A Quick and Practical Approach to Secure a Chronic Fatigue Syndrome Diagnosis: The Novel Functional Limitation Index
Abstract
:1. Introduction
2. Material and Methods
2.1. Study Group
- CFS group: Patients already diagnosed with a definitive CFS by other clinical specialists, following the Fukuda diagnostic criteria [5] (Appendix A). These patients had limited symptoms, including those mentioned above and were referred to our clinic for that reason. Many of them required a study to assess disabilities. Patients with doubtful or incomplete CFS diagnoses were not included.
- Healthy cohort: Healthy patients who wanted to collaborate, without any limiting disease or condition and who did not perform regular or scheduled physical activity. They were studied in the context of routine health checkups.
- Sportspeople/trained cohort: Healthy athlete patients at an amateur level, understood as such, who trained weekly for more than 8–10 h of medium–high intensity (Mitchell Classification) [4].
2.2. Study Protocol and Procedures
- Three minutes no-load pedaling warm-up.
- Maximum test with progressive load of 15 w/m until the end of the test (maximum O2 consumption, VO2 max).
- Rest of three minutes with rest on the bicycle or minimal pedaling, at the patient’s decision.
- Supramaximal test started at the power equivalent to 50% of the maximum power reached in the test with a progression of 15 w every 10 s, until the exhaustion of the patient (supramaximal O2 consumption, VO2 smax).
- Rest period, without pedaling, until the patient recovered completely.
2.3. Statistical Analysis
3. Results
4. Discussion
4.1. General Considerations
4.2. Cardiopulmonary Exercise Testing in CFS
4.3. CFS Pathophysiology
4.4. CFS and FLI Rationale
5. Limitations
6. Conclusions
Author Contributions
Funding
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Abbreviations
BR < 35% | Ventilatory reserve (maximum ventilation vs. voluntary ventilation VMV) |
EQO2 | O2 equivalent |
FEV1 | Forced Expiratory volume in one second (spirometry) |
FLI | Functional limitation index |
FVC | Forced Vital Capacity |
HR AT | Heart rate at the anaerobic threshold (VT1) |
HR M/T | Maximum heart rate achieved with respect to the theoretical maximum |
Pulse O2 | O2 pulse vs. heart rate (inotropic function) |
MVV | Maximum voluntary ventilation (FEV1*40, convention) |
VE | Ventilation |
V.ESTIM | Estimated ventilation. |
VO2m | Peak (maximum) O2 consumption |
VO2m/t | Peak O2 consumption reached compared with the theoretical |
VO2m/sm | Relationship between maximum O2 consumption and supramaximal (second peak) |
VO2sm/t | Supramaximal consumption (2 peak) vs. theoretical |
VO2sm/m | Supramaximal O2 consumption (second peak) vs. máximum (first peak) |
VE/VCO2 (EQ. CO2) | CO2 equivalent |
VO2/W | Relationship between O2 consumption and power |
Wmax | Peak (Maximum) power |
W m/t | Peak (Maximum) power compared with the theoretical |
W/K | Power to weight ratio |
Appendix A
Appendix A.1. Data (Prospectively) Recorded by Protocol in the Present Study
- −
- Age, gender.
- −
- Anthropometric Data: Weight, height, BMI, % fat, muscle and water, Fat/Muscle Ratio, BMI-Corrected.
- −
- Spirometric Data: FVC, FEV1, FEV1/FVC, FEV at 25.50 and 75%, classified later in the Muller graph.
- −
- Ergospirometric data: They were analyzed according to the 9 Wassermman graphs and all the parameters derived from them.
- VO2 peak, VO2 in AT (first threshold QR = 1), VO2 entry into the lactic anaerobic phase (QR = 1.3), VO2 entry into the alactic anaerobic phase (QR = 1.10), measured in Supramaximal VO2 (SM VO2) at the end of recovery.
- VO2 peak/VO2 SM
- FLI. Functional Limitation Index (VO2 peak/VO2 SM)/(VO2 SM/VO2 predicted)
- O2 pulse (VO2/HR) at AT and at peak effort.
- VO2/W ratio
- W peak and at each of the above thresholds
- Power/weight ratio
- CO2 production
- O2 and CO2 equivalents
- PTE of O2 and CO2
- VE peak
- MVV (FEV1*40)
- Ventilatory Reserve (BR, Breath Reserve) (VMV − VE peak)/VMV, in %
- Energy expenditure at rest, AT and peak effort
Appendix A.2. Fukuda et al., CFS Diagnostic Criteria (1994) [5]
- Persistent fatigue (at least six months) or intermittent, unexplained, recurring or with a defined onset, not resulting from recent efforts; does not improve with rest; leads to a noticeable reduction in the patient’s previous usual activity.
- Exclusion of other diseases that can cause chronic fatigue.
- Recent concentration or memory impairments.
- Odynophagia.
- Painful cervical or axillary lymph nodes.
- Myalgias.
- Polyarthralgias without signs of inflammation.
- Recently onset headaches or headaches with different characteristics from the usual ones.
- Non-refreshing sleep.
- Post-exertional malaise lasting more than 24 h.
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Variable | CFS+ | CFS− | p-Value |
---|---|---|---|
Gender (Female) | 85.2% | 25.5% | <0.001 |
Age | 46.2 (9.3) | 41.2 (13.8) | <0.001 |
Weight | 66.3 (12.9) | 77.3 (14.3) | <0.001 |
VO2m | 20.4 (6.3) | 38.0 (9.6) | <0.001 |
VO2m/t | 76.8 (16.7) | 114.8 (24.1) | 0.093 |
Wmax | 118.2 (33.4) | 220.86 (58.9) | <0.001 |
W m/t | 87.4 (19.0) | 122.9 (25.5) | <0.001 |
W/K | 87.4 (19.0) | 3.04 (0.7) | <0.001 |
FC M/T | 84.7 (9.8) | 93.0 (10.7) | <0.001 |
FC AT | 120.5 (20.7) | 137.5 (18.1) | <0.001 |
VO2/W | 11.38 (1.9) | 13.0 (1.7) | <0.001 |
VO2m/sm | 140.4 (31.2) | 114.3 (13.2) | <0.001 |
VO2sm/t | 57.1 (15.0) | 100.8 (25.2) | <0.001 |
FLI | 2.7 (1.26) | 1.2 (0.4) | <0.001 |
VO2sm/m | 0.7 (0.1) | 0.9 (0.0) | <0.001 |
VE | 46.1 (14.3) | 90.1 (25.1) | <0.001 |
EQO2 | 33.5 (5.5) | 31.5 (4.1) | <0.001 |
VE/VCO2 | 27.2 (5.3) | 24.8 (3.6) | <0.001 |
Pulse O2 | 9.0 (2.5) | 17.3 (4.9) | <0.001 |
VEF1 | 2.65 (0.7) | 3.7 (0.7) | <0.001 |
MVV | 70.5 (54.7) | 147.4 (30.1) | <0.001 |
V.ESTIM | 51.5 (12.1) | 85.4 (24.5) | <0.001 |
BR < 35% | 55.2 (12.3) | 37.9 (13.3) | <0.001 |
Variable | CFS+ Female | CFS+ Male | Healthy Female | Healthy Male | Trained Female | Trained Male | p-Value * |
---|---|---|---|---|---|---|---|
Age | 46.8 (8.9) | 42.8 (11.3) | 43.6 (9.4) | 46.1 (13.7) | 32.7 (10.3) | 36.1 (14.2) | <0.001 |
Weight | 64.6 (11.9) | 77.2 (14.4) | 61.3 (12.9) | 81.2 (12.0) | 59.4 (5.9) | 77.2 (11.4) | <0.001 |
VO2m | 19.3 (5.1) | 26.7 (8.5) | 28.6 (6.3) | 33.9 (5.7) | 42.3 (5.9) | 46.6 (7.4) | <0.001 |
VO2m/t | 77.0 (16.7) | 75.4 (16.5) | 104.6 (19.2) | 105.1 (17.1) | 148.0 (28.5) | 124.54 (23.0) | 0.350 |
Wmax | 109.5 (24.3) | 168.1 (35.5) | 147.9 (26.6) | 213.3 (38.5) | 200.5 (25.9) | 271.5 (38.6) | <0.001 |
W m/t | 87.8 (19.2) | 85.1 (18.6) | 118.9 (19.6) | 110.3 (22.7) | 155.5 (20.2) | 132.6 (24.8) | <0.001 |
W/K | 1.73 (0.4) | 2.27 (0.7) | 2.45 (0.5) | 2.67 (0.4) | 3.39 (0.4) | 3.6 (0.6) | <0.001 |
FC M/T | 83.9 (9,7) | 89.1 (9.4) | 94.5 (14.2) | 92.7 (7.3) | 92.4 (4.5) | 92.8 (12.6) | <0.001 |
FC AT | 121.5 (21.6) | 114.8 (14.8) | 129.0 (16.8) | 135.4 (17.9) | 142.6 (33.3) | 142.3 (13.9) | <0.001 |
VO2sm | 13.9 (4.3) | 22.1 (7.3) | 23.6 (6.3) | 29.9 (5.9) | 38.5 (5.3) | 42.8 (7.6) | <0.001 |
VO2m/sm | 143.5 (31.9) | 123.2 (19.1) | 123.1 (12.7) | 115.0 (14.9) | 109.0 (6.2) | 109.3 (9.3) | <0.001 |
VO2sm/t | 56.1 (14.9) | 62.6 (14.1) | 85.9 (19.0) | 91.4 (19.1) | 135.2 (23.1) | 112.9 (22.7) | <0.001 |
FLI | 2.84 (1.3) | 2.12 (0.8) | 1.52 (0.4) | 1.33 (0.4) | 0.83 (0.1) | 1.01 (0.27) | <0.001 |
VO2sm/m | 0.72 (0.1) | 0.82 (0.1) | 0.82 (0.1) | 0.88 (0.1) | 0.91 (0.0) | 0.92 (0.1) | <0.001 |
VE | 42.8 (11.9) | 65.3 (12.3) | 58.9 (12.5) | 87.9 (16.0) | 84.1 (13.9) | 110.2 (21.1) | <0.001 |
EQO2 | 33.8 (5.7) | 31.7 (3.8) | 33.6 (4.2) | 31.4 (4.0) | 32.9 (2.6) | 30.4 (3.9) | <0.001 |
VE/VCO2 | 27.9 (5.2) | 23.7 (4.1) | 26.0 (3.8) | 24.7 (2.9) | 24.3 (2.9) | 24.3 (4.1) | <0.001 |
Pulse O2 | 8.4 (1.8) | 12.8 (2.6) | 10.3 (1.9) | 17.4 (3.3) | 14.5 (2.1) | 21.5 (2.8) | <0.001 |
VEF1 | 2.51 (0.5) | 3.89 (0.6) | 2.77 (0.4) | 3.82 (0.6) | 3.01 (0.3) | 4.13 (0.6) | <0.001 |
MVV | 63.6 (51.3) | 147.7 (23.6) | 110.8 (16.1) | 152.8 (23.0) | 120.4 (13.7) | 165.3 (24.0) | <0.001 |
V.ESTIM | 48.4 (8.7) | 69.5 (12.8) | 62.2 (9.6) | 85.8 (13.8) | 39.3 (12.3) | 106.7 (13.9) | <0.001 |
BR < 35% | 55.2 (12.6) | 55.2 (10.5) | 46.3 (12.2) | 41.2 (11.0) | 29.7 (11.4) | 32.6 (13.2) | <0.001 |
Study Group | FLI Mean Z-Score (SD) | p-Value |
---|---|---|
Gender (all) | <0.001 | |
| 0.38 (1.07) −0.56 (0.52) | |
Health status | <0.001 | |
| 0.55 (1.02) −0.68 (0.35) | |
CFS + Gender | 0.006 | |
| 0.63 (1.05) 0.05 (0.67) | |
CFS – Gender | 0.072 | |
| 0.43 (0.43) 0.32 (0.32) | |
Training level | <0.001 * | |
| 0.55 (1.02) −0.54 (0.37) −0.88 (0.21) |
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Corbalán, J.A.; Feltes, G.; Silva, D.; Gómez-Utrero, E.; Núñez-Gil, I.J. A Quick and Practical Approach to Secure a Chronic Fatigue Syndrome Diagnosis: The Novel Functional Limitation Index. J. Clin. Med. 2023, 12, 7157. https://doi.org/10.3390/jcm12227157
Corbalán JA, Feltes G, Silva D, Gómez-Utrero E, Núñez-Gil IJ. A Quick and Practical Approach to Secure a Chronic Fatigue Syndrome Diagnosis: The Novel Functional Limitation Index. Journal of Clinical Medicine. 2023; 12(22):7157. https://doi.org/10.3390/jcm12227157
Chicago/Turabian StyleCorbalán, Juan Antonio, Gisela Feltes, Daniela Silva, Eduardo Gómez-Utrero, and Iván J. Núñez-Gil. 2023. "A Quick and Practical Approach to Secure a Chronic Fatigue Syndrome Diagnosis: The Novel Functional Limitation Index" Journal of Clinical Medicine 12, no. 22: 7157. https://doi.org/10.3390/jcm12227157