Oxygen Consumption and Heart Rate Responses During Five Active Exercises

Oxygen Consumption and Heart Rate Responses During Five Active Exercises PAMELA RUZICKA DEHNE and ELIZABETH J . PROTAS . Oxygen consumption (V02) an...
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Oxygen Consumption and Heart Rate Responses During Five Active Exercises PAMELA RUZICKA DEHNE and ELIZABETH J . PROTAS

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Oxygen consumption (V02) and heart rate (HR) responses during five active exercises from a cardiac rehabilitation program were measured in 12 healthy female subjects aged 20 to 30 years. The Vo2 value was determined by collecting expired gases using an open-circuit method. Resting HR and Vo2 values were established while the subjects were positioned supine for 10 to 20 minutes. Exercise values were recorded while the subjects performed five different active exercise bouts consisting of various combinations of upper and lower extremity range-of-motion exercises in the supine or semi-Fowler positions. These exercises were adopted from a stage 1 bedside cardiac rehabilitation program. These activities resulted in low cardiovascular responses: an HR increase of less than 8 bpm and a Vo2 increase of less than 2.0 mL.kg - 1.min -1 .

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Key Words: Heart rate, Oxygen consumption, Physical therapy.

Cardiovascular disease is one of the major causes of death in the United States. Despite the prevalence of the disease, 85% of patients with cardiovascular disease survive episodes of acute myocardial infarction (AMI).1,2 Cardiac rehabilitation, thus, has become an important part of the medical management of the patient with cardiovascular disease. A rehabilitation program is initiated when the patient is hospitalized during the acute and immediate postacute phases of recovery. Rehabilitation of the patient with AMI involves supervised low-intensity exercise and ambulation aimed at minimizing the deconditioning effects of bed rest. During this phase, a patient frequently progresses from simple supine or sitting range-of-motion exercises to more extensive periods of upright exercise before discharge. Clinical trials over the past 25 years have demonstrated that a limited amount of exertion does not increase the incidence of cardiac complications during recovery3 and apparently prevents the deconditioning associated with inactivity. Early supervised physical activity should be oriented toward cardiac work loads that are below the patient's cardiac capacity to ensure the benefits of physical therapy and to avoid the risks of cardiac strain.1,4 The clinician, therefore, must be aware of the cardiovascular stress imposed by certain activities so that only those activities that are within the patient's cardiac capacity are used. Knowledge of metabolic and cardiac demands for each exercise or physical activity are crucial for the

Mrs. Dehne was a student in the master's degree program, Division of Physical Therapy, Texas Woman's University, Houston, TX, when this study was conducted. She is currently Clinical Coordinator, Meyer Children's Rehabilitation Institute, Physical Therapy Department, 444 S 44th St, Omaha, NE 68131 (USA), and Assistant Instructor, Division of Physical Therapy Education, University of Nebraska Medical Center, 42nd and Dewey, Omaha, NE 68105. Dr. Protas is Coordinator of Graduate Programs, Division of Physical Therapy, Texas Woman's University. This study was completed in partial fulfillment of the requirements for Mrs. Dehne's master's degree, Texas Woman's University. This article was adapted from a presentation at the Combined Sections Meeting of the American Physical Therapy Association, Houston, TX, February 5-8, 1984. This article was submitted May 10, 1984; was with the authors for revision 42 weeks; and was accepted December 5, 1985.

Volume 66 / Number 8, August 1986

protection of the patient from excessive myocardial stress in the acute stages of cardiac care. Studies on the cardiorespiratory effects of passive exercise have been conducted.5,6 Smith used heart rate (HR), respiratory rate, and tidal lung volume to determine the effects of passive exercise on cardiorespiratory function.5 The results of her study reflected no significant differences between measures. . Smith also found no increase in oxygen consumption (Vo2) with passive motion of the knee and elbow joints.6 Not many studies have been conducted on the effects of active exercise used in the acute stages of cardiac rehabilitation.2,7-10 Insufficient data are available, therefore, to justify the use of specific low-intensity exercise regimens that simply are presumed to be low intensity. Currently, no quantitative measurements exist of energy expended during active participation in these low-intensity activities.2 In some programs, patients with an uncomplicated AMI are encouraged to sit up at bedside and actively flex and extend their feet, legs, and arms and to use a portable commode two or three days post-AMI.11 Nurses, physicians, and physical therapists currently do not have a thorough understanding of the cardiac work required by these activities. Because of the insufficient knowledge of the cardiac requirements imposed by various daily activities, the restrictions placed on cardiac patients are not systematically uniform or realistic. Patients often perform necessary activities at home that require far greater cardiac effort than activities that were prohibited during their hospital stay. To implement the most advantageous rehabilitation plan, clinicians must be aware of the cardiovascular demands of activities. Information concerning the cardiovascular demands of various activities performed in the early stages of rehabilitation programs is inadequate. Knowledge is needed of standardized, graded, low-level activities used in post-AMI rehabilitation. The purpose of this study was to determine Vo2 and HR responses during five active exercises that are used in the earliest stages of cardiac rehabilitation when the patients are the most unstable. The results of this study will provide a meaningful reference for the physiological demands of these activities. 1215

METHOD Subjects Twelve healthy female physical therapy students, aged 20 to 30 years, volunteered to participate in this study. A brief medical history of each participant was obtained to ensure that none had current respiratory problems and that none had previous cardiorespiratory or musculoskeletal complications that might restrict their activity and influence the results. The subjects were instructed to abstain from smoking and heavy exercise for one hour before data collection. They also were asked to refrain from eating either a light meal within one hour or a heavy meal within three hours of the beginning of the experiment.

with the pillows under the head and knees on a plinth in a quiet and darkened treatment room. The subjects were instructed to relax with their eyes closed and to remain silent for 10 to 20 minutes with the breathing apparatus on. Soft background music was played for relaxation. Resting records were taken at this time to determine steady-state values. Five successive, stable minute-volume values were considered to be the steady-state criterion. Expired air was collected for one minute after a steady state had been attained. The sample then was analyzed with the Beckman LB-2 and OM-14 gas analyzers. Oxygen consumption was calculated from fractional values of oxygen and carbon dioxide and from minute volumes.12

Equipment A headset, plastic mouthpiece, noseclip, one-way valve, flexible hose, Wright* respirometer, and 30- and 120-L meteorological balloons were used to collect expired air. The Wright respirometer was used to measure ventilation volume. Oxygen content was measured with a Beckman OM-14† oxygen analyzer, and carbon dioxide was measured with a Beckman LB-2† carbon dioxide analyzer. Before each procedure, the gas analyzers were calibrated with room air and a sample of known gas concentration. The respirometer was calibrated with an air sample from a Collins Vitalometer‡ (Fig. 1). In addition, a quiet treatment room, plinth, pillows, and stopwatch were required. Fig. 2. Subject in the supine position for exercises A, B, and C. Fig. 3. Subject in the semi-Fowler position for exercises D and E.

Fig, 1. Arrangement of the equipment used during the procedure.

Procedure The subjects were familiarized with the equipment and then fitted with a noseclip, a Daniels§ one-way breathing valve with a 70-cc dead space, a Daniels§ headset, and a Collins‡ rubber mouthpiece. The inlet side of the valve remained open to room air and the outlet side was attached to aflexiblehose and a Wright respirometer. A Collins‡ t-shaped stopcock connected the respirometer to the meteorological balloons that were used to collect the expired air. The subjects' weight was recorded and they then were positioned supine * Precision Scientific, 3737 W Courtland St, Chicago, IL 60647. † Beckman Instruments, Inc, 3900 River Rd, Schiller Park, IL 60176. ‡ Warren E. Collins, Inc, 220 Wood Rd, Boston, MA 02184. § R-Pul Co, 116 S Clark Ave, Los Altos, CA 94022.

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After the relaxation period, the investigator (P.R.D.) demonstrated the active ROM exercises, which then were performed by each subject. The exercise order was randomized by selecting a number from a hat. Exercises were performed at a rate of 30 bpm. A metronome beat was used to ensure a steady rate of performance. The subjects were positioned supine with a pillow under the head for the first three exercises (Fig. 2) and were in the semi-Fowler position for the last two exercises (Fig. 3). The exercises were selected from the cardiac care unit stage of a typical cardiac rehabilitation program.13 Each exercise constituted an exercise bout. Subject 1, for example, performed exercise A (bout 1) and rested, then performed exercise C (bout 2) and rested, and continued the randomized sequence until all five exercises had been completed. After each exercise bout, the subjects were instructed to rest until the steady state was attained again with five PHYSICAL THERAPY

RESEARCH TABLE 1 Means and Standard Deviations for Heart Rate, Oxygen Consumption, and Metabolic Equivalent (METa)Values for 12 Healthy Subjects at Rest and During Exercise Exercise Rest A HR (bpm) Vo 2 (mL.kg - 1 min - 1 ) METs a

61 ± 9 3.16 ±0.71

62 ± 9 3.64 ± 0.79 1.19 ±0.29

B

C

D

E

66 ± 9 4.09 ± 0.84 1.32 ±0.27

68 ± 9 4.79 ± 0.85 1.53 ±0.15

69 ± 8 4.27 ± 0.01 1.38 ±0.33

69 ± 8 4.77 ± 0.99 1.52 + 0.21

One MET equals 3.5 mL O 2 .kg - 1 mirr-1.

consecutively consistent minute volumes. The five exercises performed were as follows: Exercise A. Supine position with a pillow under the head: bilateral ankle ROM for 10 repetitions (per component). Ankle ROM components included abduction, adduction, supination, pronation, plantarflexion,dorsiflexion, and circumduction. Each repetition of the ROM was performed in rhythm with the metronome and each component was performed consecutively, without stopping, until all of the components were completed. Exercise B. Supine position: bilateral ankle ROM and upper extremity (UE) ROM for 10 repetitions (per component) with one-minute rest periods between each UE ROM exercise and between the UE ROM exercises and the ankle ROM exercises. Active UE ROM components included shoulder flexion, shoulder abduction, horizontal shoulder abduction, and elbow flexion. Exercise C. Supine position: UE and lower extremity (LE) ROM for 10 repetitions (per component) with one-minute rest periods between exercises. Lower extremity ROM components included unilateral hipflexion,kneeflexion,and hip abduction. Each motion was performed separately, first on the right leg and then on the left leg. Exercise D Exercise/Components

Repetitions

Shoulder flexion

Exercise D. Semi-Fowler position: bilateral UE ROM for 10 repetitions (per component) with one-minute rest periods between each component (Fig. 4). Exercise E. Semi-Fowler position: bilateral UE and unilateral LE ROM for 10 repetitions (per component) with oneminute rest periods between each component. After completion of the last exercise, the subject was given a 10- to 20-minute rest period to return to the resting rate obtained at the beginning of the experiment. Expired air was collected during each entire exercise bout and during the initial andfinalresting periods. The gas samples were analyzed immediately with the Beckman LB-2 and OM-14 gas analyzers. Heart rate was recorded using a Narco11 biotelemetry unit. Two surface electrodes were attached over the subject's sternum with 1-in (about 2 cm) spacing. The receiver unit was connected to the inlet plug of the high-gain coupler on the Narco physiograph desk model DMP-4B.11 The biotelemetry battery unit was taped to the subject's thorax at an optimal position to avoid creating movement artifact. The initiation of exercise was recorded by the event marker on the physiograph. Ventilation volume was recorded throughout each exercise and rest period. Data Analysis

A one-way analysis of variance .(ANOVA) for repeated measures was performed on the Vo2 values, which were expressed as milliliters per kilogram of body weight per minute, and on the HR values. The F ratio proved to be significant at the .05 level, and a Newman-Keuls mean separation procedure was used.

10x

RESULTS Shoulder abduction

10x

Horizontal abduction

10x

Elbow flexion

10x

Fig. 4. Figures of exercise D. 11

Narco Bio-Systems, Inc, 7651 Airport Blvd, Houston, TX 77061.

Volume 66 / Number 8, August 1986

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Means and standard deviations for HR, Vo2, and metabolic equivalent (MET, where one MET equals 3.5 mL 0 2 .kg-1. min-1) are reported in Table 1. The HR ranged from a low of 61 ± 9 bpm at rest to a high of 69 ± 8 bpm for UE exercises in the semi-Fowler position. Oxygen consumption increased from 3.16 mL.kg-1 .min-1 ± 0.7 mL.kg-1 .min-1 at rest to a high of 4.79 ± 0.9 mL.kg-1 .min-1 and 4.77 ± 0.9 mL.kg-1 . min-1 for combined UE and LE ROM in the supine and semi-Fowler positions, respectively. The MET requirements reflect the generally low Vo2 requirements of the ROM activities in that no MET values exceeded 1.53 ± 0.15. The ANOVA resulted in a significant F ratio of 30.21 (p < .001) for mean HR values (Tab. 2). We found significant differences (p < .05) in the HR responses among rest- and 1217

TABLE 2 Analysis of Variance Results for Heart Rate

a

Source

df

SS

MS

F

Ss Treatment Error TOTAL

11 5 55 71

3,963 873 318 5,154

174.60 5.78

30.21 a

p

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