During normal inhalation, the diaphragm and muscles of the chest wall work to pr

Question

During normal inhalation, the diaphragm and muscles of the chest wall work to produce a negative pressure in the thorax, leading to an influx of air into the lungs. During exhalation, the muscles relax, and the pressure in the thorax becomes less negative, allowing the elastic recoil of the lungs to push air out.

A patient with paralyzed respiratory muscles cannot generate the negative thoracic pressure necessary for inhalation. An external device called a mechanical ventilator can be used to enable respiration. Positive pressure mechanical ventilators work by using a pump to generate a positive pressure (greater than atmospheric pressure) to inflate the lungs, then reducing the applied pressure and allowing the natural recoil of the lungs to push the air back out for exhalation. In contrast, in order to inhale normally, a person must generate a negative pressure (i.e., less than atmospheric pressure).

During normal inhalation, the diaphragm and muscles of the chest wall work to produce a negative pressure in the thorax, leading to an influx of air into the lungs. During exhalation, the muscles relax, and the pressure in the thorax becomes less negative, allowing the elastic recoil of the lungs to push air out. A patient with paralyzed respiratory muscles cannot generate the negative thoracic pressure necessary for inhalation. An external device called a mechanical ventilator can be used to enable respiration. Positive pressure mechanical ventilators work by using a pump to generate a positive pressure (greater than atmospheric pressure) to inflate the lungs, then reducing the applied pressure and allowing the natural recoil of the lungs to push the air back out for exhalation. In contrast, in order to inhale normally, a person must generate a negative pressure (i.e., less than atmospheric pressure) Complete the following statement about positive pressure ventilation. Positive pressure ventilation will cardiac output and cardiac output will be greater during the phase of ventilation increase; inspiratory increase; expiratory O decrease; inspiratory Odecrease; expiratory

Explanation / Answer

During positive pressure ventilation, there is an increase in intrathoracic pressure. This increase in intrathoracic pressure decreases the venous return to heart and therefore the cardiac output decreases. During expiration, there is a decrease in intrathoracic pressure and therefore venous return increases which in turn increases the cardiac output.

Therefore, positive pressure ventilation will decrease the cardiac output and cardiac output will be greater during the expiratory phase of ventilation (option 4).

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