Physiology

Valve Pathophysiology¶

Lesion	HR	Rhythm	Preload	Afterload	Contractility	Avoid
AS	60-80	NSR essential	Maintain	Maintain	Support	Tachycardia, hypotension, vasodilators
AR	80-100	NSR preferred	Maintain	Reduce	Support	Bradycardia, high SVR
MS	60-80	NSR essential	Maintain	Maintain	Preserve	Tachycardia, AF with fast rate
MR	80-100	NSR preferred	Maintain	Reduce	Support	Bradycardia, high SVR
TR	80-100	NSR preferred	RV preload	Reduce PVR	Support RV	Hypoxia, hypercarbia, N2O

Stenosis = Slow and Full — fixed orifice needs time and pressure

Regurgitation = Faster and Forward — faster HR reduces regurgitant fraction, lower afterload promotes forward flow

CVSpecificMonitors¶

PA Catheter¶

CVP¶

Loss of a Wave:
A fib or V pacing without atrial contraction
Large a Wave:
Atria emptying against high resistance
Tricuspid stenosis, diastolic dysfx, ischemic heart, RVH, AV dissociation, junctional, V paced, PVC
Large v Wave:
Tricuspid regurg

When PAOP Does NOT Predict LVEDV¶

Overestimates
Impaired LV compliance ie. ischemia
Mitral valve disease
Left to right cardiac shunt
Tachycardia
PPV
PEEP
COPD
Pulmonary hypertension
Non west zone III placement of PAC
Underestimates
Aortic insufficiency

SVO2 Interpretation¶

\[ SvO_2 = {SaO_2} - {VO_2 \over 1.38 * 10 * CO * Hgb} \]

flowchart 

    A[SVO2] --> C[High > 80]
    A[SVO2] --> D[Low  < 60]
    A[SVO2] --> B[Normal 60-80]
    C --> E[Anesthesia, Acidosis, Toxins]
    D --> F[SaO2]
    F --> G[Normal]
    F --> H[Dec SaO2]
    H --> I[Inc FiO2 and/or PEEP]
    G --> J[Cardiac Output]
    J --> K[CI < 2]
    J --> L[CI > 2]
    K --> M[SVV or similar]
    M --> N[Low < 10]
    M --> U[High > 10]
    U --> V[Give Fluids]
    N --> O[Inotropes]
    L --> P[Hgb]
    P --> Q[Low < 8]
    Q --> R[Blood]
    P --> S[Normal > 8]
    S --> T[Analgesia vs Sedation]

Systemic Vascular Resistance SVR¶

\[ SVR = {MAP- CVP \over CO }{(80)} \]

Cardiac and Respiratory¶

Starling Curve!¶

Ficks Law of Diffusion¶

Blood to organ can be calculated using a marker substance if the amount of marker uptake per time, concentration venous and arterial of marker are known.

\[ CO = {\dot VO_2 \over Ca - Cv} = {(125ml/min) * (BSA) \over CaO_2 - CvO_2} \]

\[ Oxygen Carrying Capacity = CaO_2 = {(Hgb * SaO_2 * 1.34) + (PaO_2 * 0.003)} \]

Law of Laplace¶

Arteries and AAA¶

The assumption is that the structure described is cylindrical.

\[ Wall Tension (Cylinder) = {Pressure * Radius \over Wall Thickness} \]

Left Ventricle and Alveoli¶

The assumption is that the structure described is spherical. Surfactant does help to lower the surface tension in the alveoli.

\[ Wall Tension (Sphere) = {Pressure * Radius \over 2 * Wall Thickness} \]

Poiseuille's Law for Flow or Resistance¶

The original law was presented for flow through a cylinder. If the equation is rearranged it represents resistance through that cylinder. Both are described below.

Flow¶

\[ Q = {\pi r^4 \over 8L\eta }{(\Delta P)} \]

Resistance¶

\[ R = {8L\eta \over \pi r^4 }{(\Delta P)} \]

Subclavian Steal¶

EKG¶

EKG Basics¶

For a great video lecture series about 2.75 hrs long check out EKG interpretation Video Lectures

The Rule of Fours¶

Four Initial Features¶

History and Clinical Picture¶

Clinical picture is arguabley the most important part. History taking is also important but clinical features can be quite informative.

Rate¶

Normal 60-100. Not too fast or too slow!

Rhythm¶

Hopefully sinus...but it can be anything! How do you know? First it's a good idea to know some rhythms and then work through the EKG in an organized manner. You already have the rate so it's fast, slow, or normal. Next:

Regular or irregular R-R
P wave with every QRS
QRS with every P
PR interval
QRS Interval
Ectopy
Identify!

Axis¶

Normal axis is -30 to + 90.

Axis Deviation In Depth¶

Check out Life In The Fast Lane for tons of EKG knowledge and examples!

For an in depth analysis of axis deviation check out EKG Axis Interpretation

Ever wonder how the axis is calculated? You use the axis circle and draw vectors. These vectors are summed using the x intercept and the intersection point on the circle. This new vector is the axis deviation! For a thorough explanation and more examples check out Super Axis Man SAM

Four Waves¶

P¶

Check out lead II for the best P wave morphology!

QRS¶

Look in all leads for the presence of Q waves. Also note the QRS amplitude and R wave progression in leads V1-V6.

T¶

Look in all leads for the presence of T waves. Be sure to note any inverstion, flattening, and the concordance vs discordance with the QURS complex.

U¶

Are the U waves present or not?

Four Intervals¶

PR¶

Normal is 0.12-0.2 seconds or 3-5 little squares. Longer means a first degree heart block, but shorter can be mean WPW, junctional rhythms, and some syndromes.

QRS¶

Normal is 0.12seconds or less or less than 3 little squares. Widened QRS indicates a conduction defect or delay.

ST¶

This can be the most important thing at which to look!

QT¶

Easiest to use the EKG machine measurements and ensure it is not prolonged! ( QT > 450)