ENDURANCE TRAINING IMPROVES SKELETAL MUSCLE ELECTRICAL ACTIVITY IN ACTIVE COPD PATIENTS
Gosselin N, Lambert K, Poulain M, Martin A, Prefaut C, Varray A Muscle Nerve. 2003;28(6):744-753. Sport, Performance, Health Laboratory, Faculty of Sport Sciences, 700 Av du Pic St Loup, 34090 Montpellier, France. [email protected]
The effect of endurance training on muscle electrical activity during general exercise testing was investigated in physically active patients with chronic obstructive pulmonary disease (COPD). Before and after rehabilitation, patients performed identical incremental exercise tests. Pulmonary gas exchange, venous lactate and pyruvate concentrations, and the quadriceps electromyographic signal were sampled every minute throughout exercise testing. Three weeks of rehabilitation increased exercise capacity without modifying pulmonary function. M-wave amplitude, root mean square (RMS) of electromyographic activity, and RMS/oxygen uptake were increased significantly during post-rehabilitation testing at the same exercise intensity compared to pre-rehabilitation. Median frequency was significantly lower after training. These modifications reflect greater muscle excitability, greater muscle activation for the same level of exercise, and higher recruitment of slow-twitch fibers. Pulmonary rehabilitation in active COPD patients may normalize the electrical activity of skeletal muscles during incremental dynamic exercise. The electromyographic signal confirms neuromuscular changes after endurance training.
Abstract Commentary: Exercise training improves many aspects of skeletal muscle function among patients with COPD, including strength and endurance, at least in part by improving muscle oxidative enzyme capacity. This study by Gosselin and colleagues furthers our knowledge of the mechanisms by which exercise training improves muscle function for COPD patients. The authors have shown that endurance training can lead to increased electrical muscle activation and excitability for a given level of exercise (based on electromyogram signals), with increased recruitment of endurance type muscle fibers.
BENEFITS OF SUPPLEMENTAL OXYGEN IN EXERCISE TRAINING IN NONHYPOXEMIC CHRONIC OBSTRUCTIVE PULMONARY DISEASE PATIENTS
Emtner M, Porszasz J, Burns M, Somfay A, Casaburi R Am J Respir Crit Care Med. 2003;168(9):1034-1042 (Epub 2003 Jul 17)
Supplemental oxygen improves exercise tolerance of normoxemic and hypoxemic chronic obstructive pulmonary disease (COPD) patients. We determined whether nonhypoxemic COPD patients undergoing exercise training while breathing supplemental oxygen achieve higher intensity and therefore improve exercise capacity more than patients breathing air. A double-blinded trial was performed involving 29 nonhypoxemic patients (67 years, exercise SaO2 > 88%) with COPD (FEV1 = 36% predicted). All exercised on cycle ergometers for 45 minutes, 3 times per week for 7 weeks at high-intensity targets. During exercise, they received oxygen (3 L/minute) (n = 14) or compressed air (3 L/minute) (n = 15). Both groups had a higher exercise tolerance after training and when breathing oxygen. However, the oxygen-trained group increased the training work rate more rapidly than the air-trained group. The mean +/- SD work rate during the last week was 62 +/- 19 W (oxygen-trained group) and 52 +/- 22 W (air-trained group) (P < .01). After training, endurance in constant work rate tests increased more in the oxygen-trained group (14.5 minutes) than in the air-trained group (10.5 minutes) (P < .05). At isotime, the breathing rate decreased four breaths per minute in the oxygen-trained group and one breath per minute in the air-trained group (P = .001). We conclude that supplemental oxygen provided during high-intensity training yields higher training intensity and evidence of gains in exercise tolerance in laboratory testing.
Abstract Commentary: Studies of exercise training for COPD patients have shown that endurance training at both low and high intensity can improve exercise endurance. However, high intensity aerobic training is needed to achieve physiologic gains in aerobic fitness such as increased VO2max and delay in anaerobic threshold, with resultant decrease in ventilatory requirement. However, some patients are unable to exercise at high intensity. Although supplemental oxygen can help improve exercise tolerance, its use is conventionally reserved for persons with resting and/or exercise-related hypoxemia. This study by Emter and colleagues demonstrates that supplemental oxygen used during exercise training by non-hypoxemic patients can enable patients to perform higher intensity training compared to training while breathing room air. This may in turn enable patients to achieve physiologic gains in aerobic fitness than would otherwise not be possible. Further work is needed to clarify which patients are most likely to benefit from this intervention in the context of pulmonary rehabilitation programs.
CORONARY ARTERY CALCIUM SCORE COMBINED WITH FRAMINGHAM SCORE FOR RISK PREDICTION IN ASYMPTOMATIC INDIVIDUALS
Greenland P, LaBree L, Azen SP, Doherty TM, Detrano RC JAMA 2004;291(2):210-215.
Background: Current prediction models for coronary risk stratification, including the Framingham Risk Score (FRS), have limitations. Quantification of coronary artery calcium score (CAC) using computed tomography (CT) has been suggested to improve risk assessment to guide preventive treatment intensity.
Objective: This study aimed to determine whether CAC assessment combined with FRS among asymptomatic adults provides information superior to either method alone and whether the combined approach can more accurately guide primary preventive strategies for patients with coronary heart disease (CHD) risk factors.
Methods: The South Day Heart Watch is a prospective observational population-based study comprised of 1461 asymptomatic adults (> 45 years) with at least one coronary risk factor. Subjects underwent CT examination and were contacted yearly for up to 8.5 years. Main outcome measures included nonfatal myocardial infarction (MI) or CHD death.
Results: 1029 participants were included in the analysis. During the median 7 year follow-up, 84 patients experienced either a nonfatal MI or CHD death. An FRS of > 20% predicted the risk of MI or CHD death (hazard ratio [HR] of 14.3, compared to an FRS <10%). A CAC of >300 also predicted the risk of MI or CHD death (HR of 3.9, compared to a CAC of zero). Across categories of FRS >10%, CAC was predictive of coronary risk; this additive predictive value was not seen among patients with FRS <10%. The mean area under the receiver operating characteristic curve for FRS plus CRC was 0.68, which was significantly greater than that for FRS alone.
Conclusions: This study demonstrates that a high CAC can modify the predicted risk obtained from FRS alone. This is especially true for patients in the intermediate-risk category for whom clinical decision-making is most uncertain.
Comments: Risk stratification is only clinically relevant if risk can be modified to reduce future events. In this study, CAC does not predict risk in patients whose FRS is <10%; this supports the current consensus not to use this modality for population screening. For high-risk patients (FRS > 20%), CAC adds little to one's clinical decision making. For those patients in the intermediate risk category however, CAC does provide additive information. Improving a clinician's ability to risk stratify an individual patient is important, however this has to be balanced by the additive cost conferred by diagnostic testing in an asymptomatic patient.
POOR CONTROL OF RISK FACTORS FOR VASCULAR DISEASE AMONG ADULTS WITH PREVIOUSLY DIAGNOSED DIABETES
Saydah SH, Fradkin J, Cowie CC JAMA 2004;291:335-342
Background: The current state of control of risk factors for vascular disease among individuals with diabetes mellitus in the United States is unknown.
Objectives: To examine 1999-2000 national data on control of risk factors for vascular disease among adults with previously diagnosed diabetes and to assess trends during the past decade.
Methods: Review of data from the Third National Health and Nutrition Examination Survey (NHANES III) and NHANES 1999-2000, which are cross-sectional surveys of a nationally representative sample of the non-institutionalized civilian US population. Participants were adults aged 20 years and older with previously diagnosed diabetes who participated in both the interview and examination in either cohorts. Levels of glycosylated hemoglobin (HbA1c), blood pressure, and total serum cholesterol were the main outcome measures in reference to target goals.
Results: In NHANES 1999-2000, only 37% of participants achieved the target goal of HbA1c level < 7% and 37.2% of participants were above the recommended "take action" HbA1c level of 8%; these values were not different from NHANES III. Only 35.8% of participants achieved the target of systolic blood pressure (SBP < 130 mmHg) and diastolic blood pressure (DBP < 80 mmHg); these values were also not different from NHANES III. Over half (51.8%) of the participants had total cholesterol levels of 200 mg/dL or greater; this is lower than the 66.1% from NHANES III (p < 0.001). In total, only 7.3% of adults with diabetes in NHANES 1999-2000 attained recommended goals for all risk factors, ie, HbA1c < 7%, BP < 130/80, and total cholesterol < 200 mg/dL.
Conclusion: Further public health efforts are needed to control risk factors for vascular disease among individuals with diagnosed diabetes.
Comments: These are sobering data from NHANES 1999-2000. There is clearly a disconnect with regards to evidence-based recommendations and actual individual patient care. The reasons for this "gap" are multiple and solutions will likewise require a concerted effort not only by the medical practitioners but also by the lay community and our government leaders. To achieve the goal of Healthy People 2010, we need to start by implementing the most simple of guidelines in our clinics, one patient at a time.