Background Contrast baths have been adopted widely in clinics. However, the time ratio of heat to cold modalities has not been well established.
Objective The purpose of this study was to explore the effect of time ratio on brachial artery mean blood velocity (aMBV) and determine the optimal duration in the second heating phase.
Design This was a within-participant, repeated-measures, experimental study.
Methods Thirty-four young volunteers who were healthy were recruited. Each participant performed 2 kinds of contrast baths within 2 separate sessions. In the first trial with a fixed time ratio, participants immersed their left hands in a 40°C hot bath for 3 minutes and then in an 18°C cold bath for 1 minute. This procedure was repeated 3 times. In the second trial, after the initial 3-minute hot bath and 1-minute cold bath, a 10-minute 40°C hot bath immersion was adopted as the second cycle. A color Doppler ultrasound scanner was used to measure aMBV, which was used to calculate the percentage of change related to the baseline (aMBV%) and the fluctuation in the heating phases (ΔaMBV%).
Results In the first trial, compared with the first heating phase, the ΔaMBV% was significantly lower by 57% and by 46% in the second and third heating phases, respectively. In the second trial, the ΔaMBV% beyond the 7th minute did not reach a significantly lower level.
Limitations The results cannot be generalized to elderly individuals or patients with medical conditions.
Conclusion A longer duration in the second heating phase during contrast baths was required to produce a sufficient fluctuation in blood flow.
Contrast baths, a therapeutic modality using repeated alternation of hot water (eg, 38–44°C) and cold water (eg, 10–18°C) immersions, have been proposed to increase blood flow to the immersed area by a type of “pumping” action without causing accumulation of additional edema.1 Evidence suggests that heat-induced blood flow changes in the conduit vessels of either upper or lower limbs resulted mainly from a change in blood velocity rather than from a change in vessel diameter.2–4 The increases in blood flow could be attributed primarily to the fluctuations of blood flow velocity occurring between the heating and cooling cycles. These fluctuations have been suggested to bring more nutrition and oxygen for soft tissue repair at the moment between early cryotherapy and subsequent thermotherapy intervention. Hence, contrast baths have commonly been adopted to relieve the symptoms associated with local inflammatory processes secondary to tissue trauma,1 to promote soft tissue healing,5 and to enhance physical recovery after training and competition.6 A recent systematic review,7 however, indicated that evidence regarding the efficacy of contrast baths for physical recovery is still insufficient. One of the possible reasons is that some critical parameters of contrast baths have not been well established.5,7–9 For example, various time ratios between hot and cold modalities (eg, 1:1, 2:1, 3:1, 4:1, and 5:5 minutes) have been quoted.5,6,8,10–13
In instructional texts, a fixed time ratio of 3 or 4 minutes (hot) to 1 minute (cold) for 4 to 5 cycles is most often recommended. However, the time ratio often is determined by clinical observation and experience rather than changes in arterial blood flow.1,5,11,14 The changes in arterial blood flow have been suggested to be a reliable measure to disclose the clinical significance of contrast baths.8,9,11 Some studies indicated that the use of contrast baths can produce significant fluctuations of skin blood flow during a 16-minute treatment, as well as a gradually increasing skin blood flow after each succeeding hot water immersion alternated with cold immersion.15,16 Using strain gauge plethysmography, Fiscus et al11 noted the opposite finding—that the maximum arterial blood flow achieved during the hot water phase of the contrast baths was reduced with successive immersions, although the findings indicated significant fluctuations of artery blood flow. Fiscus and colleagues' findings imply that the duration of hot water immersion in the second, third, and fourth cycles of contrast baths with a fixed time ratio might be so short that it cannot produce sufficient elevation in blood flow. Accordingly, we propose that a prolonged hot water immersion in the second cycle of contrast baths might produce a greater arterial blood flow.
The purpose of this study was to investigate the effect of time ratio between hot and cold applications on artery mean blood velocity (aMBV) during contrast baths using a color Doppler ultrasound scanner. Doppler ultrasound is a sophisticated and contemporary noninvasive technology offering a continuous recording scheme to detect artery blood flow in the absence of color noise from other sources. In addition, Doppler ultrasound technique has been suggested to provide sufficient temporal resolution for monitoring blood flow with a quick change.17 The brachial artery, a conveniently accessible conduit artery of the forearm, was used to estimate the aMBV and to quantify blood flow changes in the immersed hand. We hypothesized that: (1) contrast baths with a 3:1 fixed time ratio would not produce sufficient blood flow subsequent to the first cycle of hot-cold water immersion, and (2) contrast baths with a prolonged hot-water immersion in the second cycle would allow us to determine the optimum duration in hot water necessary to achieve an optimal fluctuation in arterial blood flow subsequent to the first hot-cold cycle.
Thirty-four right-handed volunteers who were healthy (20 female and 14 male, with a mean age of 21.5 years, range=20–27) were recruited through announcements in undergraduate courses. Participants were included if they were 20 years of age or older and consented to the study. Volunteers were excluded if they were susceptible to hemorrhage, had surface infections, or had insensitive skin affecting their perception of the extent of heat or cold applied, or if they had a history of any cardiovascular problems or neurological, musculoskeletal, or dermatological conditions that might induce an adverse response to thermal modalities. Physical characteristics, including an average height of 163 cm (SD=6), an average body weight of 59 kg (SD=7), an average heart rate of 73 bpm (SD=9), and an average systolic/diastolic blood pressure of 105/70 mm Hg (SD=14/9), were collected from the participants. Written informed consent was obtained before each participant entered the study.
Two stainless-steel tanks with thermostatic controls were used to keep the bath water at the temperatures of 40°C (hot bath) and 18°C (cold bath). All participants were instructed not to engage in strenuous physical exercises and not to overeat for at least 2 hours before the experiment. In addition, the participants were requested to relax during the experiment to prevent unnecessary muscle activity that could cause skin temperature changes. After instrumentation, the participants were instructed to sit comfortably in a chair with the height adjusted to allow them to put their left hands into either the hot or cold water bath while maintaining an even shoulder level. Ambient air temperature was controlled at 26°C. After a 20-minute rest period, the participants were instructed to put their left hands alternately into the hot and cold water baths to the level of the wrist and rest their left elbows on the edge of the water tank. Two experimental trials were performed over the course of 2 sessions that were separated by a minimum of 48 hours to prevent temperature contaminants. In the first trial, a fixed time ratio of contrast baths was adopted. Participants immersed their left hands into the hot bath for 3 minutes and then the cold bath for 1 minute. This procedure was repeated 3 times, and the total duration was 12 minutes. In the second trial, participants put their left hands into the hot bath to the same level as in the first trial for 3 minutes followed by the cold bath for 1 minute, and then a prolonged (10-minute) hot water only immersion served as the second cycle. The total duration was 14 minutes. During application of contrast baths, participants' sensations and pulse rates were monitored continuously.
The blood velocity of the brachial artery was measured by a color Doppler ultrasound scanner (Medison SonoAce 9,900, Samsung Medison, Korea) with 5-MHz operating frequency for pulsed Doppler transmitted from a (7 MHz) linear array transducer. With the support of color-flow imaging, an optimal signal through the center of the artery proximal to the cubital fossa was determined as the clearest image of the anterior and posterior walls.18 The sound beam of pulsed Doppler was electronically angled 60 degrees relative to the artery.19 While the optimal signal was obtained, the ultrasound probe was fixed and the ultrasound gate was adjusted to the total width of the artery. A 1.5-minute signal recorded before the commencement of contrast baths was averaged as a baseline. After the onset of contrast baths, the signals of each 30-second were averaged as an interval. Consequently, there were 6 intervals during a 3-minute heating phase, 2 intervals during a 1-minute cooling phase, and 20 intervals during a 10-minute heating phase. For each interval, the percentage changes in aMBV related to the baseline (ie, aMBV%) were calculated using the following equation:
The ΔaMBV% represented the fluctuation in the heating phase and was calculated using the following equations:
For the first cycle, .
For the second and third cycles,
A repeated-measures analysis of variance, followed by post hoc least significant difference tests, was used to evaluate the differences in the aMBV% among intervals. Differences were considered significant at P<.05. Statistical analyses were performed with SPSS for Windows version 17.0 (SPSS Inc, Chicago, Illinois).
In the first trial with a fixed time ratio, the aMBV% values increased progressively during each 3-minute heating phase and decreased rapidly during each 1-minute cooling phase (Figure, graph A). However, in the follow-up heating phases, there was a failure to gain the higher blood velocity seen in the first heating phase. This loss can be expressed as a significantly lower ΔaMBV%. Thus, in comparison to the first heating phase, the ΔaMBV% were significantly lower by 57% (95% confidence interval [CI]=13%–101%, P=.001) in the second phase and by 46% (95% CI=0%–92%, P=.045) in the third heating phase (Table). However, no significant difference in the ΔaMBV% between the second and third heating phases was found (P=.129).
In the second trial, with a prolonged (10-minute) hot water immersion in the second cycle of contrast baths, the aMBV% values increased progressively during the first 3-minute heating phase, decreased rapidly during the 1-minute cooling phase, and then increased progressively during the succeeding 10-minute heating phase (Figure, graph B), nearly achieving the velocities seen at the end of the first heating phase. Although, in comparison to the first heating phase, the values of ΔaMBV% were significantly lower (P<.05) during the first several intervals in the 10-minute heating period, the values beyond the seventh minute (mean difference=28%, 95% CI=0%–56%, P=.054) were not significantly lower. The evidence indicated that a fixed 3:1 ratio did not provide the greatest therapeutic fluctuations in blood velocities and that a ratio of 7:1 and beyond would be preferable.
We investigated the effect of contrast baths with different ratios of heating to cooling time on the brachial artery blood velocity in young men and women. The main findings were that: (1) contrast baths with a fixed time ratio of 3:1 caused fluctuations in artery blood velocity through a 12-minute intervention, with a noted reduction in the extent of fluctuations in artery blood velocity during the follow-up immersions, and (2) contrast baths with a prolonged hot water immersion in the second cycle produced sufficient fluctuations in artery blood velocity, as well as providing a continuously increasing aMBV% that achieved the maximum benefit in fluctuation beyond the seventh minute.
Consistent with our hypothesis, a prolonged hot water immersion in the second cycle of contrast baths could create an adequate fluctuation in artery blood velocity. Our results are compatible with the suggestion that the period of immersion of an extremity in hot water should be increased gradually during subsequent treatment phases.20 In addition, an earlier study by Woodmansey et al21 supports our hypothesis that contrast baths with a longer heating phase (eg, 6 or 7 minutes) could produce a better reaction in blood flow. Because contrast baths have been proposed to increase blood flow with a fluctuant type, it is feasible to assume that the optimal timing of contrast baths could be set at 3:1:8 (hot to cold to hot) ratios merely in the first 3 phases.
It is necessary to explain why the second trial was designed to end the application with a hot water immersion instead of cold water immersions, such as the first trial. The main reason is that in this study, we mainly examined how long the second heating phase should be to produce more fluctuation in artery blood flow after a brief cooling phase. This study design does not imply that we recommend ending the application with a hot water immersion, except as might be determined according to the patient's condition. Our results also did not support that a 7-minute hot water immersion in the third heating phase would produce a significant fluctuation as reported in the second heating phase. In addition, the relationship between a prolonged hot water immersion and accumulation of additional edema is unclear in this study. A systematic review indicated there is conflicting evidence regarding the impact of contrast baths on edema.9 Further investigation regarding this impact is needed.
In this study, we demonstrated that contrast baths produce significant fluctuations of blood flow in the brachial artery. The brachial artery scanned by Doppler ultrasound was located at a depth of more than 1.5 cm below the skin in our study, which can be considered a deep level. This result is incompatible with a systematic review by Breger Stanton et al9 in which increased blood flow was noted at a superficial level rather than at an intramuscular (deep) level after application of contrast baths. Although the detected brachial artery and downstream arteries mostly lie between muscles, it seems unlikely to ascribe the fluctuations in brachial artery blood flow to the changes in intramuscular temperatures. Several studies have shown that contrast baths can induce significant fluctuations of temperature at skin and subcutaneous levels, but not at the intramuscular (deep) level.5,8,13,21,22 One of the explanations is that a local spinal cord reflex induced by exposure of superficial heat could stimulate the cutaneous receptors, causing a decrease in postganglionic sympathetic adrenergic outflow to the smooth muscles of blood vessels, which results in vasodilation of local or remote blood vessels and consequently increases blood flow.14 Another probable explanation is that the brachial artery is upstream in the conduit artery of forearm and hand; hence, the fluctuations in brachial artery blood flow could be considered a reflection of arterial blood inflow variations in the immersed hand.
Although contrast bath–induced fluctuations in artery blood flow have been demonstrated in previous studies, the pattern of increased blood flow in the heating phase seems inconsistent with our finding.11,16 Using strain gauge plethysmography, Fiscus et al11 noted that artery blood flow of the lower leg increased rapidly and reached a plateau after application of a hot bath. In our study, the plateau in arterial blood flow was not found during each 3-minute heating phase of contrast baths with a fixed time ratio, but a significant plateau in arterial blood flow was observed in a prolonged (10-minute) heating phase. A possible explanation is that the use of strain gauge plethysmography often is associated with the use of occlusion cuff pressure, and this cuff pressure has been suggested to restrict the change in the volume of the limb segment.11 Evidence indicates that a cuff occlusion pressure of 50 mm Hg can decrease the artery blood flow by approximately 28%.19 Hence, when using strain gauge plethysmography, the heat-induced increases in artery blood flow would rapidly fill the restricted volume in the limb segment caused by cuff pressure, which then would produce a plateau in blood flow influx. Another probable explanation is the level of limb submersion. In the study by Fiscus et al,11 the lower leg below the knee joint line was submerged. The hydrostatic pressure within the water tank would decrease the volume of the limb segment.
Measuring with laser Doppler flowmetry, Petrofsky et al16 indicated that the blood flow of the immersed foot increased gradually during the heating phase, and more influx of blood flow was observed with successive immersions. In our study, the increased blood flow was reduced with successive immersions. Laser Doppler flowmetry is a technique for measuring the changes in frequency shift of the reflected laser light caused by moving red blood cells. Due to the limited skin penetration of laser light, the blood flow detected by laser Doppler has been considered a result of red blood cell flux in skin microvascular bed, predominantly in capillaries that are downstream from arterioles.23 In contrast, the blood flow investigated in our study is measured in the brachial arteries that are upstream to arterioles.
There were a few limitations to this study that should be considered. First, young individuals who were healthy were recruited in this study. The use of these individuals does not allow us to generalize these results to people with a medical condition and elderly people. Second, our results are limited to the contrast baths with a 3:1 hot to cold ratio. Third, only changes in arterial blood velocity rather than clinical outcome were investigated. Some variables between arterial blood velocity and clinically important outcomes have not been well identified.
This study revealed that contrast baths with a fixed time ratio of 3:1 produced decreased blood velocity in hot water immersion after the first cycle. In addition, contrast baths with a prolonged hot water immersion in the second cycle produced sufficient blood velocity. This information is valuable because a fixed-time ratio of contrast baths has been used widely in clinical practice as a means to increase blood flow. We suggest that further studies involving contrast baths with prolonged hot water immersions in each succeeding heating phase alternated with 1-minute cold immersion should be performed to determine whether this protocol may cause accumulation of edema or diminished fluctuations of blood flow in the third or fourth heating cycle. In addition, further investigation regarding the clinical significance of our findings for people with disorders and for the elderly population is needed. For clinical application of contrast baths, it is important to set up an adequate time ratio if the treatment goals are to increase blood flow without causing accumulation of additional edema and to promote soft tissue healing at the moment between early cryotherapy and subsequent thermotherapy intervention.
All authors provided concept/idea/research design and writing. Mr Shih and Dr W-L. Lee provided data collection, participants, and facilities/equipment. Dr Wu, Dr C-W. Lee, and Mr Shih provided data analysis. Dr Wu provided project management. Dr Wu, Dr C-W. Lee, and Dr Huang provided consultation (including review of manuscript before submission). The authors thank the participants involved in the study and all of the students for their contributions to data collection and analysis.
The study was approved by the Institutional Review Board at the Buddhist Tzu Chi General Hospital.
- Received November 16, 2010.
- Accepted October 21, 2011.
- © 2012 American Physical Therapy Association