The spectrum of left ventricular-right atrial communications in the adult: essentials of echocardiographic assessment.

Left ventricular-right atrial communication may be a congenital defect or can result from trauma, endocarditis, or valve replacement. Traditionally the preoperative diagnosis of this entity was made during cardiac catheterization, but recent advances in echocardiography, particularly color Doppler imaging, have greatly facilitated the noninvasive diagnosis of left ventricular-right atrial communication. We present four cases of left ventricular-right atrial communication, each identified by two-dimensional and color Doppler imaging. One case is a congenital defect, two were identified years after cardiac surgery, and one presents as an unusual complication of myocardial infarction. Optimal views for identifying this defect are discussed along with clues to quantifying its hemodynamic significance.

Role of diprotonated phosphate in evoking muscle reflex responses in cats and humans.

Lactic acid and H+ evoke muscle reflexes that raise sympathetic nerve activity. Whether these substances are direct afferent stimulants or markers for the acidification of other substances is unknown. Diprotonated phosphate (H2PO4-), a possible mediator of fatigue, increases as the cell acidifies and phosphate is produced. Its role in evoking muscle reflexes is unknown. We used 31P-nuclear magnetic resonance to measure forearm muscle H+ and H2PO4- and microneurography to measure muscle sympathetic nerve activity (MSNA, peroneal nerve) during a handgrip protocol designed to dissociate H+ from H2PO4-. Ischemic handgrip (50% maximal voluntary contraction x 2 min) was followed by a 1-min rest period during which the muscle was freely perfused. This was followed by a second bout of ischemic handgrip and a 5-min recovery. In seven of eight subjects, MSNA correlated with H2PO4-, whereas it correlated with pH in only one subject. To determine whether muscle reflex responses are evoked by H+, lactic acid, monoprotonated phosphate (HPO4(2-), or H2PO4-, we injected H+, lactate, H2PO4- [all 50 mM in 10 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) buffered to pH 6], and HPO4(2-) (50 mM, pH 7.5 in 10 mM HEPES) into the arterial supply of the triceps surae of the cat (n = 9) as we measured mean arterial blood pressure (MAP). H2PO4- increased MAP more than HPO4(2-), H+, or lactate (27.1 +/- 3.7 vs. 5.0 +/- 1.3, 4.6 +/- 3.1, and 7.7 +/- 3.2 rise in mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)