Table 1.
Baseline Participant Characteristics in Quintiles of Heart Rate Recovery (HRR, bt/min)
| Variables | HRR≤5 | 6≤HRR≤10 | 11≤HRR≤15 | 16≤HRR≤22 | HRR≥23 | Total | P value |
|---|---|---|---|---|---|---|---|
| N (% of total) | 1151 (23.0%) | 1036 (20.7%) | 946 (18.9%) | 926 (18.5%) | 949 (18.9%) | 5008 | – |
| Demographics | |||||||
| Age (years) | 64.3±8.8 | 65.6±8.5* | 65.5±8.4* | 64.6±8.5 | 64.0±8.2 | 64.8±8.5 | <0.001 |
| Sex Male, n (% of quintile) | 613 (53.3%) | 530 (51.2%) | 482 (51.0%) | 437 (47.2%)* | 447 (47.1%)* | 2509 (50.1%) | 0.018 |
| BMI (kg/m2) | 28.1±6.2 | 29.2±6.3* | 29.1±6.1* | 29.3±6.4* | 29.0±6.6* | 28.9±6.3 | <0.001 |
| Race, Non-Hispanic White, n (%) | 674 (58.6%) | 730 (70.5%)* | 712 (75.3%)* | 668 (72.1%)* | 639 (67.3%)* | 3423 (68.4%) | <0.001 |
| Smoking status, n (% of quintile) | |||||||
| Former smoker | 616 (53.5%) | 604 (58.3%) | 597 (63.1%)* | 567 (61.2%)* | 594 (62.6%)* | 2978 (59.5%) | <0.001 |
| Current smoker | 535 (46.5%) | 432 (41.7%) | 349 (36.9%)* | 359 (38.8%)* | 355 (37.4%)* | 2030 (40.5%) | <0.001 |
| Smoking (pack-years) | 46±25 | 44±23 | 43±23 | 42±22* | 40±21* | 43±23 | <0.001 |
| Comorbidities, n (% of quintile) | |||||||
| Cardiovascular disease | 171 (14.9%) | 135 (13.0%) | 133 (14.1%) | 102 (11.0%)* | 80 (8.4%)* | 621 (12.4%) | <0.001 |
| Hypertension | 603 (52.4%) | 566 (54.6%) | 471 (49.8%) | 440 (47.5%) | 427 (45.0%)* | 2507 (50.1%) | <0.001 |
| Diabetes | 214 (18.6%) | 209 (20.2%) | 150 (15.9%) | 159 (17.2%) | 122 (12.9%)* | 854 (17.1%) | <0.001 |
| 6-min walk test | |||||||
| 6MWD (m) | 362.9±118.8 | 388.5±113.8* | 412.0±111.0* | 425.2±114.0* | 446.0±124.8* | 404.7±120.2 | <0.001 |
| HR pre-walk (bt/min) | 75±13 | 74±12 | 73±12* | 73±12* | 71±11* | 73±12 | <0.001 |
| SpO2 pre-walk (%) | 96.0±3.3 | 96.0±2.9 | 96.1±2.6 | 96.4±2.3* | 96.5±2.6* | 96.2±2.8 | <0.001 |
| HR end-of-walk (bt/min) | 86±17 | 94±16* | 98±16* | 102±15* | 112±16* | 98±18 | <0.001 |
| HR 1-min post (bt/min) | 87±17 | 86±16 | 85±15* | 83±15* | 79±15* | 84±16 | <0.001 |
| SpO2 end-of-walk (%) | 93.2±6.2 | 93.6±5.0 | 93.8±5.2 | 94.1±5.1* | 93.1±6.2 | 93.5±5.6 | 0.001 |
| SpO2 1-min post (%) | 95.6±4.2 | 95.9±3.5 | 96.1±3.4* | 96.6±3.1* | 96.8±2.8* | 96.2±3.5 | <0.001 |
| Pulmonary function | |||||||
| Post-BD FEV1%pred (%) | 75.6±24.6 | 76.9±24.9 | 79.8±23.9* | 80.7±22.9* | 83.9±22.6* | 79.2±24.0 | <0.001 |
| Post-BD FVC%pred (%) | 85.8±17.7 | 86.0±17.6 | 87.7±17.4 | 88.2±17.3* | 90.9±17.1* | 87.6±17.5 | <0.001 |
| Post-BD FEV1/FVC (%) | 66.3±15.2 | 66.9±15.5 | 68.3±14.3* | 69.1±13.4* | 70.0±13.2* | 68.0±14.5 | <0.001 |
| DLCO%pred (%) | 70.5±22.0 | 74.5±21.1* | 77.2±21.6* | 76.9±20.5* | 77.2±21.1* | 75.1±21.4 | <0.001 |
| Quantitative chest CT | |||||||
| Emphysema (%) | 1.8 (0.5–6.8) | 1.8 (0.5–5.9) | 1.6 (0.5–5.1) | 1.5 (0.5–4.7) | 1.2 (0.3–3.6)* | 1.5 (0.4–5.2) | <0.001 |
| Gas trapping (%) | 16.3 (6.9–32.9) | 14.3 (5.7–28.0) | 12.9 (6.3–27.9)* | 12.5 (5.5–28.0)* | 12.1 (5.3–23.2)* | 13.5 (5.9–28.4) | <0.001 |
| Pi10 (mm) | 2.36±0.62 | 2.28±0.57* | 2.24±0.57* | 2.22±0.53* | 2.20±0.55* | 2.27±0.57 | <0.001 |
| WA (%) | 51.2±8.6 | 50.6±8.2 | 49.9±8.4* | 49.3±8.1* | 48.8±8.3* | 50.0±8.4 | <0.001 |
| AWT (mm) | 1.06±0.23 | 1.05±0.22 | 1.03±0.22 | 1.01±0.21* | 0.99±0.21* | 1.03±0.22 | <0.001 |
Notes: Data are presented as mean±SD or median (25th and 75th percentiles), or number (percent). *P<0.05 (with Bonferroni correction) for comparison with individuals with HRR≤5 bt/min, obtained from one-way ANOVA or Kruskal–Wallis tests or z-test (for proportions).
Abbreviations: HRR, heart rate recovery; BMI, body mass index; SpO2, oxygen saturation by pulse oximeter; 6MWD, 6-minute walk distance; BD, bronchodilator; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; DLCO, diffusing capacity of the lungs for carbon monoxide; DLCO%pred, percentage of predicted DLCO, adjusted for haemoglobin concentration and altitude; CT, computed tomography; Pi10, square root wall area of a 10-mm perimeter airway; WA, segmental wall area percentage; AWT, segmental airway wall thickness.