Many changes occur in body systems as a result of aging Benison, 1986; Berman, 1988; Fitzgerald, 1985). These changes are usually not noticeable at rest but may be significant during times of unaccustomed stress, such as that which occurs with physical activity. Although such stress on an aging body may pose a risk, the physiological benefits of regular physical activity far outweigh the costs associated with a sedentary lifestyle (Benison, 1986), Quality of life may be heightened, capability for work and recreation may be improved, and the degree of functional decline in the elderly may be attenuated (Fitzgerald, 1985).
A number of studies have examined exercise capacity and exercise conditioning in groups of healthy elderly subjects (DeVries, 1970; Seals, 1984; Suominen, 1977). Researchers have demonstrated a diminished exercise capacity in the elderly as compared with younger subjects (Ades, 1990). However, little is known about the effect exercise has on oxygen saturation in the elderly, and whether or not normal oxygen saturation (O2Sat) levels are maintained in this segment of the population. This lack of available knowledge regarding oxygen saturation levels is of concern. In addition, it has not been documented whether exercise, by reducing oxygen saturation, increases the risk for ischemia and subsequent cardiac events in the elderly postcarcliacevent subject. Thus, the evaluation of the risk-benefit ratio of exercise as a therapeutic intervention by simultaneously evaluating O2Sat and ratepressure product (RPP) responses to exercise in this at-risk population of subjects was the primary objective of this study.
REVIEW OF LITERATURE
It has been shown that the normal pulmonary partial pressure of oxygen is decreased in the elderly (Knudson, 1981). Recently, oxygen saturation has also been shown to decrease with age (Ogburn-Russell, 1990). The traditional viewpoint regarding the effects of exercise on arterial blood gases is that no change occurs from rest to submaximal work in the partial pressure of oxygen in arterial blood and the percent of hemoglobin saturated with oxygen (Powers, 1984). Both Dempsey and associates (1982) and Young and Woolcock (1978) have reported that the partial pressure of oxygen may fall during leg exercise. It would follow, then, that the oxygen saturation would also fall.
Blom and associates (1988) suggested that mild activity did not significantly effect O2Sat levels in their subjects (aged 20 to 90), due to the S-shaped oxyhemoglobin dissociation curve. Of 106 patients who exercised on a treadmill until they could no longer continue, Kelly and associates (1986) reported that 36 had changes in oxygen saturation of 2% or more, while 26 had changes of 4% or more. They noted that when measuring oxygen saturation, small changes in arterial oxygen tension do not substantially alter oxygen saturation in the upper, flat segment of the oxyhemoglobin dissociation curve.
Powers and associates (1984) studied the influence of incremental arm and leg work on oxygen saturation. Nine participants, with a mean age of 27, engaged in an incremental armcrank test and an incremental cycleergometer test. It was discovered that oxygen desaturation occurs with both arm and leg exercises. However, little change in oxygen saturation occurred until the subjects reached greater than 70% of maximal oxygen consumption (VO2tnax)/ with the greatest change occurring after reaching 90% VO21113x. It was hypothesized that this desaturation during high-intensity exercise may have occurred from a combination of a decreased partial pressure of oxygen and a right shift in the oxyhemoglobin dissociation curve.
Cardiac output and oxygen consumption during submaximal exercise in the elderly do not change from resting levels (Van Camp, 1989) due to declines in the submaximal exercise heart rate (Badenhop, 1983; Niinimaa, 1978) and augmented stroke volume (Van Camp, 1989). During maximal exercise, the maximal heart rate is also lower. The aged cardiovascular system partially compensates for this decrease by increasing venous return (Oka, 1990; Rodeheffer, 1984; Van Camp, 1989), which in turn enhances cardiac filling and allows an increase in stroke volume (Fleg, 1986). Rodeheffer and associates (1984) discovered no significant age-associated decline in cardiac output in healthy elderly at rest or during upright bicycle exercise. However, they established an age-related increase in stroke volume that was sufficient to prevent the decline in cardiac output which was expected due to the decline in exercising heart rate.
In bom submaximal and maximal levels of exercise, systolic blood pressure (SBP) increases, while diastolic blood pressure (DBF) does not change or declines (Van Camp, 1989). After training, both resting SBP and DBP decrease (Boyer, 1970; DeVries, 1970). RPP, the product of heart rate and SBP, is decreased after physical training (Nelson, 1974). As RPP increases or decreases, myocardial oxygen consumption and myocardial blood flow will also increase or decrease, respectively (Nelson, 1974). Myocardial demands for blood flow and oxygen do not necessarily correlate to the degree of exertion or metabolic demands of the body as a whole (Rowell, 1986).
VO^sub 2max^ is widely accepted as an index of cardiovascular functional capacity (Dehn, 1972; Sagiv, 1989). Several studies have found mat improvements in exercise capacity and in VO^sub 2max^ occur in the elderly as a result of exercise (Dehn, 1972; DeVries, 1970; Foster, 1989; Haber, 1984; Steinhaus, 1990). Thomas and associates (1985) reported an 18% increase in VO^sub 2max^ in elderly men following a 12-month training program. Seals and associates (1984) documented improvements in VO^sub 2max^ in older women undergoing 6 months of low-intensity exercise, followed by 6 months of high-intensity exercise. Increases in VO^sub 2max^ occurred in both levels of exercise, with a greater increase occurring after high-intensity training (Seals, 1984).
Maximum oxygen consumption is the product of maximum cardiac output and maximum arteriovenous oxygen difference (Rodeheffer, 1984). Several studies suggested that an increase in VO2013x found in elderly subjects after exercise was a result of an increase in maximal arteriovenous oxygen difference (Seals, 1984; Frontera, 1990; Merrill, 1988).
Investigations concerning the effect that exercise training has on the respiratory system have been contradictory. Research has not consistently demonstrated adaptations in lung volumes, ventilatory flow rate, and alveolar-capillary gas exchange in any age group due to increases in physical activity (Landin, 1985; Reddan, 1981). These findings may support the contention that "the lung-thorax system (with few exceptions) has a near optimum response to steady-state exercise and that oxygen transport is more critically dependent upon cardiovascular function" (Reddan, 1981). However, DeVries (1970) found a significant increase in vital capacity and minute volume in elderly men following an exercise program. Walker (1986) also found increases in minute volume, pulmonary arterial pressure, and pulmonary diffusing capacity in response to training.
A longitudinal design was used to determine if exercise over a course of 6 weeks produced changes in oxygen saturation, heart rate, respiration, DBF, SBP, and RPP.
The sample consisted of 10 persons over the age of 58 who were undergoing physical conditioning by participating in the DePaul Health and Fitness Institute: Cardiac Rehabilitation Phase II (DHFI). Fifteen individuals were admitted to DHFI during the duration of this study. Two individuals did not meet the age requirements, one declined to participate, and two were unable to complete the study due to debilitating illness and insurance restrictions. Participants were fully informed, and each signed a consent form. All participants were postacute cardiac event and were participating due to physician recommendations. Admission diagnoses included myocardial infarctions, angioplasty, aortic valve replacement, and coronary artery bypass grafting.
The age range was 59 to 88 years, with a mean of 66.1 years. Ninety percent were male. Five subjects indicated that they participated in regular exercise prior to their cardiac incidence. Five participants regularly used a stationary bike outside of the program, during the study (mean use in minutes per week was 46 ±21). All participants engaged in walking during the study (mean of 3.94 miles per week ± .87).
DHFI is an outpatient program of DePaul Hospital in Cheyenne, Wyoming, designed for the individual who has had a cardiac event within the previous year. The program consists of 36 1-hour sessions of prescribed and monitored exercise. The sessions consists of 5 to 10 minutes of warm-up and stretching exercises, 30 minutes of physical conditioning with prescribed equipment, and 5 to 10 minutes of cool-down and stretching exercises.
Analysis of the Procedure
A repeated-measures analysis of variance (ANOVA) was used to test for significant differences between the means of oxygen saturations of participants, as well as other measurements of cardiopulmonary functioning, at weeks 1, 3, and 6, pre-, during, and postexercise. When the F value from the ANOVA indicated overall significance, a Scheffé posthoc comparison test was used to determine the exact location of the significance. An alpha level of .05 was set as the acceptable level of significance.
A MET is a unit of energy costrelated to workload (Erb, 1979). One MET "represents the approximate rate of oxygen consumption of a seated individual at rest" (American College of Sports Medicine, 1986). One MET is an oxygen consumption of approximately 3.5 ml kg^sup -1^ min^sup -1^. As METs are multiples of the resting rate of oxygen consumption, an individual exercising at 2 METs is consuming oxygen at twice the resting rate. For this study, METs were used to:
* represent the rate of an individual's energy cost during exercise;
* measure an individual's physical work capacity; and
* measure the metabolic requirement of a task during the program.
Equipment used for this study included hand-held sphygmomanometers, a Nellcor N-IO Portable Pulse Oximeter (NPPO) and treadmills, and Air Dyne and Monarch cycle ergometers for data collection during exercise.
Calculation of MET Levels
Individual MET levels on the various cycle ergometers or treadmills were determined by the exercise physiologist using metabolic equations described in Guidelines far Exercise Testing and Prescription (American College of Sports Medicine, 1986).
Respiration, Blood Pressure, and Pulse
Respiration rate and blood pressures were taken by the investigator. All pulses were taken with the NPPO. Accuracy of these pulses was verified by comparing a random pulse reading (either pre-, during-, or postexercise pulse) of the NPPO to the participant's radial pulse as palpated by the investigator on each data-collection day.
All oxygen saturations were taken by the investigator with an NPPO. Hess and associates (1986) found that when oxygen saturation was between 77% and 100%, the arterial oxygen saturations of the NPPO had a 0.96 correlation with arterial oxygen saturations obtained from arterial blood gases and measured with a cooximeter. They concluded that while the differences between the NPPO and the co-oximeters were statistically significant, the difference was too small to be clinically important.
Each participant completed a graded exercise test that was used to determine the individual's target heartrate range (THRR) and starting MET level. The exercise physiologist scheduled appropriate equipment for the ordered MET level of each participant. As conditioning occurred, the MET levels were changed (by increasing the intensity or workload of the equipment) to maintain the individual's THRR.
Initial data were gathered within 1 week of the day that participants started the exercise program. Heart rate, respiration rate, SBP, DBP, and O2Sat levels were collected on that starting date and weekly for 6 weeks. These measures were obtained on all participants at three points of each data-collection day:
* prior to the beginning of warmup exercises (pre);
* after at least 5 minutes of exercising (during); and
* after cool-down and stretching exercises were completed (post).
The workload or power output eliciting the desired starting MET level for week 1 was recorded. For the purpose of data collection, at weeks 3 and 6, participants were again asked to exercise at their initial workloads so that cardiorespiratory responses to the same initial MET level following conditioning could be evaluated. Participants used the same exercise equipment for data collection at each of the measurement timepoints.
A self-report exercise log was recorded for each participant. This log recorded any walking or bicycling that the participants performed between exercise sessions. Total minutes of bicycling and total miles of walking were recorded for each week.
The exercise program resulted in a significant conditioning effect so that mean exercising MET levels doubled, going from 2± .17 METs at the outset (week 1) to 4 ± .37 METs by the week-6 measurement time-point. As shown in the Table and Figures 1 through 3, the main findings of the study were statistically significant reductions for heart rate, SBP, and RPP, all during exercise over the 6-week course of the exercise-conditioning program. There were no significant changes in the pre- or postexercise measurements. Changes in heart rate were statistically significant (p = .002) during exercise, both at weeks 3 and 6, when compared with week 1. The mean heart rate at week 1 was 102 bpm. The heart rate dropped to a mean of 89 bpm at week 3, with a further decrease to a mean of 83 bpm at week 6. There were no significant changes in the mean heart rate between weeks 3 and 6.
The changes in SBP also were found to be statistically significant during exercise. When compared with week 1, a significance value of .002 was present both at week 3 and week 6. The mean SBP at week 6 was 121 mm Hg; at week 3, it was 122 mm Hg. This was a decrease from the initial SBP of week 1 (134 mm Hg). There were no significant changes in the mean SBP between weeks 3 and 6.
No changes in RPP, either pre- or postexercise, were observed for the duration of the study. However, RPP during exercise showed a significant (p = . 0001) decline at weeks 3 and 6. The mean RPP fell to 10,724 bpm mm Hg at week 3 after an initial finding of 13,657 bpm mm Hg. Week 6 showed a further decline to 9,970 bpm mm Hg. Respiratory rate and O2Sat levels showed no changes either going from pre- to during- to postexercise, or from week 1 to weeks 3 or 6.
There is little literature documenting the effect of age on oxygen saturation. Ogburn-Russell and Johnson (1990) have reported that oxygen saturation of the well elderly is lower than that of younger persons. It has also been noted that the normal pulmonary partial pressure of oxygen is decreased in the elderly (Knudson, 1981). This decrease in partial pressure could potentially contribute to a decrease in oxygen saturation (Ogburn-Russell , 1990). The current study found oxygen saturation to be well-maintained during exercise in this population, as shown by the values seen at the outset of the study. Consequently, it is perhaps not surprising that over the course of the 6-week program, neither increments nor decrements in oxygen saturation were observed.
Effects of a 6-Week Rehabilitation Exercise Program in Elderly Posfcarcffac-Evenf Patients
The findings from this study contradict those of previous studies concerning respiratory rates and conditioning. Nordrehaug and associates (1989) found that postmyocardial infarction subjects, undergoing 4 weeks of training, experienced a decline in breathing frequency during submaximal exercise levels.
These findings also contradict previous investigations regarding the effect of exercise on DBP. For example, DeVries (1970) found a significant decrease in resting DBF of subjects completing 6 weeks in an exercise program. Blumenthal and associates (1989) also reported significant changes in subjects' DBF after 4 months of aerobic training.
While heart rate decreased before and after exercise over the 6-week period, the reductions were not significant. Sidney (1981) reported that a slowing of the resting pulse is not a common finding in conditioned elderly persons. Heart rate was significantly lower (p = . 002) during exercise both at week 3 and week 6. These results are in agreement with the directional changes during and postexercise reported in the literature (Badenhop, 1983; Niinimaa, 1978).
Nordrehaug and associates (1989) noted a significant drop in heart rate during submaximal exercise levels after training. Seals and associates (1984); Haber and associates (1984); and Niinimaa and Shephard (1978) also reported that heart rate decreased after submaximal exercise training. In contrast, Merrill (1988) reported no changes in heart rate after training at submaximal and maximal exercise levels. Although it is not significant, Steinhaus and associates (1990) noted a 4-beats-perminute decline in recovery heart rate following 4 months of aerobic training.
Heart Rate (beats per minute)
Systolic Blood Pressure (mm Hg)
Rate-Pressure Product (beats per minute x mm Hg)
There are many reports in the literature detailing changes in resting SBP due to conditioning. Steinhaus and associates (1990) reported a lower resting SBP after 4 months of aerobic conditioning, while DeVries (1970) noted a decline in resting SBP after 6 weeks. Changes over time in during- and postexercise blood pressures are not as welldocumented.
In aus study, resting blood pressures did not change significantly over the course of the study. However, blood pressures during exercise for weeks 3 and 6 were found to be significantly lower (p = . 002), as compared to week 1. This finding, combined with a lowered heart rate found during exercise, indicated that myocardial oxygen consumption during exercise, as estimated from RPP, also decreased over a period of 6 weeks.
Hedback and associates (1990) determined that the use of betablocking agents influences RPP. They analyzed three subgroups:
* those on continuous beta-blocking therapy before and after coronary artery bypass grafting (CABG);
* those without any beta-blocking therapy; and
* those who were taking betablocking therapy prior to CABG, but not after.
They reported that post-CABG subjects who were being treated with beta-blocking agents, as well those who had never taken beta-blocking agents, had a lower RPP after 1 year of physical training in a cardiac rehabilitation program, even after attaining pre-CABG workloads. The findings from the current study support those of Hedback and associates (1990), in that conditioning appeared to improve myocardial oxygen demands for a given MET level, as estimated from RPP.
The study sample included individuals with a variety of illnesses and who were taking a variety of medications. There were no controls for additional factors, such as admitting diagnosis, starting MET levels, age, diet, lifestyle, and pre- or duringstudy exercise levels. All of those factors may have affected individual exercise intensity.
This study was conducted over a 6-week period. Expanding the length of the study to allow individuals more time to increase their intensity of conditioning may have resulted in additional changes. Further desirable modifications in the methodology would include obtaining a larger sample. The convenience sample may not have been large enough to detect significant differences in cardiopulmonary measures at weeks 1, 3, and 6, which showed directional trends, such as DBP. In addition, the size may not allow for generalizations to the larger population of elderly. Further studies should control for outside exercise and starting MET levels. This would allow for a better comparison between individuals.
Much of the literature is based on examination of the effect of exercise on either males or females. There is little documentation comparing the effects of similar exercise programs on the basis of gender. Neither is there much documentation regarding the effects of exercise on the "very old" (aged 85 and older). Since the sole "very old" subject in this study and the one female subject showed improvements in O2SaI levels/ heart rate, and blood pressure, a comparison of age groups and gender may reveal further changes in cardiopulmonary functioning due to exercise.
Although the limitations of this study must be considered when offering implications for nursing practice, the results of this study will add information to the growing body of knowledge on the effects of exercise in the elderly. The monitoring and evaluation of blood pressure, pulse, and respirations are basic nursing responsibilities. The results of this study will assist nurses to evaluate these measurements in relationship to physical conditioning.
The use of portable pulse oximeters is rapidly becoming standard practice in many nursing care settings. Pulse oximetry is a quick, noninvasive means of monitoring oxygénation. Pulse oximeters can be used to supervise individual response to activity in almost any setting. Decisions for continued or progressive activity can men be made based upon objective data. However, more information is needed regarding appropriate ranges of oxygen saturation, as measured by a pulse oximeter, for elderly persons in different activity settings.
The results suggest that physical conditioning does not affect oxygen saturation in the elderly. However, as a result of physical conditioning, pulse, SBP, and RPP all showed significant beneficial changes. The findings, with respect to RPP (an indirect measurement of myocardial oxygen consumption), indicate after a 6-week exercise conditioning program that the heart's requirement for oxygen at a given MET load is significantly reduced in cardiac-event subjects. Such a program would therefore appear to provide cardioprotective effects to this population.
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Effects of a 6-Week Rehabilitation Exercise Program in Elderly Posfcarcffac-Evenf Patients