Effect and mechanical mechanism of spontaneous breathing on oxygenation and lung injury in mild or moderate animal ARDS.

OBJECTIVE: The present study aimed to determine the effect and mechanical mechanism of spontaneous breathing during mechanical ventilation on oxygenation and lung injury using Beagles dogs mild or moderate acute respiratory distress syndrome (ARDS) model. METHODS: After inducing mild or moderate ARDS by infusion of oleic acid, Eighteen Beagles dogs were randomly split into Spontaneous breathing group (BIPAPSB, n = 6), and Complete muscle paralysis group (BIPAPPC, n = 6),Six Beagles without ventilator support comprised the control group. Both groups were ventilated for 8 h under BIPAP mode. High-pressure was titrated TV to 6 ml/kg. A multi-pair esophageal balloon electrode catheter was used to measure respiratory mechanics and electromyogram. End-expiratory lung volume (EELV), gas exchange and respiratory variables were recorded in the process of mechanical ventilation. The contents of Interleukin (IL)-6 and IL-8 in lung tissue were measure using qRT-PCR. Besides, lung injury score was calculated in the end of mechanical ventilation. RESULTS: Based on the comparable setting of ventilator, BIPAPSB group exhibited higher safety peak transpulmonary pressure, abdominal pressure, EELV and P/F(PaO2/FiO2) than BIPAPPC group, whereas mean transpulmonary pressure, the mRNA levels of the IL-6 and IL-8 in the lung tissues and lung injury score in BIPAPSB group were lower than those in BIPAPPC group. CONCLUSION: In mild to moderate ARDS animal models, during mechanical ventilation, SB may improve respiratory function and reduce ventilator-induced lung injury. The mechanism may be that spontaneous inspiration up-regulates peak transpulmonary pressure and EELV; Spontaneous expiration decreases mean transpulmonary pressure by up-regulating intra-abdominal pressure, thereby reducing stress and strain.

An Analysis of Respiratory Muscle Paralysis of Adult Patients in Guillain-Barré Syndrome: A Retrospective Analysis.

Respiratory muscle paralysis is known as a very common complication of Guillain-Barré syndrome (GBS). However, most research has focused on its later stages rather than its earlier stages, including the prognosis of patients with this condition, or factors that act as early predictors of risk. Therefore, our study aimed to identify early predictors of respiratory muscle paralysis in patients with GBS and determine the short-term prognosis of such patients. We recruited 455 GBS patients (age ≥ 18) who had been hospitalized in the First Affiliated Hospital of Harbin Medical University between 2016 and 2021, retrospectively. We recorded clinical and laboratory data and used linear and logistic regression analysis to investigate the relationship between early clinical, examination results, and subsequent respiratory muscle paralysis. Among the 455 patients, 129 were assigned to a respiratory muscle paralysis group and 326 were assigned to a non-respiratory muscle paralysis group. Compared with the non-affected group, the time from onset to admission was shorter (p = 0.0003), and the Medical Research Council (MRC) score at admission and discharge was smaller in the affected group (p < 0.0001). Compared with the non-affected group, the affected group had higher Hughes and Erasmus GBS Respiratory Insufficiency Score (EGRIS) scores at admission and longer hospital stays (p < 0.0001). Patients in the affected group were more likely to have bulbar palsy and lung infections (p < 0.0001). To conclude, bulbar palsy, a higher EGRIS score and Hughes score at admission, a lower MRC score, and a shorter time between onset and admission, are all predictive risk factors for respiratory muscle paralysis in patients with GBS. An increase in any of these factors increases the risk of muscle paralysis. Patients with respiratory muscle paralysis have a poorer short-term prognosis than those without respiratory muscle paralysis. Therefore, we should attempt to identify patients with one or more of these characteristics in the early stages of admission, provide ventilation management, and administer IMV treatment if necessary.

The Necessity of a Locally Active Antidote in the Clinical Practice of Botulinum Neurotoxin Therapy: Short Communication.

Recently, it was demonstrated that copper complexes and 3,4-diaminopyridine can effectively reduce the activity of the botulinum neurotoxin light chain. The aim of the present study was to indicate that treatment with an antidote may have a major influence, not only on the extremely rare disease of botulism, but also on the much more frequently occurring side effects experienced during BoNT therapy. This was a retrospective chart review of patients who were regularly treated with BoNT for various indications. The percentage of patients with clinical signs of overdosing was determined. In patients with facial dystonia, double vision and ptosis occurred as side effects. In patients with cervical dystonia, neck weakness and dysphagia were observed as the most frequent side effects. In oromandibular and oropharyngeal dystonia, abnormal tongue movements and dysphagia occurred frequently. In writer's cramp and mild post-stroke hand spasticity, severe paresis of the injected and non-injected finger muscles was observed. Additionally, in the BoNT treatment of pain syndromes (such as tension headaches or migraines), neck weakness may occur. Across all indications for clinical BoNT applications, clinical signs of BoNT overdosing may occur in up to 5% of the BoNT-treated patients. Therefore, the development of an antidote for BoNT overdoses would be very much appreciated and would have a major influence on the management of BoNT therapy.

[Determining the degree of risk of postoperative complications in patients with a benign tumor of the parotid salivary gland]. / Opredelenie stepeni riska vozniknoveniya posleoperatsionnykh oslozhnenii u patsientov s dobrokachestvennoi opukhol'yu okoloushnoi slyunnoi zhelezy.

THE AIM OF THE STUDY: Determination of the risk of postoperative complications in patients after surgical treatment of benign neoplasms of the parotid salivary glands. MATERIAL AND METHODS: The results of treatment of 228 patients with benign neoplasms of the parotid salivary gland in the period from 2019 to 2021 were analyzed. A questionnaire of 7 questions was formed the answers to which allowed patients to be assigned to a certain risk group: low, medium, high or extremely high. This gradation allows choosing the optimal method and scope of surgical treatment for each patient individually. RESULTS: Patients of the first and second groups (low and medium risk) are characterized by the occurrence of temporary isolated facial nerve dysfunction with a short recovery period (up to 1 month), as well as sialocele associated with the preservation of a fragment of the gland. For the patients of the third and fourth groups (high and extremely high risk) in which parotidectomy was performed typical features included persistent paresis of facial muscles and facial soft tissue asymmetry. CONCLUSION: A personalized approach based on determining the degree of risk of postoperative complications helps surgeon in deciding on the scope of surgical treatment from subtotal resection to total parotidectomy.

Botulinum toxin type A applications for masticatory myofascial pain and trigeminal neuralgia: what is the evidence regarding adverse effects?

OBJECTIVES: The objective of the study was to conduct a systematic review of literature assessing botulinum toxin type A (BoNT-A) safety and adverse effects in the treatment of myofascial pain (MFP) and trigeminal neuralgia (TN). MATERIALS AND METHODS: The search for articles by two specific researchers involved the PubMed, EMBASE, Web of Science, and Scopus databases. Specific terms were used, and no publication time and language restrictions were applied. Clinical trials that investigated the effects of BoNT-A among participants with myofascial pain in masticatory muscles or trigeminal neuralgia were considered eligible for this systematic review. Data for each study were extracted and analyzed according to a PICO-like structured reading. RESULTS: The search strategy provided 436 citations. After analysis, 16 citations were included, seven for MFP and nine for TN. In all studies, BoNT-A was well tolerated and improved pain. The most common adverse effects were temporary regional weakness, tenderness over the injection sites, and minor discomfort during chewing. Most studies reported a spontaneous resolution of adverse effect. CONCLUSIONS: It can be concluded that BoNT-A treatment is well tolerated, since minor adverse effects were the most frequently reported; however, it is recommended that future studies aim to assess the safety and possible adverse effects of multiples applications or high doses of this treatment. CLINICAL RELEVANCE: BoNT-A has been increasingly diffused in dentistry, being used for the management of masticatory myofascial pain and trigeminal neuralgia. Nonetheless, there is no consensus about its efficacy and adverse effects that could occur when this treatment is applied.

Post-operative paralysis and elective ventilation reduces anastomotic complications in esophageal atresia: a systematic review and meta-analysis.

AIM OF STUDY: The repair of esophageal atresia (EA) carries an increased risk of anastomotic leak and stricture formation, especially in patients with anastomotic tension. To minimize this risk, pediatric surgeons perform elective post-operative muscle paralysis, positive-pressure ventilation, and head flexion (PVF) to reduce movement and tension at the anastomosis. We systematically reviewed and analyzed the effect of post-operative PVF on reducing anastomotic complications. METHODS: Embase, MEDLINE, Web of Science, and PubMed databases were used to conduct searches. Articles reporting pediatric EA undergoing primary anastomosis, anastomotic complications, and comparisons between patients who received post-operative PVF to those who did not were included. Odds ratios (OR) for all post-operative anastomotic complications were calculated using random effects modelling. MAIN RESULTS: Three of the 2268 papers retrieved met inclusion criteria (all retrospective cohort studies). There were no randomized controlled trials. Post-operative PVF showed a significant reduction in anastomotic leak (OR 0.07; 95% CI 0.01-0.35) when compared to no PVF. Stricture formation was not statistically different between groups. Potential sources of bias include patient allocation. CONCLUSIONS: Based on available data, our analysis indicates PVF may reduce anastomotic post-operative leak. To confirm these results, a prospective study with clearer definitions of treatment allocation should be performed.

Muscle paralysis induces bone marrow inflammation and predisposition to formation of giant osteoclasts.

Transient muscle paralysis engendered by a single injection of botulinum toxin A (BTxA) rapidly induces profound focal bone resorption within the medullary cavity of adjacent bones. While initially conceived as a model of mechanical disuse, osteoclastic resorption in this model is disproportionately severe compared with the modest gait defect that is created. Preliminary studies of bone marrow following muscle paralysis suggested acute upregulation of inflammatory cytokines, including TNF-α and IL-1. We therefore hypothesized that BTxA-induced muscle paralysis would rapidly alter the inflammatory microenvironment and the osteoclastic potential of bone marrow. We tested this hypothesis by defining the time course of inflammatory cell infiltration, osteoinflammatory cytokine expression, and alteration in osteoclastogenic potential in the tibia bone marrow following transient muscle paralysis of the calf muscles. Our findings identified inflammatory cell infiltration within 24 h of muscle paralysis. By 72 h, osteoclast fusion and pro-osteoclastic inflammatory gene expression were upregulated in tibia bone marrow. These alterations coincided with bone marrow becoming permissive to the formation of osteoclasts of greater size and greater nuclei numbers. Taken together, our data are consistent with the thesis that transient calf muscle paralysis induces acute inflammation within the marrow of the adjacent tibia and that these alterations are temporally consistent with a role in mediating muscle paralysis-induced bone resorption.

Diagnosis and management of unilateral thyroarytenoid muscle palsy.

The objective of this study is to assess and propose a method of diagnosis and management of patients with unilateral thyroarytenoid muscle palsy (TAMP). This is a retrospective review of clinical records. The records of seven patients diagnosed as having idiopathic TAMP were reviewed. Despite the adductive and abductive functions of the vocal folds being within normal range, apparent palsy was seen in the unilateral thyroarytenoid muscle of these patients. TAMP was confirmed by laryngeal electromyography, and the adductive and abductive movements of the vocal folds were evaluated as the mobility of the arytenoid cartilages by three-dimensional computed tomography and endoscopy. Most of patients with TAMP had been diagnosed as having other diseases or normal, and in one patient, it took over 6 years to establish a correct diagnosis. Two patients recovered by conservative treatment; however, in five patients, TAMP remained even after 6 months. In 4 of those 5 patients, treatment with hyaluronic acid injections was performed. In the remaining patient, surgical treatment, namely, nerve-muscle pedicle flap implantation was performed, which resulted in a favorable recovery of phonation. The average maximum phonation time (MPT) of all patients was extended from 11.4 (±4.4) s before treatment to 19.9 (±4.3) s after treatment, and the pitch range was also increased from 25.1 (±7.2) to 34.6 (±5.8) semitones following our management course. Our results indicate that there is a possibility that TAMP can be diagnosed and treated sufficiently. Therefore, further research toward establishing the concept of and treatment for TAMP is anticipated.

Muscle Fibrosis, NF-κB, and TGF-ß Are Differentially Altered in Two Models of Paralysis (Botox Versus Neurectomy).

Objective: Volumetric muscle loss results in intramuscular axotomy, denervating muscle distal to the injury and leading to paralysis, denervation, and loss of muscle function. Once the nerve is damaged, paralyzed skeletal muscle will atrophy and accumulate noncontractile connective tissue. The objective of this study was to determine differences in connective tissue, atrophy, and inflammatory signaling between two paralysis models, botulinum toxin (Botox), which blocks acetylcholine transmission while keeping nerves intact, and neurectomy, which eliminates all nerve-to-muscle signaling. Approach: Twenty male Sprague Dawley rats were randomized and received a sciatic-femoral neurectomy (SFN), Botox-induced muscle paralysis of the proximal femur muscles, quadriceps femoris, hamstrings, and calf muscles (BTX), or sham. Muscle force was measured 52 days postsurgery, and samples were collected for histology, protein, and mRNA assays. Results: SFN and BTX decreased twitch and tetanic force, decreased fiber size by twofold, and increased myogenic expression compared with controls. SFN increased the levels of all major extracellular matrix proteins correlating with fibrosis [e.g., laminin, fibronectin, and collagen type(s) I, III, VI]. SFN also increased profibrotic and proinflammatory mRNA compared with BTX and controls. Innovation: SFN and BTX were similar in gross morphology and functional deficiencies. However, SFN exhibited a higher amount of fibrosis in histological sections and immunoblotting. The present study shows evidence that nerve signaling changes NF-κB and TGF-ß signaling, warranting future studies to determine the mechanisms involved. Conclusion: These data indicate that nerve signaling may influence fibrogenesis following denervation, but the mechanisms involved may differ as a function of the method of paralysis.

Comparison of the effects of selected aminoglycoside antibiotics on motor behaviors in mice.

Aminoglycoside antibiotics (AGs) can cause neuromuscular blockade and paralysis of skeletal muscles. To compare the paralytic effects of selected AGs on some motor behaviors in mice, 24 male mice were divided into four groups. Each group was given one of AGs (gentamicin, dihydro-streptomycin, apramycin and amikacin) at incremental doses that increased half-logarithmically compared to the therapeutic dose (16.00 mg kg-1). Motor behavioral tests included open field test, inclined plane, horizontal bars, static rods, parallel bars and rotarod. Finally, the data were analyzed using descriptive and analytical statistics. Gentamicin and dihydrostreptomycin at 32.00 times of the therapeutic dose produced complete paralysis of the limbs, respiratory arrest, and even death in some animals. However, apramycin and amikacin did not show significant effects on skeletal muscle and motor behaviors at 32.00 times of the therapeutic dose. After administration of apramycin at 100 times of the therapeutic dose, four out of six mice (66.67%) died from respiratory depression. Amikacin at this dose did not cause animal death, although it caused some changes in motor behaviors with a significant difference in comparison with control values. Gentamicin demonstrated significantly more potent effects on motor behaviors compared to the other AGs. Overall, the order of potency was gentamicin > dihydrostreptomycin > apramycin > amikacin. High doses of AGs could impair the skeletal muscle function and disrupt motor behaviors in mice. Furthermore, the paralytic potency of selected AGs on skeletal muscle was significantly different.

Recurrent Thyrotoxic Periodic Paralysis As the Sole Clinical Manifestation of Untreated Hyperthyroidism.

Thyrotoxic periodic paralysis (TPP) is a complication of hyperthyroidism that predominantly affects the Asian population. Episodes of muscle paralysis typically coincide with symptoms of hyperthyroidism. However, we present a unique case of TPP in a 32-year-old African American patient where TPP served as the primary manifestation of thyrotoxicosis. The patient was discharged with a resolution of symptoms after correcting electrolyte abnormalities.

Paralysis of the trapezius muscle: evaluation and surgical management.

Background: Paralysis of the trapezius muscle most commonly results from iatrogenic injury to the spinal accessory nerve. Methods: The clinical presentation and physical examination findings of trapezius palsy have been well characterized, but unfortunately the diagnosis of this condition is oftentimes missed or delayed, sometimes leading to unnecessary surgery on the rotator cuff or tendon of the long head of the biceps. Results: The diagnosis can be confirmed using electromyography with nerve conduction studies. Although nonoperative treatment may help some patients with temporary neurapraxia of the spinal accessory nerve, nerve repair with or without nerve grafting should be performed soon for patients suspected of a nerve transection. Nerve transfers can be considered within the first year after the injury when nerve repair and grafting cannot be completed. For chronic trapezius palsy, transfer of the levator scapulae and rhomboids has been refined and represents a very successful surgical procedure. Rarely, scapulothoracic arthrodesis is considered for individuals with failed tendon transfers or multiple nerve involvement. Conclusion: Trapezius palsy is oftentimes missed. An accurate diagnosis allows consideration of various treatment modalities that have been reported to provide good outcomes for properly selected patients.

Staphylococcus epidermidis Bacteremia in an Older Patient With Guillain-Barré Syndrome With Fever of Unknown Origin: A Case Report.

Guillain-Barré syndrome (GBS) is an immune-mediated disorder that affects the peripheral nerves, often leading to weakness, numbness, and paralysis. Although GBS does not induce immunosuppression, severe cases can render patients vulnerable to infection due to various complications. We present the case of a 70-year-old woman who developed GBS following a Mycoplasma infection. The patient's prolonged GBS symptoms led to an immunocompromised state, resulting in sepsis due to bacteremia caused by methicillin-resistant Staphylococcus epidermidis. Respiratory muscle paralysis necessitated intubation and mechanical ventilation, predisposing the patient to aspiration pneumonia. Prolonged hospitalization increases the risk of infection, as exemplified by catheter-related bloodstream infections and respiratory bacterial colonization. Although GBS does not inherently suppress immunity, its complications, such as musculoskeletal and respiratory failure, can mimic immunodeficiency, necessitating comprehensive management. A system-based approach should address neurological deficits and potential complications, emphasizing collaboration among medical specialties. This case highlights the importance of recognizing GBS-related challenges and adopting a holistic strategy for effective patient care.

Characterization of Serotype CD Mosaic Botulinum Neurotoxin in Comparison with Serotype C and A.

Botulinum neurotoxin (BoNT), produced by Clostridium botulinum, cleaves proteins involved in neurotransmitter release, thereby triggering flaccid paralyses, which are responsible for botulism. BoNT is classified into seven serotypes (BoNT/A-G); BoNT/A and BoNT/B are used as medical therapeutics and anti-wrinkle reagents. In this study, we investigated the efficacy of BoNT/CD, a mosaic toxin of BoNT/C and BoNT/D, to assess its potential as a therapeutic alternative for BoNT/A. In a cultured neuron assay, BoNT/CD cleaved syntaxin and SNAP-25 with higher efficacy than BoNT/C and BoNT/A. Intramuscularly administrated BoNT/CD induced dose-dependent muscle paralysis, and the paralysis lasted ~21 days in a mouse digit abduction score assay (BoNT/A-induced paralysis lasted ~30 days). BoNT/C failed to induce local paralysis without systemic toxicity. Multiple alignment analyses of the amino acid sequences of the receptor binding domain (HC) of eight BoNT/CDs and two BoNT/Ds showed sequence clustering in five groups. Comparing BoNT/CD strain 003-9 (BoNT/CD003-9) and strain 6813 (BoNT/CD6813) showed that both BoNT/CDs displayed similar efficacies in cultured neurons, but BoNT/CD003-9 displayed higher efficacy in a mouse model than BoNT/CD6813. These findings suggest that BoNT/CD may be a potential alternative for patients who do not respond to existing BoNT-based therapeutics.

The humeral suspension technique: a novel operation for deltoid paralysis.

Isolated deltoid paralysis is a rare pathology that can occur after axillary nerve injury due to shoulder trauma or infection. This condition leads to loss of deltoid function that can cause glenohumeral instability and inferior subluxation, resulting in rotator cuff muscle fatigue and pain. To establish dynamic glenohumeral stability, a novel technique was invented. Humeral suspension is achieved using a double button implant with non-resorbable high strength cords between the acromion and humeral head. This novel technique was used in two patients with isolated deltoid paralysis due to axillary nerve injury. The results indicate that the humeral suspension technique is a method that supports centralizing the humeral head and simultaneously dynamically stabilizes the glenohumeral joint. This approach yielded high patient satisfaction and reduced pain. Glenohumeral alignment was improved and remained intact 5 years postoperative. The humeral suspension technique is a promising surgical method for subluxated glenohumeral joint instability due to isolated deltoid paralysis.

Erigeron annuus flower absolute prolongs botulinum neurotoxin A-induced muscle paralysis and inhibits neurotransmitter release-linked responses.

This study aimed to determine the effects of Erigeron annuus (L.) Pers. (EAP) flower absolute (EAPFAb) on neurotransmitter release-blocking events and muscle paralysis induced by botulinum neurotoxin type A (BoNT/A). For this study, EAPFAb was extracted from EAP flowers by solvent extraction and its composition was determined by GC/MS. Neurotransmitter release and SNARE protein expression were examined in PC12 cells by ELISA and immunoblotting. Rat hind limbs were tested for muscle paralysis. EAPFAb contained 23 components and prolonged the duration of BoNT/A-induced rat hind limb muscle paralysis. EAPFAb reduced neurotransmitter release induced by elevated extracellular potassium levels and attenuated SNARE protein expression in PC12 cells. These findings demonstrate that EAPFAb prolongs BoNT/A-induced muscle paralysis action, probably by inhibiting releases of neurotransmitters that are regulated by SNARE proteins in neural cells. EAPFAb may be a promising material for prolonging BoNT/A action.

Nemaline Myopathy Initially Diagnosed as Right Heart Failure with Type 2 Respiratory Failure.

Nemaline myopathy (NM) is a rare muscle disease with various clinical types. In some cases, NM can lead to type 2 respiratory failure and right heart failure. We herein report a patient with congenital NM with nebulin gene mutation who presented with acute right heart failure and type 2 respiratory failure due to respiratory muscle paralysis after upper respiratory tract infection, needing a permanent ventilator for assistance. However, the limb and trunk muscle strengths were within normal limits. This case showed that NM should be considered as a cause of right heart failure and type 2 respiratory failure.

Mind the Gap: Acetazolamide Prolonged Periods without Paralysis in a Girl with Andersen-Tawil Syndrome.

We present a case report of a 13-year-old girl with Andersen-Tawil Syndrome (ATS), a rare genetic disorder which is characterized by dysmorphic features, ventricular arrhythmias, and frequent episodes of muscle paralysis that interfere with daily activities and social engagement. After the introduction of off-label treatment with acetazolamide periods without paralysis lengthened, our patient became more independent of the help of her parents and required a wheelchair less frequently, thus improving her social life. Based on our experience, we recommend a trial of acetazolamide in patients with ATS.

Differential Effects of Neurectomy and Botox-induced Muscle Paralysis on Bone Phenotype and Titanium Implant Osseointegration.

Metabolic bone is highly innervated by both sensory and sympathetic nerves. In addition to skeletal development, neural regulation participates in local bone remodeling, which is important for successful osseointegration of titanium implants. Neurectomy is a model used to investigate the lack of neural function on bone homeostasis, but the relative impacts of direct denervation to bone or denervation-induced muscle paralysis are less well defined. To investigate this difference, we used two nerve intervention models, sciatic and femoral neurectomy (SFN) v. botox-induced muscle paralysis (BTX) and assessed the resulting femoral bone phenotype and Ti implant osseointegration. Male Sprague Dawley rats (19) were randomly divided into three groups: implant control (n = 5), SFN (n = 7), and BTX (n = 7). Ti implants (microrough/hydrophilic [modSLA], Institut Straumann AG) were placed in the distal metaphysis of each femur on day 24 post-SFN or BTX. Bone and muscle were examined on day 28 after implant insertion. Both nerve intervention models impaired osseointegration. MicroCT and histology indicated that both models had reduced trabecular bone formation. Only BTX reduced cortical bone formation and increased cortical bone porosity. BTX resulted in more bone loss characterized by the least trabecular and cortical bone, as well as osseointegration. Osteoblasts isolated from the tibia exhibited a model-specific phenotype when they were grown on Ti substrates in vitro. Neurectomy caused more severe muscle atrophy than botox injection. These results indicate that neural regulation directly modulates bone formation and osseointegration. Muscle paralysis modulated the effects of loss of neural inputs into bone, supporting the hypothesis that mechanical loading of bone is a factor in achieving successful osseointegration. The different effects of botox and neurectomy on bone phenotype indicated that the sensory and sympathetic nerves had a role in the osseointegration process.

Biological and Biochemical Characterization of Coronado Island Rattlesnake (Crotalus helleri caliginis) Venom and Antivenom Neutralization.

The Baja California Peninsula has over 250 islands and islets with many endemic species. Among them, rattlesnakes are the most numerous but also one of the least studied groups. The study of island rattlesnake venom could guide us to a better understanding of evolutionary processes and the description of novel toxins. Crotalus helleri caliginis venom samples were analyzed to determine possible ontogenetic variation with SDS-PAGE in one and two dimensions and with RP-HPLC. Western Blot, ELISA, and amino-terminal sequencing were used to determine the main components of the venom. The biological and biochemical activities demonstrate the similarity of C. helleri caliginis venom to the continental species C. helleri helleri, with both having low proteolytic and phospholipase A2 (PLA2) activity but differing due to the absence of neurotoxin (crotoxin-like) in the insular species. The main components of the snake venom were metalloproteases, serine proteases, and crotamine, which was the most abundant toxin group (30-35% of full venom). The crotamine was isolated using size-exclusion chromatography where its functional effects were tested on mouse phrenic nerve-hemidiaphragm preparations in which a significant reduction in muscle twitch contractions were observed. The two Mexican antivenoms could neutralize the lethality of C. helleri caliginis venom but not the crotamine effects.