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      During all breath-holds, the chest slowly deflates by ~250 ml/min. During single prolonged breath-holds of > 5 min., this causes the left breast to move linearly at 2 mm/min. (± 0 standard error) dorsally (Parkes et al., 2016) and the diaphragm to move linearly at 3 mm/min. (range 1-5mm)  cranially (van Dijk et al., 2021). When using such prolonged breath-holds for radiotherapy, this would alter tumour position. Here we studied whether the mechanical ventilator can be used to re-inflate the chest during the breath-hold. Simply applying continuous inflation during breath-holding is ineffective because the larynx may close. Instead, we tested here whether subjects could be instructed at intervals to attempt a minimal inhalation using their diaphragm. This could trigger the ventilator to superimpose a constant inflation of short duration. The net effect of these short inflations should be to maintain the chest inflated until the breakpoint (i.e., to have abolished the slow deflation).

          Single prolonged breath-holds of > 5 min. were induced by mechanical hyperventilation and preoxygenation (Parkes et al., 2016) with Hamilton MR1 or T1 non-invasive ventilators in 8 healthy volunteers. In 5, chest circumference was measured continuously with a wrap-around band connected to a spring-loaded resistor. In 3 others, diaphragm position was measured in the MRI using a 1D navigator acquisition at 2 Hz frequency.

            During single prolonged breath-holds in 5 subjects  ( mean duration 7 min. (±1 se min)), they were instructed to attempt a minimal inhalation each time deflation had reached an arbitrary threshold level. This enabled the chest to remain at the inflation circumference at breakpoint (figure 1). During prolonged breath-holds in 3 subjects (mean duration 6  min. (± 1), they were instructed to attempt a minimal inhalation once or twice every minute (figure 2a). Here, while the diaphragm briefly descended and re-ascended by ~5 mm during each inhalation, for ~90% of time the diaphragm position remained stable within 4 mm of its mean position (figure 2b). At breakpoint the diaphragm was within 3 ± 1 se mm of its starting position.

     We demonstrate how instructing healthy volunteers to perform this manoeuvre can overcome the deflation that normally occurs during all breath-holds. Training patients with thoracic or abdominal tumours to perform this manoeuvre during prolonged breath-holds could prevent the chest deflating. This could reduce tumour movement during, and increase the usable breath-hold duration available for radiotherapy treatment.

Parkes MJ, et al., (2016) B J Radiol 89, 20160194.

 van Dijk IW et al., (2021) ESTRO OC-0339.