Theory of Arterial pressure

Theory of Arterial Pressure Flow down a pipe follows a pressure gradient....the degree of flow is directly proportional to the pressure gradient. In other words, more pressure, more flow.

Theory of Arterial Pressure On the other hand Flow is inversely related to resistance. In other words, more resistance, less flow.

Theory of Arterial Pressure P1 - P2 Flow = resistance Flow is directly proportional to the pressure gradient and inversely proportional to resistance

Must keep the flow going! Without oxygen rich blood flow the tissues will die.

Theory of Arterial Pressure In the vascular system. The pressure gradient is created by the pumping action of the heart, how much resistance is encountered, then, controls the amount of blood flow in the capillaries. These two factors control blood pressure.

Theory of Arterial Pressure Important point: The vascular area is fairly huge for one small muscular pump to fill…without the appropriate amount of resistance the heart could not maintain the blood pressure! So what? Who needs blood pressure?

Not enough resistance

Theory of Arterial Pressure The arterioles offer the most resistance in the vascular system.

Theory of Arterial Pressure Notice the big drop in arterial pressure that occurs in the arterioles, this resistance is due to smooth muscle constriction in the arterioles. Smooth muscle constriction is controlled by nerves, hormones, and other “vasoactive” substances.

Theory of Arterial Pressure Precapillary sphincters also control capillary blood flow to specific groups….these respond to local stimuli as well as nervous stimuli (sympathetic versus parasympathetic).

Theory of Arterial Pressure The sum of this resistance throughout the entire body is called: Systemic Vascular Resistance

Theory of Arterial Pressure The pressure gradient created by the heart is important because…It keeps oxygen rich blood moving to the tissues. Heart action alone, however, is not enough, appropriate resistance is important also. Measured arterial blood pressure is a function of both

Theory of Arterial Pressure Arterial pressure is: ~120 mmHg Systolic / 80 mmHg Diastolic Capillary Pressure is: ~30 mmHg, dropping to ~15

Theory of Arterial Pressure Mean Arterial Pressure formula: MAP = Systolic + (Diastolic X2) 3 Why not just average the Systolic and Diastolic? Answer: You spend twice as much time in diastole than systole

Theory of Arterial Pressure Fun Fact What percentage of blood is in the arterial system? 11%

Theory of Arterial Pressure What mechanisms maintain blood pressure? Cardiac output increases or decreases Stroke volume Heart rate Resistance changes Radius of arterioles Nervous control (Sympathetic Vs. Parasympathetic) Local mediators

. Cardiac Output Q = (HR)(SV) Where HR is heart rate Where SV is stroke volume .

Relationship Between Cardiac output and Blood pressure There is a direct relationship between Cardiac output and blood pressure. If resistance stays the same, cardiac output and blood pressure are directly proportional. Q = ABP

Theory of Arterial Pressure Another mechanism that controls blood pressure is a feedback loop from the baroreceptors in the aorta and carotid artery. For example: Mashing on the carotid artery, in the right spot, might fool the body into thinking the pressure is too high. The effect would be a sudden drop in heart rate via this feedback loop.

Oakes, Clinical Practitioners Pocket Guide to Respiratory Care 1996