Introduction

Intensive care generally refers to the care of patients who are critically ill or injured, thereby requiring constant monitoring, frequent assessment and thoughtful intervention to facilitate a successful recovery. A thorough understanding of human physiology and how to support or correct alterations from the norm is essential in the treatment of such patients. Critical illness often affects the entire body and a multi-system approach must be considered. This chapter will address fundamentals of physiology, pathology and treatment of patients you will encounter in an intensive care setting.

Cardiovascular system

Simply, the cardiovascular system is composed of the heart and an extensive network of blood vessels. Its function is to deliver oxygen (perfusion) and nutrients to the entire body and take away the by-products of the body's utilization. While seemingly elementary, returning to this basic concept helps make the complexities of this intricate process understandable.

Physiology

The heart

The heart has four chambers, four valves, and is composed of specialized conduction tissue; its purpose is to pump blood throughout the body. The heart itself is perfused by right and left coronary arteries arising directly from the aorta. The left coronary artery leaves the aorta and is referred to as the ‘left main stem’ before it bifurcates into the circumflex artery and the left anterior descending (LAD) artery.

CARDIOVASCULAR SYSTEM

Cardiac anatomy

The heart has four chambers, four valves, and specialized conduction tissue. It is generally referred to as having left and right-sided chambers, but in humans the interatrial septum and inter-ventricular septum are located in a plane some 45° from the sagittal plane (Fig. 8.1). The right atrium and ventricle are therefore located anterior and to the right of the corresponding left atrium or ventricle. It is useful to bear this in mind when visualizing the cardiac chambers through echocardiograms (ECHO) or when assessing traumatic injuries to the chest wall.

Cardiac valves

The aortic and pulmonary valves are similar in structure and function, and consist of three components:

The aortic valve leaflets are referred to by clinicians as the left coronary, right coronary, and non-coronary leaflets. The fibrous annulus is shaped like a three-pronged coronet from which the valve leaflets are suspended. Valve stenosis may arise when the valve leaflets are fused or stiff and the annulus narrows; valve incompetence results from abnormalities of the valve leaflets and/or dilation of the annulus. The sinuses of Valsalva are important for initiating valve closure. They prevent the valve leaflets from being pressed flat against the aortic wall during systole, and eddy currents within the sinuses help initiate valve closure in diastole.