ALTERNATING VERSUS SYNCHRONOUS VENTILATION OF LEFT AND RIGHT LUNGS INPIGLETS

Objective: We tested whether alternating ventilation (AV) of each lung (i.e. with a phase difference of half a ventilatory cycle) would decr ease central venous pressure and so increase cardiac output when compa red with simultaneous ventilation (SV) of both lungs. Theory: If, duri ng AV, the inflated lung expands partly via compression of the opposit e lung, mean lung volume will be smaller during AV than SV. As a conse quence, mean intrathoracic pressure (as cited in the literature), and therefore, central venous pressure will be smaller. Design: The experi ments were performed in seven anaesthetized and paralyzed piglets usin g a double-piston ventilator. Minute ventilation was the same during A V and SV. Starting at SV, we alternated three times between AV and SV for periods of 10 min. Results: During AV, central venous pressure was decreased by 0.7 mmHg and cardiac output was increased by 10+/-4.4% ( mean, +/-SD) compared with SV. AV also resulted in increased arterial pressure. During one-sided inflation with closed outlet of the opposit e lung, a pressure rise occurred in the opposite lung, indicating comp ression. Conclusion: The higher cardiac output during AV than SV can b e explained by the fact that central venous pressure is lower during A V. This lower central venous pressure is very probably due to the lowe r mean intrathoracic pressure caused by compression of the opposite lu ng during unilateral inflation.