Determinants of Aortic Pressure Variation During Positive-Pressure Ventilation in Man: Results

5 Sep

Determinants of Aortic Pressure Variation During Positive-Pressure Ventilation in Man: ResultsIn total, 114 apnea/positive-pressure ventilation sequences in 15 patients were collected. The quality of the recorded images on videotapes using the criteria of Schnittger et al was assessed by two observers, each blinded to the interpretation of the other. Only data from sequences accepted by both observers were subjected to further analysis. Based on this screening criteria, 70 of the sequences (61%) were then analyzed. Thirty-six sequences were in open chest conditions, with 18 being recorded before bypass; whereas 34 sequences were in closed chest conditions, with 13 being recorded before bypass. Some subjects had more than one sequence acceptable for a specific condition. add comment
In these cases, the individual runs were compared in order to assess the reproducibility of the measurements. Intracondition variability was a < 10% maximal difference in LV EDA and a < 2.5 mm Hg maximal difference in SAP during apnea. The first run was chosen for subsequent analysis. Based on this algorithm, we compared the effect of positive-pressure ventilation relative to apnea in 11 subjects during the closed chest condition (5 before bypass) and 14 subjects during the open chest condition (10 before bypass). All subjects remained hemodynamically stable throughout the study protocol, and they were without the use of IABP counterpulsation or changes in inotropic therapy (Table 1).
Effects of Positive-Pressure Ventilation on SAP and LV Area
There was an increase or no change in SAP in 22 of the sequences (88%) during positive-pressure inspiration. When SAP increased, the increase in airway and arterial pressure occurred together. If SAP decreased, the decrease occurred during expiration. SAP never increased during expiration. The magnitude of increase or decrease in SAP was similar among subjects (Table 2). Overall, SAP increased by 2.3 ± 2.7 mm Hg and decreased by 3.7 ± 3.5 mm Hg with inspiration and expiration, respectively.

Table 2—Changes in SAP Following a Positive-Pressure Breath

Conditionsn% SAP UpA Up, mm Hg% SAP DownA Down, mm Hg
All sequences252.3 ± 2.72.4 ± 2.63.1 ± 3.03.7 ± 3.5
Prebypass152.5 ± 2.32.8 ± 2.32.3 ± 2.52.7 ± 2.7
Postbypass101.4 ± 2.41.7 ± 3.04.4 ± 3.45.2 ± 4.1
Open chest142.4 ± 2.82.8 ± 3.02.1 ± 1.9t2.4 ± 2.1t
Closed chest111.6 ± 1.81.9 ± 2.14.5 ± 3.6t5.3 ± 4.2t
FAC < 30%61.2 ± 0.71.3 ± 0.73.2 ± 3.13.8 ± 3.4
FAC > 30%192.3 ± 2.72.7 ± 2.93.1 ± 3.03.6 ± 3.5