The effects of a low frequency acoustic waveform on peripheral vascular disease: a pilot study
L. L. Candela, 1
H.W.Wallmann, 2,a
C. S.Witt 1,b
1 Department of Nursing, University of Nevada, Las Vegas, USA
2 Department of Physical Therapy, University of Nevada, Las Vegas, USA
SUMMARY. Objective: To evaluate the effects of a low frequency acoustic waveform on peripheral vascular disease (PVD). Design: Pilot study utilizing a one-group pre-intervention, post-intervention design. Setting: Adults withperipheral vascular disease were recruited through local advertisements. The study was conducted at a local facility housing the electroacoustic transducer. Intervention: A 25-min exposure to an electroacoustic transducer. Outcome measures: Pre- and post-measurement of Doppler ultrasound blood-flow velocities in 10 arteries, ankle brachial index (RBI), foot assessment, and 1-week post telephone survey. Results: A significant increase was noted in the right ankle brachial index (RABI) but not the left. Blood flow increased in all arteries, significantly in four. Thirteen participants reported improvement in symptom of peripheral vascular disease over the following week. Conclusions: While conclusions must be viewed cautiously, the significant differences noted warrant further study to examine effects of acoustic waveforms on peripheral vascular disease. © 2002 Elsevier Science Ltd. All rights reserved.
INTRODUCTION
Peripheral vascular disease (PVD) is a disease of middle and older age, with symptoms appearing in men around age 45 and women by age 55–60. Every 2 years, for the next 50years, up to 1.3 million people can expect to develop disabling PVD in the United States. Symptoms vary with the extent of the disease. Intermittent claudication, pain felt in the calf while walking that is relieved with rest, is a hallmark symptom most frequently associated with PVD and is a strong diagnostic indicator of the disease. The presence of intermittent claudication can severely limit one’s ability to walk, ultimately leading to further impairment of peripheral circulation. Symptoms tend to worsen in 10–20% of people. Staples of PVD treatment have included lifestyle change, vasoactive medications, and interventional radiological procedures or bypass surgery with grafting. The use of interventional procedures, such as arterial angioplasty or stent placement is limited to more severe cases. One year following angioplasty or stent placement, some 80–90% of patients maintain arterial patency. Despite surgical and interventional advances, as many as 7% of all patients with PVD will go on to require amputation for critical limb ischemia within 5 years of symptom onset.
The literature is rich with research investigating the effects of various treatments on PVD, with studies involving lifestyle change centering primarily on exercise (i.e., walking), smoking cessation, the use of medications to alter blood viscosity, and chelation therapy.
Unfortunately, none of these studies has provided clear, consistent evidence of PVD symptom improvement. This has continued to fuel the search for new methods and alternative therapies that may decrease the pain and disability so often associated with progressive PVD.
L.L. Candela RN, MS, CCRN, EdD, Assistant Professor of Nursing, Depar tment of Nursing, College of Health Sciences, University of Nevada, 4505 Maryland Parkway, Box 453018, Las Vegas, NV 89154-3018, USA. Tel.: +1 702 895 2443; Fax: +1 702 895 4807; E-mail: lcandela@ccmail.nevada.edu
Effects of sound
Recently, healing effects from acoustic waveforms in a specific low frequency range were anecdotally noted in people experiencing various diseases or injuries. As a result, research has been undertaken to study the effects of audible sound on disease, specifically PVD.
Earlier investigations into the effects of sound on the body utilizing frequencies ranging from infrasound (inaudible less than 16 Hz) to ultrasound (inaudible greater than 20mHz) were performed throughout the 1960s and into the 1970s and revealed no detrimental effects or safety hazards from whole body exposure for short periods of time. Some researchers found that prolonged exposure to noise levels above 90dB resulted in hearing loss. However, it soon became clear that hearing impairment was only one of many important effects that sound could have on the body. Many of the later studies examined the physiological effects of sound on endocrine function in rats as well as humans, with some researchers finding increased activity of the corticoadrenal and adrenergic functions as well as an inhibition of the inflammatory response.
Although some older studies can be cited, few, if any, have been conducted in the past 20 years. The model work presented in many of these studies supports the idea that sound at low frequency levels is no threat to health except for a loss of hearing sensitivity in those studies that use excessively high decibel levels for prolonged periods of time. None of these studies examined the effects of vibration and low frequency audible sound on disease. Electroacoustic transducers are widely used in medical applications. Modem transducers often utilize the piezoelectric effect for converting electrical energy to acoustic energy. An alternating current applied to the material produces mechanical vibrations, in turn producing acoustic waves. Piezoelectric elements, therefore, are especially well suited to form the vibratory driving elements in electroacoustic transducers. Using new technology, the purpose of this study was to examine the effects of a low frequency acoustic waveform on PVD.
METHODS
Sample
Adult volunteers were recruited from the community through local newspaper advertisements, which requested that interested people with medically diagnosed PVD attend one of several scheduled 30-min information sessions. Institutional review board approval and informed oral and written consents were obtained from eligible participants.
Design
The pilot study utilized a one-group pre-intervention, post-intervention design. Researchers emphasized the importance of continuing usual patterns of activity and exercise, diet, hydration, rest, and medications prior to the study.
The setting for the study was a local facility housing the electroacoustic transducer (Fig. 1). On the day of the study, prior to the intervention, participants completed a brief background questionnaire. Arm and ankle blood pressures were obtained to determine baseline ankle brachial index (ABI) measurements. The ABI was calculated by dividing the highest systolic ankle pressure by the highest systolic brachial pressure. Generally, 1.0or greater is normal, 0.5–0.9 represents mild to moderate disease, and less than 0.5 represents critical ischemia. Registered nurses completed routine color, movement, and sensation (CMS) peripheral circulation assessments of the feet. The assessment included palpation of skin temperature (warm, cool, and cold), color (flesh, pale, reddish, and bluish), and sensation (present or absent). To increase reliability, both nurses completed all assessments. Utilizing a Doppler flow ultrasound, both legs were examined by a certified ultrasound technician. The common femoral, superficial femoral, popliteal, tibial, and dorsalis pedis arteries were measured for flow velocity.14 Following these pre-intervention measurements, participants were escorted to a room for the intervention. Thermostats were set consistently at 78 ◦F throughout the facility. However, ambient room temperature was not measured.
The intervention consisted of sitting in a chair for 25 min during which time the acoustic generator was turned on. Participants were asked to wear headphones through which relaxation music could be controlled by individual volume dials. Post-intervention measurements were taken for the same variables following the treatment. A 1-week follow-up telephone survey was conducted to assess any changes in PVD symptoms following the session.
Equipment
A portable Doppler ultrasound unit was used to measure blood flow velocity. Using a hand-held transducer, an ultrasound technician applied conductive gel on the area of vessel to be examined. The velocity was recorded on a screen in waveform patterns that correlated with flow centimeters per second. The pulsed flow ultrasound is not considered to be 100% exact because blood flow is pulsatile and is not uniform across the vessel. However, the calculated mean frequencies are highly reliable and are considered diagnostic in terms of evaluating the extent of peripheral artery disease (available online: www.mcbroom.btinternet.co.uk/medict/frames/Title.htm).
The intervention was performed using an electroacoustic transducer, which consists of a metal cylinder and sleeve that house an arrangement of hollow piezoelectric cylinders to form a piezoelectric stack. These vibrate together as a unit and provide the driving mechanism in achieving wall vibrations for the acoustic waves.
A key facet of this technology is the efficiency in which electrical energy is converted to mechanical movement. The transducer is capable of operating at high efficiency, while resonating at a specified frequency. Additionally, it resonates with an omnidirectional beam pattern. The frequency used in this study lies in the range from 500 to 800 Hz.
Fig. 1 Electroacoustic transducer.
Instruments
A background questionnaire was developed by the researchers to gather information on age, gender, length of time diagnosed with PVD and symptoms associated with PVD. A brief follow-up survey was designed to assess PVD symptoms after 1 week. This 1-week time frame was selected based upon anecdotal reports of duration of symptom improvement. The survey utilized yes/no responses to a series of questions relating to PVD symptoms. The instruments were pre-tested on five adult members of the community for readability
Data analysis
Blood flow data were analyzed using the SPSS statistical package for Windows®, release 10.0. Means and S.D. were calculated for the outcome variables. Independent t-tests were used to compare differences in outcome variables between pre- and post-test means. The Bonferroni correction to the alpha level (0.05/5) for each side involving the vessels was applied and the resulting alpha levels were set at 0.01. The ABI alpha level was set at 0.05.
RESULTS
Fifteen people meeting the criteria participated in the study. The 10males and 5 females had a mean age of 73.9 ± 10.6 years. The length of time participants had been medically diagnosed with PVD ranged from 1 year to longer than 20years, with a mean of 8.5 years. The participants reported a variety of PVD symptoms including pain, numbness, tingling, muscle fatigue, squeezing pressure, cramps, and swelling. Walking and standing were the positions most frequently reported to cause discomfort.
Incomplete data exist for several of the dependent variables because of the severity of disease and the difficulty in obtaining readings on many of the involved vessels. Therefore, the number of recorded measurements varied for each participant. Information on participants with complete pre- and post-intervention data is summarized in Tables 1 and 2.
Comparison of data
Comparisons of pre- and post-data for each of the vessels examined are reported in Table 1. The means of all participants’ demonstrated changes in blood flow for all of the vessels examined. However, given the Bonferroni correction, a significant difference was found between pre- and post-measures for only 1 of the 10 vessels investigated: left superior femoral artery (LSF) (P < 0.001). Participants demonstrated significantly increased mean scores for the right ankle brachial index (RABI), (P = 0.05). The ABI data are reported in Table 2.
Little change was noted between the pre- and post-foot assessment. Three of the 15 participants experienced a change in foot color from pale to flesh color. Additionally, foot temperature improved from cool to warm on three participants. Lastly, three participants who initially felt no sensation to sharp touch were able to perceive the sharp sensation following the intervention.
Changes noted between pre-intervention symptoms and 1-week post-intervention symptoms are summarized in Table 3. Of the 15 participants, 13 reported improvement in one or more PVD symptoms during the week following the intervention. Prior to the intervention, there were 23 reports of leg pain, numbness, or tingling. One week after the intervention, that number had dropped to 15, an overall reduction of 35%.
Participants were asked to identify the positions causing the most leg discomfort. Walking and standing were the most identified positions of pain, followed by sitting and lying down. In the 1-week telephone follow up, complaints of position discomfort with walking had decreased 25%, while standing and sitting position complaints had both dropped by 50%. For the one participant who experienced discomfort while lying down, no change was noted after 1 week. The distance that participants were able to walk before feeling PVD symptoms ranged from across the room to more than one block. Before the intervention, only five participants reported being able to walk more than one block before feeling PVD symptoms. One week later, nine participants reported that they could walk more than one block, an increase of 80%. The duration of symptom improvement ranged from 2 to 5 days, with one participant reporting improvement in walking distance and pain reduction for one full month.
DISCUSSION
The present study was designed to evaluate the effects of a low frequency acoustic waveform on PVD. Although a significant increase in blood flow velocity was only noted in one vessel as well as the RABI, it was demonstrated that exposure to the acoustic waves at the designated frequency increased the blood flow velocity pre to post in all of the 10vessels examined. We are unable to corroborate the results obtained with other studies because of the novelty of this intervention. Studies involving infrasound (i.e., under 16 Hz) have yielded diverging results. Some of these researchers examined blood pressure changes during infrasonic exposure, reporting increased diastolic and decreased systolic pressures, while others explored the effects of infrasound on the auditory and non-auditory systems. However, the results of these studies cannot be extrapolated to the present study because frequency and pressure ratios (decibels) are very different.
The characteristics of acoustic frequency involved in the physiological reactions are mostly unknown. It is believed that peripheral vascular disorders involve changes in vessel structure and function. Therefore, conclusions must be viewed cautiously. The significant differences, however, certainly warrant further study.
The study had several limitations. The small sample size and lack of control group are threats to internal validity. There are numerous factors that affect blood flow velocity that the study did not attempt to control for, including underlying vessel size, stress level and endogenous hormone release, heart rate, cardiac output, hydration status, use of medications, diet, smoking status, use of herbs or vitamins, or the presence of concurrent diseases.
The relationship between warmth and vessel dilation is well documented. Although the individual room thermostats were set at 78 ◦F, room temperatures were not measured. The possibility of highly variable temperatures within the facility is a significant weakness in the study.
The follow-up telephone survey relied on participant recall of subjective information. While useful, this type of information would be strengthened through the use of more objective data, such as follow-up ultrasound, ABI, and nursing assessment of the feet. The use of dichotomous responses limited the range of data that could be obtained. A revised survey should include range-type responses. This will make the survey more sensitive to degrees of symptoms versus merely presence of symptoms.
Based on these preliminary findings, a larger scale study has begun which is double blinded and utilizes randomized control and treatment groups. The study should yield more objective information in determining the acoustic wave effects in alleviating PVD symptoms.
ACKNOWLEDGEMENTS
The authors wish to thank Mr. Al Cassone for his assistance in the completion of this study.
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