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Epidemic of Obesity

Epidemic of Obesity. Mayo Clinic Health Letter, Medical Essay, 1997. NHANES III, 28% of Overweight Adults, 27 < BMI < 31 ( ~ 19 Million). NHANES III, 36% of Obese, BMI > 31 ( ~ 22 Million). 33% of M-to-M Obese, 30 < BMI < 43. Prevalence of Breathlessness with Exertion

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Epidemic of Obesity

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  1. Epidemic of Obesity Mayo Clinic Health Letter, Medical Essay, 1997

  2. NHANES III, 28% of Overweight Adults, 27 < BMI < 31 (~ 19 Million) NHANES III, 36% of Obese, BMI > 31 (~ 22 Million) 33% of M-to-M Obese, 30 < BMI < 43 Prevalence of Breathlessness with Exertion in Overweight & Obese Individuals 40 35 30 25 Percent (%) 20 15 10 5 0 Sin, etal, ArchInternMed, 1996

  3. 10 8 6 RPB (Borg scale 0-10) 4 2 0 Obese without Breathlessness (n=8, BMI 36+5) Obese with Breathlessness (n=8, BMI 37+4) Intensity of Breathlessness on Exertion After 6 min of cycling at 60 W *

  4. . VO2 - Work Rate Relationship Woman 49 yr 163 cm 154 kg DOE . VO2 (Observed) Extreme Obesity 3 . VO2 (Predicted) 2 VO2 (L/min) . 1 0 0 20 40 60 80 100 120 Work Rate (W)

  5. Women VO2 (%Predicted) . Obese Without & With Breathlessness Cardiovascular Exercise Capacity Women Men 120 80 40 0 Obese Lean Obese Lean

  6. Lung Volume Subdivisions Lean Obese Mayo Clinic Health Letter, Medical Essay, 1997

  7. Obese FRC Obese RV MRI at Various Lung Volumes Obese TLC

  8. Absolute Volume (L) 6 4 2 0 Flow-Volume Loop in Extreme Obesity 8 49 yr 163 cm 154 kg DOE 4 Flow (L/sec) Flow (L/sec) 0 Volume below TLC (L) -4 0 1 2 3 4 Volume (L)

  9. Theoretical Effects of Chest Wall Obesity Rib cage fat Posterior subcutaneous abdominal fat Anterior subcutaneous abdominal fat Lean Obese LOAD LOAD Visceral fat Inspiratory ? Force

  10. 4 3 O2 Cost of Breathing (ml/L) 2 1 0 Obese without Breathlessness n=8, BMI 36+5 Obese with Breathlessness n=8, BMI 37+4 Work of Breathing *

  11. Obese with Breathlessness Obese without Breathlessness Relationship between Work of Breathing and Breathlessness 4 3 O2 Cost of Breathing (ml/L) 2 y = 0.20x + 1.46 R2 = 0.57 1 0 0 2 4 6 8 10 RPB (Borg scale 0-10)

  12. Obese without Breathlessness Obese with Breathlessness 5 4 3 O2 Cost of Breathing (ml/L) 2 y = 0.59x - 0.42 1 R2 = 0.62 0 0 2 4 6 8 Anterior Subcutaneous Abdominal Fat (kg) Work of Breathing and Fat Distribution

  13. Obesity of the Chest Wall

  14. Abdominal Fat Mayo Clinic Health Letter, Medical Essay, 1997

  15. Potential Mechanisms of Dyspnea during Exercise Air Hunger Corollary discharge from respiratory motor activity in brainstem respiratory centers + Chemoreceptor feedback Effort/Work Corollary discharge from cortical motor centers + Respiratory Mechanoreceptor feedback Chest Tightness Pulmonary receptor feedback Altered Respiratory Mechanics Increasing Respiratory Impedance -Low lung volume breathing -Decreased chest wall compliance -Expiratory flow limitation -Increased pulmonary resistance Obesity -Increased oxygen cost of breathing and increased abdominal fat distribution Without Dyspnea on Exertion With Dyspnea on Exertion

  16. Mahler, etal, AJRCCM, 1996

  17. Patient Specific Clusters Mahler, etal, AJRCCM, 1996

  18. Respiratory Sensations in Mild-to-Moderately Obese Women

  19. Summary • 1. Dyspnea on exertion is prevalent in mild-to-moderate obesity • 2. Shortness of breath on exertion does not appear to be associated with CV deconditioning • 3. There are significant obesity-related changes in respiratory mechanics at rest and during exercise in mild-to-moderate obesity • 4. Shortness of breath on exertion appears to be associated with an increased work of breathing and abdominal fat distribution • 5. Obesity-related changes in respiratory mechanics, O2 cost of breathing, and abdominal fat distribution appear to change respiratory muscle efferent and afferent signals and these changes give rise to the primary sensation of work or effort to breathe

  20. Thank You

  21. Potential Mechanisms of Dyspnea The word ‘dyspnea’ subsumes a variety of unpleasant respiratory perceptions described by terms such as chest tightness, excessive breathing effort, and air hunger. At least three separable ‘qualities’ of uncomfortable breathing sensations have been identified in the laboratory termed ‘Effort or work,’ ‘Air hunger,’ and ‘Tightness.’ ‘Effort or work’ of breathing is perceived when the work of breathing is increased by high minute ventilation (rate or tidal volume) or in the lab by external impedance to inspiration. ‘Air hunger’ is the conscious perception of the urge to breathe. It is described as ‘not getting enough air,’ ‘uncomfortable urge to breathe,’ and is the sensation felt at the end of a long breath hold. Subjects often comment that intense air hunger is a threatening or frightening sensation. ‘Chest tightness’ is specific to asthmatic bronchoconstriction.

  22. Study Details To examine the basic mechanism of breathing discomfort (dyspnea) in obesity, we will use a debriefing session and a modified dyspnea questionnaire of qualitative respiratory sensation descriptors to investigate the qualities of respiratory sensations and the mechanisms of breathing discomfort in obese subjects during exertion. We propose that the mechanism of this breathing discomfort is related to changes in respiratory muscle efferent and afferent signals associated with the increased oxygen cost of breathing, which is in turn associated with altered respiratory mechanics and fat distribution, and that these changes give rise to the primary sensation of work or effort to breathe rather than the sensations of air hunger or chest tightness. These techniques have not been attempted in obese subjects.

  23. Potential Applications for Identifying Types of Respiratory Sensation • Establish a specific diagnosis (e.g., a pts selection of descriptors may direct diagnostic testing) • To determine quality of discomfort ask the pt to note two to three statements that best describe dyspnea (similar to asking for characteristics and qualities of chest) • In pt with two concurrent diseases, selected descriptors may help identify which condition is the cause of dyspnea (e.g., ‘tightness of asthma from ‘work’ of COPD) • Distinguish progression of underlying disease from CV deconditioning secondary to disease process • Descriptor questionnaire may also be used to evaluate mechanisms whereby a specific intervention relieves dyspnea (e.g., asthma tightness from airways as well as work effort of Raw) Mahler etal AJRCCM, 1996

  24. Inspiratory Force Theoretical Effects of Chest Wall Obesity Lean Obese LOAD LOAD ?

  25. Women Men 120 80 VO2 (%Predicted) 40 . 0 Lean Obese Lean Obese

  26. 500 Obese with breathlessness Obese without breathlessness 400 y = 3.5x + 0.21 R2 = 0.99 300 VO2 (mL/min) y = 2.0x + 0.19 R2 = 0.99 200 . Eucapnic Voluntary Hyperpnea 100 Rest 0 0 20 40 60 80 . VE (L/min)

  27. Implications of Lung Volume on Airflow 12 8 4 Flow (L/sec) IC ERV 0 FRC -4 TLC RV -8 0 2 4 6 8 Volume (L)

  28. Addition to Figure 1: Functional Capacity vs Fitness Level . VO2 (%Pred) VO2 (%Pred) . . VO2 (ml/kg/min) 100 30 . 25 80 20 60 VO2 (ml/kg/min) 15 40 10 20 5 0 0 Maximal Exercise Rest Workload

  29. Lung Volume and Gas Distribution

  30. Ventilatory Limitations in Obesity Ventilatory Limitations in Patients with Chronic Airflow Limitation (CAL) Patients with Chronic Airflow Limitation (CAL) 8 8 4 4 Flow (L/s) Flow (L/s) 0 0 - - 4 4 4 4 2 2 Volume (L) Volume (L) Babb Rodarte Babb Rodarte etal etal JAP JAP & & MSSE MSSE 1991, 1992, and 1993 1991, 1992, and 1993 Lean Obese Mayo Clinic Health Letter, Medical Essay, 1997 Babb, DeLorey, etal JAP, Annals Int Med, RespPhysiolNeurobiology, Int J Obes 2002, 2003, 2004, 2005

  31. Ventilatory Limitations in Obesity Ventilatory Limitations in Patients with Chronic Airflow Limitation (CAL) Patients with Chronic Airflow Limitation (CAL) 8 8 4 4 Flow (L/s) Flow (L/s) 0 0 - - 4 4 4 4 2 2 Volume (L) Volume (L) Babb Rodarte Babb Rodarte etal etal JAP JAP & & MSSE MSSE 1991, 1992, and 1993 1991, 1992, and 1993 Lean Obese Mayo Clinic Health Letter, Medical Essay, 1997 Babb, DeLorey, etal JAP, Annals Int Med, RespPhysiolNeurobiology, Int J Obes 2002, 2003, 2004, 2005

  32. Absolute Volume (L) 6 4 2 0 Flow-Volume Loop in Extreme Obesity 8 49 yr 163 cm 154 kg DOE 4 Flow (L/sec) Flow (L/sec) 0 Volume below TLC (L) -4 0 1 2 3 4 Volume (L)

  33. Exercise Flow-Volume Loops 10 Expiration FVC Exercise 5 Rest 0 Flow (L/sec) -5 Inspiration -10 4 3 2 1 0 4 3 2 1 0 Volume (L)

  34. 8 49 yr 163 cm 154 kg DOE 4 Flow (L/sec) 0 Absolute Volume (L) -4 0 6 4 2 0 Volume (L)

  35. 12 VE (L/min) 8 . . 4 0 40 80 120 160 200 Flow (L/s) 4 0 60 3 40 -4 2 20 TLC RV -8 1 0 0 2 4 6 8 0 0 40 80 120 VOLUME (L) . VE (L/min) Exercise and Breathing Pattern 160 120 80 40 0 LOAD (W) Frequency (bpm) Tidal Volume (L)

  36. . Figure 1: VO2 - Work Rate Relationship Plot response side-by-side to predicted normal response VO2 (L/min) Observed . 3 Considerably more information is learned from CPET about CV fxn and Gx when the external work is known - cycle is better for this reason Linear relationship, independent of age, sex, or Ht. Predicted maximal work rate and VO2 displayed 2 1 Predicted Response 0 0 20 40 60 80 100 120 Work Rate (W)

  37. Addition to Figure 1: Functional Capacity vs Fitness Level . VO2 (%Pred) VO2 (%Pred) . . VO2 (ml/kg/min) 100 30 . 25 80 20 60 VO2 (ml/kg/min) 15 40 10 20 5 0 0 Maximal Exercise Rest Workload

  38. Altered Respiratory Mechanics Increasing Respiratory Impedance -Low lung volume breathing -Decreased chest wall compliance -Expiratory flow limitation -Increased pulmonary resistance Obesity -Increased oxygen cost of breathing and increased abdominal fat distribution Without Dyspnea on Exertion With Dyspnea on Exertion Potential Mechanisms of Dyspnea during Exercise Air Hunger Corollary discharge from respiratory motor activity in brainstem respiratory centers + Chemoreceptor feedback Effort/Work Corollary discharge from cortical motor centers + Respiratory Mechanoreceptor feedback Chest Tightness Pulmonary receptor feedback

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