Respiratory Physiology[the Ins and Outs] Jim Pierce Bi 145a Lecture 18, 2009-10
Pulmonary Ventilation Compare and Contrast
Ventilation Perfusion Matching • We have seen that proper gas exchange depends on both ventilation and perfusion • How do we make sure that each lung unit is both ventilated and perfused?
Ventilation Perfusion Matching • How do we match ventilation and perfusion?
Ventilation Perfusion Matching • When a lung is not ventilated, the pAO2 falls • Then, the vasculature constricts • Then, the perfusion decreases
Ventilation Perfusion Matching • When a lung is not perfused, the pACO2 falls • This causes bronchoconstriction • This leads to decreased ventilation.
Ventilation Perfusion Matching • Thus, VQ matching is based on: • Airways and the vessels sending air and blood away from mismatched areas.
Ventilation Perfusion Matching • This is a great system to compensate for a focal problem (like pneumonia) • It can be dangerous, however…
Ventilation Perfusion matching • If there is a global problem with ventilation or perfusion, the whole lung tries to send air or blood elsewhere. • This is a problem. • ARDS
Pulmonary Function • How do we adjust pulmonary function to compensate for changes in the periphery?
Pulmonary Function • Ultimately, the job of the cardiopulmonary system is to deliver oxygen to the periphery • As oxygen is used by the periphery, carbon dioxide is returned.
Pulmonary Function • The cardiovascular system is responsible for delivering the oxygen to the periphery. • The periphery is responsible for extracting oxygen from the blood • The venous blood carries the resulting carbon dioxide back to the lung • The pulmonary system, then, needs to compensate to excrete that carbon dioxide.
Pulmonary Function • How do we increase the delivery of oxygen to the periphery? • DO2 = CartO2 * CO • CO = HR * SV • CO = BP / SVR
Pulmonary Function • Why doesn’t an increase in the CO cause a decrease in the oxygenation of the blood?
Pulmonary Function • Answer: • Built-in Reserve
Pulmonary Function • What kinds of Carbon Dioxide stresses do we need to deal with? • Increased / Decreased production of CO2 • pH abnormalities affecting CO2 excretion
Pulmonary Function • There are two types of protons carried in the blood • “Volatile acids” that result from CO2 conversion to bicarbonate and protons • “Non-volatile acids” that result from proton dissociation from other molecules (lactic acid, protein metabolism)
Pulmonary Function • To increase the disposal of CO2 and remove volatile protons, we simply increase alveolar ventilation • Minute Ventilation = Respiratory Rate * Tidal Volume
Pulmonary Function • Increased production of CO2 and volatile acid occurs primarily because of a change in metabolic substrates to fats
Pulmonary Function • What about pH problems not related to carbon dioxide? • They can occur by two mechanisms • 1) the wrong number of protons • 2) the wrong amount of buffer
Pulmonary Function • The wrong number of protons can happen for a variety of reasons: • Too many made (lactic acid, protein metabolism) • Too many lost (vomiting stomach acid, renal losses) • Not enough lost (renal failure)
Pulmonary Function • The wrong amount of buffer can happen for two reasons: • Too much buffer (ingestion of alkali, infusion of buffer) • Too little buffer (loss of buffer with diarrhea, loss of buffer through kidney)
Pulmonary Function • Since pH changes can affect cellular respiration and CO2 excretion, the lung must be able to compensate for pH changes. • Ventilation changes cause pCO2 changes • pCO2 changes cause pH changes
Pulmonary Function • A high pH is called an alkalemia • A low pH is called an acidemia • A particular derangement that causes an increase in pH is called an alkalosis • A particular derangement that causes a decrease in pH is called an acidosis.
Pulmonary Function • If an acidosis or alkalosis is caused by changes in ventilation, it is called a Respiratory acidosis/alkalosis • If is not caused by ventilation, then it is called a Metabolic acidosis/alkalosis
Pulmonary Function • As we will see in acid-base physiology, the lung compensates for pH changes by changing ventilation and therefore changing pCO2
Mechanical Ventilation Jim Pierce Bi 145a Bonus Lecture
Mechanical Ventilation ... is a therapy. What are the indications? What is the end point? How do we administer it? How do we assess it?
Lung Functions Oxygenation Ventilation Neurohormonal
Indications for Mechanical Ventilation Acute Respiratory Failure (66%) Acute Respiratory Distress Syndrome Heart Failure (through pulmonary edema/hypertension) Pneumonia Sepsis Complications of Surgery Trauma Coma (15%) Acute Exacerbation of Chronic Obstructive Pulmonary Dz (13%) Neuromuscular Disease (5%) Esteban A, Anzueto A, Alia I, et al. How is mechanical ventilation employed in the intensive care unit? An international utilitzation review. American Journal of Respiratory Critical Care Medicine2000; 161: 1450-1458