the heart and its gadgets

Measurement techniques

• Electrocardiogram - for cardiac electrophysiology

Electrocardiograph (ECG, or EKG [from the German Elektrokardiogramm]) is a transthoracic interpretation of the electrical activity of the heart over time captured and externally recorded by skin electrodes.^[1] It is a noninvasive recording produced by an electrocardiographic device. The etymology of the word is derived from the Greek electro, because it is related to electrical activity, cardio, Greek for heart, and graph, a Greek root meaning "to write". In English speaking countries, medical professionals often write EKG (the abbreviation for the German word elektrokardiogramm) in order to avoid confusion with EEG

• Sphygmomanometer and stethoscope - for blood pressure 

A sphygmomanometer or blood pressure meter is a device used to measure blood pressure, comprising an inflatable cuff to restrict blood flow, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just starting, and at what pressure it is unimpeded. Manual sphygmomanometers are used in conjunction with a stethoscope.

• Pulse meter - for cardiac function (heart rate, rhythm, dropped beats)

A heart rate monitor is a personal monitoring device which allows a subject to measure his heart rate in real time or record his heart rate for later study. Early models consisted of a monitoring box with a set of electrode leads which attached to the chest.

• Pulse - commonly used to determine the heart rate in absence of certain cardiac pathologies

 In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed against a bone, such as at the neck (carotid artery), at the wrist (radial artery), behind the knee (popliteal artery), on the inside of the elbow (brachial artery), and near the ankle joint (posterior tibial artery). The pulse can also be measured by listening to the heart beat directly (auscultation), traditionally using a stethoscope.

• Heart rate variability 

- used to measure variations of time intervals between heart beats

• Nail bed blanching test 

- test for perfusion

• Vessel cannula or catheter pressure measurement 

- pulmonary wedge pressure or in older animal experiments

Perfectly demarcated heart.

HEART

   

Surface anatomy of the human heart. The heart is detached by:

- A radius of 9 cm to the left of the midsternal line (apex of the heart)
-The seventh right sternocostal articulation
-The upper border of the third right costal cartilage 1 cm from the right sternal line
-The lower border of the second left costal cartilage 2.5 cm from the left lateral sternal line.

 

Human heart removed from a 64-year-old male

 

 

 

 

 

 

 

Each year, the heart pumps more than 1,848 gal (7,000 l) of blood through a closed system of about 62,100 mi (100,000 km) of blood vessels. This is more than twice the distance around the equator of the Earth. As blood circulates around the body, it picks up oxygen from the lungs, nutrients from the small intestine, and hormones from the endocrine glands, and delivers these to the cells. Blood then picks up carbon dioxide and cellular wastes from cells and delivers these to the lungs and kidneys, where they are excreted. Substances pass out of blood vessels to the cells through the interstitial or tissue fluid that surrounds cells.

The adult heart is a hollow cone-shaped muscular organ located in the centerof the chest cavity. The lower tip of the heart tilts toward the left. The heart is about the size of a clenched fist and weighs approximately 10.5 oz (300 g). Remarkably, the heart beats more than 100,000 times a day and close to2.5 billion times in the average lifetime. A triple-layered sac, the pericardium surrounds, protects, and anchors the heart. A liquid pericardial fluid located in the space between two of the layers, reduces friction when the heartmoves.

The heart is divided into four chambers. A partition or septum divides it into a left and right side. Each side is further divided into an upper and lowerchamber. The upper chambers, atria (singular atrium), are thin-walled. Theyreceive blood entering the heart, and pump it to the ventricles, the lower heart chambers. The walls of the ventricles are thicker and contain more cardiac muscle than the walls of the atria, enabling the ventricles to pump blood out to the lungs and the rest of the body. The left and right sides of the heart function as two separate pumps. The right atrium receives oxygen-poor blood from the body from a major vein, the vena cava, and delivers it to the right ventricle. The right ventricle, in turn, pumps the blood to the lungs via the pulmonary artery. The left atrium receives the oxygen-rich blood from the lungs from the pulmonary veins, and delivers it to the left ventricle. The left ventricle then pumps it into the aorta, a major artery that leads to all parts of the body. The wall of the left ventricle is thicker than the wall of the right ventricle, making it a more powerful pump able to push blood through its longer trip around the body.

CLOSED CARDIOVASCULAR SYSTEM

The cardiovascular systems of humans are closed, meaning that the blood never leaves the network of blood vessels. In contrast, oxygen and nutrients diffuse across the blood vessel layers and enters interstitial fluid, which carries oxygen and nutrients to the target cells, and carbon dioxide and wastes in the opposite direction

One-way valves in the heart keep blood flowing in the right direction and prevent backflow. The valves open and close in response to pressure changes in the heart. Atrioventricular (AV) valves are located between the atria and ventricles. Semilunar (SL) valves lie between the ventricles and the major arteries into which they pump blood. The "lub-dup" sounds that the physician hearsthrough the stethoscope occur when the heart valves close. The AV valves produce the "lub" sound upon closing, while the SL valves cause the "dup" sound. People with a heart murmur have a defective heart valve that allows the backflow of blood.The heart cycle refers to the events associated with a single heartbeat. The cycle involves systole, the contraction phase, and diastole, the relaxation phase. In the heart, the two atria contract while the two ventricles relax. Then, the two ventricles contract while the two atria relax. The heart cycle consists of a systole and diastole of both the atria and ventricles. At the end of a heartbeat all four chambers rest. The rate of heartbeat averages about75 beats per minute, and each cardiac cycle takes about 0.8 seconds.