The role of P21-activated kinase (Pak1) in sinus node function

Sinoatrial node (SAN) dysfunction (SND) and atrial arrhythmia frequently occur simultaneously with a hazard ratio of 4.2 for new onset atrial fibrillation (AF) in SND patients. In the atrial muscle attenuated activity of p21-activated kinase 1 (Pak1) increases the risk for AF by enhancing NADPH oxidase 2 dependent production of reactive oxygen species (ROS). However, the role of Pak1 dependent ROS regulation in SAN function has not yet been determined. We hypothesize that Pak1 activity maintains SAN activity by regulating the expression of the hyperpolarization activated cyclic nucleotide gated cation channel (HCN). To determine Pak1 dependent changes in heart rate (HR) regulation we quantified the intrinsic sinus rhythm in wild type (WT) and Pak1 deficient (Pak1-/-) mice of both sexes in vivo and in isolated Langendorff perfused hearts. Pak1-/- hearts displayed an attenuated HR in vivo after autonomic blockage and in isolated hearts. The contribution of the Ca2+ clock to pacemaker activity remained unchanged, but Ivabradine (3 μM), a blocker of HCN channels that are a membrane clock component, eliminated the differences in SAN activity between WT and Pak1-/- hearts. Reduced HCN4 expression was confirmed in Pak1-/- right atria. The reduced HCN activity in Pak1-/- could be rescued by class II HDAC inhibition (LMK235), ROS scavenging (TEMPOL) or attenuation of Extracellular Signal-Regulated Kinase (ERK) 1/2 activity (SCH772984). No sex specific differences in Pak1 dependent SAN regulation were determined. Our results establish Pak1 as a class II HDAC regulator and a potential therapeutic target to attenuate SAN bradycardia and AF susceptibility.

Effects of diaphragmatic control on multiparametric analysis of the sniff nasal inspiratory pressure test and inspiratory muscle activity in healthy subjects

BACKGROUND

We investigated the influence of diaphragmatic activation control (diaphC) on the relaxation rate, contractile properties and electrical activity of the inspiratory muscles of healthy subjects. Assessments were performed non-invasively using the sniff inspiratory pressure test (SNIP) and surface electromyography, respectively.

METHODS

Twenty-two subjects (10 men and 12 women) performed 10 sniff maneuvers in two different days: with and without diaphC instructions. For the SNIP test with diaphC, the subjects were instructed to perform intense activation of the diaphragm. The tests with the best SNIP values were used for analysis.

RESULTS

The maneuver with diaphC when compared to the maneuver without diaphC exhibited significant lower values for: SNIP (p <0.01), maximum relaxation rate (MRR) (p <0.01), maximum rate of pressure development (MRPD) (p <0.01), contraction times (CT) (p = 0.02) and electrical activity of the sternocleidomastoid (SCM) (p <0.01), scalene (SCL) (p = 0.01) and intercostal (CI) (p = 0.03) muscles. In addition, the decay constant (tau, τ) and relaxation time (½ RT) did not present any changes.

CONCLUSION

The diaphragmatic control performed during the SNIP test influences the inspiratory pressure and the contractile properties of inspiratory muscles. This occurs due to changes in the pattern of muscle recruitment, which change force velocity characteristics of the test. Thus, instruction on diaphC should be encouraged for better performance of the SNIP test and for evaluation targeting the diaphragm muscle activity.

Effects of diaphragmatic control on the assessment of sniff nasal inspiratory pressure and maximum relaxation rate

OBJECTIVE:

To assess the influence of diaphragmatic activation control (diaphC) on Sniff Nasal-Inspiratory Pressure (SNIP) and Maximum Relaxation Rate of inspiratory muscles (MRR) in healthy subjects.

METHOD:

Twenty subjects (9 male; age: 23 (SD=2.9) years; BMI: 23.8 (SD=3) kg/m²; FEV₁/FVC: 0.9 (SD=0.1)] performed 5 sniff maneuvers in two different moments: with or without instruction on diaphC. Before the first maneuver, a brief explanation was given to the subjects on how to perform the sniff test. For sniff test with diaphC, subjects were instructed to perform intense diaphragm activation. The best SNIP and MRR values were used for analysis. MRR was calculated as the ratio of first derivative of pressure over time (dP/dt_max) and were normalized by dividing it by peak pressure (SNIP) from the same maneuver.

RESULTS:

SNIP values were significantly different in maneuvers with and without diaphC [without diaphC: -100 (SD=27.1) cmH₂O/ with diaphC: -72.8 (SD=22.3) cmH₂O; p<0.0001], normalized MRR values were not statistically different [without diaphC: -9.7 (SD=2.6); with diaphC: -8.9 (SD=1.5); p=0.19]. Without diaphC, 40% of the sample did not reach the appropriate sniff criteria found in the literature.

CONCLUSION:

Diaphragmatic control performed during SNIP test influences obtained inspiratory pressure, being lower when diaphC is performed. However, there was no influence on normalized MRR.

Educational interventions for improving control of blood pressure in patients with hypertension: a systematic review protocol

INTRODUCTION

The aim of this review is to evaluate the effectiveness of educational interventions on improving the control of blood pressure in patients with hypertension.

METHODS

Randomised controlled trials including patients over 18 years of age, regardless of sex and ethnicity, with a diagnosis of hypertension (either treated or not treated with antihypertensive medications) will be assessed in our analysis. We will electronically search four databases: MEDLINE, CINAHL, PEDro and ScienceDirect. There will be no language restrictions in the search for studies. The data will be extracted independently by two authors using predefined criteria. Disagreements will be resolved between the authors. The risk of bias will be assessed using the Cochrane risk of bias tool. After searching and screening of the studies, we will run a meta-analysis of the included randomised controlled trials. We will summarise the results as risk ratio for dichotomous data and mean differences for continuous data.

ETHICS AND DISSEMINATION

The review will be published in a journal. The findings from the review will also be disseminated electronically and at conference presentations.

TRIAL REGISTRATION NUMBER

PROSPERO CRD4201401071.

Costs and benefits of pulmonary rehabilitation in chronic obstructive pulmonary disease: a randomized controlled trial

OBJECTIVE

The current study evaluated the costs and benefits of a simple aerobic walking program for patients with chronic obstructive pulmonary disease (COPD).

METHOD

This was a blinded randomized controlled clinical trial that recruited 72 patients diagnosed with COPD, 40 of whom were included in the study and divided into two groups [control group (CG) and pulmonary rehabilitation group (GPR)]. We assessed pulmonary function, distance covered during the 6-minute walk test (6MWT), respiratory and peripheral muscle strength, health-related quality of life (HRQOL), body composition, and level of activities of daily living (ADLs) before and after an 8-week walking program. The financial costs were calculated according to the pricing table of the Brazilian Unified Health System (SUS).

RESULTS

Only 34 of the 40 patients remained in the final sample; 16 in the CG and 18 in the GPR (FEV1: 50.9 ± 14% predicted and FEV1: 56 ± 0.5% predicted, respectively). The intervention group exhibited improvements in the 6MWT, sensation of dyspnea and fatigue, work performed, BODE index (p<0.01), HRQOL, ADL level (p<0.001), and lower limb strength (p<0.05). The final mean cost per patient for the GPR was R$ 148.75 (~US$ 75.00) and no patient significantly exceeded this value. However, 2 patients in the CG did exceed this value, incurring a cost of R$ 689.15 (~US$ 345.00).

CONCLUSION

Aerobic walking demonstrated significant clinical benefits in a cost-efficient manner in patients with COPD.

Desensitization of myofilaments to Ca2+ as a therapeutic target for hypertrophic cardiomyopathy with mutations in thin filament proteins

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a common genetic disorder caused mainly by mutations in sarcomeric proteins and is characterized by maladaptive myocardial hypertrophy, diastolic heart failure, increased myofilament Ca(2+) sensitivity, and high susceptibility to sudden death. We tested the following hypothesis: correction of the increased myofilament sensitivity can delay or prevent the development of the HCM phenotype.

METHODS AND RESULTS

We used an HCM mouse model with an E180G mutation in α-tropomyosin (Tm180) that demonstrates increased myofilament Ca(2+) sensitivity, severe hypertrophy, and diastolic dysfunction. To test our hypothesis, we reduced myofilament Ca(2+) sensitivity in Tm180 mice by generating a double transgenic mouse line. We crossed Tm180 mice with mice expressing a pseudophosphorylated cardiac troponin I (S23D and S24D; TnI-PP). TnI-PP mice demonstrated a reduced myofilament Ca(2+) sensitivity compared with wild-type mice. The development of pathological hypertrophy did not occur in mice expressing both Tm180 and TnI-PP. Left ventricle performance was improved in double transgenic compared with their Tm180 littermates, which express wild-type cardiac troponin I. Hearts of double transgenic mice demonstrated no changes in expression of phospholamban and sarcoplasmic reticulum Ca(2+) ATPase, increased levels of phospholamban and troponin T phosphorylation, and reduced phosphorylation of TnI compared with Tm180 mice. Moreover, expression of TnI-PP in Tm180 hearts inhibited modifications in the activity of extracellular signal-regulated kinase and zinc finger-containing transcription factor GATA in Tm180 hearts.

CONCLUSIONS

Our data strongly indicate that reduction of myofilament sensitivity to Ca(2+) and associated correction of abnormal relaxation can delay or prevent development of HCM and should be considered as a therapeutic target for HCM.

Chest physiotherapy for pneumonia in children

BACKGROUND

Pneumonia is an inflammatory lung disease and it is the greatest cause of deaths in children younger than five years of age worldwide. Chest physiotherapy is widely used in the treatment of pneumonia because it can help to eliminate inflammatory exudates and tracheobronchial secretions, remove airway obstructions, reduce airway resistance, enhance gas exchange and reduce the work of breathing. Thus, chest physiotherapy may contribute to patient recovery as an adjuvant treatment even though its indication remains controversial.

OBJECTIVES

To assess the effectiveness of chest physiotherapy in relation to time until clinical resolution in children (from birth up to 18 years old) of either gender with any type of pneumonia.

SEARCH METHODS

We searched CENTRAL 2013, Issue 4; MEDLINE (1946 to May week 4, 2013); EMBASE (1974 to May 2013); CINAHL (1981 to May 2013); LILACS (1982 to May 2013); Web of Science (1950 to May 2013); and PEDro (1950 to May 2013).We consulted the ClinicalTrials.gov and the WHO ICTRP registers to identify planned, ongoing and unpublished trials. We consulted the reference lists of relevant articles found by the electronic searches for additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that compared chest physiotherapy of any type with no chest physiotherapy in children with pneumonia.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected the studies to be included in the review, assessed trial quality and extracted data.

MAIN RESULTS

Three RCTs involving 255 inpatient children are included in the review. They addressed conventional chest physiotherapy, positive expiratory pressure and continuous positive airway pressure. The following outcomes were measured: duration of hospital stay, time to clinical resolution (observing the following parameters: fever, chest indrawing, nasal flaring, tachypnoea and peripheral oxygen saturation levels), change in adventitious sounds, change in chest X-ray and duration of cough in days. Two of the included studies found a significant improvement in respiratory rate and oxygen saturation whereas the other included study failed to show that standardised respiratory physiotherapy and positive expiratory pressure decrease the time to clinical resolution and the duration of hospital stay. No adverse effects related to the interventions were described. Due to the different characteristics of the trials, such as the duration of treatment, levels of severity, types of pneumonia and the techniques used in children with pneumonia, as well as differences in their statistical presentation, we were not able to pool data. Two included studies had an overall low risk of bias whereas one included study had an overall unclear risk of bias.

AUTHORS' CONCLUSIONS

Our review does not provide conclusive evidence to justify the use of chest physiotherapy in children with pneumonia due to a lack of data. The number of included studies is small and they differed in their statistical presentation.

Long-term rescue of a familial hypertrophic cardiomyopathy caused by a mutation in the thin filament protein, tropomyosin, via modulation of a calcium cycling protein

We have recently shown that a temporary increase in sarcoplasmic reticulum (SR) cycling via adenovirus-mediated overexpression of sarcoplasmic reticulum ATPase (SERCA2) transiently improves relaxation and delays hypertrophic remodeling in a familial hypertrophic cardiomyopathy (FHC) caused by a mutation in the thin filament protein, tropomyosin (i.e., α-TmE180G or Tm180). In this study, we sought to permanently alter calcium fluxes via phospholamban (PLN) gene deletion in Tm180 mice in order to sustain long-term improvements in cardiac function and adverse cardiac remodeling/hypertrophy. While similar work has been done in FHCs resulting from mutations in thick myofilament proteins, no one has studied these effects in an FHC resulting from a thin filament protein mutation. Tm180 transgenic (TG) mice were crossbred with PLN knockout (KO) mice and four groups were studied in parallel: 1) non-TG (NTG), 2) Tm180, 3) PLNKO/NTG and 4) PLNKO/Tm180. Tm180 mice exhibit increased heart weight/body weight and hypertrophic gene markers compared to NTG mice, but levels in PLNKO/Tm180 mice were similar to NTG. Tm180 mice also displayed altered function as assessed via in situ pressure-volume analysis and echocardiography at 3-6 months and one year; however, altered function in Tm180 mice was rescued back to NTG levels in PLNKO/Tm180 mice. Collagen deposition, as assessed by Picrosirius Red staining, was increased in Tm180 mice but was similar in NTG and in PLNKO/Tm180 mice. Extracellular signal-regulated kinase (ERK1/2) phosphorylation increased in Tm180 mice while levels in PLNKO/Tm180 mice were similar to NTGs. The present study shows that by modulating SR calcium cycling, we were able to rescue many of the deleterious aspects of FHC caused by a mutation in the thin filament protein, Tm.

Effects of nicotine administration in a mouse model of familial hypertrophic cardiomyopathy, α-tropomyosin D175N

The effects of nicotine (NIC) on normal hearts are fairly well established, yet its effects on hearts displaying familial hypertrophic cardiomyopathy have not been tested. We studied both the acute and chronic effects of NIC on a transgenic (TG) mouse model of FHC caused by a mutation in α-tropomyosin (Tm; i.e., α-Tm D175N TG, or Tm175). For acute effects, intravenously injected NIC increased heart rate, left ventricular (LV) pressure, and the maximal rate of LV pressure increase (+dP/dt) in non-TG (NTG) and Tm175 mice; however, Tm175 showed a significantly smaller increase in the maximal rate of LV pressure decrease (-dP/dt) compared with NTGs. Western blots revealed phosphorylation of phospholamban Ser16 and Thr17 residue increased in NTG mice following NIC injection but not in Tm175 mice. In contrast, phosphorylation of troponin I at serine residues 23 and 24 increased equally in both NTG and Tm175. Thus the attenuated increase in relaxation in Tm175 mice following acute NIC appears to result primarily from attenuated phospholamban phosphorylation. Chronic NIC administration (equivalent to smoking 2 packs of cigarettes/day for 4 mo) also increased +dP/dt in NTG and Tm175 mice compared with chronic saline. However, chronic NIC had little effect on heart rate, LV pressure, -dP/dt, LV wall and chamber dimensions, or collagen content for either group of mice.

Ablation of iNOS delays cardiac contractile dysfunction in chronic hypertension

We investigated the role of inducible NOS (iNOS) on cardiac function during the development of left ventricular hypertrophy. Hypertrophy was induced by pressure-overload via short-term (2.5 months) or long-term (6.5 months) aortic banding (AoB) in wild-type (WT) and iNOS knock out (iNOSKO) mice. Cardiac function was then assessed via echocardiography, in situ hemodynamics and papillary muscle force measurements. Quantitative RT-PCR and Western blots were used to measure expression of hypertrophic gene markers and proteins respectively. Our data demonstrate that increased afterload via AoB leads to increased expression of iNOS that is associated with cardiac dysfunction. In pressure-overload induced hypertrophy, iNOSKO delays both the expression of hypertrophic markers and contractile dysfunction without causing significant changes in the level of hypertrophy. Moreover, after long-term AoB, iNOSKO animals exhibited increased basal cardiac function and an improved response to beta-adrenergic stimulation compared to long-term AoB WT animals. In conclusion, our data demonstrate that NO production via iNOS plays an important role in modulating cardiac function after moderate AoB that mimics long-term hypertension in humans.

Adaptation of the Threshold IMT with double spring load allows higher inspiratory pressure for muscle training

PURPOSE

We aimed to evaluate the functionality of an adapted inspiratory muscle training device designed to allow pressures higher than 41 cmH(2)O that can be precisely controlled. The adaptation was made in a commercially available Threshold IMT device, and the opening pressures and linearity of load were evaluated in an experimental setting.

METHODS

The original IMT Threshold device was modified by inserting a second spring load juxtaposed to the original spring and then the modified device was coupled to a system designed to assess the range of opening pressures. Linear regression was used to test the correlation between the visual pressure scale of the original device and the opening pressure load obtained from the adapted device.

RESULTS

For the modified device, we found a range of load from 13.9 +/- 0.7 to 85.6 +/- 0.7 cmH(2)O. Linear regression analysis of our data found an excellent relation between the modified device's opening pressure and the preset opening pressure marked on the visual scale in the original device, y = -1.275 + 2.08x, r(2) = 0.99 and P = 0.0001.

CONCLUSION

The Threshold IMT adaptation proposed here is simple, affordable, precise, safe and allows for a high degree of reproducibility. It also achieves pressures higher than 41 cmH(2)O that can be used when training inspiratory muscles.

The effect of myosin regulatory light chain phosphorylation on the frequency-dependent regulation of cardiac function

Although it has been suggested that in cardiac muscle the phosphorylation level of myosin regulatory light chain (RLC) correlates with frequency of stimulation, its significance in the modulation of the force-frequency and pressure-frequency relationships remains unclear. We examined the role of RLC phosphorylation on the force-frequency relation (papillary muscles), the pressure-frequency relation (Langendorff perfused hearts) and shortening-frequency relation (isolated cardiac myocytes) in nontransgenic (NTG) and transgenic mouse hearts expressing a nonphosphorylatable RLC protein (RLC(P-)). At 22 degrees C, NTG and RLC(P-) muscles showed a negative force-frequency relation. At 32 degrees C, at frequencies above 1 Hz, both groups showed a flat force-frequency relation. There was a small increase in RLC phosphorylation in NTG muscles when the frequency of stimulation was increased from 0.2 Hz to 4.0 Hz. However, the level of RLC phosphorylation in these isolated muscles was significantly lower compared to samples taken from NTG intact hearts. In perfused hearts, there was no difference in the slope of pressure-frequency relationship between groups, but the RLC(P-) group consistently developed a reduced systolic pressure and demonstrated a decreased contractility. There was no difference in the level of RLC phosphorylation in hearts paced at 300 and 600 bpm. In RLC(P-) hearts, the level of TnI phosphorylation was reduced compared to NTG. There was no change in the expression of PLB between groups, but expression of SERCA2 was increased in hearts from RLC(P-) compared to NTG. In isolated cardiac myocytes, there was no change in shortening-frequency relationship between groups. Moreover, there was no change in Ca(2+) transient parameters in cells from NTG and RLC(P-) hearts. Our data demonstrate that in cardiac muscle RLC phosphorylation is not an essential determinant of force- and pressure-frequency relations but the absence of RLC phosphorylation decreases contractility in force/pressure developing preparations.

Expression of Slow Skeletal Troponin I in Adult Mouse Heart Helps to Maintain the Left Ventricular Systolic Function During Respiratory Hypercapnia

Compared with the adult, neonatal heart muscle is less sensitive to deactivation by acidic pH. We hypothesized that expression of slow skeletal troponin I (ssTnI), the embryonic isoform, in adult heart would help maintain left ventricular (LV) systolic function during respiratory hypercapnia. We assessed LV function by transthoracic 2D-targeted M-mode and pulsed Doppler echocardiography in transgenic (TG) mice in which cardiac TnI was replaced with ssTnI and in nontransgenic (NTG) littermates. Anesthetized mice were ventilated with either 100% oxygen or 35% CO 2 balanced with oxygen. Arterial blood pH with 35% CO 2 decreased to the same levels in both groups of animals. In the absence of propranolol, the LV fractional shortening was higher in TG compared with NTG mice throughout most of the experimental protocol. LV diastolic function was impaired in TG compared with NTG mice both at 100% oxygen and 35% CO 2 because E-to-A wave ratio of mitral flow was significantly lower, and E-wave deceleration time and LV isovolumic relaxation time were longer in TG compared with NTG mice. When compensatory mechanisms that occur through stimulation of β-adrenergic receptors during hypercapnia were blocked by continuous perfusion with propranolol, we found that NTG mice died within 3 to 4 minutes after switching to 35% CO 2 , whereas TG mice survived. Our experiments demonstrate the first evidence that specific replacement of cardiac TnI with ssTnI has a protective effect on the LV systolic function during hypercapnic acidosis in situ.