1. The rate of heart beat increased with temperature and was three times as high in the active as in the inactive animal. 2. The rate of shell valve movement rose and the rate of heart beat fell when the foot was extended. 3. The rates of heart beat and shell valve movement decreased when the water was saturated with carbon dioxide. This heart response remained when the visceral ganglion was de...

Heart beat monitoring is vital to ensuring healthiness of the human cardiovascular system, but availability of a simple and low-cost heart beat monitoring device that does not require expert medical personnel to handle still remains a challenge especially in rural and semiurban areas of developing countries like Nigeria. This paper describes the design and implementation of a simple, reliable, ...

During a normal lifetime, the heart may beat over 2 billion times, but the mechanisms by which the heart beats are initiated remain a subject of intense investigation. Since the discovery of a pacemaker current (I(f)) in 1978, multiple studies have shown that rhythmic changes in membrane voltage (the "membrane voltage clock") underlie the mechanisms of automaticity. The I(f) is a depolarization...

A goal of clinicians caring for heart transplant recipients has been to use heart rate variability as a noninvasive means of diagnosing graft rejection. The determinants of beat-to-beat variability in the surgically denervated heart have yet to be elucidated. We used an isolated, blood buffer-perfused porcine heart preparation to quantitatively assess the relationship between coronary perfusion...

Pericardial constraint and ventricular interaction influence left ventricular (LV) performance when preload is high. However, it is unclear if these constraining forces modulate LV filling when the heart is unloaded, such as during upright posture, in humans. Fifty healthy individuals underwent right heart catheterization to measure pulmonary capillary wedge (PCWP) and right atrial pressure (RA...

Methods to correct the QT interval for heart rate are often in disagreement and may be further confounded by changes in autonomic state. This can be problematic when trying to distinguish the changes in QT interval by either drug-induced delayed repolarization or from autonomic-mediated physiological responses. Assessment of the canine dynamic QT-RR interval relationship was visualized by novel...

Historically, the heart rate corrected QT (QTc) interval has been the standard method to assess for impaired ventricular repolarization, particularly for drug development. However, QTc does not reflect changes in autonomic state or QT-RR hysteresis which can also affect the interpretation of arrhythmogenic risk. With the advent of more accurate algorithms to automatically measure the QT interva...