Relationship between metabolic syndrome and hypercapnia among obese patients with sleep apnea

Table 1 Characteristics of the study patients

	OSA without hypercapnia (n = 72)	OSA with hypercapnia (n = 25)	P value
Age, yr	44.6 ± 11.2	45.6 ± 12.3	0.731
Men, n (%)	67 (93)	24 (96)	0.960
BMI, kg/m2	33.8 ± 4.1	33.6 ± 3.4	0.790
Waist circumference, cm	109.3 ± 10.4	110.7 ± 11.6	0.567
Systolic blood pressure, mmHg	118.6 ± 35.5	129.3 ± 30.6	0.183
Diastolic blood pressure, mmHg	71.5 ± 22.1	76.6 ± 18.9	0.313
Total cholesterol, mg/dL	195.6 ± 39.9	202.2 ± 25.3	0.439
Triglycerides, mg/dL	150.0 (94.0)	164.0 (93.0)	0.351
HDL cholesterol, mg/dL	43.7 ± 7.8	41.9 ± 9.1	0.360
Fasting blood glucose, mg/dL	110.3 ± 29.8	114.6 ± 38.5	0.567
HbA1c %	6.4 ± 1.4	6.3 ± 1.2	0.923
Uric acid, mg/dL	5.7 ± 3.0	6.7 ± 3.4	0.173
CRP, mg/dL	0.1 (0.2)	0.2 (0.3)	0.275
Epworth Sleepiness Scale	11.0 (8.0)	10.5 (9)	0.862
Awake PaO2, Torr	79.9 ± 8.7	75.8 ± 8.2	0.042
Awake PaCO2, Torr	41.0 ± 2.9	46.6 ± 2.5	<0.001
Medications, n (%)
Antihypertensive	18 (25)	8 (32)	0.675
Antidyslipidemic	1 (1)	2 (8)	0.162
Antidiabetic	4 (6)	1 (4)	0.999
Antihyperuricemic	5 (7)	1 (4)	0.999

BMI: Body mass index; CRP: C-reactive protein; HbA1c: Glycosylated hemoglobin A1c; HDL: High density lipoprotein; OSA: Obstructive sleep apnea; PaCO₂: Arterial partial pressure of carbon dioxide; PaO₂: Arterial partial pressure of oxygen.

Table 2 Sleep study data

	OSA without hypercapnia (n = 72)	OSA with hypercapnia (n = 25)	P value
TST, min	333.5 ± 82.7	330.6 ± 69.7	0.876
Total AHI, events/h	60.8 ± 20.5	65.6 ± 26.1	0.353
Obstructive	58.0 ± 21.9	64.8 ± 26.6	0.206
Central	0.3 (0.9)	0.3 (0.6)	0.815
Time spent SO2< 90%/TST, %	46.1 (54.7)	56.9 (60.0)	0.128
Lowest SO2, %	69.5 ± 9.2	68.8 ± 7.8	0.764
Arousal index, events/h	55.2 ± 24.1	59.1 ± 25.1	0.491
Sleep stages, %TST
N1	40.5 ± 16.7	45.2 ± 18.7	0.245
N2	44.8 ± 13.2	39.4 ± 15.1	0.094
N3	2.3 (9.0)	6.1 (9.7)	0.817
REM	9.1 (6.2)	10.8 (5.7)	0.494

AHI: Apnea-hypopnea index; OSA: Obstructive sleep apnea; REM: Rapid eye movement; SO₂: Oxyhemoglobin saturation; TST: Total sleep time.

Table 3 Results of logistic regression analyses

	OR (95%CI)	P value	OR (95%CI)	P value
Awake PaO2 (1 Torr increase)	0.94 (0.89-0.99)	0.047	0.94 (0.89-0.99)	0.043
Metabolic syndrome	2.72 (1.01-7.30)	0.047	2.85 (1.04-7.84)	0.042
Awake PaO2 (1 Torr increase)	0.94 (0.89-0.99)	0.047	0.94 (0.89-1.00)	0.052
Metabolic score (1-point increase)	1.65 (1.01-2.68)	0.044	1.66 (1.01-2.74)	0.048

PaO₂: Arterial partial pressure of oxygen.

Table 4 Summary of studies investigating the prevalence of daytime hypercapnia in Japanese obese patients with obstructive sleep apnea

Ref.	n	Population	Prevalence of daytime hypercapnia (PaCO2 ≥ 45 Torr)
Akashiba et al[25]	172	OSA (AHI ≥ 20 events/h) with Obesity (BMI ≥ 30 kg/m2)	32.0%
Harada et al[26]	162	OSA (AHI ≥ 5 events/h) with Obesity (BMI ≥ 30 kg/m2)	12.3%
Current research	97	OSA (AHI ≥ 30 events/h) with Obesity (BMI ≥ 30 kg/m2)	25.8%

AHI: Apnea-hypopnea index; BMI: Body mass index; OSA: Obstructive sleep apnea; PaCO₂: Arterial partial pressure of carbon dioxide.