Cardiac cycle

About: Cardiac cycle is a research topic. Over the lifetime, 3290 publications have been published within this topic receiving 96159 citations.

Modeling pressure-area relations of coronary blood vessels embedded in cardiac muscle in diastole and systole.

Abstract: Pressure-cross-sectional area (P-A) relations of a (thick-walled) arteriole and (thin-walled) small vein (both maximally dilated), embedded in cardiac muscle in both static systole and diastole at slack length and at 90% of maximal length (Lmax), were calculated. The elastic properties of cardiac muscle and vessel wall per se were taken into account. Muscle fibers and vessels were assumed to run in parallel. The muscle tissue (fibers + collagen) was assumed to be incompressible, homogeneous, nonlinearly elastic, and transversely isotropic. Cross-fiber stress-strain relations were assumed to be proportional to those in fiber direction. It is predicted that cardiac muscle in diastole has little effect on the P-A relation of the arteriole but strongly affects that of the small vein. In systole, the myocardium strongly affects the P-A relations of both vessels. Isometric transition from static diastole to static systole (isometric "contraction") was found to reduce arteriolar and venous area (at constant pressures of 35 and 7 mmHg, respectively) by approximately 50 and 40, respectively. Contraction with a 14% shortening was found to reduce these areas by 48 and 32%, respectively. The differences in the results for the two vessels were found to be determined mainly by their difference in the ratio of outer to inner radius. Furthermore, it was found that the area reductions are much larger for contractions (with or without shortening) than for muscle stretch per se. It is concluded that the change in elastic properties and, more specifically, development of stress in cross-fiber direction of the cardiac muscle during contraction causes the area reductions of coronary vessels.

Respiration, heartbeat, and conscious tactile perception

Abstract: Previous studies have shown that timing of sensory stimulation during the cardiac cycle interacts with perception. Given the natural coupling of respiration and cardiac activity, we investigated here their joint effects on tactile perception. Forty-one healthy participants reported conscious perception of finger near-threshold electrical pulses (33% null trials) and decision confidence while electrocardiography, respiratory activity, and finger photoplethysmography were recorded. Participants adapted their respiratory cycle to expected stimulus onsets to preferentially occur during late inspiration / early expiration. This closely matched heart rate variation (sinus arrhythmia) across the respiratory cycle such that most frequent stimulation onsets occurred during the period of highest heart rate probably indicating highest alertness and cortical excitability. Tactile detection rate was highest during the first quadrant after expiration onset. Inter-individually, stronger respiratory phase-locking to the task was associated with higher detection rates. Regarding the cardiac cycle, we confirmed previous findings that tactile detection rate was higher during diastole than systole and newly specified its minimum at 250 - 300 ms after the R-peak corresponding to the pulse wave arrival in the finger. Metacognitive efficiency for yes- responses was also modulated across the cardiac cycle reaching an optimum at the end of diastole. Expectation of stimulation induced a transient heart deceleration which was more pronounced for unconfident decision ratings. Inter-individually, stronger post-stimulus modulations of heart rate were linked to higher detection rates. In summary, we demonstrate how tuning to the respiratory cycle and integration of respiratory-cardiac signals are used to optimize performance of a tactile detection task. Significance statement Mechanistic studies on perception and cognition tend to focus on the brain neglecting contributions of the body. Here, we investigated how respiration and heartbeat influence tactile perception: Respiration phase-locking to expected stimulus onsets corresponds to highest heart rate (and presumably alertness/cortical excitability) and correlates with detection performance. Tactile detection varies across the heart cycle with a minimum 250 - 300 ms after heart contraction, when the pulse reaches the finger. Lower detection was associated with disturbed metacognition, indicating – together with our previous finding of unchanged early ERPs - that this effect is not a peripheral physiological artifact but a result of cognitive processes that model our body’s internal state, make predictions to guide behavior, and might also tune respiration to serve the task.

Intramyocardial pressure and distribution of coronary blood flow during systole and diastole in the horse.

Abstract: Transmural myocardial blood flow was measured with microspheres in systole and in diastole, along with intramyocardial pressure, in seven anaesthetised horses. Intramyocardial pressures were measured with a miniature manometer implanted in the tip of a 16-gauge needle. Peak systolic intramyocardial pressure decreased from subendocardium to subepicardium and never exceeded intraventricular pressure. Systolic blood flow decreased from epicardium to endocardium where it did not differ from zero. Diastolic blood flow increased from epicardium to subendocardium, but then decreased in the most endocardial layer to a level not different from the immediate subepicardial layer. The horse was a useful model for studying these parameters because the ventricular walls are so thick and the heart rate is so slow that injections may be made during various phases of the cardiac cycle. These results of transmural myocardial blood flow and intramyocardial pressure measured in the same animal are identical with those of others, except for the reduction in subendocardial blood flow compared with the layers just epicardial to that.

Vessel tracking: prospective adjustment of section-selective MR angiographic locations for improved coronary artery visualization over the cardiac cycle.

Abstract: To follow the motion of the coronary artery in magnetic resonance angiography, the authors evaluated vessel tracking, a method for prospective adjustment of the section location as a function of the delay from the cardiac trigger In 10 volunteers and four patients, this method allowed the vessel to be maintained in the plane of acquisition throughout the cardiac cycle With a single-phase multisection sequence, vessel-tracking acquisitions had an efficiency of 068 ± 004 for both the right and left coronary arteries compared with 019 ± 003 for a non–vessel-tracking acquisition (P < 001)