Chest wall kinematics and respiratory muscle coordinated action during hypercapnia in healthy males

The present study was designed to verify whether during hypercapnic stimulation, as we had previously found during exercise or walking, the partitioning of the respiratory motor output is equally distributed to the muscles of chest wall compartments to assist diaphragm function. We studied chest wall kinematics and respiratory muscle recruitment in seven healthy men during rebreathing of a hypercapnic-hyperoxic gas mixture (CO₂ RT). Data were compared with those previously obtained during either cycling exercise or walking. The chest wall volume (Vcw), assessed by optoelectronic plethysmography (OEP), was modeled as the sum of the volumes of the lung-apposed rib cage (Vrc,p), diaphragm-apposed rib cage (Vrc,a) and abdomen (Vab). Esophageal (Pes), gastric (Pga) and transdiaphragmatic (Pdi=Pga–Pes) pressures were simultaneously recorded. Velocity of shortening (V) and power (W=PxV) of the diaphragm (Wdi), rib cage muscles (Wrcm) and abdominal muscles (Wabm) were also calculated. During CO₂ RT the progressive increase in end-inspiratory Vcw resulted from an increase in both end-inspiratory Vrc,p and Vrc,a, while the progressive decrease in end-expiratory Vcw was entirely due to the decrease in end-expiratory Vab. The increase in Vrc,p was proportionally slightly greater than that in Vrc,a. The end-inspiratory increase and end-expiratory decrease in Vcw were accounted for by inspiratory rib cage (RCM,i) and abdominal (ABM) muscle recruitment, respectively. Wdi, Wrcm and Wabm progressively increased. However, while most of Wdi was expressed in terms of velocity of shortening, most of Wrcm and Wabm was expressed as force or pressure. A comparison of CO₂ results with data obtained during exercise revealed: (1) a gradual vs. an immediate response, (2) a similar decrease in Vab,e and Pabm, (3) an apparent lack of any difference in ABM recruitment, (4) less gradual ABM relaxation, (5) no drop in Pdi but a similar Wdi change and decrease in pressure-to-velocity ratio of the diaphragm. We have found that in healthy humans: (1) the increased motor output with hypercapnia is equally distributed between RCM and ABM to minimize transdiaphragmatic pressure and (2) data on chest wall kinematics and respiratory muscle recruitment are only partly in line with those obtained during walking or cycling exercise.     

Development of respiratory muscle contractile fatigue in the course of hyperpnoea

To assess the development of inspiratory and expiratory muscle fatigue during normocapnic hyperpnoea, we studied fourteen healthy men performing 8 min hyperpnoea, 6 min pause, 8 min hyperpnoea, etc., until task failure. Twitch transdiaphragmatic (P_di,tw) and gastric (P_ga,tw) pressures were measured during cervical and thoracic magnetic nerve stimulation, before hyperpnoea, after every 8 min of hyperpnoea, and at task failure (i.e., at 25.3 ± 4.7 min). P_di,tw decreased during the first 16 min (−28 ± 7%, p < 0.001) and P_ga,tw during the first 8 min (−20 ± 7%, p < 0.001) of hyperpnoea without further change until task failure. During inspiration, the pressure–time-product of oesophageal pressure (PTP_oes) increased relative to PTP_di during the first 16 min (+11 ± 21%, p < 0.05). Similarly, during expiration, PTP_oes increased relative to PTP_ga during the first 8 min (+10 ± 16%, p < 0.05). Also, blood lactate concentration and respiratory sensations significantly increased during the first 8 min (+1.0 ± 0.5 mmol l⁻¹, p < 0.001) and 16 min (breathlessness +1.6 ± 1.8 points, respiratory effort +5.9 ± 2.2 points, p < 0.001), respectively. We conclude that, during hyperpnoea, contractile fatigue of the diaphragm and abdominal muscles develops long before task failure and may trigger an increased recruitment of rib cage muscles.     

Effects of an opioid on respiratory movements and expiratory activity in humans during isoflurane anaesthesia

Opioids increase abdominal muscle activity during anaesthesia. We proposed that opioid activity during anaesthesia would change chest wall size and movement, and contribute to ventilation. Using an optical system to measure chest wall volume, we studied 10 patients during isoflurane anaesthesia, first under the influence of an opioid and then after reversal with naloxone. Measurements were made during quiet breathing and with carbon dioxide stimulation. Airway occlusion pressure was measured to assess inspiratory and expiratory muscle activity. Chest wall volume decreased with the onset of spontaneous breathing, and decreased further when breathing was stimulated by carbon dioxide. Reversal of opioid activity increased chest wall volume. Breathing movements were predominantly abdominal. Opioid action affected the timing and amplitude of breathing but the pattern of abdominal movement was not affected. Since opioids augment abdominal muscle action during expiration, the unchanged pattern of movement can be attributed to both diaphragm and abdominal activity displacing the abdominal wall reciprocally, in the inspiratory and expiratory phases of the respiratory cycle, respectively.     

Effect of voluntary respiratory efforts on breath-holding time

INTRODUCTION: Near the end of a maximal voluntary breath-hold, re-inhalation of the expired gas allows an additional period of breath-holding, indicating that the breaking point does not depend solely on chemical drive. We hypothesized that afferents from respiratory muscle and/or chest wall are significant in breath-holding. METHODS: Nineteen normal adults breathed room air through a mouthpiece connected to a pneumotachograph and were instructed to breath-hold with and without voluntary regular respiratory efforts against an occluded airway. RESULTS: Fifty one trials with and 53 without respiratory efforts were analyzed. The mean number of efforts per minute was 19+/-2.3 and the mean lowest airway pressure (P(aw)) -16.6+/-5.4 cmH(2)O. Breath-holding time (BHT) did not differ without (33.0+/-18.2 s) and with (29.3+/-12.3 s) efforts. In five patients arterial blood gasses were measured before and at the end of breath-holding and they did not differ between trials without and with efforts, indicating similar chemical drive. Our results suggest that afferents from respiratory muscle and/or chest wall are not the major determinants of BHT.     

Esophageal pressure as an estimate of average pleural pressure with lung or chest distortion in rats

Pressure–volume curves of the lungs and chest wall require knowledge of an effective ‘average’ pleural pressure (Ppl_av), and are usually estimated using esophageal pressure as Pl_es–V and Pw_es–V curves. Such estimates could be misleading when Ppl becomes spatially non-uniform with lung lavage or shape distortion of the chest. We therefore measured Pl_es–V and Pw_es–V curves in conditions causing spatial non-uniformity of Ppl in rats. Pl_es–V curves of normal lungs were unchanged by chest removal. Lung lavage depressed PL_es–V but not Pw_es–V curves to lower volumes, and chest removal after lavage increased volumes at PL ≥ 15 cmH₂O by relieving distortion of the mechanically heterogeneous lungs. Chest wall distortion by ribcage compression or abdominal distension depressed Pw_es–V curves and Pl_es–V curves of normal lungs only at Pl ≥ 3 cmH₂O. In conclusion, Pes reflects Ppl_av with normal and mechanically heterogeneous lungs. With chest wall distortion and dependent deformation of the normal lung, changes of Pl_es–V curves are qualitatively consistent with greater work of inflation.     

Chest wall kinematics and Hoover's sign

BACKGROUND: No attempt has been made to quantify the observed rib cage distortion (Hoover's sign) in terms of volume displacement. We hypothesized that Hoover's sign and hyperinflation are independent quantities. METHODS: Twenty obstructed stable patients were divided into two groups according to whether or not they exhibited Hoover's sign during clinical examination while breathing quietly. We evaluated the volumes of chest wall and its compartments: the upper rib cage, the lower rib cage and the abdomen, using optoelectronic plethysmography. RESULTS: The volumes of upper rib cage, lower rib cage and abdomen as a percentage of absolute volume of the chest wall were similar in patients with and without Hoover's sign. In contrast, the tidal volume of the chest wall, upper rib cage, lower rib cage, their ratio and abdomen quantified Hoover's sign, but did not correlate with level of hyperinflation. CONCLUSIONS: Rib cage distortion and hyperinflation appear to define independently the functional condition of these patients.     

Chest wall kinematics, respiratory muscle action and dyspnoea during arm vs. leg exercise in humans

Aim: We hypothesize that different patterns of chest wall (CW) kinematics and respiratory muscle coordination contribute to sensation of dyspnoea during unsupported arm exercise (UAE) and leg exercise (LE). Methods: In six volunteer healthy subjects, we evaluated the volumes of chest wall (V_cw) and its compartments, the pulmonary apposed rib cage (V_rc,p), the diaphragm‐abdomen apposed rib cage (V_rc,a) and the abdomen (V_ab), by optoelectronic plethysmography. Oesophageal, gastric and trans‐diaphragmatic pressures were simultaneously measured. Chest wall relaxation line allowed the measure of peak rib cage inspiratory muscle, expiratory muscle and abdominal muscle pressures. The loop V_rc,p/V_rc,a allowed the calculation of rib cage distortion. Dyspnoea was assessed by a modified Borg scale. Results: There were some differences and similarities between UAE and LE. Unlike LE with UAE: (i) V_cw and V_rc,p at end inspiration did not increase, whereas a decrease in V_rc,p contributed to decreasing CW end expiratory volume; (ii) pressure production of inspiratory rib cage muscles did not significantly increase from quiet breathing. Not unlike LE, the diaphragm limited its inspiratory contribution to ventilation with UAE with no consistent difference in rib cage distortion between UAE and LE. Finally, changes in abdominal muscle pressure, and inspiratory rib cage muscle pressure predicted 62% and 41.4% of the variability in Borg score with UAE and LE, respectively (P < 0.01). Conclusion: Leg exercise and UAE are associated with different patterns of CW kinematics, respiratory muscle coordination, and production of dyspnoea.     

Compartmental Analysis of Breathing in the Supine and Prone Positions by Optoelectronic Plethysmography

Optoelectronic plethysmography (OEP) has been shown to be a reliable method for the analysis of chest wall kinematics partitioned into pulmonary rib cage, abdominal rib cage, abdomen, and right and left side in the seated and erect positions. In this paper, we extended the applicability of this method to the supine and prone positions, typically adopted in critically ill patients. For this purpose we have first developed proper geometrical and mathematical models of the chest wall which are able to provide consistent and reliable estimations of total and compartmental volume variations in these positions suitable for clinical settings. Then we compared chest wall (CW) volume changes computed from OEP( V _CW) with lung volume changes measured with a water seal spirometer (SP) ( V _SP)in 10 normal subjects during quiet (QB) and deep (DB) breathing on rigid and soft supports. We found that on a rigid support the average differences between V _SP and V _CW were –4.2% ± 6.2%, –3.0% ± 6.1%, –1.7% ±7.0%, and –4.5% ± 9.8%, respectively, during supine/QB, supine/DB, prone/QB, and prone/DB. On the soft surface we obtained –0.1% ± 6.0%, –1.8% ± 7.8%, 18.0% ± 11.7%, and 10.2% ± 9.6%, respectively. On rigid support and QB, the abdominal compartment contributed most of the V _CW in the supine (63.1% ± 11.4%) and prone (53.5% ± 13.1%) positions. V _CW was equally distributed between right and left sides. In the prone position we found a different chest wall volume distribution between pulmonary and abdominal rib cage (22.1% ± 8.6% and 24.4% ± 6.8, respectively) compared with the supine position (23.3% ± 9.3% and 13.6% ± 3.0%). © 2001 Biomedical Engineering Society. PAC01: 8763Lk, 8719Uv     

Influence of respiratory activity on the cardiac response pattern to mental effort

A group of 32 healthy adult volunteers completed three blocks of a reaction time task that varied in the degree of controlled processing load. A rest period preceded each of the task blocks. The task blocks were presented in the order of either increasing or decreasing cognitive load. For each of the six periods, mean values and spectral measures of heart rate and respiration variability were calculated. The spectral measures were obtained for three different frequency bands. Differences between the cardiac measures of the task and preceding rest periods were compared with respect to differences in task load and the order of task presentation. All comparisons were carried out while adjusting for respiratory variability in the corresponding frequency band. The frequency band in which task load-related changes in heart rate variability became manifest appeared to be dependent on the individual's breathing pattern.     

Transfer Impedance of the Respiratory System by Forced Oscillation Technique and Optoelectronic Plethysmography

To estimate the transfer impedance of the respiratory system we applied pressure forcing at the mouth from 1 to 24 Hz in eight healthy subjects and used optoelectronic plethysmography (OEP) to measure volume changes of the chest wall and its different compartments: pulmonary rib cage abdominal rib cage and abdomen (AB). Spectral analysis allowed assessment of input impedance and total and compartmental and transfer impedances. As expected, averaged values of and were similar at low frequencies (<8 Hz) while they progressively differed at high frequencies. The percentage contributions of and to were, respectively, 35.3±1.4SD, 13.8±1.4, and 50.8±2.8 at low frequencies (<8 Hz) and 63.1±5.5, 20.7±5.2, and 16.2±2.3 at higher frequencies (>10 Hz). The validation of our approach was based on the comparison with a physical model comprised of a rubber membrane stretched over and attached to the lip of a bowl. We conclude that the combination of forced oscillations with OEP provides the simultaneous assessment of and it does not require the use of a plethysmographic chamber and it allows the separation between the different rib cage-abdominal pathways. © 2001 Biomedical Engineering Society. PAC01: 8719Uv, 8780-y, 8763Lk     

Effects of loading on upper airway and respiratory pump muscle motoneurons

The functional outcomes of respiratory muscle loading by chemical (e.g. hypercapnia), mechanical (i.e. external mechanical loading) or ventilatory (e.g. exercise) factors can be either positive, such as through an increase in pressure-generating capacity of the inspiratory muscles or detrimental, such as by fatigue. Neurophysiological responses to respiratory muscle loading can occur at one or more points along the pathway from motor cortex to muscle. This paper describes the respiratory pump and upper airway motoneuron responses to the imposition of acute loads including processes of pre-activation, respiratory reflexes, potentiation and fatigue. It also considers changes suggestive of adaptation to chronic loading either from specific respiratory muscle training programs or as part of disease processes such as chronic obstructive pulmonary disease or obstructive sleep apnoea.     

Impact of laparoscopic surgery on thoracoabdominal mechanics and inspiratory muscular activity

Objective

To evaluate the effect of laparoscopic surgery on pulmonary volume distributions and inspiratory muscles activity. Respiratory consequences associated with postoperative pain were also evaluated.

Methods

This study enrolled 20 patients without lung disease performed spirometry and chest wall kinematic analyses (i.e., chest wall, upper and lower ribcage and abdominal volumes), and measured the activity of inspiratory muscular before and 2 days after laparoscopic surgery. Pain was also assessed.

Results

After laparoscopy, the patients demonstrated decreased volumes in all three thoracoabdominal compartments: abdomen (ABD), upper and lower rib cage (URC and LRC, respectively) compared with the pre-operative measurements: ABD = 0.38 ± 0.20 L vs. 0.55 ± 0.25 L; URC = 0.45 ± 0.18 L vs. 0.55 ± 0.21 L; and LRC = 0.31 ± 0.18 L vs. 0.41 ± 0.23 L; p < 0.05. A reduction in the inspiratory muscular activity after surgery was also observed (sternocleidomastoid: 10.6 ± 5.1 × 10⁻³ mV vs. 12.8 ± 6.3 × 10⁻³ mV; intercostals: 16.8 ± 12.4 × 10⁻³ mV vs. 25.1 ± 21.3 × 10⁻³ mV; p < 0.05). In addition, lower volumes during deep breathing were observed in patients who reported significant pain than those who did not (0.51 ± 0.17 L vs. 0.79 ± 0.29 L; p < 0.05, respectively).

Conclusion

Laparoscopic surgery reduces chest wall ventilation and inspiratory muscular activity during deep breathing. The effects appear to depend on the patient's reported pain level.     

Effects of preoperative inspiratory muscle training in obese women undergoing open bariatric surgery: respiratory muscle strength, lung volumes, and diaphragmatic excursion

OBJECTIVE:

To determine whether preoperative inspiratory muscle training is able to attenuate the impact of surgical trauma on the respiratory muscle strength, in the lung volumes, and diaphragmatic excursion in obese women undergoing open bariatric surgery.

DESIGN:

Randomized controlled trial.

SETTING:

Meridional Hospital, Cariacica/ES, Brazil.

SUBJECTS:

Thirty-two obese women undergoing elective open bariatric surgery were randomly assigned to receive preoperative inspiratory muscle training (inspiratory muscle training group) or usual care (control group).

MAIN MEASURES:

Respiratory muscle strength (maximal static respiratory pressure – maximal inspiratory pressure and maximal expiratory pressure), lung volumes, and diaphragmatic excursion.

RESULTS:

After training, there was a significant increase only in the maximal inspiratory pressure in the inspiratory muscle training group. The maximal expiratory pressure, the lung volumes and the diaphragmatic excursion did not show any significant change with training. In the postoperative period there was a significant decrease in maximal inspiratory pressure in both the groups. However, there was a decrease of 28% in the inspiratory muscle training group, whereas it was 47% in the control group. The decrease in maximal expiratory pressure and in lung volumes in the postoperative period was similar between the groups. There was a significant reduction in the measures of diaphragmatic excursion in both the groups.

CONCLUSION:

The preoperative inspiratory muscle training increased the inspiratory muscle strength (maximal inspiratory pressure) and attenuated the negative postoperative effects of open bariatric surgery in obese women for this variable, though not influencing the lung volumes and the diaphragmatic excursion.     

Electromyographic monitoring of respiratory muscle activity in dyspneic infants and toddlers

The aim of this study was to investigate whether the changes that occurred in the clinical asthma score (CAS) correlated with the changes in the respiratory electromyographic (EMG) activity over the days during admission to hospital in dyspneic infants and toddlers. Sixteen infants and toddlers (9 males) were studied during admission and 7 days after discharge. The CAS was used to assess the severity of dyspnea and consists of five items: respiration rate, wheezing, retractions, observed dyspnea, and inspiration-to-expiration ratio. Each item was scaled 0, 1, or 2, with a maximum score of 10. Electrical activity from the diaphragm (di) and intercostal muscles (int) was derived from surface electrodes. The logarithm of the EMG-Activity-Ratio (log EMGAR; ratio of mean peak-to-bottom EMG activity during admission to the hospital, to that at baseline, 7 days after discharge) was used as EMG parameter. For assessing the association between the repeated observations of the CAS and the EMG measurements we used the quantity r2 obtained with analysis of covariance. On the day of admission the patients had a mean CAS of 5.9 +/- 1.2. On the day of discharge the mean CAS decreased significantly to 2.1 +/- 1.6, indicating that the CAS returned to normal values. In line with this observation, a significant decrease in the log EMGARdi and log EMGARint was observed during the stay in the hospital. Over all subjects the correlation coefficient (r) of log EMGARdi versus CAS was 0.71, log EMGARint versus CAS was 0.67, and the mean log EMGAR versus CAS was 0.75 (p < 0.01, for all values). The correlation coefficients of subjects of < or = 1 year seemed to be lower than those of subjects of > 1 year of age (p < 0.01) and female subjects showed higher correlation coefficients than males. This study showed a moderate, but significant, relationship between the changes that occurred in the CAS and the changes in respiratory EMG activity during admission to hospital in dyspneic infants and toddlers. Moreover, the correlation coefficients of the combined leads of the intercostals and diaphragm (mean log EMGAR) were higher than those of the separate leads. The EMG measurements would extend diagnostic possibilities and would provide an objective measure to evaluate the clinical course of the disease and the efficacy of therapy in infants and toddlers with recurrent wheezing disorders.     

The role of the fusimotor system with respect to the contribution of the diaphragm and the intercostal muscles to the respiratory tidal volume

Summary The efferent electrical activity in the phrenic nerve can be quantified in such a way that it gives a good correlation to tidal volume. After administration of the drug benzoctamine this relationship changes: more phrenic nerve activity is needed for the same tidal volume. No changes were found in the neuro-muscular transmission from the phrenic nerve to the diaphragm. There was no alteration in dynamic compliance of the lungs or in airway resistance. The afferent phrenic nerve activity from proprioceptors in the diaphragm did not change. It seems unlikely that respiratory neurons in the brainstem were affected since the sensitivity of the respiratory system to CO₂ did not change.It is known that the tonic fusimotoneuron activity is suppressed at a supraspinal level by benzoctamine. Since intercostal muscles have muscle spindles and the diaphragm hardly has any, the intercostal muscle activity will be affected more than diaphragmatic activity by benzoctamine. This could actually be shown by quantifying the electromyogram of inspiratory external intercostal muscles.The tidal volume regulation is controlled by the vagal feedback loop. In order to reach a certain tidal volume after administration of benzoctamine, the contribution of the diaphragm has to increase because the activity of the intercostal muscles is diminished.     

Modeling human diaphragmatic electromyogram and airflow responses to imperceptible mechanical loads

We used an esophageal electrode to measure the amplitude and timing responses of diaphragmatic electrical activity and airflow in response to flow resistive and elastic loads at or below the threshold for conscious detection, applied pseudorandomly to the oral airway of eight normal human subjects. The mechanical and neural parameter responses to mechanical loading were cross-correlated with the pseudorandom loading sequence to obtain estimates of the impulse responses. We convolved the resultant impulse response estimates with the loading sequence to obtain the responses predicted from the linear component of the generalized Wiener kernel model. Highly significant correlations and close correspondence were found between the model-predicted and ensemble-averaged experimental responses for nearly all neural and mechanical parameters in all subjects. For nearly every aspect of the pattern, with few exceptions, the response to these small load perturbations in all eight subjects was adequately explained by an impulse response, leaving negligible nonlinearity to require higher-order cross-correlations. These results indicate that the estimated impulse responses accurately model the dynamics of the neural and mechanical responses in human subjects for the types and magnitudes of loads applied. This study supports use of the pseudorandom loading technique to determine the neural and mechanical responses to imperceptible mechanical loads in conscious humans.     

Myelinated nerve fiber supply and muscle spindles in the respiratory muscles of cat: Quantitative study

Summary The present study was undertaken to provide quantitative data on the myelinated fibers of the phrenic and intercostal nerves and the number of spindles in the main respiratory muscles of the cat.The myelinated component of the phrenic and intercostal nerves was studied in the cat. Histograms of sequency distributions as a function of nerve fiber diameter were established for normal nerves. Certain nerves were then examined 35 to 40 days after excision of the dorsal spinal ganglia. The muscle spindles of the corresponding muscles were counted and localized, and, on the basis of several morphological criteria, were classified with those usually described in the interosseous muscles.The study of the nerves, as that of the spindles, demonstrates clear differences of proprioceptive innervation among the respiratory muscles. The lateral part of the diaphragm and the Triangularis sterni have practically no spindles. The external muscles of the first thoracic spaces are very rich in spindles. Respiratory muscles can be ranged in an almost continuous manner between these two extremes.     

Redox modulation of contractile function in respiratory and limb skeletal muscle

For the last half century, scientists have studied the biological importance of free radicals in respiratory and limb muscles. We now know that muscle fibers continually produce both reactive oxygen species (ROS) and nitric oxide (NO) and that both cascades play critical roles in contractile regulation. Under basal conditions, muscle-derived ROS and NO exert opposing effects. Low-level ROS activity is an essential part of the homeostatic milieu and is required for normal force production whereas NO derivatives function as a brake on the system, limiting force. The modulatory effects of ROS and NO are disrupted by conditions that exaggerate production including mechanical unloading, inflammatory disease, and strenuous exercise. Marked increases in ROS or NO levels cause contractile dysfunction, resulting in muscle weakness and fatigue. These principles provide a foundation for ongoing research to identify the mechanisms of ROS and NO action and develop interventions that protect muscle function.