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Effects of the components of positive airway pressure on work of breathing during bronchospasm.

Miro AM, Pinsky MR, Rogers PL - Crit Care (2004)

Bottom Line: Theoretically, expiratory positive airway pressure (EPAP), by reducing expiratory breaking, may be as important as inspiratory positive airway pressure (IPAP) in reducing work of breathing during acute bronchospasm.CPAP and EPAP similarly increased EELV above control by 93 +/- 16 ml and 69 +/- 12 ml, respectively.The increase in EELV by IPAP of 48 +/- 8 ml (P < 0.01) was significantly less than that by CPAP and EPAP.

View Article: PubMed Central - HTML - PubMed

Affiliation: Cardiopulmonary Research Laboratory, Department of Anesthesiology/Critical Care Medicine, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, USA.

ABSTRACT

Introduction: Partial assist ventilation reduces work of breathing in patients with bronchospasm; however, it is not clear which components of the ventilatory cycle contribute to this process. Theoretically, expiratory positive airway pressure (EPAP), by reducing expiratory breaking, may be as important as inspiratory positive airway pressure (IPAP) in reducing work of breathing during acute bronchospasm.

Method: We compared the effects of 10 cmH2O of IPAP, EPAP, and continuous positive airwaypressure (CPAP) on inspiratory work of breathing and end-expiratory lung volume (EELV) in a canine model of methacholine-induced bronchospasm.

Results: Methacholine infusion increased airway resistance and work of breathing. During bronchospasm IPAP and CPAP reduced work of breathing primarily through reductions in transdiaphragmatic pressure per tidal volume (from 69.4 +/- 10.8 cmH2O/l to 45.6 +/- 5.9 cmH2O/l and to 36.9 +/- 4.6 cmH2O/l, respectively; P < 0.05) and in diaphragmatic pressure-time product (from 306 +/- 31 to 268 +/- 25 and to 224 +/- 23, respectively; P < 0.05). Pleural pressure indices of work of breathing were not reduced by IPAP and CPAP. EPAP significantly increased all pleural and transdiaphragmatic work of breathing indices. CPAP and EPAP similarly increased EELV above control by 93 +/- 16 ml and 69 +/- 12 ml, respectively. The increase in EELV by IPAP of 48 +/- 8 ml (P < 0.01) was significantly less than that by CPAP and EPAP.

Conclusion: The reduction in work of breathing during bronchospasm is primarily induced by the IPAP component, and that for the same reduction in work of breathing by CPAP, EELV increases more.

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Animal model instrumentation. AB, abdomen signal; BiPAP™, apparatus delivering inspiratory positive airway pressure and continuous positive airway pressure (Respironics, Monroeville, PA, USA); Pabd, abdominal pressure; Part, arterial pressure; Paw, airway pressure; Ppl, pleural pressure; RC, rib cage signal; SUM, summed signal from rib cage and abdomen.
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Figure 1: Animal model instrumentation. AB, abdomen signal; BiPAP™, apparatus delivering inspiratory positive airway pressure and continuous positive airway pressure (Respironics, Monroeville, PA, USA); Pabd, abdominal pressure; Part, arterial pressure; Paw, airway pressure; Ppl, pleural pressure; RC, rib cage signal; SUM, summed signal from rib cage and abdomen.

Mentions: Eighteen fasting mongrel dogs (19.6 ± 0.5 kg) were anesthetized with pentobarbital (30 mg/kg), intubated (9.0 mm ID), and ventilated (10–15 ml/kg, fractional inspired oxygen 0.4–0.5, frequency adjusted to maintain the end-tidal partial carbon dioxide tension in the range 35–40 mmHg). Anesthesia was maintained with pentobarbital (1 mg/kg per hour). Temperature was kept between 36–38°C by external heat. Airway pressure (Paw) was measured 5 cm from the distal end of the endotracheal tube. Heart rate was derived from the electrocardiogram, arterial pressure from a peripheral arterial catheter, and pulmonary arterial pressure and pulmonary arterial occlusion pressure from a balloon-tip pulmonary arterial catheter. Infusion of 0.9 N NaCl was done to keep the end-expiratory pulmonary arterial occlusion pressure between 7 and 10 mmHg. A 5 cm air-filled balloon catheter placed in the mid-chest via 5 cm laporotomy was used to measure pleural pressure (Ppl). Accuracy of Ppl was validated as previously described [14]. Another balloon catheter was placed below the left hemidiaphragm to measure abdominal pressure (Pabd). Respiratory inductive plethysmography bands (Respitrace 900SC, NIMS, North Bay Village, FL, USA) were placed around the rib cage and abdomen (Fig. 1). The animals were then placed prone and allowed to stabilize for 30 min.


Effects of the components of positive airway pressure on work of breathing during bronchospasm.

Miro AM, Pinsky MR, Rogers PL - Crit Care (2004)

Animal model instrumentation. AB, abdomen signal; BiPAP™, apparatus delivering inspiratory positive airway pressure and continuous positive airway pressure (Respironics, Monroeville, PA, USA); Pabd, abdominal pressure; Part, arterial pressure; Paw, airway pressure; Ppl, pleural pressure; RC, rib cage signal; SUM, summed signal from rib cage and abdomen.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC420031&req=5

Figure 1: Animal model instrumentation. AB, abdomen signal; BiPAP™, apparatus delivering inspiratory positive airway pressure and continuous positive airway pressure (Respironics, Monroeville, PA, USA); Pabd, abdominal pressure; Part, arterial pressure; Paw, airway pressure; Ppl, pleural pressure; RC, rib cage signal; SUM, summed signal from rib cage and abdomen.
Mentions: Eighteen fasting mongrel dogs (19.6 ± 0.5 kg) were anesthetized with pentobarbital (30 mg/kg), intubated (9.0 mm ID), and ventilated (10–15 ml/kg, fractional inspired oxygen 0.4–0.5, frequency adjusted to maintain the end-tidal partial carbon dioxide tension in the range 35–40 mmHg). Anesthesia was maintained with pentobarbital (1 mg/kg per hour). Temperature was kept between 36–38°C by external heat. Airway pressure (Paw) was measured 5 cm from the distal end of the endotracheal tube. Heart rate was derived from the electrocardiogram, arterial pressure from a peripheral arterial catheter, and pulmonary arterial pressure and pulmonary arterial occlusion pressure from a balloon-tip pulmonary arterial catheter. Infusion of 0.9 N NaCl was done to keep the end-expiratory pulmonary arterial occlusion pressure between 7 and 10 mmHg. A 5 cm air-filled balloon catheter placed in the mid-chest via 5 cm laporotomy was used to measure pleural pressure (Ppl). Accuracy of Ppl was validated as previously described [14]. Another balloon catheter was placed below the left hemidiaphragm to measure abdominal pressure (Pabd). Respiratory inductive plethysmography bands (Respitrace 900SC, NIMS, North Bay Village, FL, USA) were placed around the rib cage and abdomen (Fig. 1). The animals were then placed prone and allowed to stabilize for 30 min.

Bottom Line: Theoretically, expiratory positive airway pressure (EPAP), by reducing expiratory breaking, may be as important as inspiratory positive airway pressure (IPAP) in reducing work of breathing during acute bronchospasm.CPAP and EPAP similarly increased EELV above control by 93 +/- 16 ml and 69 +/- 12 ml, respectively.The increase in EELV by IPAP of 48 +/- 8 ml (P < 0.01) was significantly less than that by CPAP and EPAP.

View Article: PubMed Central - HTML - PubMed

Affiliation: Cardiopulmonary Research Laboratory, Department of Anesthesiology/Critical Care Medicine, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, USA.

ABSTRACT

Introduction: Partial assist ventilation reduces work of breathing in patients with bronchospasm; however, it is not clear which components of the ventilatory cycle contribute to this process. Theoretically, expiratory positive airway pressure (EPAP), by reducing expiratory breaking, may be as important as inspiratory positive airway pressure (IPAP) in reducing work of breathing during acute bronchospasm.

Method: We compared the effects of 10 cmH2O of IPAP, EPAP, and continuous positive airwaypressure (CPAP) on inspiratory work of breathing and end-expiratory lung volume (EELV) in a canine model of methacholine-induced bronchospasm.

Results: Methacholine infusion increased airway resistance and work of breathing. During bronchospasm IPAP and CPAP reduced work of breathing primarily through reductions in transdiaphragmatic pressure per tidal volume (from 69.4 +/- 10.8 cmH2O/l to 45.6 +/- 5.9 cmH2O/l and to 36.9 +/- 4.6 cmH2O/l, respectively; P < 0.05) and in diaphragmatic pressure-time product (from 306 +/- 31 to 268 +/- 25 and to 224 +/- 23, respectively; P < 0.05). Pleural pressure indices of work of breathing were not reduced by IPAP and CPAP. EPAP significantly increased all pleural and transdiaphragmatic work of breathing indices. CPAP and EPAP similarly increased EELV above control by 93 +/- 16 ml and 69 +/- 12 ml, respectively. The increase in EELV by IPAP of 48 +/- 8 ml (P < 0.01) was significantly less than that by CPAP and EPAP.

Conclusion: The reduction in work of breathing during bronchospasm is primarily induced by the IPAP component, and that for the same reduction in work of breathing by CPAP, EELV increases more.

Show MeSH
Related in: MedlinePlus