Effect of diaphragmatic contraction on the action of the canine parasternal intercostals.

The inspiratory intercostal muscles enhance the force generated by the diaphragm during lung expansion. However, whether the diaphragm also alters the force developed by the inspiratory intercostals is unknown. Two experiments were performed in dogs to answer the question. In the first experiment, external, cranially oriented forces were applied to the different rib pairs to assess the effect of diaphragmatic contraction on the coupling between the ribs and the lung. The fall in airway opening pressure (deltaPa(O)) produced by a given force on the ribs was invariably greater during phrenic nerve stimulation than with the diaphragm relaxed. The cranial rib displacement (Xr), however, was 40-50% smaller, thus indicating that the increase in deltaPa(O) was exclusively the result of the increase in diaphragmatic elastance. In the second experiment, the parasternal intercostal muscle in the fourth interspace was selectively activated, and the effects of diaphragmatic contraction on the deltaPa(O) and Xr caused by parasternal activation were compared with those observed during the application of external loads on the ribs. Stimulating the phrenic nerves increased the deltaPa(O) and reduced the Xr produced by the parasternal intercostal, and the magnitudes of the changes were identical to those observed during external rib loading. It is concluded, therefore, that the diaphragm has no significant synergistic or antagonistic effect on the force developed by the parasternal intercostals during breathing. This lack of effect is probably related to the constraint imposed on intercostal muscle length by the ribs and sternum.     

The effect of lung inflation on the inspiratory action of the canine parasternal intercostals.

Inflation induces a marked decrease in the lung-expanding ability of the diaphragm, but its effect on the parasternal intercostal muscles is uncertain. To assess this effect, the phrenic nerves and the external intercostals were severed in anesthetized, vagotomized dogs, such that the parasternal intercostals were the only muscles active during inspiration, and the endotracheal tube was occluded at different lung volumes. Although the inspiratory electromyographic activity recorded from the muscles was constant, the change in airway opening pressure decreased with inflation from -7.2+/-0.6 cmH2O at functional residual capacity to -2.2+/-0.2 cmH2O at 20-cmH2O transrespiratory pressure (P<0.001). The inspiratory cranial displacement of the ribs remained virtually unchanged, and the inspiratory caudal displacement of the sternum decreased moderately. However, the inspiratory outward rib displacement decreased markedly and continuously; at 20 cmH2O, this displacement was only 23+/-2% of the value at functional residual capacity. Calculations based on this alteration yielded substantial decreases in the change in airway opening pressure. It is concluded that, in the dog, 1) inflation affects adversely the lung-expanding actions of both the parasternal intercostals and the diaphragm; and 2) the adverse effect of inflation on the parasternal intercostals is primarily related to the alteration in the kinematics of the ribs. As a corollary, it is likely that hyperinflation also has a negative impact on the parasternal intercostals in patients with chronic obstructive pulmonary disease.     

Determination of joint efforts in the human body during maximum ramp pushing efforts

Determining with accuracy, the internal efforts in the human body is a great challenge in Biomechanics, particularly in Physical Therapy and Ergonomics. In this context, the present study develops a human body model that permits a non-invasive determination of the joint efforts produced by a seated subject performing maximum ramp pushing efforts. The joint interactions during these experiments are provided by a dynamic inverse model of the human body, using a symbolically generated recursive Newton-Euler formalism. The theoretical investigation is presented in two steps, with increasing complexity and relevance:The dynamic model confirms some previous studies of the effects of biomechanical factors on the performance of the task and is proposed as an accurate method for determining the joint efforts in dynamic contexts. Finally, this application is a preliminary benchmark case that will be extended to: *physical therapy, in order to analyse the joint and muscle efforts in various motion contexts, particularly for patients with fibromyalgia and patients with lumbar diseases; *accidentology, in order to analyse and simulate car occupant dynamics before a crash.     

Abdominal muscle use during quiet breathing and hyperpnea in uninformed subjects

Although there is electromyographic evidence for abdominal muscle activity during quiet breathing in standing subjects, several studies have shown, or assumed, that subjects normally breathe on their relaxation characteristics. This latter observation would by itself suggest that abdominal muscles do not contract during quiet breathing. To test this assumption we observed abdominal and rib cage displacements with magnetometers in 17 uninformed subjects. During quiet breathing most subjects showed evidence of tonic or phasic abdominal muscle contraction while standing and sitting but not supine. Subjects studied during hyperpnea immediately following exercise-showed evidence of greater abdominal muscle contraction than at rest. We conclude that most subjects standing at rest normally contract their abdominal muscles.     

Similar ventilation distribution in normal subjects prone and supine during tidal breathing.

Multiple-breath washout (MBW) tests, with end-expiratory lung volume at functional residual capacity (FRC) and 90% O(2), 5% He, and 5% SF(6) as an inspired gas mixture, were performed in healthy volunteers in supine and prone postures. The semilog plot of MBW N(2) concentrations was evaluated in terms of its curvilinearity. The MBW N(2) normalized slope analysis yielded indexes of acinar and conductive ventilation heterogeneity (Verbanck S, Schuermans D, Van Muylem A, Paiva M, Noppen M, and Vincken W. J App Physiol 83: 1907-1916, 1997). Also, the difference between SF(6) and He normalized phase III slopes was computed in the first MBW expiration. Only MBW tests with similar FRC in the prone and supine postures (P > 0.1; n = 8) were considered. Prone and supine postures did not reveal any significant differences in curvilinearity, N(2) normalized slope-derived indexes of conductive or acinar ventilation heterogeneity, nor SF(6)-He normalized phase III slope difference in the first MBW expiration (P > 0.1 for all). The absence of significant changes in any of the MBW indexes suggests that ventilation heterogeneity is similar in the supine and prone postures of normal subjects breathing near FRC.     

Activation of the human cortex during visual attention and selection

Cortical activation in visual discrimination tasks was estimated by measurement of the CNV (contingent negative variation) and N1-P3 components of visual ERPs in frontal, parietal, occipital and temporal leads recorded in 18 young healthy adults. In all investigated tasks, the maximal values of CNV and ERPa were observed in parietal regions. The estimation of cortical readiness state (CNV) is quite a useful procedure in the attention tasks because amplitude and stability of ERPs depend on preceding cortical excitability. The prevalence of parietal activation in visual attention tasks may be considered as the dominance of occipito-parietal way (stream) in human visual attention system.     

Control of breathing and brain activation in human subjects seen by functional magnetic resonance imaging.

Functional magnetic resonance imaging (fMRI) was used to demonstrate the brain activation during transition from unconscious to conscious breathing in seven healthy human subjects. In right-handed volunteers, the activated areas were found in both hemispheres. The medial part of the precentral gyrus (area 4) was constantly activated in the left hemisphere. Additional activated areas were demonstrated in the premotor cortex and in the posterior parietal cortex. The activated cortical sites exhibited analogous distribution in the right hemisphere. In two out of the seven subjects. activated sites were also observed in the cerebellar hemispheres, and in the lentiform and caudate nuclei.     

Thermoregulatory and respiratory responses in asthmatic and nonasthmatic subjects breathing cold and warm air during exercise in the cold

1.

The effects of whole-body exposure to ambient temperature of −15 °C on thermoregulatory and respiratory responses in asthmatic and nonasthmatic subjects were investigated. The subjects were exposed to inhalation of cold dry and warm humid air during 30 min submaximal exercise.     

Physical stresses at the air-wall interface of the human nasal cavity during breathing.

The nose is the front line defender of the respiratory system and is rich with mechanoreceptors, thermoreceptors, and nerve endings. A time-dependent computational model of transport through nasal models of a healthy human has been used to analyze the fields of physical stresses that may develop at the air-wall interface of the nasal mucosa. Simulations during quiet breathing revealed wall shear stresses as high as 0.3 Pa in the noselike model and 1.5 Pa in the anatomical model. These values are of the same order of those known to exist in uniform large arteries. The distribution of temperature near the nasal wall at peak inspiration is similar to that of wall shear stresses. The lowest temperatures occur in the vicinity of high stresses due to the narrow passageway in these locations. Time and spatial gradients of these stresses may have functional effects on nasal sensation of airflow and may play a role in the well-being of nasal breathing.     

Regulation of breathing during exercise

This paper reviewed in short neural and humoral factors which might be responsible for inducing exercise hyperpnea. As one of the neural factors afferent signals which arise in the exercising limbs and are transmitted via group III or IV high threshold sensory fibres were involved. The other neural factor is command signals originating in the central nervous system and being fed onto the respiratory center. Hypothalamic locomotor region is assumed to be a possible locus to integrate these peripheral and central neural signals. There are enough evidences to believe that humoral factors mediated via cardiac output is also essential for the hyperpnea. Changes in VCO2 is well correlated with those of VE in dynamic as well as in steady-state response. Oscillations in PaCO2 can be assumed to play a role to link metabolic CO2 changes to those in ventilation. Thus, no single factor can explain the whole process of exercise hyperpnea. Poon's optimization model may give a key to integrate complicated and coflicting experimental results in a unique concept.     

Differential activation among five human inspiratory motoneuron pools during tidal breathing.

Neural drive to inspiratory pump muscles is increased under many pathological conditions. This study determined for the first time how neural drive is distributed to five different human inspiratory pump muscles during tidal breathing. The discharge of single motor units (n = 280) from five healthy subjects in the diaphragm, scalene, second parasternal intercostal, third dorsal external intercostal, and fifth dorsal external intercostal was recorded with needle electrodes. All units increased their discharge during inspiration, but 41 (15%) discharged tonically throughout expiration. Motor unit populations from each muscle differed in the timing of their activation and in the discharge rates of their motor units. Relative to the onset of inspiratory flow, the earliest recruited muscles were the diaphragm and third dorsal external intercostal (mean onset for the population after 26 and 29% of inspiratory time). The fifth dorsal external intercostal muscle was recruited later (43% of inspiratory time; P < 0.05). Compared with the other inspiratory muscles, units in the diaphragm and third dorsal external intercostal had the highest onset (7.7 and 7.1 Hz, respectively) and peak firing frequencies (12.6 and 11.9 Hz, respectively; both P < 0.05). There was a unimodal distribution of recruitment times of motor units in all muscles. Neural drive to human inspiratory pump muscles differs in timing, strength, and distribution, presumably to achieve efficient ventilation.     

Single motor unit recordings in human geniohyoid reveal minimal respiratory activity during quiet breathing

Maintenance of airway patency during breathing involves complex interactions between pharyngeal dilator muscles. The few previous studies of geniohyoid activity using multiunit electromyography (EMG) have suggested that geniohyoid shows predominantly inspiratory phasic activity. This study aimed to quantify geniohyoid respiration-related activity with single motor unit (SMU) EMG recordings. Six healthy subjects of normal body mass index were studied. Intramuscular EMG recordings of geniohyoid activity were made with a monopolar needle with subjects in supine and seated positions. The depth of the geniohyoid was identified by ultrasound, and the electrode position was confirmed with maneuvers to isolate activity in geniohyoid and genioglossus. Activity was recorded at 85 sites in the geniohyoid during quiet breathing (45 supine and 40 seated). When subjects were supine, 33 sites (73%) showed no activity during breathing and 10 (22%) showed tonic activity. In addition, one site showed a tonic SMU with increased expiratory discharge, and one site in another subject had one unit with expiratory phasic activity. When subjects were seated, 27 sites (68%) in the geniohyoid showed no activity, 12 sites (30%) showed tonic activity that was not respiration related, and one unit at one site showed phasic expiratory activity. The average peak discharge frequency of geniohyoid motor units was 16.2 ± 3.1 impulses/s during the "geniohyoid maneuver," which was the first part of a swallow. In contrast to previous findings, the geniohyoid shows some tonic activity but minimal respiration-related activity in healthy subjects in quiet breathing. The geniohyoid has little active role in airway stability under these conditions.     

Contraction type influences the human ability to use the available torque capacity of skeletal muscle during explosive efforts

The influence of contraction type on the human ability to use the torque capacity of skeletal muscle during explosive efforts has not been documented. Fourteen male participants completed explosive voluntary contractions of the knee extensors in four separate conditions: concentric (CON) and eccentric (ECC); and isometric at two knee angles (101°, ISO101 and 155°, ISO155). In each condition, torque was measured at 25 ms intervals up to 150 ms from torque onset, and then normalized to the maximum voluntary torque (MVT) specific to that joint angle and angular velocity. Explosive voluntary torque after 50 ms in each condition was also expressed as a percentage of torque generated after 50 ms during a supramaximal 300 Hz electrically evoked octet in the same condition. Explosive voluntary torque normalized to MVT was more than 60 per cent larger in CON than any other condition after the initial 25 ms. The percentage of evoked torque expressed after 50 ms of the explosive voluntary contractions was also greatest in CON (ANOVA; p < 0.001), suggesting higher concentric volitional activation. This was confirmed by greater agonist electromyography normalized to M(max) (recorded during the explosive voluntary contractions) in CON. These results provide novel evidence that the ability to use the muscle's torque capacity explosively is influenced by contraction type, with concentric contractions being more conducive to explosive performance due to a more effective neural strategy.     

Spatio-temporal characterization of intercostal activity during breathing in the cat

It is envisaged that the motor control of the intercostal musculature--an assembly of mobile structures--can be characterized in terms of a conceptual spatially continuous control function, that underlies the discretely distributed muscular activity and reflects an inferred global dynamic control of the thoracic cage during breathing. The global control function is estimated by the spatio-temporal pattern obtained by averaging in time and space and interpolation of multichannel simultaneous intercostal EMG recording in the anaesthetized cat. Different examples of the experimental preparation in the presence of stimuli of different kinds are analysed. The resultant signal patterns are found to be self-consistent and capable of exhibiting systematically differing features in systematically differing experimental conditions, thus supporting the validity of the analysis and the choice of the estimator. It is concluded that a more detailed analysis of the requirements of this approach is then warranted. Such requirements are discussed, and, specifically, results that bear on the adequacy of spatial sampling rate are presented. It is suggested that such methods offer a promising approach in the study of motor control strategies of the respiratory apparatus.     

Influence of forward leaning and incentive spirometry on inspired volumes and inspiratory electromyographic activity during breathing exercises in healthy subjects

Breathing exercises (BE), incentive spirometry and positioning are considered treatment modalities to achieve lung re-expansion. This study evaluated the influence of incentive spirometry and forward leaning on inspired tidal volumes (V_T) and electromyographic activity of inspiratory muscles during BE. Four modalities of exercises were investigated: deep breathing, spirometry using both flow and volume-oriented devices, and volume-oriented spirometry after modified verbal instruction. Twelve healthy subjects aged 22.7 ± 2.1 years were studied. Surface electromyography activity of diaphragm, external intercostals, sternocleidomastoid and scalenes was recorded. Comparisons among the three types of exercises, without considering spirometry after modified instruction, showed that electromyographic activity and V_T were lower during volume-oriented spirometry (p = 0.000, p = 0.054, respectively). Forward leaning resulted in a lower V_T when compared to upright sitting (p = 0.000), but electromyographic activity was not different (p = 0.606). Inspired V_T and electromyographic activity were higher during volume-oriented spirometry performed after modified instruction when compared with the flow-oriented device (p = 0.027, p = 0.052, respectively). In conclusion BE using volume-oriented spirometry before modified instruction resulted in a lower work of breathing as a result of a lower V_T and was not a consequence of the device type used. Forward leaning might not be assumed by healthy subjects during situations of augmented respiratory demand.