Respiratory muscle weakness and normal ventilatory drive in dilative cardiomyopathy

BACKGROUND: In dilative cardiomyopathy several factors influence dyspnoea.Patients with chronic heart failure may demonstrate impairmentof breathing pattern, ventilatory drive and respiratory musclestrength, as well as reduction of ventilatory efficiency. Thepurpose of this study was to evaluate whether dilative cardiomyopathyis accompanied by changes in breathing pattern, respiratorymuscle weakness and ventilatory neural drive. METHODS: We investigated 47 patients (36 men, mean age=47·8±11·2years) with chronic heart failure due to dilative cardiomyopathy,and 30 healthy subjects (10 men, mean age=35·4±11·7years) served as controls. Patients and controls underwent evaluationof left ventricular ejection fraction by 2D echocardiography,spirometry, body plethysmography, mouth occlusion pressure andrespiratory muscle strength, as well as by submaximal treadmillexercise testing with gas exchange measurements. The patients'results were compared to controls and predicted standard normalvalues, and evaluated for differences according to the degreeof severity of functional impairment. RESULTS: Patients with dilative cardiomyopathy demonstrated a slightreduction in lung volumes (15% of the patients with obstructiveand 15% with restrictive lung function pattern) and diffusioncapacity (20·4±6·8 vs 15·4±6·7ml. min^–1 . kPa^–1; P<0·01). In neuraldrive, as assessed by mouth occlusion pressure, there was nosignificant difference between patients and controls. Therewas a slight but significant reduction in respiratory musclestrength, as assessed by measuring maximal inspiratory pressurein patients with dilative cardiomyopathy (6·7±2·4kPavs 8·6±3·5kPa; P<0·01). The observedchanges were more pronounced in the severe chronic heart failurepatients (with a reduction in ventilatory efficiency) whereasno relationship among indices of cardiac or respiratory functionwas found. CONCLUSION: Patients with chronic heart failure due to dilative cardiomyopathydevelop respiratory muscle weakness without changes in neuralventilatory drive, and slight changes in breathing pattern relatedto the severity of the disease.     

Ionic currents and action potentials in rabbit,rat, and guinea pig ventricular myocytes

Summary Distinct differences exist in action potentials and ionic currents between rabbit, rat, and guinea pig ventricular myocytes. Data obtained at room temperature indicate that about half of the rabbit myocytes show prominent phase 1 repolarization and transient outward current. Action potentials in guinea pig ventricular myocytes resemble those from rabbit myocytes not exhibiting phase 1 repolarization; and guinea pig myocytes do not develop transient outward current. Rat ventricular action potentials are significantly shorter than those from rabbit and guinea pig ventricular myocytes. Unlike rabbit and guinea pig myocytes, rat ventricular myocytes also exhibit a prominent phase 1 and lack a well defined plateau phase during repolarization. All rat ventricular myocytes exhibit a transient outward current which can be best fitted by a double exponential relation. There are no significant differences between the amplitude, voltage dependence and inactivation kinetics of the inward calcium currents observed in rabbit, rat and guinea pig. The steady-state current-voltage relations between –120 mV and –20 mV, which mostly represent the inward rectifier potassium current are similar in rabbit and guinea pig. The amplitude of this current is significantly less in rat ventricular myocytes. The outward currents activated upon depolarization to between –10 and +50 mV are different in the three species. Only a negligible, or absent, delayed rectifier outward current has been observed in rabbit and rat; however, a relatively large delayed rectifier current has been found in guinea pig. These large interspecies variations in outward membrane currents help explain the differences in action potential configurations observed in rabbit, rat, and guinea pig.     

Short-Chain Fatty Acids Induce Cytoskeletal and Extracellular Protein Modifications Associated with Modulation of Proliferation on Primary Culture of Rat Intestinal Smooth Muscle Cells

Short-chain fatty acids are the main end products of bacterial fermentation of carbohydrates. Their role on the metabolism and biology of colonocytes is now well characterized. However, the functional consequences of their presence on intestinal smooth muscle cells remain poorly studied. We aimed to assess the effect of different short-chain fatty acids on ileal and colonic smooth muscle cells in primary culture and on A7R5 line. Butyrate (above 0.1 mM) inhibited A7R5 cell proliferation, while at low concentration (0.05 to 0.5 mM) butyrate significantly stimulated the proliferation of ileal and colonic myocytes in primary culture. An inhibition was observed at higher concentrations. Collagenous and noncollagenous protein synthesis was stimulated by butyrate. Moreover, butyrate stimulated actin and myosin expression. Thus, butyrate, which is produced by dietary fiber fermentation, may affect intestinal muscles by directly acting at the molecular level on myocytes.     

Influence of metabolic inhibition by NaCN on electrical and mechanical activities of frog atrial fibers: Studies using current and voltage clamp

Voltage clamp experiments have documented that after 10 min NaCN treatment: (1) there is a reduction in both action potential duration and plateau amplitude associated with a reduction in the contractile strength; (2) in Ringer tetrodotoxin there is a marked reduction in the magnitude of the slow inward current and the corresponding tension; (3) there is a negative shift in the reversal potential of the slow inward current.In previous work it was suggested that during metabolic inhibition the lack of high energy compounds leads to an increase in the intracellular free Ca²⁺ concentration, thereby decreasing the Ca²⁺ driving force. However, the present study has shown that excess Ca²⁺ in the bathing solution was unable to increase the slow inward current amplitude during NaCN treatment, although the $\text{I}\text{V}$ relationship showed a restoration of the Ca²⁺ driving force. On the other hand the application of 10^?7m adrenaline during poisoning induced a rapid increase in both the slow inward current and the phasic contraction amplitude. It is concluded that NaCN reduces the slow inward current and the corresponding tension, decreasing both Ca²⁺ driving force and slow channel conductance. The marked increase in both slow inward current and phasic component of contraction with adrenaline suggests that under these conditions cyclic AMP is made available in spite of metabolic inhibition, thereby preventing the increase of internal free Ca²⁺ concentration, and also increasing the slow channel conductance.     

Clusters of proliferating endothelial cells and smooth muscle cells in rabbit carotid arteries

Schwarz and Benditt found clustering of replicating cells in aortic endothelium in 1976 and discussed how homeostasis of the arterial wall is maintained through this nonrandom distribution of replicating cells. However, it is still unclear how cells of vascular walls turnover. In order to address this issue, we evaluated distribution of the cells in mitotic cycle, labeled by Ki67‐immunostaining, in serial histological sections of twelve carotid arteries of six adult male Japanese rabbits. As a result, a total of 1713 Ki67‐positive endothelial cells (ECs) and 1247 Ki67‐positive smooth muscle cells (SMCs) were identified. The Ki67‐positivity rate in ECs and SMCs were about 0.048% and 0.0027%, respectively. Many of the Ki67‐positive cells clustered in two (EC, 37%; SMC, 33%), three to four (EC, 8%; SMC, 28%), and five to eight cells (EC, 5%; SMC, 10%). Clusters having more than eight cells were not found. Thus, it can be speculated that the cell division of proliferating ECs and SMCs occur four times at most. These novel findings offer great insights for better understanding of the mechanism that underlies cell number regulation of the blood vessel.     

The immediate effect of osteopathic cervical spine mobilization on median nerve mechanosensitivity: A triple-blind,randomized, placebo-controlled trial

Background

Neurodynamics is a clinical medium for testing the mechanical sensitivity of peripheral nerves which innervate the tissues of both the upper and lower limb. Currently, there is paucity in the literature of neurodynamic testing in osteopathic research, and where there is research, these are often methodologically flawed, without the appropriate comparators, blinding and reliability testing.

Exercise training improves the IL-10/TNF-α cytokine balance in the gastrocnemius of rats with heart failure

Objective

This study examined the effects of exercise training (ExT) upon concentration of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and interleukin-10 (IL-10) in the gastrocnemius of rats with heart failure (HF) induced by left coronary artery ligation.

Knee joint angle and vasti muscle electromyograms during fatiguing contractions

We compared vasti muscle electromyograms for two knee joint angles during fatiguing tetanic contractions. Tetanic contraction of the knee extensors was evoked for 70 s by electrical stimulation of the femoral nerve at knee joint angles of 60° (extended, with 0° indicating full extension) and 110° (flexed) in eight healthy men. Surface electromyography was recorded from the vastus intermedius (VI), vastus lateralis (VL) and vastus medialis (VM) muscles. Knee extension force and M‐wave amplitudes and durations were calculated every 7 s, which were normalized by the initial value. Normalized knee extension force was decreased at the flexed knee joint angle compared with that of the extended knee joint angle (P<0·05). Decreased normalized M‐wave amplitude and increased normalized M‐wave duration of the VI were greater at the flexed knee joint angle than the extended knee joint angle (P<0·05), whereas those for the VL and VM were similar (P>0·05). These results suggest that peripheral fatigue profiles of the VI might be greater at the flexed than the extended knee joint angles, but that of VL and VM might be similar in the tested range of knee joint angles (i.e. 60°–110°) during continuous tetanic contraction induced by electrical stimulation. Therefore, greater reduction of knee extension force at the flexed knee joint angle than the extended knee joint angle may reflect fatigue development of the VI more than other quadriceps femoris components.