Info Dump on Quantifying the Pulse Change
1. Baseline Circulation
Normal brachial artery flow: ~100 mL/min per 100g of tissue at rest.
Radial pulse amplitude (palpable strength): Directly linked to systolic blood pressure and local vascular resistance.
2. What Happens When You Clamp Your Armpit
Muscle contraction (pectoralis, biceps) increases intravascular resistance.
Resistance roughly follows Poiseuilleβs Law where r is vessel radius:
A strong contraction may reduce vessel diameter 10β20% in the brachial region, increasing resistance downstream.
3. Pressure & Flow Impact
For a healthy adult at rest:
Systolic BP: ~120 mmHg Radial pulse pressure (difference between systolic & diastolic): ~40 mmHg
With compression:
Vessel narrowing (20%) β Resistance increases ~1.5Γ (due to r^4). Flow to the forearm drops β30β40%. Pulse amplitude drop at wrist: Palpable intensity may reduce by ~30β50%, depending on muscle strength and how completely you occlude.
4. Heart Rate Influence
If youβre also doing a Valsalva manoeuvre (holding breath & tensing), you can:
Increase thoracic pressure β transiently reduce venous return Drop stroke volume β weaker pulse (again, temporary)
This can make your radial pulse feel both faint and slightly erratic for 5β10 seconds.
So How Detectable Is This?
To an inexperienced examiner: Might think your pulse is weak or momentarily absent. To a trained clinician: Theyβd move to carotid or brachial pulse and find you out instantly. (But John couldn't since the 'pedestrians' pulled him away) ECG machine: *laughs*
