Table 2.
Sample Characteristics by Quartile of Respiratory Event Duration
| Quartiles | Statistical Tests | ||||||
|---|---|---|---|---|---|---|---|
| Q1 (Longest) | Q2 | Q3 | Q4 (Shortest) | Quartile Difference(P Value) | Spearman’s ρ | Trend Test(P Value) | |
| Apnea duration, s | |||||||
| Range | (24.1, 57.6] | (20.6, 24.1] | (17.7, 20.6] | [11.2, 17.7] | NA | NA | NA |
| Mean (SD) | 27.80 (3.72) | 22.17 (0.98) | 19.18 (0.81) | 15.91 (1.25) | NA | NA | NA |
| n | 1,428 | 1,428 | 1,428 | 1,428 | NA | NA | NA |
| Age, yr* | 66 (11) | 63 (11) | 63 (11) | 61 (11) | <0.001 | +0.17 (P < 0.001) | <0.001 |
| BMI, kg/m2† | 27.4 (4.8) | 28.1 (4.9) | 28.5 (5.1) | 28.5 (5.4) | <0.001 | −0.09 (P < 0.001) | <0.001 |
| Gender, % female‡ | 47 | 49 | 53 | 61 | <0.001 | NA | <0.001 |
| AHI, events/h† | 12.0 (14.7) | 8.5 (12.2) | 8.6 (11.9) | 5.6 (9.6) | <0.001 | +0.19 (P < 0.001) | <0.001 |
| Minimum SaO2, %† | 84.0 (8.4) | 85.9 (6.1) | 85.6 (6.2) | 86.5 (5.4) | <0.001 | −0.11 (P < 0.001) | <0.001 |
| Sleep time, h* | 6.0 (1.1) | 6.0 (1.1) | 6.0 (1.1) | 6.0 (1.1) | n.s. | −0.03 (n.s.) | <0.10 |
| Sleep efficiency, %* | 81.2 (10.7) | 81.5 (10.3) | 81.5 (10.3) | 81.9 (10.5) | n.s. | −0.02 (n.s.) | n.s. |
| % time in REM* | 19.1 (6.8) | 19.6 (6.8) | 19.5 (7.1) | 19.1 (6.9) | <0.05 | −0.00 (n.s.) | n.s. |
| WASO, min† | 65 (46) | 63 (45) | 60 (42) | 58 (43) | <0.001 | +0.07 (P < 0.10) | <0.001 |
| Arousal index, h−1† | 19.4 (11.5) | 18.7 (10.8) | 19.3 (10.1) | 19.3 (10.3) | <0.10 | −0.02 (n.s.) | n.s. |
| % sleep < 90% saturation† | 4.3 (10.8) | 2.9 (9.1) | 3.4 (9.8) | 3.4 (11.4) | <0.01 | +0.10 (P < 0.001) | <0.10 |
| Race, %‡ | <0.01 | NA | NA | ||||
| African American | 6 | 9 | 10 | 10 | |||
| White | 88 | 84 | 84 | 84 | |||
| Other | 6 | 7 | 6 | 6 | |||
| Smoking status, %‡ | <0.001 | NA | NA | ||||
| Current | 6 | 8 | 9 | 16 | |||
| Former | 45 | 44 | 45 | 39 | |||
| Never | 49 | 49 | 45 | 45 | |||
| Prevalent disease, %‡ | |||||||
| Hypertension | 50 | 42 | 43 | 39 | <0.001 | NA | <0.001 |
| Diabetes | 8 | 8 | 8 | 8 | n.s. | NA | n.s. |
| CHD | 15 | 11 | 11 | 9 | <0.001 | NA | <0.001 |
| Stroke | 5 | 4 | 3 | 2 | <0.01 | NA | <0.001 |
| HF | 6 | 3 | 3 | 2 | <0.001 | NA | <0.001 |
| Any CVD§ | 20 | 14 | 14 | 11 | <0.001 | NA | <0.001 |
| Outcomes | |||||||
| Deaths | 385 | 301 | 315 | 286 | <0.001 | NA | <0.001 |
| Follow-up time, person-years | 14,171 | 14,461 | 14,534 | 14,659 | NA | NA | NA |
| Mortality rate per 1,000 person-years | 27.2 | 20.8 | 21.7 | 19.5 | NA | NA | <0.001 |
Definition of abbreviations: AHI = apnea–hypopnea index; BMI = body mass index; CHD = coronary heart disease; CVD = cardiovascular disease; HF = heart failure; NA = no analysis; n.s. = not significant; Q = quartile; WASO = wake after sleep onset.
Data presented as mean (SD) or %, unless otherwise noted. Bivariate correlation coefficients (Spearman’s rho) against event duration were calculated for continuous measures. Trends across quartiles were assessed by the Cochran-Armitage trend test or by linear regression against quartile number.
Differences among quartiles were assessed by one-way ANOVA when variances were equal.
Differences among quartiles were assessed by Wilcoxon/Kruskal-Wallis test when variances were unequal (Bartlett test).
Differences among quartiles in proportions were assessed by χ2 test.
Any prevalent CHD, stroke, or HF.