D A Sidney | PubMed Health

PubMed1997

Negative-impedance ventilation and pressure support ventilation: a comparative study.

Negative impedance ventilation (NIV) is a novel mode of assisted mechanical ventilation (AMV) in which the pressure support is regulated to continuously track inspiratory flow and/or volume. In this study, we have evaluated the efficacies of NIV and inspiratory pressure support (IPS) ventilation in a model of central airway obstruction in six rabbits. For both AMV modes there was an inverse relationship between the intrinsic work of breathing and alveolar pressure. Compared to IPS, NIV was found to: (1) achieve the same degree of ventilatory unloading and similar level of pulmonary ventilation with considerably lower alveolar pressure; (2) better restore the normal tidal volume and respiratory frequency; (3) yield a shorter inspiratory duty cycle, thereby helping to rest the respiratory muscles and preclude intrinsic positive end-expiratory pressure. We conclude that NIV is more efficacious than IPS in negating airway obstruction and offers a better trade-off between the risks of respiratory muscle fatigue and pressure induced complications.

Airway Resistance↗

PubMed1995

Ventilatory responses to dead space and CO2 breathing under inspiratory resistive load.

To investigate how breathing is controlled during CO2 stimulation, steady-state ventilatory responses to rebreathing through a tube (DS) and inspiring a fixed PCO2 (INH) were compared in healthy human subjects. Tests were performed in hyperoxia with (IRL) and without (NL) an inspiratory resistive load (15 cmH2O.l-1.s at 1 l/s). The mean slope of the minute ventilation (VE)-end-tidal PCO2 relationship was significantly higher in DS-IRL than in INH-IRL [1.86 +/- 0.67 (SD) vs. 1.40 +/- 0.32 l.min-1.Torr-1, P < 0.01], and it was significantly different between INH-NL and INH-IRL (1.64 +/- 0.41 vs. 1.40 +/- 0.32 l.min-1.Torr-1, P < 0.05) but not between DS-NL and DS-IRL (1.85 +/- 0.72 vs. 1.86 +/- 0.67 l.min-1.Torr-1). The slope of the VE-tidal volume relationship was significantly lower in DS-NL than in INH-NL (19.6 +/- 3.8 vs. 21.2 +/- 5.1 min-1, P < 0.05), but other comparisons in breathing pattern between NL and IRL and between DS and INH failed to reach significance. We concluded that 1) alterations in alveolar PCO2 temporal profile by DS could induce changes in VE-end-tidal PCO2 sensitivity and ventilatory pattern, 2) these changes may be modified by increased mechanical impairment resulting from IRL, and 3) carotid chemoreceptor mediation is not necessary for the observed effects of DS.

Adult↗