Page 418 - Cardiac Nursing

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394 P A R T III / Assessment of Heart Disease
arousals in sleep. Based on measures of HRV and electroen- difference in HRV between active and inactive individuals is par-
cephalography, it appears that periodic leg movements in sleep ticularly large in older individuals. 88 Also, type and intensity of
are caused by changes in sympathetic activity rather than leading activity is important. Resistance (weight) training does not signif-
to it. 79 icantly increase HRV 89 but endurance (aerobic) training alone 89
or in combination with stress management can significantly in-
Body Position crease HRV. 90 Moderate (8 kcal/kg/week) or high (12 kcal/kg/
week) intensity levels of cardiovascular exercise appear to be re-
Body position and the frequency of positional change are closely quired for significant HRV improvement. 91
related to whether the person is awake or asleep. During sleep, an
individual usually exhibits fewer and less dramatic changes in Obesity and Diet
body position. Whether the patient is asleep or awake, body posi- Obese individuals, as measured by body mass index, are character-
tion should be considered in the interpretation of HRV. Compar- ized by increased resting sympathetic tone: faster heart rates, higher
81
ative evaluations for treatment or intervention should be based on LF power, and lower HF power. Other researchers have not found
assessment that is consistent for positioning. significant associations between body mass index and HRV in
In terms of vertical positioning, HRV is significantly reduced healthy adolescents 92 or between body mass index and SNS activ-
from supine to sitting and further decreased from sitting to stand- ity markers in mild to moderately obese healthy adults. 93 Rabbia
94
80
ing positions. In healthy subjects, change from supine to standing et al. suggest that ANS function is dependent on duration of obe-
positions also reduces vagal input (low HF), increases the LF:HF, sity. Specifically, compared with lean adolescents, measures of SNS
59
and reduces LF power. Postural changes evoke a greater HRV re- activity were increased in subjects with recent ( 4 years) obesity
sponse in women than in men, 81 although this difference was not but not chronic obesity. HRV reduced significantly with duration
59
found elsewhere. ANS postural change responses are blunted with of obesity. Orthostatic (lying to standing) stress testing indicates a
increased age. 59,81 blunted autonomic response in obese individuals. 81
Recumbent positioning that enhances vagal tone in the cardiac The relationship of diet to HRV is gaining attention. Levels
care patient could promote recovery by reducing cardiac demand of total cholesterol and low-density lipoprotein cholesterol are
and, subsequently, the risk of malignant cardiac events. The right significant predictors of reduced HRV in “healthy” individuals
lateral position is associated with a higher vagal tone (higher HF) with hypercholesterolemia. 95 Omega-3 fatty acid supplementa-
than either the left lateral or the supine positions. This position- tion and fish-based oils in particular, are associated with increased
based vagal enhancement is consistently found in individuals with HRV. 96,97 Compared with low salt diets (1 mmol/kg sodium,
coronary artery disease, 82 in patients during the acute phase of an 1 mmol/kg potassium), high salt diets (4 mmol/kg sodium,
MI, 83 and in patients with CHF. 84 Healthy individuals also show 1 mmol/kg potassium) significantly increase HF power. 98 Indi-
vagal predominance with the right lateral position, 82 although viduals who are chronically underweight and undernourished
this observation is not reported consistently. 84 show reduced total power, LF power, and HF power compared
Position-related differences in HRV may be an important fac- with underweight well-nourished or normal-weight well-nourished
tor in sudden infant death syndrome. Compared with sleeping in individuals. 99
the supine position, sleeping prone is recognized as a significant
risk factor for sudden infant death syndrome and is associated Smoking and Environmental Exposures
with lower HRV in term infants at 1 and 3 months of age. 85 Smoking has an immediate impact on HRV, characterized by an
Preterm infants are especially at risk for sudden infant death syn- acute decrease in cardiac PSNS activity and a surge in systemic
drome. HRV assessment of these high-risk patients measured dur- SNS activity, including increased heart rate. 100,101 The long-term
ing a daytime nap showed significantly reduced HRV and reduced and dose-related effects of smoking on HRV are less clear. Some
PSNS activity in the prone versus supine position at 1 and researchers report that smoking, including passive smoke expo-
3 months of corrected age. 86 These results lend support for pro- sure 102 and especially chronic heavy smoking ( 25 cigarettes per
moting sleep in the supine position. day), reduces HRV and vagal activity. 100 However, a significant
association is not found consistently. 59,81,93
General Health Exposure to metals (i.e., iron, manganese, aluminum, copper,
zinc, chromium, lead, nickel) in the form of particulate matter has
Results from the Atherosclerosis Risk in Communities (ARIC) been associated with decreased nighttime HRV (rMSSD) in
Study, a large population-based study of middle-aged men and boiler-maker workers. 103,104 Short-term exposure to sulfur dioxin
women, support that low HRV is associated with increased mor- has also been found to lead to a reduction in vagal activity. 105
tality rates that are not attributable to cardiovascular risk factors More studies related to environmental exposures, and lead expo-
87
or to other disease conditions. This suggests that low HRV may sure in particular, are needed to confirm trends for negative im-
be a sensitive indicator for poor general health in addition to an pact on HRV. 106
index of cardiovascular risk.
A major contributor to general health is lifestyle. Many aspects Alcohol
of lifestyle have been explored with respect to impact on HRV HRV is one approach used to explore the cardioprotective and
patterns. These include physical activity, obesity and diet, smok- cardioputative effects of alcohol. Although population-based
ing, and alcohol and coffee consumption. study results indicate that alcohol is not a significant lifestyle
factor affecting HRV in healthy adults, 59,93 other research sup-
Physical Activity ports that the relationship is more complex. In one study in-
Physically active individuals tend to have lower heart rates and in- volving a randomized crossover design, findings suggest that
88
creased HRV compared to those with a sedentary lifestyle. The moderate regular alcohol consumption in healthy individuals