PULMONARY PHYSIOLOGY

Gary L. Weinstein M.D.

Director of Pulmonary and Critical Care Medicine

Presbyterian Hospital of Dallas

Physiology for Dummies

“Good Air In, Bad Air Out”

Physiology for Psychologists

Take Slow, Deep, “Cleansing” Breaths

Physiology for Internists

• Remember (review ?) your little orange book from 1st year med school on Respiratory Physiology by Dr. West

• You MUST understand normal physiology to understand abnormal physiology

• You may BORROW my tape on normal lung sounds (especially if you have insomnia)

Physiology

• The respiratory system is composed of – the conducting airways (nose, mouth, larynx,

trachea, bronchial tree)– the lungs (terminal bronchioles, alveoli)– the parts of the CNS concerned with control of

the system (pons, medulla, cortex, Vagus…)– the chest wall (muscles of respiration, rib cage)

Physiology

• Functions of the respiratory system include– O2 extraction from the external environment– CO2 elimination from the body– maintenance of acid-base balance (along with

other TRIVIAL organs)– phonation– defense from the outside world– metabolism (e.g. ACE I ACE II)

Physiology

Physiology

Physiology

• Defense: each day about 10,000 liters of air is inspired along with dust, pollen, ash, microorgansims, toxic gases, particulates…

• Jobs include– air conditioning - by the time air reaches the

alveoli, it is at body temp and 100 % humidified– olfaction - a shallow sniff bring air to the nose

but not to the lung allowing “retreat”

Physiology• Jobs (cont’d)

– filtration• nasal hairs trap 10 - 15 um particles

• in addition, particles > 10 um impact onto the septum and turbinates as well as the nasopharynx

• tonsils and adenoids provide immunologic defense against biologically active materials

• particles 2 - 5 um sediment via gravity in the smaller airways and become trapped in the mucous that lines the airways, then are transported up and out

• particles 0.1- 0.5 um mainly stay suspended as aerosols and about 80 % of them are exhaled

Physiology

Physiology

Physiology

Physiology

Physiology

Physiology

Physiology

Control of Ventilation

Central Controller

Pons, medulla, ...

Input output

Sensors Effectors

Chemoreceptors, Respiratory muscles

lung and other receptors

Physiology

Physiology

• Lung and other receptors1) pulmonary stretch receptors

– lie within the airway smooth muscle

– impulses travel in the vagus nerve

– result in a slowing of respiratory rate

2) irritant receptors

– lie between airway epithelial cells

– stimulated by noxious gases, cigarette smoke, inhaled dusts and cold air

– impulses travel up the vagus and the reflex effects include bronchoconstriction and hyperpnea

Physiology

3) J receptors (juxta-capillary)– impulses pass up the Vagus and result in rapid,

shallow breathing– may play a role in the dyspnea a/w left heart

failure and ILD

4) Nose and upper airway receptors– respond to mechanical and chemical stimulation

with sneezing, coughing and bronchoconstriction

Physiology

• 5) Joint and muscle receptors– Impulses from moving limbs are believed to be

part of the stimulus to ventilation during exercise

Physiology• Fun Facts

– Alveolar surface area is 50-100 square meters– There are approx. 300 million alveoli, each 1/3

mm in diameter– The blood-gas interface is approx. 0.5 microns– O2 and CO2 move by simple diffusion– Anatomic dead space is approx. 1 ml/lb. body wt– Each RBC spends about 1 sec in the capillary

network and transverses 2 - 3 alveoli– Surfactant, made by type II pneumocytes,

dramatically lowers alveolar surface tension