The influence of mouth pressure on the cardiovascular response during inspiratory muscle loading at a constant transdiaphragmatic pressure.

Abstract

Purpose: To investigate whether the cardiovascular response during inspiratory pressure-threshold loading (ITL) is augmented by higher mouth pressure (P_m) when transdiaphragmatic pressure is maintained, and whether greater negative intrathoracic pressure increases intra-breath fluctuations in mean arterial pressure (MAP).

Methods: Sixteen healthy participants (6 females) completed two, 5-min ITL tasks while targeting a transdiaphragmatic pressure of 65 cmH₂O, breathing rate of 15 breaths/min, and duty cycle of 0.7. In one task, absolute P_m was low (20-30 cmH₂O; low P_m task), while in the other task it was higher (40-50 cmH₂O; high P_m task).

Results: Both tasks resulted in an increase in heart rate (HR; low P_m: + 13 [95% Confidence Interval: 7,19] beats/min; high P_m: + 15 [9,21] beats/min; P < 0.0001] and MAP (low P_m: + 12 [5,19] mmHg; high P_m: + 11 [4,18] mmHg; P < 0.0001). For the high P_m task, the HR response was greater (+ 3 [2,5] beats/min; P < 0.0001), the MAP response was lower (-2 [-4,0] mmHg; P = 0.0209), and there was a greater inspiratory-expiratory MAP difference (P = 0.0009), compared to the low P_m task.

Conclusion: Increasing P_m during ITL elicited a greater HR response and a blunted MAP response. The smaller changes in MAP during inspiration compared to expiration during the high compared to low P_m task may suggest an influence of negative intrathoracic pressure on cardiac loading. Future studies are required to determine how cardiac output changes with increases in P_m.