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Arterial oxygen saturation and peak VO2 during nasal and oral breathing

Wood, R.J. and Morton, A.R., 'Arterial oxygen saturation and peak VO2 during nasal and oral breathing', Proceedings of the American College of Sports Medicine Annual Conference, Medicine and Science in Sport and Exercise, Supplement to Vol 27(5), pS2, May 1995.

The occurrence of lowered arterial O2 saturation (%SaO2) in some athletes indicates that for them exercise is limited by the ventilatory system, which some studies have suggested may be due to an inadequate exercise ventilation (Ve). To investigate this, a ventilation limitation was created by making subjects breathe solely through their nose, and the effect on arterial O2 saturation was studied. Fourteen moderately trained subjects (8 males, 6 females) performed two maximal multistage continuous treadmill running tests. In each test, the subjects’ expired air was collected via a face mask (Hans Rudolph, Model 7910-large), the oral only breathing condition (control) achieved by wearing a nose-clip and the nasal only breathing condition achieved by taping the mouth closed. Oxygen consumption was determined by open circuit spirometry every 30 seconds, end every minute %SaO2 (Ohmeda Biox 3700e pulse oximeter) and Rating of Perceived Breathlessness (TPB) were recorded. The table below shows the results of the variables measured at peak VO2 (mean +/- sd) and the paired t-test significance level.

  oral nasal t-test
VO2 (l/min) 3.90 ± 0.95 3.34 ± 0.84 p < 0.01
Ve (l/min) 134.9 ± 30.5 87.4 ± 24.2 p < 0.01
%SaO2 95.1 ± 2.0 93.3 ± 3.4 p < 0.05
RPB 8.2 ± 1.4 8.3 ± 1.6 ns

Despite a 35% difference in Ve between conditions, there was only a 14% difference in VO2. More than half of the difference in VO2 was explained by the difference in Ve (r2=0..54). The ventilatory limitation as created by nasal breathing had a relatively small effect on %SaO2 levels. At peak VO2, %SaO2 was highly variable, there being only a poor correlation between %SaO2 and V2 (r=0.18) or Ve/VO2 (r=0.31). The low correlations between %SaO2 and ventilatory parameters, and the relatively small difference in %SaO2 between conditions, indicate that factors other than Ve are the major contributors to %SaO2 levels during exercise under these conditions.

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