Diaphragm Research Articles

Ventilator-Induced Diaphragm Dysfunction: Influence of Animal Species

PURPOSE: In rats, controlled mechanical ventilation (CMV) induced a profound reduction in diaphragm (DIA) muscle force-generating capacity as early as 24h, whereas in rabbits a similar decline was observed after 48h. Conflicting responses in rats and rabbits were extended to high-dose of methylprednisolone (MP). In rats, high-dose MP had a protective effect on CMV-induced DIA dysfunction (Respir Research 2010), whereas in rabbits had a deleterious effect (Muscle Nerve 2011). This study aimed to determine DIA force-generating capacity in animal model of critical-illness myopathy in which both cisatracurium (NM) and high-dose MP were administered in rats and rabbits receiving CMV for 48 h.

Differences in mRNA expression of calpains, calpastatin isoforms and calpain/calpastatin ratios among bovine skeletal muscles

Messenger RNA (mRNA) expression of calpain-1 (µ-calpain), -2 (m-calpain), -3 (p94), small subunit (calpain-4; 28 kDa), and three types of calpastatin (CSTN) isoform were investigated for 10 skeletal muscles of Holstein cattle by real-time and/or semi-quantitative reverse transcription polymerase chain reaction. Noticeably, effect of muscle type was observed on 28 kDa expression (P < 0.001) with a tendency of higher 28 kDa expression in myosin heavy chain (MyHC)-2x-rich muscles compared to MyHC-slow-rich muscles. The CSTN-I and -III expression in Longissimus thoracis (LT) showed the lowest value among the muscles tested. Moreover, 28 kDa/CSTN-I ratio was higher in the diaphragm (DP), psoas major (PM), and LT than those in the lingual muscles (TN), masseter (MS) and pectoralis (PP) (P < 0.05). Calpain-1/CSTN I, calpain-2/CSTN I in LT and PM were higher than that in TN (P < 0.05). Calpain-3/CSTN-I and -III in LT and/or PM showed higher values than that in TN (P < 0.05). These results indicated that the calpain and CSTN expressions are regulated by muscle type, suggesting especially by muscle fiber type. Calpains/CSTN-I ratios, especially 28 kDa/CSTN-I, may account for higher extent of post mortem proteolysis previously observed in LT and PM muscles.

Mutual Interaction of Airway Reflexes – Effects of Nasopharyngeal vs. Tracheo-bronchial Stimulations

VEGA 1/0038/09 (prof. Jakus) and EC sources European Regional Development Fund (CECR) M E T H O D S Experimental animal: 22 anesthetized spontaneously breathing cats of both sexes (3.6±0.3 kg) Anaesthesia: sodium pentobarbital (35 mg / kg i.p. initially, then 1-3 mg / kg i.v. as needed) Monitoring: respiratory rate, blood pressure (BP), end tidal CO2 concentration, and body temperature (37 – 38 oC) Recording parameters: BP, esophageal pressure (EP), electromyograms of the diaphragm (DIA) and abdominal muscles (ABD) Stimulation: AspR mechanical probing of nasopharyngeal mucosa with thin nylon fiber loop or short air pressure pulses via pharyngostomy Cough continuos mechanical probing of tracheobronchial mucosa with thin nylon fiber loop for 10, 15, or 20 s Data analysis: Number of coughs and AspRs Peak inspiratory (I) and expiratory (E) EP Amplitudes of DIA and ABD electromyographic moving averages Durations of cough I and E phases, active E period and relative motor quiescence (inter-cough intervals) during cough, total cough cycle (Wang et al. 2009), latencies from the beginning of cough stimulation to the DIA activation and to the maximum of ABD activity in the first cough in the trial, cough related DIA and ABD activity, the overlapping of DIA and ABD cough activity Interactive cough – AspR trials were compared to the preceding and following control cough trials The results are given as: means ± S.E.M. Statistical processing was performed by GraphPad Instat software using appropriate tests: paired test and Wilcoxon matched pairs test P<0.05 was deemed as significant Mutual Interaction of Airway Reflexes – Effects of Nasopharyngeal vs. Tracheo-bronchial Stimulations

Diaphragm and limb muscles adapt differently to chronic normobaric hypoxia in mice

The adaptation of skeletal muscle to high altitude includes loss of oxidative capacity and smaller fiber size. Past studies focused on limb muscles, less active while animals adapt to lower Po2. In contrast, the diaphragm (DIA) increases its activity during hypoxia and may retain its endurance. We hypothesized that chronic hypoxia would not affect endurance, mitochondrial function or fiber size in the mouse DIA. Adult male mice were kept in normoxia (Control) or normobaric hypoxia (Hypoxia, FIO2= 10%) for 4 weeks. We measured endurance in vitro, mean fiber area (MFA), and mitochondrial function in DIA and leg muscles. The Hypoxia leg muscles had less endurance, but there was no difference between Control and Hypoxia DIA. MFA was unchanged in the Hypoxia leg muscles and 25% smaller in DIA (p<0.001). Mitochondrial respiration rates in Hypoxia leg muscles were slower: state 2 decreased 19%, state 3, 31% and state 4, 18%, p<0.05 for all comparisons. There were similar changes in the Hypoxia DIA: state 3 decreased 29% and state 4, 17%, p<0.05. However, Hypoxia altered mitochondrial composition differently in the two muscles: leg muscle mitochondria had less respiratory complex IV, while DIA mitochondria had more respiratory complexes IV and V and less UCP3. These data demonstrate that DIA retains its endurance during chronic hypoxia, probably due to shorter diffusion distances and optimized mitochondrial energy production.

Effects of gestation and transition diets, piglet birth weight, and fasting time on depletion of glycogen pools in liver and 3 muscles of newborn piglets1

The experiment was conducted to assess the effects of maternal nutrition in late gestation on glycogen pools of newborn piglets of different birth weights and to assess how rapidly the glycogen pools in the liver and 3 muscles are mobilized during fasting. Until d 108 of gestation, 48 sows were fed a gestation standard diet (GSD) with low dietary fiber (DF, 17.1%), or 1 of 3 diets with high DF (32.3 to 40.4%) consisting of pectin residue (GPR), potato pulp (GPP), or sugar-beet pulp (GSP). From d 108 until farrowing, sows were fed 1 of 6 transition diets with low or high dietary fat: one group received a standard diet (TSD; control) containing 3% animal fat, another group received the TSD diet + 2.5 g/d of hydroxy-methyl butyrate as topdressing (THB), and 4 other groups received diets with 8% added fat from coconut oil (TCO), sunflower oil (TSO), fish oil (TFO), or 4% octanoic acid + 4% fish oil (TOA). Two piglets per litter (the second and fifth born) were blood sampled, and 1 was killed immediately after birth, whereas the other, depending on the litter, was killed after 12, 24, or 28.5 to 36 h (mean 32.5 h) of fasting. Samples of liver, LM, M. semimembranousus (SM), and M. diaphragm (DP) were collected and analyzed for glycogen concentration. No dietary effects (P > 0.20) on glycogen concentrations in liver, LM, SM, or DP were observed. The weight of the liver was affected by gestation diet (P < 0.05) and was greater in GSD and GSP piglets (36.7 and 36.3 g) than in GPR piglets (32.6 g), and intermediate (33.6 g) in GPP piglets. Liver weight, estimated muscle mass, and glycogen pools (P < 0.001) were affected by birth weight, whereas glycogen concentrations in liver and LM, SM, and DP muscles were not (P > 0.05). Liver weight; glycogen concentrations in liver, LM, SM, and DP; and glycogen pools in liver and muscles decreased (P < 0.001) with increasing duration of fasting, and at 32.5 h of fasting, glycogen concentration was reduced by 80% in liver, 64% in DP, 46% in SM, and 36% in LM. Based on a broken-line model, labile glycogen in SM, a locomotory muscle, was estimated to be depleted after 16.4 h of fasting. In conclusion, piglet size had a major impact on estimated glycogen pools, whereas sow nutrition in late gestation had a minor impact, if any. Furthermore, varying proportions of pools of glycogen present in liver and selected muscles were mobilized, and data indicate that newborn piglets are fatally depleted of energy after 16 h of fasting.

Regional Differences In Gene Expression Profile In 2A Arterioles Isolated From Different Types Of Skeletal Muscle

It has been previously shown that arterioles isolated from skeletal muscles of different fiber type composition or from different sections within the same skeletal muscle have distinct vasomotor responses to vasoactive agents involved in blood flow control. PURPOSE: To gain insights into potential determinants of these inhomogeneous vasomotor responsiveness the purpose of this study was to contrast and compare the transcriptional profile of isolated second order arterioles (2As) from the diaphragm (DIA) and red (RED) and white (WHITE) portion of gastrocnemius muscle of rats. METHODS: Twelve male Wistar rats were anesthetized and the gastrocnemius and diaphragm muscles were harvested and promptly placed in cold RNA stabilization reagent. A single 2A arteriole from each muscle section was carefully isolated, cleared of the surrounding muscle fibers and stored for analysis. Total RNA was extracted, reverse transcribed and amplified and the resulting cRNA was biotinylated and then hybridized to the Illumina® RatRef-12 Expression BeadChip (21,910 probes). RESULTS: Microarray analysis revealed that 202 gene elements were differentially expressed (1.5 fold difference) between RED and DIA. Genes involved in morphogenesis and tissue growth/development particularly exhibited different levels of expression between these two types of arteriole. In sharp contrast, only 11 genes showed more than 1.5 fold difference between WHITE and DIA. Of interest, the expression of alpha-1B adrenergic receptor was slightly higher in RED arterioles compared to DIA (1.25 fold, p=0.01) and WHITE (1.34 fold, p=0.002). Finally, the most marked distinct profile was found in the comparison between arterioles from the gastrocnemius muscle. Indeed, 435 genes, many linked to tissue morphogenesis and contraction, were found to be differentially expressed between RED and WHITE. We also found that the adenosine A2a receptor had a higher expression in RED vs. WHITE (1.33 fold, p=0.006). CONCLUSION: These observations demonstrate that substantial differences in the transcriptional profile exist between arterioles from different types of skeletal muscle. Of note, the greatest number of genes exhibiting different expression was observed from comparison of arterioles from different sections of the same muscle (RED vs. WHITE). Furthermore, the similarity between DIA and WHITE suggests that differences in global gene expression cannot be explained only by regional differences in fiber type composition and/or oxidative capacity. Support: NIH #HL36088 and Fulbright/ CAPES

Exercise capacity in hamsters with elastase-induced emphysema compared to normal controls

The purpose of this study was to determine whether hamsters with elastase-induced emphysema (EMP) would demonstrate a reduction in exercise capacity compared to control (CON) hamsters and whether changes in activity levels, muscle function and structure could explain any changes in exercise capacity. Peak oxygen consumption and daily activity levels were measured on two occasions. Inspiratory capacity under deep anesthesia, in vitro measurements of muscle force and fatigability for the diaphragm (DIA) and extensor digitorum longus (EDL) and fiber proportions, muscle cross-sectional area and fiber specific SDH activity from the DIA, EDL and vastus lateralis (VLA) were obtained. Inspiratory capacity was 60% higher in the EMP compared to CON hamsters (p=0.0004). Activity levels and exercise capacity were not significantly different between EMP and CON hamsters. Muscle strength and fatigability, fiber proportions, muscle cross-sectional area and fiber specific SDH activity were similar between EMP and CON hamsters. In conclusion, in hamsters, elastase-induced emphysema did not reduce maximal exercise capacity.

Intracellular Ca2+ transients during fatigue in intact skeletal muscle: role of Ca2+ in low frequency fatigue

We previously reported a surface fluorometry method for measurement of intracellular Ca2+ in intact skeletal muscles. Here we employ this method to examine mechanisms of muscle fatigue. Mouse epitrochlearis (EPI) and diaphragm (DIA) muscles were mounted in vertical chambers, stretched to LO, and loaded with Rhod‐2 AM. Force and intracellular Ca2+ were recorded at several stimulation frequencies, and muscles were then contracted with periodic increases in train frequency (0.16, 0.2, 0.25, 0.33, 0.5, 1 train/sec). Fatigue was defined by a 50% reduction in force. EPI and DIA showed markedly different times to fatigue, as expected (~7.0 min for EPI vs. ~10.8 min for DIA). Ca2+ transients (peak ΔF) showed no initial decline, but later decreased by ~22% for EPI and ~27% for DIA. Baseline Rhod‐2 fluorescence increased in both muscles during fatigue (EPI ~77% of peak ΔF, DIA ~58% of peak ΔF), indicating mitochondrial Ca2+ accumulation. Following 15 min of recovery, max tetanic force recovered fully while forces at lower frequencies were reduced from baseline (low‐frequency fatigue). In contrast, intracellular Ca2+ transients recovered fully at both high and low stimulation frequencies in this preparation suggesting that the primary mechanism for low frequency fatigue is related to inhibition of the contractile elements and not to processes involved in Ca+2 release. NHLBI 53333.

Carbachol injection into the pontine reticular formation depresses laryngeal muscle activities and airway reflexes in decerebrate cats

To understand the role of cholinoceptive, medial pontine reticular formation (mPRF) neurons in the control of upper airway, pharyngolaryngeal reflexes, we measured activities of intrinsic laryngeal muscles (posterior cricoarytenoid, PCA; thyroarytenoid, TA), diaphragm (DIA), genioglossus (GG) and a neck muscle (trapezius) in unanesthetized, decerebrated, spontaneously breathing cats with and without mPRF carbachol injections. The ethimoidal nerve was electrically stimulated to evoke sneezing, and the superior laryngeal nerve to evoke the laryngeal reflex, swallowing, and coughing. Carbachol reduced the amplitudes of the spontaneous electromyographic activities in the neck, TA, PCA, GG, and DIA to 7%, 30%, 54%, 45% and 71% of control, respectively, reduced the respiratory rate to 53% without changes in expiratory CO 2 concentration; the magnitude of the laryngeal reflex in the TA muscle to 56%; increased its latency by 13%; and reduced the probability of stimulus-induced sneezing, swallowing, and coughing to less than 40%. These changes lasted more than 1 h. These data demonstrate that important upper airway reflexes are suppressed by increasing cholinergic neurotransmission in the mPRF. Because acetylcholine release in the mPRF changes in accordance with sleep–wake cycles, the present findings are relevant to the control of upper airway reflexes during various vigilance states.

Respiratory rehabilitation with abdominal weights: a prospective case study

Objective: Abdominal weights was used to strengthen the diaphragm of a C6 ASIA (A) tetraplegic subject with the aim of studying the long term effect of the technique as a part of respiratory rehabilitation. Setting: Department of Physical Medicine and Rehabilitation, Christian Medical College, Vellore, Tamil Nadu, India. Study Design: Prospective case study. Material and methods: The peak EMG amplitude of the diaphragm (DIA), intercostals (INT) and sternoclidomastiod (SCM) were assessed using a surface EMG and inspired lung volume (ILV) was assessed using an adjustable portable spirometer. The measurements were repeated after 3, 6, 9 and 12 months of inspiratory muscle training for a period of 15 minutes daily, 6 days a week for 12 months. Results and discussion: Peak amplitudes recorded by the EMG of DIA and SCM muscles showed a progressive increase, INT muscle did not show a consistent change. INV showed a gradual rise from 1772ml to 2760 ml over the study period. These values have the following significance: 1) Use of abdominal weights as a part of respiratory rehabilitation has beneficial long term effects; 2) In patients with tetraplegia, respiratory muscles in particular the diaphragm, are trainable in terms of muscle efficiency; 3) The improvement in the muscle efficiency obtained during the early rehabilitation can be maintained or improved using simple non sophisticated exercises like abdominal weights post discharge. Conclusions: Abdominal weights can be used as an effective adjunct to pulmonary rehabilitation in improving the efficiency of diaphragm on a long term basis, thereby reducing the risks associated with pulmonary complications.

The movement of the diaphragm monitored by ultrasound imaging: Preliminary findings of diaphragm movements in classical singing

This study will by ultrasound imaging (USI) investigate the movement of the diaphragm (DPH) during classical singing. Due to the complex structures of the DPH both the anterior and dorsal sections of the DPH will be investigated. The movement of the anterior section is surveyed by performing a transabdominal scan from the right hypochondrium. The movement of the dorsal section is surveyed by examining the movement of the left kidney. We conclude that USI is a promising tool for surveying the movement of the DPH. Especially the anterior section is easily assessed; however, also the dorsal section may indirectly be surveyed by USI of the movement of the left kidney.

Effectiveness of Residential Water-Use Restrictions under Varying Levels of Municipal Effort

<b>Background &amp; Aims:</b> Sepsis triggers skeletal muscle contractile dysfunction and fiber atrophy. In this study, we evaluated the differential effects of sepsis on the ventilatory and limb muscle fiber atrophy and tested whether sepsis-induced fiber atrophy is the result of decreased expression of various myofilament proteins. <b>Methods:</b> Adult C57/Bl6 mice underwent cecal ligation and perforation (CLP group) to induce severe sepsis. Group 2 underwent sham surgical procedure (Sham group). The diaphragm (DIA) and tibialis anterior (TA) muscles were examined after 24, 48 and 96h of the surgical procedure. Fiber atrophy was quantified from muscle fiber cross sectional areas. Myofilament proteins were quantified both at the mRNA and protein levels using qPCR and immunoblotting. <b>Results:</b> Sepsis triggered transient DIA fiber atrophy (24h) whereas more persistent fiber atrophy was evident in the TA (24, 48 and 96h). In addition, mRNA and protein levels of Myosin Heavy Chain (MyHC), Myosin Light Chain (MyLC), Troponin-T, Troponin-C and Tropomyosin were strongly decreased both in the DIA and TA by sepsis while α-Actin and Troponin-I levels were not influenced by sepsis. The decrease in MyHC and MyLC protein contents was sustained even after 96h of sepsis while the decline in Troponin-T, Troponin-I, Troponin-C and Tropomyosin mRNA and protein levels was restricted to 24 and 48h after induction of sepsis. <b>Conclusions:</b> Sepsis triggers more severe and sustained muscle atrophy in limb muscles than in the diaphragm. Sepsis-induced atrophy is caused by decreased contractile and regulatory myofilament protein levels as a result of both increased proteolysis and decreased transcription.

Effects of 14 days of microgravity on fast hindlimb and diaphragm muscles of the rat

The purpose of the present study was to determine the effects of 14 days of microgravity on specific rat fast-twitch muscles, and to compare these data with previous data from rat fast-twitch muscles exposed to microgravity for 10 days (Kraemer et al. 2000). Hindlimb muscles containing predominately fast fibers [extensor digitorum longus (EDL), superficial "white" (GSW) and deep "red" (GDR) gastrocnemius] and the diaphragm (DIA) were removed from flight and ground-based control animals and analyzed for: muscle mass, fiber type distribution, cross-sectional area, and myosin heavy chain (MHC) isoform content. Gravitational unloading for 14 days caused significant decreases in muscle mass (8-9%) and cross-sectional area of almost all fiber types (10-35%) from both EDL and gastrocnemius muscles. However, microgravity had little effect on fiber type composition in these muscles with significant changes occurring only in the EDL type IID fiber population (9.5% decrease). Similarly, relative MHC isoform content was only slightly altered by exposure to microgravity (increased content of MHCIIa in flight EDL). No changes in area, fiber type percentages, or MHC isoform content were detected in the DIA following the 14-day spaceflight. Similar to data gathered following a 10-day spaceflight (Kraemer et al. 2000), the 14-day flight did not appear to cause significant slow-to-fast (I --> IIA) or fast-to-faster (IIA --> IID --> IIB) transformations in hindlimb muscles containing predominantly fast-twitch fibers. However, the longer period of gravitational unloading did result in additional loss in muscle fiber cross-sectional area with involvement of more major fiber types.

Stimulation of the rat medullary raphe nuclei induces differential responses in respiratory muscle activity

Neural control circuits that coordinate the motor activity of the diaphragm (DIA) and the geniohyoid muscle (GH) are potentially involved in pathological conditions such as various forms of sleep apnea. Here we investigated a differential role of the raphe magnus (RMg), pallidus (RPa) and the obscurus (ROb) nuclei in the neural control of DIA and GH muscle activity in rats under volatile anesthesia. In order to characterize a topographical organization of the raphe nuclei we analyzed changes in DIA and GH during high-frequency stimulation (HFS, 10-130 Hz, 60 micros pulse width, 40-160 microA, 30s). HFS of the RMg and the ROb induced apnea, in the latter case apnea was associated with massive tonic discharge in the GH. By contrast, HFS of the RPa induced tachypnea. At caudal stimulation sites the tachypnea was accompanied by tonic DIA activity and cessation of GH. These data suggest a differential distribution of inhibitory and excitatory drives of DIA and GH muscles within distinct raphe nuclei.

A Role for Forkhead Transcription Factors (FOXOs) in Disuse Atrophy of the Human Diaphragm (DIA) Associated with Mechanical Ventilation (MV)

We (Levine et al, NEJM, in press) have demonstrated that the combination of complete DIA inactivity and MV (i.e. DIA inact + MV) elicits marked atrophy of human DIA myofibers due to increased proteolysis. To assess the role of FOXOs 1 and 3 in effecting this atrophy, we biopsied the costal DIA of 10 brain dead organ donors prior to organ harvest (i.e., case subjects) and compared them to intra‐operative biopsies obtained from the DIA of 10 patients undergoing lung surgery (i.e., controls). Cases exhibited DIA inact + MV for much longer periods of time than controls (i.e., 18–69 hours versus 2–3 hours). We then isolated RNA from each DIA biopsy and we carried out real‐time reverse transcriptase PCR to assess the relative gene expressions of FOXOs 1 and 3, Atrogin‐1, and MuRF‐1 genes. In comparison to controls, case diaphragms exhibited the following fold increases in relative transcript number: FOXO 1, 5.6 (p&lt;0.001); FOXO 3, 2.0 (p&lt;0.04); Atrogin‐1, 2.6 (p&lt;0.05), and MuRF‐1, 4.9 (p&lt;0.01). These results are consistent with the concept that (a) case diaphragms increase transcription of FOXOs 1 and 3 that bind to the promoter region of the ubiquitin ligase genes (i.e., Atrogin‐1 and MuRF‐1); (b) increased mRNA expression of these latter genes increases the rate of proteolysis via the ubiquitin‐proteasome pathway; and (c) thereby accounts for some portion of the myofiber atrophy noted in case DIA. Supported by NIH Grant R01‐HL‐078834.

Effect of IGF‐I and rapamycin on diaphragm muscle atrogenes with malnutrition

We recently reported that the addition of rapamycin to IGF‐I decreased P‐Akt in the diaphragm (DIA) with acute nutritional deprivation (ND). As Akt impacts on pathways mediating proteolysis, the aim was to evaluate the influence of IGF‐I and rapamycin on rat DIA atrogenes with ND. Groups: 1) Controls (CTL); 2) ND (20% of food intake for 4 days); 3) ND+IGF‐I; and 4) ND+IGF‐I+rapamycin. DIA mRNA was analyzed by real‐time PCR. Foxo1 and 3a increased 2.3 and 2.9‐fold with ND, while Foxo4 decreased by 46%. IGF‐I reduced Foxo1 and 3a to CTL levels, while Foxo4 increased 2.5‐fold. Rapamycin negated all IGF‐I effects. ND increased MAFbx/Atrogin1 and MuRF1 by 2.7 and 19‐fold, with no change in E3‐[alpha]II. IGF‐I decreased these atrogenes to near CTL levels. Rapamycin returned these E3 ligases to ND levels. ND increased caspase 3 (important in myofibrillar disassembly) 4.8‐fold. IGF‐I decreased it to 1.5‐fold CTL. Rapamycin increased abundance to ND levels. ND increased myostatin (negative regulator of muscle mass) 2.4‐fold. IGF‐I reduced it to 0.78 CTL levels while rapamycin negated IGF‐I effects. We conclude that IGF‐I significantly reduces atrogenes and their regulators with ND. These positive effects were reversed with rapamycin, an mTOR inhibitor. We speculate that influences on mTOR feedback negatively on Akt and/or other regulators of pathways mediating protein degradation. Funded by NIH HL‐071227

Capillary supply, fibre types and fibre morphometry in rat tibialis anterior and diaphragm muscles after intermittent exposure to hypobaric hypoxia

Three groups of sedentary male rats were exposed to intermittent hypobaric hypoxia (IHH) for 22 days (4 h/day, 5 days/week) in a hypobaric chamber at a simulated altitude of 5,000 m. Tibialis anterior (TA) and diaphragm (DG) were removed at the end of the programme (H group), and 20 or 40 days later (P20 and P40 groups). A control group (C) was maintained at sea-level pressure and their TA and DG were compared to those of the experimental rats at the end of the IHH programme, and also 20 and 40 days later. We measured the fibre morphometry and capillaries of each muscle. Our results demonstrate that IHH does not change the fibre type composition (with reference to either their contractile or oxidative properties) for most muscle regions of the muscles analysed analysed. We found few significant differences in muscle capillarity and fibre morphometry for TA after IHH. However, IHH did induce some statistically significant changes in DG: capillary density of the H rats (736 capillaries/mm2) increased compared to C animals (610 capillaries/mm2). Although IHH did not change the fibre capillarization or morphometric parameters of fast fibre types, we observed reductions ranging from 7 to 13% in fibre area, perimeter and diffusion distances between C and H for slow fibres. Moreover, these morphometric changes accounted for increases of 10-20% in capillarization, fibre unit area and fibre unit perimeter. This indicates that SO fibres are more sensitive to IHH than both fast fibre types.

Post-tetanic count at adductor pollicis is a better indicator of early diaphragmatic recovery than train-of-four count at corrugator supercilii

Because the intensity of neuromuscular block at the diaphragm (DIA) is indirectly assessed, the electromyographic measurements of the DIA (DIA(EMG)) from surface electrodes were related to information provided by visual estimation of neuromuscular transmission at the adductor pollicis (AP) and the corrugator supercilii (CSC) during recovery from vecuronium block. Twelve adult patients were studied during balanced anaesthesia. After induction of anaesthesia and tracheal intubation without neuromuscular blocking agent, supramaximal stimulations were applied to phrenic, ulnar and facial nerves. During recovery from vecuronium 0.1 mg kg(-1) an independent observer blinded to DIA(EMG) counted visually detectable train-of-four (TOF) at CSC (TOF(CSC)) and post-tetanic AP (PTC(AP)) responses. Times to recovery of PTC(AP) = 1, <or=5, <10 and >10, and TOF(CSC) = 1-4 responses were related to DIA(EMG). Values are means (sd). Reappearance of the first response to PTC(AP) occurred significantly (P < 0.05) earlier and for a lower recovery of DIA(EMG) than that of TOF(CSC) [24 (8) min vs 33 (9) min, and 10 (10)% vs 25 (8)%, respectively]. With PTC(AP) <or= 5 response, DIA(EMG) recovery was 21 (11)%. Recovery of TOF(CSC) = 1 and 2 coincided with DIA(EMG) recovery of 25 (8)% and 47 (9)%, respectively. PTC(AP) may better reflect early recovery of vecuronium-induced DIA paralysis than TOF(CSC). The findings suggested that PTC(AP) <or= 5 warranted deep neuromuscular block of the DIA.

Heart failure alters matrix metalloproteinase gene expression and activity in rat skeletal muscle

Heart failure is associated with a skeletal muscle myopathy with cellular and extracellular alterations. The hypothesis of this investigation is that extracellular changes may be associated with enhanced mRNA expression and activity of matrix metalloproteinases (MMP). We examined MMP mRNA expression and MMP activity in Soleus (SOL), extensor digitorum longus (EDL), and diaphragm (DIA) muscles of young Wistar rat with monocrotaline-induced heart failure. Rats injected with saline served as age-matched controls. MMP2 and MMP9 mRNA contents were determined by RT-PCR and MMP activity by electrophoresis in gelatin-containing polyacrylamide gels in the presence of SDS under non-reducing conditions. Heart failure increased MMP9 mRNA expression and activity in SOL, EDL and DIA and MMP2 mRNA expression in DIA. These results suggest that MMP changes may contribute to the skeletal muscle myopathy during heart failure.

Diaphragm and intercostal surface EMG and muscle performance after acute inspiratory muscle loading

We examined the effect of an acute bout of submaximal non-fatiguing inspiratory loading (IL) on maximal inspiratory pressure (MIP), and on the activation of the diaphragm (DI) and intercostals (IC) using surface electromyography (sEMG). After baseline measurements, 12 healthy subjects performed two sets of 30 inspiratory efforts at a load equivalent to 40% of their initial MIP. MIP and maximal DI and IC sEMG activity were recorded after the first and second set of IL, and 15 min after task cessation. After IL, MIP reached (+/-S.E.M.) 111+/-4% (P=0.032) of baseline values, and during MIP, DI and IC root mean square (RMS) sEMG amplitude increased significantly above baseline (143+/-21%, P=0.039 and 137+/-33%, P=0.016, respectively). The significant increase in MIP and RMS amplitude after IL suggests that MIP efforts were initially submaximal, and that prior loading enabled full activation. The changes in DI and IC RMS amplitude may also reflect an improvement in the synergy between them during these maximal efforts.