Aquatic Osteopathy Treatment Assessment by Infrared Thermography on Healthy Subjects After Thermoneutral Water Immersion

Abstract

Objective

Aquatic osteopathy (AO) is a recent discipline that has not yet demonstrated its value compared with existing therapies. This study compared AO with aquatic therapy (AT)—that is, thermoneutral water immersion—using infrared thermography on healthy individuals to assess differences in cutaneous body temperature.

Methods

Fifty-five healthy individuals were immersed in thermoneutral water for 1 hour and then underwent AO treatment, with application of a classic diagnosis routine and subsequent manual therapy. Thermograms were recorded to measure the distribution of skin surface temperature throughout the entire body after 1 hour of immersion in thermoneutral water (AT) and compared with thermograms taken after AO.

Results

Visual analysis of the thermograms showed that there were thermographic differences between the 2 groups. A statistical analysis revealed significant differences between post-AT and post-AO thermograms (P = .002): the mean variance in cutaneous body temperature was significantly lower in the post-AO group than in the post-AT group. Therefore, cutaneous body temperatures were more homogeneous after AO than after AT.

Conclusion

Cutaneous thermal reactions were more homogenous after AO than after AT alone, with cutaneous temperatures returning closer to normal than after AT alone. These reactions may be related to physiological reactions due to a decrease in vasoconstriction or trigger points. Further studies are needed to clarify these physiological reactions to establish the mechanisms of AO and thus better define its indications.

Introduction

Every year in France, 500 000 patients are treated using aquatic therapy (AT; also known as hydrotherapy, thalassotherapy, balneotherapy, spa therapy, etc).¹ Aquatic therapy is defined as immersion in thermoneutral water without exercise and as the use of water for its therapeutic benefits.² Benefits are particularly manifest in the field of rheumatology,³ with reduced pain, less joint soreness, and increased grip strength. Aquatic therapy also has positive effects on respiratory diseases (facilitating expiration⁴), cardiovascular illnesses (less pain, swelling, and limping in individuals with varicose veins^5,6), and psychosomatic diseases,^7,8 and has an analgesic effect on the musculoskeletal system (neck pain, back pain, fibromyalgia, rheumatoid arthritis or osteoarthritis,⁹ and management of postoperative rehabilitation).

According to its temperature and hydrostatic pressure, water affects the physiology of the circulatory system.¹⁰ Hydrostatic pressure causes the heart rate to drop while increasing cardiac output, decreases peripheral resistance due to an increase in arterial vasodilatation, increases venous return, and reduces swelling caused by extracellular intravasation fluids in the blood.^11,12 Dermal application of heat does not increase tissue temperature beyond 2 cm under the skin.¹³ The deeper physiological responses related to immersion in warm water result in particular from the release of humoral factors that relieve deep pain.¹⁴ Thermotherapy is practiced in warm water¹² (35°C ± 2°C) called thermoneutral.¹⁵ At this temperature, the human body does not expend energy for thermoregulation.¹⁶ There are various thermotherapy immersion temperatures (33°C, 35°C, and 37°C), and physiological responses vary proportionally with the increase in water temperature, reaching their maximum after 15 minutes at constant temperature.¹⁵ Warm water leads to muscular relaxation,^17,18 and the aquatic environment also induces a soothing sensation, leading to an analgesic effect via the release of endorphins.^19,20 All these physiological responses are targeted in AT sessions of 50.7 ± 12.2 minutes.²¹

Infrared thermography is a quick, painless, and noninvasive way to measure skin temperature, which varies with the vasodilation of blood vessels.²² Infrared thermography has medical applications23, 24, 25 and is a new diagnostic tool for breast cancer,²⁶ carpal tunnel syndrome,²⁷ and vascular ischemic pain,²⁸ as well as identifying scar tissue.²⁹ Water is opaque to infrared radiation; therefore, infrared thermography cannot be used in water. However, it can be used immediately after water immersion to measure skin temperature and its distribution across the body, reflecting the physiological changes arising from immersion. Furthermore, increases ranging from 0.7°C to 1°C above normal body temperature on a thermogram may suggest pain.^22,30 Infrared thermography can objectively measure this variation in skin surface temperature, which may reflect the microvascular perfusion changes in painful areas.³¹ Infrared thermography has already been used to indirectly assess the analgesic efficiency of manual therapy such as physiotherapy on coccydynia,³² and holds promise for osteopathic treatment of vertebral somatic dysfunction^33,34 and for assessing the effect of this treatment.^35,36 Somatic dysfunctions are thought to cause physiological disturbance of the local nervous system, particularly the sympathetic nervous system, which produces local subcutaneous vasoconstriction and trigger points.³⁷ Infrared thermography can provide objective evidence for local subcutaneous vasoconstriction, indicated by cold spots,^38,39 and latent or active trigger points,⁴⁰ visualized as hot spots⁴¹ in individuals even if they report no pain.⁴²

Aquatic-therapy outcomes43, 44, 45 are comparable to osteopathic-treatment outcomes.46, 47, 48 For example, similar to osteopathic manual treatment,44, 45, 46 aquatic exercise (supervised by a fitness instructor to prevent falls) helps improve balance control in older people⁴³; supervised aquatic exercise helps decrease knee osteoarthritis pain⁴⁴; and AT with and without a physiotherapist⁴⁵ helps alleviate chronic lower back pain.⁴⁸ Therefore, osteopathic manipulation in water attempts to combine the effects of osteopathic therapy with those of thermoneutral water immersion (AT). Osteopathic treatment in thermoneutral water is increasingly used, and is called aquatic osteopathy (AO).⁴⁹ Aquatic osteopathy is based on the conventional application of osteopathic techniques in an aquatic environment, so as to reap the additional benefits of AT. Aquatic osteopathy is performed by a practitioner in water and should not be confused with AT, which consists of simple immersion without exercise or manipulation. Aquatic osteopathy also uses the aquatic environment to allow movement in all 3 dimensions, which is impossible in classic osteopathic therapy owing to the physical constraint of the therapy table. Aquatic osteopathy is a recent practice, described by practitioners, but there are no published studies to objectively attest to its additional benefits for patients compared with AT.

Therefore, the aim of this study was to measure the effects of AO on human thermal physiology using infrared thermography and compare them with thermoneutral water immersion (AT) alone.

Methods

We recruited 55 participants at the Champs-sur-Marne university campus (students, teachers, staff, etc). Inclusion criteria were to be physically healthy and over 18 years of age (for consent). Exclusion criteria were any condition that could affect the distribution of body temperature, such as infections with febrile syndrome, metabolic disorders, hormonal diseases, rheumatoid arthritis, tuberculosis, syringomyelia, multiple sclerosis, cervical radiculopathy, lateral sclerosis, neck amyotrophy, Raynaud disease, cancer, unconsolidated fracture, tendinitis, trauma, and muscle pain for less than 3 weeks. Similarly, individuals taking drugs such as central nervous system agents (neuroleptics or benzodiazepines), peripheral nervous system medication (vasodilators, antihypertensives), or anti-inflammatory drugs orally or by infiltration within the last 3 months were excluded. Individuals undergoing osteopathic treatment were also excluded to avoid other external sources of change in body temperature. Any individuals participating in another biomedical research study at the time of analysis were also excluded, so as not to cause interference or false diagnoses. After an oral explanation of the experiment, participants signed a consent form explaining the possible risks and authorized the use of data upon the condition of anonymity, in accordance with the ethical standards of the National Research Committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The study was approved by the local ethics committee.

Participants were led to a quiet locker room to change into swimwear. Swimwear was as minimal as possible and long hair was tied back to increase thermal data coverage and limit artifacts.

To stabilize cutaneous body temperature,⁵⁰ participants waited 8 minutes to acclimate to an environment stabilized at 26°C (± 1°C) and 55% humidity (±10%), well within the comfort zone (40%-70% relative humidity). After acclimation, the first thermogram reading (t0) was taken. This was intended as a practice run to introduce the measurement protocol to the participants and rehearse the position to adopt for thermogram acquisition. The thermograms acquired at t0 were not intended for use in the analysis. After this practice run, participants got into the pool, with water at 32°C.¹⁵ Because infrared radiation is filtered by water, readings were taken after participants left the water.⁵¹ Before thermographic measurements, participants’ skin temperature was stabilized in thermoneutral water for 1 hour⁵² to obtain a baseline measurement, for subsequent comparison of the effect of AO. We chose this duration because it is the maximum duration of therapy in thermoneutral water.²¹ Cardiovascular effects occur within 15 minutes maximum.¹⁵

After immersion, the participants dried off without rubbing, to avoid overheating the skin, and then waited the 8-minute acclimation time⁵⁰ to reach thermal stability and provide a stable and reliable thermogram. We checked that the cutaneous temperature was stable over time using video recordings in infrared thermography during the waiting phase for all participants. Cutaneous temperature was stable at 8 minutes, as suggested by Roy et al.⁵⁰ Thus, only 1 thermogram taken after 8 minutes was needed to carry out the analysis. A reading (t1) was performed in the experiment area. Thereafter, participants returned to the pool for an AO treatment of 30 minutes. Three practitioners treated participants using the global AO treatment, which is the systematic application of a somatic-dysfunction diagnosis routine and treatment of dysfunction across the entire body. Somatic dysfunctions are impaired or altered functions of related components of the somatic system. They are diagnosed by assessment of soreness, asymmetry of motion, and relative position, stiffness, and tissue-texture changes.⁵³ The somatic dysfunction diagnosis routine is described in The Principles of Palpatory Diagnosis and Manipulative Techniques as⁵³ a routine for examining the patient, offering the examiner an efficient method for obtaining information about the patient. The examiner records findings according to the anatomical regions conventionally described in medicine.⁵³ Global AO treatment has 3 main principles: rhythm, routine, and rotation. The practitioner uses a long-lever arm technique and all 3 spatial dimensions to test and treat all degrees of freedom of joint motion.⁴⁹ To test and treat joints, the practitioner places his or her hands on either side of the joint to mobilize it and determine the presence or absence of somatic dysfunction. Upon diagnosis of somatic dysfunction, with his or her hands in the same position the practitioner carries out a rhythmic alternation of direct and indirect techniques, respectively, in the direction of restriction and the direction of ease. This is used to guide the manual therapy while the dysfunctional area is palpated to obtain continuous feedback of the physiological response to the induced motion.⁵³ Joint correction is complete when the practitioner feels a change in tissue condition characterized by better movement quality and quantity. The routine treatment begins at the sacroiliac joint on the side with anterior iliac rotation. The practitioner tests and treats the sacroiliac joint for freedom of motion, then moves on to the next ipsilateral joint: hip then knee, ankle, foot, shoulder, arm, elbow, wrist, and hand. Then he or she tests and treats spinal joints: sacrum, lumbar, dorsal, and cervical joints. To finish the routine, he or she tests and treats contralateral joints beginning with shoulder, arm, elbow, wrist, hand, hip, knee, ankle, and foot. If the practitioner does not diagnose dysfunction on a joint, he or she proceeds directly to the next joint. The same protocol as before was applied to perform the second measurement (t2; Fig 1).

Fig 1.

Flowchart of the experimental protocol.

Equipment

The A320 series 27 camera by FLIR Systems (Wilsonville, OR) was installed and turned on 45 minutes before the first measurement was taken to allow the components to reach thermal stability. This camera, using long infrared waves (7-14 μm), is particularly well suited for measuring skin temperature. The relatively low temperature of skin can be analyzed using long-wave cameras, which have high emissivity in this spectral band (0.98) and very good noise reduction. Finally, this spectral range allows the use of bolometer cameras, which are less expensive than quantum cameras and therefore easier to use in a medical office. The readings must be taken perpendicularly to the subject. The camera is mounted on a tripod with a laser level.

The experiment area (Fig 2) was chosen to avoid air drafts and to limit temperature variations. A marker was placed on the ground at 170 cm from the camera to take a thermal image centered on the spine. This distance is short enough to ignore the influence of the atmosphere. The participant was turned with his or her back to the camera and the posterior part of the heel on the position marker.

Fig 2.

Picture of the experiment area, with camera in the foreground and participant's position in the background.

Methods of Analysis

We analyzed the thermograms using different methods. First, we visually inspected the raw thermograms. We used the same scale for optimal comparison. We then extracted the raw data in a spreadsheet and truncated all artifact signals because they do not correspond to body infrared signals.

We computed and plotted the temperatures observed on the thermal images collected. Figure 3 shows the 2 curves corresponding to the temperatures at t1 and t2. These plots show 2 series of peaks. The first is located near an average temperature of about 28°C, and the second is located at an average temperature of about 32°C. The first series of peaks corresponds to the thermal signature of the environment: the bottom of the swimsuit and hair. The second series of peaks corresponds to the human thermal signature. We therefore analyzed only the second series of peaks on all thermograms. However, these average temperature values were specific to each participant. We therefore used thermal thresholds (minimum temperature [Tmin] and maximum [Tmax] for each participant) for all the participants analyzed.

Fig 3.

Distribution of temperature frequencies for a representative participant.

Tmin corresponds to the temperature measured between the 2 peaks and has the lowest frequency of occurrence. Tmax is the maximum temperature observed. These 2 parameters therefore determine the heat signature of the participant. Figure 4 shows the thermogram obtained for the analysis of participant 1 after the introduction of the threshold criteria. It shows the heat signature after truncation using the Tmin and Tmax thresholds. This step retains only the participant's temperatures.

Fig 4.

Silhouette obtained after signal processing for participant 1.

We quantified the observed temperature fluctuations using statistical variance, which describes the dispersion around an average value. In our study, we expected lower variance in body temperatures after AO treatment (t2) compared with those collected after AT alone (t1). Our calculations of variance were performed on the truncated values (corresponding to the distribution of body temperatures). We calculated the mean variance and drew a box-and-whisker plot to observe the change in variance after 1 hour in thermoneutral water (AT) and after AO.

Data normality was verified by kurtosis and asymmetry coefficients. A paired Student's t test was used to compare mean variances for each subject after AT (t1) and after AO (t2). Statistical significance was set at P ≤ .05. The analysis was performed using Statistica version 8.0.725 software.

Results

Participant Characteristics

The study included 55 healthy participants, of whom 21 were men and 34 were women. The mean (± SD) age was 26 years (±5 years). The average height was 170 cm (± 8 cm), the average weight 69 kg (±8 kg), and the average body mass index 24 kg/m² (±2 kg/m²).

Raw Thermograms

One participant was chosen as representative of the study population. Figure 5A shows the thermal image obtained after the thermal cutaneous stabilization of the representative participant in thermoneutral water. It shows overall heterogeneity in skin temperature, with many hot zones in the upper thoracic area, a hot zone in the thoracolumbar area, and very cold zones on the limbs. Figure 5B, the thermal image obtained after AO treatment, shows notable temperature homogenization, with cold zones showing increased temperatures and warm zones showing cooler temperatures. These important zones whose temperatures were monitored were named points of interest (POIs).

Fig 5.

Thermogram of a representative participant, as measured with a FLIR A320 thermographic camera, 1 hour after immersion in thermoneutral water (t1; A) and after aquatic osteopathic treatment (t2; B).

Statistical Results

Analysis of mean variance revealed that participants’ temperature distributions after AT and after AO were significantly different (mean ± SD post-AT variance across all subjects = 1.48 ± 0.58; mean post-AO variance across all subjects = 1.21 ± 0.5; paired Student's t test, P = .002; Fig 6).

Fig 6.

Box-and-whisker plot of mean variances for 55 participants after 1 hour in thermoneutral water and after aquatic osteopathic treatment. SE, standard error.

Discussion

Visual inspection showed a decrease in the number of POIs between thermal images after AO (t2) compared with thermal images after immersion in thermoneutral water (AT; t1). After AO, the POIs showed more homogeneous temperatures that were closer to the overall mean cutaneous temperature. This homogenization was confirmed by analysis of temperature distribution (Fig 3), which shows curves with a smoother distribution around the participant's mean value. The analysis of mean variance quantified this homogenization precisely. The mean variances in body temperature after AT and after AO across all participants (Fig 4) confirmed the results for all participants. The temperature distribution after immersion in thermoneutral water was significantly different from that after AO (P = .002). Our findings demonstrate modified cutaneous temperature distribution following AO treatment, suggesting that AO initiates the physiological responses that lead to a more homogenous distribution of cutaneous body temperature.

The main difficulty in the experiment was the presence of water after immersion. However, our protocol ensured accuracy because subjects dried off without rubbing. Similarly, data processing eliminated the artifacts caused by the swimsuit or damp hair. These elements were not POIs and were filtered out. Choosing the proper thermal image and processing the thermogram are essential for an accurate analysis of body temperatures. The analysis of mean variance requires as many data points of body temperature as possible to increase the accuracy of the results. The thermograms show values that are similar to those usually found in the literature without water immersion23, 24, 25 and with it.⁵¹ Thus, infrared thermography is a tool suitable for use after immersion, provided that a suitable protocol is applied. It can analyze the effects of AO on the thermal physiology of the human body and objectively measures the resulting thermal homogenization. The tool is fast, painless, and low cost, and its protocol is easily reproducible, making it useful for medical research.

The physiological reactions described in thermotherapy^11,14 present at t1 were accentuated at t2, whereas the physiological reactions are no longer expected in AT after this time (50.7 ± 12.2 minutes).²¹ Aquatic osteopathy was performed after 60 minutes of thermoneutral immersion. Therefore, AO improves on simple immersion in thermoneutral water by leading to a homogenization of skin temperature, which suggests that changes in physiological reactions occur. Several studies^32,33,36 suggest that the POIs in the paraspinal regions correspond to somatic dysfunctions. Modifying POI temperatures mirrors a similar reaction previously observed in manual therapy using infrared thermography³⁶ and indicates that AO corrects somatic dysfunctions that persist after thermotherapy alone. Pain and heat are linked and assessable by infrared thermography.^22,35

Warm areas are associated with pain^54,55 but also with myofascial trigger points.⁴¹ Simons et al identify 2 kinds of trigger points: active and latent, which are respectively painful and painless.⁴⁰ Infrared thermographic skin measurements can provide useful information for evaluating subcutaneous latent trigger points⁴¹ in individuals without pain, as in our study.⁴² Latent trigger points can be “activated” and converted into active trigger points and therefore become symptomatic⁵⁶; warm POIs are areas predisposed to musculoskeletal pain in healthy individuals. Cold spots are linked to local subcutaneous vasoconstriction caused by a defensive physiological response.^38,39 Trigger points and local subcutaneous vasoconstriction result from an increase in central nervous system activity on the POI, disturbed by a local somatic dysfunction that induces the physiological process.³⁷ In this study, homogenization occurred in both directions: warm POIs cooled down and cold POIs warmed up. Importantly, temperature homogenization was significant after AO but not after AT. Therefore, AO induces more short-term subcutaneous physiological reactions than AT alone and thus nicely complements AT. The literature suggests that the physiological reactions involved may be the reaction of trigger points and local subcutaneous vasoconstriction, but this needs a specific protocol to be confirmed. This study cannot conclude as to the persistence of the measured effects over time or the definitive attenuation of local subcutaneous vasoconstriction and trigger points. Studying the persistence of effects requires a randomized single-blind clinical trial with objective infrared thermography measurements. Although movements during AO were not performed at high velocity, we do not know whether these movements may have influenced the thermography results. Any clinical study on this subject must take this additional factor into account by including a placebo treatment to compare with AO's effects.

In this study, AO treated only somatic dysfunctions. We did not link POIs with any specific pathology here because we recruited healthy participants only. Future studies could explore this therapeutic approach in individuals with specific pathologies or pain.

Various studies have been conducted using AT or osteopathic treatment, particularly with an aim to improve balance control in older individuals⁴⁶ and decreasing chronic low back pain^45,48 or knee osteoarthritis pain.^44,47 Further studies are necessary to quantify the results of these 2 types of therapy used together compared with isolated AT or osteopathic therapy or AO. Also, studies need to be conducted to determine whether cutaneous body temperature is a reliable indicator of trigger points and subcutaneous vasoconstriction. These indicators could then be used to establish the AO mechanisms of action to better define indications. Studies of this type are already underway.

Conclusion

In conclusion, this study shows the usefulness of infrared thermography—applied using a specific protocol—for assessing body temperature in individuals who had been immersed in thermoneutral water.

This study also demonstrates the promising beneficial effects of AO, which has more pronounced effects on cutaneous temperature reactions than thermoneutral water immersion, stabilizing and homogenizing temperatures after treatment. These reactions may be related to physiological responses, such as the decrease in local subcutaneous vasoconstriction and trigger points.