Archive for the ‘Mechanical Ventilation’ Category


Since the Hering-Breuer reflex is variably active in humans, ventilator-delivered tidal volume variation could affect Voff in some individuals. Tidal volume delivered during one breath would affect the subsequent breath, altering Voff. Our analysis relies heavily on meaned data, reducing the chance of showing a statistically significant effect of tidal volume (or flow rate) on Voff. Because of this, although we were unable to demonstrate it, the possibility of delivered tidal volume affecting Voff still exists. A combined effect of tidal volume and flow rate variation greater than their individual effects may exist as well. A larger number of patients would be necessary to address these issues. (more…)

  • Comments Off on Diaphragmatic Contraction during Assisted Mechanical Ventilation: Conclusion
  • Diaphragmatic Contraction during Assisted Mechanical Ventilation: DiscussionThis study provides direct electromyographic evidence of persistent diaphragmatic contractile activity in patients with a variety of diseases requiring mechanical ventilation in the assist/control mode. Persistent diaphragmatic contraction during ventilator-assisted breaths has been indirectly demonstrated in normal animals and humans by measuring airway pressure and in ill humans by measuring the mechanical work of breathing. Inspection of the diaphragmatic EMG allows precise determination of contraction duration thus facilitating the study of tidal volume and flow rate alteration on the contractions duration. We chose to express the duration of electromyographic activity in terms of inspired tidal volume because available evidence suggests that volume feedback from stretch receptors, in part, controls inspiratory duration. review
    (more…)

  • Comments Off on Diaphragmatic Contraction during Assisted Mechanical Ventilation: Discussion
  • Two approaches were used to decide if there was an effect of delivered flow rate or tidal volume on the Voff. Data were grouped by flow rate and then by tidal volume. First, for all patients, regardless of delivered volume, Voff values at the lowest flow rates (^1.0 times spontaneous) were compared to Voff values at highest flows (^2.0 times spontaneous). Similarly, for all patients, regardless of delivered flow, Voff values at lowest delivered tidal volumes were compared to Voff values at highest volumes. Second, the mean slope of all of the Voff vs tidal volume and then Voff vs flow rate regressions were tested for significant difference from zero using Students t-test; a significant difference (p<0.05) supported an effect of flow rate or tidal volume on Voff. (more…)

  • Comments Off on Diaphragmatic Contraction during Assisted Mechanical Ventilation: Results
  • Diaphragmatic Contraction during Assisted Mechanical Ventilation: Calibrated volume ventilatorA calibrated volume ventilator (Puritan-Bennett 7200) was used to perform the experiment. Patients were observed for one hour on settings previously chosen by their attending physicians. The subjects were then allowed to breathe spontaneously (without assistance) through the ventilator for a target period of five minutes. Tidal volume, inspiratory flow rate, and diaphragmatic EMG were recorded simultaneously for five to seven sequential spontaneous breaths at the end of the five-minute period. Patients 1 and 7 were unable to breathe spontaneously for this length of time, so data were recorded after only two to three minutes of spontaneous breathing. Subjects then rested for ten minutes on their original ventilator settings. Five to seven assisted breaths at nine combinations of tidal volume and flow rate derived from the measured values during spontaneous breathing were delivered in random order. Tidal volumes of 1, 1.5, 2, and 2.5 times the patients spontaneous tidal volume and flow rates of 0.5, 1, 1.5, 2, and 2.5 times the spontaneous flow rate were used. Only nine tidal volume-flow rate combinations (of the 20 possible) were attempted with each patient, in order to reduce the possibility of fatigue. Combinations with high tidal volume and low flow rate were frequently omitted, as they interfered with adequate expiratory time. After another ten-minute rest, controlled breaths were delivered at the same tidal volume-flow rate combinations. other
    (more…)

  • Comments Off on Diaphragmatic Contraction during Assisted Mechanical Ventilation: Calibrated volume ventilator
  • Ten intubated patients receiving mechanical ventilation were studied (Tables 1 and 2). At the time of study, the patients were clinically stable, capable of some spontaneous ventilation, and without positive end-expiratory pressure. The patients were judged ready for weaning from the ventilator by their attending physicians, and mechanical ventilation was discontinued shortly after the study except in patients 1 and 7. These two patients had evidence of paradoxical abdominal motion during spontaneous breathing and therefore may have had diaphragmatic fatigue. (more…)

  • Comments Off on Diaphragmatic Contraction during Assisted Mechanical Ventilation: Materials and Methods
  • Diaphragmatic Contraction during Assisted Mechanical VentilationDecent data indicate that during assisted mechanical ventilation the diaphragm continues to contract after triggering the ventilator, dispelling the commonly held belief that diaphragmatic muscle contraction ceases after the machine is triggered. Variations in airway pressure and measurements of the mechanical work of breathing have been cited by some authors as evidence of continued inspiratory muscle contraction. Ayres et al showed that patients with COPD who were ventilated with intermittent positive-pres-sure breathing have lower airway pressures during assisted breaths than during controlled unassisted breaths of the same tidal volume. The same observation has been made in normal humans and in animals. Marini and associates demonstrated that patients with pulmonary disease may perform significant amounts of muscle work during assisted mechanical ventilation. These data provide strong indirect evidence for continued diaphragmatic contraction beyond triggering the ventilator; however, the duration of this contraction and the factors influencing the duration of inspiratory muscle contraction have not been well characterized during mechanical ventilation in humans with illness.
    (more…)

  • Comments Off on Diaphragmatic Contraction during Assisted Mechanical Ventilation
  • Categories


    Advertising


    Most Popular

    • None found

    Recent Comments

    • None found