Inspiratory Muscle Training Improves Intercostal and Forearm Muscle Oxygenation in Patients With Chronic Heart Failure: Evidence of the Origin of the Respiratory Metaboreflex.

BACKGROUND: The impact of inspiratory muscle training (IMT) on respiratory and peripheral muscle oxygenation and perfusion during inspiratory muscle fatigue in patients with chronic heart failure (HF) has not been established. METHODS AND RESULTS: Twenty-six patients with chronic HF were randomly assigned to either 8 weeks of IMT or a control group. Inspiratory fatigue was induced by means of a progressive inspiratory resistive loading protocol until there was an inability to sustain inspiratory pressure, when the inspiratory muscle metaboreflex should be activated. The main outcomes were intercostal and forearm muscle oxygen saturation and deoxygenation as measured by means of near-infrared spectroscopy (NIRS) and blood lactate levels. Inspiratory muscle strength was increased by 78% (P <.001) after 8 weeks of participation in the IMT group. IMT attenuated the reduction of oxygen saturation in intercostal and forearm muscles and the increase in blood lactate during respiratory fatigue (P <.001 and P <.05, respectively). These changes were different from the control group (P <.01, P <.05, and P <.05, respectively). After 8 weeks, similar increases in oxygen consumption, mean arterial pressure, heart rate, stroke volume, and cardiac output were observed in both groups during respiratory fatigue. CONCLUSIONS: This randomized controlled clinical trial demonstrates that IMT attenuates the respiratory muscle oxygen demand-delivery mismatch during respiratory fatigue in patients with chronic HF.

Intrinsic transient tracheal occlusion training and myogenic remodeling of rodent parasternal intercostal fibers.

It is recognized that diaphragm muscle plasticity occurs with mechanical overloads, yet less is known about synergistic parasternal intercostal muscle fiber remodeling. We conducted overload training with intrinsic transient tracheal occlusion (ITTO) exercises in conscious animals. We hypothesized that ITTO would yield significant fiber hypertrophy and myogenic activation that would parallel diaphragm fiber remodeling. Sprague-Dawley rats underwent placement of a tracheal cuff and were randomly assigned to receive daily 10 min sessions of conscious ITTO or observation (sham) over 2 wk. After training, fiber morphology, myosin heavy chain (MHC) isoform composition, cross-sectional area, proportion of Pax7-positive nuclei, and presence of embryonic MHC (eMHC) were quantified. Type IIx/b fibers were 20% larger after ITTO training than with sham training (ITTO: 4,431 +/­ 676 µm2, sham: 3,689 +/­ 400 µm2, p < 0.05), and type I fibers were more prevalent after ITTO (p < 0.01). Expression of Pax7 was increased in ITTO parasternals and diaphragm (p < 0.05). In contrast, the proportion of eMHC-positive fibers was increased only in ITTO parasternals (1.2% [3.4%­0.6%], sham: 0% [0.6%­0%], p < 0.05). Although diaphragm and parasternal type II fibers hypertrophy to a similar degree, myogenic remodeling appears to differ between the two muscles.

Determinants of inspiratory muscle strength in healthy humans.

We investigated (1) the relationship between the baseline and inspiratory muscle training (IMT) induced increase in maximal inspiratory pressure (P(I,max)) and (2) the relative contributions of the inspiratory chest wall muscles and the diaphragm (P(oes)/P(di)) to P(I,max) prior to and following-IMT. Experiment 1: P(I,max) was assessed during a Müeller manoeuvre before and after 4-wk IMT (n=30). Experiment 2: P(I,max) and the relative contribution of the inspiratory chest wall muscles to the diaphragm (P(oes)/P(di)) were assessed during a Müeller manoeuvre before and after 4-wk IMT (n=20). Experiment 1: P(I,max) increased 19% (P<0.01) post-IMT and was correlated with baseline P(I,max) (r=-0.373, P<0.05). Experiment 2: baseline P(I,max) was correlated with P(oe)/P(di) (r=0.582, P<0.05) and after IMT PI,max increased 22% and Poe/Pdi increased 5% (P<0.05). In conclusion, baseline P(I,max) and the contribution of the chest wall inspiratory muscles relative to the diaphragm affect, in part, baseline and IMT-induced P(I,max). Great care should be taken when designing future IMT studies to ensure parity in the between-subject baseline P(I,max).

Evaluation of a respiratory muscle biofeedback procedure-effects on heart rate and dyspnea.

Patients with respiratory diseases or anxiety frequently complain about dyspnea, which may be partly related to chronic tension of respiratory muscles and/or dynamic hyperinflation. In two experiments we tested a biofeedback technique that recorded electromyographic (EMG) activity from a bipolar surface electrode placement over the right external intercostal muscles with visual signal feedback. Healthy participants were tested in their ability to alter the signal. Heart rate was measured continuously throughout training trials. In the second experiment, dyspnea was rated on a modified Borg scale after each trial. Participants were able to increase their EMG activity considerably while heart rate and dyspnea increased substantially. Changes in EMG activity were achieved mostly by manipulating accessory muscle tension and/or altering breathing pattern. Thus, the technique is capable of altering respiratory muscle tension and associated dyspnea. Further studies may test the procedure as a relaxation technique in patients with respiratory disease or anxiety.

The association between upper trapezius activity and thorax movement in classical singing.

This study aimed to examine in classical singing the phasing of the activity in upper trapezius (TR) to upper and lower thorax movement and to the phasing of activity in the intercostals (INT) and in the lateral abdominal (OBL) muscles. Electromyographic (EMG) activity was recorded from the TR, INT, and OBL muscles on the right side. Thorax movement (TX) was traced with two strain gauge sensors placed around the upper and lower thorax. Four professional opera singers (soprano, mezzo, tenor, and baritone) and four advanced student classical singers (three sopranos and one mezzo) participated. Three of the professional singers were 33 years, and one was 40 years. The students were between 23 and 30 years. Different arias, freely chosen by the singers from their professional repertoire, served as the singing task for the opera singers. All students sang "Summertime" from Porgy and Bess. All subjects performed their task three times with variation in vocal loudness (normal, forte, piano). Thereafter, for all subjects, a biofeedback (BF) procedure was performed on TR to lower TR activity and a repeat performance of the singing tasks was carried out. EMG activity from the three recording sites and upper and lower TX circumference were compared before and after BF. A phasing of upper TR activity to INT and OBL activity was discovered, all muscles supporting the expiration phase. During phonation, the upper TR contributes in the compression of upper TX, thus serving as an accessory muscle of expiration. Group results from both opera singers and student singers showed that EMG activity was significantly lowered after BF. The lowered TR activity resulted in an expanded upper TX circumference and less TX respiratory movement after BF.

Muscle activity in professional classical singing: a study on muscles in the shoulder, neck and trunk.

This study aimed to examine whether changes in the activity of shoulder and neck muscles have consequences for the activation of primary breathing muscles. It further aimed to compare muscle loading levels of professional and student singers. Four professional opera singers participated in the study. Previous unpublished recordings of 4 to 16 student singers and one opera singer were included to allow comparison of EMG loading levels between student and professional singers. Electromyographic (EMG) recordings of trapezius (TR), sternocleidomastoideus (STM), intercostals (INT), rectus abdominis (RC) and the lateral abdominal muscles (OBL) were performed. EMG biofeedback (BF) was performed on TR and STM to lower the activity in these two muscles and the potential change in EMG activity of INT, RC and OBL were examined. Three singing tasks were performed: aria, sustained tones and extreme tones. Each task was performed three times with variation in volume or pitch. Following the first performance of the singing tasks, the BF session was carried out and muscle activity recorded in a repeat performance of the same tasks. The EMG activity levels of all muscles were compared before and after BF. We found no significant effect of reduced TR/STM activity on the activation of INT, RC and OBL. Professional opera singers activated the TR, INT, RC and OBL muscles to higher levels than the student singers did. Another finding was large inter-subject variation in muscle usage, showing an idiosyncratic composition of the muscle contribution to subglottal pressure.

Reduction in ventilator response to CO2 with relaxation feedback during CO2 rebreathing in normal adults.

BACKGROUND: Previous studies have shown that relaxation biofeedback reduced time on the ventilator for the difficult-to-wean patients. OBJECTIVE: To test the hypothesis that the underlying mechanism of biofeedback ventilator weaning was the reduction of neural respiratory drive (NRD). DESIGN: Prospective, linear regression analysis. SETTING: Critical care medicine department in tertiary health care hospital. SUBJECTS: Fifteen healthy adult volunteers were randomly assigned to the biofeedback group, and 15 healthy adult volunteers were randomly assigned to a control group. INTERVENTIONS: Relaxation feedback was administered while a single variable, PaCO2, was inputted to the respiratory control system and the output measured. While rebreathing 7% CO2/93% O2, the biofeedback group received a baseline session and a relaxation feedback session and the control group received a baseline session and a no feedback session. MEASUREMENTS AND RESULTS: During relaxation feedback, there was a significant (p < 0.001 to p < 0.05) reduction in the slope of minute ventilation (VI), mean inspiratory flow (VT/TI), occlusion pressure in 0.1 s from onset of inspiration (P100), respiration rate (RR), and diaphragm (DA) EMG compared to baseline. We also found the above breathing parameters decreased significantly for relaxation feedback (p < 0.001-0.05), compared to baseline, at maximum end-tidal CO2 (64 +/- 1.2 mm Hg) (all data are expressed as mean +/- SE). The decrease for VI = -4.65 +/- 1.17 L/min, DA EMG = -0.4 +/- 0.21 microV, P100 = -1.13 +/- 0.56 cm H2O, VT/ TI = -144 +/- 82.91 ml/s, and RR = -3.1 +/- 0.79 breaths/min. No significant changes occurred in these parameters for the control group. CONCLUSIONS: We conclude that the addition of the behavioral input of relaxation feedback results in decreasing the values of respiratory parameters that reflect NRD.

Artificial ventilation by means of electrical activation of the intercostal/accessory muscles alone in anesthetized dogs.

We have previously shown that large inspired volumes can be achieved in phrenicotomized animals by intercostal/accessory muscle activation via spinal cord stimulation. In the present study, we evaluated the utility of this technique to provide complete ventilatory support for prolonged time periods (6 to 8 h, selected arbitrarily). In 10 deeply anesthetized dogs, a single electrode was introduced onto the epidural surface of the spinal cord and positioned at the T2-T3 spinal level. Bilateral phrenicotomy was performed in all animals to prevent possible diaphragm activation. The spinal cord was rhythmically stimulated approximately 13 times/min with trains of 15- to 20-Hz impulses of sufficient amplitude to achieve inspired volumes of 13 to 15 ml/kg and pressure-time index (product of duty cycle and delta P/Pmax) of less than 0.15 with each contraction. Level of alveolar ventilation was monitored by end-tidal PCO2 and intermittent arterial blood gas measurements. Mean inspired volume and minute ventilation were 236 +/- 7.84 (SE) ml and 3.12 +/- 0.13 (SE) L/min, respectively, and not significantly different between the first and sixth hours of continuous stimulation. Mean duty cycle (Ti/Ttot) was 0.26 +/- 0.01. Mean airway pressure (delta P) during prolonged electrical stimulation under conditions of airway occlusion was 8.05 +/- 0.61 (SE) cm H2O. Mean ratio of delta P/Pmax was 0.47 +/- 0.03 (SE) cm H2O; mean pressure-time index was 0.12 +/- 0.01 (SE). There was no evidence of system fatigue, as evidenced by the lack of any significant shift in the pressure frequency curve over a 6-h time period.(ABSTRACT TRUNCATED AT 250 WORDS)

Inspiratory muscle function following abdominal weight exercises in healthy subjects.

Three indexes of inspiratory muscle function were evaluated in 20 healthy young adults before and after a six-week program of diaphragmatic breathing exercises. Thrice weekly, each subject performed 30 maximal voluntary diaphragmatic contractions in the supine position with a moderately heavy weight (range: 7-23 kg, or 15.4-50.7 lb) placed on the anterior abdominal wall to resist diaphragmatic descent. This protocol failed to improve 1) inspiratory capacity, 2) peak inspiratory flow rate, and 3) maximal pressures generated by the inspiratory muscles under static conditions. These finding indicated that this commonly used isotonic exercise regimen does not increase the maximal shortening, velocity of shortening, or strength of the diaphragm in healthy subjects. On the other hand, most subjects increased the maximal weight they found tolerable, performed the exercise more rapidly, and reported that their initial discomfort either waned or disappeared by the end of the program. These latter observations suggest that the exercise program might have improved inspiratory muscle endurance.

Regulation of the activity of respiratory muscles during sleep.

This review concerns studies on the electrograms of respiratory muscles carried out in unrestrained sleeping cats. The respiratory unit discharges of the diaphragm and intercostal muscles undergo only quantitative changes from quiet wakefulness to synchronized sleep. Intercostal postural activity is also evident whereas such activity is practically absent in diaphragmatic electrograms. During desynchronized sleep the activity, both postural and respiratory, of intercostal muscles is tonically depressed and highly irregular, while diaphragmatic electrograms are scarcely affected, except for random disturbances related to the phasic events of this stage of sleep (rems, muscle twitches). The changes in the activity of intercostal muscles do not depend on modifications of the activity of respiratory centres as phrenic motor neurones are not tonically depressed. Only strong phasic influences of non-respiratory brain stem structures may affect phrenic motor neurones during desynchronized sleep. The depression of intercostal respiratory activity during this stage of sleep rather depends on the tonic inhibitory influences of brain stem structures on spinal motor neurones affecting also intercostal postural activity. The respiratory frequency during desynchronized sleep increases and decreases above eupneic and below polypneic values of synchronized sleep, respectively. Such a phenomenon cannot be related to the tonic brain stem inhibition of spinal motor neurones occurring during desynchronized sleep as it is unlikely that the same influence may elicit two opposite effects. These effects can be better explained on the basis of a release of respiratory centres from higher controls, particularly hypothalamic. In conclusion, the clear dichotomy in respiratory motor innervation between synchronized and desynchronized sleep reveals a basic change in respiratory regulation whose functional significance is still obscure.