Carbon dioxide respiratory response during positive inspiratory pressure in COPD patients

Role of ventilatory drive in asthma and chronic obstructive pulmonary disease

The ventilatory drive is affected by several factors such as chemosensitivity, basal arterial oxygen or carbon dioxide tension, mechanical impedance, and respiratory muscle dysfunction. Blunted ventilatory drive or a decrease in the perception of dyspnea in bronchial asthma and chronic obstructive pulmonary disease (COPD) could lead to a decrease in the alarm reaction to dangerous situations such as severe airway obstruction, severe hypoxemia, or severe hypercapnia. This could delay management and treatment, causing an increase in the morbidity and mortality of patients with bronchial asthma and COPD. The ventilatory drive to chemical stimuli can be altered by a beta-2-agonist, oxygen administration; and lung volume reduction, and an increased dyspnea sensation may be improved by corticosteroid, chest wall vibration, or lung volume reduction. The ventilatory drive has been found to play a key role in determining the severity of asthma and COPD.

Physiological effects of alveolar, tracheal, and "standard" pressure supports

Pressure support (PS) is characterized by a pressure plateau, which is usually generated at the ventilator level (PS(vent)). We have built a PS device in which the pressure plateau can be obtained at the upper airway level (PS(aw)) or at the alveolar level (PS(A)). The effect of these different PS modes was evaluated in seven healthy men during air breathing and 5% CO(2) breathing. Minute ventilation during air breathing was higher with PS(A) than with PS(aw) and lower with PS(vent) (16 +/- 3, 14 +/- 3, and 11 +/- 2 l/min, respectively). By contrast, there were no significant differences in minute ventilation during 5% CO(2) breathing (25 +/- 5, 27 +/- 7, and 23 +/- 5 l/min, respectively). The esophageal pressure-time product per minute was lower with PS(A) than with PS(aw) and PS(vent) during air breathing (29 +/- 26, 44 +/- 44, and 48 +/- 30 cmH(2)O. s, respectively) and 5% CO(2) breathing (97 +/- 40, 145 +/- 62, and 220 +/- 41 cmH(2)O. s, respectively). In conclusion, during PS, moving the inspiratory pressure plateau from the ventilator to the alveolar level reduces pressure output, particularly at high ventilation levels.