Tuesday, March 24, 2009

Reflex bradycardia



Reflex bradychardia is an abnormal bradycardia (decrease in body pulse rate) in response to certain stimuli.[1]

Blood Pressure (BP)is determined by cardiac output (Q) times total peripheral resistance (TPR); the formula would be BP= Q x TPR. An increase in either cardiac output or total periferal resistance (or both), will increase blood pressure. The increased blood pressure is sensed by baroreceptors. In order to maintain homeostasis, the baroreceptors signal the parasympathetic nervous system neurons of the vagus nerve to fire and release Acetylcholine. The acetylcholine released causes the heart rate to slow down and decreases cardiac output, thus decreasing blood pressure. This effect is called Reflex Bradycardia.

Parasympathetic signals from the vagus nerve to the heart is believed to cause reflex bradycardia in most cases.[2]


Stimuli causing reflex bradycardia include:

Link

9 comments:

Ibnu Shaukani on March 24, 2009 at 12:44 AM said...

cushing's triad/reflex :
1) hypertension
2) reflex bradycardia
3) irregular breathing

When MAP (Mean Arterial Pressure) is less than ICP (Intracranial Pressure), the hypothalamus increases sympathetic stimulation of the heart, resulting in vasoconstriction, increased contractility, and increased cardiac output. The increase in blood pressure is detected by baroreceptors in the carotid arteries, triggering a parasympathetic response via vagal stimulation and inducing bradycardia. Bradycardia may also be stimulated by impinging on the vagal nerve due to increased intracranial pressure causing a stimulate parasympathetic response.

The Cushing reflex is usually seen in the terminal stages of acute head injury and may indicate imminent herniation. It can also be seen after the intravenous administration of norepinephrine and similar drugs.

Source : cik wiki

gg on March 24, 2009 at 1:23 AM said...

cik wiki dek non...
hmmm layan jela

soyabean~ said...

sharing the equations;

mean arterial pressure(MAP)=diastolic BP + 1/3(systolic BP-diastolic BP)

cranial perfusion pressure(CPP)=MAP-intracranial pressure(ICP)

normal CPP=60-100, normal ICP=05-15
all units are in mmHg, of cos.

body needs to ensure dat MAP is alwayz greater than ICP for cerebral perfusion to exist.

juz addition, cushing triad may indicates cerebral hemorrhages(high ICP due to trauma,SOL, or herniation.)

soyabean~ said...

the irregular breathing is due to..??,
my source says bcoz of hypothalamic stimulation.

haidarrealm on March 24, 2009 at 6:32 AM said...

reflex bradycardia n relative bradycardia benda yg same ke?i thought relative bradycardia ni yg kat dlm patient who suppose to have high bp but have a normal bp instead..usually during fever..btol ke???

Ibnu Shaukani on March 24, 2009 at 7:47 AM said...

to haidarrealm, x sama haidar. aku silap wat post.

When a person has a fever, the pulse usually increases along with the temperature. Relative bradycardia refers to a pulse-temperature deficit, with the pulse less than that expected for a given temperature.

Slalu kalo 1 degree temperture increase, pulse akan naik dlm 15 bpm. kalu pulse not increase, kite kata die relative brady. occur selalu dlm infection mcm lepto, malaria, typhoid, dengue.

ooooo said...

Relative bradycardia

When a person has a fever, the pulse usually increases along with the temperature. Relative bradycardia refers to a pulse-temperature deficit, with the pulse less than that expected for a given temperature.

Criteria for using relative bradycardia in clinical diagnosis:
(1) age of patient >= 13 years
(2) temperature >= 102°F and <= 106°F
(3) The pulse is taken simultaneously with the temperature,
(4) The patient has normal sinus rhythm with no arrhythmias, second or third degree heart block, or pacemaker.

Temperature
Pulse in Beats per Minute
102°F (38.9 °C)=110
103°F (39.5 °C)=120
104°F (40.0 °C)=130
105°F (40.6 °C)=140
106°F (41.1 °C)=150

pulse in beats per minute =
(10 * (temperature in °F)) – 910

Infectious causes of relative bradycardia:

(1) Legionnaires' disease
(2) psittacosis
(3) Q fever
(4) typhoid fever
(5) typhus
(6) malaria
(7) babesiosis
(8) leptospirosis
(9) yellow fever
(10) dengue fever
(11) Rocky Mountain spotted fever

Noninfectious causes of relative bradycardia:
(1) beta-blockers
(2) CNS lesions
(3) malignant lymphoma
(4) factitious fever
(5) drug-related fever

Relative bradycardia is not found with the "typical" bacterial pneumonias.

Source:http://www.medal.org/visitor/www%5CActive%5Cch6%5Cch6.01%5Cch6.01.08.aspx

harap membantu :)

Ibnu Shaukani on March 24, 2009 at 8:13 AM said...

thanx Ooooo..

Anonymous said...

inc. ICP... hypothalamus increase sympha at heart...direct effect ke ni?? tapi ada x sesapa penah dgr.. ?? inc. ICP > reduce blood supply to vasomotor center (medulla) > directly activate that centre > symphat. stimulation....n same as the rest yg azizi crite.. sbb penah tulis..tp x ingt dr mn.. huhu

 

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