Effect of Open and Closed Chest Conditions
In both closed and open chest conditions (Fig 6), increases in SAP (A up) occurred in phase with the positive-pressure inspiration (86% open and 82% closed), whereas the A down occurred in expiration. The A down was greater in the closed than in the open chest condition (Table 2; p < 0.05). Changes in SA after positive-pressure ventilation were minimal (mean open chest change, —0.1 ± 1 cm2 and mean closed chest change, -0.2 ± 0.8 cm2), and they were not significantly different between open and closed chest conditions, with SA decreasing in 55% of the closed and in 50% of the open chest condition runs. Interestingly, in the closed chest condition, both EDA and ESA decreased during the positive-pres-sure inspiration in all the sequences, whereas in the open chest condition, this occurred in only 57% of the sequences (p < 0.05). Furthermore, EDA and ESA decreased more in the closed compared with the open chest condition (p < 0.05).
Cumulative SA Deficit and A Down
There was no measurable relation between the maximal decrease in SAP after a breath and the cumulative SA deficit (summed SA decrease relative to apneic SA; Fig 7). The cumulative SA deficit was higher in the postbypass period, and this was associated with a greater decrease in EDA (p < 0.05). The presence of an open or closed chest did not influence this relation. fully
A Fourier analysis of the LV area and arterial pressure was done. In the closed chest condition, an SAP harmonic signal at the same frequency as the airway signal was found in 55% of the runs, whereas it was invariably seen in all of the LV area signals. In the open chest condition, this common harmonic signal was present in only 36% and 64% of the SAP and LV area signals, respectively. However, the phase angles of the SAP and LV area signals relative to the airway signal were different. The airway phase angle slightly preceded the arterial in > 80% of the runs by approximately one heartbeat in both the open and closed chest condition, and the two signals had indistinguishable phase angles in 15% of the runs. The airway pressure and the echo area were never in identical phase. In the closed chest condition, the change in the SAP signal preceded the change in the echo area in all cases, with the SAP tending to increase while the echo area was decreasing. In the open chest condition, this occurred 67% of the time.
Figure 6. Relation between percent change in SAP and changes in LV area during open chest (left column) and closed chest (right column) conditions. ■ = SA; • = EDA; ▲ = ESA.
Figure 7. Relation between the fall in SAP expressed as A down and the sum of the SA difference (sum = SAa — SAx for all patients during the open and closed chest condition and for patients with a fractional area of contraction < 30% or > 30%).