Cardiac Work Efficiency Research Articles

Oxygen delivery and cardiac output during exercise following oral phosphate-glucose

Phosphate has been proposed as an ergogenic aid since it may enhance O2 delivery and cardiac work efficiency by increasing plasma phosphate (P Pi), red blood cell phosphate (RBC Pi), 2,3-diphosphoglycerate (DPG), RBC adenosine triphosphate (ATP), and P50. In 10 normal, fasting males we measured cardiac output (Q) by CO2 rebreathing, heart rate (HR), O2 deficit (O2DEF), and O2 consumption (VO2) during cycle ergometer exercise (60% of peak VO2). Stroke volume (SV) and arteriovenous O2 difference (A-VO2) were calculated. Following a baseline blood sample (BASE) for P Pi, RBC Pi, DPG, RBC ATP, and P50 (3 h before exercise), a single oral dose of dicalcium phosphate (129 mmol) and glucose (500 ml/10% sol, PHOS), or placebo (PLA), was administered in a random, crossover, double-blind fashion. Blood sampling was repeated immediately before and after exercise (PRE-EX and POST-EX). PHOS induced increases in P Pi (3.87 to 4.35 mg.dl-1, P less than 0.05), RBC Pi (3.86 to 4.63 mg.dl-1, P = 0.08), DPG (11.8 to 13.1 mumol.g-1 Hb, P less than 0.05), RBC ATP (4.2 to 4.4 mumol.g-1 Hb, P less than 0.05), and P50 (26.8 to 27.9 mm Hg, P less than 0.05) from BASE to PRE-EX. All variables remained elevated through the exercise period, as evidenced by higher levels than BASE at POST-EX (P less than 0.05). However, P50 was not different across conditions at PRE-EX (PHOS P50 = 27.9, PLA P50 = 28.3 mm Hg) or POST-EX (PHOS P50 = 28.0, PLA P50 = 28.1 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac energetics: significance of mitochondria.

The mitochondrial activity as the energy producing step during biological oxidation was observed at rest and its regulation by the energy consuming auxotonic contractile work, depending on the preload, afterload and beat rate in isolated superfused left guinea pig atria. The mitochondrial activity was measured by (1) continuous determination of the O2 uptake rate, (2) the rate of 14CO2 production from labelled glucose or FFA and (3) separate measurements of the atrial ATP-, ADP-, AMP-, CP- and NAD-concentrations, for determination of the energy state. Some results, with points of general interest, are reported and discussed, including this model, former studies about cardiac energetics and the efficiency of cardiac work, reviewed recently.

Influences on the efficiency of cardiac work.

The efficiency of cardiac work measured in isolated guinea pig atria can be influenced by change of the heart rate or the stroke work due to electric stimulation or drug actions: An increased cardiac performance caused by enhanced heart rate needs considerably more oxygen than an increase of the total cardiac work to the same degree due solely to a positive inotropic action. Oxidation of long and short chain fatty acids lowers the efficiency of cardiac work connected with negative inotropic effects. An increase of the heart rate is followed by a shift to the oxidation of carbohydrates, at rest to the oxidation of FFA. Long chain fatty acids are not sufficient for the increased demand of energy in the cardiac muscle at high heart rates and are then poorly oxidized. The problems connected with the Ca++ binding of FFA in the cardiac cytoplasm after inhibition of their oxidation well be discussed.