| Summary: | Arterial desaturation in fit athletes, during exercise at an
intensity greater than or equal to 90% of VO₂ max has been
reported by a number of authors yet the etiology of these changes
remain obscure. Inadequate pulmonary ventilation due to a blunted
respiratory drive, or lung mechanics has been implicated as a
factor in the etiology of this phenomenon. It was the purpose of
this experiment to investigate the relationship between arterial
desaturation and ventilatory response to hypoxia (HVR). Twelve
healthy male subjects ( age = 23.8 ± 3.6 yrs., height = 181.6 ±₋₁
5.6 cms., Weight = 73.7 ± 6.2 kg., VO₂ max = 63.2 ± 2.2 ml .kg
. -1 2 .min⁻¹) performed a five minute exercise test on a treadmill at
100% of VO₂ max. Arterial samples for pH, PCO₂, PO₂, and SaO₂
were withdrawn via an indwelling arterial cannula at rest and
every 15s throughout the exercise test. The blood gas samples
were analyzed with an Instrument Laboratories 1306 blood gas
analyzer. Ventilation and VO₂ were measured by a Beckman
metabolic measurement cart. On a separate occasion the
ventilatory response to hypoxia (HVR) was determined by recording
VE as progressive hypoxia was induced by adding N₂ to a mixing
chamber. SaO₂ was measured using a Hewlett-Packard ear oximeter; to maintain isocapnia small ammounts of CO₂ were added to the
open circuit system. ANOVA for repeated measured was used to
evaluate changes in blood gases, ventilation, and VO₂. Simple
linear regression and multiple linear regression was used to
evaluate the relationship between the changes in SaO₂ and HVR and the descriptive variables. Subjects showed a significant
decline in arterial saturation and PO₂ over the course of the
test (p < 0.01,and p < 0.01). Four subjects (Mild) exhibited
modest decreases in SaO₂ to (94.6 ± 1.9%), three (Moderate)
showed an intermediate response (SaO₂ 91.6 ± 0.1%) and five
(Marked) demonstrated a marked decrease in arterial saturation
(SaO₂ = 90.0 + 1.2%). The differences in PO₂ and SaO₂ between
Mild and Marked groups were significant ( p < 0.05, and p <
0.01); there were no significant differences between groups in
VE, VO₂, pH or PCO . There was no significant correlation between the lowest SaO₂ reached and HVR, or any of the descriptive
variables. Nine subjects did not reach maximal VE (as determined
by the VO₂ max test) on the exercise test, two subjects 2
exhibited similar ventilation, and the remaining subject exceeded maximal VE, but fell into the Mild group with respect to desaturation. Oxygen uptake exceeded that recorded for the VO₂ max determination for four of the five subjects in the Marked group; the remaining subjects demonstrated lower or similar values. It was concluded that arterial desaturation was not related to blunted hypoxic drive. === Education, Faculty of === Curriculum and Pedagogy (EDCP), Department of === Graduate
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