**HP 41C and DM41L: 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:

X: Lead I positive deflection - Lead I negative deflection

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 )

Result: Lead II net deviation

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**

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)

Eddie

All original content copyright, © 2011-2019. Edward Shore. Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited. This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.