From inside the P-V maneuvers, good transient reduced total of blood pressure levels is possibly noticed
All infants tolerated the measurements well. There were no incidents of hypoxia or bradycardia; in fact, transcutaneous Po2 usually increased during the repeated inflations.
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The recording of P-V curves (15, 16) always preceded FRC measurements. Before and after obtaining each P-V diagram, the lungs were manually inflated with ten large breaths to counteract atelectasis and standardize the volume history. P-V measurements were done as follows: the equipment shown in Figure 1 was attached to the endotracheal tube, and the lungs were inflated by a syringe, attempting to reach an airway pressure just above 30 cm H2O, which was maintained for about 2 s. During the following passive deflation to zero airway pressure, the expired flow was interrupted for 80 ms every 160 ms by a fast, computer-controlled, electromagnetic valve (Harting 08300320120, Siemens Elema, Stockholm, Sweden), so that exhalation occurred in small portions. Airway flow was measured by a heated pneumotachograph (Fleisch no. 00, Lausanne, Switzerland; linearity flow range = 0-100 mL/s) connected to a differential pressure transducer (MP 45-1-871; < ±2.5 cm H2O; Validyne, Northridge, CA), and the expired volume between the interruptions was calculated by integration of the flow signal with a computer (PDP , Digital Equipment Corp., Marlboro, MA). Airway pressure was measured by a pressure transducer (SCX01DN, SenSym, Rugby, UK) at the end of each occlusion and was assumed to equal alveolar pressure. Static P-V curves were drawn by an X-Y-writer (HP 7575A). Measurements were discarded if the curves showed signs of spontaneous breathing. The first few interrupter cycles occurred while the investigator’s finger prevented the lungs from emptying(Fig. 1), and a constant pressure during these cycles assured that no leak was present. Continue reading “From inside the P-V maneuvers, good transient reduced total of blood pressure levels is possibly noticed”
