HEMODYNAMIC-EFFECTS OF RESISTIVE BREATHING

To examine the acute hemodynamic effects induced by large swings in intrathoracic pressure such as may be generated by obstructive lung disease, airway obstruction was simulated by means of two different fixed external alinear resistances and the results were compared with those for unobstructed breathing (C). Eight normal subjects breathed through external resistances during inspiration (I) expiration (E), or both (IE) at rest (Re) and exercise (Ex). The resistances were chosen to induce similar mouth pressure (Pm) swings at Re and Ex. Pleural pressures (Ppl) were found to correlate closely with Pm. During IE resistive breathing mean swings in PM were -31 and +19 cmH2O at Re and -38 and +22 cmH2O at Ex, with a corresponding decrease in minute ventilation (-30 and -18%) and an increase in end-tidal PCO2 (+5.6 and +4.2 Torr); these were associated with an increase in heart rate (.DELTA.HR = 4 and 6 beats/min) and systolic systemic arterial pressure (.DELTA.Psa8 = 10 and 14 Torr at Re and Ex, respectively). O2 consumption and cardiac output did not change. The myocardial O2 consumption, estimated from the product HR. (.hivin.Psas - .hivin.Ppl), increased by 17 and 20% at Re and Ex, respectively. Changes in mechanics, gas exchange, and hemodynamics were less pronounced during I or E resistive loading. It is concluded that breathing through a tight external resistance during IE at Re and Ex increases the metabolic load on the myocardium.