Friday, April 19, 2024
4/19/2024
PROJECT SUMMARY: Heart failure (HF) disproportionally afflicts the aged impairing muscle O2 transport, crippling the quality of life and predisposing the diaphragm to failure. This scenario has become all-too-common with the COVID-19 pandemic revealing HF as a major comorbidity and elderly patients disproportionally represented in the death toll. Established HF animal models overwhelmingly utilize young rather than old animals. Pathophysiologically, HF in aged individuals (HF+Aged) is a profoundly different disease from that in younger animals. Therefore, the mechanistic bases for dysfunction and therapeutic countermeasures must be addressed specifically in this population. HF compromises multiple O2 transport systems (especially respiratory, cardiovascular and muscular) with these effects coalescing in decreased skeletal muscle microcirculatory blood-myocyte O2 flux. This proposal address the mechanistic bases for HF+old-age-induced diaphragm dysfunction from a novel vertically-integrated perspective and assesses whether nitrate therapy and/or the sGC activator (BAY 60-2770) can protect, preserve or recover diaphragm vasomotor control in HF+Aged animals specifically during mechanical ventilation (MV). Preliminary data support that both HF+Aged muscle O2 delivery dysregulation can be ameliorated by strategies that increase nitric oxide (NO) bioavailability i.e., nitrate supplementation and target sGC. We will address the global hypothesis that, in HF+Aged rats, diaphragm vascular dysfunction reduces diaphragm O2 delivery and is exacerbated by MV via decreased NO bioavailability. Multi-targeted therapeutic interventions directed towards central and peripheral O2 transport system control will restore deficits in diaphragm capillary function and restore the O2 delivery/utilization balance. Strengths of our approach include: 1. Resolving and partitioning the perfusive and diffusive mechanisms impairing diaphragm O2 delivery in HF+Aged and with MV. 2. Our unique intravital diaphragm microscopy model facilitates direct observation of the microcirculation with high temporal fidelity determination of blood-myocyte O2 flux using phosphorescence quenching during contractions. 3. Circumventing the technical impossibility of making precise micron-level spatial [NO] measurements in contracting muscle by determining directly the endogenous NO contribution to capillary hemodynamics. 4. Providing novel empirical evidence supporting optimal treatment strategies for older HF patients with and without MV. 5. Testing, for the first time, the latest model of capillary function and blood-myocyte O2 flux during contractions. The proposed studies will provide novel and important data addressing diaphragm dysfunction in HF+Aged defining their mechanistic bases and assess the efficacy of feasible treatment strategies for older HF patients and especially those undergoing MV.
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