Mild hypoxia

[dan_76]

I have been suffering from lightheadedness and feel like fainting for couple of years without any medical explanation. I have been diagnosed with moderate obstructive sleep apnea and I am using CPAP machine now.

What bothers me is that my apnea events have come down. I only have zero to 5 events per night. But still I am desaturated <90% 5-10% of the time during nights. Otherwise my saturation is between 90-95%. During day my saturation is 95-96%. What I consider strange as well is that my respiratory rate is higher while sleeping than when I am awake. According to CPAP data my respiratory rate before falling asleep and after waking up is around 9 /min and during my sleep it's around 15 /min. I have understood that respiratory rate should go down when sleeping and also that 9 /min is considered slow.

I had arterial blood gas analysis done and it was otherwise normal except my pO2 was 9kPa or 67 mmHg.

My lungs have been tested (x-ray, diffusion capacity, spirometry) and results were "normal".

1. Is it possible that my symptoms are related to blood oxygen levels?
2. Is it possible that sleep apnea is causing lowered oxygen levels during daytime?
3. Can there be other causes for desaturation, because I still get it even apneas have been eliminated?

[David Tinkelman, M.D.]

Reduction of apneic events to “zero to 5 per night” is a terrific response and I would not be at all concerned about the slight increase in your nocturnal respiratory rate (still in the normal range)  It is quite unlikely that your bouts of “lightheadedness and feel like fainting” are a consequence of obstructive sleep apnea and another cause should be sought (for example a fall in blood pressure or an abnormal heart rhythm).

If you live at sea level the arterial blood gas p02 value of 67, if valid, is quite abnormal.  It would be normal at an altitude of around 5,000 feet.   Also, a p02 of 67 at sea level is not consistent with the normal pulmonary function tests you cite and, if valid might be on the basis of abnormal blood flow within your heart, via what is called an atrial septal defect with what is called a right to left shunt.  You should ask your doctor about this possibility as if present, it could also account for  lightheadedness and a feeling of fainting.

Good luck

[ChrisBSRRT]

It's not uncommon for certain patients to require oxygen during sleep only. At night your metabolism slows down as well as your heart rate and respiratory rate. In order for this to take place a sleep study would be required in order to determine how much oxygen you need bled into the cpap system. Need this retest in order for insurance to cover it, and the MD needs the test to write the prescription for oxygen.


This is what I'm gathering from the information you gave me, assuming all your cardiac tests checked out.

[dan_76]

Chris, thanks for your thoughts.

My CPAP has been set to operate automatically in range from 4 to 20. Typically it stays between 6-15 throughout the night.

Is it possible that I am still not breathing properly even my AHI is practically zero according to the machine's diagnostics?

What comes to cardiac issues there should be nothing from with my heart (ECG's, echo, stress...) only that my resting heart rate is sometimes low during daytime as well (varies typically between 50-65) and during the night goes down to low 40's according to oximeter.

[ChrisBSRRT]

Have you gained or lost any weight since your last sleep study? CPAP pressure settings commonly need to be adjusted over a period of time to meet a therapeutic level. When your blood oxygen decreases your respiratory rate and heart rate should increase. I common see patients that require supplemental oxygen only during the night while asleep. Seeing as your pulmonary tests are normal, perhaps there's a cardiac component, but I would first consider the need to adjust the CPAP settings. If the driving pressure is too low to relieve the obstruction your body will starve for air and deoxygenate...and at the same time cause an increased resp rate and heart rate.

[dan_76]

Additional information: I am obese (BMI 37) and do not smoke.