Acute thoracoabdominal and hemodynamic responses to tapered flow resistive loading in healthy adults

We investigated the acute physiological responses of tapered flow resistive loading (TFRL) at 30, 50 and 70% maximal inspiratory pressure (PImax) in 12 healthy adults to determine an optimal resistive load. Increased end-inspiratory rib cage and decreased end-expiratory abdominal volumes equally contributed to the expansion of thoracoabdominal tidal volume (captured by optoelectronic plethysmography). A significant decrease in end-expiratory thoracoabdominal volume was observed from 30 to 50% PImax, from 30 to 70% PImax, and from 50 to 70% PImax. Cardiac output (recorded by cardio-impedance) increased from rest by 30% across the three loading trials. Borg dyspnoea increased from 2.36 ± 0.20 at 30% PImax, to 3.45 ± 0.21 at 50% PImax, and 4.91 ± 0.25 at 70% PImax. End-tidal CO2 decreased from rest during 30, 50 and 70 %PImax (26.23 ± 0.59, 25.87 ± 1.02 and 24.30 ± 0.82 mmHg, respectively). Optimal intensity for TFRL is at 50% PImax to maximise global respiratory muscle and cardiovascular loading whilst minimising hyperventilation and breathlessness.