Heart failure (HF) is a major public health problem associated with significant mortality and morbidity, especially for those over age 65. Worldwide, more than 23 million adults ages 25 and older have HF. One in nine deaths in 2009 included HF as a contributing cause.

The American Heart Association/American College of Cardiology guidelines define HR as "a complex clinical syndrome that can result from any structural or functional cardiac disorder that impairs the ability of the ventricle to fill or eject blood." The guidelines emphasize that "it is largely a clinical diagnosis that is based on a careful history and physical examination."

About half of people who develop HF die within five years of diagnosis. HF costs the United States an estimated $30.7 billion each year, including the cost of healthcare services, medications to treat HF, and missed days of work. It is projected that the prevalence of HF will increase by 46 percent from 2012 to 2030.

HF with preserved ejection fraction is the fastest-growing form of HF and is nearly exclusively found in older patients — particularly women in whom 90 percent of new HF cases are HF with a preserved ejection fraction (HFpEF). The primary symptom of those with HFpEF is extreme intolerance to exercise, which dramatically affects quality of life.

Most studies have examined the mechanisms of exercise intolerance in HF by measuring hemodynamic and metabolic responses during peak aerobic exercise. However, the time course of the change in pulmonary oxygen uptake (pulmVO2) in the recovery period after exercise also provides important clinical and prognostic information.

A recent study provides new insight into the different forms of HF by comparing leg blood flow, oxygen extraction and oxygen uptake (VO2) after constant load sub-maximal unilateral knee extension (ULKE) exercise in patients with HF who had reduced ejection fraction (HFrEF) compared to those with preserved ejection fraction (HFpEF).

Researchers at the University of Texas at Arlington's College of Nursing and Health Innovation included 10 older (68±10yrs) HF patients with either dilated hearts not pumping blood well or stiff hearts unable to relax properly after exercising. Patients were recruited from the Alberta Heart Failure Etiology and Analysis Study. All patients were clinically stable (NYHA class I and II) with no medication change in the past three months.

Usually, measuring blood flow and oxygen extraction is tedious and invasive process. However, this team of researchers developed a technique using magnetic resonance imaging (MRI) technology to determine off-kinetics (mean response times, MRT) for leg VO2 and its determinants.Study participants performed an incremental exercise test (50 knee extensions/minute) using this custom designed MRI compatible ULKE exercise device.

Study results showed that leg blood flow and oxygen uptake recovery took longer in the patients with dilated hearts. This was the first investigation to simultaneously measure and compare muscle blood flow, oxygen extraction and VO2 kinetics in the rest-recovery period after sub-maximal ULKE exercise in HFrEF and HFpEF patients — an important breakthrough in distinguishing between different types of HF and identifying different pathologies.

Implications of these study results include targeting new therapies to increase blood flow, improving exercise tolerance and developing more effective exercise rehabilitation for HF patients.