Abstract
BackgroundBreathing in humans is dually controlled for metabolic (brainstem commands) and behavioral purposes (suprapontine commands) with reciprocal modulation through spinal integration. Whereas the ventilatory response to chemical stimuli arises from the brainstem, the compensation of mechanical loads in awake humans is thought to involve suprapontine mechanisms. The aim of this study was to test this hypothesis by examining the effects of inspiratory resistive loading on the response of the diaphragm to transcranial magnetic stimulation.ResultsSix healthy volunteers breathed room air without load (R0) and then against inspiratory resistances (5 and 20 cmH2O/L/s, R5 and R20). Ventilatory variables were recorded. Transcranial magnetic stimulation (TMS) was performed during early inspiration (I) or late expiration (E), giving rise to motor evoked potentials (MEPs) in the diaphragm (Di) and abductor pollicis brevis (APB). Breathing frequency significantly decreased during R20 without any other change. Resistive breathing had no effect on the amplitude of Di MEPs, but shortened their latency (R20: -0.903 ms, p = 0.03) when TMS was superimposed on inspiration. There was no change in APB MEPs.ConclusionInspiratory resistive breathing facilitates the diaphragm response to TMS while it does not increase the automatic drive to breathe. We interpret these findings as a neurophysiological substratum of the suprapontine nature of inspiratory load compensation in awake humans.
Highlights
Breathing in humans is dually controlled for metabolic and behavioral purposes with reciprocal modulation through spinal integration
Increases in the automatic drive to breathe facilitate the diaphragm response to transcranial magnetic stimulation (TMS). This is true during quiet tidal breathing [4], where such inspiration-related facilitation has been described during wake and sleep. This is true during CO2-stimulated breathing [5], that accelerates the diaphragm response to TMS applied during both inspiration and expiration
R0, resistance of either 5 (R5) and R20 correspond to breathing against no resistance, against a resistance of 5 cmH2O/L/s, and against a resistance of 20 cmH2O/L/s, respectively
Summary
Breathing in humans is dually controlled for metabolic (brainstem commands) and behavioral purposes (suprapontine commands) with reciprocal modulation through spinal integration. Increases in the automatic drive to breathe facilitate the diaphragm response to transcranial magnetic stimulation (TMS). This is true during quiet tidal breathing [4], where such inspiration-related facilitation has been described during wake and sleep. This is true during CO2-stimulated breathing [5], that accelerates the diaphragm response to TMS applied during both inspiration and expiration
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