523
Accuracy of Pulse Oximetry during Exercise Stress Testing L. H. Norton , B. Squires 2,
NR
Craig 3,
G. McLeay 3, R McGrath K I. Norton2'4
John Hunter Hospital, Newcastle 2 University of Newcastle South Australian Sports Institute 4University of New South Wales
tests has become increasingly important in clinical medicine (3,
McLeay,
L. H. Norton, B. Squires, N P Craig, G. P McGrath and K. I. Norton, Accuracy of Pulse
Oximetry during Exercise Stress Testing. Tnt J Sports Med. Vol 13, No 7, pp 523—527, 1992. Accepted after revision: June 23, 1992
15).
Recent technological advances have enabled pulse oximetry to be used to continuously monitor arterial oxygen saturation levels (Sa02) during rest (9) and exercise (7, 11, 12,13,21), using subjects with (5,16) and without (6,19) known disease and at altitude (8). The advantages of pulse oximetry
include the ease of use, non-invasiveness, patient comfort,
Pulse oximetry is used extensively during exercise stress-testing in the clinical and sports medicine
portability and that it is relatively inexpensive. However, there are a number of factors that may affect the accuracy of oximetry when used during exercise and which have yet to be thoroughly
settings. There are few validation studies to assess the appro-
tested. These include possible motion artifacts, influence of
priateness of using pulse oximetry under conditions of
sweating and local tissue perfusion. For example, the effects of stress-induced (exercise or other) sympathetically-mediated va-
potentially compromised peripheral blood flow. To study the accuracy of pulse oximetry during severe exercise stress, 10 athletes undertook 3 bouts of exhaustive exercise; once at an
intensity requiring TO2max (max), once at 115 % of \:'O2max (Smax), and once at Smax while F102 was increased to 0.30. The results indicate relatively large underestimations occur when pulse oximetry is used to estimate %Sa02 during exercise, when compared to the criterion samples of gas analysis in arterial blood. These differences were exacerbated as the exercise intensity increased from a mean(± SE) difference of 2.9 0.7 %Sa02 at max to 4.6 0.7 %Sa02 at Smax. Breathing a higher F102 reversed the hypoxemia that occurred during the normoxic exercise, however, pulse oximetry measurements failed to detect this alteration in %Sa02. Estimates of oxygen saturation during severe exercise using pulse oximetry should be viewed with caution, as potentially large errors may occur.
Key words
Pulse oximetry, oxygen saturation, stresstesting, peripheral blood flow, supramaximal exercise, hypoxemia
soconstrictor drive, which reduces skin blood flow would. theoretically, pose the greatest influence on pulse oximetry accuracy under these conditions (4, 10, 18). Exercise studies in
patients with respiratory and/or circulatory disease have yielded inconsistent results. Ries et al. (16) found high correla-
tions between directly measured Sa02 levels and those estimated by two oximeters. Conversely, Hansen and Casaburi (5) reported a variety of responses ranging from significant underestimation to appreciably greater pulse oximetry levels in their patients during heavy exercise. They also found no differences between measurement techniques under resting conditions and in some patients during exercise.
There have been a number of recent studies utilizing pulse oximetry reporting significant arterial hypoxemia (as low as 85 %Sa02) in some highly trained athletes during exercise at sea level (12,13,21). This has led to the belief that the pulmonary system is the limiting factor to performance in these endurance athletes (2,14). Consequently, it is now becoming a common practice for sports science/medicine specialists to routinely monitor athletes for Sa02 levels during exhaustive exercise (using pulse oximetry) in an attempt to determine limitations to performance. There are relatively few reports of
validation studies to determine the appropriateness of pulse oximetry use in athletic populations during exercise (1,7,20).
Introduction Exercise stress testing in the clinical setting is used as a valuable diagnostic technique to investigate the presence of cardiorespiratory abnormalities during physical stress that may not be descernable under resting conditions. The meas-
urement of arterial blood oxygenation during these exercise
Meaningful use of oximetry in a range of experimental and clinical settings requires further validation studies. If there is serious discrepancy between actual and estimated Sa02 levels, this may have important implications in the interpretation of measurements made during exercise testing in clinical medicine and sports science.
Therefore, the purpose of this study was to mt. J. Sports Med. 13 (1992) 523—527 Georg Thieme Verlag Stuttgart New York
compare measurements of oxygen saturation estimated by pulse
oximetry with those measured and calculated from directly
Downloaded by: University of British Columbia. Copyrighted material.
Abstract
524 mt. .1 Sports Med. 13 (1992)
L. H. Norton, B. Squires, N. P Craig, G. McLeavy, P McGrath, K. I. Norton
sampled arterial blood during resting and exercising conditions in trained athletes.
The experimental protocol consisted of 3 work-
bouts on the ergometer at the following intensities, 1) at a workrate equivalent to that at which maximum oxygen uptake
Subjects Ten subjects were used in this study. All were healthy, non-smoking adult males and each gave their informed written consent prior to the experiment. All procedures used in this study were performed in accordance with the guiding ethi-
cal principles for human experimentation outlined by the National Health and Medical Research Council of Australia. In particular, all subjects were given a detailed description of the test protocol with special emphasis being placed upon the risks associated with the invasive procedures to be used.
The subjects ranged in physical abilities and included 1 recreational runner, 4 competitive triathietes, a mountain bike cyclist (8 times national champion), and 4 Olympic cycling medalists including a recent world champion. The subjects were deliberately chosen in order to improve the likelihood of finding significant arterial desaturation during exercise,
which has been estimated to occur in about 50% of highly trained endurance athletes (2, 14).
Test protocol
Subjects reported to the laboratory on at least 2 occasions prior to the day of the experiment for purposes of habituation and familiarization to staff, equipment and experimental protocol. On each of these visits, the subjects performed
a graded exercise test on a bicycle ergometer to volitional fatigue. During these workbouts, pulse oximetry was performed
and the results used to establish reproducibility of measurements at various levels of physical exertion. These tests also provided information necessary to set appropriate workrates during the experimental phase of the study.
On the experimental day the subjects reported
to the laboratory and a brief kinanthropometric profile was obtained. This involved measurements of height, weight and six skinfold sites in order to estimate relative body-fat levels (22). Following this, a catheter was inserted into the radial artery of
(VO2max) was reached (max), 2) at a workrate requiring 115 %
of VO2max (Smax), and 3) at a workrate requiring 115% of VO2max while the subjects were given an increased fraction (F102 = 0.30) of inspired oxygen (Smax-H). The workbouts were designed to be of extreme relative intensity and to last no longer than 4mm in duration. Each test was conducted in an identical fashion with the administration being randomised to preclude any bias arising from the order of exercise. There was 1 hr between consecutive workbouts.
During the exercise test POSaO2 was recorded every 15 s while ABSaO2 was measured once only during the final 30s. The mean POSaO2 for the corresponding 30s was used in all futher statistical analyses.
Blood-gas Analysis Cannula patency was maintained using positive
pressure infusion (3 ml hr') of heparinised saline (10 units ml-'). The sampling procedure involved withdrawal of the saline flush followed by anaerobic collection of a 2.5 ml blood sample into a heparinized syringe (Preza-Pak II). The syringe was immediately capped and placed into ice-slush. Analysis of blood-gas status was performed in duplicate within 30 mm of
collection. Blood was analysed using a blood gas analyser (Ciba-Corning, model 278) which directly measured blood pH, PO2 pCO2 and calculated oxygen saturation (%Sa02) based on
these measures (17). In five of the subjects blood was also analysed using a hemoximeter (Radiometer, model OSM3) which measured %Sa02 directly from a 35 l.tl sample of arterial blood. Additionally, fractions of carboxyhemoglobin,
methemoglobin and sulfhemoglobin (dyshemoglobins) were measured (as a percentage of total hemoglobin) using the same sample. The blood-gas values were adjusted for core body temperature pre-exercise and during the exercise bouts. Temperature was monitored via a rectal temperature probe inserted 12 cm past the anal sphincter. The probe was positioned and taped in place by the subject prior to the first exercise workrate.
Statistical Analyses
the non-dominant arm and sutured into position. The catheter was inserted by an anesthetist under aseptic conditions. Once the catheter had been securely positioned, the subjects were instructed to sit comfortably in position on a bicycle ergometer (modified Repco wind-loaded). Heart rate (HR) was continu-
peated measures was used to determine if there were any differences among variables measured during the 3 exercise tests. In
ously monitored throughout the tests using electrocardiography, with leads positioned in the standard VS configuration. Subjects
the case of a significant F-ratio, post-hoc analysis was performed using Fisher's LSD test. Paired t-tests were used for
were connected to a respiratory valve so that ventilation (VE) and oxygen uptake (V02) could be measured during the testing. These variables were calculated in the usual way via an automated metabolic assessment system (Ametek, model OCM-2),
The statistical analyses were performed using Statview SE+ software package (Abacus). ANOVA with re-
comparison between pre-exercise measurements when normoxia data was combined.
Results
with values averaged for each 30s period. An ear probe for oximetric measures (Ohmeda Biox pulse oximeter 3700R) was placed on the ear lobe following a 30 s massage with an alcohol (70 %) pad, the cable was taped and an ear probe retainer used to prevent excessive movement of the oximeter according to the manufacturers recommendations (Ohmeda handbook). Baseline
re-exercise) measurements for HR, VE, V02 and for both direct (arterial blood; ABSaO2) and indirect (oximetric; POSaO2) oxygen saturation values were taken following 15 mm
of rest before each workbout.
The physical and VO2max characteristics of the subjects used in this study are shown in Table 1. The low body fat and high VO2max levels of the subjects make it apparent that they were all highly trained. Each subject was able to complete all 3 workrates, with the exception of one subject where, due to technical difficulties, data for the hyperoxic exercise condition was not recorded. Workrates averaged (± SE) 376
during maximal exercise and 432±8 W for the supramaximal exercise tests. Average time completed for the 3
Downloaded by: University of British Columbia. Copyrighted material.
Methods
mt. i Sports Med. 13 (1992) 525
Accuracy of Pulse Oximetiy during Exercise Stress Testing Table 1 Descriptive statistics for the subjects used in this study.
1
2
3 4 5 6
Age (yrs)
Height (cm)
Mass (kg)
24 20
177.9 181.7 172.0 187.3 181.5 181.0 181.8 173.3 179.0
66.9 82.4 60.0 78.2 73.5 80.0 71.6 68.0
174.1
69.7
6.4 6.5 9.3 9.6 6.8 12.6 8.6
178.9 1.5
73.4 2.3
21 18
35 32
7
19
8 9
20
10
i SE
22 18 23 1.9
%Body fat
83.1
VO2max
Time
Max
(ml. mint kg1)
Variable
6.2 8.2
72.5
Hemox! pre-ex
59.1
Sa02
ex
93.1
8.1
58.4 66.5 70.9 53.9 75.7
ABSaO2 (%)
pre-ex ex
78.6 63.7 76.2
pre-ex
(%)
ex
HR
pre-ex
8.2 0.6
67.6 2.8
POSaO2
Smax-H
Smax
97.7± .1
97.9± .1 94.5± .5
98.8± .1
97.5± 2a 93.2± 5a
97.6± .2 94.2± .5
98.9± .1 98.3± .2
97.3± .3
97.2± .3
90.3± 9*
89.6±1.0*
97.5± .5 90.5±1.3*
.8
83.3±4.3b
98.4± .3
(b.miri1) ex
188.1
100.8±7.2 189.4±2.9
189.3±2.8
VE
pre-ex
(I . min1)
ex
13.8±1.7 143.2 83a,b
15.2 1.5 158.8 8.8
156.3 6.5
43.6±2.3 98.3±0.4
52.5±3.4 98.9
49.8±2.9 99.0±0.4
95.1
15.6±1.4
workrates was 4.0±0.0 mm (max), 2.9±0.1mm (Smax) and 2.9 mm (Smax-H).
%HRmax pre-ex ex
During the testing there were no pathological indices with respect to ECG, arterial blood gases or lung function. In the 5 subjects for which dyshemoglobin fractions were for carboxyhemoglobin, measured, values averaged 0.3 0.4 0.02% for methemoglobin and undetectable levels were
#Oxygen saturation measured using a hemoximeter; n = 5. *Denotes significant difference between ABSaO2 and POSaO2 values under same condition. Significant difference between max and Smax-H (a), max and Smax (b), and Srnax and Smax-H (c). p < 0.05.
found for sulfhemoglobin. There were no significant differences between directly measured Sa02 and calculated Sa02 from arterial blood samples in the 5 subjects. Mean differences were 0.4
0.1 % under all conditions at rest (n = 15) and 0.3 0.2% during the exercise conditions (n= 15; see Table 2). Further statistical analyses of oxygen saturation measured using the hemoximeter were not computed due to small numbers (n =5).
Correlation analysis indicated good intra-individual reproducibility for pulse oximetry measurements during the pre-experimental tests when comparisons were made at several submaximal and maximal intensities (r= 0.87; mean
differenceO.9±l.3 %Sa02; n=46). Table 2 indicates pre-exercise and exercise measurements for arterial oxygen saturation, ventilation and heart rate across the 3 exercise conditions. There were significantly higher pre-exercise and exercise ABSaO2 levels during the hyperoxic than during the normoxic conditions. ABSaO2 levels fell significantly during exercise under both normoxic conditions while remaining essentially unchanged for the hyperoxic condition. Corresponding POSaO2 levels showed a decrease for all 3 exercise conditions.
%Sa02 difference 10
9
8 7 6 5 4
• NORMOXIA o HYPEROXIA
3
2 V
MAX
PRE-EXERCISE
SMAX
WORKRATE Fig. 1 Mean (± SE) oxygen saturation differences (ABSaO2—POSaO2), pre-exercise and for the 3 exer-
cise conditions. indicates difference is significant (p
Accuracy of Pulse Oximetry during Exercise Stress Testing L. H. Norton , B. Squires 2,
NR
Craig 3,
G. McLeay 3, R McGrath K I. Norton2'4
John Hunter Hospital, Newcastle 2 University of Newcastle South Australian Sports Institute 4University of New South Wales
tests has become increasingly important in clinical medicine (3,
McLeay,
L. H. Norton, B. Squires, N P Craig, G. P McGrath and K. I. Norton, Accuracy of Pulse
Oximetry during Exercise Stress Testing. Tnt J Sports Med. Vol 13, No 7, pp 523—527, 1992. Accepted after revision: June 23, 1992
15).
Recent technological advances have enabled pulse oximetry to be used to continuously monitor arterial oxygen saturation levels (Sa02) during rest (9) and exercise (7, 11, 12,13,21), using subjects with (5,16) and without (6,19) known disease and at altitude (8). The advantages of pulse oximetry
include the ease of use, non-invasiveness, patient comfort,
Pulse oximetry is used extensively during exercise stress-testing in the clinical and sports medicine
portability and that it is relatively inexpensive. However, there are a number of factors that may affect the accuracy of oximetry when used during exercise and which have yet to be thoroughly
settings. There are few validation studies to assess the appro-
tested. These include possible motion artifacts, influence of
priateness of using pulse oximetry under conditions of
sweating and local tissue perfusion. For example, the effects of stress-induced (exercise or other) sympathetically-mediated va-
potentially compromised peripheral blood flow. To study the accuracy of pulse oximetry during severe exercise stress, 10 athletes undertook 3 bouts of exhaustive exercise; once at an
intensity requiring TO2max (max), once at 115 % of \:'O2max (Smax), and once at Smax while F102 was increased to 0.30. The results indicate relatively large underestimations occur when pulse oximetry is used to estimate %Sa02 during exercise, when compared to the criterion samples of gas analysis in arterial blood. These differences were exacerbated as the exercise intensity increased from a mean(± SE) difference of 2.9 0.7 %Sa02 at max to 4.6 0.7 %Sa02 at Smax. Breathing a higher F102 reversed the hypoxemia that occurred during the normoxic exercise, however, pulse oximetry measurements failed to detect this alteration in %Sa02. Estimates of oxygen saturation during severe exercise using pulse oximetry should be viewed with caution, as potentially large errors may occur.
Key words
Pulse oximetry, oxygen saturation, stresstesting, peripheral blood flow, supramaximal exercise, hypoxemia
soconstrictor drive, which reduces skin blood flow would. theoretically, pose the greatest influence on pulse oximetry accuracy under these conditions (4, 10, 18). Exercise studies in
patients with respiratory and/or circulatory disease have yielded inconsistent results. Ries et al. (16) found high correla-
tions between directly measured Sa02 levels and those estimated by two oximeters. Conversely, Hansen and Casaburi (5) reported a variety of responses ranging from significant underestimation to appreciably greater pulse oximetry levels in their patients during heavy exercise. They also found no differences between measurement techniques under resting conditions and in some patients during exercise.
There have been a number of recent studies utilizing pulse oximetry reporting significant arterial hypoxemia (as low as 85 %Sa02) in some highly trained athletes during exercise at sea level (12,13,21). This has led to the belief that the pulmonary system is the limiting factor to performance in these endurance athletes (2,14). Consequently, it is now becoming a common practice for sports science/medicine specialists to routinely monitor athletes for Sa02 levels during exhaustive exercise (using pulse oximetry) in an attempt to determine limitations to performance. There are relatively few reports of
validation studies to determine the appropriateness of pulse oximetry use in athletic populations during exercise (1,7,20).
Introduction Exercise stress testing in the clinical setting is used as a valuable diagnostic technique to investigate the presence of cardiorespiratory abnormalities during physical stress that may not be descernable under resting conditions. The meas-
urement of arterial blood oxygenation during these exercise
Meaningful use of oximetry in a range of experimental and clinical settings requires further validation studies. If there is serious discrepancy between actual and estimated Sa02 levels, this may have important implications in the interpretation of measurements made during exercise testing in clinical medicine and sports science.
Therefore, the purpose of this study was to mt. J. Sports Med. 13 (1992) 523—527 Georg Thieme Verlag Stuttgart New York
compare measurements of oxygen saturation estimated by pulse
oximetry with those measured and calculated from directly
Downloaded by: University of British Columbia. Copyrighted material.
Abstract
524 mt. .1 Sports Med. 13 (1992)
L. H. Norton, B. Squires, N. P Craig, G. McLeavy, P McGrath, K. I. Norton
sampled arterial blood during resting and exercising conditions in trained athletes.
The experimental protocol consisted of 3 work-
bouts on the ergometer at the following intensities, 1) at a workrate equivalent to that at which maximum oxygen uptake
Subjects Ten subjects were used in this study. All were healthy, non-smoking adult males and each gave their informed written consent prior to the experiment. All procedures used in this study were performed in accordance with the guiding ethi-
cal principles for human experimentation outlined by the National Health and Medical Research Council of Australia. In particular, all subjects were given a detailed description of the test protocol with special emphasis being placed upon the risks associated with the invasive procedures to be used.
The subjects ranged in physical abilities and included 1 recreational runner, 4 competitive triathietes, a mountain bike cyclist (8 times national champion), and 4 Olympic cycling medalists including a recent world champion. The subjects were deliberately chosen in order to improve the likelihood of finding significant arterial desaturation during exercise,
which has been estimated to occur in about 50% of highly trained endurance athletes (2, 14).
Test protocol
Subjects reported to the laboratory on at least 2 occasions prior to the day of the experiment for purposes of habituation and familiarization to staff, equipment and experimental protocol. On each of these visits, the subjects performed
a graded exercise test on a bicycle ergometer to volitional fatigue. During these workbouts, pulse oximetry was performed
and the results used to establish reproducibility of measurements at various levels of physical exertion. These tests also provided information necessary to set appropriate workrates during the experimental phase of the study.
On the experimental day the subjects reported
to the laboratory and a brief kinanthropometric profile was obtained. This involved measurements of height, weight and six skinfold sites in order to estimate relative body-fat levels (22). Following this, a catheter was inserted into the radial artery of
(VO2max) was reached (max), 2) at a workrate requiring 115 %
of VO2max (Smax), and 3) at a workrate requiring 115% of VO2max while the subjects were given an increased fraction (F102 = 0.30) of inspired oxygen (Smax-H). The workbouts were designed to be of extreme relative intensity and to last no longer than 4mm in duration. Each test was conducted in an identical fashion with the administration being randomised to preclude any bias arising from the order of exercise. There was 1 hr between consecutive workbouts.
During the exercise test POSaO2 was recorded every 15 s while ABSaO2 was measured once only during the final 30s. The mean POSaO2 for the corresponding 30s was used in all futher statistical analyses.
Blood-gas Analysis Cannula patency was maintained using positive
pressure infusion (3 ml hr') of heparinised saline (10 units ml-'). The sampling procedure involved withdrawal of the saline flush followed by anaerobic collection of a 2.5 ml blood sample into a heparinized syringe (Preza-Pak II). The syringe was immediately capped and placed into ice-slush. Analysis of blood-gas status was performed in duplicate within 30 mm of
collection. Blood was analysed using a blood gas analyser (Ciba-Corning, model 278) which directly measured blood pH, PO2 pCO2 and calculated oxygen saturation (%Sa02) based on
these measures (17). In five of the subjects blood was also analysed using a hemoximeter (Radiometer, model OSM3) which measured %Sa02 directly from a 35 l.tl sample of arterial blood. Additionally, fractions of carboxyhemoglobin,
methemoglobin and sulfhemoglobin (dyshemoglobins) were measured (as a percentage of total hemoglobin) using the same sample. The blood-gas values were adjusted for core body temperature pre-exercise and during the exercise bouts. Temperature was monitored via a rectal temperature probe inserted 12 cm past the anal sphincter. The probe was positioned and taped in place by the subject prior to the first exercise workrate.
Statistical Analyses
the non-dominant arm and sutured into position. The catheter was inserted by an anesthetist under aseptic conditions. Once the catheter had been securely positioned, the subjects were instructed to sit comfortably in position on a bicycle ergometer (modified Repco wind-loaded). Heart rate (HR) was continu-
peated measures was used to determine if there were any differences among variables measured during the 3 exercise tests. In
ously monitored throughout the tests using electrocardiography, with leads positioned in the standard VS configuration. Subjects
the case of a significant F-ratio, post-hoc analysis was performed using Fisher's LSD test. Paired t-tests were used for
were connected to a respiratory valve so that ventilation (VE) and oxygen uptake (V02) could be measured during the testing. These variables were calculated in the usual way via an automated metabolic assessment system (Ametek, model OCM-2),
The statistical analyses were performed using Statview SE+ software package (Abacus). ANOVA with re-
comparison between pre-exercise measurements when normoxia data was combined.
Results
with values averaged for each 30s period. An ear probe for oximetric measures (Ohmeda Biox pulse oximeter 3700R) was placed on the ear lobe following a 30 s massage with an alcohol (70 %) pad, the cable was taped and an ear probe retainer used to prevent excessive movement of the oximeter according to the manufacturers recommendations (Ohmeda handbook). Baseline
re-exercise) measurements for HR, VE, V02 and for both direct (arterial blood; ABSaO2) and indirect (oximetric; POSaO2) oxygen saturation values were taken following 15 mm
of rest before each workbout.
The physical and VO2max characteristics of the subjects used in this study are shown in Table 1. The low body fat and high VO2max levels of the subjects make it apparent that they were all highly trained. Each subject was able to complete all 3 workrates, with the exception of one subject where, due to technical difficulties, data for the hyperoxic exercise condition was not recorded. Workrates averaged (± SE) 376
during maximal exercise and 432±8 W for the supramaximal exercise tests. Average time completed for the 3
Downloaded by: University of British Columbia. Copyrighted material.
Methods
mt. i Sports Med. 13 (1992) 525
Accuracy of Pulse Oximetiy during Exercise Stress Testing Table 1 Descriptive statistics for the subjects used in this study.
1
2
3 4 5 6
Age (yrs)
Height (cm)
Mass (kg)
24 20
177.9 181.7 172.0 187.3 181.5 181.0 181.8 173.3 179.0
66.9 82.4 60.0 78.2 73.5 80.0 71.6 68.0
174.1
69.7
6.4 6.5 9.3 9.6 6.8 12.6 8.6
178.9 1.5
73.4 2.3
21 18
35 32
7
19
8 9
20
10
i SE
22 18 23 1.9
%Body fat
83.1
VO2max
Time
Max
(ml. mint kg1)
Variable
6.2 8.2
72.5
Hemox! pre-ex
59.1
Sa02
ex
93.1
8.1
58.4 66.5 70.9 53.9 75.7
ABSaO2 (%)
pre-ex ex
78.6 63.7 76.2
pre-ex
(%)
ex
HR
pre-ex
8.2 0.6
67.6 2.8
POSaO2
Smax-H
Smax
97.7± .1
97.9± .1 94.5± .5
98.8± .1
97.5± 2a 93.2± 5a
97.6± .2 94.2± .5
98.9± .1 98.3± .2
97.3± .3
97.2± .3
90.3± 9*
89.6±1.0*
97.5± .5 90.5±1.3*
.8
83.3±4.3b
98.4± .3
(b.miri1) ex
188.1
100.8±7.2 189.4±2.9
189.3±2.8
VE
pre-ex
(I . min1)
ex
13.8±1.7 143.2 83a,b
15.2 1.5 158.8 8.8
156.3 6.5
43.6±2.3 98.3±0.4
52.5±3.4 98.9
49.8±2.9 99.0±0.4
95.1
15.6±1.4
workrates was 4.0±0.0 mm (max), 2.9±0.1mm (Smax) and 2.9 mm (Smax-H).
%HRmax pre-ex ex
During the testing there were no pathological indices with respect to ECG, arterial blood gases or lung function. In the 5 subjects for which dyshemoglobin fractions were for carboxyhemoglobin, measured, values averaged 0.3 0.4 0.02% for methemoglobin and undetectable levels were
#Oxygen saturation measured using a hemoximeter; n = 5. *Denotes significant difference between ABSaO2 and POSaO2 values under same condition. Significant difference between max and Smax-H (a), max and Smax (b), and Srnax and Smax-H (c). p < 0.05.
found for sulfhemoglobin. There were no significant differences between directly measured Sa02 and calculated Sa02 from arterial blood samples in the 5 subjects. Mean differences were 0.4
0.1 % under all conditions at rest (n = 15) and 0.3 0.2% during the exercise conditions (n= 15; see Table 2). Further statistical analyses of oxygen saturation measured using the hemoximeter were not computed due to small numbers (n =5).
Correlation analysis indicated good intra-individual reproducibility for pulse oximetry measurements during the pre-experimental tests when comparisons were made at several submaximal and maximal intensities (r= 0.87; mean
differenceO.9±l.3 %Sa02; n=46). Table 2 indicates pre-exercise and exercise measurements for arterial oxygen saturation, ventilation and heart rate across the 3 exercise conditions. There were significantly higher pre-exercise and exercise ABSaO2 levels during the hyperoxic than during the normoxic conditions. ABSaO2 levels fell significantly during exercise under both normoxic conditions while remaining essentially unchanged for the hyperoxic condition. Corresponding POSaO2 levels showed a decrease for all 3 exercise conditions.
%Sa02 difference 10
9
8 7 6 5 4
• NORMOXIA o HYPEROXIA
3
2 V
MAX
PRE-EXERCISE
SMAX
WORKRATE Fig. 1 Mean (± SE) oxygen saturation differences (ABSaO2—POSaO2), pre-exercise and for the 3 exer-
cise conditions. indicates difference is significant (p
