(41C) Basic EKG Calculations
11-30-2019, 02:43 PM
Post: #1
 Eddie W. Shore Senior Member Posts: 1,015 Joined: Dec 2013
(41C) Basic EKG Calculations
Introduction

The program calculates the following:

* Lead II magnification, in mm
* The mean axis deviation
* The mean axis magnitude

Given:

* Lead I positive deflection, in mm
* Lead III negative deflection, in mm

The mean axis deviation and magnitude are calculated by a rectangular conversion by the following coordinates:

Y: Net Lead I deflection * 0.5774 + Net Lead III deflection * 1.1547
Mean axis deviation: θ - 57°

The program also:

* Converts between the heart rate (rpm) and the R-R interval
* Use either parameter to calculate the Q-T interval, in seconds

heart rate = 60/R-R
Q-T interval = √(R-R)*0.39

The program is a translation of HP 67/HP 97 Basic EKG Determination, which itself is a translation of Steven A. Conrad's HP-65 program (HP-65 Users' Library Program). See the source listed below.

Notes:

1. Clear the assignments of keys A (Σ+) through E (LN) before running the program. This must be done outside the programming environment. Clear assignments to keys by ASN (blank) (designated key).

Example: Clear assignment from A: [ shift ] (ASN) [ALPHA] [ALPHA] [ Σ+ ]

2. Running EKG will turn the User Keyboard on.

3. The program will set the calculator to degrees mode.

4. This program was entered on an HP 41C, and it should work on any simulator and Swiss Micros DM41.

Instructions:

1. Run EKG.

2. Determine Lead I net deviation and store it to register 01:
(in User's Mode) positive deviation Lead I [ENTER] negative deviation Lead I ( A )

3. Determine Lead II net deviation, storing net Lead III net deviation to register 03 and Lead II net deviation to register 02:
(in User's Mode) positive deviation Lead III [ENTER] negative deviation Lead III ( B )

4. Compute Mean Axis:
(in User's Mode) ( C ) deviation is displayed [ R/S ] magnitude is displayed

5a. Convert heart rate to R-R:
(in User's Mode) heart rate (bpm) ( D )
-or-
5b. Convert R-R to heart rate:
(in User's Mode) R-R ( D )

6. Compute Q-T.
(in User's Mode) ( E )

HP 41C/DM41 Program: EKG
Code:
 01 LBL T^EKG 02 SF 27 03 GTO 00 04 LBL A 05 -  06 STO 01 07 ^T III:_  08 ARCL X 09 AVIEW 10 RTN 11 LBL B 12 - 13 STO 03 14 RCL 01 15 + 16 STO 02 17 ^T II:_  18 ARCL X 19 AVIEW 20 RTN 21 LBL C 22 RCL 01 23 ENTER↑ 24 0.5774 25 * 26 RCL 03 27 ENTER↑ 28 1.1547 29 * 30 + 31 ENTER↑ 32 RCL 01 33 R-P 34 X<>Y 35 57 36 - 37 ^T DEV= 38 ARCL X 39 AVIEW  40 STOP 41 X<>Y 42 ABS 43 ^T MAG= 44 ARCL X 45 AVIEW 46 RTN 47 LBL D 48 ENTER↑ 49 ENTER↑ 50 60 51 X<>Y 52 / 53 X<=Y? 54 GTO 05 55 ^T RATE= 56 ARCL X 57 AVIEW 58 RTN 59 LBL 05 60 ^T R-R= 61 ARCL X 62 AVIEW 63 RTN 64 LBL E 65 X>Y? 66 X<>Y 67 SQRT 68 0.39 69 * 70 ^T Q-T= 71 ARCL X 72 AVIEW  73 RTN 74 LBL 00 75 RTN 76 END

Example

I+ = 2.8 mm, I- = 1.1 mm
III+ = 2.5 mm, III- = 1.4 mm
Heart Rate = 86 bpm

Keystrokes:

XEQ "EKG"
(User Mode is On)
2.8 [ENTER] 1.1 ( A )
Display: III: 1.7000

2.5 [ENTER] 1.4 ( B )
Display: II: 2.8000

( C )
Display: DEV=-4.0516
[ R/S ]
Display: MAG=2.8214

86 (D)
Display: R-R=0.6977

(E)
Display: Q-T=0.3258

Source:

"Basic EKG Determinations" HP-67/97 User's Library Solutions: Cardiac. Hewlett Packard. Corvallis, OR. (no date given, but I estimate this to be circa 1974)