Acta Anaesthesiol Scand 1990: 34: 421-429
Ventilation-perfusion relationships and atelectasis formation in the supine and lateral positions during conventional mechanical and differential ventilation C. KLINGSTEDT, G. HEDENSTIERNA, S. BAEHRENDTZ, H. LUNDQVIST, A. STRANDBERG, L. TOKICS and B. BRISMAR Departments of Anesthesiology and Internal Medicine I, Sodersjukhuset, Department of Clinical Physiology, Uppsala University Hospital and Departments of Anesthesiology, Surgery and Roentgenology, Huddinge University Hospital, Sweden
Patients without respiratory symptoms were studied awake and during general anesthesia with mechanical ventilation prior to elective surgery. Ventilation-perfusion (V,/Q) relationships, gas exchange and atelectasis formation were studied during five different conditions: 1) supine, awake; 2) supine during anesthesia with conventional mechanical ventilation (CV); 3) in the left lateral position during CV; 4) as 3) but with 10 cm of positive end-expiratory pressure (PEEP) and 5) as 3) but using differential ventilation with selective PEEP (DV+SPEEP) to the dependent lung. Atelectatic areas and increases of shunt blood flow and blood flow to regions with low V,/Q ratios appeared after induction of anesthesia and CV. With the patients in the lateral position, further V,/Qmismatch with a fall in Pao, and increased dead space ventilation was observed. Atelectatic lung areas were still present, although the total atelectatic area was slightly decreased. Some of the effects caused by the lateral position could be counteracted by adding PEEP. Perfusion of regions with low V,/Qratios and venous admixture were then diminished, while Pao, was slightly increased; shunt blood flow and dead space ventilation were essentially unchanged. During CV + PEEP, there was a decrease in cardiac output, compared to CV in the lateral position. DV+SPEEP was more effective than CV+PEEP in decreasing shunt flow and increasing Pao, in the lateral position; in addition to this, cardiac output was not affected. Received 23 3.0 1989, accepted f o r publication 5 December 1989
Key words: Anesthesia; atelectasis; position; positive end-expiratory pressure; tomography; ventilation-perfusion.
During anesthesia and muscle paralysis, ventilation is distributed towards the non-dependent parts of the lung (1-3), presumably as a result of airway closure and alveolar collapse in the dependent lung regions (4, 5). Perfusion, on the other hand, due to gravitational forces, is mainly distributed towards the dependent parts of the lung ( 6 , 7). This anesthesia-induced ventilationlperfusion (u,/Q mismatch manifests itself clinically in an increased alveolo-arterial 0, tension difference (8).Application of a positive end-expiratory pressure (PEEP) increases functional residual capacity (FRC) and improves ventilation of dependent lung regions (9). However, the increased intrathoracic pressure impedes cardiac output (10) and causes a further diversion of blood flow towards dependent lung regions ( 1 1). Body position also affects both ventilation and circulation (1 2). The lateral position is used in several surgical procedures but its effect on the %'& distribution is not clear. Moreover, the lateral position allows the
ventilation of dependent and non-dependent lung regions to be physically separated since the lungs can be ventilated separately with a double-lumen endobronchial tube. The lateral position is consequently used during differential ventilation (DV) with selective PEEP (SPEEP) to the dependent lung. This method permits ventilation of each lung in proportion to its perfusion (1 1). It also creates a lower overall intrathoracic pressure with less effect on cardiac output (13). The purpose of this investigation was to study both the effects on the %'&distribution in the lung when moving the patient from the supine to the lateral position and the effects of using either general PEEP or DV with SPEEP in the lateral position. The multiple inert gas elimination technique developed by Wagner et al. (14, 15) was used, which allows a multi-compartmental analysis of the %'& distributions in the lung. In some of the patients, this technique was combined with computerized tomography (CT) in order to ana-
422
C. KLINGSTEDT ET AL.
o,/
lyze the correlation between atelectasis formation, distribution and oxygenation during the different body positions and ventilation modes.
a
PATIENTS AND METHODS Patients A total of 15 patients, 12 men and 3 women, were studied during general anesthesia prior to elective surgery. The age range was 34 to 70 years (mean 53.2 years) and all patients had a normal body configuration (weight 71.3k9 kg and height 177 & 7 cm). Seven of the patients were active smokers, three smoking more than 10 cigarettes/day. All patients were free from cardio-pulmonary disease, as judged by history, physical examination, chest x-ray and ECG. Informed consent was obtained in each case, and the study was approved by the local Ethical Committee. Anesthesia and ventilation After an i.v. dose of atropine (0.25-0.5 mg), anesthesia was induced with a bolus dose of thiopental (2-5 mg/kg) in combination with either flunitrazepam (0.01 mg/kg) or diazepam (0.1 mg/kg). Muscular relaxation was induced with pancuronium bromide (0.1 mg/kg), and the patients were intubated with a disposable, double-lumen, left main bronchial catheter with high-volume, low-pressure cuffs (Broncho-Cath, National Catheter Corp. 35 or 37 Fr). To ensure that no air leaks between the lungs were present, the tube position was checked thus: while one lung was ventilated, the other channel of the double-lumen tube was connected to a short piece of tubing ending 1-2 cm below the surface in a water trap. If no air bubbles were seen, the system was considered air tight. Anesthesia was maintained with enflurane (0.3-1.0%) in an airloxygen mixture, with additional doses of pancuronium and thiopental given as required. The inspired oxygen fraction was kept at approximately 0.4 (except during the awake measurements when the patients were breathing air). Inspired oxygen and mixed expired carbon dioxide concentrations were checked with mass spectrometry. During anesthesia, minute ventilation was adjusted to approximately 80% of the awake value. The patients were ventilated with one or two ventilators (Siemens-Elema Servo-ventilator 9OOC). During differential ventilation, the ventilators were electronically synchronized, thereby keeping the respiratory frequency equal and the start of inspiration simultaneous for both lungs. One of the ventilators was used as the “master”, controlling the other, “slave”. Both ventilators delivered a squarewave flow, with an inspiratory time of 25% and an end-inspiratory pause of 10% of the total respiratory cycle. The respiratory frequency was 12/min and the total tidal volume for each patient was kept nearly constant at 8-10 ml/kg throughout the study. During differential ventilation, the total tidal volume was equally divided between the two lungs. The PEEP level used during both general and selective PEEP was 10 cmH,O ( 1 kPa). was measured with a spirometer Total minute ventilation (0,) (Wright respirometer, BOC). Catheterization, cardiac output and blood gases Systemic arterial, right atrial, pulmonary arterial and pulmonary capillary wedge (PCWP) pressures were recorded via catheters inserted in a radial artery and in the pulmonary artery. Cardiac output was determined by thermodilution (CO Computer 9520A, Edwards Labs.). Arterial and mixed venous oxygen and carbon dioxide tensions (Pao,, Pvo,, Paco,, Pvco,) were measured with standard electrode techniques (Radiometer ABL2). Hemoglobin concentration and oxygen saturation were determined spectrophotometrically (CO Oximeter, IL). Venous admixture ((L/(L)was calculated according to
the Berggren shunt equation (16) and alveolo-arterial oxygen tension differences (P(A-a)o,) from a simplified alveolar gas equation: P(A-a)o,= FIO,*(P, - P,,,)
- Paco,/RQ- Pao,
where RQwas assumed to be 0.8, and where Fro,, P, and P,, stand for inspired oxygen fraction, barometric pressure and water vapor pressure at 37”C, respectively.
Ventilation-perfusion ratios Six inert gases (sulphur hexafluoride, ethane, cyclopropane, halothane, ether and acetone) were dissolved in isotonic saline and infused into a peripheral vein at a rate of 180 ml/h. After an equilibration period of 40 min, arterial and mixed venous blood and mixed expired gas were collected simultaneously for gas chromatography (Sigma 3 Perkin-Elmer) ( 1 7). Blood-gas partition coefficients were determined by a two-step procedure (18). The retention (ratio of arterial to mixed venous concentrations) and excretion (ratio of mixed expired to mixed venous concentrations) for each gas were plotted against the blood-gas partition coefficients. These relationships were used to derive the corresponding ventilation and perfusion distributions using numerical computer analysis with enforced smoothing (14, 19). Data from the fr,/Qstudies are presented as fractions of the total pulmonary ventilation or perfusion going to regions with different Qratios. In addition to this, data on mean values and log standard deviations for ventilation (vmean, vsd) and perfusion (amean, Qsd) distributions and physiological dead space/tidal volume (Vd phys/Vt) fractions are presented. The fit of the ventilation and perfusion distributions to the raw retention and excretion data were tested by recalculating the retention and excretion for each gas from distributions. The sum of the squared differences the derived between the measured and calculated retentions and excretions, the remaining sum of squares (RSS), was less than or equal to 6 in 46 of the 56 studies made in all (median=2.15) (cf. Wagner & West (20)).
vA/
v,/Q
Computerized tomograply of the chest With the patient in the supine position, an initial scout view of chest and abdomen was obtained. A transverse C T scan was then performed immediately above the level of the diaphragm. In the lateral posture, an initial scout view was also obtained, followed by a transverse C T scan at the same level as in the supine position. Thoracic areas were measured by planimetry on the transverse CT scans using a computer connected to the tomograph. The inner margins of the thoracic cage were used as a boundary. Mediastinal organs and, in an occasional scan, parts of the diaphragm were thus included in the areas. Atelectatic areas were identified and the area was expressed as a percentage of the total transverse thoracic area at that level. All CT scans were made during apnea at end-expiration. When PEEP was used, it was maintained during the CT scans. The CT scan time was 5 s at 125 kV and 115 mAs and the slice thickness was 8 rnm (Somatom 2, Siemens). Procedure and statistics After catheterization, the inert-gas infusion was started and continued for 40 min before measurements were started. Five patients were studied awake, with hemodynamic and gas exchange measurements performed with the patient in the supine position and breathing room air. The rest of the study was performed with the patient anesthetized and connected to the ventilator (Fro,: 0.4). After at least 15 min of stable anesthesia, new hemodynamic and gas exchange measurements were made. Finally, the patients were placed in the left lateral position for repeated assessments of gas exchange and hemodynamics. Three different modes of ventilation were studied with the patients in the lateral position: conventional ventilation (CV, with free distribution of the tidal volume between the two lungs), CV with general
42 3
0,/QDURING ANESTHESIA Table 1
Ventilation and central circulation data. Minute ventilation (0,)and cardiac output (Qt)in 1. min-I. Vascular pressures in mmHg (kPa) and heart rate (HR) in beats. min-I. All values are given as means+ s.e.mean. The statistical analysis was divided into 3 separate parts (see Procedure and Statistics). 1. The awake results were compared to those obtained during supine conventional mechanical ventilation t zero end-expiratory pressure (CV+ZEEP); 2. Supine CV+ZEEP was then compared to lateral CV+ZEEP, and 3. The 3 ventilation modes in the lateral position were compared with one another (PEEP= positive end-expiratory pressure; DV + SPEEP = differential ventilation + selective PEEP). Position and ventilation
TIE
Supine awake (n=5) Supine CV+ZEEP (n=6) LateralCV+ZEEP ( n = 15) Lateral cv+PEEP (n=9) LateralDV+SPEEP ( n = 15)
Qt
7.71k1.11
6.40f0.33"
6.31 +0.2Ib
5.68k0.32
6.58k0.16
4.92f0.24' ( n = 14) 4.10 f 0.40
6.78 f 0.20
(n=8)
6.50k0.19
4.80+0.30" (n=14)
Systemic arterial mean
95k3" (12.7k0.4) 76k3 (10.1 fO.4) 78+3 (10.4k0.4) 86 f 4d (11.5f0.5) 88+3 (11.7f0.4)
Pulmonary arterial HR
Systolic
6854"
21+3" (2.8k0.4) 80f3b 19+2b (2.5 f 0.3) 69f2 23fZd (3.1k0.3) 67 f 3 33 k 3 (4.420.4) 69k3 24k Id (3.2k0.1)
Diastolic
Mean
Pulmonary capillary wedge
Right atrial
8f1" 14+1" 8kl 65 1 (l.lkO.1) (1.9fO.l) (l.lkO.1) (0.8kO.l) 9 k Ib 13k I b 7k 1 5k 1 (1.2k 0.1) (1.7 k 0.1) (0.9f 0.1) (0.7 k 0.1)
Il+ld 15+ld 8fld 421d (1.5kO.l) (2.OkO.1) ( l . l f O . 1 ) (0.5f0.1) 17 k 2 23 k 2 16 f 2 10 k 1 (2.3k0.3) (3.1f0.3) (2.1fO.3) (1.3kO.l) 12+ Id 1 7 + Id 1Ok Id 6k Id (1.6f0.1) (2.3f0.1) (1.3kO.l) (0.8f0.1)
Significant differences:"Supine awake vs. supine CV t ZEEP (P
Ventilation-perfusion relationships and atelectasis formation in the supine and lateral positions during conventional mechanical and differential ventilation C. KLINGSTEDT, G. HEDENSTIERNA, S. BAEHRENDTZ, H. LUNDQVIST, A. STRANDBERG, L. TOKICS and B. BRISMAR Departments of Anesthesiology and Internal Medicine I, Sodersjukhuset, Department of Clinical Physiology, Uppsala University Hospital and Departments of Anesthesiology, Surgery and Roentgenology, Huddinge University Hospital, Sweden
Patients without respiratory symptoms were studied awake and during general anesthesia with mechanical ventilation prior to elective surgery. Ventilation-perfusion (V,/Q) relationships, gas exchange and atelectasis formation were studied during five different conditions: 1) supine, awake; 2) supine during anesthesia with conventional mechanical ventilation (CV); 3) in the left lateral position during CV; 4) as 3) but with 10 cm of positive end-expiratory pressure (PEEP) and 5) as 3) but using differential ventilation with selective PEEP (DV+SPEEP) to the dependent lung. Atelectatic areas and increases of shunt blood flow and blood flow to regions with low V,/Q ratios appeared after induction of anesthesia and CV. With the patients in the lateral position, further V,/Qmismatch with a fall in Pao, and increased dead space ventilation was observed. Atelectatic lung areas were still present, although the total atelectatic area was slightly decreased. Some of the effects caused by the lateral position could be counteracted by adding PEEP. Perfusion of regions with low V,/Qratios and venous admixture were then diminished, while Pao, was slightly increased; shunt blood flow and dead space ventilation were essentially unchanged. During CV + PEEP, there was a decrease in cardiac output, compared to CV in the lateral position. DV+SPEEP was more effective than CV+PEEP in decreasing shunt flow and increasing Pao, in the lateral position; in addition to this, cardiac output was not affected. Received 23 3.0 1989, accepted f o r publication 5 December 1989
Key words: Anesthesia; atelectasis; position; positive end-expiratory pressure; tomography; ventilation-perfusion.
During anesthesia and muscle paralysis, ventilation is distributed towards the non-dependent parts of the lung (1-3), presumably as a result of airway closure and alveolar collapse in the dependent lung regions (4, 5). Perfusion, on the other hand, due to gravitational forces, is mainly distributed towards the dependent parts of the lung ( 6 , 7). This anesthesia-induced ventilationlperfusion (u,/Q mismatch manifests itself clinically in an increased alveolo-arterial 0, tension difference (8).Application of a positive end-expiratory pressure (PEEP) increases functional residual capacity (FRC) and improves ventilation of dependent lung regions (9). However, the increased intrathoracic pressure impedes cardiac output (10) and causes a further diversion of blood flow towards dependent lung regions ( 1 1). Body position also affects both ventilation and circulation (1 2). The lateral position is used in several surgical procedures but its effect on the %'& distribution is not clear. Moreover, the lateral position allows the
ventilation of dependent and non-dependent lung regions to be physically separated since the lungs can be ventilated separately with a double-lumen endobronchial tube. The lateral position is consequently used during differential ventilation (DV) with selective PEEP (SPEEP) to the dependent lung. This method permits ventilation of each lung in proportion to its perfusion (1 1). It also creates a lower overall intrathoracic pressure with less effect on cardiac output (13). The purpose of this investigation was to study both the effects on the %'&distribution in the lung when moving the patient from the supine to the lateral position and the effects of using either general PEEP or DV with SPEEP in the lateral position. The multiple inert gas elimination technique developed by Wagner et al. (14, 15) was used, which allows a multi-compartmental analysis of the %'& distributions in the lung. In some of the patients, this technique was combined with computerized tomography (CT) in order to ana-
422
C. KLINGSTEDT ET AL.
o,/
lyze the correlation between atelectasis formation, distribution and oxygenation during the different body positions and ventilation modes.
a
PATIENTS AND METHODS Patients A total of 15 patients, 12 men and 3 women, were studied during general anesthesia prior to elective surgery. The age range was 34 to 70 years (mean 53.2 years) and all patients had a normal body configuration (weight 71.3k9 kg and height 177 & 7 cm). Seven of the patients were active smokers, three smoking more than 10 cigarettes/day. All patients were free from cardio-pulmonary disease, as judged by history, physical examination, chest x-ray and ECG. Informed consent was obtained in each case, and the study was approved by the local Ethical Committee. Anesthesia and ventilation After an i.v. dose of atropine (0.25-0.5 mg), anesthesia was induced with a bolus dose of thiopental (2-5 mg/kg) in combination with either flunitrazepam (0.01 mg/kg) or diazepam (0.1 mg/kg). Muscular relaxation was induced with pancuronium bromide (0.1 mg/kg), and the patients were intubated with a disposable, double-lumen, left main bronchial catheter with high-volume, low-pressure cuffs (Broncho-Cath, National Catheter Corp. 35 or 37 Fr). To ensure that no air leaks between the lungs were present, the tube position was checked thus: while one lung was ventilated, the other channel of the double-lumen tube was connected to a short piece of tubing ending 1-2 cm below the surface in a water trap. If no air bubbles were seen, the system was considered air tight. Anesthesia was maintained with enflurane (0.3-1.0%) in an airloxygen mixture, with additional doses of pancuronium and thiopental given as required. The inspired oxygen fraction was kept at approximately 0.4 (except during the awake measurements when the patients were breathing air). Inspired oxygen and mixed expired carbon dioxide concentrations were checked with mass spectrometry. During anesthesia, minute ventilation was adjusted to approximately 80% of the awake value. The patients were ventilated with one or two ventilators (Siemens-Elema Servo-ventilator 9OOC). During differential ventilation, the ventilators were electronically synchronized, thereby keeping the respiratory frequency equal and the start of inspiration simultaneous for both lungs. One of the ventilators was used as the “master”, controlling the other, “slave”. Both ventilators delivered a squarewave flow, with an inspiratory time of 25% and an end-inspiratory pause of 10% of the total respiratory cycle. The respiratory frequency was 12/min and the total tidal volume for each patient was kept nearly constant at 8-10 ml/kg throughout the study. During differential ventilation, the total tidal volume was equally divided between the two lungs. The PEEP level used during both general and selective PEEP was 10 cmH,O ( 1 kPa). was measured with a spirometer Total minute ventilation (0,) (Wright respirometer, BOC). Catheterization, cardiac output and blood gases Systemic arterial, right atrial, pulmonary arterial and pulmonary capillary wedge (PCWP) pressures were recorded via catheters inserted in a radial artery and in the pulmonary artery. Cardiac output was determined by thermodilution (CO Computer 9520A, Edwards Labs.). Arterial and mixed venous oxygen and carbon dioxide tensions (Pao,, Pvo,, Paco,, Pvco,) were measured with standard electrode techniques (Radiometer ABL2). Hemoglobin concentration and oxygen saturation were determined spectrophotometrically (CO Oximeter, IL). Venous admixture ((L/(L)was calculated according to
the Berggren shunt equation (16) and alveolo-arterial oxygen tension differences (P(A-a)o,) from a simplified alveolar gas equation: P(A-a)o,= FIO,*(P, - P,,,)
- Paco,/RQ- Pao,
where RQwas assumed to be 0.8, and where Fro,, P, and P,, stand for inspired oxygen fraction, barometric pressure and water vapor pressure at 37”C, respectively.
Ventilation-perfusion ratios Six inert gases (sulphur hexafluoride, ethane, cyclopropane, halothane, ether and acetone) were dissolved in isotonic saline and infused into a peripheral vein at a rate of 180 ml/h. After an equilibration period of 40 min, arterial and mixed venous blood and mixed expired gas were collected simultaneously for gas chromatography (Sigma 3 Perkin-Elmer) ( 1 7). Blood-gas partition coefficients were determined by a two-step procedure (18). The retention (ratio of arterial to mixed venous concentrations) and excretion (ratio of mixed expired to mixed venous concentrations) for each gas were plotted against the blood-gas partition coefficients. These relationships were used to derive the corresponding ventilation and perfusion distributions using numerical computer analysis with enforced smoothing (14, 19). Data from the fr,/Qstudies are presented as fractions of the total pulmonary ventilation or perfusion going to regions with different Qratios. In addition to this, data on mean values and log standard deviations for ventilation (vmean, vsd) and perfusion (amean, Qsd) distributions and physiological dead space/tidal volume (Vd phys/Vt) fractions are presented. The fit of the ventilation and perfusion distributions to the raw retention and excretion data were tested by recalculating the retention and excretion for each gas from distributions. The sum of the squared differences the derived between the measured and calculated retentions and excretions, the remaining sum of squares (RSS), was less than or equal to 6 in 46 of the 56 studies made in all (median=2.15) (cf. Wagner & West (20)).
vA/
v,/Q
Computerized tomograply of the chest With the patient in the supine position, an initial scout view of chest and abdomen was obtained. A transverse C T scan was then performed immediately above the level of the diaphragm. In the lateral posture, an initial scout view was also obtained, followed by a transverse C T scan at the same level as in the supine position. Thoracic areas were measured by planimetry on the transverse CT scans using a computer connected to the tomograph. The inner margins of the thoracic cage were used as a boundary. Mediastinal organs and, in an occasional scan, parts of the diaphragm were thus included in the areas. Atelectatic areas were identified and the area was expressed as a percentage of the total transverse thoracic area at that level. All CT scans were made during apnea at end-expiration. When PEEP was used, it was maintained during the CT scans. The CT scan time was 5 s at 125 kV and 115 mAs and the slice thickness was 8 rnm (Somatom 2, Siemens). Procedure and statistics After catheterization, the inert-gas infusion was started and continued for 40 min before measurements were started. Five patients were studied awake, with hemodynamic and gas exchange measurements performed with the patient in the supine position and breathing room air. The rest of the study was performed with the patient anesthetized and connected to the ventilator (Fro,: 0.4). After at least 15 min of stable anesthesia, new hemodynamic and gas exchange measurements were made. Finally, the patients were placed in the left lateral position for repeated assessments of gas exchange and hemodynamics. Three different modes of ventilation were studied with the patients in the lateral position: conventional ventilation (CV, with free distribution of the tidal volume between the two lungs), CV with general
42 3
0,/QDURING ANESTHESIA Table 1
Ventilation and central circulation data. Minute ventilation (0,)and cardiac output (Qt)in 1. min-I. Vascular pressures in mmHg (kPa) and heart rate (HR) in beats. min-I. All values are given as means+ s.e.mean. The statistical analysis was divided into 3 separate parts (see Procedure and Statistics). 1. The awake results were compared to those obtained during supine conventional mechanical ventilation t zero end-expiratory pressure (CV+ZEEP); 2. Supine CV+ZEEP was then compared to lateral CV+ZEEP, and 3. The 3 ventilation modes in the lateral position were compared with one another (PEEP= positive end-expiratory pressure; DV + SPEEP = differential ventilation + selective PEEP). Position and ventilation
TIE
Supine awake (n=5) Supine CV+ZEEP (n=6) LateralCV+ZEEP ( n = 15) Lateral cv+PEEP (n=9) LateralDV+SPEEP ( n = 15)
Qt
7.71k1.11
6.40f0.33"
6.31 +0.2Ib
5.68k0.32
6.58k0.16
4.92f0.24' ( n = 14) 4.10 f 0.40
6.78 f 0.20
(n=8)
6.50k0.19
4.80+0.30" (n=14)
Systemic arterial mean
95k3" (12.7k0.4) 76k3 (10.1 fO.4) 78+3 (10.4k0.4) 86 f 4d (11.5f0.5) 88+3 (11.7f0.4)
Pulmonary arterial HR
Systolic
6854"
21+3" (2.8k0.4) 80f3b 19+2b (2.5 f 0.3) 69f2 23fZd (3.1k0.3) 67 f 3 33 k 3 (4.420.4) 69k3 24k Id (3.2k0.1)
Diastolic
Mean
Pulmonary capillary wedge
Right atrial
8f1" 14+1" 8kl 65 1 (l.lkO.1) (1.9fO.l) (l.lkO.1) (0.8kO.l) 9 k Ib 13k I b 7k 1 5k 1 (1.2k 0.1) (1.7 k 0.1) (0.9f 0.1) (0.7 k 0.1)
Il+ld 15+ld 8fld 421d (1.5kO.l) (2.OkO.1) ( l . l f O . 1 ) (0.5f0.1) 17 k 2 23 k 2 16 f 2 10 k 1 (2.3k0.3) (3.1f0.3) (2.1fO.3) (1.3kO.l) 12+ Id 1 7 + Id 1Ok Id 6k Id (1.6f0.1) (2.3f0.1) (1.3kO.l) (0.8f0.1)
Significant differences:"Supine awake vs. supine CV t ZEEP (P
