Blood flow and blood pressure Enas Sabah MSc. Human Physiology

Blood flow is the amount of blood that passes through a given point in the circulation in a given period of time. Blood flow is expressed in milliliter per minute or litter per minute. The overall blood flow in the total circulation of an adult person at rest is about 5000 ml/min.

Blood flow through a blood vessel is determined by two factors: (1) pressure difference of the blood between the two ends of the vessel, also called “pressure gradient” along the vessel, which is the force that pushes the blood through the vessel. (2) the impediment to blood flow through the vessel, which is called vascular resistance.

In which F is blood flow, ∆P is the pressure difference (P1 - P2) between the two ends of the vessel, and R is the resistance. This formula states that the blood flow is directly proportional to the pressure difference but inversely proportional to the resistance.

Types of blood flow: 1. Laminar ( streamline or silent ) flow 2 Types of blood flow: 1.Laminar ( streamline or silent ) flow 2.Turbulent ( noisy ) flow   A, Two fluids (one dyed red, and the other clear) before flow begins; B, the same fluids 1 second after flow begins; C, turbulent flow, with elements of the fluid moving in a disorderly pattern.

Blood pressure: Blood pressure means the force exerted by the blood against any unit area of the vessel wall. B.P = C.O X P.R its measured in millimeter of mercury When one says that the pressure in a vessel is 50 mm Hg, it means that the force exerted is sufficient to push a column of mercury against gravity up to a level 50 mm high. Occasionally, pressure is measured in centimeters of water (cm H2O).

Factors affecting blood pressure

Activation of the sympathetic nervous system, results in increased heart rate and force of muscular contractions, as well as peripheral vasoconstriction. Vasomotor fibers, sympathetic nerve fibers that innervate the vessel's smooth muscle layer. release norepinephrine, a powerful vasoconstrictor. A vasoconstrictor is a substance that causes blood vessels to constrict, as a result peripheral resistance increase and the blood pressure raise.

Cardiac Output Cardiac output is simply the amount of blood pumped by the heart per minute. An increase in cardiac output results in increased blood pressure. Cardiac Output = Heart Rate X Stroke Volume Heart rate (HR), is the number of heart beats per minute (bpm).

stroke volume (SV) is the volume of blood pumped from the left ventricle per beat. Anything that affects heart rate or stroke volume affects cardiac output and thus blood pressure.

Methods for measuring blood pressure: Direct method by putting a canula into the right atrium Indirect method which include both palpatory and auscultatory method Indirect method: Palpatory method: The radial pulse is palpated with the pulps of the index and middle finger. The pressure cuff of the sphygmomanometer is wrapped over the upper arm and then inflated above the level at which the radial pulse disappears. Then gradually the pressure is lowered until the pulse returns which correspond to systolic B.P.

Auscultatory method: The brachial artery is first palpated and the diaphragm of the stethoscope is applied lightly over it. The cuff is then inflated to 30 mm Hg above the systolic pressure previously determined by the palpatory method. From changes in the quality of the Korotkoff’s sound the systolic and diastolic B.P are determined.

Korotkoff’s sounds are sounds heard by the stethoscope applied over an artery with its lumen occluded by an inflated cuff and then gradually deflated. The sounds occur in 5 successive phases: Phase 1: appearance of the sound which is produced by forceful opening of the brachial artery during systole Phase 2: softening of the sounds Phase 3: increase in sound intensity Phase 4: muffling of the sound Phase 5: disappearance of the sound

Both phase 2 and 3 are due to turbulent flow of blood through partially occluded vessel. Systolic B.P corresponds to the pressure recorded at phase 1, and diastolic B.P can be taken either at phase 4 or 5.

Hypertensive Emergency American Heart Association (AHA) classification of blood pressure (18 years and older): Category systolic, mmHg diastolic, mmHg Hypotension < 90 < 60 Desired 90–119 60–79 Prehypertension 120–139 80–89 Stage 1 Hypertension 140–159 90–99 Stage 2 Hypertension 160–179 100–109 Hypertensive Emergency ≥ 180 ≥ 110

Risk Factors for Hypertention Modifiable risk factors Lack of physical activity An unhealthy diet, especially one high in sodium Being over weight or obese Lipidemia Diabetes alcoholism Smoking Stress

Non-Modifiable risk factors: Family history Gender Age Race African-Americans tend to develop high blood pressure more often than people