Toxoplasmosis epidemic in a population of urbanised allied rock-wallabies (Petrogale assimilis) on Magnetic Island (Yunbenun), North Queensland

A mortality event involving 23 allied rock-wallabies (Petrogale assimilis) displaying neurological signs and sudden death occurred in late April to May 2021 in a suburban residential area directly adjacent to Magnetic Island National Park, on Magnetic Island (Yunbenun), North Queensland, Australia. Three allied rock-wallabies were submitted for necropsy, and in all three cases, the cause of death was disseminated toxoplasmosis. This mortality event was unusual because only a small, localised population of native wallabies inhabiting a periurban area on a tropical island in the Great Barrier Reef World Heritage Area were affected. A disease investigation determined the outbreak was likely linked to the presence of free-ranging feral and domesticated cats inhabiting the area. There were no significant deaths of other wallabies or wildlife in the same or other parts of Magnetic Island (Yunbenun) at the time of the outbreak. This is the first reported case of toxoplasmosis in allied rock-wallabies (Petrogale assimilis), and this investigation highlights the importance of protecting native wildlife species from an infectious and potentially fatal parasitic disease.

Fetal echocardiographic features associated with bicuspid aortic valve

BACKGROUND

Prenatal diagnosis of bicuspid aortic valve is challenging. Bicuspid aortic valve is often associated with aortic dilation.

METHODS

Fetuses with postnatally confirmed bicuspid aortic valve were gestational age-matched with normal controls. Complex lesions were excluded. Aortic valve and arch measurements by two blinded investigators were compared.

RESULTS

We identified 27 cases and 27 controls. Estimated fetal weight percentile was lower in cases than controls. Seven cases had one or more significant lesions including perimembranous ventricular septal defects (n = 2), isolated annular hypoplasia (n = 2), and/or arch hypoplasia/coarctation (n = 4). Fetuses with bicuspid aortic valves had significantly smaller median z-scores of the aortic annulus (-1.60 versus -0.53, p < 0.001) and root (-1.10 versus -0.53, p = 0.040), and larger ratios of root to annulus (1.32 versus 1.21, p < 0.001), sinotubular junction to annulus (1.07 versus 0.99, p < 0.001), ascending aorta to annulus (1.29 versus 1.18, p < 0.001), and transverse aorta to annulus (1.04 versus 0.96, p = 0.023). Leaflets were "doming" in 11 cases (41%) and 0 controls (p = 0.010), "thickened" in 10 cases (37%) and 0 controls (p = 0.002). We noted similar findings in the subgroup without significant additional cardiac defects.

CONCLUSIONS

The appearance of doming or thickened aortic valve leaflets on fetal echocardiogram is associated with bicuspid aortic valve. Compared to controls, fetuses with bicuspid aortic valve had smaller aortic annulus sizes (possibly related to smaller fetal size) without proportionally smaller aortic measurements, resulting in larger aortic dimension to annulus ratios. Despite inherent challenges of diagnosing bicuspid aortic valve prenatally, these findings may increase suspicion and prompt appropriate postnatal follow-up.

Six Month Follow-up of Patients With Multi-System Inflammatory Syndrome in Children

BACKGROUND AND OBJECTIVES

Myocardial dysfunction and coronary abnormalities are prominent features of multisystem inflammatory syndrome in children (MIS-C). In this study we aim to evaluate the early and midterm outcomes of MIS-C.

METHODS

This is a longitudinal 6-month cohort study of all children admitted and treated for MIS-C from April 17 to June 20, 2020. Patients were followed ∼2 weeks, 8 weeks, and 6 months postadmission, with those with coronary aneurysms evaluated more frequently.

RESULTS

Acutely, 31 (62%) patients required intensive care with vasoactive support, 26 (52%) had left ventricular (LV) systolic dysfunction, 16 (32%) had LV diastolic dysfunction, 8 (16%) had coronary aneurysms (z score ≥2.5), and 4 (8%) had coronary dilation (z score <2.5). A total of 48 patients (96%) received immunomodulatory treatment. At 2 weeks, there was persistent mild LV systolic dysfunction in 1 patient, coronary aneurysms in 2, and dilated coronary artery in 1. By 8 weeks through 6 months, all patients returned to functional baseline with normal LV systolic function and resolution of coronary abnormalities. Cardiac MRI performed during recovery in select patients revealed no myocardial edema or fibrosis. Some patients demonstrated persistent diastolic dysfunction at 2 weeks (5, 11%), 8 weeks (4, 9%), and 6 months (1, 4%).

CONCLUSIONS

Children with MIS-C treated with immunomodulators have favorable early outcomes with no mortality, normalization of LV systolic function, recovery of coronary abnormalities, and no inflammation or scarring on cardiac MRI. Persistence of diastolic dysfunction is of uncertain significance and indicates need for larger studies to improve understanding of MIS-C. These findings may help guide clinical management, outpatient monitoring, and considerations for sports clearance.

Continuous and intermittent administration of intravenous sildenafil in critically ill infants with pulmonary hypertension

Intravenous (IV) sildenafil may be administered as a continuous infusion or intermittent bolus dosing in infants with pulmonary hypertension (PH). We aimed to compare these delivery methods.

METHODS

We retrospectively evaluated subjects less than 12 months old treated with IV sildenafil for PH. Vital signs, oxygen requirement, vasoactive-inotropic score (VIS), and echocardiogram results before and after sildenafil initiation, and the need for discontinuation due to side effects, were noted.

RESULTS

Forty-three subjects were identified (23 continuous, 20 intermittent). There were clinically significant differences in PH classifications between groups. The continuous group was significantly younger (p = 0.010) with higher baseline severity of illness suggested by higher inspired oxygen (FiO₂ ) and VIS (p = 0.012). After sildenafil initiation, there were no significant differences in changes in blood pressure, oxygen saturation, FiO₂ , or VIS between groups, and no difference in the number of subjects requiring discontinuation due to side effects (4 continuous, 1 intermittent, p = 0.351). Eight continuous group subjects (34.8%) and 3 intermittent group subjects (15.0%) died (p = 0.024), but echocardiographic improvement in PH degree was more common in the continuous group (77.8% vs. 33.3%, p = 0.007).

CONCLUSION

In this small cohort of infants treated with continuous or intermittent IV sildenafil, in the setting of different baseline characteristics between groups, there were no significant differences in changes in vital signs, VIS, FiO₂ , or need for discontinuation of therapy due to side effects. Higher continuous group mortality may be explained by greater baseline illness severity, but larger prospective, randomized studies are required to investigate these different delivery methods.

Examining the Utility of Coronary Artery Lack of Tapering and Perivascular Brightness in Incomplete Kawasaki Disease

BACKGROUND

In 2017, the AHA published revised guidelines for the diagnosis of Kawasaki disease (KD). In the absence of compelling data supporting or refuting the utility of lack of tapering (LT) and perivascular brightness (PB), expert panel consensus removed LT and PB from consideration. We hypothesize that LT and PB are unreliable, subjective findings, non-specific to KD, which can be seen in systemic febrile illnesses without KD and in normal controls.

METHODS

We performed a single-center retrospective study from 1/2008 to 12/2016. De-identified coronary artery (CA) echocardiographic clips from patients 0-10 years old were interpreted blindly by six pediatric cardiologists. Subjects were grouped as follows: (1) healthy: afebrile with benign murmur, (2) KD: IVIG treatment, 4-5 clinical criteria at presentation, (3) incomplete KD (iKD): IVIG, 1-3 clinical criteria, (4) Febrile: ≥3 days of fever, no IVIG, KD not suspected. The presence or absence of LT and PB was recorded. Inter-rater and intra-rater reliabilities were analyzed using intra-class correlation coefficient, Fleiss' Kappa and Cohen's Kappa coefficients.

RESULTS

We interpreted 117 echocardiograms from healthy (27), KD (30), iKD (32), and febrile (28) subjects. Analysis showed moderate agreement in CA z score measurements. LT and PB were observed by most readers in control groups. LT exhibited fair inter-reader agreement (reliability coefficient 0.36) and PB slight inter-reader agreement (reliability coefficient 0.13). Intra-rater reliability was inconsistent for both parameters.

CONCLUSIONS

LT and PB are subjective, poorly reproducible features that can be seen in febrile patients without KD and in healthy children.

Subclinical Decrease in Myocardial Function in Asymptomatic Infants of Diabetic Mothers: A Tissue Doppler Study

Infants of diabetic mothers (IDMs) with hypertrophic cardiomyopathy are recognized to have impaired myocardial performance, but less is known about ventricular function in IDMs without hypertrophy. We hypothesized that in asymptomatic newborns with normal two-dimensional echocardiographic evaluations, pulsed wave tissue Doppler imaging (TDI) would suggest a subclinical decrease in the cardiac function of IDMs compared to infants of non-diabetics (nIDMs). This is a retrospective cohort study of asymptomatic neonates ≥36 weeks gestation, at 0-7 days of life, with normal standard echocardiograms. Systolic (S'), early diastolic (E'), and late diastolic (A') TDI velocities were measured at the mitral valve (MV) annulus, basal interventricular septum (IVS), and tricuspid valve (TV) annulus, and averaged from three consecutive cardiac cycles. Demographic, perinatal, and echocardiographic variables were compared between IDM and nIDM groups. Of 631 subjects, 75 IDMs were identified. The mean gestational age of the entire cohort was 39.33 weeks (±1.26), birth weight 3.44 kg (±0.56), and body surface area (BSA) 0.21 m² (±0.02). IDMs had significantly greater birth weight and BSA, lower gestational age, older maternal age, and higher incidence of maternal obesity and hypertension than nIDMs (p < 0.001). On multivariable analysis, IDMs had significantly lower S' (p ≤ 0.03) and E' (p < 0.001) velocities, and higher E/E' ratios (p < 0.001) at the MV, IVS, and TV than nIDMs. In asymptomatic newborn IDMs without cardiac hypertrophy, pulsed wave TDI suggests a subclinical decrease in systolic and diastolic myocardial function compared to nIDMs.

Assessing Myocardial Function in Infants with Pulmonary Hypertension: The Role of Tissue Doppler Imaging and Tricuspid Annular Plane Systolic Excursion

Transthoracic echocardiography is the most common noninvasive method of evaluating pulmonary hypertension (PH) in infants. Identification of reliable, quantitative indices of myocardial function may enhance the diagnostic value of echocardiography in this population. We hypothesized that pulsed wave tissue Doppler imaging (TDI) and tricuspid annular plane systolic excursion (TAPSE) would be reproducible measurements and would suggest decreased ventricular function, in infants with PH. This retrospective case-control study involved subjects diagnosed clinically and echocardiographically with PH at <12 months of age, matched with controls by age and gestational age (GA). TAPSE was measured by M-mode in the apical 4-chamber view. TDI velocities were averaged from three consecutive cardiac cycles. Observers were blinded to patient identity and clinical status. Fifty-seven subjects, including 35 term or near-term infants ≥35 weeks GA [mean GA 39 weeks (±1.7), median age 1 day (range 0-2)] and 22 preterm infants [median GA 25.4 weeks (24.1-26.6), age 66 days (4-128)], were matched with 57 controls. Subjects with PH had lower TAPSE (term p < 0.001, preterm p = 0.03) and TAPSE indexed to body surface area (term p < 0.001, preterm p = 0.005). Mitral annular, septal, and tricuspid annular systolic (S') and early diastolic (E') TDI velocities were also decreased compared to controls (all p < 0.05). Intraclass correlation demonstrated 84-99% agreement between observers in measuring TDI and 92% for TAPSE. Intraobserver reliability for these measures was 98-99% and 96%, respectively. We concluded that TDI and TAPSE are reproducible indices of myocardial function and may serve as useful adjuncts to standard echocardiographic measures in infants with PH.

Repair of Anomalous Left Coronary Artery From the Right Pulmonary Artery: A Series of Nine Cases

BACKGROUND

Repair of anomalous left coronary artery from the right pulmonary artery presents a particular technical challenge to the congenital cardiac surgeon. There is disagreement in the literature over the optimal technique for this defect, with some authors advocating for unroofing of the periaortic segment of coronary artery, while others prefer direct aortic reimplantation of the artery.

METHODS

We performed a retrospective study examining outcomes of patients who were repaired for this anomaly at our institution. In-hospital and outpatient follow-up data were analyzed.

RESULTS

Nine patients were identified. Most patients had poor left ventricular function at the time of surgery. All patients in our series were repaired using the direct coronary transfer technique. To date there were no mortalities among the study participants. At last follow-up, all patients with available echocardiograms had normal ventricular function. One patient required reoperation for anastomotic stenosis.

CONCLUSIONS

We demonstrate that using the technique of direct coronary transfer to the aorta, we have achieved excellent results with repair of this defect.

Redistribution of cell membrane probes following contraction-induced injury of mouse soleus muscle

Our aim was to study how mouse skeletal muscle membranes are altered by eccentric and isometric contractions. A fluorescent dialkyl carbocyanine dye (DiOC18(3)) was used to label muscle membranes, and the membranes accessible to the dye were observed by confocal laser scanning microscopy. Experiments were done on normal mouse soleus muscles and soleus muscles injured by 20 eccentric or 20 isometric contractions. Longitudinal optical sections of control muscle fibers revealed DiOC18(3) staining of the plasmalemma and regularly spaced transverse bands corresponding in location to the T-tubular system. Transverse optical sections showed an extensive reticular network with the DiOC18(3) staining. Injured muscle fibers showed distinctively different staining patterns in both longitudinal and transverse optical sections. Longitudinal optical sections of the injured fibers revealed staining in a longitudinally-oriented pattern. No correlations were found between the abnormal DiOC18(3) staining and the reductions in maximal isometric tetanic force or release of lactate dehydrogenase (P > or = 0.32). Additionally, no difference in the extent of abnormal staining was found between muscles performing eccentric contractions and those performing the less damaging isometric contractions. However, many fibers in muscles injured by eccentric contractions showed swollen regions with marked loss of membrane integrity and an elevated free cytosolic calcium concentration as observed in Fluo-3 images. In conclusion, a loss of cell membrane integrity results from contractile activity, enabling DiOC18(3) staining of internal membranes. The resulting staining pattern is striking and fibers with damaged cell membranes are easily distinguished from uninjured ones.

Eccentric contraction-induced injury in normal and hindlimb-suspended mouse soleus and EDL muscles

The primary objective of this study was to compare the magnitude of injury in mouse extensor digitorum longus (EDL) and soleus muscles induced by high-force eccentric contractions. A second objective was to study the effect of altering the daily loading of the muscles through hindlimb suspension (HS) on the injury. One of two protocols was performed in vitro: 1) 15 eccentric contractions (n = 20: 10 EDL and 10 soleus muscles) or 2) 15 isometric contractions (n = 20: 10 EDL and 10 soleus muscles). After the protocol, the decrements in contractile performance and lactate dehydrogenase (LDH) release were measured at 15-min intervals over 1 h. Immediately after the eccentric contraction protocol, markedly greater decrements in maximal isometric tetanic force (Po) occurred in the normal EDL than in the normal soleus muscles (60.7 +/- 4.2 vs. 7.6 +/- 2.1%, P < or = 0.0001). LDH release immediately after the eccentric contraction protocol was 2.7-fold greater in the normal EDL than in the normal soleus muscles. To investigate the role of recent loading of the muscles in the injury, EDL (n = 9) and soleus (n = 10) muscles from mice subjected to HS for 14 days performed the eccentric contraction protocol. HS resulted in greater decrements in contractile performance for the soleus muscles (decreases in Po immediately after the protocol for HS and normal soleus muscles were 31.0 +/- 1.8 and 7.6 +/- 2.1%, respectively; P < or = 0.0001) but not for the EDL muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Eccentric contraction-induced injury of mouse soleus muscle: effect of varying [Ca2+]o

The objective of this study was to determine the effect of varying extracellular Ca2+ concentration ([Ca2+]o) on eccentric contraction-induced muscle injury. Isolated mouse soleus muscles (n = 64) performed either 20 eccentric or 20 isometric contractions over a 40-min period in a Krebs buffer containing 0.5, 1.25, or 5.0 mM Ca2+. Measurements of contractile function and lactate dehydrogenase accumulation in the buffer were then made every 15 min for 2 h. Prostaglandin E2, leukotriene B4, and tyrosine accumulation in the incubation medium and total muscle [Ca2+] were measured at the end of the experiment. Reductions in maximal isometric tetanic force for muscles immediately after performance of 20 eccentric and 20 isometric contractions were 21.1 +/- 1.4 and 1.2 +/- 0.7%, respectively. Total muscle [Ca2+] was 28-37% higher in muscles that performed eccentric contractions than in those that performed isometric contractions. However, estimates made with a confocal laser scanning microscope and fluo 3 do not indicate that there was a difference in free cytosolic [Ca2+] between fibers from injured and control muscles. Also, leukotriene B4, prostaglandin E2, and tyrosine accumulation in the buffer from muscles that performed eccentric contractions was not elevated over that from muscles that performed isometric contractions. Furthermore, lactate dehydrogenase accumulation and reductions of contractile function over the 2-h incubation period were not enhanced by higher [Ca2+]o or influenced by the type of contraction. These findings suggest that muscles that were injured by eccentric contractions were able to buffer the increased influx of extracellular Ca2+, maintain a normal free cytosolic [Ca2+], and avoid activation of Ca(2+)-sensitive degradative pathways.

Motion suppression improves quantification of rat liver volume in vivo by magnetic resonance imaging

In response to the presence of certain compounds, rat liver weight can increase. Under the assumption that the liver density does not change, the liver volume will increase as well. To develop the capability to monitor this process noninvasively over time, we used liver volumes determined from MR images to estimate the in vivo liver volumes and weights of normal rats. We acquired multislice, spin-echo images from 18 rats using several protocols for suppression of motion artifacts. We found that volumes determined from data obtained using a combination of gradient moment nulling and respiratory gating, or a combination of signal averaging and "retarded" (after the pi pulse) phase-encoding, produced the most accurate estimates of in vivo liver volume and weight.

Excitation failure in eccentric contraction-induced injury of mouse soleus muscle

1. Histological evidence suggests that the force deficit associated with eccentric contraction-induced muscle injury is due to structural damage to contractile elements within the muscle fibre. Alternatively, the force deficit could be explained by an inability to activate the contractile proteins. It was the objective of this study to investigate the latter possibility. 2. Mouse soleus muscles were isolated, placed in an oxygenated Krebs-Ringer buffer at 37 degrees C, and baseline measurements were made. The muscle then performed one of three contraction protocols: (1) twenty eccentric (n = 10 muscles); (2) ten eccentric (n = 12); or (3) twenty isometric (n = 10) contractions. At the end of the injury protocol, measurements were made during performance of a passive stretch, twitch and tetanus. Next, force was recorded during exposure of the muscle to buffer containing 50 mM caffeine. 3. Decrements in maximal isometric tetanic force (P0) observed for muscles in the twenty eccentric, ten eccentric, and twenty isometric contraction protocols were 42.6 +/- 4.2, 20.0 +/- 2.3 and 3.9 +/- 2.4%, respectively. However, the caffeine-elicited forces in muscles from the three protocols were not different when corrected for initial differences in P0 (64.9 +/- 1.3, 64.2 +/- 2.1 and 68.9 +/- 2.5% of pre-injury P0). The peak caffeine-elicited force was 118.4 +/- 8.6% of post-injury P0 for the muscles in the twenty eccentric contraction protocol, which was significantly different from that observed for the other protocols (71.8-80.2% post-injury P0). These findings indicate that the force deficit in this muscle injury model results from a failure of the excitation process at some step prior to calcium (Ca2+) release by the sarcoplasmic reticulum. 4. In an attempt to locate the site of failure, intracellular measurements were made in injured muscles to test whether injury to the sarcolemma might have resulted in a shift of the resting membrane potential of the muscle fibre. However, microelectrode measurements of resting membrane potential for muscles in the twenty eccentric contraction protocol (-74.4 +/- 0.6 mV) were not different from muscles in the twenty isometric contraction protocol (-73.4 +/- 1.0 mV). These data suggest that membrane resting conductances were normal and are compatible with the idea that the ability of the injured fibres to conduct action potentials was probably not impaired.

Elevations in rat soleus muscle [Ca2+] with passive stretch

Previous work has demonstrated that muscular injury in rat soleus muscles resulting from eccentric contractions (downhill walking) is accompanied by elevations in mitochondrial [Ca2+] (MCC). Muscles are stretched during eccentric contractions, and there is evidence in the literature that stretch of the cell membrane induces Ca2+ influx in various tissues, including skeletal muscle. The purpose of this study was to determine if passive stretch of rat soleus muscles will induce increases in total muscle [Ca2+] (TCC) and MCC. Soleus muscles from female rats (51-122 g) were isolated and incubated in vitro for 2 h at resting length (Lo) or at the maximal in situ length (S). TCC (+62%) and MCC (+56%) were elevated in the S muscles. Also, there was a 63% reduction in maximal twitch tension in the S muscles. ATP concentration, phosphocreatine concentration, and lactate release between Lo and S muscles were the same, indicating that impaired metabolism was not responsible for the observed differences in [Ca2+] and force production between Lo and S muscles. Increases in TCC in the S condition indicate that stretch results in Ca2+ influx from the extracellular space, which is supported by the observation that when S muscles were incubated in Ca(2+)-free buffer, TCC and MCC did not increase. High concentrations of verapamil (0.25-0.75 mM) blocked the elevations in TCC and MCC in the S muscles, but the magnitude of the drug concentration required makes it questionable whether the effect resulted from specific blockade of slow voltage-sensitive Ca2+ channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanical factors in the initiation of eccentric contraction-induced injury in rat soleus muscle

1. Mechanical factor(s) associated with the initiation of eccentric contraction-induced muscle injury were investigated in isolated rat soleus muscles (n = 180; 42 protocols with 4-6 muscles per protocol). Five eccentric contractions were performed with 4 min between contractions. Three levels of peak eccentric contraction force (100, 125 and 150% of pre-injury maximal isometric tetanic tension, P0), length change (0.1, 0.2 and 0.3 muscle length, L0) and lengthening velocity (0.5, 1.0 and 1.5 L0/s) were utilized. Force was varied with stimulation frequency (10-150 Hz). The eccentric contractions were initiated at muscle lengths of 0.85 or 0.90 L0. Following the fifth eccentric contraction, the muscle was incubated in Krebs-Ringer buffer for 60 min. Peak isometric twitch tension (PT), P0, maximal rate of tension development (+ dP/dt), maximal rate of relaxation (-dP/dt), and creatine kinase (CK) release were measured prior to the five eccentric contractions and at 15 min intervals during the incubation period. Total muscle [Ca2+] was measured after 60 min incubation. 2. The mean (+/- S.E.M.) initial decline in P0 for the muscles performing the most injurious protocol was 13.6 +/- 4.8% (n = 6); P0 in control muscles immediately following performance of five isometric contractions was elevated 1.2 +/- 1.0% (n = 8). These means were different at probability, p = 0.005. Mean [ATP] in muscles immediately following the isometric control and most injurious protocols, respectively, were 16.30 +/- 1.49 and 19.84 +/- 1.38 mumol/g dry wt (p = 0.229). 3. Decrements in P0, PT, +dP/dt, and -dP/dt immediately after the injury protocol were related most closely to the peak forces produced during the eccentric contractions; greater initial declines in P0, +dP/dt and -dP/dt were also observed at higher lengthening velocities independent of peak force. Slow declines in P0 and -dP/dt during the 60 min incubation following the injury protocol were greatest for muscles performing contractions at the longer initial length. CK release was independent of all mechanical factors with the exception of lengthening velocity. CK activity at 45 and 60 min into the incubation period was greater for muscles lengthened at the highest velocity used (1.5 L0/s). Mean total muscle [Ca2+] for muscles performing the eccentric contractions was elevated by 38% over isometric control muscles but the elevation was unrelated to any of the four mechanical factors. 4. These data support the hypothesis that eccentric contraction-induced injury is initiated by mechanical factors, with muscle tension playing the dominant role.(ABSTRACT TRUNCATED AT 400 WORDS)

Materials fatigue initiates eccentric contraction-induced injury in rat soleus muscle

1. The initiation of exercise-induced muscle injury is thought to be the result of high tensile stresses produced in the muscle during eccentric contractions. Materials science theory suggests that high tensile stresses could initiate the injury during the first eccentric contraction (normal stress theory) or after multiple eccentric contractions (materials fatigue). It was the objective of this study to investigate the two possibilities. 2. Rat soleus muscles (n = 66; 11 protocols with 6 muscles per protocol) were isolated, placed in an oxygenated Krebs-Ringer buffer at 37 degrees C, and baseline measurements were made. The muscle then performed an injury protocol which consisted of between zero and ten eccentric contractions (muscle starting length = 0.90 soleus muscle length, L0; length change = 0.25 L0; velocity = 1.5 L0/s; peak force = 180% maximal isometric tetanic tension (P0); time between contractions = 4 min; total duration of the injury protocol = 40 min). At the end of the injury protocol, the muscle was incubated in buffer for 1 h; every 15 min, an isometric twitch and tetanus were performed and lactate dehydrogenase (LDH) release was measured. Total muscle [Ca2+] was measured at the end of the incubation. 3. Change-point regression analysis indicates that at 0 min into the incubation, declines in P0, maximal rate of tension development (+dP/dt), maximal rate of relaxation (-dP/dt), and muscle stiffness (dP/dx) became significantly greater after eight eccentric contractions (p < or = 0.05). No relation was found between the number of eccentric contractions performed and the LDH activity at 0 min into the incubation, although after 60 min of incubation, LDH activity in the buffer was linearly related to eccentric contraction number (p = 0.01). There was no relationship between total muscle [Ca2+] and eccentric contraction number. These findings support the materials fatigue hypothesis of exercise-induced muscle injury.

Verapamil-induced creatine kinase loss from rat slow and fast muscles

The purpose of this study was to determine the dose-response relationship between verapamil HCl and creatine kinase (CK) release from isolated rat slow (soleus, S) and fast (flexor digitorum profundus, F) skeletal muscles. Total CK activity in F muscle was approximately 2x greater than in S muscle. For both S and F muscles, CK release as a function of verapamil concentration in the incubation medium was linear (r = 0.94); the slope of the line for F muscle was 4.5x that of the S muscle. S and F muscles lost up to 38-44% of their total CK activity during the 2 hr incubation. The CK activity lost to the medium was 100% of the MM isoform. The mechanism of the enzyme release is not known.

Rat skeletal muscle mitochondrial [Ca2+] and injury from downhill walking

The purpose of this study was to evaluate the relationship between mitochondrial Ca2+ concentration (MCC) and the extent of muscle injury in rats that have performed prolonged downhill walking (eccentric exercise). MCC was used as an indicator of elevated [Ca2+] in the muscles, and injury was estimated from histochemical analysis of muscle cross sections by determining the numbers of intact fibers per unit area in the muscles. Elevations in MCC in the soleus and vastus intermedius muscles over time postexercise were inversely related (P less than 0.05) to the number of intact fibers per square millimeter in the respective muscles after downhill walking. Verapamil administration attenuated the elevation in MCC and injury in histochemical sections resulting from the downhill walking in soleus muscle, but intraperitoneal injection of the chelators EDTA or ethylene glycol-bis(beta-aminoethylether)-N,N,N',N'- tetraacetic acid significantly attenuated the increases in MCC and injury to both the vastus intermedius and soleus muscles in the downhill walkers. The chelators appear to exert their "protective" effects within the specific muscles that show the injury and do not significantly affect serum [Ca2+]. It is concluded that increases in MCC occur during exercise-induced fiber injury and that elevations in cellular Ca2+ may have a role in the etiology of the injury process.

Blood flow distribution in rat muscles during preexercise anticipatory response

Previous work has suggested that preexercise "anticipatory" blood flow distribution in the muscles of rats is influenced by the intensity of the preceding conditioning or training program. The purpose of this study was to carefully control the conditioning programs for control, low-speed conditioned, and high-speed conditioned rats to determine the respective effects on preexercise mean arterial pressure (Pa), heart rate (HR), and blood flow distribution in muscles and other organs. Control (daily placement on treadmill, no exercise), low-speed conditioned (daily treadmill walking up a 12 degree incline at 15 m/min), and high-speed conditioned (daily treadmill galloping up a 12 degree incline at 50 m/min) rats were conditioned for 2-4 wk in their respective programs. On the experimental day, the circulatory variables were measured immediately before exercise by using the same preexercise regimen as during the conditioning sessions. Pa, HR, and blood flow distribution were the same in control and low-speed conditioned rats (P greater than 0.05). However, in high-speed conditioned rats, HR (+9%), Pa (+7%), and white gastrocnemius muscle (+46%) blood flow were higher than in controls (P less than 0.05). The higher white muscle flow was the result of the higher Pa and lower resistance to flow. These data demonstrate that specific changes in preexercise anticipatory blood flow distribution among muscles occur during exercise conditioning programs and that the changes are dependent on the intensity of the conditioning regimen. The mechanisms responsible for the adaptations are not known.

Leukoencephalomalacia in a white-tailed deer from North Carolina

Leukoencephalomalacia similar to equine leukoencephalomalacia occurred in a white-tailed deer (Odocoileus virginianus) from North Carolina. The deer was recumbent and stuporous when presented for examination. It was believed that the disease resulted from ingestion of moldy field corn, infected with Fusarium moniliforme.

Distribution of microspheres in plantaris muscles of resting and exercising rats as a function of fiber type

The purpose of this study was to determine histologically the distribution of microspheres (MSs) (14 micron), and hence the relative distribution of blood flow, in rat plantaris muscle relative to the fiber types (fast-twitch-oxidative-glycolytic [FOG], fast-twitch-glycolytic [FG], and slow-twitch-oxidative [SO]). Three conditions were investigated: 1) preexercise standing; 2) treadmill locomotion at 15 m/min (fast walking); and 3) treadmill locomotion at 60 m/min (moderate galloping). The MS suspension (containing 1 x 10(6) MSs) was infused into the ascending aorta via a catheter in the carotid artery under each of the 3 conditions so that MSs were distributed to the tissues in proportion to their respective blood flows. Sections (20 micron) of the plantaris muscle were cut and assayed for reduced nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR) and myofibrillar adenosine triphosphatase (ATPase) activities so the fibers could be typed as SO, FOG, or FG. MSs were located in the NADH-TR sections, and the fibers next to the MSs were classified and counted. The observed numbers of fibers of each type in each condition that were adjacent to MSs were compared to the predicted number of adjacent fibers based on the assumption the MSs were randomly distributed in the tissue. This analysis demonstrated that MSs (and blood flows) were preferentially distributed to SO fibers during preexercise, to SO and FOG fibers during slow locomotion, and to FOG fibers during fast locomotion. The data support the contention that blood flow is distributed in muscles of conscious animals as functions of fiber type and exercise intensity.

Pulmonary impedance in dogs measured by forced random noise with a retrograde catheter

Retrograde catheter and forced random noise techniques were combined to study the distribution of resistance and compliance in dogs following the inhalation of aerosols containing 2.5 and 5.0 mg/ml of histamine. Mean base-line peripheral resistance was 0.367 cmH2O . l-1 . s, agreeing with previous estimates. After correction for the endotracheal tube, the mean central airway resistance was 0.040 cmH2O . l-1 . s, considerably lower than previous estimates. This discrepancy was attributed to an overcorrection for the endotracheal tube resistance. The lower histamine dose caused a substantial increase in peripheral resistance, a relatively small increase in central resistance, and substantial decreases in total and peripheral compliance. After the higher histamine dose, changes in peripheral resistance and both compliances were similar to those obtained with the lower dose; however, the increase in central resistance was much larger than at the lower dose. The difference between total and peripheral compliance yielded estimates of airway compliance of 0.00306 l/cmH2O before and 0.00104 l/cmH2O after 2.5 mg/ml of histamine.

Evaluation of two bronchofiberscopic methods of culturing the lower respiratory tract

We evaluated 2 methods of obtaining lower respiratory tract secretions in 46 patients. One method used an open-end brush-in-catheter system, and the other used a plugged telescoping double-catheter-overbrush device. After passing a bronchofiberscope transnasally into the trachea, one or the other system was advanced under direct vision into the tracheal lumen and the brush advanced without touching the tracheal wall. The brush was removed and its tip cultured. Using the brush-in-catheter system, 83% (19/23) of brush cultures were positive and similar to simultaneously obtained nasopharyngeal cultures. The brush tip from the plugged telescoping double-catheter device was sterile in 100% of the subjects (10/10). Thus, open-end brush-in-catheter systems are not suitable for use in culturing the lower airways because of contamination within the inner channel of the bronchofiberscope from upper airway secretions. The recently introduced plugged telescoping brush system appears suitable for this purpose.

Detection of respiratory mechanical dysfunction by forced random noise impedance parameters

Respiratory mechanical parameters were computed from forced random noise impedance data in normal adults (group 1), asymptomatic smokers (group 2), and patients with obstructive pulmonary disease (group 3). Mean values for all derived parameters were significantly different (p less than 0.025) for group 3. Mean values of resonant frequency, the ratio of low-frequency (5 to 9 Hz) resistance to high-frequency resistance (15 to 19 Hz), and conductance normalized by height, were significantly different (p less than 0.05) between groups 1 and 2. This approach appears to yield respiratory mechanical parameters that are sensitive to mechanical alterations induced by early pulmonary disease. The rapid, noninvasive, and effort-independent nature of this approach make it especially useful for epidemiologic studies and for studies of "noncooperative" subjects.