The dynamics of the coronary venous system in the dog

Effect of cardiac-locomotor coupling on the metabolic efficiency of pedalling

Coupling between cardiac and locomotor rhythms (CLC) has been reported while subjects exercise at cadences that are natural to them. The hypothesis that oxygen consumption (VO2) would be lower when subjects pedalled at the rate producing 1:1 coupling of heart and pedalling rates than when they pedalled at noncoupled rates was tested with 12 men on a cycle ergometer. At a moderate power output based on their VO2max, subjects pedalled at six different pedalling rates while VO2 and heart rate were measured. The pedalling rates were the preferred frequency, frequencies 15 and 30% above and below the preferred frequency, and the 1:1 coupled frequency. In 8 of the 12 subjects it was possible to fit their data with significant regression equations relating VO2 to pedalling rate, but in no subject was the 1:1 coupled state energetically beneficial, suggesting that any functional significance of CLC is unrelated to metabolic efficiency.

The role of intramyocardial pressure during coronary sinus interventions: a computer model study

A model consisting of an arterial, a capillary, and a venous compartment was developed to reproduce experimentally determined hemodynamic results of the arterial and venous sides of the coronary circulation. From the model, intramyocardial flow between capillaries and veins, which is inaccessable to measurement, was then estimated. Results are given for normal perfusion and coronary sinus occlusion conditions. For both conditions, intramyocardial pressure was varied within the model in order to study its impact on intramyocardial flow. For low and moderate intramyocardial pressures under coronary sinus occlusion, retrograde flow from veins to capillaries was seen to increase with increasing intramyocardial pressure. However, for very high values of intramyocardial pressure, which are close to left ventricular pressure, retrograde flow declined.

The effect of locomotion speed on the anterior tibial intramuscular pressure of normal humans

We examined the hypothesis that anterior tibial intramuscular pressure increases with the speed of locomotion. A solidstate pressure transducer was placed near the tip of an intramuscular fluid-filled catheter and each of ten normal subjects walked, jogged and ran barefoot, at 1.5, 2.5 and 3.5 m s-1 respectively, on a treadmill to which they had been previously familiarized. The pressure signals during ten gait cycles from each subject were sampled at 600 Hz and were averaged at each speed. The peak pressures increased in magnitude as a function of increasing locomotion speed, while the mean pressure remained constant.

Functional characteristics of intramyocardial capacitance vessels during diastole in the dog

In order to evaluate the functional characteristics of the intramyocardial capacitance vessels during prolonged diastole, we analyzed the response of coronary vein flow after stepwise changes of coronary artery pressure in anesthetized open-chest dogs by using our newly developed laser Doppler velocimeter with an optical fiber. The peripheral portion of the great cardiac vein was isolated and the optical fiber tip was inserted into the vessel. The left anterior descending coronary artery was cannulated and connected to a reservoir to regulate coronary perfusion pressure. Intracoronary adenosine administration was carried out to avoid any change in coronary vasomotor tone. After 15 seconds of occlusion of the perfusion route, the heart was arrested by pacing-off. Two seconds later, coronary perfusion pressure was increased stepwise to a preset target pressure. This procedure was repeated by changing target pressure at 4 (or 5) different pressure levels (31-105 mm Hg). The great cardiac vein flow became zero due to the cardiac arrest and remained at zero for a moment (dead time) after the initiation of reperfusion. Then the flow reappeared and increased with first order time delay. The presence of dead time indicates the existence of unstressed volume, and the first order time delay represents the product of resistance and capacitance. The unstressed volume with a minimal vasomotor tone for perfusion pressure of 60-90 mm Hg was 5.2 +/- 2.2 ml per 100 g left ventricle, which is comparable to coronary blood flow for several beats. The capacitance at perfusion pressure of 60-90 mm Hg was 0.08 +/- 0.04 ml/mm Hg per 100 g left ventricle, while that at low perfusion pressure (30-50 mm Hg) was 0.14 +/- 0.09 ml/mm Hg per 100 g left ventricle. These results indicate that the intramyocardial capacitance vessels have two functional components, and that the phasic nature of coronary vein flow is solely the result of the myocardial squeezing of the blood in the capacitance vessels.