THE EFFECT OF ARTERIAL O2 SATURATION AND HE ART RATE ON BLOOD PRESSURE DURING HYPOXIA

A periodic increase in blood pressure (BP) occurs during apneic episodes in patients with obstructive sleep apnea (OSA). Several factors including hypoxemia and an increase in heart rate (HR) were reported to be responsible for this increased BP. To examine the contribution of these two factors in increasing BP, 35 healthy male subjects (mean age±SD= 23.64±3.80) were studied in three experimental conditions, each condition for two minutes, including breathing room air at rest (normoxic), breathing low 02 (10%) air (hypoxic), and exercising on an ergometer while breathing room air (exercise). During the last minutes of each condition, changes in mean BP (ΔmBP), HR (ΔHR), and arterial O2 saturation (,ΔSaO2) were measured. The results showed that ΔmBP and ΔHR were significantly higher in both hypoxic and exercise conditions than normoxic condition (p<0 .00 1 for both cases). However, , ΔSaO2 was significantly lower in the hypoxic state compared to normoxic conditions. There was no significant difference in ΔHR between hypoxic and exercise groups, but both ΔmBP and , ΔSaO2 were significantly lower in hypoxic than exercise conditions (p<0.005 and p< O. OOl for ΔmBP and , ΔSaO2, respectively). There was a weak correlation between ΔmBP and ΔHR in the hypoxic condition (r=0.3, p<0.05), but the correlation between ΔmBP and ΔHR in the exercise condition was stronger (r=0.57, p< 0.001). These results indicated that although hypoxemia contributes to increased BP during hypoxia, an increase in HR is a stronger mechanism for this phenomenon.