OBJECTIVE: To explore the preventive effect of transcutaneous phrenic nerve stimulation on ventilator-induced diaphragmatic dysfunction (VIDD) in patients requiring invasive mechanical ventilation. METHODS: A randomized controlled trial was conducted. The patients requiring invasive mechanical ventilation admitted to the intensive care unit (ICU) of Jiaxing First Hospital from November 2022 to December 2023 were enrolled. Participants were randomized into the control group and the observation group using a random number table. The control group was given ICU standardized nursing intervention, including turning over and slapping the back, raising the head of the bed, sputum aspiration on demand, aerosol inhalation, oral care, and monitoring of airbag pressure and gastric retention, the observation group was given additional transcutaneous phrenic nerve stimulation intervention on the basis of ICU standardized nursing intervention. The stimulation intensity was set to 10 U, the pulse frequency was set to 40 Hz, and the stimulation frequency was set to 12 times/min. Transcutaneous phrenic nerve stimulation was administered once a day for 30 minutes each time, for a total of 5 days. Diaphragm thickening fraction (DTF) and arterial blood gas parameters on days 1, 3, and 5 of intervention were compared between the two groups. After 5 days of intervention, other parameters including the incidence of VIDD, duration of mechanical ventilation, and length of ICU stay were compared. RESULTS: A total of 120 patients requiring invasive mechanical ventilation were enrolled, with 16 dropouts (dropout rate was 13.33%). Ultimately, 51 patients in the control group and 53 patients in the observation group were analyzed. Baseline characteristics, including gender, age, body mass index (BMI), acute physiology and chronic health evaluation II (APACHE II) score, albumin (Alb), hemoglobin (Hb), and disease type, showed no significant differences between the two groups. DTF in both groups gradually increased over duration of intervention [DTF on days 1, 3, and 5 in the control group was (20.83±2.33)%, (21.92±1.27)%, and (23.93±2.33)%, respectively, and that in the observation group was (20.89±1.96)%, (22.56±1.64)%, and (25.34±2.38)%, respectively], with more significant changes in DTF in the observation group, showing time effects (F_time = 105.975, P < 0.001), intervention effects (F_intervention = 7.378, P = 0.008), and interaction effects (F_interaction = 3.322, P = 0.038). Arterial blood gas parameters did not differ significantly before intervention between the groups, but after 5 days of intervention, arterial partial pressure of oxygen (PaO₂) in the observation group was significantly higher than that in the control group [mmHg (1 mmHg≈0.133 kPa): 100.72±15.75 vs. 93.62±15.54, P < 0.05], and arterial partial pressure of carbon dioxide (PaCO₂) was significantly lower than that in the control group (mmHg: 36.53±3.10 vs. 37.69±2.02, P < 0.05). At 5 days of intervention, the incidence of VIDD in the observation group was significantly lower than that in the control group [15.09% (8/53) vs. 37.25% (19/51), P < 0.05], and both duration of mechanical ventilation and length of ICU stay were significantly shorter than those in the control group [duration of mechanical ventilation (days): 7.93±2.06 vs. 8.77±1.76, length of ICU stay (days): 9.64±2.35 vs. 11.01±2.01, both P < 0.05]. CONCLUSIONS Transcutaneous phrenic nerve stimulation can improve diaphragmatic and respiratory function in patients receiving invasive mechanical ventilation, reduce the incidence of VIDD, and shorten the duration of mechanical ventilation and length of ICU stay.
Humans ; Transcutaneous Electric Nerve Stimulation ; Respiration, Artificial/adverse effects* ; Diaphragm/physiopathology* ; Phrenic Nerve ; Intensive Care Units ; Male ; Female ; Middle Aged

OBJECTIVE: To analyze the imaging and clinical features of diaphragm dysfunction in patients who underwent selective cardiac sternotomy with diaphragm ultrasound and chest CT. METHODS: A prospective cohort study was conducted. The patients undergoing selective cardiac sternotomy in the cardiac and vascular surgery department of Tianjin Medical University General Hospital from June to September 2023 were enrolled. Bedside ultrasound was performed on the day before surgery, within 24 hours of extubation, and on the 7th day after surgery to measure diaphragm excursion (DE) and diaphragm thickness (DT), and to calculate the diaphragm thickening fraction (DTF). The distance from the diaphragm's apex to the thorax's apex in the chest CT scout view was measured before and after the operation, and the diaphragm elevating fraction (DEF) was calculated. Patients were divided into two groups based on whether diaphragm dysfunction (DE < 1 cm) occurred on the 7th day after surgery. The change patterns of imaging indicators were analyzed in both groups. The clinical data of both groups before, during, and after surgery were compared. RESULTS: In total, 67 patients who underwent cardiac sternotomy were enrolled. Among them, 24 patients developed diaphragm dysfunction within 24 hours after extubation; on the 7th day after surgery, 19 patients (28.4%) still exhibited diaphragm dysfunction, while 48 patients (71.6%) did not. Ultrasonic examination of the diaphragm revealed that, compared with the non-diaphragm dysfunction group, patients in the diaphragm dysfunction group exhibited varying degrees of decrease in DE and DTF before and after surgery, with a more significant decrease on the left side, and the differences were statistically significant on the 7th day after surgery [DE (cm): 1.06±0.77 vs. 1.59±0.63, DTF: 19.3% (14.8%, 21.1%) vs. 21.3% (18.3%, 26.1%), both P < 0.05]. There was no statistically significant difference in DT between the two groups at each time point. Changes in bilateral DE and DTF revealed that the non-diaphragm dysfunction group experienced early transient postoperative weakening of diaphragm function, followed by rapid recovery to the preoperative level on the 7th day after surgery, unlike the diaphragm dysfunction group. There were no significant differences between bilateral DE in the two groups on the day before surgery, and the left DE was significantly lower than the right DE within 24 hours after extubation and on the 7th day after surgery in the diaphragm dysfunction group (cm: 0.93±0.72 vs. 1.45±0.70 within 24 hours after extubation, 1.06±0.77 vs. 1.70±0.92 on the 7th day after surgery, both P < 0.05) but no significant difference was found in bilateral DT or DTF. The chest CT scan showed that, the incidence of postoperative diaphragm elevation was 61.2% (41/67), and 38.8% (26/67) did not, while no statistically significant difference in DEF was found between the two groups, nor within each group on both sides. Analysis of the clinical data showed a higher proportion of atrial fibrillation and pulmonary hypertension before surgery [atrial fibrillation: 36.8% (7/19) vs. 10.4% (5/48), pulmonary hypertension: 15.8% (3/19) vs. 2.1% (1/48), both P < 0.05], a higher incidence of high-flow oxygenation and pneumonia during surgery [high-flow oxygenation: 52.6% (10/19) vs. 25.0% (12/48), pneumonia: 73.7% (14/19) vs. 45.8% (22/48), both P < 0.05], and a longer duration of mechanical ventilation and length of intensive care unit (ICU) stay [duration of mechanical ventilation (hours): 47.0 (38.0, 73.0) vs. 24.5 (20.0, 48.0), length of ICU stay (hours): 69.0 (65.0, 117.5) vs. 60.0 (42.3, 90.6), both P < 0.05] in the diaphragm dysfunction group as compared with those in the non-diaphragm dysfunction group. CONCLUSIONS There was a high incidence of diaphragm dysfunction after cardiac sternotomy, which reflected the early transient postoperative weakening of diaphragm function, followed by rapid recovery to the preoperative level in most patients, predominantly on the left side. Diaphragm dysfunction, which was associated with atrial fibrillation and pulmonary hypertension significantly increased the incidence of postoperative pneumonia and prolonged the duration of mechanical ventilation and length of ICU stay.
Humans ; Diaphragm/physiopathology* ; Prospective Studies ; Sternotomy/adverse effects* ; Ultrasonography ; Postoperative Complications/diagnostic imaging* ; Tomography, X-Ray Computed ; Male ; Female ; Middle Aged ; Aged ; Cardiac Surgical Procedures/adverse effects*

Background: Neural respiratory drive (NRD) using diaphragm electromyography through an invasive transesophageal multi-electrode catheter can be used as a feasible clinical physiological parameter in patients with chronic obstructive pulmonary disease (COPD) to provide useful information on the treatment response. However, it remains unknown whether the surface diaphragm electromyogram (EMGdi) could be used to identify the deterioration of clinical symptoms and to predict the necessity of hospitalization in acute exacerbation of COPD (AECOPD) patients. Methods: COPD patients visiting the outpatient department due to acute exacerbation were enrolled in this study. All patients who were subjected to EMGdi and classical parameters such as spirometry parameters, arterial blood gas analysis, COPD assessment test (CAT) score, and the modified early warning score (MEWS) in outpatient department, would be treated effectively in the outpatient or inpatient settings according to the Global Initiative for Chronic Obstructive Lung Disease guideline. When the acute exacerbation of the patients was managed, all the examination above would be repeated. Results: We compared the relationships of admission-to-discharge changes (Δ) in the normalized value of the EMGdi, including the change of the percentage of maximal EMGdi (ΔEMGdi%max) and the change of the ratio of minute ventilation to the percentage of maximal EMGdi (ΔVE/EMGdi%max) with the changes of classical parameters. There was a significant positive association between ΔEMGdi%max and ΔCAT, ΔPaCO, and ΔpH. The change (Δ) of EMGdi%max was negatively correlated with ΔPaO/FiOin the course of the treatment of AECOPD. Compared with the classical parameters including forced expiratory volume in 1 s, MEWS, PaO/FiO, the EMGdi%max (odds ratio 1.143, 95% confidence interval 1.004-1.300) has a higher sensitivity when detecting the early exacerbation and enables to predict the admission of hospital in the whole cohort. Conclusions The changes of surface EMGdi parameters had a direct correlation with classical measures in the whole cohort of AECOPD. The measurement of NRD by surface EMGdi represents a practical physiological biomarker, which may be helpful in detecting patients who should be hospitalized timely.
Diaphragm ; physiopathology ; Electromyography ; methods ; Forced Expiratory Volume ; physiology ; Hospitalization ; Humans ; Pulmonary Disease, Chronic Obstructive ; metabolism ; physiopathology ; Spirometry ; Vital Capacity ; physiology

BACKGROUNDThe antagonistic actions of anticholinesterase drugs on non-depolarizing muscle relaxants are theoretically related to the activity of acetylcholinesterase (AChE) in the neuromuscular junction (NMJ). However, till date the changes of AChE activity in the NMJ during sepsis have not been directly investigated. We aimed to investigate the effects of sepsis on the antagonistic actions of neostigmine on rocuronium (Roc) and the underlying changes of AChE activity in the NMJ in a rat model of cecal ligation and puncture (CLP).

METHODSA total of 28 male adult Sprague-Dawley rats were randomized to undergo a sham surgery (the sham group, n = 12) or CLP (the septic group, n = 16). After 24 h, the time-response curves of the antagonistic actions of 0.1 or 0.5 μmol/L of neostigmine on Roc (10 μmol/L)-depressed diaphragm twitch tension were measured. Meanwhile, the activity of AChE in the NMJ was detected using a modified Karnovsky and Roots method. The mRNA levels of the primary transcript and the type T transcript of AChE (AChET) in the diaphragm were determined by real-time reverse transcription-polymerase chain reaction.

RESULTSFour of 16 rats in the septic group died within 24 h. The time-response curves of both two concentrations of neostigmine in the septic group showed significant upward shifts from those in the sham group (P < 0.001 for 0.1 μmol/L; P = 0.009 for 0.5 μmol/L). Meanwhile, the average optical density of AChE in the NMJ in the septic group was significantly lower than that in the sham group (0.517 ± 0.045 vs. 1.047 ± 0.087, P < 0.001). The AChE and AChETmRNA expression levels in the septic group were significantly lower than those in the sham group (P = 0.002 for AChE; P = 0.001 for AChET).

CONCLUSIONSSepsis strengthened the antagonistic actions of neostigmine on Roc-depressed twitch tension of the diaphragm by inhibiting the activity of AChE in the NMJ. The reduced content of AChE might be one of the possible causes of the decreased AChE activity in the NMJ.

Acetylcholinesterase ; metabolism ; Androstanols ; pharmacology ; Animals ; Cecum ; injuries ; Cholinesterase Inhibitors ; pharmacology ; Diaphragm ; drug effects ; metabolism ; Disease Models, Animal ; Ligation ; Male ; Neostigmine ; pharmacology ; Neuromuscular Junction ; enzymology ; Neuromuscular Nondepolarizing Agents ; pharmacology ; Punctures ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Sepsis ; physiopathology

OBJECTIVE: To investigate the effects of hydrogen sulfide (H2S) on contraction capacity of diaphragm in type 1 diabetic rats.
 METHODS: Thirty-two male SD rats were randomly divided into a normal group (NC), a diabetic group (DM), a NaHS treatment group (DM+NaHS) and a NaHS group (NaHS) (n=8). Intraperitoneal injection of streptozotocin was utilized to establish diabetic rat model. After the modeling, the rats in the DM+NaHS and the NaHS groups were intraperitoneally injected with 28 μmol/kg NaHS solution. 8 weeks later, the diaphragm contractility was assessed by isolated draphragm strips perfusion. The peak twitch tension (Pt), maximum tetanic tension (Po) and maximal rates of contraction/relaxation (±dT/dtmax) were determined. The alterations in diaphragm ultrastructure were observed under electron microscopy. The diaphragm weight/body weight (DW/BW) was measured. The activities of succinic dehydrogenase (SDH), lactate dehydrogenase (LDH) and sarcoplasmic reticulum Ca2+ ATPase (SERCA) were analyzed by spectrophotometric method. The mRNA levels of SERCA and prospholamban (PLB) in diaphragm were detected by RT-PCR.
 RESULTS: Compared with the NC group, there was no significant change in all measured index in the NaHS group (P>0.05), while Pt, Po and ±dT/dtmax were significantly decreased in the DM group (P<0.05). Transmission electron microscopy revealed obvious ultrastructural changes in the diaphragm. The DW/BW ratio and the activities of SDH, LDH and SERCA were decreased. The SERCA mRNA was decreased, while PLB mRNA was increased. Compared with the DM group, the diaphragm contractility and ultrastructure damage were improved in the DM+NaHS group. The DW/BW ratio and the activities of SDH, LDH and SERCA were increased. The SERCA mRNA was increased, while PLB mRNA was decreased (all P<0.05).
 CONCLUSION H(2)S can enhance the contraction capacity of diaphragm in type 1 diabetic rats, which is involved in regulating the activities of biological enzymes and the gene expressions of calcium regulatory proteins.
Animals ; Body Weight ; Diabetes Mellitus, Experimental ; physiopathology ; Diaphragm ; drug effects ; ultrastructure ; Hydrogen Sulfide ; pharmacology ; L-Lactate Dehydrogenase ; metabolism ; Male ; Muscle Contraction ; drug effects ; RNA, Messenger ; metabolism ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Sarcoplasmic Reticulum Calcium-Transporting ATPases ; metabolism ; Succinate Dehydrogenase ; metabolism ; Sulfides ; pharmacology

OBJECTIVETo observe the anesthetic efficacy and safety of bilateral ultrasound-guided supraclavicular brachial plexus block in patients undergoing arthrolysis for shoulder periarthritis.

METHODSTwenty-seven patients (ASA class I-II) undergoing bilateral shoulder joint release surgery and 24 ml received bilateral ultrasound-guided supraclavicular brachial plexus block anesthesia with 0.4% ropivacaine and 0.8% lidocaine. The visual analogue scale (VAS) scores for shoulder joint pain were recorded before and after anesthesia. The efficacy of axillary nerve, dorsal scapular nerve and suprascapular nerve block was evaluated, and the anesthetic effect and complications was assessed during surgery. Before and after anesthesia, the range of left and right diaphragmatic muscle movement was measured when the patient took a quiet breath and a deep breath.

RESULTSThe patients showed no significant variations in MAP, HR, or SpO₂after anesthesia. The VAS scores of shoulder joint pain during anteflexion, abduction, posterior extension, rotation, posterior extension and medial rotation were significantly lowered after anesthesia (P<0.05), but the left and the right diaphragm movement range showed no significant difference between quiet breath and deep breath (P>0.05). The rates of complete block of the axillary nerve and dorsal scapular nerve was 100%, and that of suprascapular nerve was 92.6%. Partial phrenic nerve block occurred in 1 case with mild local anesthetic toxicity in another.

CONCLUSIONSBilateral ultrasound-guided supraclavicular brachial plexus block in patients has excellent analgesic effect in should joint release surgery with good safely.

Amides ; Anesthetics, Local ; Brachial Plexus Block ; Diaphragm ; Humans ; Lidocaine ; Orthopedic Procedures ; Pain Measurement ; Periarthritis ; diagnostic imaging ; surgery ; Shoulder Joint ; diagnostic imaging ; physiopathology ; Ultrasonography

OBJECTIVETo study the changes in diaphragmatic function and gene expressions of calcium regulatory proteins in diabetic rats and explore the mechanism of diaphragm dysfunction in diabetes mellitus.

METHODSSD rats were randomly divided into normal control group and diabetic (induced by intraperitoneal STZ injection) group. After 4 and 8 weeks, the body weight and diaphragm to body weight ratio were measured, and the activities of succinic dehydrogenase (SDH) in the diaphragm and blood glucose were assayed. The diaphragm contractility was assessed and the alterations of diaphragm ultrastructure were observed. RT-PCR was used to detect the changes in sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) and phospholamban (PLB) mRNA expressions in the diaphragm.

RESULTSThe diabetic rats showed a significant weight loss with a lowered diaphragm to body weight ratio (P<0.01) and SDH activity (P<0.01). The peak twitch tension and maximum tetanic tension of the diaphragm were significantly lowered and the time to peak contraction and half relaxation time significantly prolonged (P<0.01) in the diabetic rats, which also exhibited a lowered tetanic force in response to stimulus (P<0.01). Transmission electron microscopy revealed obvious ultrastructural changes of the diaphragm in diabetic rats. RT-PCR showed significantly decreased SERCA and increased PLB mRNA expressions in diabetic rat diaphragm (P<0.01), and these changes intensified with time (P<0.01).

CONCLUSIONDiabetes can cause impairment of diaphragmatic ultrastructure, mitochondrial injuries, and lowered SDH activity and ATP production. Decreased SERCA and increased PLB mRNA expressions in diabetes result in reduced Ca(2+) uptake by the diaphragm sarcoplasmic reticulum to induce diaphragm dysfunction.

Animals ; Body Weight ; Calcium ; metabolism ; Calcium-Binding Proteins ; metabolism ; Diabetes Mellitus, Experimental ; metabolism ; physiopathology ; Diaphragm ; metabolism ; physiopathology ; Glucose ; metabolism ; Male ; Rats ; Rats, Sprague-Dawley ; Sarcoplasmic Reticulum ; metabolism ; Sarcoplasmic Reticulum Calcium-Transporting ATPases ; metabolism ; Succinate Dehydrogenase ; metabolism

OBJECTIVETo study the changes of inducible nitric oxide synthase (iNOS) activity and apoptosis-related genes Bcl-2, Bax and caspase-3 mRNA expressions in endotoxemia-induced rat diaphragm injury and analyze the related apoptosis mechanism.

METHODSThirty-two male SD rats were randomly divided into 4 groups (n = 8): control group (saline 0.5 ml ip), endotoxin 24 h, 48 h and 96 h group (endotoxin 12 mg/kg ip, animals were killed either 24, 48 or 96 h after injections). Body weight were measured, the ratio between diaphragm weight and body weight, activities of constitutive nitric oxide syntheses (cNOS), iNOS and succinate dehydrogenase (SDH) were also measured. The expressions of Bcl-2, Bax and caspase-3 mRNA were detected by RT-PCR analysis.

RESULTSEndotoxin induced significant reductions in diaphragm mass in endotoxin 96 h group (P < 0.05). Endotoxin increased diaphragm cNOS or iNOS activities, and they were significantly higher in endotoxin 96 h group than those in endotoxin 24 h and 48 h groups, diaphragm SDH activity was reduced, and it was lower in endotoxin 96 h group than that in endotoxin 24 h and 48 h groups (P < 0.01). Endotoxin significantly increased Bax and caspase-3 mRNA expressions, and they were higher in endotoxin 48 h and 96 h groups than those in endotoxin 24 h group (P < 0.01). Endotoxin significantly reduced Bcl-2 mRNA expression and the ratio of Bcl-2/Bax, and they were lower in endotoxin 48 h and 96 h groups than those in endotoxin 24 h group (P < 0.01).

CONCLUSIONiNOS is activated in endotoxemia-induced rat diaphragm injury. It damages mitochondria, upregulates Bax expression and downregulates Bcl-2 expression, then induces caspase-3 related apoptotic pathway. These changes may cause diaphragm injury and atrophy.

Animals ; Apoptosis ; Caspase 3 ; metabolism ; Diaphragm ; metabolism ; physiopathology ; Endotoxemia ; metabolism ; Gene Expression ; Male ; Nitric Oxide Synthase Type II ; metabolism ; Proto-Oncogene Proteins c-bcl-2 ; metabolism ; Rats ; Rats, Sprague-Dawley ; bcl-2-Associated X Protein ; metabolism

OBJECTIVETo observe the effects of Bufei Jianpi Recipe (BJR) on the diaphragmatic neural discharge and the diaphragmatic muscle function in rats with chronic obstructive pulmonary disease (COPD).

METHODSRats were randomly divided into the normal control group, the model group, the high dose BJR group (9.68 g/kg x d(-1)), the medium dose BJR group (4.84 g/kg x d(-1)), the low dose BJR group (2.42 g/kg x d(-1)), and the aminophylline group (2.3 mg/kg x d(-1)). The stable phase COPD rat model was prepared using repeated smoke inhalations and bacterial infections. The high, medium, and low dose BJR and aminophylline was respectively administered to rats from the ninth week to the twentieth week. The sampling was taken. The lung function, diaphragmatic neural discharge time (Td), and diaphragmatic neural discharge interval (Tdi), diaphragmatic neural discharge range (Rd), diaphragmatic neural discharge area (Ad), expiratory time (Tex), inspiratory time (Tin), respiratory rate (RR), respiratory excursion (RE), respiratory area (RA), and diaphragmatic muscular tension and endurance were detected.

RESULTSCompared with the normal control group, the tidal volume (TV), peak expiratory flow (PEF), and 50% tidal volume expiratory flow (EF50) significantly decreased in the model group (P < 0.01). Td, Tdi, Tex, and Tin were significantly prolonged (P < 0. 05, P < 0.01). Ad, Rd, RR, RE, RA, diaphragmatic muscular tension and endurance significantly decreased (P < 0.05, P < 0.01). The ratio of type I and IIA diaphragmatic fibers significantly increased and type IIB significantly decreased (P < 0.01). The activity of ATP decreased and the activity of SDH increased (P < 0.01). The aforesaid indices were improved to different degrees in BJR groups, especially in the high dose BJR group and the medium dose BJR group (P < 0.05, P < 0.01).

CONCLUSIONSBJR could significantly improve the diaphragmatic neural discharge and the diaphragmatic muscle function. Its efficacy was better than that of aminophylline.

Aminophylline ; pharmacology ; Animals ; Diaphragm ; drug effects ; physiopathology ; Disease Models, Animal ; Drugs, Chinese Herbal ; pharmacology ; therapeutic use ; Male ; Phrenic Nerve ; drug effects ; physiopathology ; Phytotherapy ; Pulmonary Disease, Chronic Obstructive ; drug therapy ; physiopathology ; Rats

OBJECTIVE: To observe effects of restraint position on the changes of diaphragmatic mechanical characteristic in rats, and try to explore the role of nitric oxide (NO). METHODS: Rat model of restraint position was established. Rats were divided into control group, restraint position 12h and 24h groups. The markers of respiratory functions in vivo and the biomechanical markers of diaphragmatic characteristic ex vivo were evaluated. Serum NO levels were measured with spectrophotometry. The expressions of nNOS and iNOS mRNA in diaphragm were detected using RT-PCR. RESULTS: Compared with control group, respiratory rate, tidal volume and minute ventilation were significantly decreased in the restraint position 12h and 24h groups. Pt of diaphragm significantly decreased and force-generating capacity reduced at low frequency stimulation in 12h group. Force-generating capacity over the full range reduced at low and high frequency stimulation in 24h group. Pt of diaphragm in control and restraint position groups increased after L-NNA pre-incubation. Force-frequency relationship after L-NNA pre-incubation reduced in 24h group. NO level in serum increased significantly in the restraint position groups. Diaphragmatic nNOS mRNA expression was upregulated significantly in the restraint position groups. CONCLUSION Restraint position induces the decreasement of diaphragmatic contractility and the decreasement is mediated by NO from diaphragm or circulation blood.
Animals ; Biomechanical Phenomena ; Diaphragm/physiopathology* ; Male ; Muscle Contraction/physiology* ; Muscle Tonus/physiology* ; Nitric Oxide/metabolism* ; Nitric Oxide Synthase/metabolism* ; Posture ; RNA, Messenger/metabolism* ; Rats ; Rats, Sprague-Dawley ; Respiration Disorders/physiopathology* ; Restraint, Physical ; Reverse Transcriptase Polymerase Chain Reaction