Heart Period Variability

Zajdel Yung D., Thong T., R. Beck Ellingson V. & Oken B. 2003. Effect Of Nicotine On Heart Rate Varibility. 923.5.

Exercise increases heart rate by a process of sympathetic autonomic stimulation. Sympathetic (adrenergic) nerves increase the excitability of the sino-atrial node and reduce the P-R interval .As exercise continues, the physiological changes in the body are continuously monitored by a number of physiological systems and the balance of activity of the sympathetic system (speeding up) and the parasympathetic system (slowing down) is constantly adjusted. When exercise is over, the heart rate does not drop immediately as the body has to undergo a period of re adaption to return to the resting state.

The resting heart rate fluctuates over time because it is under control of the autonomic nervous system and the fluctuations are a result of the sympathetic and parasympathetic systems trying to balance each other out.

The heart serves an important purpose within the body, pumping blood throughout the circulatory system to supply all parts of the body with vital nutrients and molecules. It pumps oxygen and nutrient rich blood to be exchanged for carbon dioxide, which is then pumped to the lungs and eliminated from the body. The movement of blood throughout the body is due to the heart’s ability to push blood along the circulatory system at a steady, unfaltering rate. This rate, known as heart rate, is regulated and can be altered at a moment’s notice by signaling within the body and heart itself. In vertebrates, the autonomic nervous system controls and regulates heart rate. The autonomic nervous system is divided into two subunits, the sympathetic nervous system and parasympathetic nervous system. The parasympathetic nerve that innervates the heart is the vagus nerve. In this laboratory experiment, the regulation of heart rate was observed by studying a certain breed of turtle, the Red-eared Slider (Trachemys scripta elegans). Both chemical and electric signaling can influence the components of the nervous

The heart rate variability (HRV) is a non-invasive index of the neural control of the heart, and may reflect the functional state of the central nervous system (18, 19). Heart rate is influenced and regulated by the sympathetic and parasympathetic components of the autonomic nervous system (20). HRV refers to constant changes in the time interval between consecutive

They are different kind of forms the P wave it represents depolarization. It indicates atrial depolarization, or contraction of the atrium. Normal duration is no longer than 0.11 seconds less than 3 small squares. Amplitude height is no more than 3 mm. No notching or peaking. The PR interval represents the time impulse initiated by the sinus node travels through the atria to the ventricular conduction system. PR interval indicates AV conduction time. The duration time is 0.12 to 0.20 seconds.

HRV is a simple and effective measurement and practical for clinical use. Many clinical uses involve patients with cardiovascular disease and athletes. Other disease states that use HRV as a marker are diabetic neuropathy, coronary

The sympathetic reflexes result from sympathetic fibres beginning in the brainstem through the spinal cord and spinal ganglia towards the heart. Heart muscles such as Purkinje fibres elicit a rhythm when the heart’s pacemaker, the sinoatrial node, is unable to do so. Question 2c: Explain how these two mechanisms of vagal escape would differ in an isolated heart preparation such as the one used in this simulated experiment versus a heart in a live animal/human. (2 marks) ANSWER:

In an effort to increase cardiac output, the sympathetic nervous system is activated, through baroreceptors in the aortic arch, as an early compensatory mechanism which provides inotropic support and maintains cardiac output (Cadwallader, 2013; Yelle & Chaudhry, 2016). These compensatory mechanisms include increased heart rate, myocardial remodeling, and increased fluid volume. Chronic sympathetic activation eventually increases the stress placed on the heart and causes further weakening in cardiac function (Markaity, 2012; Yelle & Chaudhry, 2016).

As shown in Figure 1, the P wave is a result of atrial depolarization. The QRS complex is a result of ventricular depolarization, and thus ventricular contraction, as well as atrial repolarization simultaneously. The T wave represents repolarization of ventricles and thus relaxation. The delay between the P wave and the QRS complex is known as the PQ interval or the PR interval. During this interval, the atria contract and begin to relax, and the ventricles contract at the end of this delay (VanPutte et al., 2014). This time of this interval is important for determining many heart conditions, such as an atrial blockage, as it measures the time of onset of ventricular contraction after the atria contracts. If this time period is too long,

The heart is able to do this thanks to the specialized cardiac muscle it contains. The contraction of the heart displays excitatory- contraction coupling (EC coupling) similar to skeletal muscles except the action potential in the heart originates spontaneously at the peace maker of the heart (Silverthorn, 2013). Contraction happens when a rapid depolarization occurs due to the influx and opening of sodium voltage gated channels to raise the membrane potential toward the threshold value causing a firing of action potential. The conduction and cardiac cycle starts at a resting distol state for both ventricles and atriums and is initiated with the depolarization at the SA node (Silverthorn, 2013). This causes an action potential which moves rapidly towards the AV node where the signal gets slowed down (Silverthorn, 2013).When the signal reaches this point it causes a contraction/systole stage of the right and left atriums. This causes blood to be pumped into the ventricles through the AV valves (Silverthorn, 2013). The action potential then travels to the ventricles down the bundle branches out towards the Purkinje fibers (Silverthorn, 2013). In terms of the cardiac cycle an isovolumetric contraction occurs during the pause of the signal at the AV node allowing the AV valves to close, followed by ventricular systole where the ventricles expel blood into circulation (Silverthorn, 2013). The final stage in the cardiac cycle occurs between stimulations of action potential when the ventricles and atriums are in diastole and the chambers fill with blood once again (Silverthorn,

Blood pressure is typically recorded when the heartbeats and relaxes in between, It is written

The cardiac cycle describes the coordinated and rhythmic series of muscular contractions associated with the normal heart beat.

According to UC Davis Health Sports Medicine,” Heart rate refers to the number of times the heart beats per minute, and is directly related to the workload being placed on the heart.” (UC Davis Health,2017) Heart rate can be managed by two different branches of the autonomic nervous system that supply nerve impulses to the heart. The sympathetic nervous system is the fight or flight mechanism and releases hormones like epinephrine and norepinephrine to increase heart rate. The parasympathetic nervous system is the rest and digest mechanism and releases achetylcholine, which is a hormone that will decrease the heart rate. The vagus nerve is part of the autonomic nervous system, specifically the parasympathetic system. The autonomic nervous system

Heart Rate and/or beats per minute evaluation: The participants were taken to a gym where they had access to a treadmill and dumbbell.  The procedure of the examination was explained to the participant before the exercise was performed. Prior to the performance of the exercise, we asked each individual if they had any medical concerns that needed to be cleared before participation. A resting heart rate was taken by placing two fingers on the participant 's wrist. Each thump that was felt was counted as one beat. A timer was set for 15 seconds. The amount of thumps felt after 15 seconds was then multiplied by four to obtain the total number of beats per minute. The individual then went to perform weight lifting for five minutes with the dumbbells. After five minutes have