Comparing perceived heating effect and intensity of therapeutic ultrasound between breast tissue and calf muscle in lactating women: An observational study

Abstract

Background Inflammatory conditions of the lactating breast (ICLB) can cause cessation of breastfeeding and treatment for these conditions should be optimised. Therapeutic ultrasound is the most utilised physiotherapy treatment for ICLB. However, there is no evidence that guides physiotherapists on the most appropriate therapeutic ultrasound parameters to treat ICLB, with current ultrasound treatment protocols based on evidence using musculoskeletal tissue. Therefore, it is necessary to determine whether ultrasound interacts with breast and musculoskeletal tissue differently. This study aimed to determine the difference between breast and calf muscle tissue for perception of heating from therapeutic ultrasound; and the therapeutic ultrasound intensity required to perceive warmth in healthy lactating breast tissue.Methods Fifty adult lactating women who had exclusively breastfed infants aged 6 months or fewer, were recruited from a private physiotherapy clinic in Queensland, Australia. Consent was obtained to participate in this repeated measures within subject descriptive observational study. Therapeutic ultrasound was sequentially applied to the breast and calf; in a randomly assigned order; using a continuous duty cycle of 1 MHz, 1Wcm2 intensity for an initial period of 5 minutes. Intensity was then increased by 0.1Wcm2 every 30 seconds. The intensity at which participants reported first perceived warmth and then most tolerable warmth for the breast and the calf was recorded.Results First warmth was perceived at lower intensities in the breast (Z=-3.637, p < 0.001), but there was no difference between locations for most tolerable warmth (Z=-1.165, p = 0.244). Factors associated with intensity for perception of first warmth were antidepressant use (β 0.369 95% confidence interval [95%CI: 0.103–0.635], p = 0.007) and location (β 0.286 [95%CI: 0.055–0.516], p = 0.015). Body mass index (BMI) was the only factor associated with intensity for most tolerable warmth (β 0.024 [95%CI: 0.004–0.044], p = 0.017). The range of intensities required to perceive heating in the breast were 1-2.5Wcm2.Conclusions As perception of breast and calf warmth was different, therapeutic ultrasound parameters used to treat musculoskeletal conditions may not be appropriate for ICLB. Antidepressant use and BMI influenced heat perception, highlighting the need to screen for these factors prior to therapeutic ultrasound intervention.