Resistive loaded breathing changes the motor drive to arm and leg muscles in man

The effects of slow breathing on postural muscles during standing perturbations in young adults

Maintaining standing balance is vital to completing activities in daily living. Recent findings suggest an interaction between cardiovascular and postural control systems. Volitional slow breathing can modulate the cardiovascular response and affect postural control during quiet standing. However, the effects of slow breathing during threats to standing balance have not been studied. The study examined the effect of slow breathing on the latency and amplitude of postural muscle responses to perturbations of the base of support in healthy, young adults. Twenty-seven participants completed two balance perturbation tasks in standing on an instrumented split-belt treadmill while breathing spontaneously and breathing at 6 breaths per minute. Each perturbation task consisted of 25 posteriorly directed translations of the treadmill belts every 8-12 s. Muscle latency and muscle burst amplitude were measured using surface electromyography from the right limb for the quadriceps (QUADS), medial hamstring (MH), gastrocnemii (GASTROC), soleus (SOL), and tibialis anterior (TA) muscle groups, while a respiratory belt was used to record respiratory rate. Results indicated that during the slow breathing task both muscle latency (p = 0.022) and muscle burst amplitude (p = 0.011) decreased compared to spontaneous breathing. The EMG pre-perturbation activation was not significantly different in any muscle group between conditions (p > 0.167). The study found that reducing respiratory rate to approximately 6 breaths per minute affects the neuromuscular responses in the lower limb muscles to perturbations.

Increased breathing resistance compromises the time course of rhythmical forearm movements-a pilot study

BACKGROUND AND OBJECTIVES

Skeletal muscle dysfunction is a major problem among the co-morbidities associated with chronic obstructive pulmonary disease (COPD). However, muscle weakness and increased fatigability are not the only limitations of skeletal muscle function. Motor-respiratory coordination (MRC) may occur even during movements at lowest workloads. MRC modifies the temporal pattern of motor actions, thus probably impairing motor performance and movement precision. Little attention has been paid to the question of whether motor functions may be compromised in COPD patients independent of workload and required muscle strength and endurance. The present pilot study was designed to investigate the effects of a simulated obstruction (SO) in healthy subjects on their breathing pattern and the timing of a rhythmical forearm movement.

METHODS

Twenty-one subjects performed flexion- extension movements with their right forearm at a self-chosen rate within a range between 0.2 and 0.4 Hz. After a control experiment with normal breathing, a plug with a narrow hole was inserted between face mask and pneumotachograph to simulate obstruction. Subjects were required to repeat the rhythmical forearm movement at the same rate as in the control experiment.

RESULTS

The condition of SO significantly prolonged breath duration but reduced tidal volume and ventilation. In addition, period duration of the forearm movement increased significantly under this condition while the movement-to-breathing frequency ratio remained almost constant. Increased breathing resistance was considered to cause prolonged breath duration accompanied by an increase in movement period duration. The constant near-integer ratio between movement and breathing rates indicates that the change in movement period duration resulted from MRC.

CONCLUSIONS

The findings of this pilot study demonstrate that increased breathing resistance may compromise motor performance even at lower workloads. This means that in COPD patients, not only muscle strength and endurance are reduced but, moreover, fine motor skills may be impaired. This aspect has particular importance for many everyday activities as reduced fine motor performance substantially contributes to a progressive inability of the patients to manage their daily life.

Voluntary breathing influences corticospinal excitability of nonrespiratory finger muscles

The present study aimed to investigate neurophysiologic mechanisms mediating the newly discovered phenomenon of respiratory-motor interactions and to explore its potential clinical application for motor recovery. First, young and healthy subjects were instructed to breathe normally (NORM); to exhale (OUT) or inhale (IN) as fast as possible in a self-paced manner; or to voluntarily hold breath (HOLD). In experiment 1 (n = 14), transcranial magnetic stimulation (TMS) was applied during 10% maximal voluntary contraction (MVC) finger flexion force production or at rest. The motor-evoked potentials (MEPs) were recorded from flexor digitorum superficialis (FDS), extensor digitorum communis (EDC), and abductor digiti minimi (ADM) muscles. Similarly, in experiment 2 (n = 11), electrical stimulation (ES) was applied to FDS or EDC during the described four breathing conditions while subjects maintained 10%MVC of finger flexion or extension and at rest. In the exploratory clinical experiments (experiment 3), four patients with chronic neurological disorders (three strokes, one traumatic brain injury) received a 30-min session of breathing-controlled ES to the impaired EDC. In experiment 1, the EDC MEP magnitudes increased significantly during IN and OUT at both 10%MVC and rest; the FDS MEPs were enhanced only at 10%MVC, whereas the ADM MEP increased only during OUT, compared with NORM for both at rest and 10%MVC. No difference was found between NORM and HOLD for all three muscles. In experiment 2, when FDS was stimulated, force response was enhanced during both IN and OUT, but only at 10%MVC. When EDC was stimulated, force response increased at both 10%MVC and rest, only during IN, but not OUT. The averaged response latency was 83 ms for the finger extensors and 79 ms for the finger flexors. After a 30-min intervention of ES to EDC triggered by forced inspiration in experiment 3, we observed a significant reduction in finger flexor spasticity. The spasticity reduction lasted for ≥ 4 wk in all four patients. TMS and ES data, collectively, support the phenomenon that there is an overall respiration-related enhancement on the motor system, with a strong inspiration-finger extension coupling during voluntary breathing. As such, breathing-controlled electrical stimulation (i.e., stimulation to finger extensors delivered during the voluntary inspiratory phase) could be applied for enhancing finger extension strength and finger flexor spasticity reduction in poststroke patients.

The valsalva maneuver revisited: the influence of voluntary breathing on isometric muscle strength

We assessed the effects of 4 voluntary breathing conditions on maximal voluntary isometric force of large muscle groups. Ten subjects performed maximum voluntary isometric contractions (MVICs) of knee flexion and extension, shoulder abduction and adduction, and elbow flexion and extension under all breathing conditions: normal breathing, forced inhalation, forced exhalation, and the Valsalva maneuver (VM). Forced exhalation significantly increased peak force during shoulder adduction, elbow extension, and knee extension MVIC tasks (p = 0.001, 0.024, and 0.002, respectively); the peak force during the Valsalva maneuver was not different from forced exhalation for all tested muscle groups. No voluntary breathing condition seemed to influence the peak force during the knee flexion, elbow flexion, and shoulder abduction MVIC tasks. The results demonstrate that voluntary breathing imposes a significant impact on isometric muscle strength. Given the increased cardiovascular risks associated with the Valsalva maneuver, it is highly recommended that forced exhalation be used during exercise at maximal levels, especially in repetitive repetitions.

Monitoring of vecuronium-induced neuromuscular blockade during one-lung ventilation

PURPOSE

We investigated the monitoring of neuromuscular blockade caused by vecuronium in patients receiving one-lung ventilation (OLV) anesthesia for lung surgery.

METHODS

Eighteen adult patients requiring OLV for lung surgery (OLV group) and 18 undergoing two-lung ventilation (TLV) for colon surgery (control group) were enrolled in this study. In the two groups, anesthesia was maintained with sevoflurane, fentanyl, and epidural lidocaine. Time from vecuronium 0.1 mg.kg(-1) to the onset of neuromuscular blockade; times to the return of T1, T2, T3, or T4 (the first, second, third, or fourth response of the train-of-four [TOF]); and recovery of T1/control or TOF ratio (T4/T1) were compared between the two groups.

RESULTS

Time to the onset of neuromuscular blockade in the OLV group was similar to that in the control group (289 +/- 74 vs 270 +/- 85 s [mean +/- SD]; P = 0.482). Times from vecuronium to the return of T1, T2, T3, or T4 in the OLV group did not significantly differ from those in the control group (21.9 +/- 7.0 vs 25.8 +/- 6.7 min for T1; P = 0.099). T1/control in the OLV group was significantly higher than that in the control group 50-120 min after vecuronium (P < 0.05). The TOF ratio did not differ significantly between the two groups.

CONCLUSION

During OLV for lung surgery, recovery of T1/control is accelerated in anesthetized patients receiving vecuronium.

Dyspnea as a Noxious Sensation: Inspiratory Threshold Loading May Trigger Diffuse Noxious Inhibitory Controls in Humans

Dyspnea, a leading respiratory symptom, shares many clinical, physiological, and psychological features with pain. Both activate similar brain areas. The neural mechanisms of dyspnea are less well described than those of pain. The present research tested the hypothesis of common pathways between the two sensations. Six healthy men (age 30–40 yr) were studied. The spinal nociceptive flexion reflex (RIII) was first established in response to electrical sural stimulation. Dyspnea was then induced through inspiratory threshold loading, forcing the subjects to develop 70% of their maximal inspiratory pressure to inhale. This led to progressive inhibition of the RIII reflex that reached 50 ± 12% during the fifth minute of loading ( P < 0.001), was correlated to the intensity of the self-evaluated respiratory discomfort, and had recovered 5 min after removal of the load. The myotatic H-reflex was not inhibited by inspiratory loading, arguing against postsynaptic alpha motoneuron inhibition. Dyspnea, like pain, thus induced counterirritation, possibly indicating a C-fiber stimulation and activation of diffuse noxious inhibitory descending controls known to project onto spinal dorsal horn wide dynamic range neurons. This confirms the noxious nature of certain types of breathlessness, thus opening new physiological and perhaps therapeutic perspectives.

Influences of ventilation on maximal isometric force of the finger flexors

Force production may be influenced by the phase of ventilation during which force is exerted. To examine the potential influences of ventilation on variability in maximal force measurements, we recorded peak isometric forces of the finger flexors during normal breathing, forced inspiration, forced expiration, and the Valsalva maneuver in 14 healthy adult subjects. The peak force increased significantly from forced inspiration to forced expiration (about 10%). Both forced expiration and inspiration resulted in increases in the flexor/extensor cocontraction ratio, whereas the Valsalva maneuver had no significant effects on maximal force or cocontraction ratio. Thus, this study clearly demonstrates the effects of ventilation on maximal finger force-generating capability. Ventilation needs to be controlled for accurate assessments of maximal force.

Expiratory muscles modulate negative expiratory pressure-induced flow during muscular exercise

The recruitment of expiratory muscles during exercise might be altered by the application of negative expiratory pressure (NEP) inducing a feature of expiratory flow limitation (EFL) called muscle EFL. To check this hypothesis EFL and expiratory muscle EMG (ExpEMG) were measured at rest and during exercise in eight healthy subjects. Six subjects performed isocapnic hyperventilation. At 5hPa NEP, 5/8 subjects had EFL during exercise. This limitation disappeared when NEP value was increased and did not appear during isocapnic hyperventilation. During exercise, in limited subjects, ExpEMG was significantly reduced during expiration with NEP as compared to control. Gastric pressure measured in a limited subject increased during expiration but less with NEP than without it, while this pressure measured in another, non-limited, subject decreased. An inhibitory reflex due to negative pressure could be responsible for muscle EFL by reducing expiratory muscle activity. The response to NEP during exercise should be interpreted with caution.

Facilitation of the diaphragm response to transcranial magnetic stimulation by increases in human respiratory drive

The human respiratory neural drive has an automatic component (bulbospinal pathway) and a volitional component (corticospinal pathway). The aim of this study was to assess the effects of a hypercapnia-induced increase in the automatic respiratory drive on the function of the diaphragmatic corticospinal pathway as independently as possible of any other influence. Thirteen healthy volunteers breathed room air and then 5 and 7% hyperoxic CO2. Cervical (cms) and transcranial (tms) magnetic stimulations were performed during early inspiration and expiration. Transdiaphragmatic pressure (Pdi) and surface electromyogram of the diaphragm (DiEMG) and of the abductor pollicis brevis (apbEMG) were recorded in response to cms and tms. During inspiration, Pdi,cms was unaffected by CO2, but Pdi,tms increased significantly with 7% CO2. During expiration, Pdi,cms was significantly reduced by CO2, whereas Pdi,tms was preserved. DiEMG,tms latencies decreased significantly during early inspiration and expiration (air vs. 5% CO2 and air vs. 7% CO2). DiEMG,tms amplitude increased significantly in response to early expiration-tms (air vs. 5% CO2 and air vs. 7% CO2) but not in response to early inspiration-tms. DiEMG,cms latencies and amplitudes were not affected by CO2 whereas 7% CO2 significantly increased the apbEMG,cms latency. The apbEMG,tms vs. apbEMG,cms latency difference was unaffected by CO2. In conclusion, increasing the automatic drive to breathe facilitates the response of the diaphragm to tms, during both inspiration and expiration. This could allow the corticospinal drive to breathe to keep the capacity to modulate respiration in conditions under which the automatic respiratory control is stimulated.

[The John Sutton Lecture: CSEP, 2002]. Pulmonary system limitations to exercise in health

It is commonly held that the structural capacity of the normal lung is "overbuilt" and exceeds the demand for pulmonary O2 and CO2 transport in the healthy, exercising human. On the other hand, the adaptability of pulmonary system structures to habitual physical training is substantially less than are other links in the O2 transport system. Accordingly, in some highly fit, and even in some not so fit habitually active individuals, the lung's diffusion surface, airways, and/or chest-wall musculature are underbuilt relative to the demand for maximal O2 transport. Two specific pulmonary limitations to exercise performance are proposed: (1) exercise-induced arterial hypoxemia secondary to excessive widening of the alveolar to arterial O2 difference, inadequate hyperventilation, and metabolic acidosis; and (2) highly fatiguing levels of respiratory muscle work which effectively steals blood flow from locomotor muscles via sympathetically mediated reflexes and heightens the perception of limb discomfort and dyspnea. In this brief review, we describe the characteristics and causes of each of these proposed pulmonary limitations and their consequences to maximal O2 uptake and exercise performance.

Expiratory resistive loaded breathing in humans increases fluctuations of force production in submaximal isometric quadriceps contractions

This study demonstrated that expiratory resistive loading (ERL) induced an increase in force fluctuation during a unilateral, submaximal isometric contraction of the non-dominant left vastus lateralis (VL), but did not effect force fluctuation during complex bilateral contractions. The increase in force fluctuation in the unilateral left VL contraction during ERL was not accompanied by alterations of average force production, motor unit activation (median power frequency) or airflow rate when compared to the bilateral contraction. Inspiratory RL (IRL) did not significantly affect force fluctuation in unilateral or bilateral contractions. The results concur with previous reports of ERL, but not IRL, effecting VL function and suggest that patients with obstructive diseases may also be vulnerable to reduced fine motor control.

Resistive loaded breathing has a functional impact on maximal voluntary contractions in humans

Resistive loaded breathing (RL) can modulate the electromyogram pattern during an isometric arm flexion or leg extension at 70-80% of voluntary maximal contraction (MVC). This study tested the hypothesis that an interaction between the respiratory muscle afferent activity during RL and the descending motor drive may also have a functional impact on voluntary maximal performance. Therefore, muscle contractions (100% of MVC) were performed with four muscles during phase specific expiratory (ERL) or inspiratory (IRL) resistive loading and force or the steadiness of the force produced were compared with non-RL controls. Both IRL and ERL reduced MVC in leg muscles, especially biceps femoris. IRL caused a reduction in steadiness in the same muscle. These results suggest a hitherto understated impact of RL on functional performance in leg muscles.

Changes in electromyogram during upper limb muscle contraction induced by resistive loaded breathing in humans

Expiratory only resistive loaded breathing (RL) reduces high energy electromyogram (EMG) power (EH) during an isometric contraction of a leg extensor muscle, but not an arm flexor. An interaction between afferent activity during expiratory RL and inspiratory non-loaded phases of breathing, which the contraction spanned, could have accounted for the reduced EH in these long contractions. Therefore this study tested the hypothesis that brief arm extensor muscle contractions (70% of maximal force), performed during a single phase of expiratory RL, would also exhibit reduced EH. Surprisingly, EH in triceps, but not biceps brachii was reduced significantly when the contraction was performed during inspiratory RL rather than expiratory RL. The results suggest that either (a) short and prolonged contractions or (b) motor drive to arm and leg extensors are affected differently by RL.

Activation of respiratory afferents by resistive loaded breathing modifies somatosensory evoked potentials to median nerve stimulation in humans

The cortical projections of respiratory afferents (vagus and respiratory muscle nerves) are well documented in humans. It is also shown that their activation during loaded breathing modifies the perception of tactile sensation as well as the motor drive to skeletal muscles. The effects of expiratory or inspiratory loaded breathing on somatosensory evoked potentials (SEPs) elicited by median nerve stimulation were studied in eight healthy subjects. No significant changes occurred in latencies of N20, N30 and P40 throughout the expiratory loading period, except for a significant lengthening in P1 latency compared with unloaded breathing. However, inspiratory loading induced a significant increase in peak latency of N20, N30 and P40 components. We suggest that projections of inspiratory afferents from the diaphragm and the intercostal muscles, activated by inspiratory loading, could be responsible for the lengthened latency of median nerve SEP components. Thus, respiratory afferents very likely interact with pathways of the somatosensory system.

Influence of respiratory afferents upon the proprioceptive reflex of skeletal muscles in healthy humans

Relationships between respiratory afferents and the motor drive to skeletal muscles are well documented in animals, but human data are scarce. Tonic vibratory response (TVR) elicited by mechanical tendon vibrations were explored in an arm (extensor digitorum, ED) and a leg (vastus lateralis, VL) muscle, in healthy subjects. Tendon vibrations were delivered during unloaded breathing and after 10 breathing cycles while the subject breathed through an inspiratory or expiratory resistive load in order to activate respiratory afferents. Inspiratory loaded breathing significantly enhanced TVR in ED and VL muscles whereas the effects of expiratory loading depended on the vibrated muscle (increased TVR in ED; decreased TVR in VL). These results suggest that inspiratory muscle afferents activated during inspiratory loading facilitate the gamma motor drive to arm and leg muscles whereas the activation of pulmonary vagal afferents during expiratory loading can exert a facilitating or suppressive influence on the gamma motor drive, depending on the limb muscle group.