The Respiratory System - 4 Pulmonary Function Tests and Alveolar Ventilation

Home , Dead space (physiology), Minute ventilation, Pulmonary gas pressures

The Respiratory System - 4 Pulmonary function tests and alveolar ventilation

Jennifer Carbrey Ph.D. Department of Cell Biology image by OCAL, http://www.clker.com/clipart-26501.html, public domain Respiratory System

1. Anatomy and mechanics 2. Lung volumes and compliance 3. Pressure changes and resistance 4. Pulmonary function tests and alveolar ventilation 5. Oxygen transport

6. CO2 transport and V/Q mismatch 7. Regulation of breathing 8. Exercise and hypoxia Pulmonary Function Tests

(FVC and FEV1)

• Forced Vital Capacity = maximal volume of air exhaled after a maximal inspiration.

• Forced expiratory volume in 1 second (FEV1) = individual takes a maximal inspiration and then exhales as fast as possible. The important value is the fraction of the total forced vital capacity expired in 1 second. Normal individuals expire approx. 80% of their vital capacity in this time.

• Pulmonary function tests differentiate:

Obstructive lung disease: FEV1/FVC < 80% normal forced vital capacity (FVC).

Restrictive lung disease: normal FEV1/FVC = 80% reduced forced vital capacity (FVC).

Pulmonary Function Test

7 X 6

5 VOLUME 4(LITERS) Y 3

2 Z 1

0 2 4 6 8 10 TIME (SECONDS) Y- normal X – obstructive Z - restrictive Alveolar Ventilation

150 mL

450 ml 300 mL conducting conducting 150 mL volume 150 mL volume 150 mL

300 mL

respiratory respiratory volume 3L volume 3L

Inspired air is diluted by the air remaining in the lungs from the previous breathing cycle. Alveolar Ventilation

Resp. rate Tidal volume Minute Vent. Alveolar Vent. 50 100 5000 0 10 500 5000 3500 5 1000 5000 4250

Minute Ventilation (VE) = Tidal Volume (TV) x Respiratory Rate (f)

Anatomic Dead Space (VD) = volume in conducting airways (approx. 150 mL); no exchange of gas with blood. (physiological dead space = anatomic and alveolar dead spaces)

**Alveolar Ventilation (VA) = [Tidal Volume (TV) – dead space (VD)] x f Gas Partial Pressures

• Ambient air is a gas mixture of mostly nitrogen (79%) and oxygen (21%), carbon dioxide is low (0.04%).

• Gas mixtures obey Dalton’s Law which states: sum of the partial pressures of gases = total pressure.

• PO2= FiO2 x Patm = (0.21 x 760) = 160 mmHg

• Inspired gas is warmed and humidified: Water vapor pressure = 47 mmHg therefore,

PO2 of inspired air is 0.21 x (760 - 47) = 150 mmHg

Alveolar Gas Pressure

Atmosphere PO2 = 160 mmHg PCO2 = 0.3 mmHg

Alveoli PAO2 = 105 mmHg PACO2 = 40 mmHg

Arteries PaO2 = 100 mmHg PaCO2 = 40 mmHg

Veins PvO2 = 40 mmHg PvCO2 = 46 mmHg

**Alveolar gas pressures determine systemic arterial blood gas pressures. Key Concepts

• Ventilation is the process of moving air into and out of the lungs. Minute ventilation is the total volume of air moved per minute. Alveolar ventilation is the volume of fresh air that reaches the alveoli per minute.

• Dead space volume represents the volume in the conducting zone and does not participate in gas exchange. Physiologic dead space includes the anatomical dead space and areas of the lung that are either not ventilated or not perfused.