Department of Internal Medicine and Rehabilitation Science,Tohoku University Graduate School of Medicine, Sendai, JapanJapan
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Chronic obstructive pulmonary disease (COPD) is an impor-tant and a growing cause of morbidity and mortality world-wide. Cardiovascular, musculoskeletal, metabolic, and mental co-morbidities are considered to be part of the frequently prevalent non-pulmonary sequelae of the disease.
AND RESPIRATORY MEDICINE Open Journal PUBLISHERS Editorial New Ideas on Limitations to VO : Five Major 2max Determinants for VO 2max Masahiro Kohzuki, MD, PhD Department of Internal Medicine and Rehabilitation Science,Tohoku University Graduate School of Medicine, Sendai, Japan * *Corresponding author Masahiro Kohzuki, MD, PhD Department of Internal Medicine and Rehabilitation Science,Tohoku University Graduate School of Medicine, 1-1, Seiryo-cho, Aoba-ku, Sendai, Japan; Tel. 022-717-7351; Fax. 022-717-7355; E-mail: kohzuki@med.tohoku.ac.jp Article information th th th Received: August 5 , 2018; Accepted: August 8 , 2018; Published: August 8 , 2018 Cite this article Kohzuki M. New ideas on limitations to VO : Five major determinants for VO . . 2018; 5(1): e1-e2. doi: 10.17140/PRRMOJ-5-e010 Pulm Res Respir Med Open J 2max 2max hronic obstructive pulmonary disease (COPD) is an impor- VO2max is expressed either as an absolute rate in (for ex- tant and a growing cause of morbidity and mortality world- C ample) liters of oxygen per minute (L/min) or as a relative rate in wide. Cardiovascular, musculoskeletal, metabolic, and mental co- (for example) milliliters of oxygen per kilogram of body mass per morbidities are considered to be part of the frequently prevalent 1,2 minute (e.g., mL/(kg•min)). The latter expression is often used to non-pulmonary sequelae of the disease. Increasing evidence sug- compare the performance of endurance athletes and patients. gests that extra-pulmonary effects of COPD and airflow limitation are only poorly correlated.3 Waschki, et al. found that objectively Figure shows gas transport mechanisms for coupling cel- measured physical activity is the strongest predictor of all-cause lular (internal) to pulmonary (external) respiration. The gears rep- mortality in patients with COPD.
resent the functional interdependence of the physiological compo- nents of the system. Cardiac output, pulmonary diffusion capacity, The association between physical inactivity and poor out- oxygen carrying capacity, renal function and other peripheral limi- comes are well established for patients with pulmonary disease, 4-6 tations like muscle diffusion capacity, mitochondrial enzymes, and cardiac disease, chronic kidney disease. Patients with pulmonary capillary density are all examples of VO2max determinants. disease, cardiac disease, or renal disease typically engage in a low- er level of physical activity than do the general population, which can induce a catabolic state including reduced neuromuscular func- Figure. Gas Transport Mechanisms for Coupling Cellular to Pulmonary Respiration: Five Major Determinants for VO2max tioning, reduced exercise tolerance and reduced cardiorespiratory fitness (CRF).
CRF is an important consideration, in addition to phys- ical activity, as it is a strong predictor of mortality; low CRF pre- sents a particularly high risk of death compared to other common risk factors, such as diabetes, high cholesterol or hypertension.7 CR fitness is defined as the ability of the circulatory and respiratory systems to supply oxygen during sustained physical activity and is usually expressed as maximal oxygen uptake ( VO ) during 2max maximal exercise testing.8 In 2016, the American Heart Association published a scientific statement9 recommending that CRF, quan- tifiable as VO , be regularly assessed and utilized as a clinical 2max vital sign. This statement was based on mounting evidence that The large increase in O2 utilization by the muscles (QO2) lower CRF levels are associated with high risk of cardiovascular is achieved by increased extraction of O2 from the blood perfusing disease, all-cause mortality, and mortality rates stemming from var- the muscles, the dilatation of selected peripheral vascular beds, an ious types of cancers.
increase in cardiac output (stroke volume and heart rate), an in- cc Copyright 2018 by Kohzuki M. This is an open-access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0), which Pulm Res Respir Med Open J. 2018; 5(1): e1-e2. doi: 10.17140/PRRMOJ-5-e010 crease in pulmonary blood flow by recruitment and vasodilatation gest predictor of all-cause mortality in patients with COPD. Chest of pulmonary blood vessels, and finally, an increase in ventilation. 2011; 140: 331-342. doi: 10.1378/chest.10-2521 O is taken up ( VO ) from the alveoli in proportion to the pulmo- 2 2 nary blood flow and degree of O2 desaturation of hemoglobin in 5. Cacciatore F, Amarelli C, Ferrara N, et al. Protective effect of the pulmonary capillary blood. Metabolic acidosis in chronic kid- physical activity on mortality in older adults with advanced chronic ney disease (CKD) patients promote muscle protein wasting and heart failure: A prospective observational study. Eur J Prev Cardiol. protein-energy wasting (PEW) by increasing protein degradation10 2018: 2047487318790822. doi: 10.1177/2047487318790822 and reducing protein synthesis.11 As a result, maintenance of mus- cle mass is impaired in CKD patients with altered protein turno- 6. Beddhu S, Baird BC, Zitterkoph J, Neilson J, Greene T. Physical ver rates.12 Adding to sarcopenia, metabolic acidosis, protein-en- activity and mortality in chronic kidney disease (NHANES III). Clin ergy wasting, angiotensin II, myostatin overexpression in uremia J Am Soc Nephrol. 2009; 4, 1901-1906. doi: 10.2215/CJN.01970309 contribute the etiology for muscle wasting in CKD.13 Moreover, the drug erythropoietin (EPO) can boost VO by a significant 7. Blair SN, Sallis RE, Hutber A, Archer E. Exercise therapy the 2max amount in both humans and other mammals.14 public health message. Scand J Med Sci Sports. 2012; 22, 24-28. doi: 10.1111/j.1600-0838 COPD often coexists with other diseases (comorbid- ities such as heart disease, CKD, osteoporosis) that may have a 8. Caspersen CJ, Powell KE, Christenson GM. Physical activity, ex- significant impact on prognosis. Thirty-three percent of elderly ercise, and physical fitness: Definitions and distinctions for health- patients with heart failure had COPD and 25% of elderly patients related research. Public Health Rep. 1985; 100, 126-131. with COPD also had heart failure.15 This risk of comorbid disease can be increased by the sequelae of COPD; e.g., reduced physical 9. Ross R, Blair SN, Arena R, et al. Importance of assessing cardio- activity. As super-aged society has come, the number of persons respiratory fitness in clinical practice: A case for fitness as a clinical with multimorbidity and multiple disabilities (MMD)16 and their vital sign: A Scientific Statement from the American Heart Asso- needs of rehabilitation have increased rapidly more than we have ciation. Circulation. doi: 10.1161/CIR.0000000000000461 16 expected. VO2max offers the investigator the unique opportunity to study simultaneously the cellular, cardiovascular, ventilatory and 10. Caso G, Garlick PJ. Control of muscle protein kinetics by acid- metabolic systems’ responses under conditions of precisely con- base balance. Curr Opin Clin Nutr Metab Care. 2005 ; 8: 73-76. trolled stress. This is of significant practical importance because VO measured by cardiopulmonary exercise testing, provides 11. Bailey JL, Wang X, England BK. The acidosis of chronic 2max what is probably the most sensitive assessment of the effect of renal failure activates muscle proteolysis in rats by augmenting new therapy on function of any diseased organ system whose ma- transcription of genes encoding proteins of the ATP-dependent jor function is to couple pulmonary gas exchange to cellular res- Ubiquitin-proteasome pathway. J Clin Invest. 1996; 97: 1447-1453. piration. For example, it is important to determine whether new doi: 10.1172/JCI118566 medical, surgical, and rehabilitative procedures can effectively in- tervene to improve the gas transport capability of a diseased organ 12. Mitch WE. Influence of metabolic acidosis on nutrition. Am J system.