CCP Exam Two (Part 2

What is the distending pressure (DP) and of a liquid bubble and what influences it via Laplace’s Law

-DP is how much pressure can keep this bubble open

- DP is influenced by Surface tension = directly proportional (As ST increases so does DP)

-DP is influenced by Size of the bubble= inversely proportional (As the radius increases DP decreases)

Laplace's Law assumption regarding surfactant

Assumes surfactant is NOT present (only working with the liquid-gas interface because babies have no surfactant)

Laplace's Law formula

P = 4 × ST / r

Effect of surface tension (ST) on distending pressure

Directly proportional; As surface tension increases it's harder to distend the bubble because the liquid molecules are attracted to each other due to surfactant, so the distending pressure is increased

Effect of bubble radius on distending pressure (DP)

Inversely proportional; When the radius of a bubble increases it's easier to distend the bubble and keep it open so distending pressure decreases

Behavior of two connected, different-sized bubbles with the same ST during Laplace's Law

The smaller bubble empties into the larger bubble due to the smaller bubble having greater pressure (gas going from high to low)

Does surface tension vary with bubble size in Laplace's Law?

No; ST and radius are independent until the bubble reaches its elastic limit.

Surface tension relation to bubble size

Surface tension remains constant until the bubble exceeds its natural elastic limit and ruptures.

When does Laplace's law apply?

Only after critical opening points are reached, requiring high pressure with little volume change.

Critical Opening Point (COP) analogy

Similar to the initial pressure required to pop open a new balloon.

Bubble behavior before the Critical Opening Point

A slight increase in distending pressure yields a very very very small increase in radius.

Bubble behavior after the Critical Opening Point

Radius and distending pressure are inverse; distending pressure decreases as radius increases.

Alveolar fluid and Laplace's Law

According to Laplace's law, a high Ptp (due to alveolar fluid) must be generated to keep the small alveoli open ths offset by the pulmonary surfactant (Surfactant changes the relationship)

Pulmonary Surfactant Composition

Phospholipid (DPPC) produced by Type II cells.

Structure of Pulmonary Surfactant

Has a hydrophobic end (dislikes gas phase) and a hydrophilic end (likes liquid phase).

Surfactant and Surface Tension (ST) Ratio

ST decreases in proportion to the ratio of surfactant to alveolar surface area (Large alveolus/radius = high ST = High COP) (Small alveolus/ radius = low ST = Low COP)

Surface Tension Range of Alveoli

1-5 dynes/cm in small alveoli up to 50 dynes/cm when fully distended.

Alveoli Without Surfactant

ST reaches 50 dynes/cm, requiring a high distending pressure to overcome.

Atelectasis and Critical Opening Pressure

If distending P is below critical opening = Liquid walls of the alveolus come in contact and get stuck together and start resisting re-expansion = atelectasis and at this point our COP would become really, really high to pop them apart and reopen the alveoli

Dynamic Lung Mechanics

-Study of forces in action

-Gas movement in/out of lungs

-Required pressure changes to move gas

Dynamic Lung Mechanics explained by

Poiseuille's Law and the Airway resistance equation.

Poiseuille's Law during inspiration

Ppl decreases, thoracic volume increases, bronchial airways lengthen and passively dilate.

Poiseuille's Law during expiration

Ppl increases, thoracic volume decreases, and bronchial airways decrease in diameter.

Poiseuille's Law during abnormal situations

Changes in bronchial gas flow and Ppl that alter normal gas flow.

Poiseuille's Law Formula for flow

°V = ΔPr⁴TT / 8lŋ

(ŋ)

Viscosity of gas or fluid

(ΔP)

Change in P

(l)

Length of the tube

(°V)

Gas flowing through the tube (flow)

Constants in Poiseuille's Law

TT/8

Factors increasing gas flow

Flow will increase if P and radius increase

Factors decreasing gas flow via Poisuelles’s law

Flow will decrease if viscosity and length are increased

Effect of radius decrease on flow via Poiseuille's law

If P is constant and r is decreased by half, flow decreases to 1/16th of initial flow

Poiseuille's Law for Pressure Formula

P = °V 8lŋ /r4 TT

Pressure Proportionality regarding Poisueilles’s Law for Pressure

P is directly proportional to flow, length and viscosity of the gas

Effect of Tube Radius on Pressure

P decreases in response to increased tube radius (resistance decreases by x16 when flow decreases by ½)

Airway Resistance (Raw)

Pressure difference between the mouth and the alveoli (Pta) created by the airways.

Airway Resistance (Raw) Formula

Raw = P (cmH2O) / °V (flow) (L/sec)

Normal Airway Resistance (Raw)

0.5-2.5 cm H2O/L/Sec

Laminar Flow

Streamlined gas movement parallel to tube sides at low flow rates and low P gradients, decreasing Raw.

Turbulent Flow

Random gas movement and collisions at high flow rates and high P gradients, increasing Raw.

Time Constants

Product of Raw and CL

Time constants show

How long it takes to inflate a lung region to 60% of its potential filling capacity

High Raw and High CL

Require more time to inflate (Long Time Constant)

Time Constant Formula

TC(sec) = (change in P/flow) Raw x (V/P) CL

Time Constant Relationships

Raw & CL increase = Longer TC

Dynamic Compliance (CL(dyn))

-When resistance is at play

-A product of time constants (TC are a product of r & CL)

CL(dyn) is measured

during a period of gas flow

Dynamic vs. Static Compliance in Healthy Lungs

In the healthy lung, the CL(dyn) is equal to CL(stat).

Dynamic Compliance in Obstructed Airways

The CL(dyn)/CL(stat) ratio falls at high respiratory rates because alveoli are far from the obstruction.

Resistance and Dynamic Compliance

As resistance increases, it gives us a longer time constant which decreases our dynamic compliance.

Tidal Volume (VT)

Volume of air that moves in and out of the lungs in one quiet breath. Normal: 7-9 mL/kg.

Ventilator Rate (RR)

Normal is approximately 15 bpm, with a range of 12-20 bpm.

Inspiratory to Expiratory Ratio (I:E)

Normally 1:2 (1: inspiration + 1: expiration, 1 pause).

Minute Ventilation (MV)

Calculated as RR × VT.

Total Cycle Time (TCT)

Time it takes to inspire and expire. Formula: 60 (1 minute) / RR.

Alveolar Ventilation

Inspired air that reaches the alveoli for gas exchange.

Deadspace Ventilation

Inspired gas that does not reach the alveoli

Types of Dead Space

Anatomic, Alveolar, and Physiologic.

Anatomic Dead Space

Volume of gas in conducting airways. Normal: 1 mL/lb (2.2 mL/kg) or 150 mL.

Alveolar Ventilation (VA) Formula

VA = (VT - VD)

Alveolar Minute Ventilation Formula

Total VA = VA x RR

VD formula

Dead space volume × Respiratory Rate

Total Minute Ventilation (Total MV)

Alveolar ventilation (VA) + Dead space ventilation (VD)

Alveolar dead space

Ventilation with no perfusion due to a capillary or circulation issue.

Physiologic dead space

Sum of anatomic dead space and alveolar dead space.

Individual in upright position apices pressure

Ppl at the apices is -7 to -10 cmH2O

Individual in upright position alveoli

Alveoli in the upper regions are expanded (almost total filling capacity) more than alveoli at the bases

-more distention at the apices

Individual in upright position bases Ppl

Ppl at the bases is -2 to -3 cmH2O

Blood flow at the lung bases

More blood flow at the bases = heavier = more P for support = gravity-dependent

Compliance at apices vs. bases

Alveoli at the apices have lower compliance than the alveoli at the bases

Lung Ventilation efficiency

Ventilation is much greater and more effective in the lower lung regions

Normal Tidal Volume (VT)

500 ml

Compliance (CL) and Airway Resistance (Raw) vs. VT

Directly proportional to VT

Compliance (CL) and Airway Resistance (Raw) vs. RR

Inversely proportional to RR

Effect of Increased RR on Time Constant (TC)

Shorter TC

Effect of Increased Raw on Time Constant (TC)

Longer TC

Apnea

Complete absence of spontaneous ventilation

Eupnea

Normal, spontaneous breathing

Biot Respirations

Rapid deep inspirations followed by 10-30 seconds of apnea (seen in Meningitis)

Hyperpnea

Increased depth of breathing with or without increased RR

Hyperventilation

Increased alveolar ventilation (VA) via increased RR or VT

Hypoventilation

Decreased alveolar ventilation (VA) via decreased RR or VT

Tachypnea

Increased respiratory rate (RR)

Cheyne-Stokes Respiration

Gradual increase in volume and rate followed by gradual decrease and 10-30 seconds of apnea (seen in cerebral disorders)

Kussmaul Breathing

Increased depth and rate of breathing (seen in Diabetic Ketoacidosis)

Orthopnea

Ability to breathe most comfortably in an upright position

Dyspnea

Difficulty in breathing