Acta anaesth. scand. 1977, 21, 489-496
Effects of Intercostal Nerve Blocks (Bupivacaine 0.25% and Etidocaine 0.5%)on Chest Wall Mechanics in Healthy Men SVENJAKOBSON and INGRID IVARSSON Departments of Anaesthesiology and Clinical Physiology, University Hospital, Uppsala, Sweden
Bilateral blockade of the 5th to 11 th intercostal nerves, inclusive, was produced in 14 healthy subjects. In seven, bupivacaine 0.25% was used, and in the other seven, ctidocaine 0.5%. The latter has been found to have a stronger motor-blocking action than the former. Before and after the blockade, the vital capacity (VC), peak expiratory flow rate (PEF), tidal volumes, respiratory variations in rib cage and abdominal circumferences and in oesophageal and intragastric pressures were recorded. By transthoracic electrical impedance pneumography, measures indicating changes in the functional residual capacity (FRC) were obtained. Although it was considered that changes in the parameters investigated mainly demonstrated changes in motor function, no differences were found between the drugs. With this form of blockade they seem to have equivalent effects in this respect. Thus, VC decreased by an average of 7% and PEF by 6%. Signs of a reduction of FRC after the blockade were also observed. The blockade had no effect on the partitioning of costal and abdominal breathing a t rest. Analysis of the relations between the fractions of costal and abdominal breathing and the corresponding variations in intragastric pressure gave support to the view that in normal individuals both intercostal and abdominal muscles remain passive during respiration at rest. This is thus achieved by the diaphragm alone.
Receired 10 February, accepted for publication 6 March 1977
Bupivacaine and etidocaine would seem to be the anaesthetics that today best fulfil the demands for postoperative intercostal nerve blockade. Among the clinical differences between these two drugs, the considerably greater ability of etidocaine to induce motor blockade has been pointed out (cf. RADTKE et al. 1975). Whether this ability is an advantage or a disadvantage depends upon the circumstances. I n abdominal surgery, for example, muscular paralysis is favourable, whereas in certain phases of a delivery it is undesirable. With respect to postoperative pain relief within the area of supply of the intercostal nerves, the question is less clear, however, and it is uncertain whether this factor is of any importance at all. ECBERT et al. (1961) considered that as paralysis of
the abdominal muscles limits the ability to cough, then pain-relieving blockades with this side-effect will promote rather than counteract postoperative lung complications. As yet, there is no direct evidence to confirm such a hypothesis, but it seems likely that a reduction of the muscle power will at least not be of any advantage when forced respiratory efforts are called for. EGBERTet al. arrived at their conclusions on the basis of an investigation on healthy subjects who had undergone spinal anaesthesia. Corresponding studies have been made with respect to thoracic epidural anaesthesia (see Discussion), but there appear to be no such reports concerning intercostal nerve blocks. Such an investigation was considered of value, as the effect of the
s. JAKOBSON
490
AND I . IVARSSON
blockade on motor function can be studied more clearly in healthy persons than in postoperative patients, in whom motor effects of the pain relief in itself may complicate the results. The present study on healthy subjects before and after a bilateral intercostal nerve block was therefore undertaken, with the aim of examining the effect on the vital capacity, peak expiratory flow, the partitioning of the tidal volume into fractions referable to rib cage expansion (costal breathing) and diaphragmatic descent (abdominal breathing), as well as intercostal and diaphragmatic activity and certain measures reflecting changes in the functional residual capacity (FRC). It was assumed as a prerequisite that in healthy individuals these parameters mainly reflect changes in motor function. In view of the above-mentioned difference between bupivacaine and etidocaine, the investigation also included a comparison of these two anaesthetic agents.
Ititercoslal nerue blocks
Bilateral blockade of the 5th to 11th intercostal nerves, inclusive, was induced in all subjects. T h e anaesthetic was administered with the subject lying on his side; the injections were given about 10 cm dorsally to the medio-axillary line. T h e injections into the 5th nerves were given medially to the scapula. Subjects 1-7 received bupivacaine 0.25% (Marcain", Astra Lakemedel AB) and subjects 8-14 etidocaine 0.5% (Duranestm, Astra Lakemedel AB). T h e total doses given to each subject are shown in Table I . T h e mean dose of bupivacaine in mg/kg (+s.d.) was 1.6kO.2 and of etidocaine 3. I & 0.3. All subjects reported a sensation of slight light-headedness soon after the injections were completed. This sensation persisted for about half an hour, and there seemed to be no difference in this respect between the two drugs. The intensity was considered to be dependent upon the time taken to administer the drug. No other side-effects were noted and no pneumothorax occurred, as checked by chest X-rays on completion of the investigation. The analgesia was tested by the pin-prick method. Certain segments were found not to be completely anaesthetized (see Table 1). To test further the extent of the blockade, the loss of power of the abdominal muscles was tested by instructing the subject to sit up from the supine position without using his arms. As seen in Table I , 1 1 of them could only do this with great difficulty (+ +),while the other three managed i t with moderate (+ + ) or little (+) difficulty. All of them had been able to d o this easily before the blockade. I t is evident from Table 1 that the estimated degree of abdominal motor weakness was unrelated to the number of incompletely anaesthetized segments.
+
MATERIALS AND METHODS Fourteen young men served as voluntary subjects (Table 1). They were all healthy as judged by their present state of health and health records.
Total dose, mg Subject 1
2 3 4 5 6 7 8 9 10 I1 12 13 14
Age yr
Height cm
Weight kg
23 27 25 23 25 22 23 29 26 22 32 23 26 26
185 180 186 180 181 180 187
82 75 74 69 65 67 79 85 75 72 72 74 84 69
181
179 183 186 178 193 180
1
bupivacaine etidoicane
Segments of incomplete analgesia left
I
right
Abdominal wall motor weakness
+++ +++ +++ +++ +++ + +++
I48 113 125 125 1 I3 105
105 225 225 250 250 225 225 225
+++ +++
+++ +++ +++ + ++
INTERCOSTAL NERVE BLOCKS
49 1
Table 2 Variables measured and derived in the present investigation.
vc
Vital capacity, litres, ATPS
PEF
Peak expiratory flow rate, litres/min, ATPS
VT P,,End and P,,End
Tidal volume, litres, ATPS Oesophageal and intragastric pressures, respectively, in cmH,O and relative to atmospheric pressure at the end-tidal position Changes in the pressures between the starting and end points of a n inspiration for Po, and Psb, respectively
F,,TAP
Tidal volume fraction due to abdominal breathing (F.,) ; i.e., the fraction referable to diaphragmatic descent. Estimated by thoraco-abdominal perimetry (TAP) Fsb estimated by transthoracic impedance pneumography (TTI) Tidal volume portions due to abdominal and costal breathing, respectively. Costal breathing = the volume portion referable to rib cage expansion. Displaced by the activity of the intercostal muscles and/or the diaphragm. Estimated by TAP AP.,/VT, pulmonary elastance AP,,/V,,,
abdominal elastance
APnb/V,,, rib cage elastance
The other variables presented in Table 2.
- measured
or derived - are
Vital capacity, peak expiratory pow, tidal volunre and intraoesophageal and intragastric pressures The vital capacity (VC) was measured with a Vitalograph (Vitalograph Ltd., Mortonhouse, Buckingham, England) and the peak expiratory flow rate (PEF) with a Wright's Peak Flow Meter (Airmed Ltd., Harlow, England). The tidal volume (V,) was measured by pneumotachography. A mouthpiece and nasal clip were used (Flow head: Fleisch No. 2, Godart, Bilthoven, Holland; Differential pressure transducer: E M T 32, Siemens-Elema, Solna, Sweden; Flow integrator: Respiration Analyser AN 2, Svenska Radio AB, Stockholm, Sweden). Pressures in the oesophagus (PJ and stomach (Pa,) were measured differentially against atmospheric pressure with the same polyethylene catheter (PE 240, length 110 cm, inner diameter 1.7 mm). One end was connected to a differential pressure transducer (EMT 33, SiemensElema), while the other end, which was supplied witha number of side-holes, was enclosed in a thin latex rubber balloon (Nordiska Latexfabriken, Torekov, Sweden; length 10 cm, circumference 3.6 cm). After application of surface analgesia to the nose and throat, the balloon-supplied end was passed through the nose into the oesophagus (c. 45 cm) or stomach (c. 65 cm). The balloon was first emptied by a Valsalva manoeuvre and then filled with 0.5 ml of air. The pressure levels at the end of an expiration were recorded (P,,End and P.,End), and also the pressure amplitude from the beginning to the end of an inspiration (APoeand AP,,).
If Po, decreased in relation to the atmospheric pressure during inspiration, the difference was given a positive sign. If Pa, increased, the difference was given a positive sign, and if it decreased a negative sign was given. Estimation of the fraction of abdominal breathing and changes in FRC The fraction of abdominal breathing (FPb)was calculated by two methods - thoraco-abdominal perimetry (TAP) (JAKOBSON & IVARSSON1977) and transthoracic impedance pneumography ( T T I ) (JAKOBSON et al. 1977). For TAP, two mercury-in-rubber transducers were used to detect variations in the circumference of the rib cage - at the level of the 4th costosternal joint, and of the abdomen - at umbilical level. For volumetric calibration of the variations of the circumference in question, a manoeuvre was used whereby the subject voluntarily varied the relative proportions of costal and abdominal breathing. For TTI, a four-electrode constant current impedance pneumograph was used to detect the respirationdependent variations in the transthoracic electrical impedance. The electrodes were placed at the level of the 7th rib symmetrically on both sides of the chest. When evaluating the results, the following factors, which influence these variations, are taken into account: V,, Fa, and the width of the costophrenic sinus. After a calibration procedure - utilizing TAP and the manoeuvre of variably combined costal and abdominal breathing- Fa, can be assessed by means of T T I . The larger the F,,, the larger becomes the impedance
492
s.
JAKOBSON AND I . IVARSSON
variation per unit of respired volume. However, closure of the costrophrenic sinuses will lead to a decrease in the relative impedance variation, i.e. the same effect as is produced by a decrease in F.b. Changes in the end-tidal width of the costophrenic sinuses might be assumed to correspond to changes in FRC. This gives an opportunity of detecting changes in FRC by means of the combined use of TAP and T T I . Thus, if Fab estimated by means of T A P (F,,TAP) remains unchanged when Fab estimated by means of T T I (FnbTTI) is found to decrease, this means a reduction in FRC. F,,TAP and FabTTIdo not have to be equal at the starting-point - it is the change in the difference that is important. I t should be noted that the change in FRC cannot be assessed volumetrically. Pulnionary, rib cage and abdominal elaslances The tidal volume portion referable to abdominal breathing (Vab)and costal breathing (VJ was calculated by multiplying VT by F,,TAP and 1 - F,,TAP, respectively. The ratios AP,,/VT, APab/V,, and APsb/Vab are tangential functions. The non-linearity of these functions was avoided by expressing the ratios as angles in the tangential function (El, E:c and E:b, respectively).
Examination programme VC and PEF were measured with the subjects in the sitting position. For the other recordings, they were semi-supine, with the upper half of the body elevated 30" from the horizontal plane. The procedure was as follows :
I . Measurements of VC and PEF. 2. All recordings of TAP and TTI and pneumotachography. A VT of about 1 1 and 12 breaths per min was aimed at.
3. The calibration manoeuvre which comprised variably combined costal and abdominal breathing. 4. The balloon-catheter was introduced into thr stomach, and pressure variations were recorded simultaneously with TAP and pneumotachography. A VTof about 1 1 and 12 breaths per min were aimed at. The catheter was withdrawn so that the balloon lay in the lower part of the oesophagus, and the procedure was repeated. T o avoid hypocapnia, a n extra dead space of 0.4 1 was added. 5. The intercostal nerve blocks were performed. The transducers for TAP, the electrodes for TTI and the balloon-catheter were left undisturbed. When the nerve blocks were completed, 30 min were allowed to elapse before the next point in the programme. 6. Pin-prick test and testing of abdominal motor weakness. 7. The same procedure as under point 4, except that this time the pressure recordings were started with the balloon placed in the oesophagus. O n completion of the measurements, the balloon-catheter was removed. 8. The same procedure as under point 2. 9. Measurements of VC and PEF. T h e whole programme took about 3 hours. V+, Po,, P@band the signals from T A P and T T l were recorded graphically with a multi-channel recorder (Mingograf 81, Siemens-Elema). For VC and PEF, the highest of three values was used, and for the other variables the mean value for seven breaths. In the subsequent analysis, differences were tested statistically by Wilcoxon's rank sum test. If the probability (a) that no difference existed exceeded 0.05, the difference was regarded as statistically non-significant. If a was less than 0.05, the difference was regarded as significant and is indicated in the Tables with a n asterisk. When a was less than 0.01, this is indicated in the Tables with two asterisks.
Table 3 Results obtained for some of the variables listed in Table 2. Group mean va1uesks.e. mean of 14 subjects before and after the blocks and the paired differences.
Before
vc PEF P,,End P, bEnd F,bTAP-F,bTTI
* cr ** x
Effects of Intercostal Nerve Blocks (Bupivacaine 0.25% and Etidocaine 0.5%)on Chest Wall Mechanics in Healthy Men SVENJAKOBSON and INGRID IVARSSON Departments of Anaesthesiology and Clinical Physiology, University Hospital, Uppsala, Sweden
Bilateral blockade of the 5th to 11 th intercostal nerves, inclusive, was produced in 14 healthy subjects. In seven, bupivacaine 0.25% was used, and in the other seven, ctidocaine 0.5%. The latter has been found to have a stronger motor-blocking action than the former. Before and after the blockade, the vital capacity (VC), peak expiratory flow rate (PEF), tidal volumes, respiratory variations in rib cage and abdominal circumferences and in oesophageal and intragastric pressures were recorded. By transthoracic electrical impedance pneumography, measures indicating changes in the functional residual capacity (FRC) were obtained. Although it was considered that changes in the parameters investigated mainly demonstrated changes in motor function, no differences were found between the drugs. With this form of blockade they seem to have equivalent effects in this respect. Thus, VC decreased by an average of 7% and PEF by 6%. Signs of a reduction of FRC after the blockade were also observed. The blockade had no effect on the partitioning of costal and abdominal breathing a t rest. Analysis of the relations between the fractions of costal and abdominal breathing and the corresponding variations in intragastric pressure gave support to the view that in normal individuals both intercostal and abdominal muscles remain passive during respiration at rest. This is thus achieved by the diaphragm alone.
Receired 10 February, accepted for publication 6 March 1977
Bupivacaine and etidocaine would seem to be the anaesthetics that today best fulfil the demands for postoperative intercostal nerve blockade. Among the clinical differences between these two drugs, the considerably greater ability of etidocaine to induce motor blockade has been pointed out (cf. RADTKE et al. 1975). Whether this ability is an advantage or a disadvantage depends upon the circumstances. I n abdominal surgery, for example, muscular paralysis is favourable, whereas in certain phases of a delivery it is undesirable. With respect to postoperative pain relief within the area of supply of the intercostal nerves, the question is less clear, however, and it is uncertain whether this factor is of any importance at all. ECBERT et al. (1961) considered that as paralysis of
the abdominal muscles limits the ability to cough, then pain-relieving blockades with this side-effect will promote rather than counteract postoperative lung complications. As yet, there is no direct evidence to confirm such a hypothesis, but it seems likely that a reduction of the muscle power will at least not be of any advantage when forced respiratory efforts are called for. EGBERTet al. arrived at their conclusions on the basis of an investigation on healthy subjects who had undergone spinal anaesthesia. Corresponding studies have been made with respect to thoracic epidural anaesthesia (see Discussion), but there appear to be no such reports concerning intercostal nerve blocks. Such an investigation was considered of value, as the effect of the
s. JAKOBSON
490
AND I . IVARSSON
blockade on motor function can be studied more clearly in healthy persons than in postoperative patients, in whom motor effects of the pain relief in itself may complicate the results. The present study on healthy subjects before and after a bilateral intercostal nerve block was therefore undertaken, with the aim of examining the effect on the vital capacity, peak expiratory flow, the partitioning of the tidal volume into fractions referable to rib cage expansion (costal breathing) and diaphragmatic descent (abdominal breathing), as well as intercostal and diaphragmatic activity and certain measures reflecting changes in the functional residual capacity (FRC). It was assumed as a prerequisite that in healthy individuals these parameters mainly reflect changes in motor function. In view of the above-mentioned difference between bupivacaine and etidocaine, the investigation also included a comparison of these two anaesthetic agents.
Ititercoslal nerue blocks
Bilateral blockade of the 5th to 11th intercostal nerves, inclusive, was induced in all subjects. T h e anaesthetic was administered with the subject lying on his side; the injections were given about 10 cm dorsally to the medio-axillary line. T h e injections into the 5th nerves were given medially to the scapula. Subjects 1-7 received bupivacaine 0.25% (Marcain", Astra Lakemedel AB) and subjects 8-14 etidocaine 0.5% (Duranestm, Astra Lakemedel AB). T h e total doses given to each subject are shown in Table I . T h e mean dose of bupivacaine in mg/kg (+s.d.) was 1.6kO.2 and of etidocaine 3. I & 0.3. All subjects reported a sensation of slight light-headedness soon after the injections were completed. This sensation persisted for about half an hour, and there seemed to be no difference in this respect between the two drugs. The intensity was considered to be dependent upon the time taken to administer the drug. No other side-effects were noted and no pneumothorax occurred, as checked by chest X-rays on completion of the investigation. The analgesia was tested by the pin-prick method. Certain segments were found not to be completely anaesthetized (see Table 1). To test further the extent of the blockade, the loss of power of the abdominal muscles was tested by instructing the subject to sit up from the supine position without using his arms. As seen in Table I , 1 1 of them could only do this with great difficulty (+ +),while the other three managed i t with moderate (+ + ) or little (+) difficulty. All of them had been able to d o this easily before the blockade. I t is evident from Table 1 that the estimated degree of abdominal motor weakness was unrelated to the number of incompletely anaesthetized segments.
+
MATERIALS AND METHODS Fourteen young men served as voluntary subjects (Table 1). They were all healthy as judged by their present state of health and health records.
Total dose, mg Subject 1
2 3 4 5 6 7 8 9 10 I1 12 13 14
Age yr
Height cm
Weight kg
23 27 25 23 25 22 23 29 26 22 32 23 26 26
185 180 186 180 181 180 187
82 75 74 69 65 67 79 85 75 72 72 74 84 69
181
179 183 186 178 193 180
1
bupivacaine etidoicane
Segments of incomplete analgesia left
I
right
Abdominal wall motor weakness
+++ +++ +++ +++ +++ + +++
I48 113 125 125 1 I3 105
105 225 225 250 250 225 225 225
+++ +++
+++ +++ +++ + ++
INTERCOSTAL NERVE BLOCKS
49 1
Table 2 Variables measured and derived in the present investigation.
vc
Vital capacity, litres, ATPS
PEF
Peak expiratory flow rate, litres/min, ATPS
VT P,,End and P,,End
Tidal volume, litres, ATPS Oesophageal and intragastric pressures, respectively, in cmH,O and relative to atmospheric pressure at the end-tidal position Changes in the pressures between the starting and end points of a n inspiration for Po, and Psb, respectively
F,,TAP
Tidal volume fraction due to abdominal breathing (F.,) ; i.e., the fraction referable to diaphragmatic descent. Estimated by thoraco-abdominal perimetry (TAP) Fsb estimated by transthoracic impedance pneumography (TTI) Tidal volume portions due to abdominal and costal breathing, respectively. Costal breathing = the volume portion referable to rib cage expansion. Displaced by the activity of the intercostal muscles and/or the diaphragm. Estimated by TAP AP.,/VT, pulmonary elastance AP,,/V,,,
abdominal elastance
APnb/V,,, rib cage elastance
The other variables presented in Table 2.
- measured
or derived - are
Vital capacity, peak expiratory pow, tidal volunre and intraoesophageal and intragastric pressures The vital capacity (VC) was measured with a Vitalograph (Vitalograph Ltd., Mortonhouse, Buckingham, England) and the peak expiratory flow rate (PEF) with a Wright's Peak Flow Meter (Airmed Ltd., Harlow, England). The tidal volume (V,) was measured by pneumotachography. A mouthpiece and nasal clip were used (Flow head: Fleisch No. 2, Godart, Bilthoven, Holland; Differential pressure transducer: E M T 32, Siemens-Elema, Solna, Sweden; Flow integrator: Respiration Analyser AN 2, Svenska Radio AB, Stockholm, Sweden). Pressures in the oesophagus (PJ and stomach (Pa,) were measured differentially against atmospheric pressure with the same polyethylene catheter (PE 240, length 110 cm, inner diameter 1.7 mm). One end was connected to a differential pressure transducer (EMT 33, SiemensElema), while the other end, which was supplied witha number of side-holes, was enclosed in a thin latex rubber balloon (Nordiska Latexfabriken, Torekov, Sweden; length 10 cm, circumference 3.6 cm). After application of surface analgesia to the nose and throat, the balloon-supplied end was passed through the nose into the oesophagus (c. 45 cm) or stomach (c. 65 cm). The balloon was first emptied by a Valsalva manoeuvre and then filled with 0.5 ml of air. The pressure levels at the end of an expiration were recorded (P,,End and P.,End), and also the pressure amplitude from the beginning to the end of an inspiration (APoeand AP,,).
If Po, decreased in relation to the atmospheric pressure during inspiration, the difference was given a positive sign. If Pa, increased, the difference was given a positive sign, and if it decreased a negative sign was given. Estimation of the fraction of abdominal breathing and changes in FRC The fraction of abdominal breathing (FPb)was calculated by two methods - thoraco-abdominal perimetry (TAP) (JAKOBSON & IVARSSON1977) and transthoracic impedance pneumography ( T T I ) (JAKOBSON et al. 1977). For TAP, two mercury-in-rubber transducers were used to detect variations in the circumference of the rib cage - at the level of the 4th costosternal joint, and of the abdomen - at umbilical level. For volumetric calibration of the variations of the circumference in question, a manoeuvre was used whereby the subject voluntarily varied the relative proportions of costal and abdominal breathing. For TTI, a four-electrode constant current impedance pneumograph was used to detect the respirationdependent variations in the transthoracic electrical impedance. The electrodes were placed at the level of the 7th rib symmetrically on both sides of the chest. When evaluating the results, the following factors, which influence these variations, are taken into account: V,, Fa, and the width of the costophrenic sinus. After a calibration procedure - utilizing TAP and the manoeuvre of variably combined costal and abdominal breathing- Fa, can be assessed by means of T T I . The larger the F,,, the larger becomes the impedance
492
s.
JAKOBSON AND I . IVARSSON
variation per unit of respired volume. However, closure of the costrophrenic sinuses will lead to a decrease in the relative impedance variation, i.e. the same effect as is produced by a decrease in F.b. Changes in the end-tidal width of the costophrenic sinuses might be assumed to correspond to changes in FRC. This gives an opportunity of detecting changes in FRC by means of the combined use of TAP and T T I . Thus, if Fab estimated by means of T A P (F,,TAP) remains unchanged when Fab estimated by means of T T I (FnbTTI) is found to decrease, this means a reduction in FRC. F,,TAP and FabTTIdo not have to be equal at the starting-point - it is the change in the difference that is important. I t should be noted that the change in FRC cannot be assessed volumetrically. Pulnionary, rib cage and abdominal elaslances The tidal volume portion referable to abdominal breathing (Vab)and costal breathing (VJ was calculated by multiplying VT by F,,TAP and 1 - F,,TAP, respectively. The ratios AP,,/VT, APab/V,, and APsb/Vab are tangential functions. The non-linearity of these functions was avoided by expressing the ratios as angles in the tangential function (El, E:c and E:b, respectively).
Examination programme VC and PEF were measured with the subjects in the sitting position. For the other recordings, they were semi-supine, with the upper half of the body elevated 30" from the horizontal plane. The procedure was as follows :
I . Measurements of VC and PEF. 2. All recordings of TAP and TTI and pneumotachography. A VT of about 1 1 and 12 breaths per min was aimed at.
3. The calibration manoeuvre which comprised variably combined costal and abdominal breathing. 4. The balloon-catheter was introduced into thr stomach, and pressure variations were recorded simultaneously with TAP and pneumotachography. A VTof about 1 1 and 12 breaths per min were aimed at. The catheter was withdrawn so that the balloon lay in the lower part of the oesophagus, and the procedure was repeated. T o avoid hypocapnia, a n extra dead space of 0.4 1 was added. 5. The intercostal nerve blocks were performed. The transducers for TAP, the electrodes for TTI and the balloon-catheter were left undisturbed. When the nerve blocks were completed, 30 min were allowed to elapse before the next point in the programme. 6. Pin-prick test and testing of abdominal motor weakness. 7. The same procedure as under point 4, except that this time the pressure recordings were started with the balloon placed in the oesophagus. O n completion of the measurements, the balloon-catheter was removed. 8. The same procedure as under point 2. 9. Measurements of VC and PEF. T h e whole programme took about 3 hours. V+, Po,, P@band the signals from T A P and T T l were recorded graphically with a multi-channel recorder (Mingograf 81, Siemens-Elema). For VC and PEF, the highest of three values was used, and for the other variables the mean value for seven breaths. In the subsequent analysis, differences were tested statistically by Wilcoxon's rank sum test. If the probability (a) that no difference existed exceeded 0.05, the difference was regarded as statistically non-significant. If a was less than 0.05, the difference was regarded as significant and is indicated in the Tables with a n asterisk. When a was less than 0.01, this is indicated in the Tables with two asterisks.
Table 3 Results obtained for some of the variables listed in Table 2. Group mean va1uesks.e. mean of 14 subjects before and after the blocks and the paired differences.
Before
vc PEF P,,End P, bEnd F,bTAP-F,bTTI
* cr ** x
