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More Impaired Dynamic Ventilatory Muscle Oxygenation in Congestive Heart Failure than in Chronic Obstructive Pulmonary Disease. J Clin Med 2019; 8:jcm8101641. [PMID: 31591369 PMCID: PMC6832638 DOI: 10.3390/jcm8101641] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Revised: 09/30/2019] [Accepted: 10/02/2019] [Indexed: 12/25/2022] Open
Abstract
Patients with chronic obstructive pulmonary disease (COPD) and congestive heart failure (CHF) often have dyspnea. Despite differences in primary organ derangement and similarities in secondary skeletal muscle changes, both patient groups have prominent functional impairment. With similar daily exercise performance in patients with CHF and COPD, we hypothesized that patients with CHF would have worse ventilatory muscle oxygenation than patients with COPD. This study aimed to compare differences in tissue oxygenation and blood capacity between ventilatory muscles and leg muscles and between the two patient groups. Demographic data, lung function, and maximal cardiopulmonary exercise tests were performed in 134 subjects without acute illnesses. Muscle oxygenation and blood capacity were measured using frequency-domain near-infrared spectroscopy (fd-NIRS). We enrolled normal subjects and patients with COPD and CHF. The two patient groups were matched by oxygen-cost diagram scores, New York Heart Association functional classification scores, and modified Medical Research Council scores. COPD was defined as forced expired volume in one second and forced expired vital capacity ratio ≤0.7. CHF was defined as stable heart failure with an ejection fraction ≤49%. The healthy subjects were defined as those with no obvious history of chronic disease. Age, body mass index, cigarette consumption, lung function, and exercise capacity were different across the three groups. Muscle oxygenation and blood capacity were adjusted accordingly. Leg muscles had higher deoxygenation (HHb) and oxygenation (HbO2) and lower oxygen saturation (SmO2) than ventilatory muscles in all participants. The SmO2 of leg muscles was lower than that of ventilatory muscles because SmO2 was calculated as HbO2/(HHb+HbO2), and the HHb of leg muscles was relatively higher than the HbO2 of leg muscles. The healthy subjects had higher SmO2, the patients with COPD had higher HHb, and the patients with CHF had lower HbO2 in both muscle groups throughout the tests. The patients with CHF had lower SmO2 of ventilatory muscles than the patients with COPD at peak exercise (p < 0.01). We conclud that fd-NIRS can be used to discriminate tissue oxygenation of different musculatures and disease entities. More studies on interventions on ventilatory muscle oxygenation in patients with CHF and COPD are warranted.
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Foster AJ, Platt MJ, Huber JS, Eadie AL, Arkell AM, Romanova N, Wright DC, Gillis TE, Murrant CL, Brunt KR, Simpson JA. Central-acting therapeutics alleviate respiratory weakness caused by heart failure-induced ventilatory overdrive. Sci Transl Med 2018; 9:9/390/eaag1303. [PMID: 28515334 DOI: 10.1126/scitranslmed.aag1303] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2016] [Accepted: 03/13/2017] [Indexed: 12/22/2022]
Abstract
Diaphragmatic weakness is a feature of heart failure (HF) associated with dyspnea and exertional fatigue. Most studies have focused on advanced stages of HF, leaving the cause unresolved. The long-standing theory is that pulmonary edema imposes a mechanical stress, resulting in diaphragmatic remodeling, but stable HF patients rarely exhibit pulmonary edema. We investigated how diaphragmatic weakness develops in two mouse models of pressure overload-induced HF. As in HF patients, both models had increased eupneic respiratory pressures and ventilatory drive. Despite the absence of pulmonary edema, diaphragmatic strength progressively declined during pressure overload; this decline correlated with a reduction in diaphragm cross-sectional area and preceded evidence of muscle weakness. We uncovered a functional codependence between angiotensin II and β-adrenergic (β-ADR) signaling, which increased ventilatory drive. Chronic overdrive was associated with increased PERK (double-stranded RNA-activated protein kinase R-like ER kinase) expression and phosphorylation of EIF2α (eukaryotic translation initiation factor 2α), which inhibits protein synthesis. Inhibition of β-ADR signaling after application of pressure overload normalized diaphragm strength, Perk expression, EIF2α phosphorylation, and diaphragmatic cross-sectional area. Only drugs that were able to penetrate the blood-brain barrier were effective in treating ventilatory overdrive and preventing diaphragmatic atrophy. These data provide insight into why similar drugs have different benefits on mortality and symptomatology, despite comparable cardiovascular effects.
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Affiliation(s)
- Andrew J Foster
- Department of Human Health and Nutritional Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Mathew J Platt
- Department of Human Health and Nutritional Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Jason S Huber
- Department of Human Health and Nutritional Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Ashley L Eadie
- Department of Pharmacology, Dalhousie Medicine, Saint John, New Brunswick E2L 4L5, Canada
| | - Alicia M Arkell
- Department of Human Health and Nutritional Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Nadya Romanova
- Department of Human Health and Nutritional Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - David C Wright
- Department of Human Health and Nutritional Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Todd E Gillis
- Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Coral L Murrant
- Department of Human Health and Nutritional Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Keith R Brunt
- Department of Pharmacology, Dalhousie Medicine, Saint John, New Brunswick E2L 4L5, Canada.
| | - Jeremy A Simpson
- Department of Human Health and Nutritional Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
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Tanaka T, Basoudan N, Melo LT, Wickerson L, Brochard LJ, Goligher EC, Reid WD. Deoxygenation of inspiratory muscles during cycling, hyperpnoea and loaded breathing in health and disease: a systematic review. Clin Physiol Funct Imaging 2017; 38:554-565. [PMID: 28940670 DOI: 10.1111/cpf.12473] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2017] [Accepted: 08/28/2017] [Indexed: 11/26/2022]
Abstract
Assessing inspiratory muscle deoxygenation and blood flow can provide insight into anaerobic stress, recruitment strategies and mechanisms of inspiratory muscle limitation. Therefore, this review aimed to synthesize measurements of inspiratory muscle oxyhaemoglobin (O2 Hb), deoxyhaemoglobin (HHb), blood volume and flow of the inspiratory muscles acquired via near-infrared spectroscopy (NIRS) during cycling, hyperpnoea and loaded breathing in healthy non-athletes, healthy athletes and patients with chronic obstructive pulmonary disease (COPD) or chronic heart failure (CHF). Searches were performed on Medline and Medline in-process, EMBASE, Central, Sportdiscus, PubMed and Compendex. Reviewers independently abstracted articles and assessed their quality using the modified Downs and Black checklist. Of the 644 articles identified, 21 met the inclusion criteria. Studies evaluated non-athletes (n = 9), athletes (n = 5), COPD (n = 2) and CHF (n = 5). The sample was 90% male and 73% were non-athletes and athletes. Interventions included cycle ergometry, hyperpnoea, loaded breathing, elbow flexor loading and combined loaded breathing and ergometry. Athletes and patients with CHF or COPD demonstrated deoxygenation of inspiratory accessory muscles that was often an opposite or exaggerated pattern compared to non-athletes. O2 Hb decreased and HHb increased significantly in inspiratory muscles during cycle ergometry and loaded breathing with accentuated changes during combined ergometry and loaded breathing. During different regimens of hyperpnoea or loaded breathing, comparisons of inspiratory muscles demonstrated that the sternocleidomastoid deoxygenated more than the intercostals, parasternals or scalenes. Evaluating inspiratory muscle deoxygenation via NIRS can inform mechanisms of inspiratory muscle limitation in non-athletes, athletes and patients with CHF or COPD.
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Affiliation(s)
- Takako Tanaka
- Department of Cardiopulmonary Rehabilitation Science, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan.,Department of Physical Therapy, University of Toronto, Toronto, ON, Canada
| | - Nada Basoudan
- College of Health and Rehabilitation Sciences, Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia
| | - Luana T Melo
- Department of Physical Therapy, University of Toronto, Toronto, ON, Canada
| | - Lisa Wickerson
- Department of Physical Therapy, University of Toronto, Toronto, ON, Canada
| | - Laurent J Brochard
- Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, ON, Canada.,Keenan Centre for Biomedical Research, Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, ON, Canada.,Department of Medicine, University of Toronto, Toronto, ON, Canada
| | - Ewan C Goligher
- Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, ON, Canada.,Department of Medicine, Division of Respirology, University Health Network and Mount Sinai Hospital, Toronto, ON, Canada
| | - W Darlene Reid
- Department of Physical Therapy, University of Toronto, Toronto, ON, Canada.,Toronto Rehabilitation Institute, University Hospital Network, Toronto, ON, Canada
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Exercise Dosing and Prescription-Playing It Safe: Dangers and Prescription. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1000:357-387. [DOI: 10.1007/978-981-10-4304-8_19] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Cross TJ, Sabapathy S, Beck KC, Morris NR, Johnson BD. The resistive and elastic work of breathing during exercise in patients with chronic heart failure. Eur Respir J 2011; 39:1449-57. [PMID: 22034652 DOI: 10.1183/09031936.00125011] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Patients with heart failure (HF) display numerous derangements in ventilatory function, which together serve to increase the work of breathing (W(b)) during exercise. However, the extent to which the resistive and elastic properties of the respiratory system contribute to the higher W(b) in these patients is unknown. We quantified the resistive and elastic W(b) in patients with stable HF (n = 9; New York Heart Association functional class I-II) and healthy control subjects (n = 9) at standardised levels of minute ventilation (V'(E)) during graded exercise. Dynamic lung compliance was systematically lower for a given level of V'(E) in HF patients than controls (p<0.05). HF patients displayed slightly higher levels of inspiratory elastic W(b) with greater amounts of ventilatory constraint and resistive W(b) than control subjects during exercise (p<0.05). Our data indicates that the higher W(b) in HF patients is primarily due to a greater resistive, rather than elastic, load to breathing. The greater resistive W(b) in these patients probably reflects an increased hysteresivity of the airways and lung tissues. The marginally higher inspiratory elastic W(b) observed in HF patients appears related to a combined decrease in the compliances of the lungs and chest wall. The clinical and physiological implications of our findings are discussed.
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Affiliation(s)
- Troy J Cross
- Division of Cardiovascular Diseases, Mayo Clinic, Rochester, MN, USA.
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Hamaoka T, McCully KK, Quaresima V, Yamamoto K, Chance B. Near-infrared spectroscopy/imaging for monitoring muscle oxygenation and oxidative metabolism in healthy and diseased humans. JOURNAL OF BIOMEDICAL OPTICS 2007; 12:062105. [PMID: 18163808 DOI: 10.1117/1.2805437] [Citation(s) in RCA: 222] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Near-infrared spectroscopy (NIRS) was initiated in 1977 by Jobsis as a simple, noninvasive method for measuring the presence of oxygen in muscle and other tissues in vivo. This review honoring Jobsis highlights the progress that has been made in developing and adapting NIRS and NIR imaging (NIRI) technologies for evaluating skeletal muscle O(2) dynamics and oxidative energy metabolism. Development of NIRS/NIRI technologies has included novel approaches to quantification of the signal, as well as the addition of multiple source detector pairs for imaging. Adaptation of NIRS technology has focused on the validity and reliability of NIRS measurements. NIRS measurements have been extended to resting, ischemic, localized exercise, and whole body exercise conditions. In addition, NIRS technology has been applied to the study of a number of chronic health conditions, including patients with chronic heart failure, peripheral vascular disease, chronic obstructive pulmonary disease, varying muscle diseases, spinal cord injury, and renal failure. As NIRS technology continues to evolve, the study of skeletal muscle function with NIRS first illuminated by Jobsis continues to be bright.
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Affiliation(s)
- Takafumi Hamaoka
- National Institute of Fitness and Sports, Department of Exercise Science, Shiromizu 1, Kanoya, 891-2393 Japan.
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Torchio R, Gulotta C, Greco-Lucchina P, Perboni A, Avonto L, Ghezzo H, Milic-Emili J. Orthopnea and tidal expiratory flow limitation in chronic heart failure. Chest 2006; 130:472-9. [PMID: 16899847 DOI: 10.1378/chest.130.2.472] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND Tidal expiratory flow limitation (FL) is common in patients with acute left heart failure and contributes significantly to orthopnea. Whether tidal FL exists in patients with chronic heart failure (CHF) remains to be determined. PURPOSES To measure tidal FL and respiratory function in CHF patients and their relationships to orthopnea. METHODS In 20 CHF patients (mean [+/- SD] ejection fraction, 23 +/- 8%; mean systolic pulmonary artery pressure [sPAP], 46 +/- 18 mm Hg; mean age, 59 +/- 11 years) and 20 control subjects who were matched for age and gender, we assessed FL, Borg score, spirometry, maximal inspiratory pressure (Pimax), mouth occlusion pressure 100 ms after the onset of inspiratory effort (P(0.1)), and breathing pattern in both the sitting and supine positions. The Medical Research Council score and orthopnea score were also determined. RESULTS In the sitting position, tidal FL was absent in all patients and healthy subjects. In CHF patients, Pimax was reduced, and ventilation and P(0.1)/Pimax ratio was increased relative to those of control subjects. In the supine position, 12 CHF patients had FL and 18 CHF patients claimed orthopnea with a mean Borg score increasing from 0.5 +/- 0.7 in the sitting position to 2.7 +/- 1.5 in the supine position in CHF patients. In contrast, orthopnea was absent in all control subjects. The FL patients were older than the non-FL patients (mean age, 63 +/- 8 vs 53 +/- 12 years, respectively; p < 0.03). In shifting from the seated to the supine position, the P(0.1)/Pimax ratio and the effective inspiratory impedance increased more in CHF patients than in control subjects. The best predictors of orthopnea in CHF patients were sPAP, supine Pimax, and the percentage change in inspiratory capacity (IC) from the seated to the supine position (r(2) = 0.64; p < 0.001). CONCLUSIONS In sitting CHF patients, tidal FL is absent but is common supine. Supine FL, together with increased respiratory impedance and decreased inspiratory muscle force, can elicit orthopnea, whom independent indicators are sPAP, supine Pimax and change in IC percentage.
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Affiliation(s)
- Roberto Torchio
- Fisiopatologia Respiratoria, Ospedale San Luigi Gonzaga, Orbassano, Turin, Italy.
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Hart N, Kearney MT, Pride NB, Green M, Lofaso F, Shah AM, Moxham J, Polkey MI. Inspiratory muscle load and capacity in chronic heart failure. Thorax 2004; 59:477-82. [PMID: 15170028 PMCID: PMC1747026 DOI: 10.1136/thx.2003.007724] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
BACKGROUND Although breathlessness is common in chronic heart failure (CHF), the role of inspiratory muscle dysfunction remains unclear. We hypothesised that inspiratory muscle endurance, expressed as a function of endurance time (Tlim) adjusted for inspiratory muscle load and inspiratory muscle capacity, would be reduced in CHF. METHODS Endurance was measured in 10 healthy controls and 10 patients with CHF using threshold loading at 40% maximal oesophageal pressure (Poes(max)). Oesophageal pressure-time product (PTPoes per cycle) and Poes(max) were used as indices of inspiratory muscle load and capacity, respectively. RESULTS Although Poes(max) was slightly less in the CHF group (-117.7 (23.6) v -100.0 (18.3) cm H(2)O; 95% CI -37.5 to 2.2 cm H(2)O, p = 0.1), Tlim was greatly reduced (1800 v 306 (190) s; 95% CI 1368 to 1620 s, p<0.0001) and the observed PTPoes per cycle/Poes(max) was increased (0.13 (0.05) v 0.21 (0.04); 95% CI -0.11 to -0.03, p = 0.001). Most of this increased inspiratory muscle load was due to a maladaptive breathing pattern, with a reduction in expiratory time (3.0 (5.8) v 1.1 (0.3) s; 95% CI 0.3 to 3.5 s, p = 0.03) accompanied by an increased inspiratory time relative to total respiratory cycle (Ti/Ttot) (0.43 (0.14) v 0.62 (0.07); 95% CI -0.3 to -0.1, p = 0.001). However, log Tlim, which incorporates the higher inspiratory muscle load to capacity ratio caused by this altered breathing pattern, was >/=85% predicted in seven of 10 patients. CONCLUSIONS Although a marked reduction in endurance time was observed in CHF, much of this reduction was explained by the increased inspiratory muscle load to capacity ratio, suggesting that the major contributor to task failure was a maladaptive breathing pattern rather than impaired inspiratory muscle endurance.
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Affiliation(s)
- N Hart
- Respiratory Muscle Laboratory, Royal Brompton Hospital, London, UK.
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King L. The effects of resistance exercise on skeletal muscle abnormalities in patients with advanced heart failure. PROGRESS IN CARDIOVASCULAR NURSING 2002; 16:142-51. [PMID: 11684905 DOI: 10.1111/j.0889-7204.2001.00616.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Resistance exercise increases muscular strength and endurance, which prevents injuries associated with musculoskeletal disorders, favorably alters muscle fiber type distribution, and up-regulates the genetic expression of certain enzymes seen in dysfunctional skeletal muscles. Although the benefits of resistance exercise are well documented in the literature, this form of exercise is not routinely recommended for patients with heart failure for fear of symptom exacerbation, and because of poor understanding of how best to prescribe this type of exercise. Because muscle atrophy and deconditioning states are common findings in patients with heart failure, these patients stand to benefit substantially from resistance training because this type of physical activity results in functional adaptations in the neuromuscular system. This article addresses changes in skeletal muscle pathophysiology that occur in patients with heart failure and the potential role resistance training may play in reversing this sequela, and recommends a weight lifting exercise prescription for these patients.
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Affiliation(s)
- L King
- Naval Medical Center, San Diego, CA 92134-5000, USA
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Cahalin LP. Exercise training in heart failure: inpatient and outpatient considerations. AACN CLINICAL ISSUES 1998; 9:225-43. [PMID: 9633274 DOI: 10.1097/00044067-199805000-00006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Exercise training has become increasingly important in the treatment of heart failure patients. It has long been known that the exercise tolerance of a patient with heart failure is related to his or her morbidity and mortality. Recently, it has been proved that exercise training improves cardiorespiratory function, functional status, and psychosocial status of heart failure patients. It is unknown whether these improvements will improve morbidity and mortality but quality of life appears to be enhanced. Subtle improvements in these areas may lead to a more satisfying and productive life for many heart failure patients. However, further investigation of the specific effects of such improvements is needed.
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Affiliation(s)
- L P Cahalin
- Boston University, Sargent College of Allied Health Professions, Physical Therapy Department, MA 02215, USA
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Abstract
Oxidative metabolism is the dominant source of energy for skeletal muscle. Near-infrared spectroscopy allows the non-invasive measurement of local oxygenation, blood flow and oxygen consumption. Although several muscle studies have been made using various near-infrared optical techniques, it is still difficult to interpret the local muscle metabolism properly. The main findings of near-infrared spectroscopy muscle studies in human physiology and clinical medicine are summarized. The advantages and problems of near-infrared spectroscopy measurements, in resting and exercising skeletal muscles studies, are discussed through some representative examples.
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Affiliation(s)
- M Ferrari
- Department of Biomedical Sciences and Technologies, University of L'Aquila, Italy
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Mancini D, Donchez L, Levine S. Acute unloading of the work of breathing extends exercise duration in patients with heart failure. J Am Coll Cardiol 1997; 29:590-6. [PMID: 9060898 DOI: 10.1016/s0735-1097(96)00556-6] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
OBJECTIVES This study investigated whether maximal exercise performance can be improved by acutely decreasing the work of breathing in these patients. BACKGROUND Exertional dyspnea is a frequent limiting symptom in patients with heart failure. It may result from increased work of breathing. METHODS Fifteen patients with heart failure and nine age-matched normal subjects underwent two maximal exercise tests. Subjects exercised twice in randomized, single-blind manner using room air (RA) and a 79% helium/21% oxygen mixture (He). Respiratory gas analysis, Borg scale recordings of perceived dyspnea and near infrared spectroscopy of an accessory respiratory muscle were obtained during exercise. RESULTS In normal subjects there was no significant difference in peak oxygen uptake (Vo2) ([mean +/- SD] RA 38 +/- 8 vs. He 35 +/- 7 ml/kg per min), exercise duration (RA 724 +/- 163 vs. He 762 +/- 123 s) or peak minute ventilation (RA 97 +/- 27 vs. He 97 +/- 28 liters/min, all p = NS). Only three of nine control subjects thought that exercise with the He mixture was subjectively easier. In contrast, patients with heart failure exercised an average of 146 s longer with the He mixture (RA 868 +/- 293 vs. He 1,014 +/- 338, p < 0.01). Peak Vo2 (RA 19 +/- 4 vs. He 18 +/- 5 ml/kg per min) and peak minute ventilation (RA 53 +/- 12 vs. He 53 +/- 15 liters/min) were unchanged (both p = NS). The respiratory quotient at peak exercise was lower with the He mixture (RA 1.05 +/- 0.08 vs. He 0.98 +/- 0.06, p < 0.05). Thirteen of the 15 patients thought that exercise with the He mixture was subjectively easier (p < 0.02 vs. control group). CONCLUSIONS In patients with heart failure, pulmonary factors, including respiratory muscle work and airflow turbulence, contribute to limiting exercise performance. Therapeutic interventions aimed at attenuating work of breathing may be beneficial.
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Affiliation(s)
- D Mancini
- Division of Circulatory Physiology, Columbia Presbyterian Medical Center, New York, New York 10032, USA
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