The investigation took place 205 ± 60 minutes after the end of the surgery. For technical reasons in measuring CBF, the latter was not measured in four patients during the second control period. Respiratory data are summarized in Table 1. To obtain PaC02 between 4.5 and 5.5 kPa, a tidal volume of 9.2 ±0.3 ml/kg was used during IPPV and the driving pressure of the HFJV ventilator was set at 1.0 ±0.1 bar. The Pa02 values were similar during the two types of ventilatory support. A dynamic total respiratory com­pliance of 50 ±5 ml/cm HzO was measured during IPPV. Peak inspiratory pressure was significantly (p<0.05) lower during HFJV than during the two periods of IPPV, whereas Paw remained in the same range during both modes of ventilation.

Table 1—Respiratory Variables Determined During the Three Experimental Periods

IPPV,

HFJV

IPPV2

Frequency, min1

10

100

10

I/E, %

0.33

0.5

0.33

Driving pressure, bar

1.0±0.1

Vt, ml*kg 1

9.2 ±0.3

9.2±0.3

Paw, mm Hg

4.5±0.4

4.1 ±0.4

4.8±0.5

PIP, mm Hg

17.4± 1.3

12.4 ± 1.2t

18.8± 1.4

PaC02 kPa

4.9±0.1

5.0±0.1

5.0±0.1

Pa02, kPa

16.4± 1.1

17.5± 1.2

17.1 ±1.6

FIGURE 1. Individual ISI values during the three experimental periods.

Hemodynamic data are summarized in Table 2. No significant differ­ences in any of the hemodynamic variables were detected between IPPV and HFJV Cerebral hemodynamic data are presented in Table 3. The standard deviation between measured and calculated curves of CBF values was below 1.5, indicating a good quality of CBF measurement and comparable between the three measurements. Aver­age F! and ISI values were not significantly modified by HFJV Fractional flow remained stable between both modes of ventilation, including patients with a large change of Fl or ISI. Figure 1 presents individual ISI data. The ISI ranged from 26.1 to 61.9 during IPPV! and from 26.0 to 68.3 during IPPV2. The range of ISI values was increased by 30 percent during HFJV (19.9 to 72.8). Although classic main determi­nants of CBF (PaC02, cerebral perfusion pressure, Paw, temperature) were stable during both modes of ventilation (Table 4), application of HFJV induced in one patient (patient 3) an increase and in two patients (patients 7 and 13), a decrease in CBF (FY and ISI) of more than 40 percent from IPPVi values.
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Table 2—Hemodynamic Variables Determined During the Three Experimental Periods

IPPV,

HFJV

IPPV2

MAP, mm Hg

94±4

95 ±4

96±4

HR, beats’min

96±3

96 ± 2

96±2

CI, Lmin Wn

2.5±0.1

2.5±0.1

2.6±0.1

RAP, mm Hg

7± 1

9± 1

8± 1

MPAP, mm Hg

18 ±2

22±2

20 ± 1

PCWP, mm Hg

9± 1

10±1

9± 1

SVRI, dynes*s*cm m ~2

955 ±61

940 ±63

932 ±42

PVRI, dynes*s*cm m ~2

95± 12

118 ±13

101 ±10

Table 3—Cerebral Hemodynamic Variables Determined During the Three Experimental Periods

IPPV,

HFJV

IPPV2

F, (ml*100 g~2#min~I)

56±4

53±6

56±4

ISI (units)

44±2

42 ±3

46 ±3

FF (%)

74 ±2

78 ±3

76 ±3