Determinants of Aortic Pressure Variation During Positive-Pressure Ventilation in Man: Effect of Cardiopulmonary Bypass on SAP and LV Area Relations

6 Sep
2014

Although SAP tended to vary with the phase of ventilation, no consistent pattern of SA, EDA, or ESA with ventilation could be identified. During positive-pressure inspiration, SA increased in 11 sequences (44%), decreased in 13 sequences (52%), and stayed the same in 1 sequence (4%; mean change, —0.2 ± 0.9 cm2; Table 3). The EDA increased in 5 sequences (20%), decreased in 19 sequences (76%), and stayed the same in 1 sequence (4%; mean change, —0.8 ± 1.1 cm2). The ESA increased in 3 sequences (12%), decreased in 19 sequences (76%), and stayed the same in 3 sequences (12%; mean change, —0.7 ± 0.8 cm2). Furthermore, there was no consistent relation between changes in SAP and changes in SA, EDA, or ESA (Fig 3, left) or between A down (Table 2) and changes in SA, EDA, or ESA (Fig 3, right). In most subjects, however, both EDA and ESA decreased during the positive-pressure inspiration (Fig 4), but there was no difference between the degree of decrease in EDA compared with ESA.
In the validation group, changes in LV SA were associated with concomitant changes in the electromagnetic flow probe-derived LV stroke volumes during ventilation.
Effect of Cardiopulmonary Bypass on SAP and LV Area Relations
Before bypass, SAP increased during the positive-pressure inspiration in the majority of subjects (93%; Fig 5). During this period (15 sequences), positive-pressure ventilation increased the SA in 9 sequences (60%), decreased the SA in 5 sequences (33%) and caused no change in the SA in 1 sequence (7%; mean change, 0.1 ± 0.5 cm2). The A down tended to be greater after bypass, but this did not reach statistical significance. As for the group as a whole, positive-pressure inspiration had an inconsistent effect on LV areas: EDA increased in 4 sequences (27%), decreased in 10 sequences (67%), and stayed the same in 1 sequence (7%; mean change, —0.7 ± 0.9 cm2). ESA had a similar response during positive-pressure inspiration, increasing in 2 sequences (13%), decreasing in 12 sequences (80%), and staying the same in 1 sequence (7%; mean change, —0.8 ± 0.9 cm2). After cardiopulmonary bypass, the effects of positive-pressure inspiration on SAP were similar to prebypass responses, with SAP increasing in seven sequences (70%) and decreasing in three sequences (30%). In most sequences, however, after cardiopulmonary bypass, SA, EDA, and ESA decreased 80%, 90%, and 70%, respectively, during inspiration, compared with an apneic baseline (p < 0.05). Mean apneic EDA was smaller after bypass and demonstrated a greater decrease after a positive-pressure breath than before bypass (p < 0.05). ventolin inhalers

Table 3—Changes in Sum SA and LV Area Following a Positive-Pressure Breath

ConditionsnSum SA,cm2Mean SA, cm2SA Change, cm2Mean EDA, cm2EDA Change, cm2Mean ESA, cm2ESA Change, cm2
All sequences250.8 ± 2.74.0 ± 1.4– 0.2 ± 0.99.8 ± 5.40.8 ± 1.15.8 ± 5.1-0.7 ± 0.8
Prebypass15-0.4 ± 1.4t3.6 ± 1.40.1 ± 0.5t10.5 ± 5.9t-0.7 ± 0.9t6.9 ± 6.1-0.8 ± 0.9
Postbypass102.7 ± 3.3t4.6 ± 1.2-0.7 ± 1.1t8.6 ± 4.1t– 1.1 ± 1.3t4.0 ± 3.3-0.4 ± 0.6
Open chest141.5 ± 3.14.1 ± 1.40.1 ± 1.010.1 ± 6.3-0.4 ± 1.0{6.0 ± 6.20.2 ± 0.6{
Closed chest110.0 ± 2.03.9 ± 1.30.2 ± 0.89.3 ± 3.8-1.5 ± 0.8{5.4 ± 3.9-1.2 ± 0.8{
FAC < 30%61.6 ± 3.73.4 ± 1.40.6 ± 1.117.1 ± 5.3§-1.4 ± 1.113.7 ± 4.6§0.8 ± 1.0
FAC > 30%190.6 ± 2.34.2 ± 1.30.1 ± 0.87.4 ± 2.6§-0.7 ± 1.03.2 ± 2.2§0.6 ± 0.8

Figure 3. Relation between percentage of change in SAP and changes in LV area (left column), and the relation between percentage of absolute decrease in SAP and changes in LV area (right column) during a positive-pressure breath. ■ = SA; • = EDA; ▲ = ESA.

Figure 3. Relation between percentage of change in SAP and changes in LV area (left column), and the relation between percentage of absolute decrease in SAP and changes in LV area (right column) during a positive-pressure breath. ■ = SA; • = EDA; ▲ = ESA.

Figure 4. Relation between the change in EDA and ESA after a positive-pressure breath.

Figure 4. Relation between the change in EDA and ESA after a positive-pressure breath.

Figure 5.    Relation between percentage change in SAP and changes in LV area during the prebypass (left column) and  postbypass    (right column) periods. ■ = SA; • = EDA; ▲ = ESA.

Figure 5.    Relation between percentage change in SAP and changes in LV area during the prebypass (left column) and postbypass    (right column) periods. ■ = SA; • = EDA; ▲ = ESA.

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