Table 1. Baseline Characteristics by Quartiles of Amplitude.
| Characteristic | Quartile of amplitude, counts/min | P valuea | |||
|---|---|---|---|---|---|
| 1: <2929.3 (n = 732) | 2: 2929.3 to <3552.1 (n = 733) | 3: 3552.1 to <4209.0 (n = 732) | 4: ≥4209.0 (n = 733) | ||
| Baseline characteristics | |||||
| Age, mean (SD), y | 78.1 (5.9) | 76.7 (5.4) | 75.7 (5.1) | 74.7 (4.8) | <.001 |
| White race, No. (%) | 658 (89.9) | 666 (90.9) | 666 (90.9) | 646 (88.1) | .24 |
| Educational level less than high school, No. (%) | 53 (7.2) | 32 (4.4) | 29 (4.0) | 43 (5.9) | .03 |
| Body mass index, mean (SD)b | 27.9 (4.2) | 27.3 (3.7) | 26.9 (3.7) | 26.7 (3.6) | <.001 |
| Geriatric Depression Scale score, mean (SD)c | 2.4 (2.5) | 1.8 (2.1) | 1.4 (1.9) | 1.4 (1.9) | <.001 |
| Current smoker, No. (%) | 16 (2.2) | 15 (2.0) | 13 (1.8) | 14 (1.9) | .32 |
| Alcohol use ≥14 drinks/wk, No. (%) | 35 (4.8) | 38 (5.2) | 38 (5.2) | 57 (7.8) | .001 |
| Caffeine intake, mean (SD), mg/d | 211.0 (234.4) | 235.3 (254.9) | 233.5 (235.0) | 267.5 (254.5) | <.001 |
| Physical Activity Scale for the Elderly score, mean (SD)d | 118.0 (66.7) | 139.8 (65.9) | 157.7 (70.9) | 172.3 (71.3) | <.001 |
| ≥1 IADL impairments, No. (%) | 269 (36.7) | 142 (19.4) | 103 (14.1) | 84 (11.5) | <.001 |
| Comorbidities, No. (%) | |||||
| Stroke | 40 (5.5) | 26 (3.5) | 22 (3.0) | 19 (2.6) | .02 |
| Hypertension | 412 (56.3) | 383 (52.3) | 344 (47.0) | 323 (44.1) | <.001 |
| Coronary heart disease | 253 (34.6) | 192 (26.2) | 186 (25.4) | 161 (22.0) | <.001 |
| Type 2 diabetes | 124 (16.9) | 96 (13.1) | 95 (13.0) | 72 (9.8) | .001 |
| Medication use, No. (%) | |||||
| Antidepressants | 75 (10.2) | 41 (5.6) | 56 (7.7) | 40 (5.5) | <.01 |
| Benzodiazepines | 41 (5.6) | 33 (4.5) | 28 (3.8) | 22 (3.0) | .09 |
| Sleep medication | 22 (3.0) | 12 (1.6) | 14 (1.9) | 11 (1.5) | .16 |
| Modified Mini-Mental State Examination score, mean (SD)e | 91.7 (7.3) | 93.3 (5.4) | 93.3 (5.1) | 93.2 (5.5) | <.001 |
| Nighttime sleep quality | |||||
| Total sleep time, mean (SD), h | 6.22 (1.53) | 6.53 (1.12) | 6.47 (1.10) | 6.41 (1.10) | <.001 |
| Sleep efficiency, mean (SD), % | 74.5 (15.5) | 79.5 (10.2) | 79.9 (9.9) | 79.1 (10.5) | <.001 |
| Apnea-hypopnea index, mean (SD)f | 19.7 (17.0) | 16.4 (14.5) | 16.8 (15.3) | 15.4 (13.3) | <.001 |
| Periodic limb movement index, mean (SD)g | 43.2 (41.6) | 35.0 (36.0) | 31.8 (34.2) | 31.8 (35.6) | <.001 |
Abbreviation: IADL, instrumental activities of daily living.
Calculated using χ2 tests for categorical variables, analysis of variance for normally distributed continuous variables, and Kruskal-Wallis tests for continuous variables with skewed distributions.
Calculated as weight in kilograms divided by square of height in meters.
Scores range from 0 to 15, with higher scores indicating higher depressive symptoms.
Scores range from 0 to 793, with higher scores indicating greater physical activity.
Scores range from 0 to 100, with higher scores indicating better cognitive functioning.
Measured as the number of apneas plus hypopneas per hour of sleep associated with a desaturation of at least 3%.
Indicates the frequency of periodic limb movements in sleep.