J. Physiol. (1979), 293, pp. 285-300 With 8 text-figures Printed in Great Britain
285
THE EFFECTS OF HYPERCAPNIA, HYPOXIA, EXERCISE AND ANXIETY ON THE PATTERN OF BREATHING IN MAN
BY R. R. BECHBACHE, H. H. K. CHOW, J. DUFFIN AND E. C. ORSINI From the Departments of Physiology and Anaesthesia, University of Toronto, Toronto, Canada
(Received 20 December 1978) SUMMARY
1. The pattern of breathing, defined as the relations between tidal volume and inspiratory and expiratory times, was measured during the stimulation of breathing by carbon dioxide (hyperoxic rebreathing at rest) in twenty-seven healthy, young volunteers. 2. Most of the patterns (twenty) were divisible into two parts, for low (range 1) and high (range 2) tidal volumes. The relations were curved, inverse proportionalities for both inspiration and expiration in range 2, and for expiration in range 1. The relations for inspiration in range 1 were evenly divided between those with constant inspiratory times (type 1) and those with curved, inverse proportionalities (type 2). 3. In four volunteers, direct proportionalities predominated and the patterns were scattered (type 3). 4. Eight of the volunteers (four type 1, two type 2 and two type 3 patterns) repeated the measurements and one changed from a type 1 to a type 3 pattern. 5. Nine of the volunteers also rebreathed during resting hypoxia. Two altered their patterns, and the others had patterns which were superimposed upon those measured during hyperoxic rebreathing at rest. 6. Eighteen of the volunteers also rebreathed (hyperoxic) during light exercise (25 W). Five entrained their breathing frequency to the exercise rhythm and showed exercise patterns with constant inspiratory and expiratory times. The others had patterns which were extensions of those measured during hyperoxic rebreathing at rest. 7. The pattern of breathing in range 1 was measured by steady-state methods in a further ten volunteers at rest with their eyes closed and open, and during mental arithmetic. The pooled average pattern showed that the stress of mental arithmetic shortened both inspiratory and expiratory times, and changed a type 2 pattern into a type 1 pattern. INTRODUCTION
When breathing is stimulated, both a deepening of tidal volume and an increase in frequency contribute to the rise in ventilation (Hey, Lloyd, Cunningham & Jukes, 1966). Inverse proportionalities have been observed between tidal volume (VT) and the inspiratory and expiratory times (TI and TE respectively) during breathing 0022-3751/79/4400-0081 $01.50
C
1979 The Physiological Society
26. R. BECHBACHE AND OTHERS 286 stimuli, such as carbon dioxide inhalation, for both the mean values of differing steady states (Cunningham & Gardner, 1972; Cunningham, Pearson & Gardner, 1972), and the breath-by-breath values during rebreathing (Clark & Euler, 1972; Jennett, Russell & Warnock, 1974). During rapid changes in stimulation, these proportionalities may be altered due to the differing response times for the changes in VT, T, and TE (Pearson & Cunningham, 1973; Miller, Cunningham, Lloyd & Young, 1974; Gardner, 1974; Bradley, Euler, Marttila & Roos, 1974). In contrast to the inverse proportionalities observed between breath-by-breath values under the conditions of rebreathing and between the mean values of various steady states, direct proportionalities have been observed between VT and T1, and VT and TE for breath-by-breath values obtained during any particular steady state (Priban, 1963; Dejours, Puccinelli, Armand & Dicharry, 1966; Pearson & Cunningham, 1973; Newsom Davis & Stagg, 1975). Both the direct and inverse proportionalities have been reviewed by Cunningham (1974) and by Bradley (1977). Clark & Euler (1972) described the pattern of breathing during rebreathing as being divided into three ranges. In range 1, T, and TE were constant, and independent of VT. In range 2, T, and TE were inversely proportional to VT in a curved relationship, and in range 3, T, and TE tended to increase. The intersections of these ranges displayed breakpoints in the over-all relation between VT and T1 and TE. Gardner (1977) has presented evidence for modifying this view of the pattern of breathing by showing that TE is not constant in range 1, but is inversely proportional to VT. However, the proportionality, a curved relation, is not part of the same curve seen in range 2, and a breakpoint still exists in the relation of VT and TE between range 1 and range 2. All of the previous studies have used carbon dioxide in either hyperoxia or hypoxia as the stimulus to breathing. Kay, Petersen & Vejby-Christensen (1975a, b) studied the pattern of breathing during steady-state exercise. They observed both the direct proportionalities between VT and TI, and VT and TE for the breath-by-breath values of any particular steady state, and the inverse proportionalities between the mean values of the various, steady, exercise states. These latter relations were fitted with straight lines rather than curves, and were shown to be unchanged when 2 and 3.3 kPa (15 and 25 mmHg) Pco2 was added to the air breathed during exercise, although the points for the same hypercapnia at rest do not fall on their exercise lines (Kay et al. 1975b, Fig. 2). In an earlier study, Hey et al. (1966) had presented evidence that the relation between mean VT and mean ventilation for various steady states was the same whether breathing was stimulating by either carbon dioxide or exercise. Both of these exercise studies may have been complicated by the entrainment of the breathing frequency by the rhythm of the exercise (Bechbache & Duffin, 1977). This possibility is perhaps more likely in the case of Hey et al. (1966) where breathing frequency was often observed to be a submultiple of steps per minute, than in the study of Kay et al. (1975a, b) where a constant speedometer reading was used to ensure a steady exercise rhythm. Cunningham & Gardner (1972, 1977) and Gardner (1977) have remarked upon the possible shortening of resting TE due to anxiety in their subjects, but this factor has not been studied in detail. The following report details observations of the relations between VT and TI, and
287 THE PATTERN OF BREATHING IN MAN VT and TE made in healthy young students. Three groups were studied: rebreathing during hyperoxia and hypoxia at rest; hyperoxic rebreathing at rest and during exercise; and steady state, breathing air and 2-6 % carbon dioxide at rest, with eyes open and eyes closed, and while performing mental arithmetic. TABLE 1. The physical characteristics of the volunteers Age Weight Vital capacity (1. b.t.p.s.) (yr) Volunteer (kg) Sex Hypoxia 78 5-5 26 W.C. M 5-1 73 25 M F.C. 5-6 30 80 M S.G. 23 76 M L.H. 5.7 24 84 5-6 K.H. M 24 5.3 M B.H. 80 23 59 F 3-8 C.L. 23 59 F P.O. 3.9 19 F 54 3-9 S.S. Exercise P.B. 62 23 M 48 25 S.R. 3-4 55 M 74 21 M S.C. 6-1 73 K.R. 4-9 29 M 79 D.H. 23 61 M F 4-3 N.S. 56 26 R.H. 21 5.9 M 78 75 5.9 M E.M. 22 D.L. 92 M 22 60 I.A. 28 M 60 85 W.F. 5.3 31 M 65 B.F. 5-7 79 23 M D.W. 74 M 22 5-5 M A.J. 21 82 60 METHODS
Three sets of experiments were carried out on three groups of volunteers; a hypoxia study, an exercise study and an anxiety study. All of the volunteers for this study were recruited from the University's student population, but none specialized in respiratory physiology. All were informed as to the testing procedures, but none was aware of the purpose of the experiment. They were studied at least 2 hr after the intake of food or caffeinated drink. Table 1 lists the characteristics of the students who volunteered for the exercise and hypoxia studies. Ten volunteers (seven males, three females) between the ages of 19 and 30 yr participated in the anxiety study. Apparatus The rebreathing method used in these studies was that described by Read (1967). The volunteers breathed through a low turbulence, three-way Y valve (Collins, P-319). One side was connected to a T piece through which flowed controlled gas compositions which could be breathed without rebreathing. The other side of the Y valve was connected to the rebreathing bag. The rebreathing bag was enclosed in a rigid box which was connected by wide-bore (3-8 cm) tubing to a spirometer (Med. Sci., 270 Wedge). Breath-by-breath volume and flow were obtained
288
R. R. BECHBACHE AND OTHERS
from the spirometer and written on a multi-channel, pen recorder (HP-Sanborn) at a paper speed of 10 mm/sec. Carbon dioxide and oxygen levels were monitored continuously at the mouth (Godart 146 Capnograph and Westinghouse 211M Oxygen Analyser, respectively) and written on the pen recorder. The steady-state method used in these studies was that described by Nunn (1956). The volunteers breathed through a wide-bore (3-8 cm) T piece with negligible dead-space. One side was connected with tubing to a set of rotameters providing controlled gas compositions at approximately 50 1/min. The other side of the T piece was connected to a second T piece via wide-bore tubing. One side of the second T piece was connected to a spirometer (Med. Sci., 270 Wedge) by wide-bore tubing, and the other side was connected to a controlled suction apparatus. Carbon dioxide and oxygen levels were monitored continuously at the mouth (Godart 146 Capnograph and Westinghouse 211 M Oxygen analyser respectively). Breathing volume and flow, and carbon dioxide and oxygen levels were written on a multichannel pen recorder (HPSanborn) at a paper speed of 10 mm/sec.
Hypoxia The hypoxia study was carried out on volunteers seated in a comfortable chair and wearing earphones playing classical music. They performed both hyperoxic and hypoxic rebreathing tests with a 15 min rest period between tests. Half of the volunteers did the hyperoxic rebreathing test first and half did the hypoxic rebreathing test first. During the hyperoxic rebreathing test the bag was filled with 6 1. of a gas mixture containing 50 % oxygen, 43 % nitrogen and 7% carbon dioxide. After 5 min of breathing a hyperoxic mixture containing 50% oxygen and 50% nitrogen from the set of rotameters via the T piece, and when stable end-tidal carbon dioxide and oxygen levels were obtained, the volunteers were switched with the Y valve from the T piece to the rebreathing bag. They rebreathed until end-tidal PCO, rose to 9-31 kPa (70 mmHg) or until discomfort was felt. During the hypoxic rebreathing test the bag was filled with 6 1. of a gas mixture of 7 % carbon dioxide in air, and for the 5 min period before rebreathing the volunteers breathed air via the T piece. They rebreathed until end-tidal P02 fell to 6-65 kPa (50 mmHg) or until discomfort was felt, during which time end-tidal Pco, rose to approximately 7-98 kPa (60 mmHg). The technique has been more fully described in a previous report (Duffin, Jacobson & Orsini, 1978).
Exercise The exercise study was carried out on volunteers seated on a bicycle ergometer (MonarkCrescent AB) and wearing earphones playing classical music. They performed the hyperoxic rebreathing test previously described both at rest and during exercise at 25 W and, if possible, at 50 W. A 20 min rest period was taken between tests. The carbon dioxide concentration in the bag was increased to 9-5% for the 25 W load and 11.5% for the 50 W load; since the mixedvenous carbon dioxide level increases during exercise relative to the load (Jones & Rebuck, 1973). During the exercise test, the volunteers pedalled at the required load for the initial 5 min period breathing the 50% oxygen mixture, and for the period of rebreathing. They were asked to keep a constant pedalling frequency of 50 rev/min by keeping the speedometer reading constant. Pulses corresponding to breathing period and exercise rhythm were cross-correlated using an on-line computer (Anderson & Duffin, 1976) to detect the occurrence of entrainment by a technique which has been previously described (Bechbache & Duffin, 1977).
Anxiety The anxiety study was carried out on volunteers seated in a comfortable chair and wearing earphones playing white noise. They were monitored by the steady-state method and performed two sets of tests, one breathing air and the other breathing 2-6% carbon dioxide, and separated by a 15 min rest period. Each set of tests consisted of 5 min breathing with the eyes closed and 5 min with the eyes open, followed by 4 min of mental arithmetic. The volunteers were instructed via signs placed in front of them to perform mental arithmetic to solve ten addition, subtraction and multiplication problems which were of sufficient difficulty to require 4 min of time. A stopwatch was placed in view and the written answers were scored for both speed and accuracy. Thirty breaths were recorded at the end of each test period of which twenty were analysed.
THE PATTERN OF BREATHING IN MAN
289
AnalySi8 The records for all of the tests were treated as follows. After the elimination of obviously abnormal breaths due to swallowing or sighing, VT was measured from the volume trace and converted to b.t.p.s., and T1 and T. were measured from the flow trace for every breath. For all of the rebreathing tests plots of VT V8. T, and TR were made for both the breath-by-breath values, and, as a means of smoothing the patterns, for the five-breath-average values. Plots were also made of VT V8. VT/TI for the five-breath-average values for all of the rebreathing tests. 4 VT
--4 VT
3
3
2
2
I-
R.H. 1
+1
R.H. 2
TE 3
41
TE
To t
1
2
1
2
33
3
2
1
1
v4 VT
4 VVT
3
3
o
B.F. 2
1
TE
TET ITE
I
I
2
1
1
-4 e
eCR
2
3
3
2
1
TE.P.
*.
1
° I
2
3
1
2
1
II 33
X -4 VT X
2 1
W.F. TE
1
- 2
I
VT
TE~~~~~
3
2
1
*
W:o.
2
3
4*
2
3
3
2
3a Sj 2 n 1
X
44 #
1
1
2
13
Fig. 1. Five-breath-average values of VT VS. T, and TR for five representative volunteers with type 1 breathing patterns, during hyperoxic rebreathing at rest (filled circles), at an exercise of 25 W (open circles) and at an exercise of 50 W (crosses) Arrows indicate the breakpoints between ranges 1 and 2. For the steady-state measurements of the anxiety study, the values of VT, T1 and TE for the twenty breaths were averaged for each state for all ten volunteers. Paired t tests were performed to detect significant differences in T, and TB values between the states.
IO
PHY 293
290
R. R. BECHBACHE AND OTHERS RESULTS
In an over-all assessment of the patterns of breathing observed in this study, it was found that the patterns could be classified as three different types. The first pattern, type 1, was that reported in detail by Gardner (1977) with curved relationships for all but range 1, VT vs. TI. Examples of type 1 pattern are shown in Fig. 1. The second pattern, type 2, differed from type 1 only in that the plot for VT vs. T, in 4! VT 3 3
41 VT *1.
2
'3
285
THE EFFECTS OF HYPERCAPNIA, HYPOXIA, EXERCISE AND ANXIETY ON THE PATTERN OF BREATHING IN MAN
BY R. R. BECHBACHE, H. H. K. CHOW, J. DUFFIN AND E. C. ORSINI From the Departments of Physiology and Anaesthesia, University of Toronto, Toronto, Canada
(Received 20 December 1978) SUMMARY
1. The pattern of breathing, defined as the relations between tidal volume and inspiratory and expiratory times, was measured during the stimulation of breathing by carbon dioxide (hyperoxic rebreathing at rest) in twenty-seven healthy, young volunteers. 2. Most of the patterns (twenty) were divisible into two parts, for low (range 1) and high (range 2) tidal volumes. The relations were curved, inverse proportionalities for both inspiration and expiration in range 2, and for expiration in range 1. The relations for inspiration in range 1 were evenly divided between those with constant inspiratory times (type 1) and those with curved, inverse proportionalities (type 2). 3. In four volunteers, direct proportionalities predominated and the patterns were scattered (type 3). 4. Eight of the volunteers (four type 1, two type 2 and two type 3 patterns) repeated the measurements and one changed from a type 1 to a type 3 pattern. 5. Nine of the volunteers also rebreathed during resting hypoxia. Two altered their patterns, and the others had patterns which were superimposed upon those measured during hyperoxic rebreathing at rest. 6. Eighteen of the volunteers also rebreathed (hyperoxic) during light exercise (25 W). Five entrained their breathing frequency to the exercise rhythm and showed exercise patterns with constant inspiratory and expiratory times. The others had patterns which were extensions of those measured during hyperoxic rebreathing at rest. 7. The pattern of breathing in range 1 was measured by steady-state methods in a further ten volunteers at rest with their eyes closed and open, and during mental arithmetic. The pooled average pattern showed that the stress of mental arithmetic shortened both inspiratory and expiratory times, and changed a type 2 pattern into a type 1 pattern. INTRODUCTION
When breathing is stimulated, both a deepening of tidal volume and an increase in frequency contribute to the rise in ventilation (Hey, Lloyd, Cunningham & Jukes, 1966). Inverse proportionalities have been observed between tidal volume (VT) and the inspiratory and expiratory times (TI and TE respectively) during breathing 0022-3751/79/4400-0081 $01.50
C
1979 The Physiological Society
26. R. BECHBACHE AND OTHERS 286 stimuli, such as carbon dioxide inhalation, for both the mean values of differing steady states (Cunningham & Gardner, 1972; Cunningham, Pearson & Gardner, 1972), and the breath-by-breath values during rebreathing (Clark & Euler, 1972; Jennett, Russell & Warnock, 1974). During rapid changes in stimulation, these proportionalities may be altered due to the differing response times for the changes in VT, T, and TE (Pearson & Cunningham, 1973; Miller, Cunningham, Lloyd & Young, 1974; Gardner, 1974; Bradley, Euler, Marttila & Roos, 1974). In contrast to the inverse proportionalities observed between breath-by-breath values under the conditions of rebreathing and between the mean values of various steady states, direct proportionalities have been observed between VT and T1, and VT and TE for breath-by-breath values obtained during any particular steady state (Priban, 1963; Dejours, Puccinelli, Armand & Dicharry, 1966; Pearson & Cunningham, 1973; Newsom Davis & Stagg, 1975). Both the direct and inverse proportionalities have been reviewed by Cunningham (1974) and by Bradley (1977). Clark & Euler (1972) described the pattern of breathing during rebreathing as being divided into three ranges. In range 1, T, and TE were constant, and independent of VT. In range 2, T, and TE were inversely proportional to VT in a curved relationship, and in range 3, T, and TE tended to increase. The intersections of these ranges displayed breakpoints in the over-all relation between VT and T1 and TE. Gardner (1977) has presented evidence for modifying this view of the pattern of breathing by showing that TE is not constant in range 1, but is inversely proportional to VT. However, the proportionality, a curved relation, is not part of the same curve seen in range 2, and a breakpoint still exists in the relation of VT and TE between range 1 and range 2. All of the previous studies have used carbon dioxide in either hyperoxia or hypoxia as the stimulus to breathing. Kay, Petersen & Vejby-Christensen (1975a, b) studied the pattern of breathing during steady-state exercise. They observed both the direct proportionalities between VT and TI, and VT and TE for the breath-by-breath values of any particular steady state, and the inverse proportionalities between the mean values of the various, steady, exercise states. These latter relations were fitted with straight lines rather than curves, and were shown to be unchanged when 2 and 3.3 kPa (15 and 25 mmHg) Pco2 was added to the air breathed during exercise, although the points for the same hypercapnia at rest do not fall on their exercise lines (Kay et al. 1975b, Fig. 2). In an earlier study, Hey et al. (1966) had presented evidence that the relation between mean VT and mean ventilation for various steady states was the same whether breathing was stimulating by either carbon dioxide or exercise. Both of these exercise studies may have been complicated by the entrainment of the breathing frequency by the rhythm of the exercise (Bechbache & Duffin, 1977). This possibility is perhaps more likely in the case of Hey et al. (1966) where breathing frequency was often observed to be a submultiple of steps per minute, than in the study of Kay et al. (1975a, b) where a constant speedometer reading was used to ensure a steady exercise rhythm. Cunningham & Gardner (1972, 1977) and Gardner (1977) have remarked upon the possible shortening of resting TE due to anxiety in their subjects, but this factor has not been studied in detail. The following report details observations of the relations between VT and TI, and
287 THE PATTERN OF BREATHING IN MAN VT and TE made in healthy young students. Three groups were studied: rebreathing during hyperoxia and hypoxia at rest; hyperoxic rebreathing at rest and during exercise; and steady state, breathing air and 2-6 % carbon dioxide at rest, with eyes open and eyes closed, and while performing mental arithmetic. TABLE 1. The physical characteristics of the volunteers Age Weight Vital capacity (1. b.t.p.s.) (yr) Volunteer (kg) Sex Hypoxia 78 5-5 26 W.C. M 5-1 73 25 M F.C. 5-6 30 80 M S.G. 23 76 M L.H. 5.7 24 84 5-6 K.H. M 24 5.3 M B.H. 80 23 59 F 3-8 C.L. 23 59 F P.O. 3.9 19 F 54 3-9 S.S. Exercise P.B. 62 23 M 48 25 S.R. 3-4 55 M 74 21 M S.C. 6-1 73 K.R. 4-9 29 M 79 D.H. 23 61 M F 4-3 N.S. 56 26 R.H. 21 5.9 M 78 75 5.9 M E.M. 22 D.L. 92 M 22 60 I.A. 28 M 60 85 W.F. 5.3 31 M 65 B.F. 5-7 79 23 M D.W. 74 M 22 5-5 M A.J. 21 82 60 METHODS
Three sets of experiments were carried out on three groups of volunteers; a hypoxia study, an exercise study and an anxiety study. All of the volunteers for this study were recruited from the University's student population, but none specialized in respiratory physiology. All were informed as to the testing procedures, but none was aware of the purpose of the experiment. They were studied at least 2 hr after the intake of food or caffeinated drink. Table 1 lists the characteristics of the students who volunteered for the exercise and hypoxia studies. Ten volunteers (seven males, three females) between the ages of 19 and 30 yr participated in the anxiety study. Apparatus The rebreathing method used in these studies was that described by Read (1967). The volunteers breathed through a low turbulence, three-way Y valve (Collins, P-319). One side was connected to a T piece through which flowed controlled gas compositions which could be breathed without rebreathing. The other side of the Y valve was connected to the rebreathing bag. The rebreathing bag was enclosed in a rigid box which was connected by wide-bore (3-8 cm) tubing to a spirometer (Med. Sci., 270 Wedge). Breath-by-breath volume and flow were obtained
288
R. R. BECHBACHE AND OTHERS
from the spirometer and written on a multi-channel, pen recorder (HP-Sanborn) at a paper speed of 10 mm/sec. Carbon dioxide and oxygen levels were monitored continuously at the mouth (Godart 146 Capnograph and Westinghouse 211M Oxygen Analyser, respectively) and written on the pen recorder. The steady-state method used in these studies was that described by Nunn (1956). The volunteers breathed through a wide-bore (3-8 cm) T piece with negligible dead-space. One side was connected with tubing to a set of rotameters providing controlled gas compositions at approximately 50 1/min. The other side of the T piece was connected to a second T piece via wide-bore tubing. One side of the second T piece was connected to a spirometer (Med. Sci., 270 Wedge) by wide-bore tubing, and the other side was connected to a controlled suction apparatus. Carbon dioxide and oxygen levels were monitored continuously at the mouth (Godart 146 Capnograph and Westinghouse 211 M Oxygen analyser respectively). Breathing volume and flow, and carbon dioxide and oxygen levels were written on a multichannel pen recorder (HPSanborn) at a paper speed of 10 mm/sec.
Hypoxia The hypoxia study was carried out on volunteers seated in a comfortable chair and wearing earphones playing classical music. They performed both hyperoxic and hypoxic rebreathing tests with a 15 min rest period between tests. Half of the volunteers did the hyperoxic rebreathing test first and half did the hypoxic rebreathing test first. During the hyperoxic rebreathing test the bag was filled with 6 1. of a gas mixture containing 50 % oxygen, 43 % nitrogen and 7% carbon dioxide. After 5 min of breathing a hyperoxic mixture containing 50% oxygen and 50% nitrogen from the set of rotameters via the T piece, and when stable end-tidal carbon dioxide and oxygen levels were obtained, the volunteers were switched with the Y valve from the T piece to the rebreathing bag. They rebreathed until end-tidal PCO, rose to 9-31 kPa (70 mmHg) or until discomfort was felt. During the hypoxic rebreathing test the bag was filled with 6 1. of a gas mixture of 7 % carbon dioxide in air, and for the 5 min period before rebreathing the volunteers breathed air via the T piece. They rebreathed until end-tidal P02 fell to 6-65 kPa (50 mmHg) or until discomfort was felt, during which time end-tidal Pco, rose to approximately 7-98 kPa (60 mmHg). The technique has been more fully described in a previous report (Duffin, Jacobson & Orsini, 1978).
Exercise The exercise study was carried out on volunteers seated on a bicycle ergometer (MonarkCrescent AB) and wearing earphones playing classical music. They performed the hyperoxic rebreathing test previously described both at rest and during exercise at 25 W and, if possible, at 50 W. A 20 min rest period was taken between tests. The carbon dioxide concentration in the bag was increased to 9-5% for the 25 W load and 11.5% for the 50 W load; since the mixedvenous carbon dioxide level increases during exercise relative to the load (Jones & Rebuck, 1973). During the exercise test, the volunteers pedalled at the required load for the initial 5 min period breathing the 50% oxygen mixture, and for the period of rebreathing. They were asked to keep a constant pedalling frequency of 50 rev/min by keeping the speedometer reading constant. Pulses corresponding to breathing period and exercise rhythm were cross-correlated using an on-line computer (Anderson & Duffin, 1976) to detect the occurrence of entrainment by a technique which has been previously described (Bechbache & Duffin, 1977).
Anxiety The anxiety study was carried out on volunteers seated in a comfortable chair and wearing earphones playing white noise. They were monitored by the steady-state method and performed two sets of tests, one breathing air and the other breathing 2-6% carbon dioxide, and separated by a 15 min rest period. Each set of tests consisted of 5 min breathing with the eyes closed and 5 min with the eyes open, followed by 4 min of mental arithmetic. The volunteers were instructed via signs placed in front of them to perform mental arithmetic to solve ten addition, subtraction and multiplication problems which were of sufficient difficulty to require 4 min of time. A stopwatch was placed in view and the written answers were scored for both speed and accuracy. Thirty breaths were recorded at the end of each test period of which twenty were analysed.
THE PATTERN OF BREATHING IN MAN
289
AnalySi8 The records for all of the tests were treated as follows. After the elimination of obviously abnormal breaths due to swallowing or sighing, VT was measured from the volume trace and converted to b.t.p.s., and T1 and T. were measured from the flow trace for every breath. For all of the rebreathing tests plots of VT V8. T, and TR were made for both the breath-by-breath values, and, as a means of smoothing the patterns, for the five-breath-average values. Plots were also made of VT V8. VT/TI for the five-breath-average values for all of the rebreathing tests. 4 VT
--4 VT
3
3
2
2
I-
R.H. 1
+1
R.H. 2
TE 3
41
TE
To t
1
2
1
2
33
3
2
1
1
v4 VT
4 VVT
3
3
o
B.F. 2
1
TE
TET ITE
I
I
2
1
1
-4 e
eCR
2
3
3
2
1
TE.P.
*.
1
° I
2
3
1
2
1
II 33
X -4 VT X
2 1
W.F. TE
1
- 2
I
VT
TE~~~~~
3
2
1
*
W:o.
2
3
4*
2
3
3
2
3a Sj 2 n 1
X
44 #
1
1
2
13
Fig. 1. Five-breath-average values of VT VS. T, and TR for five representative volunteers with type 1 breathing patterns, during hyperoxic rebreathing at rest (filled circles), at an exercise of 25 W (open circles) and at an exercise of 50 W (crosses) Arrows indicate the breakpoints between ranges 1 and 2. For the steady-state measurements of the anxiety study, the values of VT, T1 and TE for the twenty breaths were averaged for each state for all ten volunteers. Paired t tests were performed to detect significant differences in T, and TB values between the states.
IO
PHY 293
290
R. R. BECHBACHE AND OTHERS RESULTS
In an over-all assessment of the patterns of breathing observed in this study, it was found that the patterns could be classified as three different types. The first pattern, type 1, was that reported in detail by Gardner (1977) with curved relationships for all but range 1, VT vs. TI. Examples of type 1 pattern are shown in Fig. 1. The second pattern, type 2, differed from type 1 only in that the plot for VT vs. T, in 4! VT 3 3
41 VT *1.
2
'3
