Help pls...2 specific questions on understanding sleep study

Ok...had my sleep study about a month ago and have been lurking on here for a while. I finally got around to asking for a copy of my sleep study and was given the two page "executive study".

I plan on going back and asking for the full study (or at least one with a little more data) but I have


DATA GIVEN

a Sleep Time 267.5 minutes
b Tot time in bed 395 minutes
c Minimal oxyhemoglobin desaturation 87%
d total hypopneas 178
e Latency to sleep 31 minutes
f Sleep Stages / time
N1 3.6%
N2 89.7%
N3 0.0%
REM 6.7%


CALCULATED VALUES (calculation)

Sleep efficiency 67.7% (a / b )
Total Hypopnea Index 39.9 per hr (d / a)
Arousal Index 45.1 per hr (no clue; just ratio provided)


Question 1: Is there any relationship between Arousal Index and AHI?

Question 2: I expected to see numbers apneas as well as hypopneas as well as AHI index. Am I reading/understanding this correctly that I have a Hypopnea ONLY index of 39.9? In other words, if you add in apneas my true AHI will be that much higher?

Thanks for the assistance. I have read a lot here but couldn't find answers to above and Dr. Google was no help either.

Question 1: Is there any relationship between Arousal Index and AHI?

Many hypopneas do trigger an EEG arousal, but it is possible to score a hypopnea without an arousal under one of the two accepted rules for scoring hypopneas on a PSG. Arousals that are caused by apneas and hypopneas are included in the arousal index. But arousals can also be caused by snoring or periodic limb movements. And some arousals are scored as "spontaneous" meaning there's no clear reason why the person had an arousal. All these non-respiratory related arousals also go into the computation of the arousal index.

Question 2: I expected to see numbers apneas as well as hypopneas as well as AHI index. Am I reading/understanding this correctly that I have a Hypopnea ONLY index of 39.9? In other words, if you add in apneas my true AHI will be that much higher?

The AHI is computed by adding together the total number of OAs, CAs, and Hs scored during the sleep study and dividing by the total sleep time measured in hours. While it is a bit unusual it is possible for a person to have severe OSA and have no OAs scored during the sleep study. You appear to be such a case. In other words, my guess is that when you see all the data in the sleep study report, you will see some line that indicates there were 0 OAs scored and 0 CAs scored.

Thanks robysue.

In your answer to Question #1 (I would quote but I don't know how to do that yet ) you are just at the limit of my understanding (ok...maybe just a bit beyond) but I understand your explanation-- VERY helpful.

Regarding Question 2 on Hypopnea Index (vs AHI) I understand your point AND the math.

Very appreciative of your time in giving such well laid out answers.

Best....
WakeMeNot