Chronic beta-adrenoreceptor (beta-AR) activation increases left ventricular (LV) cavity size by promoting a rightward shift in LV diastolic pressure-volume (P-V) relations in association with increases in low-tensile strength myocardial (non-cross-linked) collagen concentrations. Because diastolic P-V relations are determined by chamber remodeling as well as by myocardial material properties (indexed by myocardial stiffness), both of which are associated with modifications in myocardial collagen cross-linking, we evaluated whether chamber remodeling or alterations in myocardial material properties govern beta-AR-mediated modifications in diastolic P-V relations. The effects of chronic administration of isoproterenol (Iso; 0.04 mg.kg(-1).day(-1) from 12 to 19 mo of age) to spontaneously hypertensive rats (SHRs) on LV cavity dimensions, LV diastolic P-V relations, myocardial collagen characteristics, myocardial stiffness constants [e.g., the slope of the LV diastolic stress-strain relation (k)], and LV chamber and myocardial systolic function were assessed. SHRs at 19 mo of age had normal LV diastolic P-V relations, marked myocardial fibrosis (using a pathological score), increased myocardial cross-linked (insoluble to cyanogen bromide digestion) type I and type III collagen concentrations, and enhanced myocardial k values. Iso administration to SHRs resulted in enlarged LV cavity dimensions mediated by a rightward shift in LV diastolic P-V relations, increased volume intercept of the LV diastolic P-V relation, decreased LV relative wall thickness despite a tendency to augment LV hypertrophy, and increased non-cross-linked type I and type III myocardial collagen concentrations. Iso administration resulted in reduced pump function without modification of intrinsic myocardial systolic function. However, despite increasing myocardial non-cross-linked concentrations, Iso failed to alter myocardial k in SHRs. These results suggest that beta-AR-mediated rightward shifts in LV diastolic P-V relations, which induce decreased pump function, are mediated by chamber remodeling but not by modifications in myocardial material properties.

The cellular signaling pathways responsible for the transition from compensated left ventricular hypertrophy (LVH) to LV dilatation (remodeling) and heart failure are unclear. As chronic administration of a beta-adrenoreceptor (beta-AR) agonist mediates the premature onset of cardiac remodeling without myocyte necrosis or myocardial dysfunction in LVH, we suggest that beta-AR activation is critical in promoting the transition from compensated LVH to cardiac dilatation. However, beta-AR mediated effects in the heart can occur via either the cyclic adenosine monophosphate (cAMP) system or via cAMP independent signaling pathways. To determine the role of cAMP in promoting adverse cardiac chamber remodeling, we evaluated whether phosphodiesterase inhibition (PDEI) promotes LV dilatation in rats with compensated LVH. The impact of chronic administration of the PDEI, pentoxifylline, on LV remodeling and function was assessed in spontaneously hypertensive rats (SHR) with compensated LVH. The PDEI mediated inotropic effects and increased cAMP concentrations in SHR. This dose of the PDEI administered for 4 months to SHR did not modify LV weight or influence intrinsic myocardial systolic function (as assessed in the absence of the PDEI) in SHR. However, the PDEI mediated the development of a right shift in LV end diastolic (LVED) pressure-internal dimension and LVED pressure-volume relations, LV wall thinning, and increments in myocardial soluble (non-cross-linked) collagen concentrations. In conclusion, chronic PDEI administration induces adverse geometric and interstitial cardiac remodeling in SHR, a finding that supports the notion that the beta-AR-cAMP system is important in mediating the progression to heart failure by promoting interstitial remodeling and LV dilatation in LVH.

Background. Accidental intraoperative hypothermia is a common and avoidable adverse event of the perioperative period and is associated with detrimental effects on multiple organ systems and postoperative patient outcomes. In a resource-limited environment, prevention of intraoperative hypothermia is often challenging. Resourceful clinicians overcome these challenges through creative devices and frugal innovations.Objective. To investigate the thermal performance of two Baragwanath Rewarming Appliances (BaRA) against that of the Hotline device to describe an optimal setup for these devices. Methods. This was a quasi-experimental laboratory study that measured the thermal performance of two BaRA devices and the Hotline device under a number of scenarios. Independent variables including fluid type, flow rate, warming temperature and warming transit distance were sequentially altered and temperatures measured along the fluid stream. Change in temperature (ΔT) was calculated as the difference between entry and exit temperature for each combination of variables for each warming device. Results. A total of 219 experiments were performed. At a temperature of 43.0°C and a transit distance of 200 cm, the BaRA A configuration either matched or exceeded the ΔT of the Hotline over all fluid type and flowrate combinations. The BaRA B configuration does not provide comparable thermal performance to the Hotline. Measured flowrates were noticeably slower than manufacturer-quoted values for all intravenous (IV) cannulae used. Conclusion. A warm-water bath at 43.0°C with 200 cm of submerged IV tubing provides thermal performance comparable to the Hotline device, with all fluid type and flowrate combinations.

The cell membrane forms an integral part of cellular homeostasis. This article will review the structure and function of physiological membranes and how the lipid bilayer plays an important role in maintaining cellular integrity, ion permeability, and membrane potential as well as being selectively permeable to certain biological substances. This review looks at the physico-chemical and structural properties of the plasma membrane which affords it the unique property of selective permeability and action potential generation. Furthermore, the mechanisms by which permeability occurs across the membrane are also discussed.