functional capacity provides important diagnostic and prognostic information in a wide variety of clinical and research settings. This scientific statement, an update of the previously published American Heart Association (AHA) document,1 highlights the major clinical and research applications of functional capacity assessment. For a comprehensive review of exercise testing, the reader is referred to the American College of Cardiology (ACC)/AHA Guidelines for Exercise Testing.2,3 Functional capacity is the ability of an individual to perform aerobic work as defined by the maximal oxygen uptake (Vo2max), that is, the product of cardiac output and arteriovenous oxygen (a−Vo2) difference at physical exhaustion, as shown in the following equation: ![Formula][1] Where HR indicates heart rate and SV indicates stroke volume. Because Vo2max typically is achieved by exercise that involves only about half of the total body musculature, it is generally believed that Vo2max is limited by maximal cardiac output rather than peripheral factors.4 Although Vo2max is measured in liters of oxygen per minute, it usually is expressed in milliliters of oxygen per kilogram of body weight per minute to facilitate intersubject comparisons. In addition, functional capacity, particularly when estimated from the work rate achieved rather than directly measured Vo, is frequently expressed in metabolic equivalents (METs), with 1 MET representing the resting energy expenditure (≈3.5 mL O2 · kg−1 · min−1). In this instance, functional capacity is commonly expressed clinically as a multiple of the resting metabolic rate. Vo2max … [1]: /embed/graphic-1.gif

Recommendations for clinical exercise laboratories: a scientific statement from the american heart association.

Abstract: The present statement provides a guide to initiating and maintaining a high-quality clinical exercise testing laboratory for administering graded exercise tests to adults. Pediatric testing has been addressed separately.1 It is a revision of the 1995 American Heart Association (AHA) “Guidelines for Clinical Exercise Testing Laboratories”2 and is designed to complement several other AHA documents related to exercise testing, including the AHA/American College of Cardiology (ACC) guidelines for exercise testing,3 the AHA’s “Exercise Standards for Testing and Training,”4 the AHA’s “Clinical Competence Statement on Stress Testing,”5 and the AHA’s “Assessment of Functional Capacity in Clinical and Research Settings.”6 Exercise testing is a noninvasive procedure that provides diagnostic and prognostic information and evaluates an individual’s capacity for dynamic exercise. Exercise testing facilities range from the sophisticated research setting to more conventional equipment in the family practitioner’s or internist’s office. Regardless of the range of testing procedures performed in any given laboratory, basic equipment, personnel, and protocol criteria are necessary to ensure the comfort and safety of the patient and to conduct a meaningful test. ### Environment Exercise testing equipment varies in size. The testing room should be large enough to accommodate all the equipment necessary, including emergency equipment and a defibrillator, while maintaining walking areas and allowing adequate access to the patient in emergency situations. It is also important that the laboratory comply with local fire standards and with procedures for other types of emergencies (eg, earthquake, hurricane). The laboratory should be well lighted, clean, and well ventilated, with temperature and humidity control. A wall-mounted clock with a sweep second hand or a digital counter is useful. The examining table should have space for towels, tape, and other items needed for patient preparation and testing. A curtain for privacy during patient preparation is useful. Minimization of interruptions …

The clinical and research applications of aerobic capacity and ventilatory efficiency in heart failure: an evidence-based review

Abstract: A hallmark symptom of heart failure (HF) is exercise intolerance, typically evidenced by excessive shortness of breath, and/or fatigue with exertion. In recent years, the physiologic response to progressive exercise using direct measures of ventilation and gas exchange, commonly termed the cardiopulmonary exercise test (CPX), has evolved into an important clinical tool in the management of patients with HF. There is currently debate regarding the optimal CPX response to apply when stratifying risk for mortality, hospitalization, or other outcomes in patients with HF. Early studies in this area focused on the application of peak VO2 in predicting outcomes in patients considered for transplantation. More recently, the focus of these studies has shifted to an emphasis on ventilatory inefficiency, in lieu of or in combination with peak VO2, in estimating risk. The most widely studied index of ventilatory inefficiency has been the minute ventilation/carbon dioxide production (VE/VCO2) slope. A growing body of studies over the last decade has demonstrated that among patients with HF, the VE/VCO2 slope more powerfully predicts mortality, hospitalization, or both, than peak VO2. A number of investigations have also simultaneously examined the diagnostic importance of peak VO2 and the VE/VCO2 slope as well as their respective response to various interventions. This review examines the body of evidence which has used aerobic capacity and ventilatory efficiency as prognostic and diagnostic markers as well as endpoints in interventional trials. Based on this evidence, recommendations for future clinical and research applications of these CPX variables are provided.

Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory, Musculoskeletal, and Neuromotor Fitness in Apparently Healthy Adults: Guidance for Prescribing Exercise

Abstract: The purpose of this Position Stand is to provide guidance to professionals who counsel and prescribe individualized exercise to apparently healthy adults of all ages. These recommendations also may apply to adults with certain chronic diseases or disabilities, when appropriately evaluated and advised by a health professional. This document supersedes the 1998 American College of Sports Medicine (ACSM) Position Stand, "The Recommended Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory and Muscular Fitness, and Flexibility in Healthy Adults." The scientific evidence demonstrating the beneficial effects of exercise is indisputable, and the benefits of exercise far outweigh the risks in most adults. A program of regular exercise that includes cardiorespiratory, resistance, flexibility, and neuromotor exercise training beyond activities of daily living to improve and maintain physical fitness and health is essential for most adults. The ACSM recommends that most adults engage in moderate-intensity cardiorespiratory exercise training for ≥30 min·d on ≥5 d·wk for a total of ≥150 min·wk, vigorous-intensity cardiorespiratory exercise training for ≥20 min·d on ≥3 d·wk (≥75 min·wk), or a combination of moderate- and vigorous-intensity exercise to achieve a total energy expenditure of ≥500-1000 MET·min·wk. On 2-3 d·wk, adults should also perform resistance exercises for each of the major muscle groups, and neuromotor exercise involving balance, agility, and coordination. Crucial to maintaining joint range of movement, completing a series of flexibility exercises for each the major muscle-tendon groups (a total of 60 s per exercise) on ≥2 d·wk is recommended. The exercise program should be modified according to an individual's habitual physical activity, physical function, health status, exercise responses, and stated goals. Adults who are unable or unwilling to meet the exercise targets outlined here still can benefit from engaging in amounts of exercise less than recommended. In addition to exercising regularly, there are health benefits in concurrently reducing total time engaged in sedentary pursuits and also by interspersing frequent, short bouts of standing and physical activity between periods of sedentary activity, even in physically active adults. Behaviorally based exercise interventions, the use of behavior change strategies, supervision by an experienced fitness instructor, and exercise that is pleasant and enjoyable can improve adoption and adherence to prescribed exercise programs. Educating adults about and screening for signs and symptoms of CHD and gradual progression of exercise intensity and volume may reduce the risks of exercise. Consultations with a medical professional and diagnostic exercise testing for CHD are useful when clinically indicated but are not recommended for universal screening to enhance the safety of exercise.

Guidelines for the prevention of stroke in patients with stroke and transient ischemic attack: a guideline for healthcare professionals from the American Heart Association/American Stroke Association

Abstract: The aim of this updated guideline is to provide comprehensive and timely evidence-based recommendations on the prevention of future stroke among survivors of ischemic stroke or transient ischemic attack. The guideline is addressed to all clinicians who manage secondary prevention for these patients. Evidence-based recommendations are provided for control of risk factors, intervention for vascular obstruction, antithrombotic therapy for cardioembolism, and antiplatelet therapy for noncardioembolic stroke. Recommendations are also provided for the prevention of recurrent stroke in a variety of specific circumstances, including aortic arch atherosclerosis, arterial dissection, patent foramen ovale, hyperhomocysteinemia, hypercoagulable states, antiphospholipid antibody syndrome, sickle cell disease, cerebral venous sinus thrombosis, and pregnancy. Special sections address use of antithrombotic and anticoagulation therapy after an intracranial hemorrhage and implementation of guidelines.

Association of All-Cause Mortality With Overweight and Obesity Using Standard Body Mass Index Categories: A Systematic Review and Meta-analysis

Abstract: Importance Estimates of the relative mortality risks associated with normal weight, overweight, and obesity may help to inform decision making in the clinical setting. Objective To perform a systematic review of reported hazard ratios (HRs) of all-cause mortality for overweight and obesity relative to normal weight in the general population. Data Sources PubMed and EMBASE electronic databases were searched through September 30, 2012, without language restrictions. Study Selection Articles that reported HRs for all-cause mortality using standard body mass index (BMI) categories from prospective studies of general populations of adults were selected by consensus among multiple reviewers. Studies were excluded that used nonstandard categories or that were limited to adolescents or to those with specific medical conditions or to those undergoing specific procedures. PubMed searches yielded 7034 articles, of which 141 (2.0%) were eligible. An EMBASE search yielded 2 additional articles. After eliminating overlap, 97 studies were retained for analysis, providing a combined sample size of more than 2.88 million individuals and more than 270 000 deaths. Data Extraction Data were extracted by 1 reviewer and then reviewed by 3 independent reviewers. We selected the most complex model available for the full sample and used a variety of sensitivity analyses to address issues of possible overadjustment (adjusted for factors in causal pathway) or underadjustment (not adjusted for at least age, sex, and smoking). Results Random-effects summary all-cause mortality HRs for overweight (BMI of 25- Conclusions and Relevance Relative to normal weight, both obesity (all grades) and grades 2 and 3 obesity were associated with significantly higher all-cause mortality. Grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality. The use of predefined standard BMI groupings can facilitate between-study comparisons.