Hemidiaphragmatic Paralysis Research Articles

An Unusual Case of Herpes Zoster Complicated by Asymptomatic Phrenic Nerve Paralysis in a Hemodialysis Patient

Herpes Zoster (HZ) is the clinical manifestation of latent Varicella Zoster Virus (VZV) reactivation which can occur several decades after the early infection by Varicella Virus. Herpes Zoster usually affects the sensory neurons but may occasionally involve motor neurons corresponding to the dermatomes affected by skin lesions, resulting in flaccid paralysis of their muscles. Phrenic nerve paralysis is commonly caused by surgical or traumatic injuries, malignant tumors, neurodegenerative disorders or idiopathic diseases. However, in rare cases, it has been reported a diaphragmatic paralysis resulting from infection by Herpes Varicella Zoster Virus (VZV). We report a case of a 58 years old man, undergoing hemodialysis, who developed a left diaphragmatic paralysis after a typical Herpes Zoster rash involving the dermatome C3-C4 on the left side. The clinical and radiological results revealed no local causes of injury to the phrenic nerve. Hemidiaphragmatic paralysis was probably related to the infection by VZV. We asked ourselves if underdosing of the antiviral therapy (in the uremic patient) or the shortness of the treatment may have contributed to the development of this complication. However we believe that the risks resulting from overdosing outweigh the benefits. Therefore further studies, especially in ESRD, would be needed in order to evaluate if the dose adjustment and/or a prolongation of the antiviral therapy may have a protective effect on the onset of diaphragmatic paralysis.

Hypercapnic respiratory distress and loss of consciousness: a complication of supraclavicular brachial plexus block

Supraclavicular brachial plexus block is a common anesthetic technique performed for surgery of the upper extremities. We experienced a case of acute hypercapnic respiratory distress with loss of consciousness during creation of an arteriovenous fistula under ultrasound-guided supraclavicular brachial plexus block using 30 mL of 0.75 % ropivacaine. We detected ipsilateral hemidiaphragmatic paralysis by means of M-mode ultrasonography of the block. We thus speculate that phrenic nerve palsy caused by supraclavicular brachial plexus block was the underlying mechanism of the event. Bedside ultrasonography played a pivotal role in making a differential diagnosis and in managing this patient.

Dynamic changes in phrenic motor output following high cervical hemisection in the decerebrate rat

Hemisection of the spinal cord at C2 eliminates ipsilateral descending drive to the phrenic nucleus and causes hemidiaphragmatic paralysis in rats. Phrenic nerve (PhN) or diaphragmatic activity ipsilateral to hemisection can occasionally be induced acutely following hemisection by respiratory stressors (i.e., hypercapnia, asphyxia, contralateral phrenicotomy) and becomes spontaneously active days-to-weeks later. These investigations, however, are potentially confounded by the use of anesthesia, which may suppress spontaneously-active crossed phrenic pathways. Experiments were performed on vecuronium-paralyzed, unanesthetized, decerebrate adult male rats and whole PhN activity recorded continuously before, during, and after high cervical hemisection at the C1 spinal level. Crossed phrenic activity recovered spontaneously over minutes-to-hours with maximal recovery of 11.8±3.1% (m±SE) in the PhN ipsilateral to hemisection. Additionally, there was a significant increase in PhN activity contralateral to hemisection of 221.0±40.4% (m±SE); since animals were artificially-ventilated, these changes likely represent an increase in central respiratory drive. These results underscore the state-dependence of crossed bulbophrenic projections and suggest that unanesthetized models may be more sensitive in detecting acute recovery of respiratory output following spinal cord injury (SCI). Additionally, our results may suggest an important role for a group of C1–C2 neurons exhibiting respiratory-related activity, spared by the higher level of hemisection. These units may function as relays of polysynaptic bulbophrenic pathways and/or provide excitatory drive to phrenic motoneurons. Our findings provide a new model for investigating acute respiratory recovery following cervical SCI, the high C1-hemisected unanesthetized decerebrate rat and suggest a centrally-mediated increase in central respiratory drive in response to high cervical SCI.

Postural disturbances resulting from unilateral and bilateral diaphragm contractions: a phrenic nerve stimulation study.

Thoracoabdominal breathing movements are a complex source of postural disturbance, but there are contradictory reports in the literature with inspiration described as having either a backward or a forward disturbing effect. To elucidate the mechanisms underlying this phenomenon, the present study studied the postural disturbance caused by isolated contractions of the diaphragm. Eight male and four female healthy subjects followed an original paradigm of phrenic nerve stimulation (bilateral and unilateral) and "diaphragmatic" voluntary sniff maneuvers in the seated and standing postures. Center of gravity (CG) acceleration was calculated from force plate recordings, and respiratory kinematics were assessed with thoracic and abdominal sensor belts. CG and respiratory signals revealed that, while seated, bilateral phrenic stimulation and sniff maneuvers consistently produced expansion of the abdomen associated with a forward peak of CG acceleration. In the standing posture, the direction of the CG peak was reversed and always directed backward. Unilateral phrenic stimulation induced an additional medial-lateral acceleration of the CG, directed toward the nonactive side while seated, but in the opposite direction while standing. These results suggest that isolated diaphragmatic contractions produce a constant disturbing pattern for a given posture, but with opposite effects between standing and seated postures. This could be related to the different biomechanical configuration of the body in each posture, corresponding to distinct kinematic patterns of the osteoarticular chain. In addition, the lateral component of the CG acceleration induced by unilateral diaphragm contractions could be clinically relevant in patients with hemidiaphragm paralysis.

Ipsilateral inspiratory intercostal muscle activity after C2 spinal cord hemisection in rats

BackgroundUpper cervical spinal cord hemisection causes paralysis of the ipsilateral hemidiaphragm; however, the effect of C2 hemisection on the function of the intercostal muscles is not clear. We hypothesized that C2 hemisection would eliminate inspiratory intercostal activity ipsilateral to the injury and that some activity would return in a time-dependent manner.MethodsFemale Sprague Dawley rats were anesthetized with urethane and inspiratory intercostal electromyogram (EMG) activity was recorded in control rats, acutely injured C2 hemisected rats, and at 1 and 16 weeks post C2 hemisection.ResultsBilateral recordings of intercostal EMG activity showed that inspiratory activity was reduced immediately after injury and increased over time. EMG activity was observed first in rostral spaces followed by recovery occurring in caudal spaces. Theophylline increased respiratory drive and increased intercostal activity, inducing activity that was previously absent.ConclusionThese results suggest that there are crossed, initially latent, respiratory connections to neurons innervating the intercostal muscles similar to those innervating phrenic motor neurons.

横隔神経麻痺を合併した機能的単心室の肺循環動態：横隔膜縫縮術およびFontan型手術前後で左右の肺循環評価を行った1例

横隔神経麻痺を合併した機能的単心室の肺循環動態：横隔膜縫縮術およびFontan型手術前後で左右の肺循環評価を行った1例

Rebuttal from Scott K. Powers, Ashley J. Smuder, David Fuller and Sanford Levine

Drs Sieck and Mantilla have presented an eloquent argument that diaphragm muscle fibre atrophy following unilateral phrenicotomy, tetrodotoxin (TTX) nerve blockade or high cervical spinal hemisection injury does not result from muscle inactivity alone. Nonetheless, we retain our position that when diaphragmatic contractile work is diminished during prolonged mechanical ventilation (MV), the ensuing diaphragm fibre atrophy occurs primarily due to decreased diaphragm contractile activity. In our response to Dr Sieck and Mantilla's position, we highlight several fundamental differences between the unilateral denervation model of diaphragm inactivity and the reduced diaphragmatic contractile work that occurs during prolonged MV. A fundamental difference between these two models of diaphragm inactivity is that prolonged MV results in atrophy of all diaphragm muscle fibre types whereas unilateral phrenic denervation promotes a transient hypertrophy of diaphragmatic type I and IIa fibres followed by atrophy of type IIx and IIb fibres. This is a unique physiological response as muscle hypertrophy does not occur in any other model of skeletal muscle inactivity. Another major difference is that diaphragm movement patterns differ markedly between the unilateral phrenic denervation model of diaphragm inactivity and MV. During MV, both hemidiaphragms move synchronously as the lungs inflate and empty. In contrast, following unilateral phrenic denervation, the contralateral hemidiaphragm contracts and shortens, thus eliciting small fibre length changes in the paralysed hemidiaphragm (Zhan et al. 1995). Since muscle fibre size is a highly regulated process controlled by mechanical signals, neurotrophic influences, and paracrine signalling which regulate muscle protein turnover (Rennie et al. 2004), the possibility exists that distortion of the paralysed diaphragm elicits an anabolic signalling response to promote hypertrophy. Importantly, not all studies report diaphragmatic hypertrophy following denervation-induced inactivity. Indeed, a study from Dr Sieck's laboratory revealed that unilateral denervation of the rat diaphragm results in a net loss of muscle protein after 5 days (Argadine et al. 2009). It follows that this deficit of muscle protein should translate into diaphragm fibre atrophy but unfortunately, this study did not report diaphragm fibre size. Further, in direct contrast to the rat data, hemidiaphragm paralysis in humans results in atrophy of diaphragm slow muscle fibres with atrophy of fast fibres occurring at a slower time course (Welvaart et al. 2011). Interestingly, these results agree with the Sieck–Mantilla initial theoretical argument that inactivity-induced diaphragm muscle fibre atrophy should occur most rapidly in slow fibres. In conclusion, based on our work and the work of others, we maintain the position that during prolonged MV, when diaphragm work against external loads is greatly diminished, the ensuing diaphragm atrophy is primarily due to decreased diaphragm contractile work.

Histopathology of Cryoballoon Ablation‐Induced Phrenic Nerve Injury

Hemi-diaphragmatic paralysis is the most common complication associated with cryoballoon ablation for atrial fibrillation, yet the histopathology of phrenic nerve injury has not been well described. A preclinical randomized study was conducted to characterize the histopathology of phrenic nerve injury induced by cryoballoon ablation and assess the potential for electromyographic (EMG) monitoring to limit phrenic nerve damage. Thirty-two dogs underwent cryoballoon ablation of the right superior pulmonary vein with the objective of inducing phrenic nerve injury. Animals were randomized 1:1 to standard monitoring (i.e., interruption of ablation upon reduction in diaphragmatic motion) versus EMG guidance (i.e., cessation of ablation upon a 30% reduction in the diaphragmatic compound motor action potential [CMAP] amplitude). The acute procedural endpoint was achieved in all dogs. Phrenic nerve injury was characterized by Wallerian degeneration, with subperineural injury to large myelinated axons and evidence of axonal regeneration. The degree of phrenic nerve injury paralleled the reduction in CMAP amplitude (P= 0.007). Animals randomized to EMG guidance had a lower incidence of acute hemi-diaphragmatic paralysis (50% vs 100%; P= 0.001), persistent paralysis at 30 days (21% vs 75%; multivariate odds ratio 0.12, 95% confidence interval [0.02, 0.69], P= 0.017), and a lesser severity of histologic injury (P= 0.001). Mature pulmonary vein ablation lesion characteristics, including circumferentiality and transmurality, were similar in both groups. Phrenic nerve injury induced by cryoballoon ablation is axonal in nature and characterized by Wallerian degeneration, with potential for recovery. An EMG-guided approach is superior to standard monitoring in limiting phrenic nerve damage.

“Trap-door” and “clamshell” surgical approaches for the management of pediatric tumors of the cervicothoracic junction and mediastinum

Background/PurposeFor pediatric tumors of the cervicothoracic junction, an isolated cervical or thoracic surgical approach provides insufficient exposure for achieving complete resection. We retrospectively examined “trap-door” and “clamshell” pediatric thoracotomies as a surgical approach to these tumors. MethodsWe searched our database for pediatric patients with cervicothoracic tumors who underwent clamshell or trap-door thoracotomy between 1991 and 2013, reviewing tumor characteristics, surgical technique, completeness of resection, morbidity, and outcome. ResultsTrap-door (n=13) and clamshell (n=4) thoracotomies were performed for neuroblastoma (n=9), non-rhabdomyosarcoma soft tissue sarcoma (n=4), germ cell tumor (n=2), rhabdomyosarcoma (n=1), and neuroendocrine small cell carcinoma (n=1). Fourteen of these cervicothoracic tumors were primary, and three were metastatic. Gross total resection was achieved in 15 patients (94%). Operative complications included vocal cord paralysis (n=2), mild upper-extremity neuropraxia (n=2), and hemidiaphragm paralysis (n=1), All but one involved encased nerves. Overall survival was 61% for the series and 80% for patients with primary tumors. Eleven (73%) of 15 patients who underwent gross total resection had no evidence of recurrence. Three patients with metastatic disease died of distant progression within 1.3years. ConclusionsGross total resection of primary cervicothoracic tumors can be accomplished with specialized exposure in pediatric patients with minimal morbidity.

Effect of Phrenic Nerve Palsy on Early Postoperative Lung Function After Pneumonectomy: A Prospective Study

The issue of phrenic nerve preservation during pneumonectomy is still an unanswered question. So far, its direct effect on immediate postoperative pulmonary lung function has never been evaluated in a prospective trial. We conducted a prospective crossover study including 10 patients undergoing pneumonectomy for lung cancer between July 2011 and July 2012. After written informed consent, all consecutive patients who agreed to take part in the study and in whom preservation of the phrenic nerve during operation was possible, were included in the study. Upon completion of lung resection, a catheter was placed in the proximal paraphrenic tissue on the pericardial surface. After an initial phase of recovery of 5 days all patients underwent ultrasonographic assessment of diaphragmatic motion followed by lung function testing with and without induced phrenic nerve palsy. Thecontrolled, temporary paralysis of the ipsilateral hemidiaphragm was achieved by local administration of lidocaine 1% at a rate of 3 mL/h (30 mg/h) via the above-mentioned catheter. Temporary phrenic nerve palsy was accomplished in all but 1 patient with suspected catheter dislocation. Spirometry showed a significant decrease in dynamic lung volumes (forced expiratory volume in 1 second and forced vital capacity; p < 0.05) with the paralyzed hemidiaphragm. Blood oxygen saturation levels did not change significantly. Our results show that phrenic nerve palsy causes a significant impairment of dynamic lung volumes during the early postoperative period after pneumonectomy. Therefore, in these already compromised patients, intraoperative phrenic nerve injury should be avoided whenever possible.

Course, Predictors of Diaphragm Recovery After Phrenic Nerve Injury During Pediatric Cardiac Surgery

Hemidiaphragm paralysis from phrenic nerve injury is a known complication of congenital cardiac surgery. Return of diaphragm function has been reported; however, prior studies on this subject have been limited by small numbers, static assessment methods, or observation of plicated or non-plicated patients alone. To describe return of function, we reviewed fluoroscopy and ultrasonography in all diagnosed cases of diaphragmatic paralysis. Surgical cases at our institution between 1991 and 2010 were identified for patients with postoperative hemidiaphragm paralysis diagnosed by chest X-ray, ultrasound, or fluoroscopy. Follow-up ultrasound and fluoroscopic studies were reviewed for return of diaphragm function. Seventy-two cases of postoperative hemidiaphragm paralysis were identified. Forty cases were plicated prior to discharge. Plicated patients were younger at time of diagnosis (median 46 days average 3.6 months; p=0.025) and had a larger proportion of single ventricle diagnoses (48% vs 16%) compared with non-plicated patients. Twenty-six patients with paralysis were excluded in follow-up due to lack of studies documenting diaphragm function after the diagnostic study. Of the remaining 46 cases, median follow-up was 353 days (range: 6 days to 17 years). Plicated and non-plicated patients regained function at similar frequency (60% and 54.8%, respectively). Plication status, Risk Adjustment for Congenital Heart Surgery (RACHS) 1 score, age at diagnosis, and side of paralysis did not predict failure of recovery. In the current era, return of diaphragm function after phrenic nerve injury sustained during congenital cardiac surgery is a known occurrence; however, predicting recovery continues to be difficult.

Effects of diaphragm plication on pulmonary function and cardiopulmonary exercise parameters

Paralysis of the diaphragm is an uncommon condition, which may result in dyspnoea on excertion and in orthopnea. In patients who have symptoms, the paralysed diaphragm is often plicated to prevent its paradoxical movement on inspiration. This procedure brings relief to many patients, but the mechanism for this improvement is not well understood. Nine symptomatic patients who underwent plication of a unilateral paralysed hemidiaphragm were prospectively evaluated. All patients underwent pulmonary function tests and cardiopulmonary exercise tests before surgery and repeated them after surgery. Patients with hemidiaphragm paralysis before surgery were found to have lower tidal volumes at any given ventilation rate during exercise than normal subjects. A clear and consistent change was found in the manner in which patients increased their ventilation during exercise after surgery. All patients showed an increase in tidal volume for a given ventilation rate, which was significant. The plication procedure reduced the respiratory rate for any exercise level in all patients, and this effect was more pronounced during exercise. In patients with hemidiaphragm paralysis who underwent a diaphragm plication exercise, tidal volumes increased and the ventilatory frequency decreased. Despite this improvement, maximal exercise capacity remained unaltered.

Transient right hemidiaphragmatic paralysis following subclavian venous catheterization: possible implications of anatomical variation of the phrenic nerve -a case report-

Phrenic nerve paralysis is an unusual complication associated with central venous catheterization. Various mechanisms have been proposed. We present a case of transient right hemidiaphragmatic paralysis after subclavian venous catheterization. We hypothesize that anatomical variation of the phrenic nerve was responsible for this complication.

A Rash Case of Hiccups

A Rash Case of Hiccups

Sonographic evaluation of a paralyzed hemidiaphragm from ultrasound-guided interscalene brachial plexus nerve block

The ultrasound-guided interscalene brachial plexus is becoming increasingly popular for anesthesia in the management of upper-extremity injuries by emergency physicians. Traditional high-volume injections of local anesthesia will also affect the phrenic nerve, leading to temporary paralysis of the ipsilateral hemidiaphragm. With direct ultrasound guidance, more precise needle placement allows for lower-volume injections that reduce inadvertent spread of local anesthetic to the phrenic nerve without decreasing the efficacy of onset of time and quality of the block. However, the risk of incidental paralysis of the hemidiaphragm is still not eliminated with low-volume intraplexus injections. This case highlights this common complication of interscalene brachial plexus nerve blocks and demonstrates how emergency physicians can easily use B-mode and M-mode ultrasound to evaluate the paralysis of the hemidiaphragm.

The effect of initial local anesthetic dose with continuous interscalene analgesia on postoperative pain and diaphragmatic function in patients undergoing arthroscopic shoulder surgery: a double-blind, randomized controlled trial

BackgroundInterscalene block (ISB) is commonly performed using 20-40 mL of local anesthetic. Spread to adjacent structures and consequent adverse effects including paralysis of the ipsilateral hemidiaphragm are frequent. Pain ratings, analgesic requirements, adverse events, satisfaction, function and diaphragmatic excursion were compared following interscalene block (ISB) with reduced initial bolus volumes.MethodsSubjects undergoing arthroscopic rotator cuff repair were randomized to receive 5, 10, or 20 mL ropivacaine 0.75% for ISB in a double-blind fashion (N = 36). Continuous infusion with ropivacaine 0.2% was maintained for 48 h. Pain and diaphragmatic excursion were assessed before block and in the recovery unit.ResultsPain ratings in the recovery room were generally less than 4 (0-10 NRS) for all treatment groups, but a statistically significant difference was noted between the 5 and 20 mL groups (NRS: 2.67 vs. 0.62 respectively; p = 0.04). Pain ratings and supplemental analgesic use were similar among the groups at 24 h, 48 h and 12 weeks. There were no differences in the quality of block for surgical anesthesia. Dyspnea was significantly greater in the 20 mL group (p = 0.041). Subjects with dyspnea had significant diaphragmatic impairment more frequently (Relative risk: 2.5; 95%CI: 1.3-4.8; p = 0.042). Increased contralateral diaphragmatic motion was measured in 29 of the 36 subjects. Physical shoulder function at 12 weeks improved over baseline in all groups (baseline mean SST: 6.3, SEM: 0.6; 95%CI: 5.1-7.5; 12 week mean SST: 8.2, SEM: 0.46; 95%CI: 7.3-9.2; p = 0.0035).ConclusionsISB provided reliable surgical analgesia with 5 mL, 10 mL or 20 mL ropivacaine (0.75%). The 20 mL volume was associated with increased complaints of dyspnea. The 5 mL volume was associated with statistically higher pain scores in the immediate postoperative period. Lower volumes resulted in a reduced incidence of dyspnea compared to 20 mL, however diaphragmatic impairment was not eliminated. Compensatory increases in contralateral diaphragmatic movement may explain tolerance for ipsilateral paresis.Trial Registrationclinicaltrials.gov. identifier: NCT00672100

A Case of Diaphragmatic Paralysis Complicated by Herpes-zoster Virus Infection

Diaphragmatic paralysis is commonly caused by surgical and traumatic injuries, malignant neoplasm, and neurodegenerative disorders. However, in rare instances, diaphragmatic paralysis due to herpes-zoster virus infection has been reported. Here, we describe an 85-year-old woman who developed left hemidiaphragmatic paralysis within 19 days of the appearance of a typical herpes-zoster rash involving the C4-5 dermatome on the left side. Clinical and radiological findings revealed no local causes of phrenic nerve lesion. The hemidiaphragmatic paralysis was thought to be caused by herpes-zoster virus infection.

Phrenic nerve injury after image-guided insertion of a tunnelled right internal jugular central venous catheter

Central venous catheters (CVC) are now commonly inserted by radiologists. Although complications are infrequent, they must be avoided where possible and recognized when they occur. We present a 10-year-old boy who developed right hemidiaphragmatic paralysis, requiring surgical plication, following US-guided insertion of a tunnelled right internal jugular CVC. The needle trajectory for internal jugular puncture must be planned to avoid the phrenic nerve.

Percutaneous sclerotherapy in neonatal and infant head and neck lymphatic malformations: a single center experience

Purpose To evaluate the clinical outcomes of percutaneous sclerotherapy for congenital head and neck lymphatic malformations in our institution. Materials and Methods Over a 7-year period, 17 children (10 M, 7 F) mean age 5.8 months (5 days to 13 months) underwent 49 sclerotherapy procedures for congenital head and neck malformations. The imaging and clinical records were reviewed for each patient. Ten of 17 had macrocystic disease; 7 of 17 had microcystic disease. Imaging response was categorized by volume reductions of 0% to 25%, 25% to 50%, 50% to 75%, or 75% to 100%. A concentration of 10 mg/mL doxycycline was used routinely via catheter in 3 instillations with a dose range of 50 to 500 mg per session as per our standard protocol in 17 of 17 patients. In more recent patients, systemic doxycycline levels were obtained after instillations. Additional treatments included direct injection doxycycline (10/17), instillation of absolute ethanol (7/17) or sodium tetradecyl sulfate (4/17), or a combination of these methods. Results Imaging improvement of ≥76% was noted in 11 of 17. Of these, 8 of 11 had macrocystic disease. Four of 17 had 51% to 75% resolution, of which 3/4 were mixed. Two of 17 children had 25% to 50% resolution with a mixed lesion. Seven of 49 peri-procedural complications: hemolytic anemia in 2 infants, hypoglycemic and metabolic acidosis in 3 neonates aged 7 to 10 days, transient hypotension during absolute alcohol instillation in 1 neonate, and self-limiting skin excoriation secondary to peri-catheter leakage of doxycycline in one neonate. Neonates prone to these systemic complications had doxycycline doses of greater than 250 mg and resulted in serum levels of >5 μg/mL but as high as 21 μg/mL. Delayed neural complications occurred in 7 of 49 procedures, Horner's syndromes in 4 of 49 procedures, transient left lip weakness in 1 of 49 procedures, right facial nerve palsy in 1 of 49 procedures, and transient left hemidiaphragm paralysis in 1/49 procedures. Conclusion Our experience with catheter directed doxycycline sclerotherapy provides excellent results for large macrocystic head and neck lymphatic malformations. Microcystic and mixed lesions continue to provide a therapeutic challenge.

Contribution of the spontaneous crossed-phrenic phenomenon to inspiratory tidal volume in spontaneously breathing rats

Spinal cord hemisection at C2 (C2HS) severs bulbospinal inputs to ipsilateral phrenic motoneurons causing transient hemidiaphragm paralysis. The spontaneous crossed-phrenic phenomenon (sCPP) describes the spontaneous recovery of ipsilateral phrenic bursting following C2HS. We reasoned that the immediate (next breath) changes in tidal volume (V(T)) induced by ipsilateral phrenicotomy during spontaneous breathing would provide a quantitative measure of the contribution of the sCPP to postinjury V(T). Using this approach, we tested the hypothesis that the sCPP makes more substantial contributions to V(T) when respiratory drive is increased. Pneumotachography was used to measure V(T) in anesthetized, spontaneously breathing adult male rats at intervals following C2HS. A progressive increase in V(T) (ml/breath) occurred over an 8 wk period following C2HS during both poikilocapnic baseline breathing and hypercapnic respiratory challenge (7% inspired CO(2)). The sCPP did not impact baseline breathing at 1-3 days postinjury since V(T) was unchanged after ipsilateral phrenicotomy. However, by 2 wk post-C2HS, baseline phrenicotomy caused a 16 ± 2% decline in V(T); a comparable 16 ± 4% decline occurred at 8 wk. Contrary to our hypothesis, the phrenicotomy-induced declines in V(T) (%) during hypercapnic respiratory stimulation did not differ from the baseline response at any postinjury time point (all P > 0.11). We conclude that by 2 wk post-C2HS the sCPP makes a meaningful contribution to V(T) that is similar across different levels of respiratory drive.