Medical Physiology Lecture #35: Respiratory Lecture #1: Pulmonary Pressures

Flashcards created from the lecture notes covering key concepts about the respiratory system and pulmonary pressures.

What is external respiration? [L35]

The overarching process of moving gases (O2 into, CO2 out of) between the external environment and body's cells.

What is pulmonary ventilation? [L35]

The act of moving fresh atmospheric air into the lungs and expelling CO2-rich air out, commonly called breathing.

What is gas exchange in the lungs? [L35]

Diffusion of O2 from alveoli into pulmonary capillaries and CO2 from capillaries into alveoli.

What is gas transport? [L35]

The movement of O2 in blood from lungs to tissues, and CO2 in blood from tissues to lungs.

What is internal respiration? [L35]

The process of gas exchange between blood in systemic capillaries and the body's cells (O2 to cells, CO2 from cells).

Major function of the respiratory system? [L35]

Facilitate gas exchange (O2 and CO2) between the body and external atmosphere.

What are the two major zones of the respiratory system? [L35]

The conducting zone and the respiratory zone.

Function of the conducting zone? [L35]

Transports air to and from the lungs, warms, humidifies, and filters inhaled air.

Components of the conducting zone? [L35]

Nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles.

Function of the respiratory zone? [L35]

The primary site for gas exchange (O2 and CO2) between air and blood.

Components of the respiratory zone? [L35]

Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

What are Type I alveolar cells? [L35]

Squamous epithelial cells forming 95% of alveolar surface, thin for efficient gas diffusion.

What are Type II alveolar cells (pneumocytes)? [L35]

Cuboidal epithelial cells that produce and secrete pulmonary surfactant.

What is surfactant? [L37]

A mixture of phospholipids (primarily DPPC) and lipoproteins that reduces surface tension in alveoli.

What is the function of surfactant? [L37]

Lowers surface tension, increases lung compliance, and prevents alveolar collapse, especially of smaller alveoli.

What are alveolar macrophages? [L35]

Phagocytic cells that remove dust and debris from alveolar surfaces, protecting the lungs.

What is the respiratory membrane? [L35]

The thin barrier for gas exchange, composed of alveolar epithelium, fused basement membranes, and capillary endothelium.

Why is the respiratory membrane thin? [L35]

To maximize the rate of gas diffusion across the alveolar-capillary barrier according to Fick's Law.

What is the diaphragm? [L36]

The primary muscle of inspiration, a dome-shaped skeletal muscle that contracts to expand the chest cavity.

What nerve innervates the diaphragm? [L36]

The phrenic nerve (C3, C4, C5 keep the diaphragm alive!).

Is quiet inspiration active or passive? [L36]

It's an active process involving the contraction of the diaphragm and external intercostal muscles.

Is quiet expiration active or passive? [L36]

It's a passive process driven by the elastic recoil of the lungs and chest wall after inspiratory muscle relaxation.

Muscles involved in forced inspiration? [L36]

Accessory muscles like the sternocleidomastoids, scalenes, and pectoralis minor activate to further expand the chest.

Muscles involved in forced expiration? [L36]

Internal intercostals and abdominal muscles contract to forcefully ↓ chest volume and expel air.

How do external intercostals aid inspiration? [L36]

Their contraction pulls the ribs upward and outward, increasing the anterior-posterior and lateral dimensions of the chest.

What is atmospheric pressure (P*atm)? [L36]

The pressure of the air surrounding the body, usually set as 0 mmHg or 0 cm H_2O for respiratory calculations.

What is alveolar pressure (P*alv)? [L36]

The pressure within the alveoli of the lungs, which changes with breathing phases.

What is intrapleural pressure (P*ip)? [L36]

The pressure within the pleural space (between visceral and parietal pleura), always negative relative to P*atm.

Normal intrapleural pressure at rest (FRC)? [L36]

Approximately -5 cm H_2O, maintaining lung expansion against chest wall recoil.

What is transpulmonary pressure (Ptp)? [L36]

The pressure difference between alveolar and intrapleural pressure (P{alv} - P{ip}), representing lung distending pressure.

Why is Ptp always positive? [L36]

Because Palv is always > Pip, preventing lung collapse and holding alveoli open.

How do pressures change during inspiration? [L36]

Diaphragm contracts ↓ Pip to -8 cm H_2O, pulling lungs open, so Palv drops below 0, causing air to flow in.

How do pressures change during expiration? [L36]

Diaphragm relaxes ↑ Pip back to -5 cm H_2O, elastic recoil ↑ Palv above 0, causing air to flow out.

What is airway resistance (R*aw)? [L38]

The opposition to airflow in the respiratory tract, primarily determined by airway radius.

Poiseuille's Law applied to airways? [L38]

Resistance (R) is inversely proportional to the radius to the fourth power (R \propto 1/r^4).

Where is airway resistance highest? [L38]

In the medium-sized bronchi (4th-7th generations), not the tiny bronchioles due to their vast number.

What is laminar flow? [L38]

Smooth, parallel airflow that occurs at lower velocities and in smaller airways, efficient.

What is turbulent flow? [L38]

Chaotic, swirling airflow occurring at higher velocities (e.g., trachea) or in diseased airways; generates breath sounds.

What is Reynolds number (Re)? [L38]

A dimensionless quantity that predicts whether flow is laminar (Re < 2000) or turbulent (Re > 2000).

What is tidal volume (TV)? [L37]

The volume of air inhaled and exhaled during a single normal, quiet breath (~500 mL).

What is inspiratory reserve volume (IRV)? [L37]

The maximum additional volume of air that can be inhaled beyond a normal tidal inspiration.

What is expiratory reserve volume (ERV)? [L37]

The maximum additional volume of air that can be forcibly exhaled after a normal tidal expiration.

What is residual volume (RV)? [L37]

The volume of air remaining in the lungs after a maximal forced expiration, preventing alveolar collapse.

What is inspiratory capacity (IC)? [L37]

The maximum volume of air that can be inspired after a normal tidal expiration (IC = TV + IRV).

What is vital capacity (VC)? [L37]

The maximum volume of air that can be exchanged in a single respiratory cycle, from maximal inspiration to maximal expiration (VC = TV + IRV + ERV).

What is functional residual capacity (FRC)? [L37]

The volume of air remaining in the lungs after a normal, quiet expiration (FRC = ERV + RV).

Why is FRC important? [L37]

It minimizes fluctuations in alveolar gas concentrations (PO2, PCO2) during respiration, stabilizing gas exchange.

What is total lung capacity (TLC)? [L37]

The total volume of air in the lungs after a maximal inspiration (TLC = VC + RV).

Which lung volumes/capacities ↑ in obstructive disease? [L38]

RV, FRC, and TLC increase due to air trapping caused by increased airway resistance.

Which lung volumes/capacities ↓ in restrictive disease? [L38]

All lung volumes and capacities (TV, IRV, ERV, RV, VC, FRC, TLC) decrease due to reduced lung expansion.

What is spirometry used for? [L37]

To measure lung volumes and capacities and detect obstructive or restrictive pulmonary diseases.

What is FEV1? [L37]

Forced Expiratory Volume in 1 second; the volume of air exhaled in the first second during a forced exhalation.

What is FVC? [L37]

Forced Vital Capacity; the total volume of air that can be forcibly exhaled after a maximal inspiration.

What does a low FEV1/FVC ratio indicate? [L37]

An obstructive pulmonary disorder, where airflow out of the lungs is impeded (e.g., asthma, COPD).

What does a low FVC with a normal or high FEV1/FVC ratio indicate? [L37]

A restrictive pulmonary disorder, where lung volumes are reduced (e.g., pulmonary fibrosis).

What diseases show an increased RV/TLC ratio? [L38]

Obstructive diseases like severe emphysema or asthma, reflecting significant air trapping.

What is anatomical dead space? [L37]

The volume of air in the conducting airways (trachea, bronchi) that does not participate in gas exchange (~150 mL).

What is alveolar dead space? [L37]

The volume of alveoli that are ventilated but not perfused (no blood flow) for gas exchange.

What is physiological dead space? [L37]

The sum of anatomical dead space and alveolar dead space, representing total wasted ventilation.

How is physiological dead space calculated? [L37]

Using the Bohr equation: VD = VT \times \frac{(PaCO2 - PeCO2)}{PaCO2} (where PeCO2 is mixed expired CO2).

What is minute ventilation (V̇E)? [L37]

The total volume of air inhaled or exhaled per minute (V_E = Tidal Volume \times Respiratory Rate).

What is alveolar ventilation (V̇A)? [L37]

The volume of fresh air that reaches the alveoli and participates in gas exchange per minute (VA = (TV - VD) \times RR).

Why is alveolar ventilation more critical than minute ventilation? [L37]

It directly reflects the effectiveness of gas exchange by accounting for air that reaches respiratory surfaces.

How does deep breathing improve alveolar ventilation? [L37]

It increases the TV relative to the fixed dead space, allowing a greater proportion of inhaled air to reach the alveoli.

What is lung compliance (C*L)? [L37]

A measure of the lung's distensibility or stretchability; C_L = \frac{\Delta V}{\Delta P}, where \Delta P is transpulmonary pressure.

Factors that increase lung compliance? [L37]

Emphysema (due to loss of elastic tissue) and adequate surfactant (↓ surface tension).

Factors that decrease lung compliance? [L37]

Pulmonary fibrosis, inadequate surfactant (neonatal RDS), pulmonary edema, and acute respiratory distress syndrome (ARDS).

How does surface tension affect lung compliance? [L37]

High surface tension in the alveoli (as in water) significantly ↓ compliance, making lungs harder to inflate.

Compliance curves: Saline-filled vs. Air-filled lungs? [L37]

Saline-filled lungs have much higher compliance because they eliminate the air-water interface and its surface tension.

What is elastic recoil? [L38]

The inherent tendency of elastic structures (like lungs) to return to their original unstretched shape after being distended.

What provides the elastic recoil of the lungs? [L38]

Elastin and collagen fibers in lung parenchyma, and the surface tension of the alveolar fluid lining.

How does elastic recoil contribute to expiration? [L38]

It provides the passive driving force to expel air during quiet expiration as inspiratory muscles relax.

How does emphysema affect elastic recoil? [L38]

Destruction of elastic fibers ↓ elastic recoil, leading to hyperinflation and difficulty expelling air.

How does fibrosis affect elastic recoil? [L38]

↑ deposition of fibrous tissue ↑ elastic recoil, making the lungs stiff and difficult to inflate (↓ compliance).

How do obstructive pulmonary diseases affect lung mechanics? [L38]

↑ airway resistance, causing air trapping, ↑ RV/FRC/TLC, ↓ FEV1/FVC ratio.

How do restrictive pulmonary diseases affect lung mechanics? [L38]

↓ lung compliance and ↓ all lung volumes/capacities (TLC, FVC), with a normal or ↑ FEV1/FVC ratio.

Typical flow-volume loop in obstructive disease? [L38]

A 'scooped-out' expiratory limb, very low peak expiratory flow rate, and ↑ residual volume.

Typical flow-volume loop in restrictive disease? [L38]

A smaller loop overall (reduced volumes), but relatively normal or even increased expiratory flow rates for the given lung volume.

What is the pulmonary circulation? [L39]

A low-pressure, high-flow system that carries deoxygenated blood from the right ventricle to the lungs for gas exchange.

How do recruitment and distension affect pulmonary vascular resistance? [L39]

They both ↓ pulmonary vascular resistance by opening previously closed capillaries (recruitment) and widening existing ones (distension).

Why is pulmonary vascular resistance low? [L39]

Due to a large number of parallel vessels and their ability to recruit and distend in response to ↑ flow.

What is hypoxic pulmonary vasoconstriction? [L39]

Constriction of pulmonary arterioles in areas of low alveolar PO2, diverting blood to better-ventilated regions; unique to pulmonary circulation.

West's Lung Zone 1 pressure relationship? [L39]

PA > Pa > P_v (Alveolar pressure > arterial > venous), leading to no blood flow (physiological dead space).

West's Lung Zone 2 pressure relationship? [L39]

Pa > PA > Pv (Arterial > alveolar > venous), flow is intermittent and driven by Pa - P_A, behaving like a waterfall.

West's Lung Zone 3 pressure relationship? [L39]

Pa > Pv > PA (Arterial > venous > alveolar), continuous flow driven by Pa - P_v, as in systemic circulation.

Which lung zone has the highest blood flow? [L39]

Zone 3 (base of the lungs) due to gravity's effect on hydrostatic pressure, leading to higher perfusion.

Bronchial vs. Pulmonary circulation: functional difference? [L39]

Bronchial circulation supplies oxygenated blood to lung tissue itself, while pulmonary circulation is for gas exchange.

What is V/Q ratio? [L39]

The ratio of alveolar ventilation (V_A) to pulmonary blood flow (Q), indicating matching of air and blood flow.

Normal V/Q ratio? [L39]

Approximately 0.8–1.0 in a healthy, young individual for the overall lung.

V/Q ratio at apex vs base of lung? [L39]

Apex: High V/Q (more V than Q, ~3.0). Base: Low V/Q (more Q than V, ~0.6).

Effect of a low V/Q ratio on PAO2 and PACO2? [L39]

PAO2 ↓ (as if shunting), PACO2 ↑ (as if hypoventilating).

Effect of a high V/Q ratio on PAO2 and PACO2? [L39]

PAO2 ↑ (as if hyperventilating), PACO2 ↓ (as if dead space).

What causes a V/Q ratio of 0 (zero)? [L39]

A true physiological shunt, where there is perfusion but no ventilation (e.g., collapsed alveolus).

What causes an infinite V/Q ratio? [L39]

Alveolar dead space, where there is ventilation but no perfusion (e.g., pulmonary embolism).

Boyle's Law states? [L39]

At a constant temperature, the pressure of a gas is inversely proportional to its volume (P1V1 = P2V2).

Application of Boyle's Law to breathing? [L39]

↑ thoracic volume results in ↓ Palv, causing air to flow in; ↓ thoracic volume ↑ Palv, forcing air out.

Dalton's Law states? [L39]

The total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the individual gases.

Application of Dalton's Law? [L39]

Allows calculation of partial pressures of O2 (PO2), CO2 (PCO2) etc. in atmospheric or alveolar air.

Henry's Law states? [L39]

The amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid.

Application of Henry's Law? [L39]

Determines how O2 and CO2 dissolve in blood plasma and equilibrate across the alveolar-capillary membrane.