Background: We have previously reported a case of a patient with multiple morbidities (COPD and cerebral stroke) who underwent deep brain stimulation (DBS) of multiple sites including the motor thalamus (Green et al., 2019). The COPD related breathlessness was abolished by DBS of the motor thalamus. We therefore hypothesized that DBS of MT relieves experimentally induced hypercapnic air hunger (AH) in patients undergoing DBS of the motor thalamus for movement disorders.

Methods: Ten patients receiving DBS therapy for tremor, who had electrodes implanted bilaterally in the Ventral Intermediate Nucleus of the MT, underwent two 5min steady state hypercapnic AH tests once with DBS in the ‘ON’ state and once in the ‘OFF’ state in random order. Patients rated AH on a 10cm visual analogue scale (VAS) every 15s. Test level of hypercapnia was the same for ON and OFF states (mean±sd end-tidal PCO2 42±3mmHg). Ventilation was constrained to the same baseline level for ON and OFF states by setting a fixed flow of fresh gas into a 3 litre anaesthetic bag from which patients inspired with a frequency of 12 breaths/min set with a metronome. AH ratings in the last min of each test were averaged and mean levels compared for ON and OFF states..

Results: Nine of ten patients rated less AH with DBS ON (median reduction -12%VAS; range -9 to -52%VAS) shown in figure 1. Only one patient rated more AH in the ON state (increase of 34%VAS). Overall mean±sd steady state AH was 52±28 %VAS for the ON state and 67±27%VAS for the OFF state. This difference was significant (P=0.03; paired t-test) and exceeded minimal clinically important difference for VAS ratings of AH (Ries, 2005).

Conclusion: DBS of the MT significantly relieved experimentally induced air hunger. We suggest that DBS of the MT may directly block the dyspnea signal ascending through the thalamus. The extent of relief suggests that DBS of motor thalamic nuclei may prove to be a viable therapy for intractable dyspnoea in select patients who are worst affected.