Page 870 - Cardiac Nursing

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846 PA R T V / Health Promotion and Disease Prevention
differences in general were not found in the rate of nonfatal re- improved myocardial function, increases in coronary artery size,
current reinfarctions in patients undergoing intervention com- and increases in the myocardial capillary-to-fiber ratio. However,
pared with control patients. such changes have been difficult to demonstrate in humans. 61
12
Recently, Taylor et al. performed an updated meta-analysis of The major morphologic outcome of a training program in humans
rehabilitation trials among patients with CHD. While the afore- is probably an increase in cardiac size; however, this adaptation
mentioned studies focused on research performed during the also appears to occur mainly in younger healthy people and is an
1970s and 1980s, the latter study included trials performed unlikely outcome among individuals older than 40 years or in pa-
through 2003. A total of 48 trials met the inclusion criteria, in- tients with heart disease. However, significant hemodynamic
cluding 8,940 patients. Compared with usual care, cardiac reha- changes have been well documented among patients with heart
bilitation was associated with reduced all-cause mortality (odds disease after training. These include reductions in heart rate
ratio 0.80) and cardiac mortality (odds ratio 0.74). In addition, (HR) at rest and any matched submaximal workload, which is
participation in cardiac rehabilitation was associated with greater beneficial in that it results in a reduction in myocardial oxygen
reductions in cholesterol, triglycerides, and systolic blood pres- demand during activities of daily living (ADLs). Other hemody-
sure. However, there were no differences between rehabilitation namic changes that have been demonstrated after training in-
and usual care groups in nonfatal reinfarctions or revascularization clude reductions in blood pressure, increases in blood volume,
rates. Importantly, the effect of rehabilitation on mortality was in- and increases in maximal oxygen uptake. The most important
dependent of chronic heart failure (CHF) diagnosis, type of reha- physiologic benefits of training among patients with heart disease
bilitation, dose of exercise intervention, length of follow-up, trial occur in the skeletal muscle. The metabolic capacity of the skele-
quality, or trial publication data. tal muscle is enhanced through increases in mitochondrial vol-
ume and number, capillary density, and oxidative enzyme con-
Physiologic Benefits of tent. These adaptations enhance perfusion and the efficiency of
43,61,62
Exercise Training oxygen extraction. Finally, an important influence of
training is a favorable effect on the risk profile in patients recov-
Regular exercise increases work capacity. Hundreds of studies have ering from MI (Display 37-2). Although this may include such
been performed cross sectionally that document higher maximum things as reductions in blood pressure, reductions in markers of
.
V
V
oxygen consumption (VO 2 max) values among active versus seden- inflammation (such as C-reactive protein), reductions in body
tary individuals or between groups after a period of training. The weight, reductions in total cholesterol and low-density lipopro-
.
V
V
magnitude of improvement in VO 2 max with training varies tein, and an increase in high-density lipoprotein, recent studies
widely, usually ranging from 5% to 25%, but increases as large as suggest that the most powerful influence of regular exercise may
50% have been reported. The degree of change in exercise capac- be an improvement in insulin sensitivity. It is also important to
ity depends primarily on initial state of fitness and intensity of note that although the effect of exercise on any single risk factor
training. Training increases exercise capacity by increasing maxi- may generally be small, the effect of continued regular exercise on
mal cardiac output and the ability to extract oxygen from the overall cardiovascular risk, when combined with other lifestyle
blood. The physiologic benefits of a training program can be classi- modifications such as proper nutrition, smoking cessation, and
fied as morphologic, hemodynamic, and metabolic (Display 37-1). medication use, can be dramatic.
Many animal studies have demonstrated significant morphologic
changes with training, including myocardial hypertrophy with Cardiovascular Effects of Immobility
The deleterious physiologic effects of prolonged bed rest have
been studied extensively. Since the late 1960s, these studies have
been an important stimulus for cardiac rehabilitation. Although
DISPLAY 37-1 Physiologic Adaptations to Physical these effects are commonly attributed to the absence of regular
Training in Humans
physical activity, an additional important factor underlying the
Morphologic Adaptations deconditioning of bed rest is the absence of normal hydrostatic
pressure caused by orthostatic stress (i.e., caused by gravity). Thus,
Myocardial hypertrophy
even short periods of bed rest (2 to 5 days) are accompanied not
Hemodynamic Adaptations
Increased blood volume
Increased end-diastolic volume
Increased stroke volume DISPLAY 37-2 Changes in Risk Factors Influenced by
Increased cardiac output Exercise Training
Reduced HR for any submaximal workload
Decrease in blood pressure
Increase in high-density lipoprotein cholesterol level
Metabolic Adaptations
Reduction in body weight
Increased mitochondrial volume and number Psychological effects
Greater muscle glycogen stores Less depression
Enhanced fat utilization Reduced anxiety
Enhanced lactate removal Improved glucose tolerance
Increased enzymes for aerobic metabolism Reduction in inflammatory markers
Increased maximal oxygen uptake Improved fitness level