4.1 Cardiac Anatomy & Physiology Refresher
Key Takeaways
- Cardiac Output (CO) equals Heart Rate (HR) multiplied by Stroke Volume (SV); a normal resting CO is roughly 4-8 L/min in healthy adults.
- Normal resting Ejection Fraction (EF) is 55-70%; an EF below 40% indicates systolic heart failure and changes exercise tolerance.
- Normal adult resting vitals: Heart Rate 60-100 bpm, Blood Pressure (BP) less than 120/80 mmHg, respiratory rate 12-20 breaths/min, oxygen saturation (SpO2) at or above 95% on room air.
- Karvonen formula uses Heart Rate Reserve (HRR) and resting HR for individualized target HR ranges; percent of HR maximum (HRmax) is a simpler estimate that ignores fitness level.
- The left anterior descending (LAD) coronary artery supplies most of the left ventricle, so LAD occlusion is the classic 'widow-maker' myocardial infarction (MI) pattern.
Why this matters for the NPTE-PTA
The Cardiovascular and Pulmonary Systems domain is 20-27 items, roughly 13% of the NPTE-PTA. Before you can answer monitoring or stop-exercise questions, you must be fluent with the basic plumbing of the heart, the cardiac cycle, and the equation that ties Heart Rate (HR) to Stroke Volume (SV).
Coronary Anatomy
The heart is fed by two main coronary arteries that branch off the aorta:
- Left main coronary artery splits into the Left Anterior Descending (LAD) and the Left Circumflex (LCx). The LAD supplies the anterior wall and most of the interventricular septum and is the most common site of large myocardial infarctions (MIs).
- Right coronary artery (RCA) typically supplies the right ventricle, inferior wall, sinoatrial (SA) node in most people, and atrioventricular (AV) node. Inferior wall MIs often involve the RCA and can produce bradycardia.
The Cardiac Cycle in One Pass
- Diastole - ventricles relax and fill (the longer phase at rest).
- Atrial kick - atria contract and top off ventricular filling.
- Isovolumetric contraction - all valves closed, pressure builds.
- Ventricular ejection - aortic and pulmonic valves open; blood leaves the heart.
- Isovolumetric relaxation - aortic/pulmonic valves close, then mitral/tricuspid valves open and diastole restarts.
Cardiac Output and Ejection Fraction
Cardiac Output (CO) = Heart Rate (HR) x Stroke Volume (SV). During exercise, HR rises first, then SV plateaus around 40-60% of max effort. If HR cannot rise (beta-blockers, sick sinus), CO climbs more slowly and the patient fatigues sooner.
Ejection Fraction (EF) = SV / End-Diastolic Volume. A normal EF is approximately 55-70%. Reduced EF categories:
| EF Range | Interpretation |
|---|---|
| 55-70% | Normal |
| 41-54% | Mildly reduced |
| 40% or less | Heart Failure with reduced EF (HFrEF) |
Normal Adult Resting Vital Signs
| Vital Sign | Typical Resting Range |
|---|---|
| Heart Rate | 60-100 beats per minute |
| Blood Pressure | less than 120/80 mmHg |
| Respiratory Rate | 12-20 breaths per minute |
| Oxygen Saturation (SpO2) | 95% or higher on room air |
| Oral Temperature | 97.0-99.0 F (36.1-37.2 C) |
Calculating a Training Heart Rate
Two methods show up on the NPTE-PTA:
Percent of HR Maximum (HRmax)
HRmax (approximate) = 220 - age. Target HR = HRmax x intensity percent. This ignores resting HR and conditioning level, so it overestimates intensity for deconditioned patients.
Karvonen (Heart Rate Reserve)
Heart Rate Reserve (HRR) = HRmax - Resting HR. Target HR = (HRR x intensity percent) + Resting HR.
Karvonen is preferred for cardiac rehabilitation because it builds the patient's resting HR into the prescription. Example: a 60-year-old patient (HRmax 160) with a resting HR of 80 prescribed 60% intensity has a target HR of (160 - 80) x 0.60 + 80 = 128 bpm. Using the simpler percent of HRmax method, 60% of 160 = 96 bpm - far too low to drive a conditioning response.
A PTA is prescribing a treadmill warm-up for a 70-year-old cardiac rehabilitation patient. Resting HR is 72 bpm and the supervising PT requests 50% Heart Rate Reserve using the Karvonen method. What target HR should the PTA use?
A patient with a recent inferior wall myocardial infarction is on a beta-blocker. During the first PTA-led ambulation, the patient's HR climbs only 4 bpm with effort. The PTA should: