Mantilla, Carlos B.

Respiratory muscles such as the diaphragm are active across a range of behaviors including ventilation and higher-force behaviors necessary for maintenance of airway patency, and minimal information is available regarding anesthetic effects on the capacity of respiratory muscles to generate higher forces. The purpose of the present study was to determine whether diaphragm EMG activity during lower-force behaviors, such as eupnea and hypoxia-hypercapnia, is differentially affected compared with higher-force behaviors, such as a sigh, in lightly anesthetized animals. In adult male rats, chronically implanted diaphragm EMG electrodes were used to measure the effects of low-dose ketamine (30 mg/kg) and xylazine (3 mg/kg) on root mean square (RMS) EMG amplitude across a range of motor behaviors. A mixed linear model was used to evaluate the effects of ketamine-xylazine anesthesia on peak RMS EMG and ventilatory parameters, with condition (awake vs. anesthetized), behavior (eupnea, hypoxia-hypercapnia, sigh), side (left or right hemidiaphragm), and their interactions as fixed effects and animal as a random effect. Compared with the awake recordings, there was an overall reduction of peak diaphragm RMS EMG across behaviors during anesthesia, but this reduction was more pronounced during spontaneous sighs (which require ~60% of maximal diaphragm force). Respiratory rates and duty cycle during eupnea and hypoxia-hypercapnia were higher in awake compared with anesthetized conditions. These results highlight the importance of identifying anesthetic effects on a range of respiratory motor behaviors, including sighs necessary for maintaining airway patency.NEW & NOTEWORTHY Respiratory muscles accomplish a range of motor behaviors, with forces generated for ventilatory behaviors comprising only a small fraction of their maximal force generating capacity. Induction of anesthesia exerts more robust effects on the higher-force diaphragm motor behaviors such as sighs compared with eupnea. This novel information on effects of low, sedative doses of a commonly used anesthetic combination (ketamine-xylazine) highlights the importance of identifying anesthetic effects on a range of respiratory motor behaviors.

There is a mediolateral gradient in activation of the parasternal intercostal (PI) muscle during inspiration. In the present study, we tested the hypotheses that serotonergic [5-hydroxytryptamine (5-HT)] input from descending central drive and/or intrinsic size-related properties of PI motoneurons leads to the differential activation of PI muscles. In dogs, PI motoneurons innervating the medial and lateral regions of the PI muscles at the T3–T5interspaces were retrogradely labeled by intramuscular injection of cholera toxin B subunit. After a 10-day survival period, PI motoneurons and 5-HT terminals were visualized by using immunohistochemistry and confocal imaging. There were no differences in motoneuron morphology among motoneurons innervating the medial and lateral regions of the PI muscle. However, the number of 5-HT terminals and the 5-HT terminal density (normalized for surface area) were greater in motoneurons innervating the medial region of the PI muscle compared with the lateral region. These results suggest that differences in distribution of 5-HT input may contribute to regional differences in PI muscle activation during inspiration and that differences in PI motoneuron recruitment do not relate to size.

Incomplete cervical spinal cord hemisection at C2 (SH) disrupts descending excitatory drive to phrenic motoneurons, paralyzing the ipsilateral diaphragm muscle. Spontaneous recovery over time is associated with increased phrenic motoneuron expression of glutamatergic N-methyl-d-aspartate (NMDA) and serotonergic 5-HT2A receptors. We hypothesized that NMDA and 5-HT2A receptor-mediated neurotransmission play a role in ipsilateral diaphragm muscle activity post-SH. Adult male Sprague-Dawley rats were implanted with bilateral diaphragm EMG electrodes for chronic EMG recordings up to 28 days post-SH (SH 28D). The extent of recovery was calculated by peak root-mean-square (RMS) EMG amplitude. In all animals, absence of ipsilateral activity was verified at 3 days post-SH. Diaphragm EMG activity was also recorded during exposure to hypoxia-hypercapnia (10% O2-5% CO2). In SH animals displaying recovery of ipsilateral diaphragm EMG activity at SH 28D, cervical spinal cord segments containing the phrenic motor nucleus (C3–C5) were surgically exposed and either the NMDA receptor antagonist d-2-amino-5-phosphonovalerate (d-AP5; 100 mM, 30 μl) or 5-HT2A receptor antagonist ketanserin (40 mM, 30 μl) was instilled intrathecally. Following d-AP5, diaphragm EMG amplitude was reduced ipsilaterally, during both eupnea (42% of pre-d-AP5 value; P = 0.007) and hypoxia-hypercapnia (31% of pre-d-AP5 value; P = 0.015), with no effect on contralateral EMG activity or in uninjured controls. Treatment with ketanserin did not change ipsilateral or contralateral RMS EMG amplitude in SH animals displaying recovery at SH 28D. Our results suggest that spinal glutamatergic NMDA receptor-mediated neurotransmission plays an important role in ipsilateral diaphragm muscle activity after cervical spinal cord injury. NEW & NOTEWORTHY Spontaneous recovery following C2 spinal hemisection (SH) is associated with increased phrenic motoneuron expression of glutamatergic and serotonergic receptors. In this study, we show that pharmacological inhibition of glutamatergic N-methyl-d-aspartate (NMDA) receptors blunts ipsilateral diaphragm activity post-SH. In contrast, pharmacological inhibition of serotonergic 5-HT2A receptors does not change diaphragm EMG activity post-SH. Our results suggest that NMDA receptor-mediated glutamatergic neurotransmission plays an important role in enhancing rhythmic respiratory-related diaphragm activity after spinal cord injury.

Abstract Background Multimodal analgesia is standard practice for total knee arthroplasty; however, the role of regional techniques in improved perioperative outcomes remains unknown. The authors hypothesized that peripheral nerve blockade would result in lower pain scores and opioid consumption than two competing periarticular injection solutions. Methods This three-arm, nonblinded trial randomized 165 adults undergoing unilateral primary total knee arthroplasty to receive (1) femoral catheter plus sciatic nerve blocks, (2) ropivacaine-based periarticular injection, or (3) liposomal bupivacaine-based periarticular injection. Primary outcome was maximal pain during postoperative day 1 (0 to 10, numerical pain rating scale) in intention-to-treat analysis. Additional outcomes included pain scores and opioid consumption for postoperative days 0 to 2 and 3 months. Results One hundred fifty-seven study patients received peripheral nerve block (n = 50), ropivacaine (n = 55), or liposomal bupivacaine (n = 52) and reported median maximal pain scores on postoperative day 1 of 3, 4, and 4.5 and on postoperative day 0 of 1, 4, and 5, respectively (average pain scores for postoperative day 0: 0.6, 1.7, and 2.4 and postoperative day 1: 2.5, 3.5, and 3.7). Postoperative day 1 median maximal pain scores were significantly lower for peripheral nerve blockade compared to liposomal bupivacaine-based periarticular injection ( P = 0.016; Hodges–Lehmann median difference [95% CI] = −1 [−2 to 0]). After postanesthesia care unit discharge, postoperative day 0 median maximal and average pain scores were significantly lower for peripheral nerve block compared to both periarticular injections (ropivacaine: maximal −2 [−3 to −1]; P < 0.001; average −0.8 [−1.3 to −0.2]; P = 0.003; and liposomal bupivacaine: maximal −3 [−4 to −2]; P < 0.001; average −1.4 [−2.0 to −0.8]; P < 0.001). Conclusions Ropivacaine-based periarticular injections provide pain control comparable on postoperative days 1 and 2 to a femoral catheter and single-injection sciatic nerve block. This study did not demonstrate an advantage of liposomal bupivacaine over ropivacaine in periarticular injections for total knee arthroplasty.

Contusion-type injuries to the spinal cord are characterized by tissue loss and disruption of spinal pathways. Midcervical spinal cord injuries impair the function of respiratory muscles and may contribute to significant respiratory complications. This study systematically assessed the impact of a 100-kDy unilateral C4 contusion injury on diaphragm muscle activity across a range of motor behaviors in rats. Chronic diaphragm electromyography (EMG) was recorded before injury and at 1 and 7 days postinjury (DPI). Histological analyses assessed the extent of perineuronal net formation, white-matter sparing, and phrenic motoneuron loss. At 7 DPI, ∼45% of phrenic motoneurons were lost ipsilaterally. Relative diaphragm root mean square (RMS) EMG activity increased bilaterally across a range of motor behaviors by 7 DPI. The increase in diaphragm RMS EMG activity was associated with an increase in neural drive (RMS value at 75 ms after the onset of diaphragm activity) and was more pronounced during higher force, nonventilatory motor behaviors. Animals in the contusion group displayed a transient decrease in respiratory rate and an increase in burst duration at 1 DPI. By 7 days, following midcervical contusion, there was significant perineuronal net formation and white-matter loss that spanned 1 mm around the injury epicenter. Taken together, these findings are consistent with increased recruitment of remaining motor units, including more fatigable, high-threshold motor units, during higher force, nonventilatory behaviors. Changes in diaphragm EMG activity following midcervical contusion injury reflect complex adaptations in neuromotor control that may increase the risk of motor-unit fatigue and compromise the ability to sustain higher force diaphragm efforts.NEW & NOTEWORTHY The present study shows that unilateral contusion injury at C4 results in substantial loss of phrenic motoneurons but increased diaphragm muscle activity across a range of ventilatory and higher force, nonventilatory behaviors. Measures of neural drive indicate increased descending input to phrenic motoneurons that was more pronounced during higher force, nonventilatory behaviors. These findings reveal novel, complex adaptations in neuromotor control following injury, suggestive of increased recruitment of more fatigable, high-threshold motor units.

Unilateral C2cervical spinal cord hemisection (SH) disrupts descending excitatory drive to phrenic motor neurons, thereby paralyzing the ipsilateral diaphragm muscle (DIAm) during ventilatory behaviors. Recovery of rhythmic DIAm activity ipsilateral to injury occurs over time, consistent with neuroplasticity and strengthening of spared synaptic inputs to phrenic motor neurons. Localized intrathecal delivery of brain-derived neurotrophic factor (BDNF) to phrenic motor neurons after SH enhances recovery of eupneic DIAm activity. However, the impact of SH and BDNF treatment on the full range of DIAm motor behaviors has not been fully characterized. We hypothesized that all DIAm motor behaviors are affected by SH and that intrathecal BDNF enhances the recovery of both ventilatory and higher force, nonventilatory motor behaviors. An intrathecal catheter was placed in adult, male Sprague-Dawley rats at C4to chronically infuse artificial cerebrospinal fluid (aCSF) or BDNF. DIAm electromyography (EMG) electrodes were implanted bilaterally to record activity across motor behaviors, i.e., eupnea, hypoxia-hypercapnia (10% O2and 5% CO2), sighs, airway occlusion, and sneezing. After SH, ipsilateral DIAm EMG activity was evident in only 43% of aCSF-treated rats during eupnea, and activity was restored in all rats after BDNF treatment. The amplitude of DIAm EMG (root mean square, RMS) was reduced following SH during eupnea and hypoxia-hypercapnia in aCSF-treated rats, and BDNF treatment promoted recovery in both conditions. The amplitude of DIAm RMS EMG during sighs, airway occlusion, and sneezing was not affected by SH or BDNF treatment. We conclude that the effects of SH and BDNF treatment on DIAm activity depend on motor behavior.NEW & NOTEWORTHY This study demonstrates that after unilateral C2spinal cord hemisection (SH), there are differences in the spontaneous recovery of diaphragm (DIAm) electromyographic activity during ventilatory compared with more forceful, nonventilatory motor behaviors. Furthermore, we show that intrathecal delivery of brain-derived neurotrophic factor (BDNF) at the level of the phrenic motor neuron pool enhances recovery of ipsilateral DIAm activity following SH, exerting main effects on recovery of ventilatory but not higher force, nonventilatory behaviors.

ABSTRACTCervical spinal hemisection at C2 (SH) removes premotor drive to phrenic motoneurons located in segments C3–C5 in rats. Spontaneous recovery of ipsilateral diaphragm muscle activity is associated with increased phrenic motoneuron expression of glutamatergic N‐methyl‐D‐aspartate (NMDA) receptors and decreased expression of α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐proprionic acid (AMPA) receptors. Glutamatergic receptor expression is regulated by tropomyosin‐related kinase receptor subtype B (TrkB) signaling in various neuronal systems, and increased TrkB receptor expression in phrenic motoneurons enhances recovery post‐SH. Accordingly, we hypothesize that recovery of ipsilateral diaphragm muscle activity post‐SH, whether spontaneous or enhanced by adenoassociated virus (AAV)‐mediated upregulation of TrkB receptor expression, is associated with increased expression of glutamatergic NMDA receptors in phrenic motoneurons. Adult male Sprague‐Dawley rats underwent diaphragm electromyography electrode implantation and SH surgery. Rats were injected intrapleurally with AAV expressing TrkB or GFP 3 weeks before SH. At 14 days post‐SH, the proportion of animals displaying recovery of ipsilateral diaphragm activity increased in AAV–TrkB‐treated (9/9) compared with untreated (3/5) or AAV–GFP‐treated (4/10; P < 0.027) animals. Phrenic motoneuron NMDA NR1 subunit mRNA expression was approximately fourfold greater in AAV–TrkB‐ vs. AAV–GFP‐treated SH animals (P < 0.004) and in animals displaying recovery vs. those not recovering (P < 0.005). Phrenic motoneuron AMPA glutamate receptor 2 (GluR2) subunit mRNA expression decreased after SH, and, albeit increased in animals displaying recovery vs. those not recovering, levels remained lower than control. We conclude that increased phrenic motoneuron expression of glutamatergic NMDA receptors is associated with spontaneous recovery after SH and enhanced recovery after AAV–TrkB treatment. J. Comp. Neurol. 525:1192–1205, 2017. © 2016 Wiley Periodicals, Inc.

Previous work investigating respiratory system mechanics in mice has reported an aging-related increase in compliance and mean linear intercept ( Lm). However, these changes were assessed using only a young (2-mo-old) and old (20- and 26-mo-old) group yet were interpreted to reflect a linear evolution across the life span. Therefore, to investigate respiratory system mechanics and lung morphometry across a more complete spectrum of ages, we utilized 2 (100% survival, n = 6)-, 6 (100% survival, n = 12)-, 18 (90% survival, n = 12)-, 24 (75% survival, n = 12)-, and 30 (25% survival, n = 12)-mo-old C57BL/6 mice. We found a nonlinear aging-related decrease in respiratory system resistance and increase in dynamic compliance and hysteresis between 2- and 24-mo-old mice. However, in 30-mo-old mice, respiratory system resistance increased, and dynamic compliance and hysteresis decreased relative to 24-mo-old mice. Respiratory system impedance spectra were measured between 1–20.5 Hz at positive end-expiratory pressures (PEEP) of 1, 3, 5, and 7 cmH2O. Respiratory system resistance and reactance at each level of PEEP were increased and decreased, respectively, only in 2-mo-old animals. No differences in the respiratory system impedance spectra were observed in 6-, 18-, 24-, and 30-mo-old mice. Additionally, lungs were fixed following tracheal instillation of 4% paraformaldehyde at 25 cmH2O and processed for Lm and airway collagen deposition. There was an aging-related increase in Lm consistent with emphysematous-like changes and no evidence of increased airway collagen deposition. Accordingly, we demonstrate nonlinear aging-related changes in lung mechanics and morphometry in C57BL/6 mice.

Background. Postthoracotomy pain syndrome (PTPS) is unfortunately very common following thoracotomy and results in decreased quality of life. The purpose of this retrospective study was to determine perioperative patient, surgical, and analgesic characteristics associated with the development of PTPS. Methods. Sixty-six patients who presented to the Mayo Clinic Rochester Pain Clinic were diagnosed with PTPS 2 months or more after thoracotomy with postoperative epidural analgesia. These patients were matched with sixty-six control patients who underwent thoracotomy with postoperative epidural analgesia and were never diagnosed with PTPS. Results. Median (IQR) hospital stay was significantly different between control patients (5 days (4, 6)) compared with PTPS patients (6 days (5, 8)), P<0.02. The total opioid equivalent utilized in oral morphine equivalents in milligrams for the first three days postoperatively was significantly different between control patients and PTPS patients. The median (IQR) total opioid equivalent utilized was 237 (73, 508) for controls and 366 (116, 874) for PTPS patients (P<0.005). Conclusion. Patients with a prolonged hospital stay after thoracotomy were at an increased risk of developing PTPS, and this is a novel finding. Patients who utilize higher oral morphine equivalents for the first 3 days were also at increased risk for PTPS.