Gandaki Medical College

By: Gyaltsen Gurung

To define and classify ventilation and perfusion

in lungs.

To describe zone of perfusion in lungs

To describe ventilation perfusion ratio in lungs

To correlate VENTILATION and PERFUSION ratio with PULMONARY TUBERCULOSIS

OBJECTIVES

VENTILATIONThe rate at which air enters or leaves the lungs.

Types : i) Pulmonary Ventilation

ii) Alveolar Ventilation

1)Pulmonary Ventilation (minute ventilation or respiratory minute volume): Is the volume of air moving in and out of respiratory tract in a given unit of time during quiet breathing.

INTRODUCTION

Pulmonary Ventilation= Tidal volume X Respiratory Rate

= 500 ml x 12/minute

= 6000 ml/minute

2) Alveolar ventilation: It is the amount of air utilized for gaseous exchange every minute.

Alveolar ventilation

= (Tidal volume – Dead space) X Respiratory Rate

= ( 500 – 150 ) ml x 12/minute

= 4200ml/minute

TYPES OF VENTILATION.....

PERFUSION: The movement of blood into

the lungs through pulmonary capillaries.

VENTILATION/PERFUSION RATIO :

It is the ratio of alveolar ventilation and the amount of blood that perfuse the alveoli.

Mathematically, V/Q = 0.84

VENTILATION AND PERFUSION

ZONES OF LUNGS

Zone 1: No blood flow

Reason: More negative intrapleural pressure alveoli size↑ & lower arterial pressure due to gravity → decrease diameter of vessels

Zone 2: Intermittent blood flow

Reason: arterial pressure is greater than alveolar and venous pressure. Whereas, venules pressure are less than alveolar pressure venules are collapsed

Zone 3: Continuous blood flow

Reason: Due to gravity, there is high pressure → vasodilation → more blood flow

ZONE OF PERFUSION

Ventilation and Perfusion

(5ml/minute)

(0.56ml/minute)

(10.3ml/minute)

Zone 1: 1.92 L/minute

Reason: Increase size of alveoli

Zone 2: 4 L/minute

Reason: intermittent size of alveoli

Zone 3: 6.5 L/minute

Reason: Decrease size of alveoli

ZONE OF VENTILATION

It is the ratio of alveolar ventilation and the amount of blood that perfuse the alveoli.

Calculation:

V/Q= alveolar ventilation ÷ pulmonary blood flow

Alveolar ventilation= 4200ml/minute

Pulmonary blood flow=5000ml/minute

So, V/Q= 0.84

Ventilation/Perfusion (V/Q) Ratio

V/Q RATIO IN LUNGS

Zone 1: Ventilation(V) >>> Perfusion(Q)

V/Q= 3.4 (high)

Zone 2: Ventilation(V) = Perfusion(Q)

V/Q= 0.8 (average)

Zone 3: Perfusion(Q) >>> Ventilation(V)

V/Q=0.63(low)

V/Q IN DIFFERENT ZONES OF LUNGS

Apical Zone of lungs : It is more infected by

Pulmonary Tuberculosis

Reasons: i) There is low perfusion.

ii) There is higher V/Q , higher PO2 and lower PCO2

(M.tubercle is strict aerobes)

iii) Less of the oxygen is carried away by the blood in apex of lungs. ( Highest O2 available)

V/Q and PULMONARY TUBERCULOSIS

Zone 1: Ventilation(V) >>> Perfusion(Q)

V/Q= 3.4 (high)

Zone 2: Ventilation(V) = Perfusion(Q)

V/Q= 0.8 (average)

Zone 3: Perfusion(Q) >>> Ventilation(V)

V/Q=0.63(low)

Apex: It is more infected by Pulmonary Tuberculosis because

SUMMARY

Guyton and Hall ( 13th edition) Text Book of Medical

Physiology

K Sembulingam and Prema Sembulingam(6th

edition) Essentials of Medical Physiology

Ananthanarayan and Paniker’s( 9th edition)

Text Book of Microbiology

REFERENCES