Motoneurone synchronization for intercostal and abdominal muscles: interneurone influences in two different species.

The contribution of branched-axon monosynaptic inputs in the generation of short-term synchronization of motoneurones remains uncertain. Here, synchronization was measured for intercostal and abdominal motoneurones supplying the lower thorax and upper abdomen, mostly showing expiratory discharges. Synchronization in the anaesthetized cat, where the motoneurones receive a strong direct descending drive, is compared with that in anaesthetized or decerebrate rats, where the direct descending drive is much weaker. In the cat, some examples could be explained by branched-axon monosynaptic inputs, but many others could not, by virtue of peaks in cross-correlation histograms whose widths (relatively wide) and timing indicated common inputs with more complex linkages, e.g., disynaptic excitatory. In contrast, in the rat, correlations for pairs of internal intercostal nerves were dominated by very narrow peaks, indicative of branched-axon monosynaptic inputs. However, the presence of activity in both inspiration and expiration in many of the nerves allowed additional synchronization measurements between internal and external intercostal nerves. Time courses of synchronization for these often consisted of combinations of peaks and troughs, which have never been previously described for motoneurone synchronization and which we interpret as indicating combinations of inputs, excitation of one group of motoneurones being common with either excitation or inhibition of the other. Significant species differences in the circuits controlling the motoneurones are indicated, but in both cases, the roles of spinal interneurones are emphasised. The results demonstrate the potential of motoneurone synchronization for investigating inhibition and have important general implications for the interpretation of neural connectivity measurements by cross-correlation.

Patient and health care professional perspectives on using telehealth to deliver pulmonary rehabilitation.

The objective of this study was to identify the necessary features of pulmonary telerehabilitation (P-TR) from the perspectives of individuals living with chronic lung disease and health care professionals (HCPs) who deliver pulmonary rehabilitation (PR). Focus groups were carried out with patients ( n = 26) and HCPs ( n = 26) to elicit and explore their opinions about the critical elements of in-person PR and ideas for how these elements could be supported using technology. A questionnaire was used to assess technology use, PR experience, and general health status. Four key elements of PR were identified as critical to P-TR: the social aspect of PR; communicating with HCPs for education and support; using biosensors for monitoring and promoting self-knowledge; and the evolution of support with progress over time. A range of technology-enabled devices and programs were suggested as means to recreate aspects of these integral elements. Consultations with patients and HCPs suggest that users are interested in technology and want to ensure it recreates the important aspects of PR. Patients and HCPs identified similar key elements for P-TR. The opinions and suggestions of patients and HCPs should be the driving force of innovation if P-TR is to succeed in improving health outcomes.

Connections between expiratory bulbospinal neurons and expiratory motoneurons in thoracic and upper lumbar segments of the spinal cord.

Cross-correlation of neural discharges was used to investigate the connections between expiratory bulbospinal neurons (EBSNs) in the caudal medulla and expiratory motoneurons innervating thoracic and abdominal muscles in anesthetized cats. Peaks were seen in the cross-correlation histograms for around half of the EBSN-nerve pairs for the following: at T8, the nerve branches innervating internal intercostal muscle and external abdominal oblique muscle and a more distal branch of the internal intercostal nerve; and at L1, a nerve branch innervating internal abdominal oblique muscle and a more distal branch of the ventral ramus. Fewer peaks were seen for the L1 nerve innervating external abdominal oblique, but a paucity of presumed α-motoneuron discharges could explain the rarity of the peaks in this instance. Taking into account individual EBSN conduction times to T8 and to L1, as well as peripheral conduction times, nearly all of the peaks were interpreted as representing monosynaptic connections. Individual EBSNs showed connections at both T8 and L1, but without any discernible pattern. The overall strength of the monosynaptic connection from EBSNs at L1 was found to be very similar to that at T8, which was previously argued to be substantial and responsible for the temporal patterns of expiratory motoneuron discharges. However, we argue that other inputs are required to create the stereotyped spatial patterns of discharges in the thoracic and abdominal musculature.

A smartphone oximeter with a fingertip probe for use during exercise training: usability, validity and reliability in individuals with chronic lung disease and healthy controls.

BACKGROUND AND AIM: Telehealth is a strategy to expand the reach of pulmonary rehabilitation (PR). Smartphones can monitor and transmit oxygen saturation (SpO2) and heart rate (HR) data to ensure patient safety during home-based or other exercise. The purpose of this study was to evaluate the usability, validity and reliability of a Kenek O2 pulse oximeter and custom prototype smartphone application (smartphone oximeter) during rest and exercise in healthy participants and those with chronic lung disease. METHODS: Fifteen individuals with chronic lung disease and 15 healthy controls were recruited. SpO2 and HR were evaluated at rest and during cycling and walking. SpO2 was valid if the mean bias was within +±2%, the level of agreement (LoA) was within ±4%; HR was valid if the mean bias was within ±5 beats per min (bpm), LoA was within ±10bpm. Usability was assessed with a questionnaire and direct observation. RESULTS: The smartphone oximeter was deemed easy to use. At rest, SpO2 measures were valid in both groups (bias <2%, lower bound LoA -2 to 3%). During exercise, SpO2 measurement did not meet validity and reliability thresholds in the patients with chronic lung disease, but was accurate for the healthy controls. HR recording during exercise or rest was not valid (LoA>10bpm) in either group. CONCLUSIONS: The smartphone oximeter did not record HR or SpO2 accurately in patients with chronic lung disease during exercise, although SpO2 was valid at rest. During exercise, patients with chronic lung disease should pause to ensure greatest accuracy of SpO2 and HR measurement.

Reliability and validity of the Brief Pain Inventory in individuals with chronic obstructive pulmonary disease.

BACKGROUND: Pain is prevalent in chronic obstructive pulmonary disease (COPD) and the Brief Pain Inventory (BPI) appears to be a feasible questionnaire to assess this symptom. However, the reliability and validity of the BPI have not been determined in individuals with COPD. This study aimed to determine the internal consistency, test-retest reliability and validity (construct, convergent, divergent and discriminant) of the BPI in individuals with COPD. METHODS: In order to examine the test-retest reliability, individuals with COPD were recruited from pulmonary rehabilitation programmes to complete the BPI twice 1 week apart. In order to investigate validity, de-identified data was retrieved from two previous studies, including forced expiratory volume in 1-s, age, sex and data from four questionnaires: the BPI, short-form McGill Pain Questionnaire (SF-MPQ), 36-Item Short Form Survey (SF-36) and Community Health Activities Model Program for Seniors (CHAMPS) questionnaire. RESULTS: In total, 123 participants were included in the analyses (eligible data were retrieved from 86 participants and additional 37 participants were recruited). The BPI demonstrated excellent internal consistency and test-retest reliability. It also showed convergent validity with the SF-MPQ and divergent validity with the SF-36. The factor analysis yielded two factors of the BPI, which demonstrated that the two domains of the BPI measure the intended constructs. The BPI can also discriminate pain levels among COPD patients with varied levels of quality of life (SF-36) and physical activity (CHAMPS). CONCLUSION: The BPI is a reliable and valid pain questionnaire that can be used to evaluate pain in COPD. SIGNIFICANCE: This study formally established the reliability and validity of the BPI in individuals with COPD, which have not been determined in this patient group. The results of this study provide strong evidence that assessment results from this pain questionnaire are reliable and valid.

Allergic angiitis of Churg and Strauss syndrome. Response to pulse methylprednisolone.

Our patient presented with widespread airspace consolidation. He was a steroid-dependent asthmatic receiving moderate doses of corticosteroid therapy. Open lung biopsy showed allergic angiitis of Churg and Strauss syndrome. The patient continued to deteriorate on high doses of prednisone. He was subsequently given four pulses of intravenous methylprednisolone with dramatic clearing noted on x-ray film and resolution of his shunt.

Ventilatory dysfunction in severe anorexia nervosa.

A 25-year-old woman suffering from chronic anorexia nervosa lost more than 50 percent of her body weight and presented with generalized muscle weakness. Pulmonary function tests showed a severe restrictive defect, and she had marked impairment of respiratory muscle strength and endurance, peripheral muscle function, and hypercapnic ventilatory responses, all of which improved following refeeding. The interaction and response to treatment of these effects on respiratory function are discussed.

Pulmonary function in individuals with a history of poliomyelitis.

We examined the relationship between the lung function of 74 individuals with a history of poliomyelitis and reports of shortness of breath during activities of daily living, and the presence of post-polio sequelae risk factors. First, we studied the spirometry of 60 individuals (group 1) and second, we studied the relationship between the spirometry of an additional 14 individuals (group 2) and their respiratory muscle strength (Pimax and Pemax). In both groups, we examined the relationship between factors associated with post-polio sequelae including ventilation at polio-onset, having contracted polio after the age of 10, and having had polio for over 35 years; and lung function. In group 1, the FEV1 and FVC were lower for individuals with shortness of breath than individuals without (p less than 0.01). With respect to risk factors, FEV1 and FVC were lower in individuals who were ventilated at polio-onset, in individuals who contracted polio over 10 years of age, and in individuals who had had polio for less, rather than more than 35 years (p less than 0.05). The results for group 2 were comparable to group 1. In addition, the observed Pimax and Pemax were significantly lower than predicted values (p less than 0.05). Although FEV1 and FVC were positively correlated with both Pimax and Pemax (p less than 0.05), Pemax was disproportionately impaired compared to Pimax (40 +/- 12.1 and 82 +/- 38.8 percent predicted respectively). We conclude that individuals with a history of poliomyelitis can have compromised lung function irrespective of shortness of breath, that risk factors such as ventilation at polio-onset and polio-onset after 10 years of age can help predict those at risk of respiratory compromise, and that the measurement of respiratory muscle strength and of Pemax in particular, can augment the assessment of lung function of these individuals. Such assessment may avert respiratory complications in the post poliomyelitis population including those secondary to health care interventions.

Energy balance in stable malnourished patients with chronic obstructive pulmonary disease.

We have measured caloric intake, energy expenditure, and the thermogenic effect of food in ten patients with stable COPD who had a history of involuntary weight loss over several years and were malnourished (< 85 percent ideal body weight). Each patient completed a 7-day food record. Indirect calorimetry was performed in the resting postabsorptive state. After placement of a nasoenteric tube, patients were randomly assigned to be refed or sham-fed (mean +/- SD, 16 +/- 3 days), following which, metabolic measurements were repeated. Indirect calorimetry was also performed before and after a large meal in each patient. Home caloric intake was 135 +/- 23 percent of resting energy expenditure. Resting energy expenditure was 94 +/- 16 percent of that predicted by the Harris-Benedict equation and did not change significantly during inpatient refeeding. Refeeding resulted in weight gain (2.4 +/- 1.9 kg, p < 0.02). A large meal caused substantial increases in energy expenditure (24 +/- 18 percent), carbon dioxide production (39 +/- 18 percent), and oxygen consumption (23 +/- 16 percent). We conclude that stable malnourished COPD patients consume adequate calories to meet average energy requirements and are not hypermetabolic. Inpatient refeeding by nocturnal nasoenteric infusion is well tolerated and results in weight gain, but the thermogenic effect of a large meal poses a considerable metabolic and ventilatory load that could precipitate acute respiratory failure.

Effect of lung inflation on diaphragmatic shortening.

The effect of lung inflation on chest wall mechanics was studied in 11 vagotomized pentobarbital sodium-anesthetized dogs. Diaphragmatic shortening (percent change from initial length at functional residual capacity, %LFRC) and transdiaphragmatic pressure swings (delta Pdi) were compared with control values over a range of positive-pressure breathing that produced a maximum increase in lung volume to 40% of inspiratory capacity. There was no change in the electromyogram of the diaphragm or parasternal intercostals during positive-pressure breathing. delta Pdi and tidal volume (VT) fell to 52 +/- 3.3 and 42.5 +/- 5% (SE) of control. This was associated with a reduction in the initial resting length of 13 +/- 1.9 and 21 +/- 2.2%LFRC (SE) in the costal and crural diaphragms, respectively. Tidal diaphragmatic shortening, however, decreased to 66 +/- 7 and 57 +/- 7 and the mean velocity decreased to 78 +/- 10 and 63 +/- 8% (SE) of control for the costal and crural diaphragms, respectively. We conclude that the reduction in diaphragmatic shortening is the main determinant of the reduced delta Pdi and VT during lung inflation and relate this to what is currently known about diaphragmatic contractile properties.

Effects of posture on abdominal muscle shortening in awake dogs.

The objective of this study was to examine the effects of posture on tonic and phasic expiratory activity of the abdominal muscles in awake dogs. Six tracheostomized dogs were chronically instrumented with sonomicrometer transducers and bipolar electromyographic electrodes placed in each of the four abdominal muscles. To determine the effects of posture on tonic and phasic activity of individual abdominal muscles, muscle resting length (Lr) and tidal length changes (%Lr), respectively, were measured in awake dogs in the left lateral decubitus (LLD), sitting, and standing (STAND) positions. The transversus abdominis Lr consistently shortened when the dog was moved from LLD to STAND and lengthened when the dog was moved from LLD to the sitting position, and the external oblique Lr consistently lengthened when the dog went from LLD to STAND. The internal oblique and rectus abdominis had no consistent changes in Lr with a change in position. All four abdominal muscles actively shortened (%Lr) more in the upright positions. In addition, the internal layer (transversus abdominis and internal oblique) actively shortened more than the external layer (rectus abdominis and external oblique). In conclusion, both tonic and phasic respiratory activity of the abdominal muscles, reflected by changes in Lr and %Lr, respectively, were affected by changes in posture.

Inspiratory and expiratory muscle function during continuous positive airway pressure in dogs.

Continuous positive airway pressure (CPAP) is known to produce activation of the expiratory muscles. Several factors may determine whether this activation can assist inspiration. In this study we asked how and to what extent expiratory muscle contraction can assist inspiration during CPAP. Respiratory muscle response to CPAP was studied in eight supine anesthetized dogs. Lung volume and diaphragmatic initial length were defended by recruitment of the expiratory muscles. At the maximum CPAP of 18 cmH2O, diaphragmatic initial lengths were longer than predicted by the passive relationship by 52 and 46% in the costal and crural diaphragmatic segments, respectively. During tidal breathing after cessation of expiratory muscle activity, a component of passive inspiration occurred before the onset of inspiratory diaphragmatic electromyogram (EMG). At CPAP of 18 cmH2O, passive inspiration represented 24% of the tidal volume (VT) and tidal breathing was within the relaxation characteristic. Diaphragmatic EMG decreased at CPAP of 18 cmH2O; however, VT and tidal shortening were unchanged. We identified passive and active components of inspiration. Passive inspiration was limited by the time between the cessation of expiratory activity and the onset of inspiratory activity. We conclude that increased expiratory activity during CPAP defends diaphragmatic initial length, assists inspiration, and preserves VT. Even though breathing appeared to be an expiratory act, there remained a significant component of active inspiratory diaphragmatic shortening, and the major portion of VT was produced during active inspiration.

Abdominal muscle activity during hypercapnia in awake dogs.

We previously found the internal abdominal muscle layer to be preferentially recruited during expiratory threshold loading in anesthetized and awake dogs. Expiratory threshold loading increases end-expiratory lung volume and hence can activate reflex pathways such as tonic vagal reflexes, which could influence abdominal muscle recruitment. Our objectives in the present study were to determine the effects of hypercapnia on abdominal muscle activation and the pattern of recruitment in awake dogs. Five tracheotomized dogs were chronically implanted with sonomicrometer transducers and fine-wire electromyogram (EMG) electrodes in each of the four abdominal muscles: transversus abdominis, internal oblique, external oblique, and rectus abdominis. Muscle length changes and EMG activity were studied in the awake dog at rest and during CO2 rebreathing. CO2 rebreathing produced a tripling of tidal volume and activation of the abdominal muscles. Despite the increase in tidal volume, there was no significant change in abdominal muscle end-inspiratory length. Both tonic and phasic expiratory shortening were greater in the internal muscle layer (transversus abdominis and internal oblique) than in the external muscle layer (external oblique and rectus abdominis). We conclude that the internal abdominal muscles are preferentially recruited by hypercapnia and vagal reflexes probably do not contribute to this differential recruitment but that segmental reflexes may be involved. The mechanical consequences of this recruitment are discussed.

Mechanical response to hyperinflation of the two abdominal muscle layers.

Abdominal muscle length changes and activity were directly examined in vivo with the use of the techniques of sonomicrometry and electromyography, respectively, in nine supine anesthetized dogs. Expiratory threshold loading was utilized to stimulate recruitment of the abdominal muscles, and lung inflations produced the passive relationships. The internal layer, consisting of the internal oblique and transversus abdominis, shortened more in expiration than the external layer, consisting of the external oblique and rectus abdominis. The internal oblique shortened to approximately 83% of its length at functional residual capacity vs. 98% for the external oblique (P less than 0.05). The results obtained during passive lung inflation indicate these internal muscles are also more influenced by changes in lung volume. The internal oblique lengthened to 115% of its length at functional residual capacity vs. 103% for external oblique at total lung capacity (P less than 0.05). The results suggest that anatomic division of the abdominal muscles into external and internal layers corresponds to functional differences in terms of both passive lengthening and active shortening during ventilation and that these differences imply variable functions of the two layers.

Phrenic motoneuron firing rates before, during, and after prolonged inspiratory resistive loading.

Phrenic motoneuron firing rates during brief inspiratory resistive loading (IRL) are high, and nearly all the motoneurons are recruited. Diaphragmatic fatigue has been difficult to demonstrate during IRL. Furthermore, evidence from studies in limb muscles has shown variable motoneuron responses to prolonged high-intensity loads. We studied phrenic motoneuron firing rates before, during, and after prolonged IRL in anesthetized rabbits. Of 117 phrenic axons, only 2 axons were not recruited; 41 axons were silent during unloaded breathing but were recruited at higher loads. Silent axons showed a more rapid increase in firing rate as the load increased. Phrenic motoneuron firing rates increased throughout the period of loading, whereas airway pressure swings did not. After prolonged IRL, higher motoneuron firing rates were needed during brief loads to produce the same airway pressure. No evidence of a decline in motoneuron firing rates was seen at any point. We conclude that the respiratory muscles can be shown to demonstrate physiological responses consistent with fatigue during prolonged IRL, and activation rates are high and remain so throughout this prolonged loading.

Regional diaphragm shortening measured by sonomicrometry.

Diaphragmatic shortening measured by sonomicrometry has been compared in the two major anatomic segments, costal and crural. Data obtained by videofluoroscopy found a variation in subsegmental shortening within segments (Sprung et al. J. Appl. Physiol. 67: 655-662, 1989). No reproducible pattern of subsegmental shortening has emerged, and the mechanisms leading to this subsegmental variation in shortening are unknown. Therefore, we compared subsegmental shortening in both segments of the diaphragm in seven supine pentobarbital-anesthetized dogs. Seven pairs of sonomicrometer transducers were implanted in the two segments, and subsegmental shortening during spontaneous breathing was measured. To determine potential mechanisms contributing to the variation in shortening, measurements were made during stimulated breathing, after epiphrenic stimulation, and during occluded breaths. We found electrical stimulation at physiological frequencies of 10 and 20 Hz reduced the variation in subsegmental shortening, whereas stimulated breathing did not. Occluded breaths showed a consistent decrease in the amount of shortening, particularly in the dome of the costal diaphragm, compared with shortening in the area of apposition. Comparison of shortening between segments revealed greater crural than costal shortening. We conclude that subsegmental variation in activation can contribute to variation in subsegmental shortening and that the afterload can effect shortening during occluded breaths.

In vivo length and shortening of canine diaphragm with body postural change.

Using sonomicrometry, we measured the in vivo tidal shortening and velocity of shortening of the costal and crural segments of the diaphragm in the anesthetized dog in the supine, upright, tailup, prone, and lateral decubitus postures. When compared with the supine position, end-expiratory diaphragmatic length varied by less than 11% in all postures, except the upright. During spontaneous breathing, the tidal shortening and the velocity of shortening of the crural segment exceeded that of the costal segment in all postures except the upright and was maximal for both segments in the prone posture. We noted the phasic integrated electromyogram to increase as the end-expiratory length of the diaphragm shortened below and to decrease as the diaphragm lengthened above its optimal length. This study shows that the costal and crural segments have a different quantitative behavior with body posture and both segments show a compensation in neural drive to changes in resting length.

Stability of evoked parasternal intercostal muscle electromyogram at increased end-expiratory lung volume.

The diaphragmatic electromyogram has been measured as an index of the level of diaphragmatic activation. The diaphragmatic electromyogram, however, even when measured by intramuscular electrodes, can be artifactually altered by a change in lung volume (A. Brancatisano, S. M. Kelly, A. Tully, S. H. Loring, and L. A. Engel. J. Appl. Physiol. 66: 1699-1705, 1989) or by a change in body position. The parasternal intercostal muscle may be less subject to the mechanisms that are believed to produce this artifactual change. We asked whether the parasternal intercostal electromyographic activity could be reliable when lung volume changes. Six supine rabbits were anesthetized with ketamine and xylazine. Fine bipolar copper wires, with their tips exposed, were inserted into the left parasternal intercostal muscle in the third interspace. A stimulus that was three times maximal was applied to the corresponding intercostal nerve, and the resulting action potential (AP) was photographed. Parasternal intercostal muscle length was measured by sonomicrometry over the vital capacity range. There were small nonsignificant changes in the AP from functional residual capacity (FRC) to total lung capacity. From FRC to residual volume there was variation in the AP. The AP was also quite stable when regional conductivity was altered but showed variation when the parasternal intercostal muscle length change was accentuated by traction on the rib cage. We conclude that the parasternal intercostal electromyographic activity can be reliably used to measure inspiratory motoneuron output to it over the range of lung volumes from FRC to total lung capacity.

Delayed poststimulus decrease of phrenic motoneuron output produced by phrenic nerve afferent stimulation.

The immediate effects of phrenic afferent nerve activation on ventilation have been shown to be both excitatory and inhibitory. Long-lasting inhibitory effects on respiratory motoneuron output have been reported after stimulation of afferent nerves from limb muscles. However, whether respiratory muscle afferent nerves can produce this effect is unknown. We therefore hypothesized that activation of phrenic afferent nerves may produce a prolonged decrease of respiratory motoneuron output. Six alpha-chloralose-anesthetized dogs were studied after vagotomy and bilateral carotid sinus nerve section. The dogs were paralyzed, and end-tidal CO2 was controlled by mechanical ventilation. The proximal end of the cut thoracic phrenic nerve was electrically stimulated for 1 min at intensities that produced activation of thin-fiber afferents. The contralateral efferent phrenic integrated electroneurogram (ENG) was recorded. During stimulation, phrenic ENG activity increased. ENG activity was recorded during recovery and reached a peak decrease compared with control of 19 +/- 11% (SD) 9.0 +/- 6 min after stimulation and returned to control after 30 min. A qualitatively similar response was seen after stimulation of the gastrocnemius nerve. We conclude that activation of thin-fiber afferents in the phrenic nerve can produce a delayed and prolonged decrease of respiratory motoneuron output similar to that of limb muscle afferent nerves.

Respiratory muscle coordination and diaphragm length during expiratory threshold loading.

Active expiration is produced by the abdominal muscles and the rib cage expiratory muscles. We hypothesized that the relative contribution of these two groups to expiration would affect diaphragmatic length and, hence, influence the subsequent inspiration. To address this question we measured the respiratory muscle response to expiratory threshold loading in spontaneously breathing anesthetized dogs. Prevagotomy, the increase in lung volume (functional residual capacity) and decrease in initial resting length of the diaphragm were attenuated by greater than 50% of values predicted by the passive relationships. Diaphragmatic activation (electromyogram) increased and tidal volume (VT) was preserved. Postvagotomy, effective expiratory muscle recruitment was abolished. The triangularis sterni muscle remained active, and the increase in lung volume was attenuated by less than 15% of that predicted by the passive relationship. Diaphragmatic length was shorter than predicted. VT was not restored, even though costal diaphragmatic and parasternal intercostal electromyogram increased. During expiratory threshold loading with abdominal muscles resected and vagus intact, recruitment of the rib cage expiratory muscles produced a reduction in lung volume comparable with prevagotomy; however, diaphragmatic length decreased markedly. Both the rib cage and abdominal expiratory muscles may defend lung volume; however, their combined action is important to restore diaphragmatic initial length and, accordingly, to preserve VT.