ATTENUATION OF ARTERIAL OXYGEN DESATURATION BY CARDIOVASCULAR REFLEXES DURING APNEA IN EXERCISING MEN.
Research field:Cardiovascular physiology
Authors:Lindholm P, Sundblad P, Linnarsson D
Address of presenting
author:		Peter Lindholm, Berzelius väg 13, Omgivningsfysiologi, Karolinska Institutet, 17177 Stockholm
E-mail:peter.lindholm@fyfa.ki.se
Phone:08-7286879
Fax:08-339702
Text of abstract Introduction
The diving response (i.e. bradycardia and peripheral vasoconstriction) is documented as an oxygen conserving reflex in diving species. It is associated with apnea, but other stimuli have additive effects, e.g. hypoxia. Whether such a reflex is of functional importance in man is still obscure. Studies in man have shown bradycardia and a rise in blood pressure during apnea but the possible oxygen-conserving effect of these cardiovascular reflexes has not been demonstrated previously.

Methods
Nine healthy male volunteers were studied. Subjects held their breath repeatedly at a lung volume of residual volume (RV) + 3.5 l air during 120W steady state dynamic leg exercise. We determined beat-by-beat heart rate and blood pressure, and ear-lobe oxygen saturation (SpO2) continuously.
The period of 25-30s into the apnea was chosen for statistical analysis.

Results
The subjects had a marked inter-individual variability in terms of bradycardia and hypertension during apneas. Bradycardic responses ranged -10 to -93 beats/min and hypertensive responses ranged +27 to +67 mmHg. There was a statistically significant correlation between the amplitude of composite cardiovascular reflexes (bradycardia(DHR) + hypertension(DMAP)) and the rate of arterial oxygen desaturation (DSaO2/Dt): DSaO2/Dt = -3.35 -0.022*DHR + 0.027*DMAP. (N=9, P<0.001, adjusted r2=0.88)

Conclusions
The rate of arterial oxygen desaturation is attenuated by cardiovascular reflexes during apnea. A strong diving response results in a temporary oxygen conservation for the duration of the apnea.

References
Lindholm, P., P. Sundblad, and D. Linnarsson. J Appl Physiol 87: 2122-7, 1999.

Keywords:hypoxemia, bradycardia, hypertension, breath holding, hypoxia

Created 2000-05-02