Summary This review tries to answer two main questions: (i) What are the neurophysiological underpinnings of the most commonly selected cluster descriptors which define the qualitative dimension of ...dyspnea in patients? (ii) How do mechanical constraints affect dyspnea? (iii) Do obstructive and restrictive lung diseases share some common underlying mechanisms? Qualitative dimensions of dyspnea, which allude to increased respiratory work/effort breathing, reflect a harmonious coupling between increased respiratory motor output and lung volume displacement in healthy subjects. Descriptors that allude to unsatisfied inspiration are the dominant qualitative descriptors in patients with a variety of respiratory diseases. It is possible that sensory feedback from a multitude of mechanoreceptors throughout the respiratory system (in the muscle, chest wall, airways and lung parenchyma) collectively convey information to the consciousness that volume/flow or chest wall displacement is inadequate for the prevailing respiratory drive. The data would lend support to the idea that: (i) an altered afferent proprioceptive peripheral feedback signals that ventilatory response is inadequate to the prevailing motor drive, reflecting neuromechanical uncoupling (NMU), (ii) mechanical constraints on volume expansion (dynamic restriction) play a pivotal role in dyspnea causation in patients with a variety of either obstructive or restrictive respiratory disorders, and (iii) all of the physiological adaptations that optimize neuromechanical coupling in obstructive and restrictive disorders are seriously disrupted so that an NMU underpins cluster descriptors of dyspnea which are similar in obstructed and in restricted patients.
Pursed-lip breathing (PLB) is a strategy often spontaneously employed by patients with COPD during distress situations. Whether and to what extent PLB affects operational lung volume is not known. ...Also, conflicting reports deal with PLB capability of decreasing breathlessness.
Twenty-two patients with mild-to-severe COPD were studied. Volumes of chest wall (CW) compartments (rib cage RC and abdomen) were assessed using an optoelectronic plethysmograph. Dyspnea was assessed by a modified Borg scale.
Compared to spontaneous breathing, patients with PLB exhibited a significant reduction (mean ± SD) in end-expiratory volume of the CW (Vcw) Vcwee; − 0.33 ± 0.24 L, p < 0.000004, and a significant increase in end-inspiratory Vcw (Vcwei; + 0.32 ± 0.43 L, p < 0.003). The decrease in Vcwee, mostly due to the decrease in end-expiratory volume of the abdomen (Vabee) − 0.25 ± 0.21 L, p < 0.00002, related to baseline FEV1 (p < 0.02) and to the increase in expiratory time (Te) r2 = 0.49, p < 0.0003 and total time of the respiratory cycle (Ttot) r2 = 0.35, p < 0.004, but not to baseline functional residual capacity (FRC). Increase in tidal volume (Vt) of the chest wall (+ 0.65 ± 0.48 L, p < 0.000004) was shared between Vt of the abdomen (0.31 ± 0.23 L, p < 0.000004) and Vt of the rib cage (+ 0.33 ± 0.29 L, p < 0.00003). Borg score decreased with PLB (p < 0.04). In a stepwise multiple regression analysis, decrease in Vcwee accounted for 27% of the variability in Borg score at 99% confidence level (p < 0.008).
Changes in Vcwee related to baseline airway obstruction but not to hyperinflation (FRC). By lengthening of Te and Ttot, PLB decreases Vcwee and reduces breathlessness.
The role of nonrespiratory peripheral afferents in dyspnea perception has not been fully elucidated yet. Our hypothesis is that fatigue-induced activation of limb muscle metaboreceptors served by ...group IV fine afferent fibers may impact on respiratory effort perception. We studied 12 healthy subjects breathing against progressive inspiratory resistive loads (10, 18, 30, 40, and 90 cmH(2)O x l(-1) x s) before and after inducing low-frequency fatigue of quadriceps muscle by repeating sustained contractions at > or = 80% of maximal voluntary contraction. Subjects also underwent a sham protocol while performing two loaded breathing runs without muscle fatigue in between. During the loaded breathing, while subjects mimicked the quiet breathing pattern using a visual feedback, ventilation, tidal volume, respiratory frequency, pleural pressure swings, arterial oxygen saturation, end-tidal partial pressure of CO(2), and dyspnea by a Borg scale were recorded. Compared with prefatigue, limb muscle fatigue resulted in a higher increase in respiratory effort perception for any given ventilation, tidal volume, respiratory frequency, pleural pressure swings, end-tidal partial pressure of CO(2), and arterial oxygen saturation. No difference between the two runs was observed with the sham protocol. The present data support the hypothesis that fatigue of limb muscles increases respiratory effort perception associated with loaded breathing, likely by the activation of limb muscle metaboreceptors.
Summary Background Analysis of chest wall kinematics can contribute to identifying the reasons why some patients benefit from pursed-lip breathing (PLB). Material and methods We evaluated the ...displacement of the chest wall and its compartments, the rib cage and abdomen, by optoelectronic plethysmography (OEP), during supervised PLB maneuver in 30 patients with mild to severe chronic obstructive pulmonary disease (COPD). Results OEP showed two different patterns. A first pattern characterized the 19 most severely obstructed and hyperinflated patients in whom PLB decreased end-expiratory volumes of the chest wall and abdomen, and increased end-inspiratory volumes of the chest wall and rib cage. Deflation of the abdomen and inflation of the rib cage contributed to increasing tidal volume of the chest wall. The second pattern characterized 11 patients in whom, compared to the former group, PLB resulted in the following: (i) increased end-expiratory volume of the rib cage and chest wall, (ii) greater increase in end-inspiratory volume of the rib cage and abdomen, and (iii) lower tidal volume of the chest wall. In the patients as a whole changes in end-expiratory chest wall volume were related to change in Borg score ( r2 =0.5, p <0.00002). Conclusions OEP helps identifying the reason why patients with COPD may benefit from PLB at rest.
It is well known that the methods actually used to track thoraco-abdominal volume displacement have several limitations. This review evaluates the clinical usefulness of measuring chest wall ...kinematics by optoelectronic plethysmography OEP. OEP provides direct measurements (both absolute and its variations) of the volume of the chest wall and its compartments, according to the model of Ward and Macklem, without requiring calibration or subject cooperation. The system is non invasive and does not require a mouthpiece or nose-clip which may modify the pattern of breathing, making the subject aware of his breathing. Also, the precise assessment of compartmental changes in chest wall volumes, combined with pressure measurements, provides a detailed description of the action and control of the different respiratory muscle groups and assessment of chest wall dynamics in a number of physiological and clinical experimental conditions.
Background: Recent studies have shown weak associations among FEV
1 , bronchial hyperresponsiveness (BHR), sputum eosinophils, and sputum eosinophil cationic protein (ECP), suggesting that they are ...nonoverlapping quantities. The statistical method of factor analysis enables reduction of many parameters that characterize the disease to a few independent factors, with each factor grouping associated parameters.
Objective: The purpose of this study was to demonstrate, by using factor analysis, that reversible airway obstruction, BHR, and eosinophilic inflammation of the bronchial tree, as assessed by cytologic and biochemical analysis of sputum, may be considered separate dimensions that characterize chronic bronchial asthma.
Methods: Ninety-nine clinically stable patients with a previous diagnosis of asthma underwent spirometry, sputum induction, and histamine inhalation tests.
Results: Most patients were nonobstructed (FEV
1 , 91% ± 20%); a low level of bronchial reversibility (FEV
1 increase after β
2 -agonist, 7.8% ± 9.2%) and BHR (histamine PC
20 FEV
1 geometric mean, 0.98 mg/mL) were found. Sputum eosinophil differential count (12.4% ± 17.7%) and sputum ECP (1305 ± 3072 μg/mL) were in the normal range of our laboratory in 38 and 22 patients, respectively. Factor analysis selected 3 different factors, explaining 74.8% of variability. Measurements of airway function and age loaded on factor I, PC
20 FEV
1 and β
2 -response loaded on factor II, and sputum ECP and eosinophils loaded on factor III. Additional post hoc factor analyses provided similar results when the sample was divided into 2 subgroups by randomization, presence of airway obstruction, degree of BHR, percentage of sputum eosinophils, or concentration of sputum ECP.
Conclusions: We conclude that airway function, baseline BHR, and airway inflammation may be considered separate dimensions in the description of chronic asthma. Such evidence supports the utility of routine measurement of all these dimensions. (J Allergy Clin Immunol 1999;103:232-7.)
In many studies of patients with muscle weakness, chronic hypercapnia has appeared to be out of proportion to the severity of muscle disease, indicating that factors other than muscle weakness are ...involved in CO2 retention. In patients with COPD, the unbalanced inspiratory muscle loading-to-strength ratio is thought to trigger the signal for the integrated response that leads to rapid and shallow breathing and eventually to chronic hypercapnia. This mechanism, although postulated, has not yet been assessed in patients with muscular dystrophy.
Twenty consecutive patients (mean age, 47.6 years; range, 23 to 67 years) were studied: 11 patients with limb-girdle dystrophy, 3 with Duchenne muscular dystrophy, 1 with Charcot-Marie-Tooth syndrome, 1 with Becker muscular dystrophy, 1 with myotonic dystrophy, 1 with facioscapulohumeral dystrophy, and 2 with amyotrophic lateral sclerosis, without any respiratory complaints. Seventeen normal subjects matched for age and sex were studied as a control group.
Routine spirometry and arterial blood gases, maximal inspiratory and expiratory muscle pressures (MIP and MEP, respectively), and pleural pressure during maximal sniff test (Pplsn), were measured. Mechanical characteristics of the lung were assessed by evaluating lung resistance (RL) and dynamic elastance (Eldyn). Eldyn was assessed as absolute value and as percent of Pplsn; Eldyn (%Pplsn) indicates the elastic load per unit of inspiratory muscle force. Breathing pattern was assessed in terms of time (inspiratory time Ti; respiratory frequency Rf) and volume (tidal volume Vt) components of the respiratory cycle.
A rapid shallow breathing pattern, as indicated by a greater Rf/Vt ratio and a lower Ti, was found in study patients compared to control subjects. Eldyn was greater in study patients, while MIP, MEP, and Pplsn were lower. Paco2 inversely related to Vt, Ti, and Pplsn (p = 0.012, p = 0.019, and p = 0.002, respectively), whereas it was directly related to Rf, Rf/Vt, Eldyn, and Eldyn (%Pplsn) (p < 0.004 to p < 0.0001). Also Eldyn (%Pplsn) inversely related to Ti, and the latter positively related to Vt. In other words, increase in Eldyn (%Pplsn) was associated with decrease in Ti, and the latter was associated with lower Vt and greater Paco2. Mechanical and breathing pattern variables were introduced in a stepwise multiple regression that selected Eldyn (%Pplsn) (p < 0.0001; r2 = 0.62) as a unique independent predictor of Paco2.
The present study shows that in patients with neuromuscular disease, elastic load and respiratory muscle weakness are responsible for a rapid and shallow breathing pattern leading to chronic CO2 retention.
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