Giulia Innocenti Bruni

Effect of limb muscle fatigue on perception of respiratory effort in healthy subjects.

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.

The respiratory muscles in eucapnic obesity: Their role in dyspnea

Regular exercise appears to be one of the best predictors of successful weight maintenance. Although physical activity and exercise are important components in the prevention and treatment of obesity, many obese adults without coexisting disorders are unable to exercise due to dyspnea on exertion. As a result they may not participate in regular physical activity. Therefore exertional dyspnea in obese adults is also an obstacle to the prevention and treatment of obesity and coexisting comorbidities. The available data suggest that increased respiratory muscle force generation, and the concomitant increase in respiratory neural drive associated with increased ventilation are an important source of sensation of respiratory effort in obese subjects. Whether activity-related breathlessness is due to either abnormal respiratory mechanical factors (flow limitation and/or chest elastic loading) or the increased metabolic demand of locomotion in obesity, or both of these together, the available data indicate that intensity of dyspnea at any given ventilation and oxygen uptake does not increase in obese subjects as compared with normal weight control subjects. Does this mean that respiratory mechanical factors are unlikely to be contributory? Nonetheless, the component of metabolic cost of breathing may not be accounted for in the measured mechanical work of breathing because of the number of included complex variables. That a decrease in efficiency of the respiratory muscles during exercise contributes to dyspnea in hyperinflating obese subjects should not be disregarded.

Chest wall kinematics and breathlessness during unsupported arm exercise in COPD patients

We hypothesised that chest wall displacement inappropriate to increased ventilation contributes to dyspnoea more than dynamic hyperinflation or dyssynchronous breathing during unsupported arm exercise (UAE) in COPD patients. We used optoelectronic plethysmography to evaluate operational volumes of chest wall compartments, the upper rib cage, lower rib cage and abdomen, at 80% of peak incremental exercise in 13 patients. The phase shift between the volumes of upper and lower rib cage (RC) was taken as an index of RC distortion. With UAE, no chest wall dynamic hyperinflation was found; sometimes the lower RC paradoxed inward while in other patients it was the upper RC. Phase shift did not correlate with dyspnoea (by Borg scale) at any time, and chest wall displacement was in proportion to increased ventilation. In conclusions neither chest wall dynamic hyperinflation nor dyssynchronous breathing per se were major contributors to dyspnoea. Unlike our prediction, chest wall expansion and ventilation were adequately coupled with each other.

Impact of a Rehabilitation Program on Dyspnea Intensity and Quality in Patients with Chronic Obstructive Pulmonary Disease

Background: It has yet to be determined whether the language of dyspnea responds to pulmonary rehabilitation programs (PRP). Objective: We tested the hypothesis that PRP affect both the intensity and quality of exercise-induced dyspnea in patients with chronic obstructive pulmonary disease (COPD). Methods: We studied 49 patients equipped with a portable telemetric spiroergometry device during the 6-min walking test before and 4 weeks after PRP. In a first screening visit, appropriate verbal descriptors of dyspnea were chosen that patients were familiar with during daily living activities. Tidal volume, respiratory frequency, inspiratory capacity, inspiratory reserve volume (IRV) and dyspnea intensity were evaluated by a modified Borg scale every minute during the test. Results: Qualitative descriptors of dyspnea were defined by three different sets of cluster descriptors (a–c) at the end of the exercise test, before and after PRP: a – work/effort (W/E); b – inspiratory difficulty (ID) and chest tightness (CT), and c – W/E, ID and/or CT. The three language subgroups exhibited similar lung function at baseline, and similar rating of dyspnea and ventilatory changes during exercise. The rehabilitation program shifted the Borg-IRV relationship (less Borg at any given IRV) towards the right without modifying the set of descriptors in most patients. Conclusions: Rehabilitation programs allowed patients to tolerate a greater amount of restrictive dynamic ventilatory defect by modifying the intensity, but not necessarily the quality of dyspnea.

Obstructive sleep apnea (OSA) does not affect ventilatory and perceptual responses to exercise in morbidly obese subjects.

We have tested the hypothesis that high mass loading effects and obstructive sleep apnea (OSA) constrain the ventilatory response to exercise in morbidly obese subjects as compared to their counterparts without OSA. Fifteen obese patients with (8) and without OSA and 12 lean healthy subjects performed incremental cycle exercise. The functional evaluation included ventilation, oxygen uptake, carbon dioxide production, end-expiratory-lung-volumes (EELV), inspiratory capacity, heart rate, dyspnea and leg effort (by a modified Borg scale). Changes in ventilation and dyspnea per unit changes in work rate and metabolic variables were similar in the three groups. Breathing pattern and heart rate increased from rest to peak exercise similarly in the three groups. Leg effort was the prevailing symptom for stopping exercise in most subjects. In conclusion, OSA does not limit exercise capacity in morbidly obese subjects. Ventilation contributes to exertional dyspnea similarly as in lean subjects and in obese patients regardless of OSA.

Airway hyperresponsiveness with chest strapping : A matter of heterogeneity or reduced lung volume?

Chest wall strapping has been recently shown to be associated with an increase in airway responsiveness to methacholine. To investigate whether this is the result of the decreased lung volume or an increased heterogeneity due to chest wall distortion, ten healthy volunteers underwent a methacholine challenge at control conditions and after selective strapping of the rib cage, the abdomen or the whole chest wall resulting in similar decrements of functional residual capacity and total lung capacity but causing different distribution of the bronchoconstrictor. Methacholine during strapping reduced forced expiratory flow, dynamic compliance, and reactance at 5Hz and increased pulmonary resistance and respiratory resistance at 5Hz that were significantly greater than at control and associated with a blunted bronchodilator effect of the deep breath. However, no significant differences were observed between selective and total chest wall strapping, suggesting that the major mechanism for increasing airway responsiveness with chest wall strapping is the breathing at low lung volume rather than regional heterogeneities.

Thoraco-abdominal motion/displacement does not affect dyspnea following exercise training in COPD patients

PURPOSE The interrelations among chest wall kinematics (displacement and configuration), ventilatory profile and dyspnea relief following cycle exercise training (EXT) have not been systematically evaluated in hyperinflated chronic obstructive pulmonary disease (COPD) patients. We hypothesize that a decrease in ventilation affects dyspnea relief, regardless of the changes in chest wall kinematics. METHODS Fourteen patients were studied before and after 24-session exercise training program. We evaluated the volumes of chest wall and its compartments (rib cage, and abdomen) using optoelectronic plethysmography. RESULTS At iso-time EXT (i) reduced ventilation, respiratory frequency and dyspnea (by Borg scale), mildly improved rib cage configuration, but left operational volumes unchanged; (ii) Borg was much smaller for any comparable inspiratory reserve volume (IRVcw), and a decrease in IRVcw was tolerated much better for any given Borg. CONCLUSIONS Regardless of the changes in chest wall kinematics, a decrease in ventilation attenuates dyspnea following EXT.

Use of Optoelectronic Plethysmography in Pulmonary Rehabilitation and Thoracic Surgery

OEP system is an optoelectronic device able to track the three-dimensional co-ordinates of a number of reflecting markers placed non-invasively on the skin of the subject [1-4]. A varia‐ ble number of markers (89 in the model used for respiratory acquisition in seated position) is placed on the thoraco-abdominal surface; each marker is a half plastic sphere coated with a reflective paper. Two TV Sensors 2008, cameras are needed to reconstruct the X-Y-Z coordinates of each marker, so for the seated position six cameras are required. Each camera is equipped with an infra-red ring flash. This source of illumination, which is not visible, is not disturbing and lets the system also operate in the dark. The infra-red beam, emitted by the flashes, is reflected by each marker and acquired by the cameras with a maximal sampling rate of 100 Hz. The signal is then processed by a PC board able to combine the signal coming from the cameras and to return, frame by frame, the three-dimensional co-ordinates of each marker. The process is simultaneously carried out for the six TV cameras needed for the seated respiratory model. Acquired data need a further operation called ‘tracking’ that is necessary to exclude possible phantom reflections and/or to reconstruct possible lost mark‐ ers (this could happens sometimes during very fast manoeuvres such exercise); at this time the obtained files contain the X-Y-Z co-ordinates of each marker during the recorded ma‐ noeuvre, then data are stored on the PC hard disk. The spatial accuracy for each marker’s position is about 0.2 mm [1]. Volumes for each compartment is calculated by constructing a triangulation over the surface obtained volume from the X-Y-Z co-ordinates of the markers and then using Gauss’s theorem to convert the volume integral to an integral over this sur‐

Optoelectronic Plethysmography for Measuring Rib Cage Distortion

The pressure acting on the part of the Rib Cage that is apposed to the costal surface of the lung is quite different from that acting on the part apposed to the diaphragm. The non uniformity of pressure distribution led Agostoni and D’Angelo (1985) to suggest that the rib cage could be usefully regarded as consisting of two compartments mechanically coupled to each other (Agostoni & D’Angelo, 1985; Jiang et al., 1988, Ward, 1992): the pulmonary rib cage (RCp), and the abdominal rib cage (RCa). The magnitude of the coupling determines the resistance to distortion and is an important parameter in the mechanics of breathing. Unitary behaviour of the rib cage was thought to be dictated by rigidity and the restrictive nature of rib articulations and interconnection. Nonetheless, important distortion of the rib cage from its relaxation configuration has been described in asthma (Ringel et al., 1983) quadriplegia (Urmey et al., 1981) and also in health individual during a variety of breathing pattern (quiet breathing, hyperventilation, single inspiration, involuntary breathing acts, such as phrenic nerve stimulation); (Crawford et al., 1983; McCool et al., 1985; Ward et al., 1992; D’Angelo, 1981; Roussos et al., 1977). In summarizing these results Crawford et al., (1983) and more recently McCool et al., (1985) concluded that the maintenance of rib cage shape needs not be attributed to inherent stiffness but may be the consequence of apparently coordinated activity of the different respiratory muscles. Under circumstance such as lung hyperinflation or when mechanical coupling between the upper rib cage (RCp) and the lower rib cage (RCa) is very loose rib cage muscle recruitment is essential to prevent paradoxical (inward) rib cage displacement. (Ward et al., 1992). Moreover the deformation of the chest wall (CW) occurring during hyperventilation and while breathing through a resistance implies that the work of breathing in these conditions is slight larger than that calculated only the basis of the volumepressure diagram. And indeed part of the force exerted by the respiratory muscles is expended to change the shape of the chest wall relative to that occurring at the same lung volume during relaxation (Agostoni & Mognoni 1966). Most of what is known about the kinematics of the chest wall i,e., the thoraco-abdomen compartment comes from studies (Sackner, 1980; Gilbert et al., 1972) using RIP (Respitrace®). However, the RIP method is subject to error, the volume being inferred from cross-sectional area changes. Also, evaluation of the breathing pattern with RIP is reliable only when the rib cage and abdomen behave with a single degree of freedom such as during